The prevalence of partial edentulism of up to 4 teeth ranges between 10% to 40% (35–44 years) and 15% to 50% (65–74 years).1 2
Dental implants supporting fixed partial dentures have demonstrated long-term clinical success.1 3 4
Immediate function implant rehabilitation has become a demand from patients because of the psychological and social effect of an immediate removable prosthesis.5,6 7 8,9 10 10
Partial rehabilitations are more exposed to load factors than single teeth rehabilitations or complete edentulous rehabilitations, placing them more at risk for implant failure, a risk that may be increased by a 4.75-fold.11
Therefore, there are several issues to be taken into account when performing a partial rehabilitation that may influence the outcome to a great extent. Load factors such as mechanical strength, implant load, leverages, implant length, occlusion, and implant alignment potentially influence bending overload of the implants in a FPR.1,12–18
Materials and Methods
This retrospective clinical study was performed in a private clinic, Maló Clinic, Lisbon, Portugal, and was approved by an independent Ethical Committee (Ethical Committee for Health, Lisbon, Portugal, Authorization No. 005/2010). This study included 199 patients, 118 females and 81 males, with an average age of 53 years (range, 26–84 years). The patients were identified from the medical records as submitted to FPR with axial implants inserted in immediate function between 1998 and 2010.
As exclusion criteria, patients with active radiotherapy or chemotherapy and using tilted implants were excluded of this study.
Fifty-six patients (28%) had a systemic condition: hepatitis (n = 2 patients), cardiovascular condition (n = 33 patients), thyroid (n = 5 patients), diabetes (n = 6 patients), osteoporosis (n = 12 patients), oncological condition (n = 4 patients), and renal condition (n = 1 patient). Seven patients presented more than one condition. Eleven patients (5.5%) were smokers.
Surgery and prosthetic placement were performed by the same team. The first implant was placed in April 1998 and the last in March 2010, and the patients were followed between 1 year and 13.5 years (average of 7 years). Distributions of implants regarding implant design, length, platform, and surface are presented in Tables 1–5 . The majority of implants regarding implant design were NobelSpeedy Groovy implants (Nobel Biocare AB, Göteborg, Sweden), whereas regarding platform, length, and surface, the majority of implants used were of regular platform, 15 mm, and with oxidized surface, respectively.
Table 1: Implant Distribution and Failures Per Position
Table 2: Implant Distribution by Type of Design
Table 3: Implant Distribution by Length
Table 4: Distribution of Implant by Platform
Table 5: Distribution of Implant by Surface
The prostheses distribution according to the number of supporting implants, FPR units (crowns), and presence or absence of cantilevers is presented in Table 6 . A total of 213 prosthetic restorations were performed, 87 prostheses in the maxilla and 126 prostheses in the mandible. The majority of rehabilitations consisted of 4 FRP units supported by 2 implants. Cantilevers were present in 50 prostheses (24%).
Table 6: Fixed Partial Rehabilitations Distribution in the Maxilla and Mandible According to the Number of Units Per Prosthesis, Number of Implants Supporting the Rehabilitation, Presence (C) or Absence (NC) of Cantilevers, and Number of Prostheses With Implants Lost (Given in Parenthesis)
Surgical Protocol
In the clinic, the presurgery and postsurgery medication regimen underwent a change at the end of 2003. Patients treated between 1996 and 2003 received the following: antibiotics presurgery and 15 days after surgery (Oraminax 1 g; Wyeth Laboratories, Azevedos, Algés, Portugal); cortisone medication (prednisone 5 mg [Meticorten; Schering-Plough Farma, Lda, Agualva-Cacém, Portugal]) was given daily in a regression mode (15–5 mg) from the day of surgery until 4 days postoperatively; anti-inflammatory medication (Nimed; Rhône-Poulenc Rorer, Lda, Mem Martins, Portugal) was administered for 2 days postoperatively starting on day 4; analgesics (clonixin [300 mg, Clonix; Janssen-Cilag Farmaceutica, Lda, Barcarena, Portugal]) were given on the day of surgery and postoperatively for the first 3 days if needed; antacid medication (omeprazole, 20 mg; Generis, Lisboa, Portugal) was given on the day of surgery and daily for 6 days postoperatively. The surgery was performed under local anesthesia (Rapicaine, 2% ep, lidocaine HC1 2% with epinephrine 1:100,000; Unipharm, Vera Cruz, Mexico); postsurgical use of chlorhexidine for 4 months (Elugel; Pierre Fabre Dermo-Cosmetique, Lda, Lisboa, Portugal; Eludril; Pierre Fabre Dermo-Cosmetique, Lda).
