The International Journal of Oral & Maxillofacial Implants, 03/2003

Purpose: The aim of this study was to analyze the biomechanics in an implant/tooth-supported system under different occlusal forces with rigid and nonrigid connectors by adopting a nonlinear finite element (FE) approach. Materials and Methods: A model containing 1 Frialit-2 implant (placed in the second molar position) splinted to the mandibular second premolar was constructed. Nonlinear contact elements were used to simulate a realistic interface fixation between the implant body and abutment screw and the sliding keyway stress-breaker function. Stress distributions in the splinting system with rigid and nonrigid connectors were observed when vertical forces were applied to the tooth, pontic, implant abutment, or complete prosthesis in 10 simulated models. Results: The displacement obtained from the natural tooth increased 11 times than that of the implant, and the peak stress values within the implant system (σI, max) increased significantly when vertical forces acted only on the premolar of a fixed prosthesis with a rigid connector. The σI, max values seen in the splinting prosthesis were not significantly different when vertical forces (50 N) were applied to the pontic, molar (implant) only, or the entire prosthesis, respectively, regardless of whether rigid or nonrigid connectors were used. Moreover, the peak stress values in the implant system and prosthesis were significantly reduced in single- or multiple-contact situations once vertical forces on the pontic were decreased. Discussion: The compensatory mechanism between the implant components and keyway sliding function of the implant/tooth-supported prosthesis could be realistically simulated using nonlinear contact FE analysis. The nonrigid connector (keyway device) significantly exploited its function only when the splinting system received light occlusal forces. Conclusion: Minimization of the occlusal loading force on the pontic area through occlusal adjustment procedures to redistribute stress within the implant system in the maximum intercuspation position for an implant/tooth-supported prosthesis is recommended.

Purpose: To evaluate the human bone tissue response to 2 surfaces (oxidized or turned) on commercially available titanium implants. Materials and Methods: Screw-type turned (control) and oxidized (test) micro-implants were manufactured in the same manner as commercially available turned and oxidized (TiUnite, Brånemark System) implants. The thickness of the oxide layer of the test implants was on average 10 µm, corresponding to the oxide thickness of the apical part of the TiUnite implant. Twenty patients received 1 test and 1 control micro-implant each during implant surgery. Before placement, the surface topography of the implants was characterized with an optical confocal laser profilometer. After a mean healing period of 6.6 months in the maxilla and 3.5 months in the mandible, the micro-implants and surrounding tissue were removed with a trephine bur. Histologic sections were produced, and the specimens were analyzed histomorphometrically. Results: Surface roughness and enlargement were greater for the oxidized implants than for the turned implants. All micro-implants, except for 2 controls, were found to be clinically stable at the time of retrieval. Histomorphometric evaluation demonstrated significantly higher bone-to-implant contact for the oxidized implants, whether placed in the maxilla or in the mandible. Significantly more bone was found inside the threaded area for the oxidized implants placed in the mandible and maxilla, but there was no difference between implants with regard to position (maxilla or mandible). Discussion: The stronger bone response to the oxidized implants may have contributed to the fact that 2 control implants but no test implants were lost. The reason for these findings may depend on one or multiple differences of the surfaces between test and control implants: (1) the thicker oxide layer itself, (2) increased surface roughness, (3) different surface morphology in terms of porosity, or (4) change in crystal structure. Conclusion: The present histologic study in human jawbone demonstrated a significantly higher bone response for anodic oxidized titanium implants than for implants with a turned surface.

Purpose: One major factor in the success and biocompatibility of an implant is its surface properties. The purposes of this study were to analyze the surface characteristics of implants after blasting and thermal oxidation and to evaluate the bone response around these implants with histomorphometric analysis. Materials and Methods: Threaded implants (3.75 mm in diameter, 8.0 mm in length) were manufactured by machining a commercially pure titanium (grade 2). A total of 48 implants were evaluated with histomorphometric methods and included in the statistical analyses. Two different groups of samples were prepared according to the following procedures: Group 1 samples were blasted with 50- µm aluminum oxide (Al2O3) particles, and group 2 samples were blasted with 50- µm Al2O3, then thermally oxidized at 800°C for 2 hours in a pure oxygen atmosphere. A noncontacting optical profilometer was used to measure the surface topography. The surface composition of the implants used and the oxide thickness were investigated with Rutherford backscattering spectrometry. Results: The different preparations produced implant surfaces with essentially similar chemical composition, but with different oxide thickness and roughness. The morphologic evaluation of the bone formation revealed that: (1) the percentage of bone-to-implant contact of the oxidized implants (33.3%) after 4 weeks was greater than that of the blasted group (23.1%); (2) the percentages of bone-to-implant contact after 12 weeks were not statistically significantly different between the groups; (3) the percentages of bone area inside the thread after 4 weeks and 12 weeks were not statistically significantly different between groups. Discussion and Conclusion: This investigation demonstrated the possibility that different surface treatments, such as blasting and oxidation, have an effect on the ingrowth of bone into the thread. However, the clinical implications of surface treatments on implants, and the exact mechanisms by which the surface properties of the implant affect the process of osseointegration, remain subjects for further study.

