The International Journal of Oral & Maxillofacial Implants, 02/1997

This study was carried out to evaluate the efficacy of poly(lactic acid) and poly(glycolic acid) (PLA/PGA) resorbable membranes in conjunction with autogenous bone grafts when used for the treatment of implant dehiscences and/or fenestrations. Nine patients with a total of 18 implants participated. Nine implants were associated with dehiscences, and 9 with fenestrations; 16 implants were in the maxilla, and 2 in the mandible. Nine defects were treated with PLA/PGA membranes (test gorup), and the nine were treated with expanded polytetrafluoroethylene (e-PTFE) membranes (control group). Second-stage surgery was performed after 6 to 7 months of healing. Overall results of the regenerative therapy of the 18 defects showed a highly significant (P .001) defect reduction, with a 93.38% (SD = 15.88) bone fill. A slightly higher percentage of bone fill was found in the e-PTFE group (98.20%) than in the PLA/PGA group (88.56%), but the difference was not statistically significant (P = .207). This study demonstrated that resorbable PLA/PGA membranes can be equally effective as e-PTFE in the treatment of implan t dehiscences and fenestrations when associated with au togenous bone chips.

The aim of this study was to histologically evaluate and compare the treatment of ligature-induced peri-implantitis using guided bone regeneration, two bone grafts alone, or guided bone regeneration combined with one of the two bone graft materials. Mandibular premolars and first molars in seven beagle dogs were extracted. After placement of Branemark implants and connection of abutments, experimental peri-implantitis was induced. Flap surgery was performed, abutments were removed, and implant surfaces were treated with an air-powder abrasive unit. Bony defects were randomly treated with either (1) debridement only; (2) debridement plus resorbable hydroxyapatite; (3) debridement plus canine demineralized free ze-dried bone; (4) debridement plus guided bone regeneration; (5) debridement plus resorbable hydroxyapatite and guided bone regeneration; or (6) debridement plus canine demineralized freeze-dried bone and guided bone regeneration. Four months after surgery, a flap was elevated and the barriers were removed. One month later, the animals were sacrificed, and the implants with their supporting peri-implant tissues were processed for histologic evaluation. Guided bone regeneration procedures resulted in the greatest amount of new bone formation, followed by bone grafts alone, and flap debridement. There was no significant difference between guided bone regeneration and both guided bone regeneration/graft combinations in terms of bone regeneration; however, the guided bone regeneration/graft combinations resulted in a greater amount of reosseointegration than all of the other treatments. Therefore, the combination of guided bone regeneration with either demineralized freeze-dried bone or resorbable hydroxyapatite appears to be the treatment of choice for plaque-induced peri-implant defects.

The aim of this study was to compare the retention and release periods of the Nobel Biocare bar and clip (MBC), Nobel Biocare ball (NB), Zest anchor (ZA), Zest magnet (ZM), and Sterngold ERA (SE) attachments on an implant-retained overdenture model. The attachments were tested using two permanently placed Branemark implants on a test model that was attached to an Instron machine (cross-head spped 50.8 mm/minute). Each attachment had one part embedded in a denturelike housing, and the other part screwed into the implants. Dislodging tensile forces were applied to the housings in two directions imulating function: vertical and oblique. Eight tests were done in two directions with three samples of each attachment. The dislodging forces generated measurements of the peak load, break load, and displacement at peak load and break load. Release periods were calculated using displacements between th e peak load and the break load and the cross-head speed. Results showed the NBC to be significantly most retentive for the break load when subjected to vertical and oblique forces with mean values and standard deviations of 2104.5 ± 506.7 g and 1958.1 ± 165.4 g, respectively. Next most retentive was the SE, followed by the ZA and NB. The ZM was significantly least retentive (127.8 ± 7.0 g and 143.5 ± 19.7 g). For the release period, results showed the NBC to have significantly the fastest release period for vertical and oblique forces (1.86 x 10 to the negative third power and 7.35 x 10 to the negative fourth power minutes). The ZM significantly had the slowest release period for those forces (3.02 x 10 to the negative second power and 2.35 x 10 to the negative second power minutes). The data suggested that the NBC could be selected when a high degree of retention and fast release period are desired. The next most retnetive was the SE, ZM was the least retentive and had the slowest release period.

Thermal changes elicited during drilling and tapping procedures used in site preparation for screw-shaped and cylindrical implants were measured in vitro in blocks of bovine cortical femure bone. Heat-senstivie thermocouples were placed in the bone specimens at 4- and 8-mm depths and at a constant distance from the periphery of the drilling site; this distance was preset for each type of bur used. Rotary cutting was performed with 10-mm-long twist drills (2- and 3-mm diameter) and triflute drills (3.3- and 4-mm diameter) running at 4,500 rpm with external irrigation. A special guide drill was used to ensure unidirectional continuous drilling with a load of 2,000 g. In addition, the effect of irrigation was evaluated during tapping procedures with 10-mm-long taps used at 20 rpm. The greatest temperature increase was observed with the 2-mm twist drill at both 4- and 8-mm depths. Significantly greater temperature increase was noted at the 8-mm depth versus the 4-mm depth with the twist d rills. Such significant difference between temperature rise at the two different drilling depths was not observed with the triblute burs. The time interval require d for the maximum temperature reached during rotary cu tting to return to baseline values was two times longer for the 2-mm twist drill than for the 3.3-mm triblute bur at both drilling depths. No statistically significant differences could be found between the maximum temperatures generated when tapping was performed with and without irrigation at both 4- and 8-mm depths. It can be suggested that the geometry of triblute burs combines cutting efficacy with greater heat dissipation capabilities than twist drills at the drilling depths of 4 and 8 mm used in this study.

