Clin Oral Impl Res 2000: 11: 361–369 Copyright C Munksgaard 2000Printed in Denmark ¡ All rights reserved

ISSN 0905-7161

Prospective study on titanium bar-retainedoverdentures: 2-year results

Walter M, Marre B, Eckelt U. Prospective study on titanium bar-retained Michael Walter 1, Birgit Marre´1,overdentures: 2-year results. Uwe Eckelt 2

Clin Oral Impl Res 2000: 11: 361–369. C Munksgaard 2000.1Poliklinik fur Zahnarztliche Prothetik;2Poliklinik fur Mund-, Kiefer- und

Within a monometallic concept 29 patients received titanium bar-retained Gesichtschirurgiemandibular overdentures on 2 IMZ implants. The study had a prospectivedesign with 3 months recall intervals. One of 58 implants failed after 11months. There were no significant differences of the mean plaque scores(Silness, Loe) and the mean sulcus bleeding scores (Muhlemann, Son) at Key words: edentulous mandible – bar-

retained overdenture – bone loss –the abutments between baseline, 12 months and 24 months. Less thanimplants – titanium – monometallic40% of the subjects showed plaque score zero at 24 months. However,concept89% exhibited sulcus bleeding score zero indicating health of the peri-

implant soft tissues in most cases. Plaque at the basal site of the bar wasProf. Dr med. dent. M. Walter,scored separately at additional measuring points located at the central areaDepartment of Prosthodontics, Medicaland the contact areas between bar and abutments. Bar plaque scoresFaculty, Technical University of Dresden,nearly doubled between baseline and 12 months and remained high at Fetscherstr.74, 01307 Dresden,

24 months. Median maximal vertical bone loss around the implants was Germany1.7 mm after 2 years. Bone loss did not exceed one quarter of the im- Tel.: π49 351 458 2706plant length in 79%. The monometallic concept in bar-retained overden- Fax: π49 351 458 5314tures on 2 implants proved its clinical suitability except for the applicability e-mail: m.walter/rcs.urz.tu-dresden.deof pure titanium for bar clips. Plaque formation beneath the bar seemsto be one of the major clinical problems. Accepted for publication 7 July 1999

Edentulous patients with atrophic mandibles oftensuffer from unstable complete dentures. Theyavoid restaurants and other public places fearingproblems with their dentures. In contrast, the in-sertion of 2 interforaminal implants in the man-dible, osseointegration taken for granted, providesthe patient with a denture of sufficient stability andretention even in cases of severely resorbed alveolarridges (Batenburg et al. 1994; Geertman et al.1996a; Chan et al. 1996). This concept with lesssurgical trauma and lower costs compared to treat-ment options requiring the insertion of 4 to 6 im-plants (Batenburg et al. 1998; Brånemark et al.1977; Albrektsson et al. 1986) is well recognized(Davis et al. 1993; Geertman et al. 1996a; Spieker-mann et al. 1995). Corrosion might evoke adversebiological effects (Geis-Gerstorfer et al. 1989) andmucosal inflammation is supposed to be a possiblecause for bone loss around implants (Kirsch &Mentag 1986; Block 1990; Henry et al. 1993). Theuse of titanium for both implants and superstruc-

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ture excludes the formation of galvanic cells reduc-ing the risk of corrosion to almost zero. Due tothe advance in technological development highprecision titanium-cast-work can be done and thefabrication of cast titanium bar constructions ispossible (Kononen et al. 1995; Wolf et al. 1997).The aim of this prospective study was to evaluatethe clinical performance of bar-retained overden-tures within a monometallic treatment concept.

Material and methodsA total of 29 patients (10 women, 19 men) wearingconventional dentures in the mandible and havingpersistent problems with them participated in thisstudy. Patients’ age ranged from 74 to 36 years(Table 1). Inclusion criteria comprised sufficientbone height in the interforaminal region measuredon OTP, the absence of a history of preprostheticsurgery or implant treatment in the mandible andno medical history contraindicating implant treat-

Walter et al.

Tabl

e1.

