Clinical Complications of Osseointegrated Implants

Knowledge regarding the types of complicationsthat can occur with dental procedures is an importantaspect of treatment planning, dentist-patient communi-cation, informed consent, and posttreatment care.Because the design of clinical implant studies has notbeen standardized, the reporting of clinical complica-tions tends to vary among studies. This variation makesit difficult to determine whether an unreported com-plication was not evaluated as part of the study’s datacollection, never occurred in that particular study, ormay have occurred but was not reported. Consequent-ly, there are only a small number of studies reportingcertain complications.

The purpose of this literature review is to identifythe types of complications that have been reported inconjunction with dental implant treatment and provide

data regarding their frequency. This article is also pre-sented as mean percentages of the available data andstatistical analysis are used only when possible. Themean percentage data are intended to reflect trendsrather than statistically valid complication rates.

MATERIAL AND METHODS

All available clinical studies from 1981 to 1997(written in English or with English abstract) thatpresented success/failure data regarding implant treat-ment were evaluated to determine the types of report-ed complications and to quantify implant loss as itrelates to type of prosthesis, arch, time, implant length,and bone quality. Also included were patient reports onsignificant complications arising from osseointegratedimplant treatments. Items excluded from this reportwere the implant studies that involved compromisedsituations or complex treatments that required bonegrafting, subantral augmentation, and so forth. Thesedata will be presented in future articles.

Clinical complications of osseointegrated implants

Charles J. Goodacre, DDS, MSD,a Joseph Y.K. Kan, DDS,b and Kitichai Rungcharassaeng, DDSc

School of Dentistry, Loma Linda University, Loma Linda, Calif.

Statement of problem. There is no comprehensive review of the literature that identifies the complica-tions reported in clinical dental implant studies.Purpose. This article attempted to determine the types of complications that have been reported and toprovide data regarding their frequency.Methods. All available clinical studies from 1981 to 1997, published in English or with English abstract,that presented success/failure data regarding implant treatment were evaluated to determine the types ofreported complications and to quantify implant loss as it relates to type of prosthesis, arch, time, implantlength, and bone quality.Results. Greater implant loss occurred with overdentures than with other types of prostheses. There wasgreater loss in the maxilla than mandible with fixed complete dentures and overdentures, whereas little archdifference was noted with fixed partial dentures. Implant loss increased with short implants and poor bonequality. The time of implant loss (preprosthetic vs postprosthetic) varied with type of prosthesis. Surgicalcomplications included neurosensory disturbance, hematoma, mandibular fracture, hemorrhage, and toothdevitalization. Initial and long-term marginal bone changes were identified. Peri-implant soft tissue compli-cations included dehiscence, fistulas, and gingival inflammation/proliferation. Mechanical complicationswere screw loosening/fracture, implant fractures, framework, resin base and veneering material fractures,opposing prosthesis fractures, and overdenture mechanical retention problems. Some studies also presentedphonetic and esthetic complications.Conclusions. Although the literature presents considerable information on implant complications, varia-tions in study design and reporting procedures limited the available data and therefore precluded properanalysis of certain complications. (J Prosthet Dent 1999;81:537-52.)

aProfessor and Dean.bAssistant Professor, Department of Restorative Dentistry.cGraduate Student, Advanced Education in Implant Dentistry.

MAY 1999 THE JOURNAL OF PROSTHETIC DENTISTRY 537

CLINICAL IMPLICATIONS

In this literature review, the clinical complications reported in implant studies havebeen identified along with frequency rates. This information will facilitate treatmentplanning and enhance communication between dentists and patients regarding theoutcomes of dental implant treatment.

CLINICAL COMPLICATIONSImplant loss as related to type of prosthesisand arch

Tables I through VII present data1-44 regarding thepercentage of implant failure (loss of the implant) asso-ciated with each type of implant prosthesis (fixed com-plete denture, overdenture, fixed partial denture, andsingle crown). The studies listed in these tables alsoprovided data that permitted a comparison of implantfailures between the maxilla and the mandible for eachtype of prosthesis, except the single crown. Althoughthe length of the studies varied considerably, differ-ences in implant loss between types of prostheses andarches were identified.

When data were combined from all the studies relat-ed to each prosthesis type and arch and a meanpercentage loss calculated, some interesting trendswere noted.

With implant fixed complete dentures, the meanfailure in the maxilla (Table I)1-8 was 9.8%, whereasmandibular mean failure was 2.7% (Table II).1-6,8,9 Forimplant overdentures (Tables III and IV),9-20 higher

failure rates were also noted for the maxilla (21.3%)than the mandible (5.0%). The highest failure rate(21.3%) for any type of prosthesis occurred with maxil-lary overdentures (Table III).10-15 There was littledifference between the maxillary and the mandibularfailure rates (6.6% and 6.2%, respectively) for implantfixed partial dentures (Tables V and VI).21-32 Implantsingle crowns had the lowest mean implant failure rateof 2.7% (Table VII).33-44

Implant loss related to type of prosthesis,time after placement, implant length, bonequality

Tables VIII through XI present studies* that identi-fied the total number of implants placed and lost witheach type of prosthesis. These studies also included dataas to whether the implant losses occurred preprosthet-ically or postprosthetically. Although the study lengthsvaried considerably, differences in implant loss betweentypes of prostheses were identified, along with data

THE JOURNAL OF PROSTHETIC DENTISTRY GOODACRE, KAN, AND RUNGCHARASSAENG

538 VOLUME 81 NUMBER 5

Table I. Implant loss in patients with implant fixed complete dentures in maxilla

Length of study (y)

Range Mean No. of implants placed No. of implants lost (%)

Adell et al1 1-9 — 100 22 (22.0)Cox and Zarb2 1-3 — 12 0 (0.0)Albrektsson et al3 1-7 — 2464 227 (9.2)Zarb and Schmitt4 5-9 — 36 1 (2.7)Jemt5 1* — 586 25 (4.3)Naert et al6 0.5-6.5 2.5 269 20 (7.4)Jemt7 5* — 449 34 (7.6)Branemark et al8 — 10 476 102 (21.4)

% Failure relative to total 4392 431 (9.8)number implants placed

*Minimum observation period.

