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The Official Jouranl of the

VOLUME 5, Issue 2, 2018

Journal of Oral & Dental Research


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The Effect of Oral Hygiene Status on the Bond Failure Rate of the Orthodontic Bracket

Munad Jihad Ashij AL-Duliamy, BDS, MSc, POP department, College of Dentistry, Mustansiriyah University, IraqCorresponding Author: Munad Jihad Ashij AL-Duliamy E.mail: [email protected]

AbstractBackground Bracket bond failure is one of the major clinical dilemmas in orthodon-tic specialty that directly affect the success of the orthodontic treatment. Objectives The objectives of the present study were to assess the effect of oral hygiene status of the patients wearing fixed orthodontic appliances on the bond failure rate of the bracket. Materials and Methods Twenty-four patients (14 females, 10 males) with age range (14-25 years) were participants and fixed orthodontic appliances were placed for them. Oral hygiene status was assessed using Orthodontic Plaque Index (OPI) with a score from zero to four. The OPI was evaluated in each patient at follow up visit three-week apart during a six-month observation period. Each bond failure (other than due to trauma) was documented on a data collection sheet remarking the date and tooth type. The effect of OPI scores on the bond failure rate was evalu-ated. Any relation between the age of the patient, gender, dental arches, sides and tooth type with the deboning behavior was evaluated and the data were analyzed statistically. Results The highest percentage of bond failure rate was apparent with oral hygiene scores three and four. The male and younger patients showed a higher percentage of bond failure. The maxillary arch exhibited a higher percentage of bond failure. Regarding tooth type, both maxillary right lateral incisors and canines had higher percentage of bond failure. Conclusion Maintaining good oral hygiene during the course of orthodontic treatment has a crucial role in the success of bond strength. Bond failure rate varies according to age, gender, dental arch, and tooth type.

Keywords: Bracket bond failure, Oral hygiene

IntroductionFixed orthodontic appliance components such as brackets, ligature elastic, archwires, and other components enhance plaque accumulation with concomitant obstruction to conventional oral hygiene procedures, and consequent development of enamel demineralization, white spot, caries and gingivitis (Pandey et al., 2016). Optimal oral hygiene requires continuous patient›s motivation, instruction and professional pro-phylactic visits (Marinia et al., 2014). Therefore, maintaining good oral hygiene before and during orthodontic treatment is one of the most important aspects of orthodontic care (Travess et al., 2004) to ensure achieving good orthodontic treatment results.Bracket bond failure is one of the major clinical dilemma in orthodontic practice. Bond failure during orthodontic treatment may lead to enamel demineralization, more cost and time spending and delaying treatment. Consequently, adversely affect the patient motivation and treatment result (Rivera-Prado et al., 2015; Sfondrini, 2017). Moreo-ver, when brackets lose their attachment to tooth structure during treatment, the

Dr.Munad Jihad Ashij AL-Duliamy


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clinician no longer has control over tooth movement, and rebonding of the bracket is often necessary. Such interruptions in the course of treatment often make obtaining treatment goals more difficult and less efficient. Success of bonding is indispensable for successful orthodontic therapy (Pseiner et al., 2010). Therefore, bonding issue has been vastly studied. A large number of research were conducted of factors that may cause bond failure, factors that influence bond strength and strategies to maxi-mize the bond success rate (Ekizer et al., 2012). Both operator and patient factors are likely to cause a bond failure including salivary contamination (Robaski et al., 2017) blood contamination (Prasad et al., 2014) occlusal interference, high mastica-tory load and tooth brushing (Vijayakumar et al., 2014). Among factors that influence bond strength are the type of bonding system (Andrew and William, 1989), bonding technique (Menini et al., 2014), density of the composite and design characteristics of the bracket such as area of bonding, mesh size, and type ( Dickinson and Powers 1980; Lombardo et al., 2013). Moreover, strategies to enhance the bond success rate are include new adhesive materials, innovative bracket base designs (Ansari et al., 2016) enamel etching procedures (Maruo et al., 2010) and sandblasting techniques (Cal-Neto et al., 2011). Although many researches have studied the different factors that affect bond failure rate of orthodontic bracket, the effect of oral hygiene status on bond failure rate has not yet been confirmed by any research. Hence, the purpose of the present study was to investigate the effect of oral hygiene status of the patient wearing a fixed orthodontic appliance on the bracket bond failure rate. The study also observed the effect on bracket bond failure of the age of the patient, gender and den-tal arches (Maxillary and Mandibular) and tooth type.

Materials and MethodsEthical approval (No.1896 at 20/6/2017) for conducting the present study was ob-tained from the scientific committee of the College of Dentistry/Al –Mustansiriyah University. Twenty-four patients (14 females, 10 males) with age range (14-25 years) were selected from a private dental clinic in Baghdad. All patients were about to un-dergo active orthodontic treatment with maxillary and mandibular fixed orthodontic appliances. The selected participants and their parents were given information about the study and informed consents were obtained.The inclusion criteria were:•The patient had not been subjected to any orthodontic treatment•Absence of deep bite. •No medications•No oral bad habits•Absence of any buccal surface caries, restoration and morphologic defects.The exclusion criteria were: •Patients who did not meet any of the above inclusion criteria. A single operator (M.J.AL_Duliamy) bonded four hundred eighty (480) straight wire brackets on maxillary and mandibular teeth. Any bond failure due to a history of trauma or application of accidental force was excluded from the data. Hence, data from only twenty patients (400 brackets) were included in the study. The duration of the observation period was 18 weeks with six follow up visits three weeks apart.



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Bonding procedurePlacement of maxillary and mandibular fixed orthodontic appliances was performed using stainless steel Bionic R Bracket System Roth Prescription, Slot (.020» x .020») Ortho Technology Company, USA on the maxillary and mandibular incisors, canines and premolars. Before bonding, each tooth was polished, etched and prepared ac-cording to manufacturer’s instructions for each product (Joo et al., 2011). Light cured Resilience composite resin adhesive (Orthotechnology, FL, USA) was used for bracket bonding. Before curing, adhesive excess was removed from bracket’s vi-cinity using a dental probe.Immediately after bonding, .014» TruFlex NiTi arch wire (Ortho Technology Company, USA) were inserted into the brackets and molar tubes slots and elastomere ligatures Power Sticks™ (Ortho Technology) were used for arch wire ligation into the brackets. Following the bonding procedure the patients were instructed about oral hygiene, diet, and care with appliance so that accidental de-bonding could be prevented.

Oral hygiene statusOral hygiene status was assessed according to the Orthodontic Plaque Index recom-mended by Beberhold et al., 2012. Briefly, determination of PI was performed as fol-lows: Following placement of a self-retaining cheek retractor and cotton rolls, Cottons tips or applicators were saturated with dental a plaque indicating solution (sodium fluorescein) and painted on the teeth. Plaque on the buccal surfaces (in the immedi-ate vicinity of the bracket) was assessed; in addition, signs of gingival inflammation were recorded. The dentition was divided into sextants (Table 1). The oral hygiene status is indicated as a score from zero to four as follows: Score:• 0: No plaque deposits on the tooth surfaces surrounding the bracket base• 1: Plaque deposits on one tooth surface at the bracket base• 2: Plaque deposits on two tooth surfaces at the bracket base• 3: Plaque deposits on three tooth surfaces at the bracket base• 4: Plaque deposits on four tooth surfaces at the bracket base and/or gingival inflam-mation indicators (plaque deposits near the gingiva did not necessarily have to be present).The highest score found per sextant was entered into the sextant table. In addition, the highest score per sextant represents the score for the dentition. The highest score of all sextants determines the current oral hygiene situation. During the follow up visit, the staining and OPI scoring were begun before activating the fixed orthodontic appliance. The single operator (M.J AL_Duliamy) was conducted the measurements. The examiner performed her analysis with satisfactory intraexaminer reliability.

Bond failure rateThe study started at the first stage of treatment (leveling and alignment stage). All patients were observed for six months during their regular orthodontic appointments to quantify the bond failure rates and proceed with the orthodontic treatment. During the evaluation period, a data collecting sheet was used for recording any bond fail-ure. The date and tooth number of recorded bond failure for each tooth were entered in the data sheet. The FDI tooth numbering system was used in recording the teeth. Patients were examined at 21-day intervals, but were instructed to observe their ap-pliances every day for monitoring any brackets debond. Again, the highest score of



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all visits was used to represent the oral hygiene status of the patient during the six-month observation period. Any relation between the age of the patient, gender, dental arches (maxillary and mandibular) and tooth type with the deboning behavior was evaluated.

Statistical AnalysisStatistical analysis of the data was carried out by SPSS version 21 using frequency, percentage and Chi-Square test.

Table 1: Division of the dentition into sextants.*FDI tooth-numbering system.Note. Reprinted from “The orthodontic plaque index: an oral hygiene index for patients with multibracket appliances,” by Beberhold K, Sachse-Kulp A, Schwestka-Poll R, Horneckerand E, Ziebolz D. 2012. Orthodontics.; 13(1): 94–99.

Results Sample categorization regarding age and gender is shown in the table (2). The table 3 demonstrates Orthodontic Plaque Index (OPI) scores. By the end of the six months observation period, seven of the four hundred brackets had failed. The percentages of occurrence of bond failure in relation to OPI scores, gender and age are shown in ta-bles (4) and (5) respectively. Regarding tooth type, bond failure occurred in two right maxillary lateral incisors, two right maxillary canines, one left maxillary lateral inci-sors, one right mandibular first premolar and one right maxillary first premolar (Ta-ble 6). The frequency of OPI scores occurrence in the six arc sextants during the six months observation period is presented in table (7). Statistical analysis by using Chi-Square test (Table 8) revealed significant difference in the OPI scores of the maxillary sextant (S1+S2+S3) from those of the mandibular sextants (S4+S5+S6). Furthermore, there were highly significant differences in the OPI scores of the right sextants (S1+S6) from those of the left sextants (S3+S4).



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Table 2: Sample categorization regarding gender and age.

Table 3: Distribution of OPI scores with in the sample.

Table 4: Failure occurrence in relation to the OPI score.

Table 5: Failure occurrence according to gender and age



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Table 6: Failure occurrence according to tooth type.

Table 7: The result of Chi-Square test comparing the OPI scores in the six arch sextants.

Table (8): The result of Chi-Square test comparing the OPI scores in arches and sides.



