The International Journal of Oral & Maxillofacial Implants, 03/1998

Screw-shaped implants made from rods of commercially pure titanium (grade 1) and titanium-aluminum-vanadium (grade 5) were machined, and the implant surface structures were numerically described before being placed in rabbit tibiae for healing periods of 1 month, 6 months, and 12 months. Quantitative comparisons of the removal torque (Ncm) necessary to loosen the implants from the bone bed were performed. Short-term (1 month) observations revealed no significant differences between the two tested materials. However, after 6 and 12 months, the commercially pure titanium implants were significantly more stable in the bone bed, as compared to the alloy samples. After 6 months, the commercially pure titanium had a mean removal torque of 29 Ncm versus 23 for the alloy (P = .01), and after 12 months, the mean removal torque was 38 Ncm for commercially pure titanium as compared to 35 Ncm for the alloy (P = .01). Quantifications of the bone tissue response to the materials did not show any significant differences; however, the commercially pure titanium showed a tendency to have a higher percentage of bone in contact with the implant as compared to the alloy screws. Bone volumes in the threads were similar. The absence of any quantitative light microscopic difference after 1 month following placement may relate to the fact that there was a sparse amount of bone, since the tissue was in the organization/granulation phase. After 6 and 12 months of follow-up, substantial bone formation had occurred, resulting in significantly increased removal torques for the commercially pure titanium samples. Keywords: bone, commercially pure titanium, histomorphometry, implants, removal torque, titanium alloy

Successful treatment of furcated molar teeth presents the periodontist and prosthodontist with a challenging dilemma. Accepted treatment modalities include chemotherapeutic maintenance, root planing, open flap debridement, modified Widman flap, bone grafting with and without guided tissue regeneration, and osseous resection with and without root removal. Determining the appropriate treatment for an individual patient that is both cost-effective and offers the greatest long-term prognosis can be a daunting task. The literature is replete with studies of different therapeutic alternatives for furcated molar teeth. A relatively new treatment option is complete removal of the tooth combined with ultimate placement of an endosseous implant and restoration with a single crown. A review of the relevant literature with special emphasis on root resection therapy and single molar implant placement is presented. The relative merits of each treatment modality and guidelines for their use are discussed. Keywords: review literature, risk factors, root furcations, root resection, single-tooth implants, survival rate

Five titanium plasma-sprayed implants were biopsied from a human volunteer 6 months after placement. Four test implants had been placed in immediate extraction sockets, while one implant was placed in a mature site and served as a control. The histologic analysis demonstrated that all five implants achieved osseointegration as demonstrated by light microscopy, whereas a varying degree of bone-implant contact was observed. The nonloaded control implant had the highest percentage of bone-implant contact, 72%, followed by the two implants placed in the canine sites presenting with a horizontal defect dimension of 1.5 mm or less. These implants were placed without a barrier membrane, but in a submerged fashion. The histometric analysis showed a mean bone-implant contact of 50% for these two implants. The lowest mean bone-implant contact (17%) was observed for the two molar implants, which had horizontal defect dimensions of 4 mm; these implants were placed in a nonsubmerged fashion with the implants perforating an expanded polytetrafluoroethylene membrane. The authors concluded that osseointegration may occur in immediate extraction sites in humans using titanium implants with a plasma-sprayed surface. The horizontal component of the peri-implant defect was apparently the most critical factor relating to the final amount of bone-implant contact. Keywords: bone-implant contact, human biopsy, immediate extraction sites, osseointegration, titanium plasma-sprayed implants

The specific aim of this study was to determine the response of alveolar bone after it was augmented vertically using distraction osteogenesis and subsequently loaded with implant restorations. Four dogs each had four implants placed horizontally into an edentulous mandibular quadrant and, after integration, a distraction osteogenesis device was fabricated in the laboratory. An osteotomy was made to allow the crest of the alveolar ridge to be distracted vertically. After 10 mm of vertical distraction, the device was stabilized with light cured resin. Following bone fill confirmation of the distraction gap at 10 weeks, two implants were placed into the ridges, one in distracted bone and one in nondistracted bone. After 4 months for implant integration, freestanding prostheses were fabricated. Crestal bone levels were evaluated throughout the period of function. Animals were sacrificed after 1 year of loading, for histologic evaluation of the bone. The vertical ridge augmentation averaged 8.85 ± 1.05 mm after 10 weeks of healing following distraction, without change over 1 year of implant loading. Histologic examination showed that bone had formed between the distracted segments, creating an augmented ridge. The average thickness of the labial cortex in the distraction gap was significantly thinner than the lingual cortex in distracted bone and the lingual and labial nondistracted cortical bone. The presence of the dental implant did not significantly affect cortical bone thickness. Serial sections showed that implants remained integrated and functional without soft tissue inflammation. Dental implants placed into alveolar ridges augmented with the technique of distraction osteogenesis maintained bone and were functional for the length of this study. Keywords: alveolar ridge augmentation, distraction osteogenesis, implant restorations