Table II. Implant loss in patients with implant fixed complete dentures in mandible

Length of study (y)


Adell et al1 1-9 — 124 14 (11.3)Cox and Zarb2 1-3 — 132 18 (13.6)Albrektsson et al3 1-8 — 5833 103 (1.8)Zarb and Schmitt4 5-9 — 238 38 (16.0)Jemt5 1* — 1613 11 (0.7)Naert et al6 0.5-6.5 2.5 320 10 (3.4)Hemmings et al9 6-10 9 132 15 (11.4)Branemark et al8 — 10 406 30 (7.4)



*References 1,4-6,9,10,12,13,17,19-23,30,33,38,40,41,45-49.

regarding the timing of the loss. The data were com-bined from all the studies related to each prosthesistype and an overall percentage loss calculated to deter-mine trends.

With implant fixed complete dentures, the com-bined data1,4-6,9,45 (Table VIII) indicated 3742implants were placed in the 6 studies and 225 were lost,for a 6.0% implant failure rate. Of the 225 implants

GOODACRE, KAN, AND RUNGCHARASSAENG THE JOURNAL OF PROSTHETIC DENTISTRY

MAY 1999 539

Table III. Implant loss in patients with implant overdentures in maxilla

Length of study (y)


Enquist et al10 0.3-5 1.5 191 58 (30.4)Naert et al11 0.3-4 1.5 12 0 (0.0)Jemt et al12 1* — 430 69 (16.0)Smedberg et al13 1.5-2.5 2 86 12 (13.5)Cune et al14 — 2 106 30 (28.3)Hutton et al15 — 3 105 29 (27.6)

% Failure relative to total 930 198 (21.3)number of implants placed


Table IV. Implant loss in patients with implant overdentures in mandible

Length of study (y)


Enquist et al10 0.3-5 1.5 148 9 (6.1)Naert et al16 — 2 87 1 (1.1)Mericske-Stern17 0.5-5.5 — 153 8 (5.2)Naert et al11 0.3-4 1.5 161 2 (1.2)Cune et al14 — 2 1071 29 (2.7)Hemmings et al9 3-9 5 68 5 (7.4)Hutton et al15 — 3 189 11 (5.8)Leimola-Virtanen et al18 3-10 5.6 153 13 (8.5)Versteegh et al19 4-9 6 135 33 (24.4)Wismeyer et al20 5.5-10 6.5 218 7 (3.2)



Table V. Implant loss in patients with implant fixed partial denture in maxilla

Length of study (y)


van Steenberghe21 0.5-3 — 40 5 (12.5)Pylant et al22 — 2 28 3 (10.7)Naert et al23 0.2-6 2.5 304 18 (5.9)Bahat24 0.4-6.5 — 732 35 (4.8)Jemt et al25 — 5 101 4 (4.0)Nevins and Langer26 — 8 652 31 (4.8)Tolman and Laney27 — 6.5 528 58 (11.0)Zarb and Schmitt28(anterior) — 5 50 3 (6.0)Zarb and Schmitt29(posterior) — 5 41 1 (2.4)Lekholm et al30 5* — 220 17 (7.7)Higuchi et al31 — 3 220 16 (7.3)





Table VI. Implant loss in patients with implant fixed partial denture in mandible

Length of study (y)


van Steenberghe21 0.5-3 — 93 7 (7.5)Gunne et al32 — 3 69 8 (11.6)Pylant et al22 — 2 74 9 (12.2)Naert et al23 0.2-6 2.5 205 12 (5.9)Jemt et al25 — 5 158 3 (1.9)Nevins and Langer26 — 8 551 25 (4.5)Zarb and Schmitt28(anterior) — 5 44 5 (11.4)Zarb and Schmitt29(posterior) — 5 64 5 (7.8)Lekholm et al30 5* — 338 19 (5.6)Higuchi et al31 — 3 330 17 (5.2)



Table VII. Implant loss in patients with implant single crown

Length of study (y)


Jemt et al33 1* — 107 3 (2.8)Babbush and Shimura34 — 5 21 0 (0.0)Fugazzotto et al35 — 3 136 3 (2.2)Jemt and Pettersson36 — 3 70 1 (1.4)Schmitt and Zarb37 — 3 40 0 (0.0)Ekfeldt et al38 1-4.5 2.5 93 2 (2.2)Laney et al39 — 3 95 3 (3.2)Cordioli et al40 0.5-5 2 67 3 (4.5)Andersson et al41 2-3 — 65 4 (6.2)Haas et al42 — 6 76 2 (2.6)Becker and Becker43 — 2 24 1 (4.2)Avivi-Arber and Zarb44 1-8 — 49 1 (2.0)



Table VIII. Implant loss and time of loss in patients with implant fixed complete dentures

Length of study (y)No. of implants No. of implants No. of lost No. lost

Range Mean placed lost (%) preprosthetic (%) postprosthetic (%)

Adell et al1 1-9 — 224 36 (16.1) 21 (9.4) 15 (6.7)Zarb and Schmitt4 5-9 — 262 30 (11.4) 21 (8.0) 9 (3.4)Jemt5 1* — 2199 36 (1.6) 24 (1.1) 12 (0.5)Naert et al6 0.5-6.5 2.5 589 30 (5.1) 18 (3.1) 12 (2.0)Jemt45 3* — 336 78 (23.2) 23 (6.8) 55 (16.4)Hemmings et al9 6-10 9 132 15 (11.4) 9 (6.8) 6 (4.6)

% Failure relative to total — 225 116 (51.6) 109 (48.4)number implants lost

% Failure relative to total 3742 225 (6.0) 116 (3.1) 109 (2.9)number implants placed


lost, 116 (3.1%) were lost preprosthetically and 109(2.9%) were lost postprosthetically. For implant over-dentures (Table IX), 1479 implants were placed in the8 studies9,10,12,13,17,19,20,46 and 232 were lost for a

combined 12.0% implant failure rate. More failures(129 of 232) occurred preprosthetically than postpros-thetically (103 of 232). The combined implant fixedpartial denture data21-23,30,47-49 (Table X) indicates


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Table IX. Implant loss and time of loss in patients with implant overdenture