In 2004, the regimen changed to the following: antibiotics presurgery and 6 days postsurgery (amoxicillin 875 mg + clavulanic acid 125 mg; Labesfal, Campo de Besteiros, Portugal); cortisone medication (prednisone 5 mg [Meticorten; Schering-Plough Farma, Lda]) was given daily in a regression mode (15–5 mg) from the day of surgery until 4 days postoperatively; anti-inflammatory medication (ibuprofen, 600 mg; Ratiopharm, Lda, Carnaxide, Portugal) was administered for 2 days postoperatively starting on day 4; analgesics (clonixin [300 mg, Clonix; Janssen-Cilag Farmaceutica, Lda]) were given on the day of surgery and postoperatively for the first 3 days if needed; antacid medication (omeprazole, 20 mg; Generis) was given on the day of surgery and daily for 6 days postoperatively. The surgery was performed under local anesthesia (articaine clorhidrate [72 mg/1.8 mL] with epinephrine [0.018 mg/1.8 mL] 1:100,000 [Artinibsa 2%; Inibsa Laboratory, Barcelona, Spain]); postsurgical use of hyaluronic acid was used on the first 2 months (Gengigel; Ricerfarma, SPa, Milano, Italy) and chlorhexidine (Elugel; Pierre Fabre Dermo-Cosmetique, Lda; Eludril, Pierre Fabre Dermo-Cosmetique, Lda) between 2 and 4 months postoperatively.
The insertion of the implants (Brånemark System Mk II, Mk III, Mk IV machined and TiUnite surface; NobelSpeedy Groovy, and NobelReplace Tapered groovy; Nobel Biocare AB) followed the standard procedures, with the following modifications5,7
A direction indicator pin (Nobel Biocare) was used for optimal implant positioning. The drilling sequence was modified by using under preparation to achieve a good primary stability to allow immediate function,5,7
The implant platform was aimed to be 0.8 mm above bone level, corresponding to the lower corner of the cylindrical part of the implant flange (for Brånemark System Mk II, Mk III, Mk IV), and flush to bone level (NobelSpeedy Groovy and NobelReplace tapered Groovy), and bicortical anchorage was established whenever needed. The minimum insertion torque for accepting the implant for immediate function was 30 N·cm. The soft tissues were readapted and sutured back into position with 4-0 nonresorbable silk suture.
Immediate Prosthetic Protocol
An acrylic resin prosthesis (crowns: Kenson, Myerson, Trinidad & Tobago up to 2003; PallaXpress, Heraeus Kulzer GmbH, Hanau, Germany onward) was manufactured to fit the definitive abutments (Nobel Biocare AB) immediately after implant insertion. The abutment types ranged from the MirusCone and EsthetiCone to the Multi-unit (Nobel Biocare AB). The abutment height was established at the gingival level, to avoid any subgingival location of the crown margin, and the prostheses were screwed. All crowns were adjusted to eliminate any contact with antagonist teeth in occlusal, lateral, or anterior movements or in any plausible parafunctional direction.
Postoperative and Definitive Prosthetic Protocols
The patients were instructed for a soft diet for 3 months. Ten days after surgery, the prostheses were removed, jet-cleaned (using an Air-Flow powder, EMS Nyon, Switzerland), and disinfected (using 0.2% chlorhexidine, Elugel, Pierre Fabre Dermo-Cosmetique); the sutures were removed; implants were checked for anchorage (clinical mobility), suppuration (by finger pressure), pain, and hygiene; the occlusion was rechecked (according to the initial protocol). After completion of the clinical monitoring the prostheses were reconnected. The procedures were repeated after 2 and 4 months, with the prostheses removed at each follow-up appointment. After 5 months, the final prostheses were fabricated and connected, consisting in metal-ceramic prostheses. Occlusion mimicked natural dentition in mutually protected occlusal scheme.