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DiscussionBracket bond failure adversely affects the success of orthodontic treatment with a fixed appliance. Maintaining good oral hygiene during orthodontic treatment is es-sential for achieving optimum result in short duration (Cozzani et al., 2016). To our knowledge, no research has studied the effect of oral hygiene status on the success of orthodontic treatment in terms of bond strength. Therefore, the present study aims to investigate the effect of oral hygiene status on the bond success rate. The Ortho-dontic Plaque Index (OPI) is a special index developed by Beberhold et al. in 2012 for patients with fixed orthodontic appliances. Beberhold et al. (2012) stated, «The OPI is ideal for diagnostic application during the fixed treatment phase». The OPI focuses on the tooth area just adjacent to the bracket›s border, which is inaccessible and harbor a plaque. Therefore, in the present study, the author used the Orthodontic Plaque Index (OPI) to assess the oral hygiene status. The results of the six-month evaluation period revealed that, the largest number of bracket failures occurred among patients that exhibited OPI scores of three and four. One explanation for this observation could be the plaque accumulation around the bracket vicinity. According to Steffen (1996), plaque accumulations prevent wash out of the acid from the tooth surface and con-sequently reduce the Ph of the oral cavity. Oncag et al. (2005) found that, increase in the enamel erosion adversely affect bracket attachment. Regarding gender differ-ences, the greatest percentage of bond failure occurred in males, which coincides with a similar finding by Aikins and Ututu (2017). This may be explained by the fact that females took more care of their oral hygiene than male. Other suggestion may be due to the bad eating habit that present in male more than female as the former usu-ally eats a junk food and a fast food snack which may contained hard food particles like burger, zinger and others. On the other hand, male may play football and other games that may lead to traumatic bracket detachment. Furthermore, males in the present study had higher OPI scores than females, which accord with the finding by Addy et al. 1990 that the plaque, bleeding and pocketing scores were higher in boys than the girls. Other previous findings include the observation by Vandana and Savi-tha (2005) that females show thinner gingiva than males. Another explanation of the present gender differences is previous studies’ revelation of a gender role in the per-ception of dental health, frequency of tooth brushing, type of toothbrush and tooth-paste and attending dental clinics (Clement C. Azodo and Barnabas Unamatokpa, 2012). Another studies concluded that females took more care of their oral hygiene, brushed their teeth significantly more often and had a better oral hygiene status than males, as well as having less biofilm Mamai-Homata et al., 2016; Mei et al., 2017. In the present study, a higher percentage of bond failure was found among younger age patients. Because younger age especially teenagers took less care of their teeth, eat more sweet and bad-carb which lead to plaque accumulation and gingival inflam-mation which adversely affect bracket attachment. Other cause, younger patients are more susceptible to trauma than older counterparts. This is in accordance with the re-sult of Aikins and Ututu (2017) who found more bracket loss among younger patients. At the same time, younger patients in the present study had higher OPI scores. This may be explained by the finding by Mei et al. (2017) that, «Less biofilm was found in adults». Another explanation is provided by the observation of Vandana and Savitha (2005) that the younger age group had significantly thicker gingiva than that of the older age group. Regarding tooth type, in the present study, a higher percentage of bond failure was found in the maxillary lateral incisor and canines teeth. These teeth



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belong to the S2, which revealed the highest OPI score in this study. This may be explained by the result of Mei et al. (2017) who found more biofilm in maxillary later-als and canines. On the other hand, this finding disagrees with the result of Elekdag-Turk et al. (2008) who observed that first and second premolars have shown three times more bracket failure rate than incisors and canines. It also disagrees with the observation by Romano et al. (2011) that more bracket failures occurred in the pos-terior region compared with the anterior region. These disagreements may be due to the differences in the criteria of sample selection as the present study excluded from the data any bond failure that showed a history of trauma or occlusal interference. Regarding OPI in sextants, there were highly significant differences in OPI scores of maxillary sextants (S1+S2+S3) from those of mandibular sextants (S4+S5+S6). This is in agreement with the result of Vandana and Savitha (2005) who found that the gingiva was seemed to be thinner in the mandibular arch than the maxilla. Further supporting evidence is the result by Mei et al. (2017) showing that, the maxillary arch has significant more biofilm than the mandibular arch. Regarding arch sides, there were significant differences in OPI scores in the right posterior sextants (S1+S6) from those in the left posterior sextants (S3+S4). This may be explained by the toothbrush motion which is highly frequent on the left side than on the right side (both buccal and palatal areas), according to Inada et al. (2014).

Conclusion•During the six-month observation period, patients with high Orthodontic Plaque In-dex OPI scores (three and four) recorded high bond failure rates. This indicates that poor oral hygiene increases the incidence of bond failure of orthodontic brackets.•Higher Orthodontic Plaque Index OPI scores, as well as high bracket failures rates, were observed in males, younger patients, and the maxillary arch.•Maxillary right lateral incisors and canines were the teeth with the most bracket loss. •Both patient and orthodontist play a role in the success of the orthodontic treatment. Patients must maintain good oral hygiene and orthodontists must motivate the patient toward good oral hygiene practice during the treatment course.

AcknowledgmentThe author is grateful to the Assistant Professors Dr. Ahmed Marzook and Dr. Moham-med Nahidha for performing the statistical analysis of the data.

Conflict of InterestThe author of this study declares no conflict of interest.

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Aikins EA, Ututu C (2017). An audit of bonding failure among orthodontic patients in a tertiary hospital in South-South Nigeria. Int J Orthod Rehabil 8: 91-5.



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Andrew L. Sonis, William Snell (1989). An evaluation of a fluoride-releasing, visible light-activated bonding system for orthodontic bracket placement American Journal of Orthodontics and Dentofacial Orthopedics 95(4):306-31.

Ansari MY, Agarwal DK, Gupta A, Bhattacharya P, Ansar J, Bhandari R (2016). Shear Bond Strength of Ceramic Brackets with Different Base Designs: Comparative In-vitro Study. J Clin Diagn Res 10:ZC64–ZC68 pmid: 28050507.

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Cal-Neto JP, Castro S, Moura PM, Ribeiro D, Miguel JA (2011). Influence of enamel sandblasting prior to etching on shear bond strength of indirectly bonded lingual ap-pliances. Angle Orthod. 81, 149–152.

Cozzani M, Ragazzini G, Delucchi A, Mutinelli S Barreca C, Rinchuse DJ, Servetto R, Piras V (2016). Oral hygiene compliance in orthodontic patients: a randomized con-trolled study on the effects of a post-treatment communication. Progress in Orthodon-tics 17:41.

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Ekizer A, Zorba YO, Uysal T, Ayrikcil S (2012). Effects of demineralization-inhibition procedures on the bond strength of brackets bonded to demineralized enamel surface. Korean J Orthod 15 (1):17–22.

Elekdag-Turk S, Turk T, Isci D, Ozkalayci N (2008). Thermocycling effects on shear bond strength of a self-etching primer. Angle Orthod 78:351–356.

Inada E, Saitoh I, Yu Y, Tomiyama D, Murakami D, Takemoto Y, et al (2014). Quantita-tive evaluation of toothbrush and arm-joint motion during tooth brushing. Clinical Oral Investigations 1–12.

Joo HJ, Lee YK, Lee DY, et al. (2011). Influence of orthodontic adhesives and clean-up procedures on the stain susceptibility of enamel after debonding. Angle Orthod. 81:334–40.

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Mamai-Homata E, Koletsi-Kounari H, Margaritis V (2016). Gender differences in oral health status and behavior of Greek dental students: A meta-analysis of 1981, 2000,



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and 2010 data. J Int Soc Prevent Communit Dent 6:60-8.

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Menini A, Cozzani M, Sfondrini MF, Scribante A, Cozzani P, Gandini P (2014). A 15-month evaluation of bond failures of orthodontic brackets bonded with direct ver-sus indirect bonding technique: a clinical trial. Progress in Orthodontics 15:70.

Oncag G, Tuncer AV, Tosun YS (2005). Acidic soft drinks effects on the shear bond strength of orthodontic brackets and a scanning electron microscopy evaluation of the enamel. Angle Orthod 75:247–253.

Pandey V, Chandra S, Dilip Kumar HP, Gupta A, Bhandari PP, Rathod P (2016). Im-pact of dental neglect score on oral health among patients receiving fixed orthodontic treatment: A crosssectional study. J Int Soc Prev Community Dent 6(2):120-4.

Prasad M, Mohamed S, Nayak K, Shetty SK, Talapaneni AK (2014). Effect of moisture, saliva, and blood contamination on the shear bond strength of brackets bonded with a conventional bonding system and self-etched bonding system. J Nat Sci Biol Med 5:123-9.

Pseiner BC, Freudenthaler J, Jonke E, Bantleon HP (2010). Shear bond strength of flu-oride-releasing orthodontic bonding and composite materials. Eur J Orthod 32:268–73.

Rivera-Prado H, Moyaho-Bernal A, Andrade-Torres A, Franco-Romero G, Montiel-Jar-quín A, Mendoza-Pinto C, et al (2015). Efficiency in bracket bonding with the use of pretreatment methods to tooth enamel before acid etching: sodium hypochlorite vs. hydrogen peroxide techniques. Acta Odontol. Latinoam. 28 79–82.

Robaski AW, Pamato S, Tomás-de Oliveira M, Pereira JR (2017). Effect of saliva con-tamination on cementation of orthodontic brackets using different adhesive systems. J Clin Exp Dent. 9 (7):e919-24.

Romano A, Rubolini D, Caprioli M, Boncoraglio G, Ambrosini R, Saino N (2011). Sex-related effects of an immune challenge on growth and begging behavior of barn swal-low nestlings. Plos One. 6:e22805.Sfondrini MF, Gandini P, Gioiella A, Zhou FX, Scribante A (2017). Orthodontic Metallic Lingual Brackets: The Dark Side of the Moon of Bond Failures? J. Funct. Biomater. 27



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(8): 1-7.

Steffen MJ. The effects of soft drinks on etched and sealed enamel (1996). Angle Or-thod. 66:449–456.

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Vandana KL, Savitha B (2005). Thickness of gingiva in association with age, gender and dental arch location Journal of Clinical Periodontology. 32(7): 828–830.

Vijayakumar RK, Jagadeep R, Ahamed F, Kanna A, Suresh K (2014). How and why of orthodontic bond failures: An in vivo study. J Pharm Bioallied Sci. 6: 85-9.



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Effects of Novel Polyetheretherketone (PEEK) Clasp Design on Retentive Force at Different Tooth

Undercuts

1Saja A. Muhsin, PhD, 2Duncan J. Wood, PhD, 2Anthony Johnson, PhD, 3Nu-noSereno, PhD, 2Paul V. Hatton, PhD. 1Prosthetic Dental Technology, College of Health and Medical Technology, Middle Technical University (MTU), Baghdad, Iraq, 2Academic Unit of Re-storative Dentistry, School of Clinical Dentistry, Faculty of Medicine Dentistry and Health, University of Sheffield, Sheffield, S10 2TA, UK, 3Juvora™ Ltd, Hill-house International, Thornton Cleveleys, Lancashire,FY5 4QD, UKCorresponding author: Saja A. MuhsinE-mail address: [email protected]

AbstractBackground The material characteristics of many thermoplastic materials, includ-ing PEEK, have been evaluated in vitro to investigate their mechanical and physical properties. However, all the manufacturers of thermoplastic materials and laboratories making non-metal clasp dentures still recommend the original denture design. Objectives To investigate the retentive force of a novel clasp design for PEEK ther-moplastic material at 3 different undercut depths with fatigue cycling equivalent to 3 years of insertion/removal use. Materials and Methods Samples (n=10) were pre-pared for the test. A novel clasp designs for PEEK and conventional design for Co-Cr were created using 3D-RPD software (DWOS). PEEK-Juvora™ clasps were fabricated using a Roland 3D-milling machine; PEEK-Optima®NI1 were thermo-pressed at 200˚C mold temperature using thermopress 400 injecting unit; while Co-Cr alloy was used to cast the metal clasps. Samples were tested at tooth undercut depths of 0.25, 0.50, and 0.75 mm. They were investigated for the retentive force at the initial fab-rication and after 1st, 2nd, and 3rd Year respectively of fatigue simulation. This was represented by clasp insertion and removal 3 times per day using fatigue chewing simulator machine. The data was statistically analyzed using ANOVA at p<0.05. Results There was a statistically significant difference (p<0.05) between the reten-tive force of the PEEK compared to Co-Cr clasps. PEEK-Juvora™ exhibited the highest retention at 3 different undercut depths over 3 years followed by PEEK-Optima®NI1 at 0.75, and 0.50mm (P<0.05). However, the initial retentive force required to dis-lodge the PEEK-Optima®NI1 clasp processed at 200 °C was statistically non-signif-icant (p>0.05) as the Co-Cr at 0.25 mm tooth undercut depth. Conclusion Clasps made of machined PEEK-Juvora™ and thermo-pressed PEEK-Optima®NI1 at 200 ˚C mold temperatures showed the most promising retentive force with a non-fracture tendency at deeper tooth undercut. This novel PEEK clasp design may improve the clasp retention, bracing, additionally to increase its durability comparing to Co-Cr clasp.