Enquist et al10 0.3-5 1.5 339 67 (19.8) 46 (13.6) 21 (6.2)Mericske-Stern17 0.5-5.5 — 153 7 (4.6) 5 (3.3) 2 (1.3)Johns et al46 1* — 510 32 (6.0) 16 (3.0) 16 (3.0)Jemt et al12 1* — 430 69 (16.0) 27 (6.3) 42 (9.7)Smedberg et al13 1.5-2.5 2 86 12 (13.9) 7 (8.1) 5 (5.8)Hemmings et al9 3-9 5 68 5 (7.4) 4 (5.9) 1 (1.5)Versteegh et al19 4-9 6 135 33 (24.4) 17 (12.6) 16 (11.8)Wismeyer and van Waas20 5.5-10 6.5 218 7 (3.2) 7 (3.2) 0 (0.0)




Table X. Implant loss and time of loss in patients with implant fixed partial denture



Jemt et al47 1-20 — 876 24 (2.7) 10 (1.1) 14 (1.6)van Steenberghe21 0.5-3 — 133 12 (9.0) 9 (6.8) 3 (2.2)Johansson and Palmqvist48 3-9 5 286 25 (8.7) 23 (8.0) 2 (0.7)Pylant et al22 — 2 102 12 (11.8) 7 (3.3) 5 (4.9)Naert et al23 0.2-6 2.5 509 29 (5.7) 17 (6.9) 12 (2.4)Jemt et al49 1* — 430 5 (1.2) 5 (1.2) 0 (0.0)Lekholm et al30 5* — 558 36 (6.5) 20 (3.6) 16 (2.9)




Table XI. Implant loss and time of loss in patients with implant single crowns



Jemt et al33 1* — 107 3 (2.8) 1 (0.9) 2 (1.9)Ekfeldt et al38 1-4.5 2.5 93 2 (2.2) 1 (1.1) 1 (1.1)Cordioli et al40 0.5-5 2 67 3 (4.5) 2 (3.0) 1 (1.5)Andersson et al41 2-3 — 65 4 (6.2) 0 (0.0) 4 (6.2)




2894 implants were placed and 143 were lost for a 4.9%implant failure rate. A larger number of implants werelost preprosthetically (91 of 143) than postprostheti-cally (52 of 143).

Implant single crown studies33,38,40,41 (Table XI)that presented data on the total number of implantsplaced and lost, along with information on the timewhen implant loss occurred, were more limited thanthat available for the other types of prostheses. Whenthis limited data (4 studies) was combined, 332implants were placed and 12 implants were lost for a3.6% implant failure rate. More implants were lost post-prosthetically (8 of 12) than preprosthetically.

A limited number of studies41,45,47,50 (Table XII)provide specific data about the time when postpros-thetic implant loss occurs. A statistical analysis of the 4studies presented such data and revealed the following:(1) Implant loss in the second year was significantlylower than in the first year (P<.05); (2) implant loss inthe third year was significantly lower than in the firstand second years (P<.05); and (3) the data indicatethere was a decreasing failure rate at least during thefirst 3 years after prosthesis placement.

Numerous studies have shown higher failurerates with shorter implants (Tables XIII andXIV).12,22,23,25,30,31,50-54 Four of the studies31,51-53

indicated the highest failure rates occurred when 7-mmimplants were used in the maxilla. In the available stud-ies,10,13,35,46,53,55 in which data permitted a compari-son of the failures rates between different bone quali-ties (Table XV), significantly higher implant failurerates were noted in type IV bone as compared withtypes I to III bone.

Several retrospective and prospective studies havereported on the incidence of implant failures beforeand after prosthesis loading.1,4,45 It has been suggestedthat preprosthetic failures can be caused by the over-



Table XII. Time of postprosthetic implant loss

No. of implants lost (%)

Type of prosthesis No. of implants placed Total 1st y 2nd y 3rd y

Jemt45* IFCD 336 55 36 (65) 11 (20) 8 (15)Jemt et al47* IFPD 876 10 7 (70) 3 (30) 0 (0)Gunne et al50* IFPD 521 13 3 (23) 8 (62) 2 (15)Andersson et al41* ISC 65 4 2 (50) 1 (25) 1 (25)

% Failure relative to total — 82 48 (59) 23 (28) 11 (13)number implants lost

% Failure relative to total 1798 82 (4.6) 48 (2.7) 23 (1.3) 11 (0.6)number implants placed

*1, 2, and 3 year data statistically compared using normal approximation to binomial test (P<.05).IFCD = Implant fixed complete dentures; IFPD = implant fixed partial dentures; ISC = implant single crowns.

Table XIII. Effect of implant length

Prostheses Description of failures

Friberg et al51 IFCD Higher failure with 7-mm implants.7-mm implants failed more in maxilla (7%) than mandible (3%).

Jemt and Lekholm52 IFCD 72 of 298 7-mm implants placed failed (24%).Jemt et al12 IOD 7 mm failed more than any other implant length in maxilla.van Steenberghe et al53 IFPD 6% failure rate in maxilla with 10-mm implants.

10% failure rate in maxilla with 7-mm implants.Naert et al23 IFPD 7 and 10 mm were the source of most failures.Pylant et al22 IFPD 7 of 12 failures were 7- and 10-mm implants.Jemt and Lekholm25 IFPD 67 of 78 failures were 7 mm implants.Gunne et al50 IFPD 12 of 13 failures were 10-mm implants.Higuchi et al31 IFPD Higher failure with 7-mm implants in maxilla (18%).

IFCD = Implant fixed complete denture; IOD = implant overdenture; IFPD = implant fixed partial denture.

Table XIV. Implant length and time of implant loss30,53,54

Implant length No. implantsNo. of implants lost (%)

(mm) placed 0-1 y 1-3 y 3-5 y

7 120 3 (2.5) 5 (4) 0 (0)10 245 15 (6) 4 (2) 3 (1)13 90 5 (6) 1 (1) 0 (0)15-20 103 0 (0) 0 (0) 0 (0)

Total 558 23 (4) 10 (2) 3 (0.5)

heating of the bone during osteotomy, infection,patients’ health status, or micromotion during the heal-ing phase.56,57 Proposed causes of postprosthetic fail-ures have included poor oral hygiene, unfavorable loadsituations, and framework misfits.45,58,59 Implantlength and bone quality have also been proposed asfactors affecting implant success, and this data alsofound higher implant failure rates in the maxilla, whichoften is comprised of type IV bone (Tables XIIIthrough XV).* Data from this literaturereview12,22,23,25,30,31,50-54 indicated a higher failurerate with short implants (Tables XIII and XIV) thatrelates to only 1 type of implant (threaded, nonsurface-coated screw), and recent studies60,61 suggest thatsurface characteristics may influence the success out-come of short implants. The 5-year data from these

2 studies reported a 4% to 6% failure rate with8-mm hydroxyapatite-coated implants in the posteriormandible.

