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Article history:Paper received 11 October 2014Accepted 13 January 2015

dental implantology, which continuously improve the outcomes,such as nano-crystalline diamond-coated titanium implants, uo-ridated implants and platelet-rich brin (PRF) as sole graftingmaterial (Metzler et al., 2013; Dasmah et al., 2014; Jeong et al.,2014).

tory restoration ofge, due to specicresidual bone vol-ne density, as wellon limitations thataxilla, especially ifnd Irinakis, 2007).s been a challenge

to restore with dental implants for an extended period of time(Schmidlin et al., 2004).

A number of innovative surgical procedures are well establishedfor successful bone management with consecutive implant place-ments in the posterior maxilla:

Sinus elevation represents the surgical approach mostcommonly used to increase the vertical amount of bone in theposteriormaxilla, and it carries predictable implant survival rates ofmore than 90% over 3e5 years (Jensen et al., 1996; Khoury, 1999;

* Corresponding author. Tel.: 49 6131 173761; fax: 49 6131 176602.

Contents lists availab

Journal of Cranio-Ma

e:

Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 414e420E-mail address: andreas.pabst@web.de (A.M. Pabst).1. Introduction

Dental implantation in the edentulous patient is widely recog-nized as a successful procedure with predictable outcomes whenperformed on sites with normal bone volume and mechanicalquality such as is typical in the interforaminal region of the lowerjaw, for example.

There exist numerous new developments and techniques in

Nevertheless, the implant-supported masticathe posterior maxilla represents a specic challenanatomical and biological conditions. Reducedume after tooth loss in combinationwith poor boas its proximity to the maxillary sinus, are comminuence implant placement in the posterior mthe tooth loss occurred a long time ago (Morand aConsequently, the atrophic posterior maxilla hareserved.Available online 22 January 2015

Keywords:ImplantImplant failure predictorPosterior maxillaSinus elevationImplant lengthImplant diameterhttp://dx.doi.org/10.1016/j.jcms.2015.01.0041010-5182/ 2015 European Association for Cranio-Ma b s t r a c t

The aim of this study was to analyze predictors for dental implant failure in the posterior maxilla.A database was created to include patients being treated with dental implants posterior to the

maxillary cuspids. Independent variables thought to be predictive of potential implant failure included(1) sinus elevation, (2) implant length, (3) implant diameter, (4) indication, (5) implant region, (6)timepoint of implant placement, (7) one-vs. two-stage augmentation, and (8) healing mode. Coxregression analysis was used to evaluate the inuence of predictors 1e3 on implant failure as dependentvariable. The predictors 4e9 were analyzed strictly descriptively.

The nal database included 592 patients with 1395 implants. The overall 1- and 5-year implantsurvival rates were 94.8% and 88.6%, respectively. The survival rates for sinus elevation vs. placement intonative bone were 94.4% and 95.4%, respectively (p 0.33). The survival rates for the short (13 mm) were 100%, 89% and 76.8%, respectively (middle-vs.long implants p 0.62). The implant survival rates for the small- (4.5 mm) were 92.5%, 87.9% and 89.6%, respectively (p 0.0425).

None of the parameters evaluated were identied as predictor of implant failure in the posteriormaxilla.

2015 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rightsc Private Practice, Oral and Maxillofacial SurgeInstitute of Medical Biostatistics, Epidemiology and Informatics (IMBEI), University Medical Center Mainz, Obere Zahlbacher Strasse 69, 55131 Mainz,GermanyAnalysis of implant-failure predictors inretrospective study of 1395 implants

Andreas Max Pabst a, *, Christian Walter a, SebastiaThomas Ziebart a, Bilal Al-Nawas a, Marcus Oliver Ka Department of Oral and Maxillofacial Surgery, University Medical Center Mainz, Augu

journal homepagaxillo-Facial Surgery. Published byhe posterior maxilla: A

hbauer a, Isabella Zwiener b,in a, c

platz 2, 55131 Mainz, Germany

le at ScienceDirect

xillo-Facial Surgery

www.jcmfs.comElsevier Ltd. All rights reserved.

axilHuynh-Ba et al., 2008; Zinser et al., 2013). However, a highly-controversial issue is whether implant survival rates are higher inaugmented sites versus non-augmented sites (Zinser et al., 2013).Some have described that implants positioned in augmented boneare ve times more likely to fail than implants placed in non-augmented sites (Carr et al., 2003), while others have found animplant survival rate of 97.5% for implants in grafted sinuses,compared to 90.3% survival rate for implants placed in the posteriormaxilla in native bone (Olson et al., 2000; Zinser et al., 2013). Otherstudies comparing implants placed in grafted sinuses to implantsplaced in the anterior maxilla found comparable survival rates(Tidwell et al., 1992; Blomqvist et al., 1996).

