the international journal of periodontics & restorative...

The International Journal of Periodontics & Restorative Dentistry

There is currently a strong need forfixed prosthodontic restorations in thepractice of dentistry.1,2 To ensureproper tooth preparation in the ante-rior sector, where esthetic require-ments are crucial, some basic consid-erations must be kept in mind.3,4

Periodontal structures must berespected and tooth preparation mustprovide a sufficient space to establisha strong and satisfactory estheticrestoration.

To create an esthetic and harmo-nious appearance between therestoration and adjacent soft tissue, anindiscernible margin for the restora-tion is typically achieved by placingthe finish line (and thus the restorationmargin) within the gingival sulcus.5

Subgingival finish line preparation, orsulcus penetration, is achieved byusing a cutting bur to gradually burythe finish line into an intracrevicularposition without violating the biologicwidth. A major disadvantage inher-ent to this procedure is the high cut-ting speed required within the nar-row gingival sulcus, which increasesthe risk of injuring the internal part ofthe marginal gingiva and periodontalconnective tissue attachment.

Ultrasonic Sulcus Penetration: A NewApproach for Full Crown Preparations

Marc Sous, DDS, PhD*Yann Lepetitcorps, PhD**Jean-François Lasserre, DDS, PhD***Ngampis Six, DDS, MSc, PhD****

Newly developed ultrasonic diamond-coated tips (UDT) have been created forsulcus penetration and intracrevicular finish line preparation and polishing. Onehundred forty-two freshly extracted premolars and molars were employed for acutting efficiency test. Dentin surface roughness was analyzed with an optical pro-filometer and a scanning electron microscope. Within a reasonable cutting time,the UDTs possessed sufficient dentin-cutting capacity. The surface roughness ofdentin prepared with the UDT can be improved by using a smaller grit size UDTor a smooth tip set at lower power, and the roughness approaches that of dentinprepared with a referenced red diamond bur. A clinical protocol of ultrasonicsulcus penetration with these developed UDTs is proposed. (Int J PeriodonticsRestorative Dent 2009;29:277–287.)

*Private Practice, Pau, France.**Professor, Université Bordeaux I, Talence, France.

***Assistant Professor, UFR d’Odontologie, Université Victor Ségalen Bordeaux II,Bordeaux, France.

****Laboratoire de Réparation et Remodelage des Tissus Oro-faciaux, Groupe MatricesExtracellulaires et Biominéralisation, Faculté de Chirurgie Dentaire, Université Paris 5,Montrouge, France.

Correspondence to: Marc Sous, 3 Boulevard d’Aragon, 64000 Pau, France;email: [email protected].

This article is based on the thesis completed by Dr Marc Sous and defended in 2003 atUniversité Victor Ségalen Bordeaux II, Bordeaux, France.

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Volume 29, Number 3, 2009

Consequently, prior to preparation,gingival displacement with a retrac-tion cord is often practiced.4,6,7

Ultrasonic instrumentation hasbeen introduced8–10 and successfullyapplied in periodontology,11,12 endo-dontics,13 restorative and prostheticdentistry,14–16 and, more recently, im-plant dentistry and oral surgery.17

Ultrasonic tips have demonstrated twoessential qualities: good tactile sense,which allows the operator to perfectlycontrol operative performance, andrespect of peripheral soft tissueintegrity.

The objective of this study was todevelop ultrasonic diamond-coatedtips (UDTs) with a deep chamfer profilefor intracrevicular finish line prepara-tion and polishing. A new approachthat uses these tips during sulcuspreparation is proposed for full crownpreparation.

Method and materials

Prior to the creation of UDTs, the fol-lowing criteria were established.

• UDTs must have a deep chamferprofile.

• They must be used in conjunctionwith a piezoelectric handpiececonnected to a generator per-forming at the vibration frequency,amplitude, and power range thathave already been proven clini-cally acceptable when used in con-tact with soft tissue in periodontics.

• UDTs must demonstrate a suffi-cient dentin cutting efficiency.

• UDTs must generate a dentin sur-face roughness close to that gen-erated by a fine grit or red dia-mond bur of 30-µm diamond gritsize (used as a reference).

• They must have an ergonomicshape with a water spray outlet.