Surgical complications

Implant surgical complications that have beenreported include neurosensory disturbance, mandibu-lar fracture, life-threatening hemorrhage, hematomaand devitalization of adjacent teeth.† Neurosensorydisturbance rates as high as 39% and as low as 0.6%(6.1% mean) have been reported‡ after stage I surgery(Table XVI). Four studies31,46,53,64 provided data thatindicated significantly lower neurosensory disturbancewhen comparisons were made at stage I surgery andafter 1 year (Table XVI). Although the incidence ratesseem to be high, the number and size of the areas


MAY 1999 543

Table XV. Effect of poor bone quality

No. implants in No. failures in No. implants in No. failures intype I-III bone type I-III bone (%) type IV bone type IV bone (%)

Engquist et al10* 141 15 198 52van Steenberghe et al53* 491 19 67 4Jaffin and Berman55* 952 29 102 36Johns et al46* 453 16 57 16Fugazzotto et al35* 851 12 512 22Smedberg et al13* 53 0 33 12

% Failure relative to number implants placed 2938 91 (3) 969 142 (15)

*The number of failures in type 4 bone was statistically compared with the number of failures occurring in types 1 to 3 bone using normal approximation to bino-mial test (P<.0001).

Table XVI. Percentage of patients experiencing paresthesia over time

No. of patients with paresthesia (%)

Total no.Type of patients Stage I Stage II Prosthesis

prosthesis treated surgery surgery placement 1st y 2nd y 3rd y 4th y 5th y

Johns et al46 IOD 98* 19 (19) — 3 (3) 1 (1) — — — —Wismeyer et al20 IOD 57 — — — — — — — 4 (7)van Steenberghe et al53 IFPD 159* 16 (10) 7 (5) — 6 (4) — — — —Henry et al54 IFPD 139 — — — — — 5 (4) — —Lekholm et al30 IFPD 132 — — — — — — — 2 (2)Astrand et al62 IFPD 46* 17 (39) — — — 9 (19) — — —Higuchi et al31 IFPD 117* 16 (14) — — 6 (5) — 5 (4) — —Avivi-Arber and Zarb44 ISC 49* 2 (4) — — — — — — —Jemt et al33 ISC 92 — 3 (3) — — — — — —Albrektsson63 IFCD/IOD 761* 4 (0.6) — — — — — — —Ellies and Hawker64 Multiple 87* 31 (36) — — 11 (13) — — — —Lazzara et al65 Multiple 625* 8 (1) — — — — — — —Allen et al66 Multiple 60* 11 (18) — — — — — — —

Total (mean%) 2002 124 (6.1)

IOD = Implant overdenture; IFPD = implant fixed partial denture; ISC = implant single crown; IFCD = implant fixed complete denture.*Represents studies included in calculation of mean paresthesia after stage I surgery.

†References 20,30,31,33,36,44,46,47,53,54,62-77.‡References 20,30,31,33,44,46,53,54,62-66.*References 10,12,13,22,23,25,30,35,46,50-55.

with affected sensation usually diminishes overtime.30,31,46,53,62 A small group of patients still exhibitpersistent neurosensory disturbance after 5 years.20,30

Mandibular fracture after implant placement is arare complication and has been reported in conjunc-tion with severely resorbed edentulous mandibles(Table XVII).63,67-72 Of the 7 studies, 2 reported frac-tures that occurred only in female patients, 2 only inmale patients, and 1 in both male and female patients;2 were not identified by sex. A link with osteoporosis inthe female patients has been suggested.67,70 The site ofan implant that was not yet osseointegrated representsan area of stress concentration and weakness; thus, rou-tine oral activities could cause a fracture without anytrauma to the mandible.67,72 Mandibular trauma isanother factor that has been linked to fractures.68

Perforation of the mandibular lingual cortex in thecanine and first premolar region during implantosteotomy can possibly injure the lingual artery or itsbranches (Table XVIII).73-76 This occurrence maylead to extensive bleeding into the submandibularspace, creating a hematoma with life-threatening acuteairway obstruction within the first few hours aftersurgery. Securing and maintaining an adequate airway

should be given the highest priority. Exploration ofthe bleeding area and management of arterial hemor-rhage is the treatment of choice.75 Knowledge, recog-nition, and effective treatment of this complication areessential.

Hematomas have been reported after implantsurgery and/or second stage surgery, which usuallyresolved completely during the normal healing phase(Table XlX).33,46,53 Implant placement in close prox-imity to an adjacent tooth with or without perforatingthe root apex may cause devitalization of that tooth,warranting endodontic therapy (Table XX).36,47,77

Marginal bone loss

Thirteen studies* have reported on the averagemarginal bone loss occurring during the first year(Table XXI). Mean loss was 0.93 mm, with a range from



Table XVII. Mandibular fracture

Description of incidence

Albrektsson63 1 patient of 508 (0.2%)Mason et al67 3 patients, all female, fractured before

loadingTolman and Keller68 7 patients; 6 female, 1 male (due to trauma)Shonberg et al69 1 patient, male, severly atrophic mandibleRothman et al70 2 of 886 (0.2%); female, suggested link

with osteoporosisNeyt et al71 2 patientsKan et al72 1 patient, male, in conjunction with inferior

alveolar nerve transposition

Table XVIII. Life-threatening hemmorhage for implantplacement

No. of patients

Laboda73 1Mason et al74 1ten-Bruggenkate et al75 2Mordenfeld et al76 1

Table XIX. Hematoma

Type of prosthesis Incidence rate (%)

Johns et al46 IOD 13van Steenberghe et al53 IFPD 29Jemt et al33 ISC 5

IOD = Implant overdenture; IFPD = implant fixed partial denture; ISC =implant single crown.

Table XX. Devitalization of adjacent teeth

No.devitalized

Prosthesis No. implants teeth

Jemt et al47 IFPD 876 1Jemt and Pettersson36 ISC 70 3Rubenstein and Taylor77 IFPD Patient treatment report about

devitalization of a tooth causedby apical nerve transection from implant placement.

IFPD = Implant fixed partial denture; ISC = implant single crown.

*References 1,2,11,22,25,30,32,39,41,46,78-80.