Keywords: Polyetheretherketone, Retentive force; Novel clasp design, Denture clasp; Tooth undercut, Removable partial denture

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IntroductionThe clasp of a removable partial denture (RPD) is often made from the same cast metal alloy as the metal framework of the denture. The most commonly used metal alloy for this purpose is a Cobalt-Chromium alloy (Blackman et al., 1991, Vallittu and Kokkonen, 1995, Mahmoud, 2007, Mahmoud et al., 2007). Nevertheless, it seems that most dental patients of all ages prefer to avoid the use of metals in dental treat-ment due to either allergy reaction (Schmalz and Garhammer, 2002, Ruff and Belsito, 2006, Van Noort, 2013, Wataha, 2000)or practical performance(Yli-Urpo et al., 1985, Vallittu et al., 1993, Powers and Wataha, 2014). Due to such increased expecta-tions, non-metal clasp dentures using thermoplastic materials have recently become a treatment option for patients (Takabayashi, 2010). Despite the fact that the mate-rial characteristics of thermoplastic resin have been studied in vitro, detailed designs of non-metal clasps are still to be produced. Clinical problems including the failure of resin clasps have been frequently encountered in the practical use of non-metal clasp dentures(Takabayashi, 2010, Takahashi et al., 2012, Tannous et al., 2012, Osada et al., 2013, Hamanaka et al., 2011). However, all the manufacturers of thermoplastic materials and laboratories making non-metal clasps still recommend the conventional clasp design. Moreover, these experiments were executed on rectangle test speci-mens that were not in clasp form, and design details for thermoplastic clasps in RPDs, such as thickness, width, and amount of undercut, to achieve appropriate retention and avoid clasp failure have not been fully established. PEEK a new biomedical ther-moplastic material was suggested as dental material (Kurtz, 2011, Stawarczyk et al., 2013, Kern and Lehmann, 2012, Schwitalla and Müller, 2013, Hallmann et al., 2012). Since JUVORA CE mark in 2012, practitioners have begun using the product(Costa-Palau et al., 2014, Zoidis et al., 2015). Clinicians have been provided with guidelines for using and designing JUVORA frameworks. PEEK’s flexibility and highly elastic na-ture through its mechanical properties could decrease the stress on abutment teeth, whilst, in addition, with conventional clasp dimensions, could affect the retention. However, no studies have reported on comparison between the traditional Cobalt-Chromium and thermo-pressed PEEK-Optima®NI1, and machining PEEK-Juvora™. From an independent point of view it appears that more scientific investigation on this topic is required. Therefore, in this study a full clasp for PEEK polymer will be de-signed and tested.

Materials and methodsIn this study a granular form of medical grade PEEK-Optima®NI1 polymer and PEEK-Juvora™ discs were used (Invibio® and Juvora™ Ltd., UK), and Co-Cr RPD casting alloy (Wironit-BEGO, Germany).

Preparing the case study modelA study model was constructed to represent an ideal RPD situation with a standard-ised undercut for a Kennedy classification class III mod.1.The working cast and mo-lar die were duplicated in hardened Type IV diestone material for scanning purposes which wasmixed according to the manufacturer’s instructions (W/P: 20 ml / 100 g), (Esthetic base® gold, type IV hard diestone, Dentona®, Germany). The same cast was used in all production procedures, with exception of the abutment molar tooth. The tooth was duplicated, trimmed and surveyed manually to achieve the different desirable undercuts of 0.25, 0.50, and 0.75 mm. The stone study cast was scanned



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using 3D Dental Wings Operating System for Removable Partial Dentures (3D DWOS-RPDs) software designer program (Dental Wings, Germany). The undercut amount was measured digitally using the depth scale. After surveying, the cast was exported into (Stl) file form to be retrieved for use in designing the PEEK and Co-Cr clasps. An injection molding technique was used to fabricate thermoplastic PEEK-Optima NI1 at 200 °C mold temperature from a milled wax pattern.

Clasp DesignThe Co-Cr clasp was designed according to the most common conventional design pattern, and the PEEK clasp was designed according to the novel dimensions devised by this study. However, the occlusal rest dimensions were the same as those used for the Co-Cr clasp. This was a spoon-shaped design, of 1 mm thickness, 3 mm width, and at right angles to the minor connector on the proximal surface(Hirota et al., 2012, Yoda et al., 2012). A pin cylinder holder was added to all the clasp designs to serve as an attachment for fixation to the sample jig holders of the testing machines.

Conventional Co-Cr Clasp DesignThe cast was digitally surveyed at zero position, the undesirable undercut was blocked, and the dimensions for the traditional Co-Cr clasp were designed using the molar tooth. The clasp arm pattern originated from a proximal plate and curved 120 degrees around the tooth surface in a single plane. Average clasp width and thickness of the designed arm was 1 mm; however, at 30 degrees they were 0.92 mm and 0.97 mm, respectively, while at 120 degrees they were 0.73 mm and 0.79 mm, respective-ly (Mahmoud et al., 2005). The clasp was designed and fabricated to 1 mm thickness, and then was finished and polished to the recommended dimensions using a digital micrometer device. The tip of the retentive clasp arm engaged with the tooth under-cuts at specific points of 0.25 mm, 0.50 mm, and 0.75 mm, the desirable undercuts, while the width and thickness of the designed reciprocal (Bracing) arm was 2 mm and this was located passively on the palatal surface of the selected tooth.

PEEK Clasp DesignThe same study cast model used to design a novel clasp pattern for PEEK material. The PEEK clasp was designed on the same molar tooth used for the Co-Cr clasp, with a design of dove-wing appearance. The clasp was designed with a novel strap arm pattern that originated from a proximal plate and curved around the buccal tooth sur-face with a dove-wing arm. The retentive clasp flange (lower part) engaged the tooth undercuts at the 0.25 mm, 0.50 mm, and 0.75 mm desirable undercut areas. The clasp was designed with a short arm for aesthetic purposes, to end buccally at the buccal groove of the molar tooth. Meanwhile, the reciprocal arm curved around the palatal tooth surface with a passive activity to end disto-palataly. The average thick-ness of the designed retentive and reciprocal arm was 1.5 mm.

Fabrication of ClaspsThe PEEK and Co-Cr digital patterns were converted to (.Stl) file forms; figure (1). This is to be fabricated into the 3D sample. For machining Clasps, the Roland milling machine milled PEEK clasps from digital patterns into 3D PEEK clasps using PEEK-Juvora™ blank discs (Roland, DWX-50, USA). This was accomplished using the vari-ous steps of the machine software processing program. The same (.Stl) file digitally



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designed for PEEK clasp was used to prepare the clasps made from thermo-pressed PEEK-Optima®NI1milled these patterns from wax blanks. After flasking; investing of the wax patterns; and wax extraction, the mold cavity was then cleaned with hot wa-ter and detergent agents. The mold left to dry for 30 seconds, and one layer of suit-able separating medium for thermo-pressing purposes was added to the mold surface and left to dry overnight (Bredent, Germany).The flasks were assembled and pre-heated in the oven before injection of the PEEK- Optima®NI1 into the mold cavity at 200 °C mold temperature. The Thermopress 400 injection molding system (Bredent, Germany) was used for injection of PEEK material. The molds were left overnight to allow slow bench-cooling to room temperature. The .Stl files of Co-Cr clasp pattern of 0.25, 0.50, and 0.75 mm undercuts were transferred to the milling machine to be milled into wax patterns. The wax patterns were sprued, invested, and cast using Co-Cr alloy (Wironit-BEGO, Germany) with a phosphate-bonded investment material using high-frequency induction melting technology with a centrifugal casting machine (Modular 3S, Italy).The entire clasp specimens were cut from their connectors; PEEK clasps finished and polished using the conventional method. Meanwhile the Co-Cr clasps were lightly cleaned using a sandblaster with airborne-particle abrasion using 80 µm aluminum oxide particles (Renfert, Germany). Then, white compound was ap-plied for dry polishing and finally the clasps were electrical polished using Electrolytic polishing unit (BEGO, Germany). A digital micrometer was used to optimise the clasp dimensions after the finishing and polishing procedures.

Figure 1: PEEK and Co-Cr clasps production route to (.Stl) file.



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Sample Grouping and Testing ProceduresNinety specimens were divided into 3 main different experimental groups according to the clasp materials: Co-Cr alloy, thermo-pressed PEEK-Optima®NI1 and machined PEEK-Juvora™. These in turn were sub-divided according to preset clasp deflection of 0.25 mm, 0.50 mm, and 0.75 mm, (n=10), which were specification designed to compare the clasps’ functions under different undercuts to the tooth surfaces. Each clasp was tested for retentive force using a Lloyd tensile testing machine (Instron Lloyd, England), and then the cycle was run for suggested cycling period using a fa-tigue chewing simulator machine (England). The sample’s retentive force was tested at initial insertion and then after 1st, 2nd and 3rd years.

Clasp Testing ProcedureThe retentive force of each clasp was measured at a crosshead speed of 30 mm/min of the tensile apparatus. The teeth designed with different undercut gauges were duplicated and molded with a base made of Rhino Rock model resin to be fixed in the lower part of the tensile jig (DB lab, UK). The distance for release of the clasp from the tooth undercut area during the testing procedure was measured for setting at 3 mm. The initial retentive force was determined for the clasp at the first insertion cy-cle, and the changes in retentive force at each interval were measured after the cy-cling period repetition as shown in figure (2). Fatigue chewing simulator machine was used to carry out fatigue cycling test. A ther-mo-cycling system circulated the hot water in the sample tank at 37 (±1˚C) through-out the experiment. An indenter of 4.25 mm ball diameter was used in this study. The clasps were subjected to cycling deflection of preset values of 0.25 mm, 0.50 mm, or 0.75 mm. Each specimen was fixed to the testing machine with screws. They were subjected to a cyclic deflection generated by the radial direction force at the tip of each clasp arm at a frequency of 100 deflection/min (2200= 1 year), (4400= 2 Years), and (6600= 3 Years). This was to represent the removing and insertion of the appliances 3 times a day figures (3) and (4).

Figure 2: Clasps under retentive force test: A. PEEK clasp and B. Co-Cr clasp.



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Figure 3: PEEK and Co-Cr clasps held by special adjustable clasp holder for cycling test.

Figure 4: Clasps under cycling test: A. PEEK clasp B. Co-Cr clasp.