UDT development stages

Experimental UDTs were developed intwo stages. During the feasibility stage,experimental UDTs of different shankshapes and coated with two differentsizes of diamond grit (126 µm and46 µm) were developed to verify that,when used, they could vibrate and cutdentin. During the optimization stage,factors such as a suitable ergonomicshape (shorter and less bent or curved),distance of diamond deposit, anddiamond thickness on the tips wereperfected, and the final tips were fabri-cated for further study. Diamond gritsizes on these UDTs were 76 µm and46 µm. An ultrasonic smooth tip wasalso developed and tested at this stage.

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Table 1 Summary of tests and analyses

Analyses

Developmental stages/ No. of Cutting group Diamond grit size (µm) teeth efficiency* SEM Profilometry*

ControlGreen diamond bur 100 5 5 5Green followed by red diamond bur 100 then 30 5 5 5

Feasibility phaseMachine 126 8 8 (16)

46 8 8 (16)Manual (three operators) 126 68 68 (117) 2

46 23 23 (40) 2Optimization phase

Manual (one operator) 76 5 5 (10) 2 5 (10)46 10 10 (23) 10 (20)76 then 46 5 5 (10) 2 5 (10)76 followed by 46; then smooth 5 5 (10) 2 5 (10)

*Numbers in parentheses = no. of surfaces measured.

Cutting efficiency test and measurement

One hundred forty-two freshly ex-tracted human premolars or molarswith no decay were collected and pre-served in a hypochlorite solution foruse in the present tests and analyses,which are summarized in Table 1.During the feasibility stage, twopreparation modes (manually ormachine-driven) were assigned at ran-dom to each tooth. Machine-drivenpreparation was performed with UDTsattached to a handpiece fixed to anapparatus developed for this purposeto control speed, direction of move-ment, and load application. Manualpreparation was performed by threedifferent operators. During the opti-mization stage, the cutting test wasperformed only manually and by oneoperator.

All experiments were performedusing the same piezoelectric hand-piece and the same power generator.Cutting efficiency was studied whenthe generator was set at S10 (scalingmode and maximum power at 10) anddetermined by the amount of tissueremoved or the difference in the dis-tance between the initial and final fin-ish lines. Cutting duration was limitedto 3 to 4 minutes. During the feasibil-ity stage, the cutting efficiency of the126-µm and 46-µm UDTs was com-pared, and during the optimizationstage, the cutting efficiency of the 76-µm and 46-µm UDTs was compared.

Specimen preparation

Each tooth was subjected to coronalpreparation in two phases (Fig 1).

1. A gross reduction with a green dia-mond bur (diamond grit size of 100 µm, #6881-31-014C, Brasseler)mounted on a turbine was per-formed to place an initial finish lineat 1 mm above the cementoe-namel junction (Fig 1, left).

2. The final finish line was defined byusing the UDTs placed at the initialfinish line and parallel to the toothaxis and then simultaneouslymoved in an apical and horizontaldirection (Fig 1, right). The UDTswere mounted on a piezoelectrichandpiece connected to a gener-ator (Suprasson P Max, Satelec-Acteon group).

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Fig 1 (left) A gross reduction of tooth tissue above the gingivalline is performed with a diamond bur mounted to a turbine. (right)With the corresponding ultrasonic tips, sulcus penetration consistsof gradually burying the finish line into the gingival sulcus with thecorresponding ultrasonic tips; cord packing for gingival retraction isnot required.

Surface roughness analysis

The area of interest is the gingival mar-gin floor of the final finish line. Dentinsurface roughness was quantitativelyanalyzed and automatically calculatedwith an optical profilometer (WYKONT1100, Veeco Instruments). A scan-ning electron microscope (SEM) wasused to qualitatively analyze the sur-face status.

Ten teeth were used as controls.Five were prepared with a green dia-mond bur (#6881-31-014C, Brasseler)and the other five were prepared withthe green diamond bur followed by ared diamond bur (#8881-31-014FC,Brasseler).

During the feasibility stage, twomanually prepared specimens fromthe 126-µm UDT group and two fromthe 46-µm UDT group were selectedfor SEM analysis. During the optimiza-tion stage, two teeth prepared withthe 76-µm UDT, two prepared with the76-µm and then the 46-µm UDTs, andtwo prepared with the 76-µm UDTthen the 46-µm UDT followed by asmooth tip were analyzed by SEM.Five to ten teeth from each group wereanalyzed with a profilometer. Adetailed distribution of the teeth is pre-sented in Table 1. The effect of varia-tions in power setting (S10, S1, or E1)was also examined.