Outcome Measures
Primary outcome measures
Primary outcome measures were prosthetic and implant survival evaluated based on function. Implant survival was further determined by fulfillment of the following criteria: clinical stability, patient reported function without any discomfort, and absence of suppuration, infection, or radiolucent areas around the implants at 5- and 10-year postsurgically.
Secondary outcome measures
Secondary outcome measures were marginal bone level and incidence of complications. In this study, marginal bone level was evaluated at 5 and 10 years of function. An outcome assessor examined all implant radiographs. Each periapical radiograph was scanned at 300 dpi with a scanner (HP Scanjet 4890; HP Portugal, Paço de Arcos, Portugal), and the marginal bone level was assessed with image analysis software (ImageJ version 1.40g for Windows; National Institutes of Health, Bethesda, MD). The reference point for the reading was the implant platform (the horizontal interface between the implant and the abutment), and the marginal bone level was assessed and defined as the most apical contact between bone and implant. The radiographs were accepted or rejected for evaluation based on the clarity of the implant threads; a clear thread guarantees both sharpness and an orthogonal direction of the radiographic beam toward the implant axis.
The following complication parameters were assessed: fracture or loosening of mechanical and prosthetic components (mechanic complications); fistula formation, pain or infection, periimplant pathology (presence of periimplant pockets >4 mm assessed with a probe calibrated to 0.25 N [Click-Probe; Kerrhawe SA, Bioggio Svizzera, Switzerland] with concurrent presence of bleeding on probing and marginal bone loss) and presence of pseudo pockets (periimplant pockets >4 mm) (biologic complications).
Statistical Analysis
Survival was calculated using life table analysis. Descriptive statistics were computed for the variables of interest (marginal bone level and incidence of biological and mechanical complications). The data were analyzed using the software SPSS for Windows version 17 (IBM SPSS, New York, NY).
Results
There were 481 implants (Nobel Biocare AB) inserted in the 199 patients, 215 implants in the maxilla and 266 implants in the mandible, with the distribution of implants regarding tooth position is presented in Table 1 . Two patients with 5 implants deceased due to unrelated causes with the implant treatment after 4 years (1 patient with 2 implants supporting a 4-unit FPR) and 8 years (1 patient with 3 implants supporting an 8-unit FPR) of follow-up, and 16 patients withdraw from the study (9%): 1 patient (with 2 implants supporting a 3-unit FPR) between 1 and 2 years; 2 patients (each with 2 implants supporting a 3-unit FPR) between 2 and 3 years; 2 patients (1 with 4 implants supporting a 6-unit FPR and 1 patient with 2 implants supporting a 4-unit FPR) between 3 and 4 years; 6 patients (3 patients with 2 implants supporting a 4-unit FPR, 1 patient with 2 implants supporting a 3-unit FPR, 1 patient with 1 implant supporting a 3-unit FPR, and 1 patient with 5 implants supporting a 9-unit FPR) between 5 and 6 years; 3 patients (2 patients with 2 implants supporting a 4-unit FPR and 1 with 2 implants supporting a 5-unit FPR) between 6 and 7 years; 2 patients (1 patient with 2 implants supporting a 4-unit FPR and 1 patient with 3 implants supporting a 5-unit FPR) between 7 and 8 years; 12 patients moved away and 4 patients were followed in another clinic.
Eight implants (maxilla: 6 and mandible: 2) failed in 6 patients, all presenting loss of integration. During the first year of follow-up, 3 patients lost 5 implants (1 patient lost 3 implants), 1 patient lost 1 implant between 6 and 7 years, 1 patient lost 1 implant between 8 and 9 years, and 1 patient lost 1 implant between 9 and 10 years, giving a cumulative implant survival rate of 98.5% and 92.7% after 5 and 10 years, respectively, using the patient as a unit of analysis (Table 7 ) and a cumulative implant survival rate of 99.0% and 96.7% after 5 and 10 years, respectively, using the implant as a unit of analysis (Table 8 ). The failed implants were removed, and after 6 months, new implants were installed, immediately loaded, and were not included in this study.