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ResultsAnalysis of the results of this study was conducted using SPSS software (22). These statistical methods included inferential statistical analysis of variation (ANOVA). Tests were performed at a confidence level of 95% and significant P-value of (P≤0.05). One-way ANOVA (Post hoc of Tukey HSD, Games-Howel, Gabrial, Hochberg, and Bon-ferroni) tests showed statistically significant differences between the tested clasp materials. Figures 5 to 8 show the retentive force of the tested material. The highest retention force over 3 years and at 3 different levels of tooth undercut was observed with PEEK-Juvora™. The highest initial retentive force of 45 N was observed with the PEEK-Juvora™ clasps of 0.75 mm undercut depth, followed by the PEEK-Optima®NI1 at 0.75 mm (35 N) and 0.50 mm (30 N). The PEEK clasps exhibited no tendency to fracture at any undercut depths over the tested period. However, the Co-Cr clasps demonstrated lower effectiveness with decreased retentive force values at different undercut depths, additionally to fracturing specimens during the cycling test. Over a test period representing 3 years of use, the mean retentive force decreased in milled PEEK-Juvora™ clasps with 1.5 mm thickness from 32 N to 29 N at 0.25 mm under-cut gauge; from 36 N to 30 N at 0.50 mm; and from 45 N to 38 N at 0.75 mm. The retentive force of the PEEK-Optima®NI1 clasps thermo-pressed at 200 ˚C mold tem-perature decreased from 22 N to 19 N at 0.25 mm undercut gauge, from 30 N to 25 N at 0.50 mm, and from 35 N to 28 N at 0.75 mm. Meanwhile retentive force of the conventional Co-Cr clasps decreased from 24 N to 18 N at 0.25 mm undercut gauge, from 28 N to 17 N at 0.50 mm, and from 34 N to 20 N at 0.75 mm. In addition, there was fracturing of specimens during the periodic cycling test starting from the 2nd year and with increased undercut depth.

Figure 5: Diagram showing the mean distribution of the clasp retentive force of the tested materials over 3 years and at tooth undercut of 0.25 mm.



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Figure 8: Diagram showing the retentive force needed to dislodge the clasps made of different materials over 3 years and at undercuts of

A. 0.25 mm; B. 0.50 mm, and C. 0.75 mm.

DiscussionA few studies have reported on the retentive forces required for clasps retention. One such study stated that 3 to 7.5 N is the retentive force required for adequate reten-tion and functioning of PRDPs, while another study found that 5 N could give an ac-ceptable degree of retention(Frank and Nicholls, 1981, Sato et al., 2001). Based on the data obtained in this investigation, the novel clasp design made from PEEK mate-rial of 1.5 mm thick showed significantly higher retention force compared to conven-tional Co-Cr claps. The greatest retentive force for PEEK clasps was found in the 1.5 mm thick clasps designed to engage the 0.75 mm undercut, followed by the 0.50 mm clasp undercut. Thermoplastic clasps might achieve clinically acceptable retention at dimensions differing from those of metal clasps, possibly requiring thicker clasp to engage a deeper undercut(Tannous et al., 2012, Kaplan, 2008, Goiato et al., 2008, Katsumata et al., 2009). Tooth shape and clasp design may affect the retentive force, and the clasp retention could be determined by the depth of the undercut available on the tooth (Davenport et al., 2001). This could be necessary due to the relatively low rigidity of the thermoplastic material compared to metals and alloys (elastic modulus: PEEK 4.0 GPa; and Co-Cr alloy 240 GPa) and may reduce the possibility of traumatic overloading (Turner et al., 1999, Kurtz, 2011). This may support the finding of Kota-keet al., and Kim et al., who found in their studies that clasps made of more elastic



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materials displayed superior resistance to retention loss (Kotake et al., 1996, Kim et al., 2004).The Co-Cr clasps exhibit some loss of retention. This current finding seems to agree with Bridgemanaet al., and Kim et al., who also found a decrease in the Co-Cr clasps retention during the simulation test(Bridgemana et al., 1997, Kim et al., 2004, Rodrigues et al., 2002). The reduction in Co-Cr clasp retention force may be related to permanent deformation of the metal (Ghani and Mahood, 1990, Kim et al., 2004,Vallittu and Kokkonen, 1995).It seems that more clinical studies are needed to evaluate the effect of PEEK clasps on the abutment teeth.

ConclusionThe results show that PEEK thermoplastic material could be used in the fabrication of clasps for RPDs, as they provide adequate retention to engage a deeper undercut area with thicker clasp even after 3 years of simulated use.

AcknowledgmentThe author thanks the Higher Committee of Educational Development in Iraq (HCED), the scholarship program that supports the most talented students in Iraq, Invibio® and Juvora™ Ltd for supplying the PEEK material for this study and the University of Sheffield for technical and lab facilities.

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BRIDGEMANA, J. T., MARKER, V. A., HUMMEL, S. K., BENSON, B. W. & PACE, L. L. 1997. Comparison of titanium and cobalt-chromium removable partial denture clasps. The Journal of Prosthetic Dentistry, 78, 187-193.

COSTA-PALAU, S., TORRENTS-NICOLAS, J., BRUFAU-DE BARBERA, M. & CABRATOSA-TERMES, J. 2014. Use of polyetheretherketone in the fabrication of a maxillary obtu-rator prosthesis: A clinical report. The Journal of Prosthetic Dentistry, 112, 680-682.

DAVENPORT, J., BASKER, R., HEATH, J., RALPH, J., GLANTZ, P. & HAMMOND, P. 2001. Prosthetics: Bracing and reciprocation. British dental journal, 190, 10-14.

FRANK, R. P. & NICHOLLS, J. I. 1981. A study of the flexibility of wrought wire clasps. The Journal of prosthetic dentistry, 45, 259-267.

GHANI, F. & MAHOOD, M. 1990. A laboratory examination of the behaviour of cast cobalt-chromium clasps. Journal of Oral Rehabilitation, 17, 229-237.

GOIATO, M., PANZARINI, S., TOMIKO, C. & LUVIZUTO, E. 2008. Temporary flexible immediately removable partial denture: a case report. Dentistry today, 27, 114, 116.HALLMANN, L., MEHL, A., SERENO, N. & HäMMERLE, C. H. 2012. The improvement of adhesive properties of PEEK through different pre-treatments. Applied Surface Sci-ence, 258, 7213-7218.



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HAMANAKA, I., TAKAHASHI, Y. & SHIMIZU, H. 2011. Mechanical properties of injec-tion-molded thermoplastic denture base resins. Acta Odontologica Scandinavica, 69, 75-79.

HIROTA, M., SHIMPO, H., SUZUKI, Y. & OHKUBO, C. 2012. Influence of metal rest in a non-metal clasp denture on pressure distribution to soft tissue. Ann Jpn Prosthodont Soc, 4, 193-200.

KAPLAN, P. 2008. Flexible removable partial dentures: design and clasp concepts. Dentistry Today, 27, 120, 122-3.

KATSUMATA, Y., HOJO, S., HAMANO, N., WATANABE, T., YAMAGUCHI, H., OKADA, S., TERANAKA, T. & INO, S. 2009. Bonding strength of autopolymerizing resin to nylon denture base polymer. Dental Materials Journal, 28, 409-418.

KERN, M. & LEHMANN, F. 2012. Influence of surface conditioning on bonding to poly-etheretherketon (PEEK). Dental Materials, 28, 1280-1283.

KIM, D., PARK, C., YI, Y. & CHO, L. 2004. Comparison of cast Ti-Ni alloy clasp reten-tion with conventional removable partial denture clasps. The Journal of Prosthetic Dentistry, 91, 374-382.

KOTAKE, M., WAKABAYASHI, N., AI, M., YONEYAMA, T. & HAMANAKA, H. 1996. Fatigue resistance of titanium-nickel alloy cast clasps. The International journal of prostho-dontics, 10, 547-552.

KURTZ, S. M. 2011. Peek Biomaterials Handbook, William Andrew Publishing.

MAHMOUD, A. 2007. Pre-overloading to extend fatigue life of cast clasps. Journal of dental research, 86, 868-872.

MAHMOUD, A., WAKABAYASHI, N., TAKAHASHI, H. & OHYAMA, T. 2005. Deflection fatigue of Ti-6Al-7Nb, Co-Cr, and gold alloy cast clasps. The Journal of Prosthetic Den-tistry, 93, 183-188.

MAHMOUD, A. A. A., WAKABAYASHI, N. & TAKAHASHI, H. 2007. Prediction of perma-nent deformation in cast clasps for denture prostheses using a validated nonlinear finite element model. Dental Materials, 23, 317-324.

OSADA, H., SHIMPO, H., HAYAKAWA, T. & OHKUBO, C. 2013. Influence of thickness and undercut of thermoplastic resin clasps on retentive force. Dental Materials Jour-nal, 32, 381-389.

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Simultaneous Indirect Sinus Lift and Implant Inser-tion. Case Report for Extreme Bone Resorption

Faaiz Alhamdani, PhD, College of Dentistry, Ibn Sina University for Medical and Pharmaceutical Sciences, Baghdad, IraqCorresponding author: Faaiz Al-Hamdanie.mail: [email protected]

AbstractBackground Sinus lift is the procedure performed to overcome shortage in alveolar bone height in posterior maxilla. Objectives Alveolar bone shortage occurs due to maxillary sinus pneumatization after tooth extraction. This might interfere with pri-mary implant stability. Materials and Methods There are two methods to elevate the sinus membrane for better accommodation of dental implant without jeopardizing the Schniderian Membrane. Direct (lateral) Approach and indirect (crestal approach). Direct approach is preferable when bone height is less than 4 mm, whereas indirect sinus approach is more suitable for cases with ≥ 5 mm bone height. However, exces-sive sinus pneumatization remains a challenge even for cases with direct sinus ap-proach. Such cases require two step procedures for implant replacement. Results It seems unlikely to achieve sinus lifting and direct implant placement for cases with extreme alveolar bone height shortage in the same surgical procedure. Conclusion In this case report indirect sinus lift has been performed utilizing IBS® CMC Technique and IBS thread design to perform one step bone implant placement for alveolar bone height of 0.5 mm.

IntroductionSinus lift is the procedure performed to overcome shortage in alveolar bone height in posterior maxilla. Alveolar bone shortage occurs due to maxillary sinus pneumatiza-tion after tooth extraction. This might interfere with primary implant stability (Lund-gren et al., 2008). There are two methods to elevate the sinus membrane for better accommodation of dental implant without jeopardizing the Schniderian Membrane. Direct (lateral) Approach and indirect (crestal approach). Direct approach (Boyne and James, 1980; Tatum, 1986) is preferable when bone height is less than 4 mm (Aly and Hammouda, 2017; Pai et al., 2017), whereas indirect sinus approach (Summers, 1994) is more suitable for cases with ≥ 5 mm bone height (Chen et al., 2009; He et al., 2013). However, excessive sinus pneumatization remains a challenge (Sharan and Madjar, 2008) even for cases with direct sinus approach. Such cases require two step procedures for implant replacement. There is no solid evidence regarding the potential of indirect sinus lift and simultaneous dental implant placement (Esposito et al., 2014). In this case report the author performed indirect sinus lift utilizing IBS® Crestal Approach with Sinus Membrane Control (CMC) Technique employing IBS® Fin Thread dental implant design to perform bone implant placement with bone augmen-tation simultaneously for alveolar bone height about 0.5 mm.