The purpose of this study was to assess the osseous response to implanted particles of an anorganic xenograft bone mineral. Bio-Oss, in six patients with severely resorbed alveolar ridges. The observation period varied between 9 and 44 months; in five of six patients, long-term bo ne regeneration around the implants was observed. Histolgoic examination of biopsy material obtained from the graft area showed Bio-Oss particles still present in all patients after the varying observation periods. This raises the question whether Bio-Oss may be regarded as a resorbable material, as previously reported.

Strain distributions that occur in the hard tissue in the region surrounding craniofacial osseointegrated implants are compared. Three commercially available implant designs were evaluated under both axial loading and axial loading with a moment in three bone configurations typical of the craniofacial region. The evaluations that used the finite element method indicated that for axial loading, the implant designs produced similar strain levels in each bone configuration. When moments as well as vertical loads were applied, the strains were three to seven times higher and variations among the designs were greater. The variations found were related to the amount of bone present in each situation, as well as the neck diameter of the implant involved.

Obturator prostheses require anchoring elements in the partially resected maxilla to provide stability and oronasal separation. Anchoring elements are usually overstressed because of the lack of collateral support. Intraoral titanium implants can provide additional retention and avoid mechanical overstress of the anchoring elements in the residual maxilla. Treatment with intraoral implants into the zygoma for the support of an obturator prosthesis is reported.

An experimental animal model is presented for the analysis of the influence of axial and nonaxial loading on bone remodeling around oral implants. Axial and nonaxial loading conditions were introduced by placing a bilaterally supported fixed partial prosthesis and a cativlever fixed partial prosthesis on two IMZ implants in the mandibles of beagle dogs. Quantitative and qualitative histologic analyses revealed different remodeling tendencies between the loading conditions. Axial loading induced a more uniform, histologically quiescent remodeling response that gradually deveased from the coronal aspect to the apex of the implant. Nonaxial loading elicited a more dynamic remodeling of the surrounding cortical and especially trabecular bone tissue.

The thin maxilla may present an anatomic limitation to the placement of endosseous implants. Separating the cortical plates and widening the alveolar ridge with simultaneous placement of implants is one surgical method for management of this problem. Guided tissue regeneration techniques may be used in conjunction with this ridge widening procedure.

Attachment clips are commonly used to provide retention for removable implant-supported overdentures. In this study, the effects of attachment clips on occlusal force transmission in four implant-supported overdentures with cantilever extensions were investigated using beam theory. Distributions of moments and of forces in overdenture, clips, cantilevered superstructure, and implants were calculated as functions of position, number, and stiffness of attachment clips. Three-, four-, and five-attachment clip configurations were analyzed. Results showed that maximum bending moments and forces in all components are strong functions of position, number, and retention of attachment clips, while the effects of attachment clip stiffness are negligible. Increasing the number of attachment clips from three to five results in a significant decrease of maximum bending moments in the superstructure and implant. For a wide range of attachment clip positioning, the maximum tensile force on the implans is as high as half the applied load. At least one attachment clip for all configurations is also subjected to tensile force, which can cause it to slip out from the superstructure and increase maximum bending moment in the superstructure and implants.

This report involves the retrospective evaluation of ITI implants placed by a group of 12 clinicians located throughout the United States. Of the 174 single implants placed in 129 patients, 151 implants (86.8%) were placed in posterior regions, and 23 were placed in anterior regions; 54.6% of the implants had a length of 10 mm or less. Ninety-two implants were restored with a screw-retained crown, and 82 were restored with a cemented crown (in function 6 months or longer). The survival rate at 6 months was 97.7%. Occlusal screw loosening had an 8.7% occurrence rate (no repeated loosening), and solid conical abutment loosening had a 3.6% occurrence rate (all in one patient). Significant radiographic bone loss was observed on 2.3% of the implants. Data suggest that ITI implants can be a satisfactory choice for posterior single tooth restorations.

In complex craniofacial reconstruction involving an implant-supported prosthesis, problems such as tumor recurrence may require additional surgical resection. The solution to such recurrence may be autogenous bone grafting or additional implant placement or both (after resection of the tumor) and revision of the prosthesis. Tumor recurrence was seen during an 11-year, 8-month follow-up of a 58-year-old woman who had had an extensive mid-face defect. The various treatments, including extraoral and intraoral prostheses, provided the patient with an acceptable quality of life without interruption in use of the prostheses.

This report presents the case of a teenager affected by hypohidrotic ectodermal dysplasia and rehabilitated with a fix ed maxillary partial prosthesis and mandibular overdenture supported by osseointegrated implants. Treatment had a major impact on patient's self-esteem, function, and esthetics.

A survey was undertaken to analyze implants placed in irradiated tissues. It was found that nine centers had placed 188 implants in 24 patients in Japan. Of 118 implants, 39 were in the maxilla, 71 were in the mandible, and 8 were in the orbital region. Seven patients underwent adjunctive hyperbaric oxygen treatment. The treatment decreased implant loss only in the maxilla. (The success rate without hyperbaric oxygen treatment was 62.5%, and that with hyperbaric oxygen treatment was 80.0% for the maxilla.) Implants 7 and 10 mm in length were at a greater risk of being lost than longer implants in the maxilla.