The International Journal of Oral & Maxillofacial Implants, 03/1999

The aim of this prospective study was to histomorphometrically evaluate at various time intervals the mineralization stage and process of an allogeneic-xenogeneic bone graft used in sinus augmentation procedures. One biopsy was taken from 20 patients at either 6, 8, 10, or 12 months after sinus augmentation. Immediately following the biopsy, an endosseous implant was placed into the biopsy site. This protocol provided 4 groups of 5 patients each, based on healing time following sinus augmentation. Using backscattered electron image analysis, the specimens were histomorphometrically analyzed to determine the volume fractions of residual cancellous bone, newly formed bone, soft tissue, bovine hydroxyapatite, and "remineralized" freeze-dried demineralized bone allograft (rDFDBA). "Remineralization" of DFDBA particles was observed in a few areas in all specimens. Polarized light microscopy showed that only the 12-month biopsies had a predominance of lamellar bone formation. The area within the biopsies that represented the residual alveolar ridge consisted of 32.6% ± 8.6% (mean ± SD) of bone. In the grafted area of the biopsies the volume fraction of newly formed bone at 12 months (20.7% ± 8.3%) was significantly higher (P .05, analysis of variance) than at 6 months (8.1% ± 3.0%). There was no statistically significant difference between newly formed bone in the inferior, central, and superior grafted areas in all 4 time intervals. This prospective study indicates that the mineralization process of an allogeneic-xenogeneic sinus graft is incomplete 6 months after the sinus augmentation procedure. New bone formation increased up to 12 months postaugmentation; however, it remained lower than the volume of residual bone. Keywords: bone formation, bovine hydroxyapatite, demineralized freeze-dried bone allograft, dental implants, histomorphometry, remineralized DFDBA, sinus augmentation

Gold screw loosening is a problem that frequently affects dental implants. The application of a preload has been the main means of preventing loosening. However, this measure has not been able to eliminate its occurrence. In this study the effect of a washer in a Brånemark-type implant on the loosening conditions of the retaining screw was investigated using a finite element simulation. The simulation indicated that a washer may significantly increase the tolerance of a screw against loosening. This is accomplished by increasing the tolerance of the implant against deformation. The addition of a customized washer to a dental implant system may offer a very simple and inexpensive solution for the persistent problem of screw loosening. Keywords: dental implant, finite element analysis, screw loosening, stiffness, washer

The histologic response of the periodontal tissues of teeth rigidly joined to implants with a fixed partial denture was evaluated using light microscopy. The fourth premolar of a dog was connected to implants placed in the first and second premolar position with a fixed partial denture. The restored teeth were under function for periods of 6, 12, 18, and 24 months, with unrestored fourth premolars as controls. The histology of the periodontal ligament on the fourth premolar was found to be similar in the control and the restored teeth. The periodontal tissues contained a minimal amount of inflammatory cell infiltrate. The crestal bone was cortical in nature, showing no periodontal breakdown. The orientation of the periodontal fibers was easily determined, indicating that minimal remodeling had taken place. The number and morphology of the blood vessels were also similar in the control and the treated teeth. The lack of inflammation and stability of the periodontal tissue suggested that the use of combination implant-to-natural-teeth restorations with rigid joints in this animal model does not result in deleterious effects on the periodontal tissues and that the forces placed on the tissues are within the remodeling capabilities of the teeth. Keywords: cementum, dental implants, intrusion, light microscopy, osseointegration, periodontal ligament

The purpose of this study was to evaluate the effect of gap width on bone healing around implants placed into simulated extraction socket defects of varying widths in 10 mongrel dogs. All premolars were removed and the alveolar ridges were reduced to a width of 7 mm. Nine weeks later, a total of 80 implants, 10 mm long by 3.3 mm wide, were placed into osteotomy sites prepared to 3 different diameters in the coronal half, simulating extraction sockets. Three experimental sites, with gap sizes of 0.5 mm, 1.0 mm, and 1.4 mm, were created; the control sites had no gap. The depth of each defect was measured at the time of implant placement. All implants were stable at the time of placement. The dogs were euthanized 12 weeks after implant placement, and blocks containing the implants and adjacent bone were submitted for histologic evaluation. Clinically, all control and test sites healed, with complete bone fill in the defect. Percentages of bone-to-implant contact were measured histologically. As the gap widened, the amount of bone-to-implant contact decreased, and the point of the highest bone-to-implant contact shifted apically. These changes were statistically significant (P .001). No statistically significant differences in bone-to-implant contact were found between the sites when the apical 4 mm of implants were compared. Within the limits of this study, the simulated extraction socket defects healed clinically, with complete bone fill, regardless of the initial gap size. However, the width of the gap at the time of implant placement had a significant impact on the histologic percentage and the height of bone-to-implant contact. Keywords: gap, gap width, histomorphometry, immediate placement, implant, osseointegration