Purpose: A 3-dimensional finite element analysis was performed to evaluate the influence of implant type and length, as well as that of bone quality, on the stress/strain in bone and implant. Materials and Methods: Two types (screw and cylinder) and 4 lengths (9.2, 10.8, 12.4, and 14.0 mm) of titanium implants were buried in 4 types of bone modeled by varying the elastic modulus for cancellous bone. Axial and buccolingual forces were applied to the occlusal node at the center of the abutment. Results: Regardless of load direction, maximum equivalent stress/strain in bone increased with a decrease in cancellous bone density. Under axial load, especially in the low-density bone models, maximum equivalent strain in cancellous bone was lower with the screw-type implant than with the cylinder- type implant. It was also lower with the longer implants than with the shorter implants. Under buccolingual load, equivalent stress/strain was influenced mainly by bone density. Discussion: This study confirms the importance of bone quality and its presurgical diagnosis for implant long-term prognosis. Implant length and type can also influence bone strain, especially in low-density bone. Conclusions: The results of this study suggest that cancellous bone of higher rather than lower density might ensure a better biomechanical environment for implants. Moreover, longer screw-type implants could be a better choice in a jaw with cancellous bone of low density.

Purpose: Reconstructive surgical treatment with osteopromotive membranes has become an integral part of implant dentistry. Nevertheless, there are still instances in which this technique alone is of limited or no benefit. The aim of the present study was to determine whether a combination of titanium membranes coated with transforming growth factor ß1 (TGF-ß1) and insulin-like growth factor I (IGF-I) is of value in the regeneration of so-called critical-size defects in the rat model. An analysis was made of whether or not locally administered antibiotics are deleterious to bone regeneration. Materials and Methods: A total of 24 rats were included in the study and were divided into 4 groups, each with 6 animals. Critical-size defects were created bilaterally and covered by titanium membranes coated with (1) polylactide, (2) polylactide and clindamycin, (3) polylactide and growth factors, or (4) polylactide, clindamycin, and growth factors. All 24 contralateral defects were covered by titanium membranes without any substrate (controls). Four weeks after treatment the animals were sacrificed. Results: In groups 3 and 4, most defects showed thin but almost complete bridging of the defects with new bone formation. In particular, clindamycin had no inhibitory effect on the regeneration of bone. Nevertheless, after 28 days, there was no significant difference between the individual groups (including controls) with respect to the total amount of newly formed bone. Discussion and Conclusion: These results support the hypothesis that coating titanium membranes with TGF-ß1/IGF-I leads to almost complete bony bridging of critical-size defects without voluminous carrier materials. Moreover, simultaneous administration of clindamycin seems possible.

Purpose: The aim of this study was to report the outcome of sinus augmentation surgery with autogenous bone grafting in routine dental implant practice. Materials and Methods: Twenty-seven sinus augmentation procedures were undertaken on 18 consecutive patients (mean age 43.7 years). The mandibular symphysis was used as the donor site for 11 patients. The iliac crest was used as a donor site for 7 bilateral cases. Results: Six patients had implants placed at the time of grafting; the other 13 had a mean bone graft consolidation period of 24.7 weeks (range 9 to 39 weeks) before implants were placed. One patient who had a repeat procedure had both immediate and delayed techniques. A total of 79 Brånemark System Mk II implants were placed in grafted bone (and 2 Mk IV implants were placed in a patient who had to have a repeat procedure) and proceeded to occlusal loading. After a mean follow-up period of 162 weeks (range 76 to 288 weeks), 16 implants failed to integrate in grafted bone, representing an 80.25% survival rate. Fourteen patients proceeded to the planned prosthesis, 3 patients had a compromised treatment plan, and 1 patient was restored conventionally. This represents 94% of patients who were rehabilitated. Discussion and Conclusion: The sinus augmentation procedure using autogenous bone grafting can increase bone volume to allow implant placement where there is insufficient bone. The survival of implants in the grafted bone, as measured by integration and successful loading, was reduced compared to implants placed in normal maxillary bone. Infection during the healing of the grafted site reduces the success of subsequent implant osseointegration.