Table XXI. Bone loss over time

Mean loss SubsequentType of Length of in 1st loss per

prosthesis study (y) year (mm) year (mm)

Adell et al1 IFCD 1-15 1.2 0.1Adell et al78 IFCD 3 0.9 0.05Cox and Zarb2 IFCD 1-3 1.6 0.1Quirynen et al79 IFCD 6 0.8 0.1Naert et al11 IOD 0.3-4 0.75 0Johns et al46* IOD 1 0.4 N/AQuirynen et al80* IOD 4 1.0† 0.05-0.1†

3.2‡ N/A‡

Gunne et al32 IFPD 2 0.4 0.1Pylant et al22 IFPD 2 1.5 0.1Jemt and Lekholm25 IFPD 5 0.4 0.1Lekholm et al30 IFPD 5 0.4 0.12Laney et al39* ISC 3 N/A 0.1Andersson41 ISC 2-3 1.3 0.2

Mean of all studies 0.93 0.1

IFCD = Implant fixed complete denture; IOD = implant overdenture; IFPD =implant fixed partial denture; ISC = implant single crown.*Not included in mean of combined data.†Mandible; implants were connected.‡Maxilla; implants were not connected.

0.4 to 1.6 mm. The mean loss that occurred per year insubsequent years was 0.1 mm, with a range from 0 to0.2 mm.

Three studies53,54,80 present data that helps quanti-fy the amount of bone loss patients experienced overtime and the number of patients who had no bone lossor gained bone (Table XXII). Only a small percentageof patients experience bone loss exceeding 2 mm. Agreater percentage of patients had 1 to 2 mm of boneloss and the highest percentage of patients experienced0.5 to 1.0 mm of bone loss. A substantial percentage ofpatients exhibited no bone loss or had bone gain. Fur-thermore, the percentage of patients experiencing bonegain increased over time (Table XXII).53,54,80

Slight marginal bone loss after implant placementhas been reported as a common phenomenon.2,30,78,81

It is thought to be the result of several contributing fac-tors: remodeling after the countersinking process,21

inadvertent stress distribution to the marginal bone byforced tightening of the implant during placement,82

or excessive loading force.1 The third criteria of implantsuccess proposed by Smith and Zarb81 is that verticalbone loss must be less than 0.2 mm annually after thefirst year of service. Quirynen et al80 suggested thatbone loss only be considered a complication when aprogressive excessive amount of bone loss is observed.

Peri-implant soft tissue complications

Peri-implant complications have included dehis-cence, fistulas, and gingival inflammation/prolifera-tion.* The exposure of implants before stage II surgerywas reported in 5 studies,1,6,33,40,44 and rangedbetween 2% and 11% (Table XXIII). Dehiscence inhighly esthetic areas may lead to a soft tissue deficit thatcompromises the final esthetic outcome and may neces-sitate soft tissue grafts.84

An adverse tissue response leading to inflamma-tion and/or gingival proliferation was reported inmany studies with an incidence range of 1% to 32%(Table XXIV).† An adverse tissue response is consid-ered the most common peri-implant complication withimplant overdentures.10,85 Soft tissue changes usuallyoccur around abutments and under bars, often becauseof poor oral hygiene, improper use of abutments andhealing caps, presence of dead spaces under the super-structure, and the lack of attached mucosa.4,10,12,44

Multiple surgeries may be needed to correct this prob-lem.12 The rate of soft tissue complications and post-placement maintenance with overdentures is reported-ly higher than with fixed complete dentures.1,5,10,12 Ithas been reported that the implant overdenturedemands more frequent recall examinations to ensuregood, long-term results.10

A number of studies‡ reported on the incidence rateof fistulas at the abutment-implant connection level(Table XXV); the range for the 10 studies was 0.002%to 25%. This peri-implant complication is often associ-ated with poor oral hygiene and/or gaps between com-ponents caused by loose abutment screws or frameworkmisfits, which occur more frequently with single crownreplacement.33,36,40,44 A good seal through crowncementation on firmly connected abutments has been


MAY 1999 545

*References 1,5,6,9,10,12,14,16,27,33,36,38,40,41,44,46,63,65,66,83.

Table XXII. Change in marginal bone level over time

% Patients with marginal bone change

Bone loss No change Bone gain

Study length (y) >2 mm 1-2 mm 0.6-1.0 mm 0.1-0.5 mm 0 mm >0 mm

van Steenberghe et al53* 0-1 2.0 9.5 20.0 26.5 27.0 15.0Henry et al54* 1-3 0.4 4.4 10.4 25.0 25.8 34.0Quirynen et al,80 0-1 0.5 5.8 41.5 29.9 20.5 1.8

FCD (mandible) 1-2 1.5 2.1 5.0 23.4 55.3 12.72-3 0 2.0 5.9 25.5 49.0 17.6

Quirynen et al,80 0-1 4.5 20.1 23.5 24.0 22.3 5.6FCD (maxilla) 1-2 0 3.9 6.8 25.7 37.1 26.5

2-3† 3.4 13.7 5.2 6.9 31.0 37.8

FCD = Fixed complete denture.*Same group of patients.†Data did not equal 100%.

Table XXIII. Implant dehiscence before stage II surgery

Type of prosthesis Incidence rate (%)

Adell et al1 IFCD 4.6Naert et al6 IFCD 12Jemt et al33 ISC 2Cordioli et al40 ISC 3Avivi-Arber and Zarb44 ISC 11

IFCD = Implant fixed complete denture; ISC = implant single crown.

†References l,5,9,l0,12,14,16,27,44,63,65,66.‡References 1,33,36,38,40,41,44,46,63,83.

proposed as an obstacle to bacterial migration and ahindrance to this type of complication.41 These soft tis-sue problems could be related to the depth of the sub-gingival location of the implant, which Cordioli et al40

described as the mucosal canal, for anterior single toothreplacements. The correct depth of the mucosal canalaround implants is still controversial. It has been sug-gested that maxillary anterior implants be placed 2 to3 mm apical to the adjacent cementoenamel junction tofacilitate esthetics and proper emergence profile.86

Some studies reported no significant clinical increasesin gingival inflammation associated with implantrestorations with subgingivally placed margins whengood oral hygiene was maintained.33,42 A thick andlong mucosal canal promotes better esthetics, whichmay result in difficulties in component seating andmaintenance of peri-implant hygiene.40

Mechanical complications

Mechanical complications include screw loosening,screw fractures, implant fractures, framework/resin/veneering material fractures, implant prosthesis frac-tures, opposing prosthesis fractures, and overdenturemechanical retention problems.* Abutment screw loos-ening was reported in a large number of studies† andranged from 2% to 45% of the abutments (Table XXVI).A difference in the incidence of loosening was notedbetween types of prostheses. The highest rate was foundwith single crowns followed by overdentures.

