implant survival and prosthetic complications of ...statement of purpose. this study examined and...

Implcomresipro

George Priest, D

aPrivate Practice, Hilton Head IslandbPrivate Practice, Atlanta, Ga.cAdjunct Faculty, Department of Clin

The Journal of Prosthetic

ant survival and prostheticplications of mandibular metal-acrylicn implant complete fixed dentalstheses

MD,a Jay Smith, DDS,b and Michael G. Wilson, MSc

Private Practice, Hilton Head Island, SC; Private Practice, Atlanta, Ga;Indiana University School of Medicine, Indianapolis, Ind

Statement of purpose. This study examined and recorded the long-term implant survival and prosthetic complications ofpatients treated with mandibular metal-acrylic resin implant complete fixed dental prostheses delivered in a private practicesetting over a 22-year period.

Material and methods. Records were examined for all patients in the authors’ private prosthodontic practices who betweenApril 1988 and April 2011 had received mandibular metal-acrylic resin implant complete fixed dental prostheses supported by4 to 8 implants and who had completed at least 1 year of follow-up after implant placement.

Results. Forty-five patients who had received a total of 247 implants met the inclusion criteria. In the course of the1- to 22-year follow-up period (mean 8 years and 3 months), only 2 implants failed (0.81%) in 1 patient before definitiveprosthetic reconstruction, which resulted in a cumulative implant survival rate of 97.78% �2.2%. No screws were foundto be loose or fractured. Individual denture-tooth fracture and chairside repair occurred 10 times in 5 patients. Becauseof wear, all the teeth had to be replaced by the laboratory 10 times in 8 patients between 5 and 12 years. Frameworkfractures occurred 6 times and affected 3 prostheses (twice for each of the 3 patients).

Conclusions. Implant failure was rare with this traditional mode of treatment and occurred before definitive restoration. Thereplacement of denture teeth due to wear or fracture was the most common prosthetic complication, and cantileveredframeworks exhibited a high risk of fracture when opposed by fixed prostheses. No fractures occurred for any of theframeworks opposed by complete dentures or removable implant prostheses. (J Prosthet Dent 2014;111:466-475)

Clinical ImplicationsImplants that support mandibular metal-resin implant complete dentalprostheses demonstrate high implant survival rates that are not affectedby prosthetic situations that require remediation over time. Cliniciansshould incorporate design parameters that address the potential ofincreased prosthetic complications when metal-resin implant completedental prostheses are opposed by teeth or fixed prostheses in themaxillary arch.

Nearly 30 years ago, Brånemark1

introduced the mandibular screw-retainedmetal-acrylic resin implant completefixed dental prosthesis (MRICFDP),originally referred to as a hybrid pros-thesis or fixed bone-anchored pros-thesis,2 to address the problemscaused by unstable and uncomfort-able mandibular dentures.3,4 Initialdata from Brånemark’s Swedish study

, SC.

ical Pharm

Dentis

population indicated exceptionally highsuccess rates for mandibular MRICFDPsand the implants that support them(100% and 97%, respectively, after 15years).5 This ground-breaking researchprovided support for a new era of im-plant treatment options for patientswho were edentulous and partiallyedentulous. Continued university-basedstudies in Sweden, Belgium, and

acology, Indiana University School of Medicin

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North America reproduced the successrates of Brånemark1 for implants andfixed prostheses in edentulous man-dibles.6-8 As noted by Kopp9 morethan 2 decades ago, “the data demo-nstrate that the mandibular hybridfixed prosthesis carries a low surgicalrisk and high restorative predictab-ility.” After documented successes forconventional implant protocols,10 early

e, Clinical Pharmacology, Indianapolis, Ind.

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June 2014 467

and immediate loading protocolsaimed at reducing treatment time alsodemonstrated predictable success in pa-tients with edentulous mandibles.10-14

Several researchers have reported highsuccess rates by using immediateloading with mandibular fixed pros-theses in private practice, but thesestudies are relatively short term (be-tween 1 and 10 years).15-19

Although success rates of both theimplants and prostheses are high forMRICFDPs, prosthetic complicationscan be problematic. Lindquist et al20

found that lost fillings in screw-accessopenings and mobile prostheses werethe most common complications asso-ciated with mandibular MRICFDPs, yetthese were easy to manage, and, in theToronto Study, Zarb and Schmitt21 re-ported that fractured screws were easilyreplaced.