Maxillary sinus grafting procedures are currently the treatment of choice when the alveolar crest of the posterior maxilla is in close approximation to the maxillary sinus. The short-term histologic and radiographic healing following sinus grafting with natural bone mineral (Bio-Oss) in the chimpanzee has been evaluated. We have previously shown by histomorphometric and radiographic analysis that the percentage of vital bone area, the vertical height, and the density of new bone in the maxillary sinus was significantly greater with anorganic bovine bone compared to bovine Type I collagen matrix. The purpose of this in vivo study was to determine the bone mineral density (BMD) of the sinus grafts, the vertical height stability, the vital bone area, and the extent of anorganic bovine bone replacement 18 months postoperatively in 4 maxillary sinuses from 4 different animals. Radiographic analysis of computed tomographic scans taken at 1.5 years revealed an average BMD of 658 mg/mL, which was not significantly different from the values found at 6.5 months. The radiographic vertical height was maintained between the 6.5- and 18-month time points. On average, the grafts were found to have a height of 14 mm. Lateral wall biopsy specimens at 7.5 months were compared to those at 18 months. With the anorganic bovine bone treatment, the percentage of vital bone area increased from 62 ± 3% to 70 ± 7% and the percentage of natural bone mineral area decreased from 19 ± 14% to 6 ± 3%. The bovine Type I collagen matrix vital bone percentage at 7.5 months was 34 ± 21%. These results demonstrate that sinus grafting with anorganic bovine bone maintains radiographic evidence of density and height stability to 1.5 years. In addition, histologic evidence supports the hypothesis that anorganic bovine bone is replaced by vital bone. Keywords: anorganic bovine bone, bone regeneration, sinus grafting

This in vitro study quantified the marginal discrepancy of the implant-to-prosthetic-crown interface on nonsubmerged dental implants restored with either a cemented or a screw-retained approach. Metal-ceramic crowns were fabricated for 20 ITI 4.1 X 10 mm solid-screw titanium implants. Ten implants received octa abutments and screw-retained crowns fabricated on premachined gold cylinders. The remaining 10 implants were restored with 5.5-mm solid abutments and metal-ceramic crowns cemented alternately with a glass-ionomer or a zinc phosphate luting agent. Inspection of the implant-crown interface was conducted using light microscopy under X50 magnification at selected stages in the process of crown fabrication. Statistical analysis revealed a significant difference (P .001) in the mean marginal fit between screw-retained (8.5 ± 5.7 µm) and luted implant-supported crowns. This difference was observed both before (54.4 ± 18.1 µm) and after cementation with glass-ionomer (57.4 ± 20.2 µm) or zinc phosphate (67.4 ± 15.9 µm). Keywords: cement, dental implant, fixed prostheses, marginal discrepancy, screw-retained

Several life-threatening complications caused by hemorrhage that can occur during the placement of dental implants in the mandibular interforaminal region have been described in the literature. The aim of this study was to assess the vascular supply to this region and delineate the relative contribution and importance of the sublingual artery versus the submental artery. Thirty-four human cadavers were dissected. Special attention was directed to the presence of a branch of the submental artery that perforates the mylohyoid muscle and thus participates in the blood supply to the floor of the mouth together with the sublingual artery. A sublingual artery was found in 71% of the specimens. A large branch of the submental artery perforating the mylohyoid muscle was found in 41% of the specimens. The point of perforation was located an average of 31 mm posterior to the menton. The high risk of injuring the vessels of the floor of the mouth can be explained by the close vicinity of these vessels to the mandibular lingual cortical plate. To prevent complications in cases of unclear anatomic identification of the fossa sublingualis, preoperative lingual probing or elevation of the periosteum of the lingual aspect of the mandible is necessary. An alternative diagnostic procedure is precise preoperative noninvasive imaging (eg, computed tomography). Keywords: endosseous implants, floor of the mouth, hemorrhage, vessels