Since augmentation procedures are also associated with com-plications, many authors advocate the optimal utilization of pre-existing, native bone. Angled placement of implants in cases withwhich only limited residual bone volume in the posterior maxilla isavailable (Del Fabbro et al., 2004), while short (

3. Results

3.1. Population characteristics

3.1.1. Patient-related variablesIn total, 592 subjects (318 women, 53.7%; 274 men, 46.3%), aged

between 14 and 84 years (mean age: women 54 years, men 58years), were included in the study. The indications for implantplacement included 141 subjects (23.8%) with a completely eden-tulous maxilla, 236 subjects (39.9%) with an edentulous posteriormaxilla and 74 subjects (12.5%) with a partially edentulous poste-rior maxilla with at least one natural tooth posterior to the implantsite. One hundred twenty seven subjects (21.5%) had a singleimplant. Fourteen subjects (2.4%) had insufcient records todetermine the indication for implant placement.

3.2. Bone bed characteristics

3.2.1. Bone-related variablesThree hundred twenty four out of 592 subjects (54.7%) were

treated with a sinus elevation; of which 269 (45.4%) were treatedwith an external sinus elevation procedure and 53 (9.0%) with an

3.3. Implant distribution

3.3.1. Implant-related variablesTable 2 summarizes the data for continuous, implant-related

variables. In total, 1395 implants were placed (770 implants inwomen [55.2%]; 625 implants in men [44.8%]). The majority ofimplants were placed more than 10 weeks after tooth loss (1074implants, 77.0%). One thousand two hundred fty seven implants(90.1%) had a length between 10 and 13 mm and 917 implants(65.7%) had a diameter between 3.6 and 4.5 mm. Nine hundredninety two implants (71.1%) healed submerged and 300 implants(21.5%) healed transmucosally.

Most of the implants were placed into the rst premolar, secondpremolar, and rst molar regions (1230 implants, 88.2%). Thepreferred implant systemwas Nobel Biocare (427, 30.6%), followedby Astra Tech (296, 21.2%) and Straumann (240, 17.2%).

3.4. Implant survival functions

The follow-up period ranged from 0 to 6.1 years. Sixty two (4.4%)of the 1395 implants were lost, most commonly within the rstyear. The 1-year implant survival rate was 94.8% (women: 96.1%,men: 93.7%) and the 5-year implant survival rate was 88.6%(women: 89.4%, men: 87.9%; Fig. 1). At the time of analysis, 740 ofthe 770 implants placed in women (96.1%), and 593 of the 625implants placed in men (94.9%) were still in situ.

3.5. Sinus oor elevation

Eight hundred thirteen (95.4%) of the 852 implants placed in a

elevation

A.M. Pabst et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 414e420416Bio-Oss 343 (24.6%)Cerasorb 82 (5.9%)ChronOs 61 (4.4%)BioBase 37 (2.7%)BoneCeramic 7 (0.5%)NanoBone 2 (0.1%)BIORESORB Macro Pore 4 (0.3%)Algipore 16 (1.1%)Bonit 11 (0.8%)Unknown 76 (5.4%)

Donor region of autogenous bone Implants [n] sinuselevation

Drilling chips 192 (13.8%)Mandibular angle 226 (16.2%)Tuber maxillae 13 (0.9%)Crista zygomaticoalveolaris 4 (0.3%)Alveolar crest 3 (0.2%)Autologous blood 2 (0.1%)internal sinus elevation procedure. In two patients (0.3%), the kindof sinus elevation was unknown. Four hundred ninety six implants(35.6%) were placed in native bone and 852 implants (61.0%) wereplaced into a sinus lift grafted maxilla. With regard to the sinuselevation (852 implants), 497 implants (58.3%) were placed in aone-stage procedure, and 355 implants (41.7%) were placed in atwo-stage procedure. With regard to the graft material for the sinuselevation, 639 implants (45.8%) were placed in elevated sinuseslled with bone substitutes. The bone substitute most often usedwas BioOss (343 implants [24.6%]). Six hundred and three im-plants (43.2%) were placed in elevated sinuses lled with autoge-nous bone. The donor region for the autogenous bone most oftenused was the mandibular angle (226 implants [16.2%]). The inu-ence of the used bone substitute as well as the donor region of theautogenous bone in the elevated sinuses has not been analyzed as apossible predictor for implant failure in the further evaluation.Table 1 presents an overview of the used bone substitutes and thedonor regions of autogenous bone.

Table 1Executive summary of the used bone substitutes and the donor regions of autoge-nous bone.

Bone substitutes Implants [n] sinusUnknown 165 (11.8%)grafted sinus, and 518 (95.7%) of the 541 implants without sinusoor elevationwere still in situ (Table 3). The 1- and 5-year survival

Table 2Executive summary of the implant-related variables (implant placement:delayed up to 2 months after tooth loss; late more than 2 months after toothloss).