In their 15-year follow-up of 76patients, Jemt and Johansson22 foundthat, although implant and prosthesissurvival rates remained high, the wearand fracture of denture teeth has been asignificant problem. A recent meta-analysis conducted by Bozini et al23

revealed a 66.6% incidence of acrylicresin fracture after 15 years of follow-up.In a Medline review, Goodacre et al24

reported an incidence of resin-veneerfracture of implant fixed dental prosthe-ses of 22%, much lower than the numberreported by Jemt and Johansson,22 butstill concluded that it was a significantcomplication. Pjetursson et al25 notedthat these maintenance issues couldbe problematic in a busy restorative orprosthodontic practice.

Fracture of prosthesis frameworks isthe most serious and costly prostheticcomplication. An incidence of 8.8% af-ter 15 years was reported by Boziniet al.23 Makkonen et al26 and Johanns-son and Palmqvist27 also observed thatthe fracture of superstructures was asignificant problem related to mandib-ular MRICFDPs. In a 5-year follow-up of37 patients, Davis et al28 observed thatthe incidence of framework fracture wasmuch higher when both arches receivedfixed implant restorations and the frac-tures occurred at the beginning of the

Priest et al

cantilever arms. Attard and Zarb29 re-ported similar results: 10 of 33 frame-works fractured after 8 to 23 years, andthe fractures occurred at the cantileversin all but 1 patient. Other researchers,however, have not detected frameworkfractures even for prostheses opposingnatural dentitions.15,30-32 In thosestudies that reported framework frac-tures, potential causes have been corre-lated with increased occlusal forceswith fixed implant restorations,33 flawsof casting technology,34 and cantileverlength.35 The present retrospective pa-tient investigation examined the survivalrate of implants that supportMRICFDPsthat were provided in a private practicesetting with both delayed and immedi-ate protocols, and were followed-up forup to 22 years. Based on the authors’data and experiences, prosthetic com-plications and methods for improvingprosthesis design and predictability alsowere examined.

MATERIAL AND METHODS

Two prosthodontists in privatepractice examined patient records con-tained in a database maintained by thepractice. It was updated weekly anddocumented patient progress as notedduring routine recall visits, emergencyexaminations, and revision appoint-ments. Inclusion criteria for patients inthis retrospective examination were thatthey were at least 16 years old; had oneof the following diagnoses, unstable oruncomfortable mandibular dentures,congenitally missing teeth, or failingremaining teeth, with a preference for afixed dental prosthesis or an intoleranceto removable prostheses; were restoredwith implants and mandibular screw-retained MRICFDPs between April1988 and April 2011; and hadcompleted at least 1 year of follow-upafter implant placement.

Forty-five patients who were treatedwith a total of 247 implants to restoretheir edentulous mandibles met theinclusion criteria. A total of 10 oralsurgeons and 3 periodontists placedthe implants; the present authorsdelivered prosthetic care, and 2 dental

laboratories fabricated the prostheses.Patients ranged in age from 16 years (apatient with ectodermal dysplasia) to86 years; the mean age was 61 years.Thirty-one patients were women, and14 were men. Follow-up time from thetime of implant placement ranged from1 to 22 years, with a mean observationtime of 8 years and 3 months. Follow-up from the time of definitive pros-thesis placement ranged from 8 monthsto 20 years 6 months, with a mean of 7years and 2 months. Although 8 pa-tients received immediate provisionalfixed dental prostheses, follow-up timewas calculated by using the seating dateof the definitive prostheses for all thepatients.

Patients who met the inclusioncriteria were reexamined for this study.Those who had moved from the areaor were unable to continue mainte-nance appointments were contactedby telephone to obtain detailed infor-mation about their implants andprostheses. If other dentists hadtreated the patients after geographicrelocation, then those dentists werecontacted, and records were reviewedwhen appropriate. Patients who weredeceased but had completed at least 1year of follow-up also were included.This type of analysis enabled a realisticappraisal of the successes, failures,and maintenance issues that are facedin a typical prosthodontic privatepractice setting. The focus of the pa-tient examination was implant surviv-al as well as mandibular prostheseslongevity and prosthesis complicationsthat required remediation. The typesof restorations in the opposing maxil-lary arches were recorded, but theircontinued status was not included inthese data.