Results

Cutting efficiency

During the feasibility stage, cuttingwith UDTs of different diamond gritsizes and different shank designsattached to the fixed apparatus didnot provide any interpretable results,since tip vibration was blocked or inter-rupted during tip translation. Thisblockage was obvious as the load onthe tip increased. The results were alsovariable when cutting was performedby different operators using the sametip. Statistical comparisons of cuttingefficiency among the three operatorsand of machine-driven versus manualcutting were therefore not possiblebecause of these confounding factorsduring the cutting procedure.

During the feasibility stage, thecutting efficiency of the 126-µm and46-µm UDTs was equivalent. Within 3to 4 minutes, an average of 0.5 to 1mm of tooth tissue was removed,depending on the operator. Duringthe optimization stage and when per-formed by one operator, the devel-oped 76-µm UDT showed better cut-ting efficiency (on average, 0.5 mmmore of cutting distance) than the 46-µm UDT (Fig 2).

Surface roughness

SEM observationThe SEM images of the finish lines pre-pared first with a green diamond aloneand by a green diamond followed bya red diamond bur are shown in Figs3a and 3b, respectively. SEM images ofthe dentin gingival floor prepared with

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Fig 2 Comparison of cutting efficiency by (top) the 46-µm UDTand (bottom) the 76-µm UDT. There was an average of 0.5 mmdifference when the cutting time was limited to 3 minutes.

46 µm

76 µm

the 126-µm and 46-µm UDTs with thepower set at S10 are shown in Figs 3cand 3d, respectively. At a higher mag-nification, the dentin surface preparedwith a green diamond bur presentedconcentric indentations, mimicking the

was proportional to the coated dia-mond grit diameter. The 46-µm UDTvisually presented a smoother surfacestatus than the 126-µm UDT (Figs 3cand 3d).

rotary mode of functioning of diamondburs (Fig 3e), whereas the UDTs pro-duced linear indentations parallel tothe horizontal tip movement (Fig 3f).The spacing and depth of indentationscreated by both cutting instruments

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Figs 3a and 3b SEM demonstrates sur-face roughness of the gingival floor pre-pared with (left) a green diamond bur aloneor (right) a green diamond bur followed bya red diamond bur attached to a turbine(bars = 0.5 mm).

Figs 3c and 3d With the generator set atS10, the surface roughness of dentin pre-pared with the first generation of UDTs isdemonstrated in a specimen prepared with(left) the 126-µm UDT and (right) the 46-µmUDT (bars = 0.5 mm).

Figs 3e and 3f The different modes ofcutting are shown as concentric indenta-tions for (left) a green diamond burattached to a turbine and (right) straightindentation lines when prepared with UDTsattached to a piezoelectric handpiece (bars= 0.25 mm).

Green diamond bur Red diamond bur

126-µm UDTS10

46-µm UDTS10

Green diamond bur Green diamond bur+ 126-µm UDT+ 46-µm UDT

Green diamond bur Red diamond bur

126-µm UDTS10

46-µm UDTS10

Green diamond bur Green diamond bur+ 126-µm UDT+ 46-µm UDT

During the optimization stage, byusing different developed UDTs, vary-ing the power setting, or by doingboth, surface roughness was improvedby either using the 46-µm tip andreducing the power setting to S1 or E1(Fig 4) or by using the smooth tip to pol-ish following the 76-µm or 46-µm UDTsand setting the power at S1 and E10(Fig 5).

Optical profilometry analysisThe average values for surface rough-ness (Ra) of dentin prepared with green

and red diamond burs and with the 76-µm UDT followed by the 46-µm UDTwith the power setting at S10 are sum-marized in Table 2. The Ra values of thespecimens prepared with both the 76-µm and the 46-µm UDTs were superiorto those seen for both diamond burs(4.97 and 4.68 versus 4.10 and 2.00,respectively). However, this surfaceroughness was improved with theUDTs when the power was reduced toS1 or E1 (Table 3) and was better thanthe value obtained with the green dia-mond bur. Moreover, when the smooth

tip was used following the 76-µm or46-µm UDT, the resultant average Ra(2.40 and 2.28 with the power set at S1and E10, respectively) approached thevalue produced by the control red dia-mond (2.00). A statistical analysis wasnot conducted between the resultsobtained from UDTs and burs becauseof the high variation in the resultsobtained from the UDTs and the con-founding factors affecting cutting effi-ciency mentioned earlier.

