The International Journal of Oral & Maxillofacial Implants, 05/1997

.

The stability and degradability of hydroxyapatite coatings on dental implants depends on the dissolution of the individual chemical phases. Hydroxyapatite-coated dental implants exhibit a range of amorphous-phase content. Two tests were conducted to observe the course of coating degradation. The first test showed degradation of both crystalline and amorphous coatings by cracking and dissolution after immersion in Ringer's solution. Concomitant saturation of the implants in the solution modified the coated surface with precipitated crystalline apatite. A second test, intended to replicate the conditions of infection by decreasing pH, illustrated preferred dissolution of the amorphous phase, liberating crystalline segments. It is expected that morphologic changes could influence the rate of bone bonding and therefore could alter or control implant-tissue interactions

Mechanical testing of the implant-tissue interface has been the focus of numerous investigations concerning the anchorage capacity of implants. The purpose of this study was to measure reverse-torque failure after 6 months of healing for three different biomaterials in the posterior jaws of four adult female baboons. The animals had all of their posterior teeth surgically extracted and, following 10 weeks of healing, 7 implants were placed in each quadrant. The biomaterials included titanium plasma-sprayed surfaces, titanium-aluminum-vanadium surfaces (both 3.8 mm x 10 mm), and a commerically pure titanium surface (3.75 mm x 10 mm). After 6 months, torque data were collected using a counterclockwise computerized torque driver and were analyzed by repeated measures analysis of variance for differences related to biomaterial, jaw, and biomaterial/jaw. Post-hoc Tukey Dramer analysis was also performed for within-group differences (a = .05 level). The biomaterial comparison reveal ed a significant difference between the titanium plasma-sprayed and the combined commerically pure titanium/titanium-aluminum-vanadium groups (analysis of variance, Tukey Kramer, P .05). The jaw comparison showed no significant difference, although the data suggest that higher forces may be required for mandibular torsional failure. The biomaterial/jaw comparison revealed that jaw differences for the mean values of commercially pure titanium and titanium-aluminum-vanadium implants were gre ater than jaw differences for mean values of titanium plasma-sprayed implants, although these differences were not statistically significant. Because of the lack of correlation between single-cycle biomechanical tests and clinical performance, it is necessary to be selective in assigning usefulness to data of this type.

This study was designed to evaluate bone formation and reosseointegration following surgical implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in peri-implantitis defects. Hydroxyapatite-coated dental implants were placed bilaterally in the mandibular and maxillary premolar area in four rhesus monkeys and were allowed to osseointegrate for 1 year. Cotton ligatures were then placed around the healinga butments, and plaque was allowed to accumulate for 11 months. Resulting circumferential peri-implantitis defects exhibited a large intrabony and horizontal component. At reconstructive surgery, peri-implantitis defects in contralateral jaw quadrants were randomly assigned to receive rhBMP-2 (0.43 mg/mL implant volume) in an absorbable collagen sponge carrier or a carrier control. The animals were sacrificed 4 months postsurgery, and block sections were preared for histometric analysis. Summary statistics included means calculated per animal. Paired t tests were used to evaluate differences between experimental conditions (n = 4). Defect depth amounted to 3.4 ± 0.9 mm and 3.2 ± 0.9 mm for rhBMP-2 and control defects, respectively. Vertical bone gain in rhBMP-2 defects (2.6 ± 1.2 mm) was significantly greater than in controls (.08 ± 0.8 mm; P .01). Reosseointegration within the confines of the defect for rhBMP-2 defects (29.0 ± 10.5%) differed significantly from that in the control (3.5 ± 2.5%; P .01). Reosseointegration within the extent of newly formed bone averaged 40.0 ± 11.0% in rhBMP-2 defects as compared to 8.9 ± 7.8% in the control (P .01). Osseointegration in resident bone amounted to 69.5 ± 6.9% and 72.6 ± 8.0% for rhBMP-2 and control defects, respectively. There is significant evidence that rhBMP-2 has potential to promote bone formation and reosseointegration in advanced peri-implantitis defects in a demanding nonhuman primate model.