Statistical methods

Although a patient could havemultiple implants, the individual pa-tient was the unit of analysis. Failuresand qualitative variables were expressedas percentages. Failure time wasdefined as the time to first implantfailure for any given patient and was

Table I. Participant data

Participants Implants Significant Complications

No. Sex

Age

(y) No.

Immediate

Delayed

Implants

Duration

(mo)

Prosthesis

Duration

(mo)

Opposing

Arch

Implant

Failure

Frame

work

Fracture

Incidence

of

Single

Tooth

Fractured

Chairside

Repair

All

Teeth

Worn

and/or

Fractured

Replaced

in Lab

Prosthesis

Replaced

1 F 43 5 Delayed 254 246 Denture 1

2 F 55 6 Delayed 252 228 Fixed imp 2 2

3 M 52 5 Delayed 250 244 Denture

4 F 50 6 Delayed 209 202 Fixed imp 2 2

5 F 40 5 Delayed 194 183 Imp over 1

6 F 86 5 Delayed 66 59 Denture

7 F 55 4 Immediate 127 28 Denture


9 F 63 5 Delayed 168 158 Fixed imp

10 M 63 8 Delayed 169 161 Denture 2





15 F 70 8 Delayed 139 133 Teeth 1

16 F 60 5 Delayed 129 125 Fix teeth/imp 2 1 1

17 F 57 5 Delayed 126 121 Fixed imp 2 2 1 2

18 M 16 5 Delayed 123 115 Imp over



21 M 58 8 Delayed 98 92 Fixed imp 3 1


23 F 72 6 Immediate 84 76 Teeth FDP

24 F 55 5 Immediate 86 81 Teeth

25 M 56 5 Immediate 85 73 Denture


27 F 54 5 Delayed 73 64 Teeth RDP


29 M 74 4 Delayed 71 65 Teeth

30 M 57 5 Immediate 69 51 Teeth

31 F 79 5 Delayed 59 53 Teeth 2 2

32 F 38 5 Delayed 56 46 Teeth


34 F 68 5 Delayed 65 60 Imp over

35 F 66 5 Immediate 65 56 Denture



(Continued)

468 Volume 111 Issue 6

The Journal of Prosthetic Dentistry Priest et al

Table I. (Continued) Participant data

Participants Implants Significant Complications

No. Sex

Age

(y) No.

Immediate

Delayed

Implants

Duration

(mo)

Prosthesis

Duration

(mo)

Opposing

Arch

Implant

Failure

Frame

work

Fracture

Incidence

of

Single

Tooth

Fractured

Chairside

Repair

All

Teeth

Worn

and/or

Fractured

Replaced

in Lab

Prosthesis

Replaced



40 M 61 5 Immediate 33 27 Fixed imp 1




44 F 61 6 Immediate 20 15 Imp over


31F 61 245 38 Delayed Mean Mean Dent/over 26 2 6 10 10 9

14M 2 failed 8 immediate 99.3 86.6 Fixed teeth/imp 19 4 cast 2 CAM

Fixed imp, fixed implant prosthesis; Imp over, implant overdenture; RDP, removable dental prosthesis; FDP, fixed dental prosthesis.

June 2014 469

estimated by using the nonparametricKaplan-Meier method.36 Because theerror rate for all inferential statistics wasset at .05, the level of the confidenceintervals was 95%. All computationswere completed with software (SAS/Base and SAS/Stat 9.1; SAS Institute).

RESULTS

Patient data, including the numberof implants and significant complica-tions, are listed in Table I. Two-hundredforty implants were placed in theinterforaminal region of the 45 pa-tients, with 28 patients classically re-stored with 5 interforaminal implants,4 patients with 4 implants, 9 patientswith 6 implants, 2 patients with 7 im-plants, and 2 patients with 8 implants.Only 7 implants were placed distal tothe mental foramina., The currentstatus of all but 1 of the patientswas obtained. Thirty-five of the 45were still active in the practice, 7 wereinterviewed by telephone, and 2 weredeceased.