Prosthesis screw loosening ranged from 1% to 38%in the 13 studies‡ reporting this complication (TableXXVII). Only 1 single crown study43 reported prosthe-sis screw loosening that was comparable to the highabutment screw loosening found with singlecrowns.33,36,38,39,41,42 In contrast, prosthesis screwloosening with overdentures tended to be lower thanabutment screw loosening.9,11,12,87 Abutment screwfractures§ (Table XXVIII) occurred less frequently thanprosthesis gold screw fractures|| (Table XXIX).

The most common complication reported with singlecrowns was abutment and/or prosthetic screw loosen-ing.38,42,43 A higher frequency of screw loosening hasbeen reported for single crown replacements in the pre-



Table XXIV. Gingival inflammation and proliferation

Type of Length of Incidenceprosthesis study (y) rate (%)

Adell et al1 IFCD 1-15 7Jemt5 IFCD 1 6Hemmings et al9 FCD 9 20Engquist et al10 IOD 1.5 25Naert et al16 IOD 2 11Jemt et al12 IOD 1 21Cune et al14 IOD 2 16Hemmings et al9 IOD 5.3 32Avivi-Arber and Zarb44 ISC 1-8 2Albrektsson63 IFCD/IOD 1-7 1Tolman and Laney27 IFCD/IOD 6.5 25Lazzara et al65 Multiple 5 6Allen et al66 Multiple 6 27

IFCD = Implant fixed complete denture; IOD = implant overdenture; ISC =implant single crown.

Table XXV. Fistula at implant-abutment level

Type of Length of Incidenceprosthesis study (y) rate (%)

Adell et al1 IFCD 1-15 2Johns et al46 IOD 1 3Quirynen et al83 IFPD 2.5 1.4Jemt et al33 ISC 1 10*Jemt and Pettersson36 ISC 3 25†

Cordioli et al40 ISC 2 4Ekfeldt et al38 ISC 2.5 2Andersson et al41 ISC 2-3 1.5Avivi-Arber and Zarb44 ISC 1-8 6Albrektsson63 IFCD/IOD 1-7 0.002

IFCD = Implant fixed complete denture; IOD = implant overdenture; IFPD =implant fixed partial denture; ISC = implant single crown.*6% with mobile abutment screws.†All in maxilla; 7% with mobile abutment screws.

*References 1,5,6,9,11-13,17-20,22,23,27,29,30,32,33,36,38,39,41-44,46,48-50,53,54,63,65,66,83,87-89.†References 6,9,11,12,30,32,33,36,38,39,41,42,50,53,65,87.‡References 6,9,11,12,23,30,43,49,50,53,54,65,88.§References 1,6,0,11,27,32,44,63,66,81,89.||References 1,6,9,11,23,27,30,50,66,81,89.

Table XXVI. Abutment screw loosening

Type of Length ofprosthesis study (y) % Loosening

Naert et al6 IFCD 2.5 6Hemmings et al9 IFCD 9 1Naert et al11 IOD 1.5 2Jemt et al12 IOD 1 2Hemmings et al9 IOD 5.3 6Naert et al87 IOD 1 18van Steenberghe et al53 IFPD 1 6Lekholm et al30 IFPD 5 5Gunne et al32 IFPD 2 2Gunne et al50 IFPD 3 3Jemt et al33 ISC 1 26Jemt and Pettersson36 ISC 3 45Ekfeldt et al38 ISC 2.5 43Laney et al39 ISC 3 11Andersson et al41 ISC 2-3 2Haas et al42 ISC 6 16Lazzara et al65 Multiple 5 2.4

IFCD = Implant fixed complete denture; IOD = implant overdenture; IFPD =implant fixed partial denture; ISC = implant single crown.

molar and molar area than in the anterior region.33,43

One suggested reason for the high incidence of screwloosening from early studies is that the abutment screwswere made of titanium, and devices capable of providingcountertorque during tightening were not available.This problem seems to be solved through the use ofgold alloy abutment screws that yield a higher screw pre-load when properly torqued.36,38,41,44 Since the intro-duction of gold alloy screws, single implant crowns havebeen placed with fewer screw loosening problems.38,44

Possible causes of screw loosening and/or fracture(Tables XXVIII and XXIX)* have included poorly fittingframeworks, bone remodeling and release of pretensionin the screw joint, reduced clamping force and screwjoint movement, and heavy occlusal forces.4,6,20,73,75,78

Implant fracture is an uncommon but significantcomplication that occurred in 96 of 6560 implants(1.5%) followed for 3 to 15 years in 9 studies†

(Table XXX). Most fractures occurred between thethird and fourth implant thread, which corresponds tothe last thread of the abutment screw.23,83 Frameworkmisfit and occlusal overload have been suggested as theprimary causes.30 Removal of fractured implants, moreoften than not, leaves a large bony defect that requiredadditional healing and treatment time. A higherincidence of implant fractures has been reportedin fixed partial dentures supported by only 2implants.25,30,49,50,53 In a survey by Rangert et al,90

most fractured implants occurred in single or doubleimplant–supported restorations in posterior partially


MAY 1999 547

Table XXVII. Prosthesis gold screw loosening

Type of Length ofprosthesis study (y) % Loosening

Naert et al6 IFCD 2.5 5*Kallus and Bessing88 IFCD >5 24*Hemmings et al9 IFCD 9 7*Naert et al11 IOD 1.5 5†

Jemt et al12 IOD 1 1†

van Steenberghe et al53 IFPD 1 6†

Henry et al54 IFPD 2‡ 5†

3‡ 4†

Lekholm et al30 IFPD 5 4†

Naert et al23 IFPD 6 6*Gunne et al50 IFPD 3 9†

Jemt et al49 IFPD 1 14*Becker and Becker43 ISC (molar) 2 38*Lazzara et al65 Multiple 5 3*

IFCD = Implant fixed complete denture; IOD = implant overdenture; IFPD =implant fixed partial denture; ISC = implant single crown.*Per implants; †per patients; ‡reported at both 2 and 3 y in the same article.