Table 7: Cumulative Implant Survival Rate for Fixed Partial Rehabilitations in Immediate Function Using the Patient as Unit of Analysis (First Implant Failure in Any Patient)
Table 8: Cumulative Implant Survival Rate for Fixed Partial Rehabilitations in Immediate Function Using the Implant as Unit of Analysis
The failures were characterized by a higher frequency in machined surface implants (4.7%) compared with anodically oxidized surface implants (0.9%). The distribution of FPRs with implant failures was 4 of 87 FPRs in the maxilla, 2 of 126 FPRs in the mandible; 2 implants supporting the FPR (4 of 6 FPRs with implant failures); 4- and 5-unit FPRs (2 of 6 FPRs with implant failures for each design) (Table 6 ). No prostheses were lost rendering a prosthetic survival rate of 100%.
Table 9 outlines the distribution of marginal bone level. Of the 278 implants followed for 5 years, 249 (90%) had a readable radiograph. The average (SD) bone level was 1.79 mm (0.93 mm) after 5 years of follow-up.
Table 9: Marginal Bone Level for Implants in Immediate Function Supporting FPRs
Of the 45 implants followed for 10 years, 36 (80%) had a readable radiograph. The average (SD) bone level was 1.89 mm (0.81 mm) after 10 years of follow-up. Considering the 36 implants with 10 years, the marginal bone loss between 5 and 10 years was 0.14 mm.
The incidence of mechanical complications was registered in 43 patients (21.6%), with an incidence rate of 14.1% and 7.5% for the provisional and definitive prostheses, respectively, and consisting in namely prosthetic screw loosening on 13 patients (6.5%) in 8 provisional prostheses and 5 definitive prostheses; abutment complications on 16 patients (8%) in 12 provisional prostheses and 4 definitive prostheses, with 15 patients presenting abutment screw loosening and 1 patient with a worn abutment; and fracture of the prosthesis on 17 patients (8.5%) with 11 provisional prostheses and 6 definitive prostheses (4 fractures of the ceramic crown, 2 chippings of the ceramic). Three patients had 2 different complications. The majority of mechanical complications occurred in FPRs of 4 units supported by 2 implants (30 of the 43 FPRs affected, 8 of them with cantilever extension), equally distributed between the maxilla and mandible. The situations were resolved by reconnecting the prosthetic and abutment screws, the worn abutment was replaced, the fractures of the provisional prostheses were addressed by mending the acrylic resin, the ceramic crown fractures were resolved by manufacturing new crowns, and the ceramic chippings were resolved by adding a composite resin. Equal to all events, the occlusion was adjusted and night guards manufactured.
The incidence of biological complications was registered in 12 patients (6%) and 16 implants (3.3%), consisting in pseudo pockets (3 implants in 3 patients) and periimplant pathology in 9 patients with 13 implants with 2 patients with more than 1 implant affected: 1 patient with 4 implants and another patient with 2 implants. Five of the patients were smokers, the majority of biological complications occurred in FPRs of 4 units supported by 2 implants (9 of the 12 FPRs affected, 3 of them with cantilever extension), and was equally distributed by the maxilla and mandible. All pseudo pockets were successfully treated through prophylaxis with scaling and polishing with 0.2% chlorhexidine gel. The periimplant pathology situations were successfully treated in the 7 patients with 7 implants through nonsurgical treatment (scaling and irrigation with 0.2% chlorhexidine gel). The patients with multiple implants affected experienced different treatment outcomes: 1 patient with 4 implants was successfully treated through nonsurgical (2 implants) and surgical treatments (2 implants) that consisted in removal of granulation tissue, scaling, and implant surface decontamination with 0.2% chlorhexidine, whereas 1 patient with 2 implants did not respond to nonsurgical or surgical treatments, with one of the implants representing one of the implant failures being removed after 115 months of follow-up and another implant that remained with a residual pocket of 5 mm. The incidence of biological complications was higher with longer follow-up: 12 of the 16 implants were affected between 50 months and 118 months of follow-up.
Seven patients (all with FPRs of 4 units supported by 2 implants) clustered biological and mechanical complications (4 FPRs in the fifth sextant).