All the patients received antibioticprophylaxis before surgery. Three

Priest et al

patients underwent grafting withautogenous bone from the iliac crestbefore implant placement, and 5 im-plants were placed in each of thesemandibles after complete healing. Twohundred twenty-two implants weremanufactured by Biomet 3i, 15 byNobel Biocare, 6 by Biohorizons, and 4by Zimmer Dental. Nineteen prosthesesopposed either natural teeth or fixeddental prostheses supported by teethor implants, 21 opposed completedentures, and 5 opposed removableimplant-retained prostheses.

In the earlier years, patients (n¼28)were treated with a 2-stage surgicalprotocol. For these patients, a surgicalguide was made by the prosthodontistsand delivered to the implant surgeon.Implants were placed and uncovered3 to 6 months later. An existing orprovisional denture that was soft linedwas placed after initial surgery andagain relined after implant uncoveringand placement of healing abutments.In later years (n¼9), implants wereplaced in a single-stage surgery andtemporarily restored with soft-lineddentures. The most recently delivered

implants were placed immediately aftertooth extraction and were immediatelyrestored with fixed provisional restora-tions that were converted chairside bythe prosthodontists from existing ornewly fabricated dentures (n¼8). Thisconversion was accomplished by at-taching temporary cylinders to the im-plants and affixing the cylinders to theprostheses intraorally with autopoly-merizing resin. The gingival surfaces ofthe prostheses were contoured andpolished, and designed to be free ofsoft-tissue contact. All interim pros-theses were screw retained and tight-ened to the force recommended by theimplant manufacturers. Access open-ings were filled first with a cotton pelletplaced over the abutment screw, fol-lowed by a layer of fast-setting polyvinylsiloxane. Patients were advised to con-sume a soft diet for 8 weeks.

All but 4 patients received theirdefinitive implant prostheses within 1year of implant placement. Impressionswere made by using an open-traytechnique. Pick-up impression copingswere splinted with dental floss andautopolymerizing acrylic resin (GC

1 Earlier use of hand waxing was replaced by virtualframework design in later prostheses.

2 Digital design files interfaced with computer-controlledmilling machines to produce precisely machined titaniumframeworks.

3 Completed titanium frameworks were processed withnanocomposite resin teeth and characterized gingival acrylicresin.


resin; GC America). Openings or win-dows were made over the impression-coping access openings in the stocktrays, and definitive impressions were

The Journal of Prosthetic Dentis

made with polyvinyl siloxane. Cast ac-curacy was then ascertained by usingcast-verification indices that were madewith temporary implant cylinders luted

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together on the casts with the sameautopolymerizing resin. The indiceswere evaluated intraorally, and impres-sions were remade if a discrepancy wasdetected. No frameworks had to besectioned and reassembled because ofmisfits.

Jaw-relation records were completedwith a facebow, occlusion rims, centricrelation record, and semi-adjustablearticulator. Early frameworks werewaxed and then cast in noble alloy(n¼17), whereas all later versions(n¼28) were virtually designed andfabricated in titanium alloy (Figs. 1, 2)with a computer-assisted design/com-puter-assisted manufacturing system(Architecture CAM StructSURE; Biomet3i). Acrylic resin or nanocompositeresin denture teeth were used for allprostheses and processed with charac-terized pink acrylic resin (Fig. 3). Pros-theses extended to 1 premolar and 1molar for 2 patients, 2 premolars and 2molars for 3 patients, and 2 premolarsand 1 molar for all remaining patients.A group function occlusal scheme wasused, which avoided excursive contactson cantilevered teeth (Fig. 4). Definitiveprostheses were seated and tightenedto the torque recommended by theimplant manufacturers (Figs. 5, 6).Earlier access openings were filled firstwith a cotton pellet over the screw,followed by a layer of gutta perchadental stopping and finished with2 mm of either acrylic resin or com-posite resin (Fig. 7). In later prostheses,Teflon plumbers tape E. I. du Pont deNemours and Company was used inlieu of cotton pellets and dental stop-ping. Postseating radiographs weremade to assess implant integration andprosthesis fit (Fig. 8). Patients wereexamined on regular recall visits, usuallybiannually, or as was required duringrevision appointments.