This retrospective study investigated the outcome of 73 telescopic implant-supported fixed prostheses. Fifty-four prostheses were entirely cement-retained, and 19 incorporated a screw-clamping unit. The rate of complications was low and in most cases minor in nature. Cement-retained prostheses involving a distal cantilevered extension required the greatest postoperative maintenance. Despite the small number of combined screw- and cement-retained prostheses, the lack of complications and ease of retrievability make this approach worthy of further study. Keywords: cantilever extensions, cement-retained prosthesis, implant, telescopic prosthesis

Three hundred two consecutive ridge augmentation procedures (289 in a buccolingual and 13 in an apico-occlusal direction) were performed in 284 patients. Gore-Tex membranes of various configurations were used in conjunction with various nonautogenous particulate materials. Two hundred ninety-one of the augmented ridges (279 buccolingual and 12 apico-occlusal augmentations) demonstrated sufficient regenerated hard tissues for implant placement in ideal prosthetic positions. This represents an overall success rate of 96%, 97% for horizontally augmented ridges and 92% for vertically augmented ridges. A total of 574 implants were placed in the augmented ridges; 346 of these implants have subsequently been uncovered and restored. Seven implants failed to achieve osseointegration, and three implants (in one patient) were lost in function, for an overall survival rate of 97% for the uncovered implants. Keywords: Gore-Tex membranes, osseointegration, ridge augmentation, survival rate

Transmission of masticatory load in mandibular implant-retained overdentures was evaluated using a three-dimensional finite element model. The reaction forces on the distal edentulous mucosa and the stress on the peri-implant bone were compared in overdentures retained either by two ball attachments or by two clips on a bar connecting two implants. In the finite element model, a 35 N load on the first mandibular molar induced a greater reaction force on the distal edentulous ridge mucosa of the nonworking side when the overdenture was anchored by ball attachments than with the clips/bar attachment. Stress on peri-implant bone was greater with the clips/bar attachment than with the ball attachment. Keywords: ball attachment, clips/bar attachment, finite element model, implants, overdenture, reaction forces, stress

The relationship between mobility assessment with the Periotest system and histologic findings was evaluated for oral implants. Five screw-type implants of pure titanium were placed in the mandibles of four monkeys. Two implants in each monkey were occlusally overloaded. These implants were brushed once a week. Plaque was allowed to accumulate around unloaded implants with abutments in the same monkeys. During the experiment, six of eight implants with occlusal overload showed increased manually detectable mobility. Two of these were lost. After 18 months of experimentation, the mobility was assessed using the Periotest system. Sections of the implants and surrounding tissue were cut. For the excessive occlusally loaded implants with manually detectable mobility, positive Periotest values were recorded, and for all other implants the values were negative (range = -7 to -2). All implants with plaque accumulation were histologically osseointegrated but showed marginal bone loss. Two of the implants with occlusal overload had lost osseointegration completely, and two other implants were osseointegrated in the apical part only. A statistically significant association between the Periotest values and the histologic bone level or the proportion of bone-implant contact was observed. If only clinically stable implants (ie, without manually detectable mobility or with a negative Periotest value) were included in the analysis, no significant correlation was found. The Periotest values revealed only slightly more information concerning the osseointegration of implants than manual mobility assessments. Keywords: alveolar bone loss, bone resorption, dental implants, diagnostic accuracy, histology, mobility assessment, occlusal overload, osseointegration, peri-implantitis, plaque accumulation, traumatic occlusion

The aim of this experimental study was to evaluate the use of prefabricated autogenous bone grafts as onlay grafts to the mandible. Excess bone of 10 x 12 x 40 mm was produced inside blocks of pyrolyzed bovine bone under a polylactic membrane coverage on the outside of the mandible in 15 adult Göttingen minipigs. After 5 months, this bone was harvested and transferred to the premolar region of the mandibular body in 10 animals. Onlay grafts of mandibular bone were used as controls for the transplanted prefabricated grafts. All grafts were fixed by primary placement of one titanium implant each. Five animals served as ungrafted controls. Evaluation was performed after 3 months and 5 months, respectively. Two animals were lost to evaluation, and one scaffold became infected. Eleven of the remaining 12 scaffolds showed sufficient bone ingrowth for grafting. Three months after transplantation, bone volume of the prefabricated grafts was almost completely preserved, with only minimal resorption in the superficial pores of the scaffolds, while the control grafts exhibited partial resorption. The titanium implants, which had been placed at the time of onlay grafting, exhibited direct bone-implant contact. Five months after grafting, all titanium implants showed complete osseointegration, with direct bone-implant contact. The grafted bone exhibited a significant increase in bone density by appositional bone formation. The control grafts were nearly completely resorbed at that time. Keywords: guided bone regeneration, onlay grafts, prefabricated bone grafts, titanium implants