The purpose of this study was to clinically evaluate experimental peri-implant breakdown. Hydroxyapatite-coated, titanium plasma-sprayed, and machined titanium-alloy surfaces were investigated. Eighty-four implants were placed in 14 beagle dogs. Pocket proving depths and clinical attachment level and mobility measurements were made. Dogs were sacrificed at 3 and 6 months. All experimental implants showed a significant loss in clinical attachment level (P .05). Increased pocket probing depths for experimental implants occurred during the first 2 months, after which a plateau was reached. At the 3- and 6-month evaluation, pocket probing depths at experimental implants were significantly increased (P .05). No differences among the three implant types were noted for clinical ttachment levels and pocket probing depths. In general, greater mobility was found with the titanium-alloy implants than with hydroxyapaptite-coated and titanium plasma-sprayed implants (P .025). In addition, mobility measurements were significantly greater for experimental titanium-alloy implants during the frist 3 months (P .05). Clinical attachment level measurements were most sensitive to peri-implant status. All implants were equally susceptible to ligature-induced peri-implant breakdown. Consequently, meticulous oral hygiene and regular maintenance care are prerequisites for successful implantology.

The role of reactive oxygen derivatives (hydroxy peroxide, hydroxyl radical, and singlet oxygen) on the precipitation of inorganic and organic complexes onto the surface of titanium implant alloys is discussed in this review. In addition, the effect of possible implication of several biologic entities surrounding the implant on the implant-tissue interface constituents is described. Evidence from relevant studies suggests that local microenvironmental byproducts and factors associated with the inflammatory response resulting from the implant-induced tissue insult may enhance the expressivity of the inherent, clinically important property of titanium to form oxides. Growth of titnium oxide may be explained through several processes derived from biologic, thermodynamic, and electrochemical approaches. The models proposed to interpret this phenomenon are often contradictory, demonstrating inward or outward from the bulk material passive film growth, with increasing or self-limiting levels of oxide formation as a function of time. However, in vivo observations are consistent with aging-induced thickening of the complexes precipitated on the implant material surface. This review attempts to clarify several critical issues pertaining to passive film formation and kinetics on titanium-alloy surfaces.

Implant-supported prostheses may benefit from the versatility of design and favorable appearance offered by telescopic restorations. This project investigated the effectiveness of 208 abutments designed and produced by Dental Imaging Associates and the 73 prostheses supported by them over a 2-year period. No complications were found in the single-tooth group, although the sample was small (n = 7). Only 8.17% of the 208 abutment screws became loose during the initial postloading period. Once retightened, 2.4% of the total loosened for the second time. Higher screw-loosening rates were found in maxillary restorations, while the inclusion of a distal cantilevered pontic produced a significant increase in maintenance requirements.

This randomized, split-mouth design study evaluated the adjunctive effect of allogeneic, freeze-dried, demineralized bone matrix on guided bone regeneration in a critical-size, supra-alveolar, peri-implant defect model. Cont ralateral supra-alveolar peri-implant defects, 5 mm in height, each including two titanium implants, were surgical ly created in five beagle dogs. Demineralized bone matrix in autologous blood eas placed over the implants in one randomly selected mandibular jaw quadrant. A s pace-making expanded-polytetrafluoroethylene membrane was used to provide guided bone regeneration bilaterall. Following a 16-week healing interval, tissue blocks were harvested and prepared for histometric analysis. Differences between experimental conditions (guided bone regen eration sites with and without demineralized bone) were evaluated using paired t tests (n = 4). Demineralized bone particles were discernible, with limited signs of resorption. The bone matrix particles appeared to be solidified within a dense connective tissue matrix and in close contact with the implants. Limited matrix remineralization was apparent adjacent to the alveolar crest. No statistically significant differeces were found between experimental conditions for any parameter examined. Peri-implant defect height averaged 5.0 ± 0.2 mm and 4.9 ± 0.4 mm, vertical bone regeneration 1.5 ± 0.9 mm and 1.1 ± .04 mm, osseointegration within the extent of the defect 10.0 ± 3.9% and 15.3 ± 5.3%, osseointeg ration within the extent of regenerated bone 30.4 ± 13.7% and 52.1 ± 17.9%, and osseointegration within the alveolar base 68.6 ± 13.1% and 74.4 ± 7.1% for guided bone sites with and without demineralized bone, respectively (P .05). The results suggest that freeze-dried demineralized bone has no adjunctive effect on guided bone regeneration in supra-alveolar peri-implant defects, that guided bone regeneration has a limited potential to enhance alveolar regeneration in this defect model, and that a 16-week healing interval appears insufficient for turnover and maturation of demineralized bone under provisions for guided bone regeneration.

Seventeen oral cancer patients (47 to 78 years, mean 67) were treated with external radiation in areas that included future implant sites. Implants were placed in the irradiated jaws after a period of 18 to 228 months (mean 88 months). The patients received 103 implants and were followed to 1 to 62 months (mean 21 months) after implant loading. The cumulative survival rate of the implants after 1 year was 97% in the mandible and 92% in the maxilla. While the irradiation dose used did not affect implant survival, this result may possibly be influenced by th e addition of hyperbaric oxygen treatment for patients receiving more than 50 Gy. Irradiation for treatment of oral cancer does not seem to reduce the survival rate of implants as compared to those placed in the nonirradiated jaw.