Patie

nts,

mea

nan

terio

rbon

ehe

ight

,im

plan

tlen

gth

and

pres

ence

ofatt

ache

dke

ratin

ized

muc

osa,

max

illar

yre

habi

litati

on.N

umbe

rofs

ubjec

ts(p

atien

ts)by

age

grou

p

Age

grou

pPa

tient

s(n

)M

ean

anter

iorb

one

heig

htIm

plan

tlen

gth

(num

bero

fim

plan

tspe

rage

grou

p)Pa

tient

swi

thM

axill

ary

reha

bilit

ation

(yrs

)Se

xatt

ache

dm

ucos

a(n

)F

M14

–20

mm

21–2

5m

m26

–30

mm

3.3¿

10m

m3.

3¿15

mm

4¿11

mm

4¿13

mm

4¿15

mm

Com

plete

RPD

(teles

copi

cRP

DNa

tura

lde

ntur

es(n

)cr

owns

)(n)

(cas

tclas

ps)(

n)tee

th(n

)

31–4

01

12

11

41–5

03

21

24

21

51–6

06

72

38

24

202

101

11

61–7

04

11

410

14

171

–80

52

43

21

29

35

2

Total

1910

89

122

43

643

722

24

1

362

ment referring to class one and two of ASA physi-cal status classification system (ASA 1963). Thebone height was measured using the Friacom-Sys-tem (Friatec, Mannheim, Germany). A pre-operat-ive assessment OTP was made with a template con-taining 5 millimetre steel spheres at the plannedimplant locations. The OTP was scanned and di-gitized. The steel spheres with known diameterwere used by the Friacom program as reference forcompensation of OTP magnification and distor-tion. Beneath both spheres the bone height wasmeasured and a mean bone height was calculated.The presence of attached keratinized mucosa wasnot mandatory. One patient underwent vestibulo-plasty during treatment. The quality of the maxil-lary rehabilitation especially with regard to oc-clusal surfaces and the position of the occlusalplane was carefully assessed. Because of short-comings 28 of 29 patients underwent concurrentrehabilitation of the maxilla. One patient had anatural dentition and no treatment need.

From April 1994 to October 1995 all patientsreceived 2 IMZ implants (Friatec, Mannheim,Germany) in the interforaminal region of the man-dible. Second-stage surgery was performed after amean time after implant installation of 3.8 months(S.D. 1.1). All patients received prefabricated ti-tanium abutments (IMZ Implant System, Friatec,Mannheim, Germany). No intramobile connectorswere used. The implants were connected by roundbars cast in a vacuum pressure casting machine(Castmatic, Dentaurum, Germany) using prefabri-cated burnout plastic patterns (Friatec, Mann-heim, Germany), the titanium investment materialRematitan plus and commercial pure titaniumgrade 1 (Castmatic, Dentaurum, Germany). Aver-age surface roughness of the bars was RaΩ0.46 mm(Hommel-Tester 2000, Hommel Werke GmbHWillingen-Schwenningen, Germany). The ac-ceptability of clinical fitting accuracy was provenby replica technique (Rechenberg et al. 1997). Theoverdenture had a conventional design and was re-tained by an experimental titanium grade 2 barclip which had been fabricated by computerizednumeric controlled milling (Friatec, Mannheim,Germany). The need for activating the clips wasindicated by the examiner. The high strength oftitanium did not allow to use the ordinary clip ac-tivating instrument. For that reason forceps werespecially modified to seize the retaining edges ofthe clip and to apply sufficient force for activation.Due to retention problems a titanium grade 4 barclip of similar shape was introduced later, in 5cases as primary supply, in 1 case for the replace-ment of a titanium grade 2 bar clip. Titaniumgrade 4 is characterized by higher strength andhardness values and lower tenacity values than ti-

Titanium bar-retained overdenture

Fig. 1. Additional measuring points for Plaque Index and bar–gingiva distance. Titanium bar clip design.

tanium grade 2. The round part between the abut-ments to which the clip is attached, was defined asactive part of the bar. The length of the active partranged between 18.5 and 9.8 mm with a mean of14 mm (Fig. 1). In order to follow the monome-tallic concept special pure titanium abutmentscrews were used. The insertion of the prostheseswas completed in May 1996.