The possibility of placing endosseous implants in the edentulous maxilla is frequently reduced by inadequate bone volume of the residual ridge. In totally edentulous maxillae with knife-edge conformation, insufficient thickness is frequently associated with insufficient height of the residual ridge in the posterior maxilla because of pneumatization of the maxillary sinuses. This surgical method combines grafting of the maxillary sinuses, onlay grafts on the buccal side of maxillary posterior segments, and sagittal osteotomy of the anterior maxilla with interpositional bone grafts. Five to six months after maxillary reconstruction, Brånemark implants were placed and, after osseointegration occurred, implant-supported dental prostheses were fabricated. Three patients have been treated with this method and 22 implants have been placed. The mean follow-up after final prosthetic rehabilitation has been 16 months; survival rate has been 100%. Despite the small number of patients and the short follow-up, preliminary results have shown very promising results. Keywords: atrophic maxilla, bone graft, endosseous implants, preprosthetic surgery

The purpose of this study was to determine implant survival rates by means of life table analyses for a cohort of patients not part of a prospective efficacy trial and treated by practitioners at varying experience levels. Prognostic variables associated with implant failure were identified by means of proportional hazards models and advanced statistical methods that account for patient effects. Ninety-nine consecutive patients treated from 1987 to 1991 with follow-up to 1994 were included in this retrospective study. A total of 384 dental implants (79.7% Brånemark, 19.3% IMZ plasma-sprayed, 1% IMZ hydroxyapatite-coated) were placed and subsequently supported 108 prostheses. Survival and proportional hazards modeling were used to generate Kaplan-Meier survival curves and to identify variables associated with implant failure. Survey data analysis was used to adjust for any patient effects for variables identified as significant through the proportional hazards models. Thirty-four implants failed over the follow-up period (median follow-up time 3.6 years), resulting in an overall failure rate of 8.9%. Seventeen of 99 patients experienced an implant failure. When prosthesis type was excluded from the modeling process, survey data analysis identified posterior location and an implant width of less than 4.0 mm as being associated with implant failure (all P .05). Keywords: dental implants, effectiveness, proportional hazards, retrospective, survey data analysis, survival analysis

A survey was undertaken to analyze osseointegrated implants placed in irradiated maxillae and mandibles. It was found that nine centers in Japan and two centers in the United States had placed 228 implants in 44 patients. Of 228 implants, 59 were placed in the maxilla, 169 in the mandible. Three of 169 implants placed in irradiated mandibles were removed; 17 of 59 were removed from maxillae. One hundred nineteen implants were placed in the mandible without adjunctive hyperbaric oxygen treatment, of which only 2 were removed. From these results, it is suggested that osseointegrated implants can be placed in the irradiated mandibles of selected patients without hyperbaric oxygen treatment. Keywords: hyperbaric oxygen treatment, irradiation, multicenter study, osseointegrated implants

Conventionally, for dental reconstruction after bone grafting of the congenital residual alveolar cleft, a fixed prosthesis or removable partial denture is used. In this paper, residual alveolar cleft reconstruction with an osseointegrated implant following secondary bone grafting is described. The patient underwent secondary bone grafting of the residual alveolar cleft at the age of 18 years. One osseointegrated implant was placed in the bone bridge 8 months after bone grafting. No problems up to 1 year after the fabrication and placement of the fixed prosthesis have been observed. Keywords: oronasal fistula, osseointegrated implant, residual alveolar cleft, secondary bone grafting

In an experimental study using the Göttingen minipig, Gore-Tex, Gore Resolut, and Vicryl barrier membranes were tested for their efficacy in guided bone regeneration. The results were compared to those of autologous periosteum. The strongest reossification was seen in the bone defects covered with Gore-Tex; however, time-dependent disintegration phenomena, which had already been observed in preliminary examinations, were clearly established. After investigations of cell cultures to which human macrophages were added, the latter findings can be interpreted as the result of a physicochemical process, since a direct attack by the macrophages was not seen in vitro. Of the membranes used, the absorbable ones tended to collapse, depending on the size of the defect that was used, and they did not enhance reossification as much as did the permanent membranes. The periosteum-covered defects showed a satisfactory degree of regeneration, and no differences were observed between freely transplanted and pedunculated periosteum. Keywords: absorbable/nonabsorbable barrier membranes, disintegration phenomena, Gore-Tex membranes, guided bone regeneration

To study the effect of chronically infected sites on the immediate placement of implants, periapical lesions were induced in the third and fourth premolars of four dogs and the contralateral teeth were used as controls. Nine months after the induction of periapical lesions, experimental and control teeth were extracted, and 28 IMZ implants were immediately placed. After a healing period of 12 weeks, the animals were sacrificed, the hemimandibles were removed, and specimens were prepared to be hard-sectioned and stained with toluidine blue. All areas healed without inflammation or exudation and all implants were clinically immobile and were radiographically determined to be surrounded by normal-appearing bone. Histologically, there were no signs of infection, and the histomorphometric analyses revealed that 28.6% and 38.7% had osseointegrated for the experimental and control implants, respectively. The difference was not statistically significant. It was concluded that chronically infected sites, such as those showing signs of periapical pathosis, may not be a contraindication for immediate implants, if certain clinical measures and preoperative and postoperative care are taken. Keywords: immediate implants, implants, IMZ, infected site, osseointegration