Purpose: The goal of this study was to evaluate microbiota and radiographic peri-implant bone loss associated with ligature-induced peri-implantitis. Materials and Methods: Thirty-six dental implants with 4 different surfaces (9 commercially pure titanium, 9 titanium plasma-sprayed, 9 hydroxyapatite, and 9 acid-etched) were placed in the edentulous mandibles of 6 dogs. After 3 months with optimal plaque control, abutment connection was performed. On days 0, 20, 40, and 60 after placement of cotton ligatures, both microbiologic samples and periapical radiographs were obtained. The presence of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia/nigrescens, Campylobacter spp, Capnocytophaga spp, Fusobacterium spp, beta-hemolytic Streptococcus, and Candida spp were evaluated culturally. Results: P intermedia/nigrescens was detected in 13.89% of implants at baseline and 100% of implants at other periods. P gingivalis was not detected at baseline, but after 20 and 40 days it was detected in 33.34% of implants and at 60 days it was detected in 29.03% of dental implants. Fusobacterium spp was detected in all periods. Streptococci were detected in 16.67% of implants at baseline and in 83.34%, 72.22%, and 77.42% of implants at 20, 40, and 60 days, respectively. Campylobacter spp and Candida spp were detected in low proportions. The total viable count analysis showed no significant differences among surfaces (P = .831), although a significant difference was observed after ligature placement (P .0014). However, there was no significant qualitative difference, in spite of the difference among the periods. The peri-implant bone loss was not significantly different between all the dental implant surfaces (P = .908). Discussion and Conclusions: These data suggest that with ligature-induced peri-implantitis, both time and periodontal pathogens affect all surfaces equally after 60 days.

Purpose: The placement of implants allows for re-establishment of function and esthetics following tooth loss. Immediate implant placement is a relatively recent procedure and has advantages, such as reduced number of surgical procedures, preservation of alveolar bone, reduction of cost and period of edentulism, and increased patient acceptance. However, there are some specific contraindications for the technique, such as the presence of an infection caused by periodontal disease and periapical lesions. The objective of this study was to evaluate the percentage of bone-implant contact of immediate implants placed in periodontally infected sites. Materials and Methods: In the first phase, periodontitis was induced with ligatures in the mandibular premolars of 5 mongrel dogs, using the contralateral teeth as controls (received prophylaxis only). After 3 months, in the second phase of the study, 40 implants were placed in the alveoli of both experimental and control teeth. After a healing period of 12 weeks, the animals were euthanized, and the hemimandibles were removed, dissected, fixed, and prepared for histomorphometric analysis of percentage of bone-implant contact. The Mann-Whitney test was used for statistical analysis. Results: The results of the histomorphometric analysis indicated mean bone-implant contact of 62.4% in the control group and 66.0% in the experimental group, a difference that was not statistically significant. Discussion: Histomorphometric results revealed similar bone-implant contact in both groups, with no signs of infection. Conclusions: It was concluded that periodontally infected sites may not be a contraindication for immediate implantation in this animal model system, if adequate pre- and postoperative care is taken.

Purpose: To evaluate long-term clinical performance of 1-stage dental implant prostheses at a single clinic, emphasizing clinical and demographic characteristics that affect implant survival. Materials and Methods: Dental records of all 308 patients (674 implants) treated with 1-stage implants at Mayo Clinic from October 1993 through May 2000 were reviewed from implant placement to last visit. Exposure and outcome variables affecting performance were collected separately to control bias in the data collection process. Additional confounding factors (age and sex) were adjusted with the stratified Cox proportional hazards model. Implant survival was determined by means of a Kaplan-Meier survival estimate. The log-rank test was used to determine the role of clinical and demographic variables in implant survival. The relative risk associated with the possible effect of clinical and demographic variables on implant survival was estimated with the Cox proportional hazards model. Results: The implant survival rate (n = 654 implants) was 97% (mean ± SD follow-up, 21.0 ± 18.8 months; range, 1 to 78 months). Performance bias was limited because nearly all patients were treated by 1 prosthodontist. Two implants failed after loading (6 and 9 months). The incidence of complications was less than 4%. Among the implant failures, use of heterogeneous bone graft was associated with 4.8 times more failures than was use of autogenous bone graft (P = .04). After augmentation, delaying implant placement for 5 to 6 months resulted in 8.6 times more failures than the rate after earlier placement (P .001). Discussion: Retrospective review of the clinical performance of a 1-stage dental implant system yielded a 97% survival rate, with no failures noted after 13 months. Prosthetic complications were low, especially for fixed implant prostheses. Conclusion: Clinical performance of 1-stage dental implant prostheses between 1993 and 2000 demonstrated a high level of predictability.