This series of dental patients(n¼45) with implants placed between1988 and 2011 was followed-up for upto 22 years. All the patients had 4 to 8implants each and a total of 247 im-plants were placed. The mean evalua-tion period was 8 years and 3 months,with a minimum follow-up of 1 year

Priest et al

4 Distal cantilevers typically extended to mandibular firstmolar and group function occlusion established.

5 Upon removal of easily cleansable interim fixed dentalprosthesis, soft tissue was observed to be relatively free frominflammation.

6 Seated prostheses functionally and esthetically integratedwith opposing complete denture.

June 2014 471

and a maximum follow-up of 22 years.During that period, 2 implants failedin 1 patient at 1.9 months, beforeprosthetic rehabilitation. By using thelower limit of the Kaplan-Meier 95%

Priest et al

confidence interval,36 the cumulativeimplant survival rate was 97.78%�2.2% for these patients. Also whenusing the lower limit of the Kaplan-Meier 95% confidence interval, these

implants were deemed successful for266.8 months in more than 93.5% ofpatients.

Minimal bone loss was observedradiographically in all the patients. Sorespots that developed during interimdenture wear occasionally required re-lief. Otherwise, no significant surgicalcomplications were documented. Mostnotably, no implants failed in anypatient after prosthetic rehabilitationduring the retrospective study period,and all patients remained in continuousfunction with fixed prostheses.

The definitive prostheses wereobserved for a mean of 7 years and 2months, with a minimum follow-up of 8months and maximum follow-up of 21years. Prosthetic complications occurredmore frequently than implant failures.Occlusal access filling materi-al dislodged in a few early patients(Fig. 9), but this was rectified by placingundercuts in the openings with aninverted cone bur to mechanically lockthe acrylic resin or composite resin inplace. The most common prostheticcomplication was the replacement of allacrylic resin teeth because of wear orfracture. This occurred 10 times, whichaffected 8 patients whose prostheseswere in service from 5 to 10 years (mean,7 years) and 2 patients whose teeth werereplaced twice (at 5 and 7 years and at 5and 12 years, respectively). More rapiddenture-tooth wear and fractured den-ture teeth were noted in prostheses thatopposed natural teeth or fixed dentalprostheses. Prosthetic tooth replace-ment unrelated to wear or fracture ofdenture teeth was required in another 10instances due to framework fracture (6)or compromised framework design (4).Fracture of individual denture teeth orthe acrylic resin that surrounded theframeworks that was repaired chairsideoccurred 10 times in 5 patients. Oneprosthesis was removed, and acrylicresin was added to the gingival aspectbecause the patient stated that the spacewas too large and was trapping food.

Framework fracture occurred 6times and involved 3 patients (twice foreach patient) and occurred early in alltreatments, between 1 and 3 years. Two

7 Occlusal screw access openings filled with cotton pellets,gutta percha dental stopping, and acrylic resin or compositeresin.

8 Postseating radiographs demonstrated nearly seamlessinterface between framework and supporting implants.

9 Early prosthesis opposing maxillary fixed dental prosthesisdemonstrated tooth wear and dislodgement of occlusal ac-cess material after 8 years in service.


of the 3 patients reported a positivehistory of parafunctional habits. Of the6 frameworks that fractured, 4 were


cast noble alloy, and 2 were computer-assisted design/computer-assisted man-ufacturing milled titanium alloy. Five of

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the 6 were completely remade, and 1was laser welded and repaired, andthen new teeth were processed. Allfractures occurred distal to the mostdistal implant and only in prosthesesthat were opposed by either naturalteeth or a fixed prosthesis supported byteeth or implants.

Four additional frameworks wereremade because of the inadequateretention of denture teeth. Nine prosthe-ses, therefore, were completely remadebecause of framework fractures or inad-equate framework design. No loose orbroken retaining or abutment screwswere reported. The only significant soft-tissue complication related to prosthesisdesign was hyperostosis beneath thedistal cantilevers of 1 patient.