Clinical and radiographic follow-upThe hygiene program included a professionalcleaning of the abutments if necessary and regularinstructions. Clinical follow-up started with a visit2 weeks after overdenture insertion (baseline) fol-lowed by quarterly recall visits during 2 years. Thefollowing parameters were evaluated, for PlI andSBI recording a periodontal probe (WHO probe,Hu Friedy PCP 11.5 B) was used:

O Plaque Index (PlI) according to Sillnes and Loe(1964) at the abutments as mean score of themesial, distal, lingual and vestibular sites of theimplant;

O Plaque Index (PlI) at the basal site of the bar atthe central area and the areas adjacent to theabutments (Fig. 1);

O Plaque Index (PlI) at the clip area of the den-ture. The denture base was inspected visually, 4categories according to PlI (Silness, Loe) werepossible: no plaque, plaque detectable only byscratching with a periodontal probe, visibleplaque, abundance of plaque;

O Sulcus Bleeding Index (SBI) according toMuhlemann and Son (1971) at the abutmentsas mean score of the mesial, distal, lingual andvestibular sites of the implant;

O Presence of calculus;O Bar–gingiva distance measured with a graded

probe (WHO probe, Hy Friedy, PCP 11.5 B) at

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the facial aspect of the bar at the same sites asadditional measuring points for PlI (Fig. 1). Themeasurements were made to the nearest mm;

O Retention of the clip as assessed by the examinerby repeatedly removing the denture. The cate-gories used were very good retention, good re-tention, moderate and poor retention;

O Wear of the clip as assessed visually by theexaminer. The categories used were no wear,slight wear, moderate and strong wear.

For radiographic follow-up Orthopantomograms(OTP) of every patient were taken preoperatively,at the time of re-entry (baseline) and 24 monthrecall. Every radiograph was scanned by a lightpass colour scanner (Linotype-Hell, Germany)and digitalized with 150 dots per inch. All radio-graphs were evaluated for the presence of peri-implant radiolucencies. The highest vertical andhorizontal level of the alveolar bone was meas-ured according to Gomez-Roman et al. (1995) atthe mesial and distal aspect from the top edge ofthe implant to the first bone contact using theknown length of the implant as a reference (Fig.2). The most negative measured value per im-plant was used in the statistical analysis. Verticalbone loss was differentiated from horizontalbone loss in order to describe the developingbone pocket. The subtraction of 0.5 mm fromthe measured value of vertical bone loss repre-senting the extraosseous zone of the IMZ im-plant as proposed by Gomez-Roman et al.(1995) was not performed.

The statistical analysis was performed withWinstatTM (Greulich Software, Staufen, Ger-many) and MicrosoftA Excel of the MicrosoftA

Office package (Microsoft, USA) includingMann–Whitney U-test and Cox-regression analy-sis. The level of significance was set to PΩ0.05.Due to multiple testing P-values were adjustedafter Bonferroni.

Fig. 2. Measurement of bone loss according to Gomez-Romanet al. (1995), modified.

Walter et al.

Table 2. Plaque Index (Sillness, Loe) and Sulcus Bleeding Index (Muhlemann, Son). Median; mean (standard deviation). Significant differences indicated by brackets (Mann–WhitneyU-test, P∞0.05)

PlI SBI Bar PlI Central bar point Prosthesis clipPlI area PlI

33 43 33 43 33 43

baseline 0.25; 0.51 (0.61) 0.5; 0.58 (0.6) 0; 0.42 (0.97) 0; 0.37 (0.64) 0; 0.25 (0.58) 0; 0.2 (0.55) 0; 0.25 (0.59) 0; 0 (0)1 year 0.25; 0.51 (0.61) 0.5; 0.56 (0.64) 1.5; 0.48 (1.34) 0; 0.43 (1.25) 1; 0.62 (0.62) 1; 0.62 (0.62) 0; 0.5 (0.64) 0; 0.23 (0.65)2 years 0.37; 0.38 (0.42) 0.25; 0.46 (0.5) 0; 0.1 (0.32) 0; 0.23 (0.51) 1; 0.67 (0.67) 1; 0.71 (0.76) 0; 0.51 (0.7) 0; 0.29 (0.66)

ResultsExcept for 1 implant which had to be removedafter 11 months because of massive bone loss ac-companied by peri-implantitis, all implants were insitu at 2 years. One patient left the study becauseof the additional insertion of 2 implants after 9months due to retention problems. There were nofurther drop-outs. Of the implants 15% had nobone loss at both localizations. Bone loss not ex-ceeding a quarter of the implant length was foundin 70% at 43 and 79% at 33 after 2 years. None ofthe implants showed bone loss reaching the apicalthird of the implant length.