Purpose: The purpose of this study was to compare the success of hydroxyapatite (HA) -coated and machined titanium (Ti) implants in a 5-year randomized, controlled clinical trial conducted at 2 centers. Materials and Methods: Each of 120 edentulous patients received HA-coated threaded, HAcoated cylindric, and machined Ti threaded implants in a randomized design using 5 or 6 implants. Digital radiographs allowed for yearly measurements of bone loss. Calibrated clinicians also measured mobility, Gingival Index, Plaque Index, probing depth, and recession. A Kaplan-Meier analysis was used to compare the proportion of ailing implants (defined as less than 2 mm of alveolar bone loss over 5 years) for each type of implant design. The criteria employed to assess implant outcome included the need for successful implants to lose less than 2 mm of bone support over the 5 years following placement of the prosthesis. Results: This analysis revealed that 95.2% of machined Ti threaded implants and 97.92% of HA-coated threaded implants were successful, while 99.0% of HA-coated cylindric implants experienced less than 2 mm of bone loss (P .06). Discussion: All types of implants placed in this study had success rates above 95%. Conclusion: Over 5 years, the success rate tended to favor HA-coated implants.

Purpose: To increase human bone graft regeneration and quality by the use of a mixture containing autologous ground calvarial bone, human recombinant tissue factor (rhTF), platelet-rich plasma (PRP), and tetracycline. Materials and Methods: Maxillary sinus floor augmentation was performed on 18 patients by grafting a "bone paste" made of PRP (1.8×106 platelets/mm3 plasma), about 1 µg rhTF, calvarial bone chips (2 to 5 mm in size), and tetracycline (10 to 30 µg/mL preparation). Five to 6 months after the surgical phase and grafting, a bone core was extracted for implant fixation, and the osseous core samples were analyzed microscopically. Results: Histology revealed vascularized connective tissue rich in lamellar bone spicules containing osteocytes and surrounded by osteoblasts. The success rate of grafting was 90.3%. In 6-month postoperative blood samples, no residual coagulating disturbances could be found. Discussion: The combination of calvarial bone chips, rhTF, PRP, and tetracycline results in a paste that is easy to handle, safe for patients, and possesses high bone-regeneration capacity. Conclusion: The generalized use in implant dentistry, oral surgery, and orthopedics of such a protocol could facilitate the healing process as well as patient safety and surgeon comfort.

Purpose: In this prospective multicenter clinical study, 1,179 3i standard threaded and self-tapping implants were followed for up to 6 years and monitored according to established success criteria. Materials and Methods: A total of 493 patients (240 men and 253 women) with a mean age of 45.1 years at implant surgery were enrolled at 6 research centers after being screened for exclusion criteria. Implants were placed according to a 2-stage surgical protocol with a minimum of 4 months of submerged healing in the mandible and 6 months in the maxilla. Restorations included 633 prostheses, the majority of which were fixed partial dentures in the posterior mandible or maxilla or single-tooth replacements in the anterior maxilla. Results: One hundred four implants (8.8%) did not meet success criteria and were designated as failures, and 222 implants (18.8%) were lost to follow-up. The cumulative success rate according to life table methods was 91.1% at 6 years. Discussion: Sixty percent of the failed implants were short (= 10 mm long), and their cumulative success rate as a group at 6 years was 89.0%, compared to 93.1% for longer implants (P .05). Thirty-three percent of all failures were implants placed in the posterior maxilla, for a 5-year cumulative success rate of 87.4%. Conclusion: It appears that limited bone dimensions and poor-quality bone have an impact on the performance of these machined-surface implants.