DISCUSSION

Results for this private practicepopulation treated over a 22-year periodwith mandibular MRICFDPs includedfavorable rates of implant survival andprosthesis stability, comparable with orhigher than reported in long-term uni-versity settings.6-8,37,38 These outcomespresented further substantiate theexisting shorter-term data on immedi-ate restorations.10,11,15-17,26,30,39 Inthis population, the few implant fail-ures that were noted occurred beforeprosthetic rehabilitation; after restora-tion, implants survived for up to 22years. All the patients remained incontinuous function with their fixedprostheses throughout the examinationperiod, although 9 prostheses had tobe completely remade (5 because offramework fracture and 4 because offramework design flaws), unrelated toimplant failure. The authors’ experiencepresented is similar to studies reviewedin the meta-analysis by Bozini et al23;prosthodontic complications did notadversely affect implant survival. Otherresearchers have recognized the sametrends: few implant failures occurred inedentulous mandibles, with most ofthose documented before restora-tion.29,40-42 Positive outcomes reportedby other researchers for immediateimplant placement and provisional

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June 2014 473

restorations10,13,14 led the authors toadopt these protocols in more recentyears. The only significant soft-tissuecomplication related to prosthesisdesign was hyperostosis beneath thedistal cantilevers of 1 patient, a com-plication also reported by Taylor.43

This framework was removed, relievedover the area of hyperostosis, andreseated, and the patient remainedcomfortable throughout the observa-tion period.

Although the Toronto study re-ported fractured screws, which wereeasily replaced,21 no screw fractureswere encountered in the present studypopulation. In the authors’ experience,screw loosening almost never occurredafter the introduction of implants withinternal abutment connections andconsistent use of torque devices. Al-though filling material dislodged inearlier patients, this became rare oncemechanical undercuts were placed inaccess openings.

Wear and/or fracture of individualresin denture teeth that were repairedchairside occurred 10 times in 5 pa-tients (incidence of 11%). As also re-ported by Purcell et al,40 anterior toothfracture was more common than pos-terior tooth fracture. Generalized wearresulted in complete replacement of theacrylic base and teeth in 10 prosthesesand 8 patients (incidence of 18%).Therefore, total complications thatrelated to tooth replacement due towear and fracture occurred 20 times in13 patients (incidence of 29%). Toothreplacement due to framework refabri-cation, unrelated to tooth wear orfracture, occurred in another 9 pros-theses. Notably, the most commonlyencountered complication, tooth re-placement, was not particularly prob-lematic in this private practice setting.Individual tooth fracture was repairedchairside, and the authors consideredreplacement of worn teeth that oc-curred over a period of years to be anormal maintenance procedure thatwas accomplished with little difficulty.The patients were made aware of thiscontingency at the beginning of treat-ment and were very accepting of these

Priest et al

revisions and the costs involved. Theseresults are in contrast to the high inci-dence of tooth fracture presented byother researchers.22,23 The disparity inthese results may be the result ofdiffering reporting methods. The pre-sent authors listed wear as a compli-cation only when tooth replacementwas necessary. All denture teeth, how-ever, demonstrated some degree ofwear over a period of years, particularlywhen opposed by fixed prostheses inthe maxillary arch.

Framework fracture occurred in 6prostheses in 3 patients, an incidenceof 13.3% per prosthesis and 6.7%per patient. In this study population,fractures occurred only when the pros-theses were opposed by natural teeth orfixed prostheses supported by teeth orimplants and usually in patientswith parafunctional habits. This inci-dence is higher than that found in themeta-analysis by Bozini et al.23 Com-plete dentures, however, opposed mostof the prostheses reviewed in thatanalysis. Davis et al28 and Attard andZarb,29 also discovered that the rate offramework fracture was higher whenboth arches received fixed implant res-torations and the fractures occurred atthe beginning of the cantilever arms.

Framework fracture in this popu-lation that occurred only whenMRICFDPs were opposed by fixed res-torations may also be related toincreased occlusal forces. Mericske-Stern and Zarb44 indicated that im-plants supporting fixed prostheses werenot likely to increase maximum occlusalforces in the presence of maxillarycomplete dentures. Jemt et al33

demonstrated that occlusal forcesincreased significantly over time whenpatients were switched from a man-dibular removable bar overdenture toa fixed prosthesis. Jacobs et al45

demonstrated a significant downwardshift of power frequency during sus-tained clenching after rehabilitationwith implant-supported overdenturesbut not with implant-supported fixedprostheses. Falk et al46 demonstratedthat 70% of the occlusal forces wereborne by the cantilever sections and

concluded that the framework wasmost vulnerable distal to the distalimplant and should have adequateheight to withstand the forces on thecantilever section.