Table XXVIII. Abutment screw fracture

Type of Length ofprosthesis study (y) % Fracture

Adell et al1 IFCD 1-15 3Zarb and Smith81 IFCD 0-9 3Naert et al6 IFCD 2.5 0.6Hemmings et al9 IFCD 9 8Zarb and Schmitt89 IFCD 9-15 5Allen et al66 IFCD 6 2Naert et al11 IOD 1.5 2Gunne et al32 IFPD 2 2Allen et al66 IFPD 6 2Avivi-Arber and Zarb44 ISC 1-8 4Albrektsson63 IFCD/IOD 1-7 0.5Tolman and Laney27 IFCD/IOD 6.5 5


*References 1,6,9,11,23,27,30,32,44,50,63,66,81,89. †References 1,6,22,23,27,30,50,66,83.

Table XXIX. Prosthesis gold screw fracture


Adell et al1 IFCD 1-15 1.5Zarb and Smith81 IFCD 0-9 19Naert et al6 IFCD 2.5 1Hemmings et al9 IFCD 9 4Zarb and Schmitt89 IFCD 9-15 7Allen et al66 IFCD 6 1Naert et al11 IOD 1.5 5Hemmings et al9 IOD 5.3 6Zarb and Schmitt89 IOD 13 3Naert et al23 IFPD 6 1Tolman and Laney27 IFPD 6.5 5.5Gunne et al50 IFPD 3 7Lekholm et al30 IFPD 5 3


Table XXX. Fractured implants

No.Type of Length of No. fracture

prosthesis study (y) implants (%)

Adell et al1 IFCD 15 1997 69 (3.5)Naert et al6 IFCD 7 564 3 (0.5)Naert et al6 IFPD 7 465 5 (1)Pylant et al22 IFPD 2 102 1 (1)Quirynen et al83 IFPD 6 509 5 (1)Lekholm et al30 IFPD 5 558 5 (1)Gunne et al50 IFPD 3 521 3 (1)Tolman and Laney27 IFCD/IOD 6.5 1778 3 (0.2)Allen et al66 Multiple 6 66 2 (3)

% Fracture relative 6560 96 (1.5)to total numberimplants placed

IFCD = Implant fixed complete denture; IOD = implant overdenture; IFPD =implant fixed partial denture.

edentulous jaws where occlusal loads were higher. Thus,it was suggested that implant fixed partial dentures besupported by 3 implants placed in a tripod alignment tominimize stress and torque distribution.30,90

Metal framework fracture* (Table XXXI) has beenattributed to inadequate metal thickness, poor solderjoints, excessive cantilever length, alloys with inade-quate strength, patients’ parafunctional habits, andimproper framework design.81,91,92 Acrylic resin basefractures5,9,12,66,89 for implant overdentures (TableXXXII) are usually caused by inadequate space for resinbetween the framework and the denture teeth, thereby,weakening the denture. The use of metal-reinforcedoverdenture bases can minimized this complication.93

Acrylic and composite fractures comprised themajority of facial/occlusal veneer material failures(Table XXXIII).23,29,30,41,44,48-50,66 With fixed partialdentures, acrylic resins and composites fractured more

often than porcelain.30,50 Recent studies where porce-lain was used instead of resin are also reporting frac-tures, but they occur less frequently than withresin.44,50 Because studies have not been able to iden-tify a single superior occlusal material, porcelain hasbeen used more frequently in recent years for estheticreasons.94,95

Four studies12,17,20,46 indicated that a small number(6% mean) of implant overdentures fractured (TableXXXIV). Fractures of conventional removable prosthe-ses have also been reported9,11,66 when they oppose animplant prosthesis (Table XXXV). Relatively high over-denture complication rates have been reported in con-junction with clips/attachments (Tables XXXVI andXXXVII).9,12,13,20,46,66,87,89 Most of the bar and clipoverdenture complications were found to be the resultof clip loosening or fracture.9,11,12 This outcome is rec-ognized as a nuisance problem,11,12 but was judged by1 author88 to be a less demanding complication thanthe problems associated with magnets or ball attach-



Table XXXI. Metal framework fracture


Adell et al1 IFCD 1-15 5Zarb and Smith81 IFCD 0-9 27Jemt and Lekholm25 IFCD 1 1Naert et al6 IFCD 2.5 5Zarb and Schmitt89 IFCD 9-15 6Naert et al11 IOD 1.5 1Jemt et al12 IOD 1 1Johns et al46 IOD 1 2Zarb and Schmitt89 IOD 13 4Albrektsson63 IFCD/IOD 0-8 2.5Tolman and Laney27 IFCD/IOD/IFPD 6.5 0.5


Table XXXII. Acrylic resin base fracture

Type of Length of No. No.prosthesis study (y) prostheses fractures (%)

Jemt5 IFCD 1 380 13 (3)Hemmings et al9 IFCD 9 25 6 (24)Jemt et al12 IOD 1 92 —(11)Hemmings et al9 IOD 5 25 1 (4)Zarb and Schmitt89 IOD 13 47 1 (2)Allen et al66 IOD 6 37 5 (14)

IFCD = Implant fixed complete denture; IOD = implant overdenture.

Table XXXIII. Facial/occlusal veneer material fracture

% Fracture

Denture AcrylicType of Length of Denture teeth and Acrylic resins and

prosthesis study (y) teeth acrylic resin resin composites Composite Porcelain Metal

Naert et al23 IFPD 2.5 — — — — 20 — —Allen et al66 IFCD 6 — — — — — 5 —Allen et al66 IOD 6 8 — — — — — —Jemt et al49 IFPD 1 — — — — 4 — —Zarb and Schmitt29 IFPD 5.2 — — 23 — — — —Johansson and Palmqvist48 IFPD 5.2 — 22 — — — — —Gunne et al50 IFPD 3 — — 13 — 30 17 20Lekholm et al30 IFPD 5 — — — 14 — — —Allen et al66 IFPD 6 — — — — — 11 —Andersson et al41 ISC 2-3 — — — — — 6 —Avivi-Arber and Zarb44 ISC 1.8 — — 6 — — 4 —

IFCD = Implant fixed complete denture; IOD = implant overdenture; IFPD = implant fixed partial denture; ISC = implant single crown.