In this study, the phenotypic expression of osteoblast progenitor cells, 2T9, on characterized titanium surfaces was examined in the rpesence of a bone morphogenetic protein-2 (BMP-2). X-ray photoelectron spectroscopy spectra indicated the presence of titanium dioxide on titanium surfaces, along with surface contaminants such as carbon and nitrogen. In the in vitro study, the activity of BMP-2-treated osteoblast cells on titanium surfaces was mar ked by significantly higher alkaline phosphatase-specific activyt and 1,25 (OH2) vitamin D3-stimulated osteocalcin production when compared to the untreated cells on titanium surfaces.

A patient with a severely atrophic right posterior mandible had three endosseous implants placed in conjunction with transposition of the inferior alveolar nerve. Three weeks following implant placement surgery, the patient experienced a spontaneous fracture of the mandible involving the two anterior implants. The two implants were removed, and the fracture was treated with open reduction and fixation with titanium mesh. The fracture healed, and the posterior implant integrated. This report suggests that the buccolingual and superior-inferior position of the mandibular canal can increase the possibility of mandibular fracture by increasing the size of the buccal cortical plate that is removed to expose the nerve during surgery.

In this study, various luting agents were evaluated to determine their retentive strengths as they pertain to the CeraOne single-tooth implant system. Ten samples of five different luting agents (zinc oxide-eugenol, glass-ionomer cement, hybrid glass-ionomer cement, composite resin, and zinc phosphate) were tested for retentive strength of the CeraOne gold cylinder to the CeraOne abutment. Under the conditions of the experiment, zinc phosphate showed a mean retentive strength 164% greater than that of glass-ionomer cement and 49% greater than that of composite resin cement. Scanning electron micrographs were taken to evaluate the effect of various luting agents on marginal opening. The measurements revealed that zinc phosphate had the greatest marginal opening, although its mean value of 62 µm is within clinically acceptable limits. Keywords: CeraOne, luting agents, marginal opening, retention

Twenty-five tooth and implant sites in nine patients were investigated for the presence of putative periodontopathic organisms, using specific DNA probes for Actinobacillus actinomycetemcomitans, Porphromonas gingivalis, Prevotella intermedia, Eikenella corrodens, Fusobacterium nucleatum, Treponema denticola, and Campylobacter recta. Five of nine patients showed a likelihood of transmission from tooth to implant sites. These patients also showed a high number of putative periodontopathic organisms present in the tooth sites tested. A significant risk was found of transmitting putative periodontopathic organisms from periodontitis sites to implant sites in the same mouth. An appropriate clinical protocol needs to be developed to address this issue. Keywords: cross-infection, dental implant, DNA probe, osseointegration, microbiology

In the posterior partially edentulous jaw, implants may be used to supplement existing natural dentition. Frequently, the maxillary sinuses and the mandibular nerve preclude the fabrication of freestanding implant-retained prostheses. However, if an implant and a natural abutment are combined, a fixed prosthesis can be fabricated, restoring the arch into the premolar area. The histories of three patients with attachments connecting implant-retained ceramotitanium crowns with crowns on natural abutments are described. A design for a rigid custom-made attachment for the Brånemark system, using standard components with a machine-duplication, spark-erosion technique, is suggested. Keywords: combination with natural teeth, dental implants, precision attachment

Implant-supported prostheses offer a solution to the problems experienced by edentulous patients with Sjögren's syndrome. These patients often find it very difficult, if not impossible, to wear conventional complete dentures. Three clinical reports provide an insight into some of the difficulties involved in treating patients afflicted with this complex multifactorial disease using the Brånemark system. Keywords: implant supported prostheses, osseointegrated implants, Sjögren's syndrome

A bone-splitting technique used for anterior single-tooth replacement was evaluated in 54 patients and 68 sites. The cumulative rate of implant survival was 93.7% (SE 4.5%) after more than 4 years. The decrease in marginal bone height ranged from 0.8 to 1.3 mm. Some reaction of the bone levels around the adjacent teeth should be anticipated (.03 to 0.5 mm). It was concluded that the bone-splitting procedure is a safe and predictable technique when performed carefully on selected patients and with the proper instrumentation. The procedure seeks to reconstruct the labial contour of the alveolar process, which is a prerequisite for optimal and lasting implant esthetics.