There were no significant differences of the meanPlI scores and sulcus bleeding scores at the abut-ments between baseline, 1 year and 2 years (Mann–Whitney U-test, Table 2). Plaque scores at the ad-ditional measurement points located at the contactareas between bar and abutments (33: PΩ0.012;43: PΩ0.003) and the clip part of the prosthesis(PΩ0.045) increased significantly from baseline to1 year. Plaque scores of the central part of the bar(PΩ0.129) increased from baseline to 1 year (Table2). Calculus at the abutments was found in 5 pa-tients at baseline, 7 patients at 1 year and 11 pa-tients at 2 years. The bar–gingiva distance in-creased from baseline to 2 years (33: PΩ0.15; 43:PΩ0.006; centre PΩ0.084) (Table 3). In 6 patients(5 times abutment 43, one time abutment 33 andbar) gingiva hyperplasia occurred, which was cor-rected by laser surgery.

Table 3. Bar–gingiva distance (mm). Mean (standard deviation). Significant differencesindicated by brackets (Mann–Whitney U-test, P∞0.05)

43 (mm) Centre of the bar 33 (mm)(mm)

baseline 3.8 (0.88) 3.6 (1.4) 3.4 (0.8)1 year 3.9 (1.5) 3.9 (1.5) 3.8 (1.5)2 years 4.7 (1.5) 4.3 (1.6) 4.8 (1.58)

Mean increase at 2 years 1.0 0.7 1.5

Mean increase at 2 years 1.0(locations summarized)

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Fifty-four OTPs with good contrast taken atbaseline and 24 month recall were included in theanalysis of bone loss using the Friacom-System(Friatec, Mannheim, Germany). Radiographicevaluation revealed no significant differences invertical and horizontal bone loss between mesialand distal side. At 2 year recall the median verticalbone loss was 1.7 mm at 33 (SD 1.5) and 1.9 mmat 43 (SD 1.5) (Fig. 3). The horizontal bone lossdoes not differ significantly between both loca-tions. At 2 year recall the median horizontal boneloss was 1.5 mm at 43 (SD 1.2) and 1.7 mm at 33(SD 1.4) (Fig. 4). No correlation between bone lossand the presence of attached keratinized mucosa,plaque scores, bleeding scores was found (Cox-re-gression test).

ComplicationsAlthough titanium bar clips developed only slightor moderate signs of wear they often needed reacti-vation and had only poor retention. The clips hadto be activated generally at every recall visit, insome patients more frequently. Four titanium clipsfractured during activating. At 2 years 12 of 24titanium grade 2 bar clips and 1 of 6 titaniumgrade 4 bar clips were still in function. Finally, goldbar clips were used to solve the retention problem.

Fig. 3. Vertical bone loss after 2 years. Median, quartiles andrange.

Titanium bar-retained overdenture

Fig. 4. Horizontal bone loss after 2 years. Median, quartilesand range.

One bar and 5 overdentures fractured. The bar wasremade, the overdentures repaired. During the sec-ond year 12 patients suffered from inflammationof the soft tissues, which was treated by irrigationwith 3% hydrogen peroxide, the local applicationof 5% Metronidazol gel and in some cases the oralapplication of Doxycyclin for 7 days. In 2 patients,in whom bone loss reached critical levels and wascombined with the absence of attached keratinizedmucosa in the lingual area an anterior mouth flooroperation including gingivaplasty was conducted.No correlation between the frequency of inflam-mation of the soft tissues and the absence of at-tached keratinized mucosa (R2Ω0.01) was found.

DiscussionBecause of the lack of a control group comparativeconclusions are rather limited. However, the ho-mogeneity and the very low drop-out ratestrengthen the validity of the results. In most studieson overdentures supported by 2 interforaminal im-plants an implant survival rate of at least 90% dur-ing an observation period up to 11 years is reported(Batenburg et al. 1998). The failure rate in our studyamounting to 1 of 58 implants at 2 years is in ac-cordance with the results of other authors (Jemt etal. 1996; Batenburg et al. 1994).