*References 1,5,6,11,12,27,46,63,81,89.

ments. It has been noted that a relatively high numberof relines were required in conjunction with the place-ment or postplacement care of implant overdentures(Table XXXVIII).9,11,12,13,20,46

Phonetic and esthetic complications

Phonetic problems were reported in 3 implant stud-ies5,12,23 and involved fixed complete dentures, over-dentures, and fixed partial dentures, but have not beenreported in conjunction with single crowns (TableXXXIX). These problems are encountered more fre-quently in the maxilla than in the mandible.5 Fixedimplant-supported prostheses in the resorbed anteriormaxilla often allow an airway escape passage that caus-es a problem with speech.5,6,96 Some authors claim thisis a time-related problem and patients usually adapt byincreasing lip pressure to prevent air leakage.5,96

Esthetic problems have been reported with fixedcomplete dentures, fixed partial dentures, and singlecrowns, but not with overdentures.33,38,52,49,66 Theseproblems included improper restoration contour, poor

shade, and exposure of implant components from gin-gival recession (Table XL).

SUMMARY AND CONCLUSIONS

This article identifies the types of complications thathave been reported in clinical studies of dental implanttreatment. Because of variations in the reporting ofcomplications, only a small number of studies presentdata about certain complications, and, thus, limits theability to analyze statistically many of the reportedcomplications. On the basis of available data, the fol-lowing conclusions are offered relative to dentalimplant complications:

1. More implants were lost with overdenture pros-theses than with fixed complete dentures, fixed partialdentures or single crowns. More implants were lost inthe maxilla than mandible with fixed complete denturesand overdentures but not with fixed partial dentures.The highest implant loss occurred with maxillary over-dentures.

2. With fixed complete dentures, the number of


MAY 1999 549

Table XXXIV. Fracture of implant overdenture

Length of No. No.study (y) prostheses fractures (%)

Meriscke-Stern17 0.5-5.5 62 3 (5)Jemt et al12 1 92 3 (3)Johns et al46 1 127 7 (6)Wismeyer et al20 6.5 57 4 (7)

% Fracture relative 338 21 (6)to total numberof prostheses

Table XXXV. Fracture of opposing prostheses

Type of Length of No. %prosthesis study (y) prostheses Fracture

Allen et al66 IFCD 6 20 40Naert et al11 IOD 1.5 86 10Hemmings et al9 IOD 5.3 25 4Allen et al66 IOD 6 37 5

IFCD = Implant fixed complete denture; IOD = implant overdenture.

Table XXXVI. Overdenture clip/attachment loosening andactivation

Length of study (y) Incidence rate (%)

Jemt et al12 1 17Johns et al46 1 36Smedberg et al13 2 56Naert et al87 2 75Hemmings et al9 5 40Allen et al66 6 5

Table XXXVII. Overdenture clip/attachment fracture andreplacement

Length of study (y) % Incidence

Jemt et al12 1 22Johns et al46 1 13Smedberg et al13 2 33Hemmings et al9 5 12Wismeyer et al20 6.5 9Zarb and Schmitt89 13 13Allen et al66 6 22

Table XXXVIII. Postplacement reline required with implantoverdentures

Length of study (y) Incidence rate (%)

Merickse-Stern17 0.5-5.5 6.5Naert et al11 1.5 18Jemt et al12 1 24Johns et al46 1 13Smedberg et al13 2 44Hemmings et al9 5 32Wismeyer et al20 6.5 28

Table XXXIX. Phonetic problems

Type ofprosthesis Incidence rate (%)

Jemt5 IFCD 8% postplacement, 3% at 1 yJemt et al12 IOD 4% phonetic resonanceNaert et al23 IFPD 8% (2 of 25 patients with

Kennedy Class IV arches)


implants lost preprosthetically was comparable to thenumber lost postprosthetically. More failures occurredpreprosthetically with overdentures and fixed partialdentures, whereas more postprosthetic failures werefound in conjunction with single crowns.

3. When comparing the times at which postprostheticimplant loss occurred, significantly fewer implants werelost in year 2 than year 1. Likewise, implant loss in year 3was significantly lower than both year 1 and year 2.

4. Higher failure rates occurred with shorterimplants (7 and 10 mm lengths). Significantly higherfailure rates were found with implants placed in type 4bone compared with those in types 1 to 3 bone.

5. Neurosensory disturbances and hematomas werethe 2 most commonly reported surgical complications.After stage I surgery, the neurosensory disturbancerates ranged from 0.6% to 39% (6.1% mean). After 1year, the disturbance rates ranged from 1% to 13%. Thehematoma incidence ranged between 5% and 29%.Other less common surgical complications includedmandibular fracture, life-threatening hemorrhage, anddevitalization of adjacent teeth.

6. The mean marginal bone loss around dentalimplants in the first year ranged from 0.4 to 1.6 mm(mean 0.93 mm) for all studies. Subsequent bone lossper year ranged from 0 to 0.2 mm, with a mean of0.1 mm per year. However, many patients evaluatedover periods from 1 through 3 years experienced nobone change or gain.

7. Three peri-implant soft tissue complications werereported. Gingival inflammation/proliferation was themost frequent complications, with the range of 1% to32%. Implant dehiscence before stage II surgery rangedbetween 2% and 11%. A range of 0.002% to 25% wasreported for fistulas that occurred at the implant-abut-ment level.

8. Screw loosening was the most frequently reportedmechanical complication. The incidence of abutmentscrew loosening ranged from 1% to 45% with a compa-rable 1% to 38% incidence range for prosthesis goldscrew loosening. More screw loosening occurred withsingle crowns than with any other types of prosthesis.

9. Prosthesis gold screws fractured more often(range of 1% to 19%) than the abutment screws (range

of 0.5% to 8%). Implant fractures were reported in9 studies with a mean incidence of 1.5%.

10. Other mechanical complications included frac-tures of the metal framework, resin base, facial/occlusalveneer material, overdenture prosthesis, and opposingprosthesis. Clip/attachment loosening and fracturewere reported with overdentures as well as the need forpostplacement relines.

11. Phonetic and esthetic problems were reported ina limited number of studies. Phonetic problems werereported with all prostheses, except single crowns andesthetic problems, involved all prostheses, except over-dentures.

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Table XL. Esthetic problems

Type of Incidence Incidenceprothesis rate rate (%) Reasons

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IFCD = Implant fixed complete denture; IFPD = implant fixed partial denture; ISC = implant single crown.

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Clinical Complications of Osseointegrated Implants