Implants [n]

Indication Edentulous maxilla 398Free-end gap 643Saddle area 183Single-tooth replacement 144

Implant region 14 and 24 40515 and 25 37716 and 26 44817 and 27 15718 and 28 8

Implant system Nobel Biocare 427 (30.6%)Astra Tech 296 (21.2%)Straumann 240 (17.2%)Camlog 219 (15.7%)Biomet 3i 100 (7.2%)DENTSPLY Friadent 90 (6.5%)Zimmer 4 (0.3%)SPI 3 (0.2%)Heraeus 3 (0.2%)BPI 2 (0.1%)Unknown 9 (0.7%)

Implant placement Immediate 55Delayed 54Late 1074

Implant Length 13 mm 65

Implant diameter 4.5 mm 192

Healing mode Submerged 992

Transmucosal 300

2002 and December 2007 with an overall 1- and 5-year survival

Fig. 2. KaplaneMeier survival curve demonstrating 1- and 5-year survival rates forimplants placed in grafted sinuses of 94.4% and 85.6% (blue line) as well as 95.4% and91,4% for implants placed in native bone (green line).

A.M. Pabst et al. / Journal of Cranio-Maxillo-Facial Surgery 43 (2015) 414e420 417rates for implants placed in a grafted sinus were 94.4% and 85.6%,respectively. The 1- and 5-year survival rates for implants placed innative bone were 95.4% and 91.4%, respectively (Fig. 2). No signi-cant difference between the two groups was detected (p 0.33).

3.6. Implant length

Thirty six of the 36 short implants (100%), 1199 of the 1257middle implants (95.4%), and 62 of the 65 long implants (95.4%)were successful (Table 3). The 1-and 5-year survival rates, respec-tively, were 100% for the short implants, 94.5% and 89.0% for themiddle implants, and 96.1% and 76.8% for the long implants (Fig. 3).Although there was no signicant difference in the survival timesbetween the middle- and long-implant groups (p 0.62), weobserved a tendency towards a better survival time of the shortimplants. Unfortunately, the hazard ratio for the short implants vs.middle or long could not be estimated with Cox regression analysis,since there were no implant failures in this group.

Fig. 1. KaplaneMeier survival curve demonstrating 1- and 5-year overall implantsurvival rates of 94.8% and 88.6% (blue line).3.7. Implant diameter

Two hundred thirty of the 242 small diameter implants (95.0%),879 of the 917 middle diameter implants (95.9%), and 182 of the192 wide implants (94.8%) were successful (Table 3). The 1-and 5-

Table 3Implant survival rates with regard to sinus elevation, implant length, and diameter.Concerning the implant length, the p-value (p 0.62) only describes the comparisonbetween the middle- and long-implants. The hazard ratio for the short vs. middle orlong implants could not be estimated, since there were no implant failures in thisgroup.

Implants [n] 1-yearSurvival(%)

5-yearSurvival(%)

p-value

Total Loss %

Gender Woman 770 30 96.1 95.7 89.4Men 625 32 94.9 93.7 87.9

Sinuselevation

Yes 852 39 95.4 94.4 85.6 P 0.33No 541 23 95.7 95.4 91.4

Implantlength

13 mm 65 3 95.4 96.1 76.8

Implantdiameter

4.5 mm 192 10 94.8 92.5 89.6year survival rates, respectively, for the small diameter implantswere 92.5% and 92.5%, for the middle diameter implants 95.8% and87.9%, as well as 92.5% and 89.6% for the wide diameter implants(Fig. 4).

Univariate analysis could not demonstrate any signicant dif-ferences in the implant survival rate between the different implantdiameters (p 0.0425).

Table 4 summarizes the implant survival rates dependent on theindication, region of placement, chronological order, and healingmode.

4. Discussion

The aim of this retrospective study was to analyze dental im-plants placed into the posterior maxilla, and to evaluate predictorsof implant failure. Altogether, 1395 implants were placed in 592patients at the University Medical Center Mainz between JanuaryFig. 3. KaplaneMeier survival curve demonstrating 1- and 5-year survival rates for theshort implants of 100% and 100% (blue line), for the middle implants of 94.5% and89.0% (green line) as well as 96.1% and 76,8% for the long implants (brown line).

MaNuHighlight

75% and 100% after a follow-up of 12e101 months (Tuna et al.,2012).

An alternative to augmentative procedures prior to implanta-tion is the use of short- and/or reduced diameter implants. Thisavoids the associated risks and costs of bone augmentation, espe-cially for elderly patients.