Although the recall interval of 3 months wasstrictly followed plaque and sulcus bleeding scoreswere less emboldening. Plaque is said to be the pri-mary etiologic factor in long-term peri-implanttissue destruction (Bauman et al. 1992). Only lessthan 40% of the patients showed score zero inplaque index at both abutments at 1 and 2 yearrecall. Remarkably high PlI values were reached atthe measuring points beneath the bar. Correspond-ing data from literature are heterogeneous due todiffering criteria of patient selection. Adell et al.(1986) found no plaque per abutment in 70–75%

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whereas Batenburg et al. (1994) report 49%, andLeimola-Virtanen et al. (1995) 39%. Gotfredsen etal. (1993) found score zero PlI in 80% of all im-plant sites at 2 year recall. In patients treated withbar constructions Gotfredsen at al. (1993) foundsignificantly higher plaque scores at the 2 year re-call than in patients with ball attachments.Kirsch & Mentag (1986) gave a direct relation be-tween implant failure and poor oral hygiene.

The importance of attached keratinized mucosafor peri-implantary health is discussed by severalauthors (Mericske-Stern et al. 1994; Gotfredsen etal. 1993). In cases with total or partial absence ofattached keratinized mucosa Gotfredsen et al.(1993) report 36% score zero PlI at abutments.Mericske-Stern et al. (1994) reported higherplaque scores and significantly more loss of attach-ment on implants when less than 2 mm of kera-tinized mucosa were present, whereas Johns et al.(1992) could find no correlation with soft tissueresponse. However, the absence of attached kera-tinized mucosa, which may give discomfort duringhome-care procedures especially in the lingual area(Adell et al. 1981), in 22 of 29 subjects in our studyhas to be taken into account when considering andcomparing plaque data. Furthermore, elderly pa-tients are often not able to systematically cleantheir implants.

SBI at 2 year recall in 78–89% shows score zeroimplying the absence of peri-implant inflam-mation. The absence of attached keratinized mu-cosa in most cases might have led to false negativeresults related to difficulties in recording mucosalinflammation (Bauman et al. 1992; Mombelli &Lang 1994). The lack of correlation between thepresence of attached keratinized mucosa and boneloss found in our study was also reported by otherauthors (Spiekermann et al. 1995; Leimola-Virtan-en et al. 1995). Gotfredsen et al. (1993), Mericske-Stern et al. (1994) and Spiekermann et al. (1995)concluded that there is no definite need for at-tached keratinized mucosa around implants, whileothers favour a vestibuloplasty in such situations(Naert et al. 1994; Batenburg et al. 1994).

Quirynen et al. (1994a) found a positive corre-lation between surface roughness, plaque growthand plaque maturation. The measured average sur-face roughness RaΩ0.46 mm of the cast titaniumbar is higher than the Ra-values 0.135 mm and 0.2mm reported for prefabricated IMZ abutments(Quirynen et al. 1994a) and standard Brånemarkabutments (Bollen et al. 1996). Subgingivallyrough abutments compared with smooth surfaces(average surface roughness from 0.103 mm–0.299mm) adhered 10 to 100 times more plaque (Quiryn-en et al. 1994a). Furthermore they report, that achange of the Ra-value from 0.09 mm to 2 mm in-

Walter et al.

creases undisturbed plaque formation in extensionand thickness 5 times (Quirynen et al. 1994a). Ona rough surface change of reversible to irreversiblebacteria bonding occurs more easily (Quirynen &Bollen 1995). Irreversible bacteria bonding makesplaque removal from rougher surfaces almost im-possible for patients resulting in a much faster re-colonization. Comparing slightly rough titaniumabutments with RaΩ0.81 mm to abutments coatedwith a 5 mm thick fluor-ethylene-prophylene layerwith RaΩ4.32 mm Quirynen et al. (1994b) foundan increased supragingival plaque maturation attitanium abutments, but no significant differencein plaque formation between both abutment typessubgingivally. Bollen et al. (1996) compared micro-biological parameters using a standard machinedtitanium (RaΩ0.2 mm) and a highly polished ce-ramic abutment (RaΩ0.06 mm). After 12 monthsno larger inter-abutment differences were found.Their results indicated that a further reduction ofthe surface roughness below RaΩ0.2 mm had nofurther effect on the microbiological adhesion nei-ther supragingivally nor subgingivally (Bollen etal. 1996). Related to these results the increasedplaque accumulation in our study might be attri-buted to the slightly higher surface roughness ofcast titanium and the additional difficulties in hy-giene due to the bar construction.