Discussion
This clinical study reported a 96.7% cumulative survival rate for this immediate function protocol with a follow-up between 1 year and 13.5 years, with 1.79 and 1.89 mm of bone level at 5 and 10 years, respectively, and furthermore, a 0.14 mm marginal bone loss between 5 and 10 years. These results are comparable with results from long-term studies including oxidized surface implants and immediate loading protocols19–21 19 20 21 10 10
The explanation for technical complications in FPR is multivariable as the biomechanics of partial rehabilitations are challenging.
Implant load is one of the possible explanations for mechanical complications and can be affected by parafunctional habits that contribute to bending overload.22
A second factor that could play an important role is the presence of leverages, such as cantilevers, where the lever arm between the position of force contact and the position of support can magnify considerably vertical and lateral forces when the prosthesis is functioning in occlusion.23 24 13 13
A third factor to influence mechanical complications could be the occlusion, as FRPs are more exposed to occlusal forces compared with single teeth (FPRs do not benefit from the protection of adjacent natural teeth) and full-arch rehabilitations (FPRs do not benefit from cross-arch stabilization). This situation was reported in a study investigating the long-term outcome of narrow-diameter implants in the rehabilitation of posterior regions, where in multivariable analysis, partial rehabilitations were identified as a risk factor with an increase of over 4-fold in the probability of implant failure when compared with single teeth rehabilitations.11 25
Implant alignment is another factor that can influence the outcome of FPRs, as a straighter implant alignment results in greater potential for bending of the implants,26
It has been investigated the optimal number of implants and units of FPRs. In our study, the majority of FPRs were supported by 2 implants, with 3 or 4 units (noncantilever). Considering the FPR as a unit of analysis, implant survival rates of 96% (48 of 50) and 98.8% (81 of 82) were registered for 3 and 4 units, respectively, nevertheless, a majority of biological complications occurring in FPRs of 4 units supported by 2 implants. These results seem to go in the same direction as a previous systematic review that reported a substantial lack of evidence to determine the optimal number and distribution of implants supporting FPRs.1
Some factors such as implant length and type of restorative material have been suggested as playing a role in the outcome of FPRs. The implant length was previously considered as a factor that could significantly influence the outcome of implant rehabilitations; however, current data suggest that short implants have the same level of clinical success as longer implants14 15 16
According to a systematic review, the influence of prosthodontic design features (abutment type, retention type, support type, and type of restorative material) on the long-term of FPRs could not be asserted from the available literature and therefore was deemed insufficient to establish unequivocal clinical guidelines.27
The incidence of biological complications demonstrated a tendency to be more frequent in longer follow-ups. This situation (especially with periimplant pathology) was previously discussed in a review study on the determination of success and failure in dental implants, suggesting a theoretical chronological relationship between implant loss and the incidence of pathology of the soft- and hard-tissue seal around implants. During the osseointegration period, the implants are more exposed to failure compared with periimplant pathology, but as follow-up time increases, dental implants are less exposed to failure and more exposed to periimplant pathology.28
The study limitations include the study being performed in a single center and in a majority of Portuguese patients which might influence the external validity of this study, and therefore, extrapolation of these results to the general population should be made with caution, taking into consideration different social and cultural backgrounds. The study strengths include the large sample, the long-term follow-up, and the low percentage of patients lost to follow-up, which accounts for a stronger study internal validity.
Future research should focus on the discrimination of factors that may affect the long-term outcome of these rehabilitations, namely on the comparison between FPRs with and without tilted implants, and the optimal number and design of FPRs.
Conclusions
The cumulative implant survival rate of 98.4% at 5 years and 96.4% after 10 years indicates that, within the limits of this study, implants inserted using an immediate function protocol to support FPRs in both jaws is a viable and safe concept in the long-term outcome. Once the rehabilitation status was finalized with the connection of the definitive prostheses, the incidence rate of mechanical complications was low, accounting for good long-term outcomes.
Disclosure
This study was supported by a Nobel Biocare AB Grant 2012-1095. P. Maló is currently a consultant for Nobel Biocare. All other authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
Approval
Ethical Committee for Health, Lisbon, Portugal, Authorization No. 005/2010.
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