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Fig 4 Surface roughness of the finish line prepared with the 76-µm UDT (S10) then the 46-µm UDT with a power setting at S1. Shown (left)under SEM and (center) at a higher magnification. (right) The calculated roughness value (Ra) for the same specimen is 2.6.

Ra = 2.6

Fig 5 Surface roughness of the finish line prepared with the 76-µm UDT (S10), the 46-µm UDT (S10, then S1 or E1), and then a smooth tipwith a power setting at E10 is shown (left) under SEM and (center) at a higher magnification. (right) The automatically calculated roughnessvalue (Ra) is 1.2 for the specimen.

Ra = 1.2

Discussion

The factors that affect vibration (andthus cutting efficiency) of UDTs havealready been determined in root-endultrasonic preparation as power, tiplength, tip orientation, and loadapplied during instrumentation.18,19

The result of the present study showsthat when UDTs were attached to afixed apparatus with a constant load,the vibration was blocked. When dif-ferent operators used the same ultra-sonic diamond tips and generator, variable results were obtained,demonstrating that factors inherent toindividual practice habits can influencethe vibration (thus cutting efficiency),eg, the pressure exerted on the tips,tip orientation with regard to the toothsurface, and tip translation speed. Themost efficient cutting was observedwhen the operator exerted optimal

pressure on the tip with an appropriatetip orientation while slowly translatingthe tip. This approach, along with thegood tactile sense provided by thetips, resembles the action of brushingor sculpting.

The authors noted during thefeasibility stage that the 126-µm and46-µm UDTs did not demonstrate asignificant difference in cutting effi-ciency, despite the presumed superiorabrasive capacity of the 126-µm UDT.This may be explained by several fac-tors, such as the distribution and thick-ness of diamond deposition affectingthe tip’s vibration. However, when thetip shape was modified to be morecurved in the optimization stage,these factors did not seem to affectthe vibration potential. The developed76-µm UDT with larger grit diameterthus showed a higher cutting efficiencythan the 46-µm UDT.

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Table 2 Surface roughness of samples whenprepared by green and red diamondburs or 76-µm and 46-µm UDTs withthe power setting at S10(Suprasson P-Max)

Cutting instrument/grit size Average Ra (µm)

Diamond bursGreen diamond, 100 µm 4.10Red diamond, 30 µm 2.00

Ultrasonic diamond tips76 µm 4.9746 µm 4.68

Table 3 Surface roughness of samples whenprepared by UDTs or a smooth tip atdifferent power settings(Suprasson P-Max)

Average Ra (µm) at different power settings

Scale Endo Endo Ultrasonic tip Mini (S1) Mini (E1) Max (E10)

Diamond-coated tips76 µm 4.50 3.75 N/A46 µm 3.30 3.01 *

Smooth tip (following 2.40 † 2.2876-µm and 46-µm UDTs)

N/A = test not performed.*Result was between 4.2 and 4.4 µm,which is not satisfactory for thepolishing objective.

†Vibration was not sufficient enough to give any polishing effect.

The present study demonstratedthat the surface generated by UDTs(indentations parallel to the horizontaltip translation) was different than thatgenerated by diamond burs (concen-tric indentations corresponding to therotary movement). The present resultsalso partially confirm the finding ofLaufer and coworkers16 that UDTs gen-erated a rougher surface than diamondburs. A reproducible, precise, andsmoother surface at the finish line playsa significant role in a prosthetic con-struction leading to the least gap spaceformation.20–24 The present studyshowed that it was possible to improvethe surface roughness in two ways:either through the use of a 46-µm UDTwith a reduced power setting (E1 or S1)or through the use of a smooth tip topolish the finish line, along with apower setting of S1 or E10.

In spite of their direct contact withsoft tissues, UDTs are atraumatic to peri-odontal tissue, as clinically observedwhen they are used for root planing inperiodontal pockets. The percussionmode of ultrasonic vibration at an

appropriate amplitude results in notearing of the soft tissue. With the sameamplitude and frequency used in peri-odontics, the UDTs developed here forsulcus penetration also carry this advan-tage. Gingival protection via the use ofa retraction cord thus becomes unnec-essary.

The final UDTs presented efficientdentin cutting capacity, as the finishline could be placed into an intracrevic-ular position for a distance of 0.5 to 1mm within 3 to 4 minutes. The work-ing time needed to perform this sulcuspenetration is longer than when agreen diamond bur is used. However,this time should be clinically accept-able as it is unnecessary to pack a cordinto the gingival sulcus.