During 1992, 100 Minimatic screw implants made of titanium alloy (titanium-aluminum-vanadium) with a machined rough acid-etched surface were placed in 63 consecutive partially edentulous patients. At second-stage surgery, which was performed after a 4- to 6-month healing period, none of the implants showed signs of mobility, peri-implant infection, or bone loss from the crest of the ridge. Each patient was restored with a fixed prosthesis and reexamined every 3 months during the first year. Periapical radiographs were taken annually up to 5 years. These revealed no signs of peri-implant radiolucencies involving any of the implants, and mean alveolar bone loss was less than 1 mm at the 5-year examination. One implant was considered a late failure because of a peri-implant infection that developed during the first year, although the implant was still functional at year 5. Another patient with 2 implants dropped out during the fifth year of the study, although both implants had been considered successful up to that point. Based on annual measurements of Plaque Index, Sulcular Bleeding Index, pocket probing depth, attachment level, width of keratinized mucosa, and hand-tested mobility, 97 of the remaining 98 implants were considered successful, resulting in a 98% success rate. This 5-year study confirms that Minimatic machined acid-etched implants provide predictable osseointegration results and supports the conclusion of other reports that titanium implants with a rough surface can fulfill the requirements of Albrektsson et al (1986) for implant success. Keywords: acid-etched implants, five-year follow-up, osseointegration, rough surface implants

Ridge augmentation was achieved through the use of guided bone regeneration procedures in pontic areas of 43 planned fixed prostheses. Measurements taken through templates, which fit over the final fixed prostheses, at the time of prosthetic placement and a mean of 123 weeks after prosthesis placement demonstrated a change of less than 0.1 mm in buccopalatal dimension of the regenerated hard tissues. Keywords: esthetic surgery, Gore-Tex, grafting, guided bone regeneration

One thousand eight hundred seventeen implants were placed in the completely edentulous maxillae of 189 patients (122 female; 67 male). The patients' mean age was 60 years (range 28 to 91 years). Three hundred fifty-six of the 1,817 implants were placed in the pterygomaxillary area, and all patients were restored with complete-arch fixed detachable prostheses. The mean number of implants per maxillary prosthesis was 9.0 (range 6 to 15). During stage II surgery and before loading, 41 pterygomaxillary implants (11.5%) were not osseointegrated and were removed. After a mean loading period of 4.68 years (range 0.06 to 9.20 years), 1 additional pterygomaxillary implant was lost. Altogether, 42 of 356 pterygomaxillary implants (11.8%) were removed. Survival rates according to implant size, bone quality, and tooth position were also recorded. This study illustrates a cumulative survival rate of 88.2% for pterygomaxillary site implant placement in edentulous maxillary arches. Keywords: Brånemark implants, complete-arch fixed detachable prostheses, osseointegration, pterygomaxillary, survival rate, tuberosity

The aim of the study was to determine the fate of demineralized freeze-dried bone allograft (DFDBA) used in conjunction with a barrier membrane in the management of extraction sockets and deficient alveolar ridges, and to compare the amount of bone formed with that found in untreated sites. Ten biopsies were obtained from 8 grafted patients. Five biopsies were harvested from untreated sites during routine implant placement and analyzed for comparison. In the socket management procedure, DFDBA was packed tightly into the socket and covered with an expanded polytetrafluoroethylene (e-PTFE) membrane. Primary closure was achieved in all cases. In the ridge regeneration procedure, cortical columns were placed in the ridge projecting outward approximately 3 mm to create and maintain space for DFDBA particles packed between them; the columns were then covered by an e-PTFE membrane. Healing time ranged from 8 to 23 months. At the time of implant placement, bone cores (7 mm X 2 mm) were harvested, fixed in 10% formalin solution, and prepared for histologic examination. At the light microscopic level, no inflammation or fibrous encapsulation was observed. New bone formation on and around DFDBA particles was widespread. Histomorphometric analysis of the grafted specimens and untreated sites was carried out using the trabecular bone volume (TBV) index. The TBV in the maxillary test specimens was 55.03%, as compared to 57.33% of control cores. Unaltered DFDBA made up 8.7% of the test specimens. In the mandibular biopsies, the TBV was 56.6%, while for the controls it was 40.9%. The volume of DFDBA still present was 2.45%. The results tended to indicate that treatment with DFDBA in conjunction with cell occlusive membranes will result in new bone formation, predominantly by the process of conduction, which appears to be similar in amount and nature to that found in cores harvested from healed nonfunctional edentulous areas. Keywords: deficient ridges, demineralized freeze-dried bone allograft, extraction sockets, guided bone regeneration, histomorphometry, osteoconduction