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Case ReportThirty years old male attended Training Dental Centre in Baghdad for dental implant in the posterior maxilla. Medical and dental histories were taken. The patient had neither history of systemic disease nor a history of maxillary sinus infection or com-plaint. Intraoral examination showed # 15 and #16 were extracted. Upper right molar (#16) was extracted seven years ago. Adequate both bucco-palatal and mesio-distal distances were available for insertion of two implants. However, the periapical radio-graph showed severe shortage of alveolar bone height in #16 areas (about 0.5 mm on digital periapical intra-oral radiography). Treatment options have been discussed with the patient and the decision was to perform indirect sinus lift using IBS® CMC Technique (Crestal Approach with sinus Membrane Control) with simultaneous dental implant insertion. No preoperative antibiotic was prescribed for the patient. Before the procedure, the patient was asked to rinse his mouth with 0.12% Chlorhexidine Digluconate (Abraham et al., 2015; Young et al., 2002) for 2 minutes. Local anaes-thesia (2% Lignocaine with 1:100 000 Epinephrine) was infiltrated before the surgi-cal procedure. Following a video demonstration of unpublished case (for 0.7mm bon height) the author decided to perform flapless indirect sinus lift procedure using Sinus Lift Technique provided by IBS and utilizing IBS Fin Thread Design. Using trephine bur, the gingival tissue over the intended implant was removed and the bone was exposed. Magic Short Drill with 1000 r/m was used to carefully to create a notch in the bony surface of alveolar cortex and provide application point for the Magic Sinus Lifter. Sinus Lifter, which was handled with hand lever, was gently tapped to preserve the sinus membrane. IBS® Magic Sinus lifter has lateral blades for controlled lifting action and a 3mm empty hallow space for offset-loading effect and control of bone block to be tapped slowly and elevate the sinus membrane up to 9 mm height. After cleaning the surgical site, the patient was asked to breathe normally to make sure that no perforation has been made on the sinus membrane. Bone substitute material (Osteon®II) was applied using IBS Bone Pusher. The cavity was filled with the mate-rial. Size 5 with 7 mm length IBS FC® Implant was inserted manually into the cavity. IBS® Torque Ratchet was used to insert the implant to the required depth. According to the manufacturer’s instruction the primary stability was achieved by 15 N. Follow-ing the procedure, the patient was given instructions to ensure very good oral hy-giene using 3 times mouth rinse daily until the closure of the wound. According to the manufacturer’s surgical protocol, second stage surgery was carried out after 8 months second stage surgery was decided. X ray examination showed elevation of maxillary sinus floor for about 9 mm. The implant was exposed and gingival former (healing abutment) was secured successfully at the implant site (Figure 3). Figure 4 shows the implant with the final prosthesis in place.

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Figure 1: (a) Preoperative photograph for the missing #15 and #16. (b) Preoperative radiograph with about 0.5 mm height in #16 areas.

Figure 2: (upper left) IBS sinus lift armamentarium(https://ibsofamerica.com/newtechnology/instrumentation/sinus-lifting-the-mechanics/) from left to right: Short Magic Drill, IBS Sinus Lifter and Bone Pusher. (upper right) postop-erative radiograph for upper right 5 and 6. It shows the uniform elevation pattern around the implant. : (lower right) periapical radiograph 8 months for the upper right# 6 postop-

eratively. (Lower left) 3D image (coronal view) for the implant in place.

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Figure 3: (a) Gingival formers secured in place. (b) Final prosthesis in position.

DiscussionInadequate bone height in the posterior maxillary area due to maxillary sinus pneu-matization remains as one of the challenges for dental implant dentistry (Schlegel et al., 2008). It is, even, more challenging in sinus lifting using crestal (indirect) ap-proach (Balaji, 2013; Louis, 2016). It is agreed that less bone height less the chance for success for dental implant. Studies have shown that bone height less than 4 mm might not be enough to ensure successful implant stability (Asawa et al., 2015; Romero-Millan et al., 2012). However, it seems there is tendency toward indirect sinus lift procedure, because it is less invasive (Shetty et al., 2016). This might be the main drive for dental implant companies to improve its chances of success utiliz-ing different surgical equipment and related techniques. These include osteotomes (Romero-Milla´n et al., 2012), maxillary sinus balloon (Penarrocha-Diago et al., 2012) and specially designed burs (Alsabbagh et al., 2017). This, in turn has been reflected by the cases reported recently in the literature challenging the reported evidence related to residual bone height. The lowest bone height as reported in the literature with indirect sinus lift was 2-4 mm (Neamat et al., 2017). Recently, the author was involved in a research on graftless indirect sinus lift using IBS CMC Technique. The research team was able to achieve primary stability for residual bone height of 1.75 mm with sinus floor elevation for 7 mm. the study results are about to be published soon. Simultaneous sinus lift and dental implant is influenced by both bone quality and quantity, which is why it has been advised to postpone dental implant insertion to a second stage surgery when bone height is less than 4 mm (Louis, 2016). The ability to achieve successful indirect sinus lift in this case might not be related to the useful-ness of sinus lifter used, but to the fin thread design (IBS®). This thread design al-lows more room between the threads for better bone and/or bone substitute material engagement with more chance of primary stability with extreme alveolar bone deficit. With thin bony plate, such as in this particular case, it might be difficult to provide controlled bone separation at the osteotomy site with open flap technique. This is why the author believes that doing flapless technique with soft tissue still attached to the bone surrounding the osteotomy site (sinus lift site) have provided support to prevent its fracture.

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ConclusionIndirect Sinus Lifting with (IBS® CMC Technique) seems to be effective in cases with crestal bone shortage (<1 mm) with minimum instrumentation and less hard and soft tissue trauma.

Acknowledgement The author would like to thank Dr. Noor Nabih for her help throughout the treatment period.

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Alsabbagh AY, Alsabbagh MM, Nahas BD, Rajih S (2017). Comparison of three differ-ent methods ofinternal sinus lifting for elevation heights of7 mm: an ex vivo study. International Journal ofImplant Dentistry 3(40):2-7.

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maxillary sinus floor augmentation. Periodontology 47(193–205.

Neamat AH, Ali SM, Boskani SW, Mahmud PK (2017). An indirect sinus floor elevation by using piezoelectric surgery with platelet-rich fibrin for sinus augmentation: A short surgical practice. Int J Case Rep Images 8(6):380–384.

Pai UY, Rodrigues S, Hegde P, Khurana N (2017). Indirect Sinus Lift Done Using “Au-togenous Core Lift” Technique in Combination with Alloplastic Phosphosilicate Putty in Atrophic Maxillary Posterior Region: A Clinical Report with 1-Year Follow-Up. Contemp Clin Dent 8(4):627-631.

Penarrocha-Diago M, Galan-Gil S, Carrillo-Garcia C, Penarrocha-Diago D (2012). Tran-screstal sinus lift and implant placement using the sinus balloon technique. Med Oral Patol Oral Cir Bucal 17(1):e122-128.

Romero-Milla´n J, Martorell-Calatayud L, arrocha MP, Garcı´a-Mira B (2012). Indirect Osteotome Maxillary Sinus Floor Elevation: An Update. Journal of Oral Implantology. XXXVIII(6):799.

Romero-Millan J, Martorell-Calatayud L, Penarrocha M, Garcia-Mira B (2012). Indirect osteotome maxillary sinus floor elevation: an update. The Journal of oral implantology 38(6):799-804.

Schlegel A, Hamel J, Wichmann M, Eitner S (2008). Comparative Clinical Results after Implant Placement in the Posterior Maxilla with and without Sinus Augmentation. The International Journal of Oral & Maxillofacial Implants 23(2):289-298.

Sharan A, Madjar D (2008). Maxillary sinus pneumatization following extractions: a radiographic study. Int J Oral Maxillofac Implants 23(1):48-56.

Shetty M, Thulasidas NHR, Hegde C (2016). An indirect sinus lift with ridge splitting procedure for implant placement: A case report. IJMDS 5(1):1088-1092.

Summers RB (1994). A new concept in maxillary implant surgery: the osteotome technique. Compendium 15(2):152, 154-156, 158 passim; quiz 162.

Tatum HJ (1986). Maxillary and sinus implant reconstructions. Dent Clin North Am 30):207.

Young MP, Korachi M, Carter DH, Worthington HV, McCord JF, Drucker DB (2002). The effects of an immediately pre-surgical chlorhexidine oral rinse on the bacterial con-taminants of bone debris collected during dental implant surgery. Clin Oral Implants Res 13(1):20-29.

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Investigating the correlation between palatal depth and width measurements in impacted maxillary canine patients by using cone beam computed

tomography 1Omar Faruq Mohammed, B.D.S., 2Alah Dawood Mahmood, B.D.S, M.Sc, PhD, 1 Erbil Health Directorate, 2 Department of Pedodontic, Orthodontic, and Pre-vention Dentistry, College of Dentistry, University of Mosul, Mosul, Iraq.Corresponding author: Omar Farouq Mohammede.mail: [email protected]

AbstractBackground Cone Beam Computed Tomography system of 3D digital acquisition can be used in various dental sections such as orthodontics, endodontic, implantology, surgery and oral diagnosis. Linear and angular measurements on Cone Beam Com-puted Tomography images are accurate, precise and can be used to assess the exact position of displaced canines. Objectives It is to investigate with cone beam comput-ed tomography the correlation between the palatal depth, width and the upper canine impaction. Materials and methods The study sample consists of 57 CBCT images of 35 patients referred to Al- Shifaa private hospital with impacted maxillary canines and 22 control patients with fully erupted canines. These were evaluated by volumetric 3D imaging to accurately localize the normal or impacted canines. The palatal depth and width of the impacted canine and control cases were measured and compared. Results The statistical descriptive analysis showed no significant difference in palatal width measurements between the control and impacted canine groups. On the other hand, the LSD test showed a significant difference in the mean of palatal depth be-tween the control cases and impacted canine cases. Conclusions Marked decreased palatal depth in impaction cases could be a factor in causing maxillary canine impac-tion

Keywords Cone beam computed tomography, impacted maxillary canine, palatal depth and width

IntroductionAn impacted tooth is a tooth which is completely or partially unerupted and is posi-tioned against another tooth, bone or soft tissue so that its further eruption is unlike-ly, described according to its anatomic position (Janakiraman et al., 2010). With the exception of third molars, maxillary canines are the most frequently impacted teeth, with prevalence ranging from 0.8% to 3.0 % (Alqerban et al., 2011). Eighty-five per-cent of impacted maxillary permanent cuspids are palatal impactions, and 15% are labial impactions. Inadequate arch space and a vertical developmental position are often associated with buccal canine impactions. If buccally impacted cuspids erupt they do so vertically, buccally and higher in the alveolus. However, due to denser

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palatal bone and thicker palatal mucosa, as well as a more horizontal position, pala-taly displaced cuspids rarely erupt without requiring complex orthodontic treatment (Gupta et al., 2012). There is a general consensus that buccal and palatal impactions have different etiologies. Although crowding has been considered the primary cause for buccal impactions, a number of causes have been attributed to palatal impactions. Currently the two most popular theories reported that have gained some degree of consensus worldwide are the guidance theory and the genetic theory (Becker, 2007). Also, the scientific community has been treating buccal and palatal canine impactions as separate entities from an etiological perspective. Nevertheless, a recent theory has emerged which suggests that buccal and palatal canine impactions have similar etiological factors (Sajnani and King, 2012). Many investigators have been trying to uncover a relationship between the widths of the maxilla, skeletally and dentally, and the occurrence of palatally displaced canine. Some studies have shown that a poste-rior cross-bite or a transverse maxillary deficiency was related to canine impaction, but these studies did not differentiate whether the impactions were buccal or pala-tal (Hong et al., 2014). The aim of this research is to measure the palatal depth and width of the maxillary impacted canine cases and compare these with the other nor-mally erupted canine cases through Cone beam computed tomography to investigate if there is any correlation between the palatal dimensions and the canine impaction.