Proposal for a new intracrevicular preparation protocol

After obtaining the final resultsfrom the optimization stage of UDTdevelopment, the authors fabricated

prototypes consisting of 76-µm and46-µm UDTs and a smooth tip (Fig6). These UDTs were then registeredand certified by the G-MED agency(a quality certification body in themedical and health field) to be usedwith safety in cl inics with aConformité Européene marking.

Clinical illustration of protocol

A number of patients requestingesthetic full crown restorations wereselected. Informed consent wasobtained prior to the beginning of theprocedure. Two phases of preparationare distinguished (see Fig 1): the rotaryphase, or supragingival or juxtagin-gival preparation, and the ultrasonicphase, or sulcus penetration. A sum-mary of proposed tips and power set-tings is provided in Table 4. Once agross reduction of tooth structureabove the gingival line with a diamondbur mounted to a turbine is com-pleted, ultrasonic sulcus penetrationcan begin. No gingival retraction with

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Fig 6 Prototypes of final developed ultra-sonic tips for sulcus penetration (left toright): 76-µm UDT, 46-µm UDT, smooth tip.

Table 4 Summary of recommended tips and power settingsfor finish line preparation, finishing, and polishing

Protocol/ Ultrasonic Power sulcus penetration step tip setting*

CompleteFinish line preparation 76 µm S10Finishing 46 µm S10Start polishing 46 µm E1Polishing Smooth S1 or E10

SimplifiedFinish line preparation and finishing 46 µm S10Polishing 46 µm S1 or E1

*The power generator for the power indicated in the table is PMax Suprasson (Satelec-Acteongroup).

a cord is necessary. Only appropriateand sufficient pressure (ie, not too high)is needed to cut efficiently withoutblockage. The operator should per-form with a sensation of sculptingrather than cutting the tooth tissue.

The 76-µm UDT is used with thepower set at S10 to gradually bury thefinish line into the gingival sulcus (Figs

To polish the finish line, first the 46-µmUDT is used with the power set at E1.This is followed by the smooth tip withthe power set at S1 or E10 (Fig 7d). Thesurrounding gingiva is not injured dur-ing preparation with the UDTs (Fig 7e).A clean impression with a sharp gingi-val margin is thus obtained (Fig 7f),and prosthetic treatment can continue.

7a and 7b). Water irrigation from thewater spray outlet aimed at the activepart of the tip provides the operatorwith a clean and clear operative field.The finish line is then completed withthe 46-µm UDT, with the power still setat S10. At this point, any sharp edgescreated by the chamfer profile of the76-µm UDT can be eliminated (Fig 7c).

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Fig 7 Protocol for finish line preparationwith UDTs.

Fig 7a (left) The complete protocolbegins with supragingival positioning of thefinish line at the end of the rotary phasewith the 76-µm UDT.

Fig 7b (right) With the power set to S10,the ultrasonic phase begins by graduallyand apically burying the 76-µm UDT in anintracrevicular position.

Fig 7c (left) The process continues withthe 46-µm UDT to complete the finish line.

Fig 7d (right) The power setting is nowchanged to S1, and the smooth tip is usedfor the final polish of the finish line.

Fig 7e (left) The resulting preparation isclean and clear, with the gingiva uninjured.

Fig 7f (right) An impression of the prepa-ration is taken, demonstrating a good andwell-defined finish line.

This protocol can be simplified byemploying only the 46-µm UDT (Table4). Following gross reduction with adiamond bur of appropriate shape,only the 46-µm UDT is used for prepa-ration and finishing steps, with thepower set at S10. Then the polishingstep is continued with the same tip,with the power set to S1 or E1. This pro-tocol takes slightly longer to achievethe equivalent cutting efficiency.

Conclusions

The developed ultrasonic diamondtips demonstrated efficient dentin cut-ting. Dentin surface roughnessobtained with the smooth tip was com-parable to that obtained with the ref-erenced red diamond bur. When usedappropriately in the clinical situationand in direct contact with gingival tis-sue, these ultrasonic tips can preciselyplace a finish line in the gingival sulcuswithout injury to the marginal peri-odontium. The obtained cervical finishline is very clear and clean, with a sharpgingival margin.

Acknowledgment

Dr Marc Sous would like to acknowledge thePôle Aquitaine Matériaux et Mécanique (CentreCondorcet, Pessac, France) for its financial assis-tance for this study. The authors also wish toexpress their gratitude to Mrs Karine Martinezfor her excellent graphic assistance.

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