The expanded experience with oral implants and supplementary augmentation techniques has opened new possibilities for treating patients with oligodontia or anodontia with fixed prostheses. A problem in treating such patients is the need to place implants in growing maxillae or mandibles, as many of these patients are children or adolescents. When implant treatment is postponed until the patient is full grown, dysfunctions become manifest, which necessitates extensive surgical measures to achieve a fixed prosthetic restoration. This report illustrates the problems associated with different concepts for the treatment of multiple aplasia with implants. The results are based on the findings of 22 patients with oligodontia who underwent surgical treatment and were followed over a period of 5 years. Two controversially treated cases are presented. Keywords: bone atrophy, dental aplasia, growth, implants, timing of implant placement

A technique is presented for interforaminal lateral augmentation of mandibles with adequate bone height, but extremely knife-edged mandibular alveolar ridges (Class IV of Cawood and Howell's classification of residual ridges), in which the crestal portion of the knife-edged ridge is used as grafting material. Following an osteotomy and rotation of the grafts by 180 degrees, the grafts were fixed to the residual ridge below the osteotomy line by means of miniscrews. All grafts showed only mild resorption after a healing period of 3 months, and it was possible to place 4 implants in the now sufficiently wide host region. Keywords: augmentation, implant placement, knife-edged ridge

Aspartate aminotransferase (AST) has been shown to be a promising host marker for periodontal disease progression. The aim of the present study was to analyze AST in the crevicular fluid (CF) of implants exhibiting peri-implantitis and to evaluate the association between AST levels and progressive attachment loss. Twenty patients who had received a total of 42 endosseous cylindric titanium implants were examined. Radiographic assessment of preexisting bone loss and clinical measurements, including electronic attachment of probing, presence or absence of plaque, bleeding on probing, and AST analysis in CF, were performed on 2 occasions 6 months apart. During this study period 13 of 168 sites in 7 patients experienced further loss of attachment greater than or equal to 1.0 mm (median 1.7 mm; interquartile range 0.4 mm). Evaluation of a positive AST test (> 300 µIU) in site-specific diagnosis revealed low positive (8%) and high negative predictive values (92%), with a sensitivity of 15% and a specificity of 83%. These results indicate that, in contrast to periodontal disease, the assessment of AST in peri-implant crevicular fluid may be of limited value as a diagnostic and prognostic marker for peri-implant disease. Keywords: aspartate aminotransferase, oral implant diagnosis, peri-implant crevicular fluid, peri-implantitis, peri-implant probing

mplants are well accepted as a means of dental rehabilitation. While integration success rates are high, crestal bone loss can occur, and it may not become apparent until stage II surgery and implant uncovering. The purpose of this study was to quantify the relationship between exposure of implants through the oral mucosa between stage I and stage II implant surgery and early changes in crestal bone height. Bone levels were measured during placement of 275 implants in the maxillae of 50 subjects. Repeated bone height measurements were obtained at implant uncovering. Fourteen implants in 7 patients were exposed to the oral cavity through the mucosa at stage II surgery. Patients with 1 or more exposed sites demonstrated a likelihood of bone loss 3.9 times greater than patients with nonexposed sites (Fisher exact test, P = .0003). These results suggest that exposure of an implant between stage I and stage II implant surgery might serve as a potential indicator of the occurrence of early bone loss. Keywords: bone loss, endosseous dental implants, implant exposure

The present study described the histologic findings of 2 implants and surrounding tissues retrieved from human irradiated bone. For the treatment of a malignant tumor, 50 Gy of irradiation after implant placement and 60 Gy of irradiation before implant placement were provided for patients 1 and 2, respectively. In patient 1, the implant and surrounding tissues were removed from the frontal bone 24 months after implant placement because of the patient's death from a tumor recurrence. In patient 2, the implant and surrounding tissues were removed from a maxillectomy site 26 months after implant placement because of tumor recurrence. In each patient, new bone formation surrounding the implants was observed. The ratio of direct bone-implant contact along the threaded implant surface was 61.3% in patient 1 and 69.0% in patient 2. The ratio of the area occupied by mineralized bone in each thread was 75.8% in patient 1 and 81.2% in patient 2. These results indicate the potential of irradiated bone to achieve osseointegration of titanium implants. Keywords: histologic study, irradiation, osseointegrated implant