The mean increase of bar–gingiva distance of 1.0mm after 2 years is in contrast to the results ofJohns et al. (1992). However, Adell et al. (1986)reported an increase of the bridge–gingiva distancearound implant abutments of fixed partial denturesinterpretating this as a shrinkage of the gingiva.Further aspects should be considered for expla-nation. The texture of the gingiva depends on nor-mal appearance of the tissues before implantation(Mombelli & Lang 1994). Thus, a gingiva hyper-trophic prior to implantation might have shrunkafter the insertion of an implant supported over-denture. Additionally, postoperative structuralchanges of gingiva texture after second stagesurgery might have occurred.

OTPs were used for radiographic evaluation asby other authors (Geertman et al. 1996a) becauseof the difficulty of precise parallel positioning ofintraoral radiographs in patients with severe re-sorption. OTPs in the frontal region are not as pre-cise as intraoral radiographs (Batenburg et al.1994; Spiekermann et al. 1995). On the other hand,Meijer et al. (1993) showed that even less preciseradiographs can be used for the detection of peri-implant bone loss. Comparing the standard devi-ations with the reported annual bone loss in litera-ture they concluded that in a population of pa-tients the mean marginal bone loss per year mustbe expected to be about 0.8 mm, which corre-

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sponds with our results. However, the values ofbone loss at 2 years were higher than reported byseveral authors (Spiekermann et al. 1995; Jemt etal. 1996; Gotfredsen et al. 1993). Interpreting ourresults it has to be emphasized that the most nega-tive value of bone loss per implant used in ourstudy gives a more pessimistic view as a meanvalue would do. The maximum of vertical boneloss is reported to occur during the first year afterabutment connection (Adell et al. 1981; Adell etal. 1986; Hammerle et al. 1996; Naert et al. 1997)which was attributed to inadequate stress distri-bution before finished bone remodelling and ef-fects of the surgical procedure. Standards for ap-proved implant systems allow a mean bone loss be-tween 1.0–1.5 mm for the first postsurgical year(Bragger 1998). Naert et al. (1997) supposed theimplant type to play a major role in the stabilityof marginal bone and bone loss. Additionally, theinsertion level of the implants may have influencedvertical bone loss in our study. The IMZ implanthas a polished 1.5 mm area intended for peri-im-plantary soft tissue attachment. Bone in contactwith this area may be more prone to resorptionthan bone in contact with the plasma-flame spray-ed area (Thomas & Cook 1985). Hammerle et al.(1996) demonstrated that the subcrestal placementof the border between the polished and the roughsurface of ITI implants resulted in an increasedbone loss during the first year of service. If boneloss found in our study would be related to theborder between polished and plasma-flame sprayedarea the subtraction of 1.5 mm from vertical boneloss values would be required. This calculationwould lead to a maximum vertical bone loss ofonly 0.6 mm (SD 1.0) after 2 years at both 33 and43. However, data on the exact circular insertionlevels are not available. Therefore, this consider-ation is merely hypothetical.

Our results confirm findings by Spiekermann etal. (1995), who found a mean horizontal bone lossof about 1 mm per year in IMZ implants at 2years. The OTP in the frontal region is not precise(Spiekermann et al. 1995) which might cause meas-urement errors, especially in the horizontal area.

The use of pure titanium bar clips was based onthe monometallic concept. They cannot be rec-ommended due to the high incidence of poor re-tention and failure at least in the shape and ma-terial used in this study.

ConclusionsThe monometallic concept in bar-retained over-dentures on 2 implants proved its clinical suit-ability except for the applicability of pure titanium

Titanium bar-retained overdenture

for bar clips. Plaque formation beneath the barseems to be one of the major clinical problems.

AcknowledgementsThe authors wish to thank the Friatec AG, Mannheim, Ger-many, for given support.