Materials and methodsThe sample of this study consisted of archive CBCT images for patients who were referred to Al-Shifaa private hospital, Dental Center, CBCT department in Erbil for localization of maxillary canine and or impacted canines. The study project was ac-cepted by the council of the College of Dentistry/Mosul University. Out of 120 patients referred by orthodontic specialists, only 35 patients (20 unilateral canine impaction and 15 bilateral impaction, with ages ranging from 17 to 31 years) who met special criteria were selected. Also, 37 fully erupted maxillary permanent teeth CBCT image cases were collected to be considered as normal cases (control group), of which only 22 cases (age range 19-31 years) were selected after meeting the following special criteria: full set of permanent dentition in the upper jaw “excluding the 3rd molar” with unilaterally or bilaterally maxillary impacted canines, no large metal restorations including crowns, no orthodontic appliances. In addition, patients with a cleft lip and or palate were excluded from the study. All cases had a class one molar relationship and a field of view of 8*5 was used in imaging of all CBCT cases in order to obtain full arch view in maxilla as that was the least field of view in this system that could com-ply with our requirements.All the images were taken by CBCT scanner (New tom, Giano 3D imaging Italy, Ver-sion 5.3) with the following specifications:- -X-ray source; high frequency, stationary anode with 90 KV and 3mA-Detector; flat panel Amorphous Silicon. -X-ray Emission time 9, 0 s. -Scan time 18 s. -Reconstruction time; 15 s. -Slice thickness; 0, 150 mm.-Images number; 337. The measurement of the palatal width in this study was accomplished by using three lines to represent the width between the first premolars in both sides and the width between the second premolars in both sides was measured in the same manner. The inter-molar widths were measured by locating the coronal plane line in the axial view on the mesio-buccal cusp position in the right side and then the coronal plane line was rotated to comply with our requirement for it to fit on both the right and left me-



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sio-buccal cusp of the first molar. Then we moved to the coronal view and scrolled the pointer up and down till we reached the maximum cusp tip point on both sides, after which we started measuring the distance between these two cusp tips using a spe-cial ruler supported by software (the length was measured in millimeters). The same method was repeated for both first and second premolars (Alam et al., 2014), as shown in figures (1, 2 and 3) respectively. The palatal depth measurement is repre-sented by the depth or height of the palate in two regions, the first premolar and first molar areas, as shown in figures (4, 5) respectively We started measuring the palatal depth on the axial view by locating the coronal plane on the sites of the upper first molars in both the left and right sides and ensuring that it passed through the center of the tooth. Then we moved to the coronal view to draw a line between the cemento-enamel junctions (C.E.J) of the two first molars. From the mid-point of this line we drew a perpendicular line up the palate and measured it with a special ruler supported by software, in order to represent the palatal height or depth in the first molar region (El Nahass and Naiem, 2016). The same procedure was repeated in the 1st premo-lar area. All the measurements were repeated by another specialist radiologist at the same time. A paired t-test was done, and non-significant differences were found for all variables at 5% probability level. The data of the sample was analyzed using sta-tistical package for social sciences SPSS version 20. Descriptive statistics were used to determine the means and standard deviation and Anova one way test was used to compare between more than two groups and to identify group(s) responsible for statistical differences we used LSD. P-value ≤0.05 was considered to be statistically significant.

Results The statistical analysis of palatal depth is shown in table (1). The mean of inter-first premolars width was higher in the control group than impacted canine groups. The value was higher in the bilateral group than in the unilateral group, with no significant difference among the groups. In the control and bilateral groups the inter-second pre-molar widths recorded nearly equal values and these were higher than the unilateral group means value, with no significant difference among the three groups. The mean value of the inter first molar width in the bilateral group was higher than in the con-trol group but no significant difference among the three groups was demonstrated. The statistical analysis of palatal depth is shown in table (2). A very high significant difference in the mean of palatal depth in the first premolar and first molar regions was identified between the control and impacted canine groups, with no significant difference within impacted canine groups.



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Figure 1: Inter first maxillary premolar width.

Figure 2: Inter second maxillary premolars width.



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Figure 3: Inter first maxillary molars width

Figure 4: Measurement of arch depth in 1st maxillary premolar region.



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Figure 5: Measurement of arch depth in 1st maxillary molar region.

Table 1. Mean ± (St.) standard deviation of palatal width of control and im-pacted canine groups.

Table 2. Mean ± (SD.) standard deviation) of palatal depth of control and im-pacted canine groups.



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DiscussionMany previous studies have tried to find the exact cause of maxillary canine impac-tion, with some relating the impaction to local space loss causes and other studies relating the impaction to systematic disorders. However, in this research we were at-tempting to find out whether there is any correlation between canine impaction and palatal depth and width. Regarding the palatal width, the result of this study showed a slight difference in the mean values among the groups but this was not statistically significant, a result that agrees with the study by Fattahi et al. (2012). Also, our re-sult is in accordance with Stanaitytė et al. (2014) who found no significant difference in maxillary width in canine impaction between the palatal and labial sides. On the other hand, our results disagree with the finding by Ali Rizvi et al. (2012) of a posi-tive association between maxillary transverse discrepancy and occurrence of impacted maxillary permanent canines, and also found that the distance between the upper first molars and pre¬molars did not differ between the palataly impacted canine and labially impacted canine groups. The result of the present study showed a marked in-crease in the mean palatal depth in the control cases, with a very high significant dif-ference between the normally erupted canine cases and the impacted canine cases, a result that agrees with Al-Khateeba et al. (2013) who found that the impaction cases exhibited smaller arch depth than the control group, thereby indicating that the pala-tal depth could be a cause of palatal canine impaction. However, our results diverge from those of Kim et al. (2012) who found that palataly displaced canine patients were an average of 2mm narrower, with a palatal vault 2.3 mm higher, than matched controls. References Alam M.K., Shahid F., Purmal K., Ahmad B. and Khamis M.F. (2014). Tooth size and Dental arch Dimension measurement through Cone beam Computed Tomography: Ef-fect of Age and Gender, Research Journal of Recent Sciences, 3 (85); 85-94.

Ali Rizvi S.A., Shaheed M., Ayub A., Ziareen S. and Masood O.(2012). Association of maxillary transverse discrepancy and impacted maxillary canines, Pakistan Oral & Dental Journal, 32, (3), 439-443.

Al-Khateeba S., Abu Alhaija E.S., Rwaite A. and Burqan B.A. (2013) Dental arch pa-rameters of the displacement and nondisplacement sides in subjects with unilateral palatal canine ectopia. The Angle Orthodontist. 83 (2); 259-265.

Alqerban A., Jacobs R., Fieuws S. and Willems G. (2011) Comparison of two cone beam computed tomographic systems versus panoramic imaging for localization of impacted maxillary canines and detection of root resorption. European Journal of Or-thodontics 33 (1); 93–102.

Becker A. (2007). Orthodontic Treatment of Impacted Teeth. 2nd Edn., Informa Healthcare, New York; USA.

El Nahass H. and Naiem S.N. (2016). Palatal bone dimensions on cone beam com-puted tomography. Implications for the palate as autogenous donor site: an observa-tional study, Int. J. Oral Maxillofac. Surg.,45 (1); 99–103.



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Fattahi H., Ghaeed F. and Alipour A.(2012).Association between maxillary canine im-paction and arch dimensions. Aust Orthod J. 28 (1); 57-62.

Gupta A, Makhija P, Bhatia V, Navlani M, Virang B. (2012). Impacted canine-diagnosis and prevention. Webmed Central dentistry.

Hong W.H., Radfar R. and Chung C.H. (2014). Relationship between the maxillary transverse dimension and palatally displaced canines: A cone-beam computed tomo-graphic study. Angle Orthodontist, 85, (3); 440-445.

Janakiraman EN., Alexander M. and Sanjay P. (2010). Prospective analysis of frequen-cy and contributing factors of nerve injuries following third-molar surgery J Craniofac. Surg. 21(3); 784–786.

Kim Y., Hyun H.K. and Jang K.T. (2012). Interrelationship between the position of im-pacted maxillary canines and the morphology of the maxilla. Am J Orthod Dentofacial Orthop, 141 (5); 556-562.

Sajnani AK. and King NM. (2012). The sequential hypothesis of impaction of maxillary canine – a hypothesis based on clinical and radiographic findings. J Craniomaxillofac Surg ., 40 (8); 375–385.

Stanaitytė R., Smailienė D. and Kaduševičius I. (2014). Tooth size discrepancies and dental arch width in patients with palatally and labially impacted maxillary canines, sveikatos mokslai / health sciences, 24 (2); 69-74.



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Effect of liner thickness and sandblasting of zirconia on the shear bond strength of veneering ceramic

Maha K. Jabbar, Msc. and Suha F. Dulaimi BDS, Msc.Department of Prosthodontic Technologies, College of Health and Medical Technologies, Middle Technical University (MTU), Baghdad, IraqCorresponding author: Suha Fadhil DulaimiEmail: [email protected]

AbstractBackground Partially stabilized tetragonal zirconia is used as the core material in all-ceramic restoration. The ceramic veneer zirconia restoration may suffer from chipping and delamination failure of ceramic veneer. Objective To evaluate the effect of stand-ardizing liner thickness and sandblasting of zirconia core on shear bond strength of veneering ceramic. Materials and Methods Forty pre-sintered zirconia cuboid sam-ples sub-divided into four groups; Group C: 10 samples without treatment at sinter-ing. Group Z1: 10 samples coated with 0.1mm liner thickness after sintering. Group Z2: 10 samples coated with 0.2mm liner thickness after sintering. Group S: -10 samples treated with sandblasting (50µm AL2O3) before sintering. Ceramic veneers were then applied with the layering technique. Following that, shear bond tests, were conducted. Results The tests showed that the liner thickness significantly affects SBS (P<0.01). Group Z1 showed a significant reduction in SBS; however, group Z2 showed a non-significant difference (P>0.05) from group C (control). Group S showed no significant difference compared to control (P>0.05). Conclusion Within limitations of the present study, the results showed that sandblasting the zirconia surface be-fore sintering with (50 µm) Al2O3 at an air pressure of 0.5 MPa for 15 seconds with a crosswise motion had no effect on the SBS of veneering ceramic. Coating the zirconia surface with 0.1mm liner decreased the SBS significantly, however; coating the sur-face with 0.2 mm liner resulted in better SBS than with the 0.1mm liner but statisti-cally was not significant from the control.