Purpose: The aim of this study was to evaluate the feasibility of using a 2-stage implant system in a single-stage procedure and to study the impact of the microgap between the implant and the abutment. Materials and Methods: Sixty edentulous patients (Cawood class V or VI) participated in this study. After randomization, 20 patients received 2 IMZ implants placed in a single-stage procedure, 20 patients received 2 IMZ implants placed in the traditional 2-stage procedure, and 20 patients were treated with 2 ITI implants (single-stage procedure). The implants were placed in the canine area of the mandible. After 3 months, mandibular overdentures were fabricated, supported by a bar-and-clip attachment. A standardized clinical and radiographic evaluation was performed immediately after prosthesis placement and after 12 and 24 months. Results: One IMZ implant of the 1-stage group and 1 IMZ implant of the 2-stage group were lost after 6 and 12 months, respectively. Apart from several significant but clinically irrelevant differences, the 3 groups did not appear to differ markedly with regard to clinical parameters during the evaluation period. The mean bone loss within the first 2 years of functioning (1.1 mm IMZ 1-stage, 0.8 mm IMZ 2-stage, 1.2 mm ITI) was comparable for the 3 groups. Discussion and Conclusions: The results of this study suggest that dental implants designed for a submerged implantation procedure can also be used in a single-stage procedure and may be as predictable as when the same implants used in a 2-stage procedure or as 1-stage implants. Placement of the microgap at the crestal level in 2-stage implants did not appear to have an adverse effect on the amount of peri-implant bone loss at 2 years in this study population.

Purpose: The purpose of this retrospective analysis of expert opinions was to optimize the level of patient information prior to implant-prosthetic treatment. Materials and Methods: Twenty-eight expert opinion reports on implant treatment cases compiled between 1996 and August 2001 were analyzed. Results: Seventy-five percent of all cases subjected to expert opinion reports revealed generally inadequate patient information. Significant associations were found between diagnostic mistakes and a lack of or inadequate information about complications that occurred (P = .04). Inadequate prosthetic or periodontal pretreatment of the patient prior to implant treatment was associated with a lack of information concerning implant and periodontal maintenance (P = .023) as well as insufficient oral hygiene status (P = .001). Discussion: In addition to a general lack of patient information, a lack of information about possible complications and inadequate information about treatment risks, treatment costs, and treatment alternatives were also found. Conclusion: Optimization of pretreatment information for patients, as well as improvement of communication with patients throughout the whole treatment and maintenance period, seem to be necessary.

Purpose: The aim of this study was to evaluate the capability of a configured titanium mesh (CTM) to serve as a mechanical and biologic device for restoring a vertically defected/resorbed alveolar ridge. Materials and Methods: The study comprised 10 severely resorbed sites in 10 patients. Pre- and postoperative ridge measurements were taken with reference to the neighboring teeth and supporting screw head base of the CTM. Bovine bone mineral served as the augmentation filler material. The metal mesh was removed after 9 months. Subsequently, root-form, screw-type implants were placed. During the implant placement phase, cylindric bone samples were retrieved from the augmented area for histopathologic and histochemical examination. Results: Upon soft tissue reflection and before augmentation, defect height, as recorded by a periodontal probe along the main threads exposed on the support screw, was between 5 and 8 mm (average 6.4 mm; SD ± 1.17). At 9 months after augmentation, during the implant placement phase, the defect height was between 0 and 2 mm (average 1.2 mm; SD ± 0.63). Differences were statistically significant (P .001). Bone height gain was between 4 and 6 mm (average 5.2 mm, SD ± 0.79), which gave an average bone fill of 81.2% (SD ± 7.98). Polarizing microscopic examination of sections stained with Picrosirius red showed a gradual increase in new lamellar bone from coronal to apical cuts, reaching the highest area percentage in the deep apical zone. Discussion: At 9 months postaugmentation using the CTM surgical technique, the quality and quantity of the newly established hard tissue appeared to be different in the coronal versus apical areas of the restored alveolar ridge. Conclusion: Although at 9 months postoperatively, the augmented alveolar ridge had different bone content, clinicohistochemical results demonstrated that this surgical technique could be a successful and predictable procedure for rebuilding a resorbed/defected ridge to accommodate endosseous implants.

Purpose: This study investigated the effects of certain systemic and local factors on resorption of the posterior mandibular residual ridge under conventional dentures and overdentures supported by 2 implants. Materials and Methods: Proportional area measurements of the posterior mandible were made on rotational tomograms taken immediately before and 5 years after treatment. The area was bounded by a line joining gonion to the lowest point of the mental foramen and the crest of the residual ridge and was expressed as a proportion of an area that was not dependent on the ridge. The use of proportions rather than actual measurements minimized errors related to magnification and distortion. Results: The estimated average reduction in height was 1.25 mm in 5 years (1.63 mm for conventional denture groups and 0.69 mm for implant overdenture groups, ie, almost 1 mm less in the overdenture group). Discussion and Conclusion: Female gender was a risk factor for greater resorption. Other factors, such as the number of years a patient had been edentulous, initial height of the mandible, and the number of dentures used, failed to show an association with resorption of the residual posterior mandibular ridge, while the statistically significant effect of age was unlikely to be clinically significant.