Another cause of framework frac-ture may be related to the imperfectionsof casting technology. Four of 17 castnoble alloy frameworks (23.5%) andonly 2 of 28 computer-assisted design/computer-assisted manufacturing tita-nium frameworks (7.1%) fractured inthis patient population. Although thetitanium frameworks were in service fora shorter period, the cast frameworksfractured early, between 1 and 3 years.Carr and Stewart34 observed that con-ventional lost-wax casting techniquesfor complete-arch implant frameworksare both imprecise and inaccurate asjudged against the passive fit require-ment. Computer-milled titanium frame-works made of homogeneous blocksof titanium have greater strength thanpotentially porous cast alloys anddemonstrate improved precision offit.47,48

Potential framework fracture alsohas been correlated with cantileverlength, although no specific correla-tion was found in the present popu-lation. In a 15-year follow-up, Lindquistet al20 concluded that cantilever lengthswere of minor importance. Sertgozand Guvener35 suggested a mandibularextension of between 15 and 20 mm tominimize risk. English49 and Takayama50

recommended a cantilever length 1.5times or 2 times, respectively, theanterior posterior curve of the implants.McAlarney and Stavropoulos,51 how-ever, indicated that the determinationof cantilever length should not bebased solely on the anterior posteriorspread of the implants but shouldalso consider the opposing occlusionand the number and distribution ofimplants.

In the present study, the incidenceof framework fracture in those resin-metal fixed prostheses opposed byfixed restorations was 25% (3 of 12patients), an unacceptable risk in theauthors’ opinion. The present resultsare similar to those of Davis et al,28


who found that cantilevered mandib-ular fixed prostheses opposed by natu-ral teeth or fixed implant prostheseshad a higher incidence of complications.

The frequency of framework frac-tures in the cantilevered sections ofmandibular prostheses opposed by fixedmaxillary dental prostheses in this studywarrants special consideration. Anobvious solution is to avoid mandibularframeworks with posterior cantileversagainst maxillary fixed prostheses, andto reserve the use of mandibular canti-levers only when opposed by maxillarydentures or removable implant pros-theses. Implants could be placed distalto the mental foramina to eliminate orshorten cantilevers. Other practicalsuggestions include keeping the canti-lever as short as possible to reduceframework stress, extending distally nofurther than the mandibular first molarfor most patients. Tipping the mostdistal implants distally will reducecantilever length without compromisingimplant success rates.52 As recom-mended by Stewart et al,53 increasedvertical framework thickness in cantilev-ered sections improves fatigue strength.Zirconia frameworksmay be a promisingalternative to titanium alloys. In atleast 1 short-term study of 10 patients,no frameworks fractured in a 3-yearperiod.54 If the vertical space for a sub-stantial framework is inadequate, thenan implant overdenture might providean alternative restorative approach.

CONCLUSION

Extensive patient documentation bynumerous researchers over the past 30years has led to significant refinements inmaterials and techniques for mandib-ular MRICFDPs, a treatment methodthat has evolved into a contemporaryoption that effectively serves the needs ofmany patients who are edentulous. Thisretrospective evaluation of 45 patientstreated withmandibularMRICFDPs and247 implants and followed up in privatepractice over a 1- to 22-year periodrevealed that

1. Implant failure was rare, with acumulative implant survival of 97.78%


�2.2%. All failures occurred beforeprosthetic reconstruction. Prostheticcomplications did not impact implantsurvival rates.

2. Cumulative survival rates wereequally high for immediately placedand provisionally restored implants andfor those placed with conventionaldelayed protocols.

3. Prosthetic complications of screwloosening and fracture were rare.

4. Tooth wear and fracture were themost common prosthetic complica-tions that required remediation.

5. Framework fracture, the mostsignificant prosthetic complication,occurred at an overall rate of 13% andonly when opposed by teeth or fixeddental prostheses supported by teeth orimplants.

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Corresponding author:Dr George Priest23 Main Street, Suite 303Hilton Head Island, SC 29928E-mail: [email protected]

AcknowledgmentThe authors thank Ms Jeannette De Wyze foreditorial assistance of this manuscript.

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