Impact of abutment rotation and angulation on marginal fit: theoretical considerations.

PURPOSE: Rotational freedom of various implant positional index designs has been previously calculated. To investigate its clinical relevance, a three-dimensional simulation was performed to demonstrate the influence of rotational displacements of the abutment on the marginal fit of prosthetic superstructures. MATERIALS AND METHODS: Idealized abutments with different angulations (0, 5, 10, 15, and 20 degrees) were virtually constructed (SolidWorks Office Premium 2007). Then, rotational displacement was simulated with various degrees of rotational freedom (0.7, 0.95, 1.5, 1.65, and 1.85 degrees). The resulting horizontal displacement of the abutment from the original position was quantified in microns, followed by a simulated pressure-less positioning of superstructures with defined internal gaps (5 µm, 60 µm, and 100 µm). The resulting marginal gap between the abutment and the superstructure was measured vertically with the SolidWorks measurement tool. RESULTS: Rotation resulted in a displacement of the abutment of up to 157 µm at maximum rotation and angulation. Interference of a superstructure with a defined internal gap of 5 µm placed on the abutment resulted in marginal gaps up to 2.33 mm at maximum rotation and angulation; with a 60-µm internal gap, the marginal gaps reached a maximum of 802 µm. Simulation using a superstructure with an internal gap of 100 µm revealed a marginal gap of 162 µm at abutment angulation of 20 degrees and rotation of 1.85 degrees. The marginal gaps increased with the degree of abutment angulation and the extent of rotational freedom. CONCLUSIONS: Rotational displacement of the abutment influenced prosthesis misfit. The marginal gaps between the abutment and the superstructure increased with the rotational freedom of the index and the angulation of the abutment.

Retrospective analysis of bar-retained dentures with cantilever extension: marginal bone level changes around dental implants over time.

PURPOSE: The aim of this study was to retrospectively determine whether a relationship exists between the length of the distal bar extension and the amount of marginal bone loss around implants supporting cantilevered bar-retained dentures. MATERIALS AND METHODS: This study was performed using data from patients who had been restored with implant-supported cantilevered bar-retained prostheses. Panoramic radiographs were obtained annually starting at the time of prosthetic loading of the implants; the protocol included a 4-year observation period. Vertical changes in the bone level were measured on the mesial and distal of implant sites with respect to a defined reference point per implant system, and radiographic distortions were compensated. Statistical analysis was performed with the Wilcoxon signed-rank test, the Spearman rank correlation test, and the two-factor nonparametric analysis for repeated measurements. RESULTS: A total of 48 edentulous patients who were consecutively treated with 313 dental implants and rehabilitated with 66 bar-retained prostheses were included in the study. Implants were used to support 30 prostheses in the maxilla (172 implants) and 36 prostheses in the mandible (141 implants). These prostheses were supported by bars with distal cantilevers of up to 12 mm. Patients with bars without cantilevers served as the control group. After 4 years, mean mesial bone loss was 2.20 +/- 0.91 mm; for distal implant sites it was 2.31 +/- 1.05 mm. The number of implants inserted and implant length did not correlate with bone loss. Jaw (maxilla versus mandible) and implant system exerted a significant influence on the amount of bone lost within the first year. Cantilever length did not influence marginal bone loss. CONCLUSION: In this clinical study, no influence of the length of cantilever extensions on crestal bone loss was found. Within the limitations of the study, the results indicate that restorations with distal bar extensions up to 12 mm are an adequate treatment option for edentulous patients.

Effects of repeated manual disassembly and reassembly on the positional stability of various implant-abutment complexes: an experimental study.

PURPOSE: The purpose of this study was to evaluate rotational, vertical, and canting changes in the position of the rotation-safe component in the implant-abutment assemblies of five different implant systems (ITI, Steri-Oss, Camlog, Astra Tech, and Replace Select) after manual removal and reassembly. MATERIALS AND METHODS: Prefabricated stainless steel models were used for each implant system, into which six implants were fixated with polymethylmethacrylate resin. Rotation-safe abutments (components) were screwed into the implants according to the manufacturers' specifications. Three test persons with varying knowledge of the theory and practice of implant dentistry manually assembled and reassembled the implant-abutment joint using each system-specific screwdriver 20 times each. A coordinate reading machine was used to detect discrepancies in position after each reassembly in relation to a coordinate system. Rotational freedom, changes in vertical height, and deviations in angulation were assessed. Statistical analysis was performed based on the nonparametric analysis of variance of repeated measurements. RESULTS: The tested complexes showed rotational freedom that ranged from 0.92 to 4.92 degrees, with significant differences between the systems. Camlog was significantly different from all other systems tested regarding rotational freedom, whereas Steri-Oss, Astra Tech, and Replace Select showed no significant difference between each other because of their nondiscrepant mean degree of rotational freedom. Vertical alterations in position ranged from 1 to 83 microm. A statistically significant difference was detected between butt-joint and beveled implant-abutment connections, with ITI and Astra Tech showing no significant difference when compared to each other, but displaying a significant difference versus all other systems tested. Canting discrepancies were not significant, with no influence of implant system or test person clearly detectable. CONCLUSION: Three-dimensional changes in the location of the abutment in relation to the implant result after manual assembly and reassembly of the implant-abutment complex.

A retrospective analysis of sandblasted, acid-etched implants with reduced healing times with an observation period of up to 5 years.

PURPOSE: The aim of this study was to evaluate the success rate of 2 different implant systems with sandblasted and acid-etched modified surfaces loaded after reduced healing periods. MATERIALS AND METHODS: One-hundred seventeen patients with a mean observation period of 3.75 years (24 to 61 months) were included in this evaluation. Chart reviews of a standardized recall program were evaluated. All 532 placed implants showed an unloaded healing time of 6 weeks in the mandible and 12 weeks in the maxilla. At abutment placement a torque value of 35 Ncm was one of the primary variables, and the success of the implants over time was determined by the criteria of Buser et al. The survival was analyzed using Kaplan-Meier method, and the probability of an event within 1 group independent of time was evaluated using the chi-square test and Fisher exact test. RESULTS: Of the 532 implants, 235 were placed in female and 297 in male patients; 448 implants were located in the maxilla and 84 in the mandible. Three implants were lost prior to abutment connection in 3 patients. Life table analyses show an overall success rate of 99.4% at 5 years, as no implants were lost after abutment connection. There was no significant association of the implant type (P = .185), gender (P = .99), or jaw (maxilla/mandible; P = .06) and the survival of the implants within this study. CONCLUSION: Based on the data found in this investigation, it can be concluded that implants with sandblasted, acid-etched surfaces can be restored after a 6- to 12-week healing period with a high predictability of success.