The literature on implant survival rates in relation to implantlength is heterogenous. Winkler et al. demonstrated a survival rateof 66.7% for short implants (7 mm) and 96.4% for long implants(16 mm) after 36 months in situ (Winkler et al., 2000). Anotherrecent study detected similar survival rates of short and long im-plants (Raviv et al., 2010). Anitua and Orive demonstrated survivalrates for short implants (

axilNo difference in the survival rate relating to the implant regioncould be detected. Only the rst molar region demonstrated amarginally lower 5-year survival rate, which may be related to theposition in the masticatory center and high mastication forces.These ndings were highlighted in the literature (Ridell et al.,2009). Conrad et al. demonstrated high survival rates in the pos-terior maxilla after 35.7 months (93.2%) (Conrad et al., 2011), andLevin et al. demonstrated survival rates of 96.2% in the premolarregion and 95.8% in the molar region after 3 years (Levin et al.,2006).

Regarding the timepoint of implant placement, immediateimplant placement demonstrated an increased failure ratecompared to delayed implant placement. The literature is dividedon this topic: Some authors describe no signicant effects of thetime-span between tooth extraction and implant placement(Esposito et al., 2011), whereas older studies have found a higherrisk of implant failure when placed immediately after toothextraction (Ibbott and Oles, 1995).

Regarding one-vs. two-stage augmentation, no signicant dif-ference could be detected as well, and these results are better thanpreviously reported in the literature. Wallace and Froum describedsurvival rates of 89.7% for the one-stage procedure and 89.6% forthe two-stage procedure (Wallace and Froum, 2003).

No difference could be detected between the two healing modes,which is in accordance with the literature (Hammerle et al., 2012).Cecchinato et al. analyzed 84 patients with respect to the effect ofhealing mode on the peri-implant bone loss, and implant success.At both research focuses, implant loss was about 2% (Cecchinatoet al., 2004).

This study has limitations based on the retrospective studydesign and some missing data. Also, the data relating risk factors toimplant failures should be interpreted with care, since the 1-yearoverall survival rate of implants placed in the posterior maxillawas very high at 94.8%. In addition, further predictors for implantfailure in the posterior maxilla (e.g. ASA status, smoking habits,mechanical bone quality, residual crestal bone height) were notassessed as risk factors for implant failure, since these factors werenot recorded in the dental records. Another shortcoming of thisstudy is that the inuence of the used bone substitute as well as thedonor region for autogenous bone in the elevated sinuses was notanalyzed as a possible predictor of implant failure. This wasattributable to the fact that the exact number of sinusus receiving acombination of bone substitute and autogenous bone was notdocumented. Consequently, this topic has been excluded from thisstudy. This topic seems to be of interest since it is still unclearwhether bone substitutes or autogenous bone for sinus oorelevation should be preferred (Nkenke and Stelzle, 2009).Furthermore, the type of prosthesis fabricated on maxillary pos-terior implants could be an important predictive factor althoughmany of the implants that failed in this studywere removed prior tobeing restored prosthetically. This study strictly focused on theimplant survival rate and excluded the success rate. Nevertheless,this kind of documentation (overall survival rate) has a high sci-entic and clinical relevance and might ensure the clearest datapresentation in our view. Compared to the current literature and tothe knowledge of the authors, this is the only study analyzing andsummarizing three of the most important possible predictors forimplant failure in the posterior maxilla (sinus elevation, implantlength and diameter) with such a high number of implants andpatients.

5. Conclusions

Within the limitations of this study, our results suggest there are

A.M. Pabst et al. / Journal of Cranio-Mno detectable predictive risk factors for implant failure in theposterior maxilla. Implants placed in maxillary areas with inade-quate bone volume, requiring sinus elevation or short anddiameter-reduced implants, were not statistically correlated withhigher implant failure. Notably, implant placement in grafted si-nuses could be used as a secure and effective therapeutic modalityin maxillary posterior sites. Unfortunately, this retrospective studyis based on only a limited number of parameters and does not allowto get a deeper insight in the aspect of risk factors for implantsurvival. Forward-looking, there are still several difcult in-dications, such as patients with alveolar clefts, bisphosphonatetherapy as well as bula free-ap mandibular reconstructions,which will require an ongoing and intensive research in dentalimplantolgy (Ferrari et al., 2013; Rachmiel et al., 2013; Dikicieret al., 2014).

Conict of interest statementThere are no conicts of interest.

Role of the funding sourceThere are no sources of support. T. Ziebart, B. Al-Nawas andM.O.

Klein received funding from the ITI Foundation for different studies.

Acknowledgements

Special thanks to Cristian Valenzuela, MD, (Laboratory ofAdaptive and Regenerative Biology, Brigham and Women's Hospi-tal, Harvard Medical School, Boston, MA, USA) and Gary F. Bouloux,MD DDS MDSc, (Division of Oral and Maxillofacial Surgery, TheEmory Clinic, Atlanta, GA, USA) for language help and proofreading.

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