Keywords: liner thickness, sandblasting, shear bond strength, zir-conia ceramic

IntroductionYttria-stabilized tetragonal zirconia (Y-TZP) opens new avenues for all-ceramic res-torations due to its superior mechanical properties, which support its application as framework material for fixed partial dentures even in loaded reconstructions in the molar region (Filser et al., 2001)To achieve optimal esthetics, zirconia cores are ve-neered with a ceramic material. Adding veneer ceramics in layers result in final resto-ration having excellent esthetic properties (Aboushelib et al., 2006; Aboushelib et al., 2008). However, clinical failures of veneered Y-TZP frameworks for a range of reasons (e.g., chipping of veneering ceramic or delamination) were reported in 13.0% of cases after an observation period of three years and 15.2% after five years (Sailer et al., 2007) Clinical success of zirconia based restoration may depend on adhesion between zirconia core and veneering ceramic (Fischer et al., 2008). Many studies have evalu-

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ated various surface treatments for improving adhesion to veneering ceramics with microstructural analysis of the zirconia-ceramic interface (Monaco et. al 2014). These include airborne-particle abrasion, liner application, polishing, and grinding, acid etch-ing, laser etching, and silica coating, among which airborne-particle abrasion and liner application are the two most commonly studied methods (Wang et al., 2014, Alghazzawi and Janowski 2016). For now, however, no standard method has been established for optimal adhesion between zirconia and veneering ceramics Yoon et al. (2014) and Martínez-Galeano et al. (2015). In addition bonding mechanism of zirco-nia core with veneering ceramic not fully understood (Al-Dohan et al., 2004, Durand et al., 2012). Other researchers recommended conduction of further studies concern-ing effects of different zirconia core treatments before or during the veneering proce-dure (Lui et al., 2012). The conflicting results of previous studies concerning adhesion between zirconia cores and veneering ceramic indicate the need for standardization of techniques (Carlos et al., 2017, Felipe et al. 2018). Improvement of adhesion be-tween the zirconia substrate and the veneering ceramic is essential for the clinical success of zirconia restorations (Fischer et al., 2008). The present study aims to eval-uate the effect of the following factors on shear bond strength:1-Standardized 0.1 mm and 0.2 mm liner thicknesses. 2-Sandblasting of zirconia core at the pre-sintering stage.

Materials and methodsForty cuboid zirconia samples (3,687 mm in height, 19.664 mm in width and length) were prepared from zirconia blank (partially sintered Y-TZP , Zahnfabrk , Germany ) using a milling machine (Kareem and Al-Azzawi, 2014).

1. Samples groupingForty zirconia samples were divided into four groups each group contains (10) sam-ples according to the surface treatment that had been applied:Group C: 10 zirconia samples were left without treatment after sintering (control group).Group Z1: 10 zirconia samples were coated with 0.1 mm liner thickness after sinter-ing.Group Z2: 10 zirconia samples were coated with 0.2 mm liner thickness after sinter-ing.Group S: 10 zirconia samples were sandblasted with 50µm AL2O3 before sintering.

2. Preparation of zirconia samples before surface treatmentPrior to surface treatment (30), zirconia samples were sintered in the furnace (VITA ZYRCOMAT 6000 MS, Germany) according to the cycle recommended by the manu-facture (high - speed sintering temperature was 1450o for 80 minutes).The remaining 10 samples were sandblasted first and then sintered. During this process, a three-dimensional volumetric shrinkage of the milled zirconia samples of approximately 20% took place based on the fact that the shrinkage factor of this type of zirconia was 1,229. Following sintering, the samples’ dimensions approximately 16mm (±0.1) in length and width, 3 mm (±0.1) in height were checked with a digital caliper, (He et al., 2014).



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3. Cleaning of zirconia samplesFor groups not treated with sandblasting (group C, Z1, Z2) after sintering samples were cleaned ultrasonically in distilled water in a digital ultrasonic cleaner (WHITE PEAKS, Germany) for five minutes to remove any surface residue and then air - dried. On the other hand, the group subjected to sandblasting (S), were cleaned ultrasoni-cally after sandblasting and before sintering. (Benetti et al., 2011).

Group CAfter sintering, this group was not subjected to any treatment, so it is considered the control group. Group Z1After sintering, to obtain the standardization of the liner (0.1, 0.2) mm thickness, a custom-made mold was designed. The mold consists of a rigid base which contains two stainless steel metal straps: the first strap has 0.1mm thickness which contains’ a hole in the center which is 4.5 mm in diameter. The second strap has 0.2 mm thick-ness and the same 4.5mm - diameter hole in the center. Through this hole, standardi-zation of liner thickness was applied to the surface of the zirconia sample.

4. Application procedure of 0.1mm Zirliner thickness on samplesThe first metal strap had 0.1mm thickness placed on the prepared surface of each sample; a liner was applied to all samples with a brush (Kim et al., 2011 ; Çömlekoglu et al. 2008). The liner (IPS e.max Ceram Zirliner, 1, Ivoclar vivodent, Schaan, Liech-tenstein) was mixed with the respective liquid (Zirliner build-up liquid, all around, Ivoclar vivodent, Schaan, Liechtenstein) to a creamy consistency according to the manufacturer’s instructions. For standardization, the same amounts of powder and liquid were mixed for all samples, for each sample (1mg) of powder with 2 drops of respective liquid was mixed to obtain the desired creamy consistency according to manufacture,(Kareem and Al-Azzawi, 2014). Then one 0.1 mm layer of liner thickness was applied to the prepared surface using a brush: this was vibrated to achieve an even, greenish color effect and then left to dry for five minutes. After that the applied Zirliner was fired, in a calibrated porcelain furnace (P3000, ivoclar vivodent, Schaan, Liechtenstein), according to the manufacturer›s instructions. After firing, the thick-ness of each sample was then measured with a digital caliper with an accuracy of 0.02mm in three different locations (left end, mid-point and right end and corrected with diamond rotary cutting instruments until the desired samples’ thickness of 3.10 mm (zirconia + liner) was achieved.

Group Z2The second metal strap has a thickness of 0.2mm which contains› a hole in the cent-er of 4.5 mm in diameter and 0.2 mm thick placed on the prepared surface of each sample. For standardization, the same amounts of liner powder and liquid were mixed for all samples, to a creamy consistency in the same manner as in group Z1 and then layered onto the prepared surface using a brush .Through this hole standardization of liner thickness, 0.2mm was carried out on the zirconia surface until an even, greenish 0.2 mm thickness was achieved; it was then fired. Next, the thickness of each sample was measured with a digital caliper and corrected with diamond bur until the desired thickness of 3.20 mm (zirconia + liner) was achieved.



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Group SBefore sintering, the working surfaces of the zirconia samples were abraded vertically in a crosswise motion of the nozzle at an air pressure of 0.5 bar for 15 seconds and at fixed distance of 10 mm between the nozzle and the surface of the samples with 50µm Al2O3 by using a sandblasting device (EASY-Blast, Bego, Germany) (Ebeid et al., 2017).Then all samples were ultrasonically cleaned in distilled water for five min-utes and then dried with air. After that, sintering was carried out in a zirconia sinter-ing furnace according to the manufacturer›s instructions.

5. Application of veneering ceramic on zirconia samplesIn order to achieve the desired dimensions of the veneering ceramic, a specially de-signed poly-methyl methacrylate (PMMA) split cylindrical mold was constructed. The mold had two diameters (outer diameter 12.5mm and inner diameter 4.5mm ).This mold was divided into two equal split parts with pins in the edge through which the two parts of the mold were secured in position (Saka and Yuzugullu, 2013). The mold was placed above the liner layer in the center of each sample. Ceramic powder (e.max Ceram, dentin A2, Ivoclar Vivadent, Schann, Liechtenstein) was mixed with an appropriate amount of the respective liquid (e.max liquid build up, Ivoclar Vivadent, Schann, Liechtenstein). For standardization, 2.7 mg was mixed with six drops of re-spective liquid for each sample to produce the desired working consistency of ceramic (Kareem and Al-Azzawi, 2014). Then the ceramic was added incrementally into the mold on the prepared surfaces of zirconia by using the layering technique, condensing the ceramic material layer by layer. After placement of each increment of ceramic, the excess moisture was removed with absorbent paper tissue and the veneering proce-dure continued until the veneer ceramic measured 4mm in thickness. Next, the split mold was carefully removed from the zirconia sample. If the veneering ceramic had any bubble or defect, these were repaired by adding some ceramic by brush without any damage to the shape or size of the veneering ceramic produced by the mold. Then, the ceramic/dentine was fired in a calibrated porcelain furnace (p 3000, Ivoclar, vivodent, Schaan, Liechtenstein). The firing of the ceramic was performed according to the manufacturer’s instructions. Because of the volumetric shrinkage during fir-ing of the porcelain, additional porcelain was added following the previous technique and fired under the same conditions to achieve the desired dimensions of ceramic (4.5 mm in diameter and 4 mm in length) (He et al., 2014). After complete firing, the dimensions of veneering ceramic were checked by digital caliper and then adjusted if needed by using a straight handpiece (Figure 1). To evaluate the SBS each sample was embedded in a silicon mold using cold cure acrylic (Kirmali et al., 2013).

Figure 1: Zirconia samples with ceramic build up after firing



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6. Bond strength testThe samples were attached to the Instron universal testing machine, (Laryee WDW- 50, China). Force was applied to the samples using a stainless steel chisel shaped piston at a constant crosshead speed of 1 mm/min until failure occurred (He et al., 2014). The tested samples were placed in the lower part (jaw) of the testing machine. While the acrylic block was held in a horizontal position in such a way that the long axis of the chisel-shaped piston is placed parallel to the veneer surface of the sam-ple, and the chisel end of the rod was positioned at the interface between the veneer surface and the zirconia square interface, The sample was secured tightly in place to ensure that the zirconia square was at a 90 degree angle to the vertical plane, the samples were stressed to failure, and a testing machine was connected with com-puter software during the testing and automatically displayed load failure force in N (Newton›s). The maximum force (N) was recorded, and the SBS (MPa) was calculated by dividing the load (N) by the surface area of the bonded area (mm2). Shear Bond strength = force in (N)/bonding area in (mm2).

7. Type of failureThe fracture samples were examined after de-bonding to determine the mode of fail-ure under the stereo-microscope (MEIJI, Japan ) at a magnification of 20X (Craig RG, 2004). Failure modes were classified as follow: (Cardelli et al., 2015).1. Adhesive: if no remnants of porcelain were found in the metal or zirconia surface.2. Cohesive: if fractures occurred within the porcelain side.3. Mixed: if remnants of porcelain were found in the ceramic/zirconia surface.

8. Scanning Electron Microscope (SEM) and elemental composition analysesOne sample was selected from each group and cleaned in an ultrasonic cleaning bath for five minutes, and then air dried. The interfacial surface was sputtered coated with gold; next the samples were mounted on an aluminum holder and analyzed with secondary electrons images were observed under a field-emission scanning electron microscope (Czech Republic, Netherlands), and photographs were taken at different magnifications- 500X with a 20 KV accelerating voltage - to examine surface morphol-ogy. The elemental composition of the same samples was qualitatively analyzed by using an energy dispersive X-ray spectroscopy (EDS) and the weight percentage of every traced element was measured (X Flash 6 L10-model, broker company-Germa-ny). The IBM SPSS statistics program Version 21 was used to carry out the statistical analysis of the current study and Microsoft Excel 2010 was used for graphics pres-entation. The usual statistical methods were used in order to assess and analyze the results; they include:

Statistical AnalysisStatistical tables including observed frequencies, percentages, arithmetic mean, and standard deviation, standard error, and range (minimum and maximum values).

Inferential StatisticsThey were used in order to accept or reject the statistical hypotheses:1. Analysis of variations (ANOVA) with the multi comparison, and the least significant difference (LSD) test. 2. Student test (t-test).