ResumeDes protheses amovibles soutenues par une barre placee surdeux implants IMZ ont ete etudiees chez 29 patients. Cette etu-de avait un but prospectif avec des intervalles de rappel de troismois. Un des 58 implants s’est montre defectueux apres onzemois. Il n’y avait aucune difference pour les moyennes des indi-ces de plaque de Silness et Loe (1964) ainsi que pour les indicesde saignement sulculaire de Muhlemann et Son (1971) au ni-veau des piliers entre l’examen de depart, douze et 24 moisapres. Moins de 40% des sujets avaient un indice de plaque deniveau zero a 24 mois. Cependant 89% avaient un indice desaignement zero, indiquant une sante paroımplantaire des tissusmous dans la plupart des cas. La plaque dentaire au niveau dusite de la barre a ete enregistree separement a differents points,localises dans la region centrale et dans les zones de contactentre la barre et les implants. Les indices de plaque dentaire auniveau de la barre ont presque double entre l’examen de departet douze mois. Ils restaient eleves a 24 mois. La mediane de laperte osseuse maximale autour des implants etait de 1.7 mmapres deux ans. La perte osseuse ne depassait pas 1/4 de lalongueur des implants dans 79% des cas. Le concept monome-tallique des protheses retenues sur une barre en titane attacheesa deux implants prouve sa fonction clinique sauf pour l’applica-bilite du titane pur pour les attaches de la barre. La formationde plaque dentaire sous la barre semble etre un des problemescliniques majeurs.

ZusammenfassungEinem Einmetallkonzept folgend erhielten 29 Patienten Unter-kieferhybridprothesen, befestigt auf einem durch zwei IMZ-Im-plantaten getragenen Titansteg. Die Studie hatte eine prospekti-ve Aussagekraft und ein dreimonatiges Untersuchungsintervall.Eines der 58 Implantate war nach 11 Monaten ein Misserfolg.Man fand keine signifikanten Unterschiede der mittleren Pla-queindices (Silness, Loe) und mittleren Sulcusblutungsindices(Muhlemann, Son) um die Implantate bei Beginn und nach 12beziehungsweise 24 Monaten. Weniger als 40% der Patientenzeigten nach 24 Monaten einen Plaqueindex von Null. 89% hat-ten aber einen Sulcusblutungsindex von Null, was in den mei-sten Fallen auf ein vollig gesundes periimplantares Gewebe hin-weist. Die Plaque auf der Unterseite des Steges wurde an zweispeziell bezeichneten Messpunkten zusatzlich bestimmt. Dereine lag in der zentralen Region und der andere an der Verbin-dungsstelle Steg/Sekundarteil. Die Plaquewerte an den Stegenverdoppelten sich zwischen Beginn und dem zwolften Monatbeinahe und verblieben bis nach zwei Jahren hoch. Der mittleremaximale vertikale Knochenverlust ubertraf in 79% aller Fallenicht mehr als 1/4 der Gesamtimplantatlange. Das Einmetall-konzept bei steggetragenen Hybridprothesen auf zwei Implan-taten zeigte eine gute klinische Machbarkeit. Einzige Ausnahmebildete die Anwendung einer Reintitanmatrize auf dem Steg.Die Plaquebildung unter dem Steg scheint jedoch in klinischerHinsicht eines der Hauptprobleme zu sein.

ResumenVeintinueve pacientes recibieron sobredentaduras mandibularesretenidas por barras de titanio sobre dos implantes IMZ dentro

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de un concepto monometalico. El estudio tuvo un diseno pros-pectivo con unos intervalos de revision de tres meses. Uno delos 58 implantes fracaso a los 11 meses. No hubo diferenciassignificativas entre los valores medios de placa (Silness, Loe) ylos valores medios de sangrado del surco (Muhlemann, Son) enlos pilares entre el momento inicial, 12 meses y 24 meses. Menosdel 40% de los sujetos mostraron valores de placa cero a los 24meses. De todos modos, el 89% mostro unos valores de sangra-do del surco cero indicando una salud de los tejidos blandosperiimplantarios en la mayorıa de los casos. La placa de la zonabasal del pilar se valoro separadamente en puntos adicionaleslocalizados en el area central y de contacto entre la barra y lospilares. Los valores de placa de la barra casi se duplicaron entrelos iniciales y 12 meses y permanecieron elevados a los 24 me-ses. La media de la perdida maxima de hueso vertical alrededorde los implantes fue de 1.7 mm despues de dos anos. La perdidaosea no excedio 1/4 de la longitud del implante en un 79%. Elconcepto monometalico en sobredentaduras retenidas por ba-rras sobre dos implantes demostro ser apropiado clınicamenteexcepto por la utilizacion de titanio en los clips de la barra. Laformacion de placa bajo la barra parece ser uno de los principa-les problemas clınicos.

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