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Results 1- Comparison of shear bond strength between the groups (C, Z1, Z2):Table 1, shows that the higher mean value for shear bond strength was registered by group C (12.441±2.284), followed by group Z2 (11.871±1.142), while, the low-est mean value was observed in group Z1 (2.539±1.108). One-way ANOVA test be-tween the studied groups showed highly significant difference (P<0.01). To examine the source of the difference among the groups (C, Z1, and Z2), further analysis of these groups was performed using the least significant difference test (LSD). Table 2, shows a highly significant difference (P<0.01) between group C and group Z1. While non-significant difference (P>0.05) found between group C and group Z2, also highly significant difference found between Z1 and Z2 groups (P<0.01).

Table 1: Descriptive statistic and one-way ANOVA for groups C, Z1, Z2

Table 2: LSD test among groups C, Z1 and Z2

2- Comparison between two groups - control and sandblast groups (C, S):Descriptive statistic showed a higher mean value in group S (14.075±2.627) followed by group C (12.441±2.284). Student test (t-test) reported in Table 3 was performed to examine the difference between group C and group S. The result showed the sta-tistically non-significant difference (P>0.05).



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Table 3: Mean distributions of Shear bond strength test (MPa) among groups C and S with Student t-test

3-Mode of failures:The results of failure mode after shear bond testing were observed with a stereomi-croscope (Meiji- Techno, Japan) at a magnification of X20. It showed that the pre-dominant mode of failure for groups S, Z1 and Z2 was a cohesive failure as shown in Figure 2, a. Meanwhile, mixed failures occurred in all groups at a low percentage as shown in Figure 2, b. Adhesive failure was observed in the group C in high percentage as shown in Figure 2, c .

Figure 2: Mode of failure: A- cohesive, B- mixed and C- adhesive.

4- SEM Observation:SEM images (Figure 3 a) for the group C samples revealed numerous scratches in-troduced by the cutting procedure during the preparation of the sample. Also fine grooves related to the scratch lines with a thin layer of veneer that remained on the surface of the zirconia substructures were partially exposed .While group Z1 clearly showed the formation of abundant micro- porosities (Figure 3 b). For images of group Z2 (Figure 3 c) show a decreased volume of porosity on areas of veneer. SEM im-ages for the group S sample showed areas of the glassy matrix (ceramic veneer) and smaller areas of sandblasted zirconia.



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Figure 3: SEM images of samples after failure: a- group C, b- group Z1, c- group Z2, and d- group S.

5- Energy dispersive X-ray spectroscopy (EDS): The chemical analyses were per-formed by EDS, on the surface of the ceramic veneer sample after shear bond testing, to assess the possible presence of zirconium that could affect the analysis at the in-terface. The EDS spectrum at the fractured interface of the Y-TZP specimen detected the existence of chemical elements as zirconia (Zr), sodium (Na), potassium( K), alu-minum (Al), silicon (Si), oxygen (O2) and carbon (C). Normalized weight percentages for each element on the interface are listed in Table 4.

Table 4: Normalized weight percentage of each element on zirconia/ veneer interface.

DiscussionMany variables may affect the core- veneer bond strength, such as the surface finish of the core, which can affect mechanical retention, development of flaws and struc-ture defects at the core- veneer interface, wetting properties, volumetric shrinkage of the veneer (Aboushelib et al., 2006) and residual stresses generated by mismatch in the thermal expansion coefficient (TEC). The coefficients of thermal expansion for the core and veneering ceramic must closely match to achieve strong interfacial bond strength. In the present study, the coefficient of thermal expansion of zirconia



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(10.5×10-6k-1) was slightly higher than that of the veneering ceramic (9.5×10-6k-1). A slightly higher coefficient for the core material causes the veneering ceramic to be in a beneficial state of residual compressive stress (Craig, 2004). In the present study, the zirconia sample was veneered by the layering technique. The layering technique has been the principal method of applying veneering ceramics to the core material (Gasparic et al., 2013). The air-abrasion of zirconia samples in the pre-sintered stage using 50µm AL2O3 particle might be a promising method of surface treatment be-cause after sintering the entire group treated in the pre-sintering stage showed the complete transformation of the monoclinic phase back to tetragonal, thus not subject-ing the zirconia to early degradation (Ebeid et al., 2017).1. Comparison of shear bond strength between the groups (C, Z1, Z2): The results of the SBS for group C showed higher mean value (12.441±2.284), in comparison to group Z2 (11.871±1.142) and group Z1 (2.539±1.108). One - way ANOVA between groups showed a highly significant difference in the P value <0.01. This result may be attributed to the fact that the zirconia surface is relatively smooth and flat. During the cutting procedure of the zirconia blank for making the samples, the milling ma-chine produced trace lines on the surface of zirconia sample. Aboushelib et al., (2008) stated that the CAD/CAM milling process, produced trace lines on the surface of the framework of zirconia materials. These lines in group C may produce micro-undercuts that caused micromechanical interlocking with the veneer ceramic material. These cutting traced lines were clearly observed in the SEM image (Figure 3 a). The failed samples showed 50% adhesive failure (delamination), 30% mixed thin layers of veneer porcelain without any defect or pores that remained on the surface of the zirconia sub-structures, and 20% co-hesive (chipping). This indicated that the crack extended along the zirconia-veneer interface. EDS analysis of the zirconia-veneer interface (Table 4) of group C revealed the presence of zirconium in the ceramic veneer layer and elements characteristic of the veneering layer (silicon as the main element). Therefore strong bonding between the veneering ceramic and the zirconia core in group C suggested that chemical bonds were established between both materials during firing (Fischer et al., 2008). The bonding between Y-TZP and the veneering porcelain for this group could be explained by the interaction between mechanical retention and chemical bond-ing forces (Spintzyk et al., 2016). The SBS of group Z1 was the lowest mean value (2.539±1.108) followed by group Z2 (11.871). The application of the Zirliner 0.1mm layer decreases the wettability of the zirconia surfaces, to a greater degree than the application of the ceramic veneer alone. In group C the absence of liner allowed con-tinuous contact between the two layers and strengthened the adhesion. This finding, is in agreement with study results of Aboushelib et al. (2008) stated that application of liner over the zirconia surface increased the chance of interfacial failure and reduce the core/veneer bond strength. Other researchers such asSailer et al., (2007), Kim et al., (2011), and Çömlekoğlu et al., ( 2008) stated that reduction in SBS was related to poor wetting of the liner over the zirconia surface and interfacial voids. Felipe et al., (2018) did not use the liner or intermediate ceramic because the ceramic mix had a larger volume than the liners. Precise explanations for bonding mechanism of zirconia core and veneering ceramic not established yet, however, researchers had put for-ward the concept of a fusion between core and veneer materials resulting in diffusion of the elements of each material across the bonded interface (Al-Dohan et al., 2004 ;Durand et al., 2012). (Aboushelib et al., 2006) state that, in a pilot study fabrication



49

showed the formation of air bubbles in the liner layer, when using a brush to apply the liner. The SEM of group Z1 Figure 3-b showed abundant round micro-porosities, present in the ceramic layer and the porosity could be the result of air trapped dur-ing the mixing or condensation of the little particles or by the gases created during the sintering. Mode of failure of group Z1 showed 90% cohesive and 10% mixed. EDS analysis (Table 4) of the zirconia - veneer interface in group Z1 revealed the existence of sodium, aluminum and silica elements with some amount of gases like oxygen, nitrogen, and carbon on zirconia surface may be led to the formation of porosity (Mo-naco et al., 2014). A study stated that after the veneering process, the amount of oxygen on the zirco-nia surface was increased and there were no exchanges of elements at the zirconia/porcelain interface. The generation of micro-porosities, at the interface was detected and assumed to be the main reason for failure (Liu et al., 2012). Reduction in the SBS of groupZ1 coincides with the results of Carlos et al. (2017) whom stated that the application of Zirliner (0.1mm thickness) reduced the bond strength of the zirconia veneer interface. However, this conflicts with Yoon et al. (2014) and Martinez-Galeano et al. (2015) ,over the cause of conflict difference in the composition of the liner used, while the present study applied standardization of liner composition and thick-ness ,unlike the previously mentioned studies. LSD test between groups C and Z2 showed no significant difference see Table 2. This could be explained according to the SEM image for this group Z2. The image in Figure 3c showed a thin layer of veneering porcelain which covered the zirconia surface with only a few defects on the surface of the core materials and much fewer micro-porosities than the Z1 group. This may be due to the fact that 0.2mm liner thickness could improve particles condensation, remove the air bubbles and induce the formation of better contact between porcelain and the zirconia substrate; however, it does not enhance the shear bond strength. The LSD test comparing group Z1 and group Z2 showed a highly significant differ-ence (P<0.01 Table 2). EDS analysis for group Z2 indicated the existence of trace elements such as Si, Na, Al and Ca in high concentrations derived from both liner and veneer material on the zirconia surface and with small amounts of gases like oxygen and absence of both nitrogen and carbon (Table 4). This indicated that the amount of gas trapped between the ceramic and zirconia were lower than group Z1. During the sintering step, the amount of glassy phase ceramic increased and the concentration of dissolved gases decreased; this improved chemical interaction by increased wetta-bility with the zirconia surface. Liu et al. (2012) reported that the good wetting is an important factor for an improved bonding and stronger adhesion can be achieved with lower contact angle and increased interfacial contact area. In addition, more residual stress was accumulated by 0.1mm liner application as concluded by Alghazzawi and Janowski (2016).

2-Comparison between group C and group S: The results of the SBS for group S sandblasting with 50µm AL2O3 before sintering showed higher mean value (14.075±2.627) but a statistically not-significant difference when compared with group C mean value (12.441±2.284 ) (see Table 3). This result may be due to using small sized 50 µm Al2O3 abrasion particles with a reduced amount of pressure (0.5 bars) in a crosswise motion used in the pre-sintered stage. The sandblasting tech-nique mentioned created micro undercuts but these were not detrimental to the zirco-nia samples. This might be due to the fact that sintering caused shrinkage of zirconia



50

samples thus making the topography although rough but not steep to act as flaw or stress concentration areas (Ebeid et. al. 2017). The SEM examination shown in Fig-ure 3-d of group S indicates that sandblasting could improve interfacial adhesion by cleaning the zirconia surface and enhancing high surface energy and wettability, al-though it showed mixed and cohesive failure. Crack path in the porcelain veneer layer and more porcelain components remained at the zirconia surface. EDS analysis at the fractured interface detected mutual diffusion between Zr and Si and existence of sodium, potassium, aluminum, indium and silica in high normal weight concentrations when compared with the group S as shown in Table 4. This finding did not concur with those of He et al., (2014), Kareem and Al-Azzawi (2014) and Fischer et al., (2008). The difference may be due to the method of samples’ preparation and commercial brand of zirconia blocks with veneering ceramic, a different technique of sandblasting, and different sandblast particle size and levels of pressure.

ConclusionWithin the limitation of this in- vitro study the following conclusions can be drawn:1. Sandblasting of zirconia core with (50µm) Al2O3 at an air pressure of (0.5) MPa for 15 seconds with a crosswise motion, had no effect on the SBS of veneering ceramic.2. Application of Zirliner with a thickness of 0.1mm on zirconia core decreased the SBS of veneering ceramic significantly.3. Application of Zirliner with a thickness of 0.2mm on zirconia core resulted in better SBS than 0.1mm but, was statistically not significant compared to the control group.

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