The effect of casting procedures on rotational misfit in castable abutments.

PURPOSE: Misfit of implant components has been linked to restorative complications such as screw loosening. Although previous studies have shown a correlation between rotational misfit and screw loosening, the impact of casting procedures on rotational misfit is lacking. The aim of this in vitro study was to evaluate the effect of casting procedures on rotational misfit of cast abutments when compared to machined titanium abutments. MATERIALS AND METHODS: Forty-eight external hexagonal implants and 48 abutments were placed in 4 groups of 12 samples each: (1) machined titanium abutments, (2) premachined palladium abutments cast-on with palladium, (3) plastic burnout abutments cast with nickel chromium, and (4) plastic burnout abutments cast with cobalt chromium. Rotational misfit between the external hexagon of the implant and the internal hexagon of the abutment was measured using standardized techniques and recorded in degrees. Mean values for each group were analyzed with analysis of variance and Tukey test. RESULTS: The mean rotational misfit was 1.21 +/- 0.57 degrees for machined titanium abutments, 1.77 +/- 130 degrees for cast-on abutments, 1.98 +/- 0.72 degrees for cast NiCr abutments, and 2.79 +/- 1.13 degrees for cast CoCr abutments. Significantly greater rotational misfit was recorded with cast CoCr abutments when compared to machined titanium abutments (P < .05). CONCLUSION: Rotational misfit was less than 2 degrees for all groups except for cast CoCr abutments, which demonstrated a significantly greater rotational misfit.

A classification system to measure the implant-abutment microgap.

PURPOSE: A large microgap at the implant-abutment interface has been reported to result in adverse effects, including screw loosening, abutment rotation, and abutment fracture. However, a standardized classification of the implant-abutment interface has not been established. The purposes of this investigation were (1) to propose a classification system based on the horizontal and vertical microgap of the implant-abutment interface and (2) to compare the implant-abutment interface in 4 groups of abutments. MATERIALS AND METHODS: Forty-eight randomly selected external hexagonal implants were paired with (1) machined titanium abutments, (2) premachined palladium abutments cast-on with palladium alloy, (3) plastic burnout abutments cast with nickel chromium alloy, and (4) plastic burnout abutments cast with cobalt chromium alloy. A comparison of the horizontal and vertical microgaps at the implant-abutment interface was completed at 8 locations on each specimen to the nearest micrometer using an optical microscope with a magnification of 150x. Group means and significant differences between groups were determined by analysis of variance and Tukey multiple-comparisons post-hoc analysis. P < .05 was the threshold for statistical significance. RESULTS: There was no significant difference between groups with respect to vertical misfit. For horizontal misfit, machined titanium abutments presented significantly higher horizontal misfit compared to other groups (P < .001). Premachined cast-on abutments had significantly higher horizontal misfit than cast NiCr abutments (P < .001). In the proposed classification system, 23% of all sites measured at the implant-abutment interface had an ideal relationship, 34% had a horizontal discrepancy only, 4% had a vertical discrepancy only, and 39% had both vertical and horizontal discrepancies. CONCLUSION: The proposed implant-abutment classification system demonstrated a way to characterize and compare the microgap at the implant-abutment interface.

Effect of casting procedures on screw loosening in UCLA-type abutments.

BACKGROUND: Screw loosening of implant restorations continues to be a complication in implant prosthodontics. Screw joints are subjected to a loss of initially applied torque because of friction and component misfit. It has been suggested that the loss of applied torque is less in machined metal abutments than in cast plastic abutments. PURPOSE: This study compared the loss of applied torque (detorque) values in machined titanium and in cast UCLA-type abutments for external hex abutment/implant interface. MATERIALS AND METHODS: Four groups of 12 samples each were evaluated: (1) machined titanium abutments, (2) premachined palladium abutments cast with palladium, (3) plastic abutments cast with nickel-chromium, and (4) plastic abutments cast with cobalt-chromium. Each abutment was torqued to 30 Ncm according to the manufacturer's instructions and detorqued three times. The mean loss of applied torque (detorque) was recorded as a percentage of the torque applied. Group means were calculated and compared using ANOVA and Tukey's LSD test. RESULTS: Mean detorque values were (1) 92.3 +/- 2.9%, (2) 81.6 +/- 5.0%, (3) 86.4 +/- 4.6%, and (4) 84.0 +/- 7.0%. Machined abutments demonstrated significantly greater detorque values compared with all cast groups (p < 0.05). No significant differences were found among cast groups. CONCLUSION: Machined abutments retained a significantly greater percentage of torque compared with cast abutments. Casting procedures decrease the percentage of applied torque, which may influence final screw joint stability.

Programa de prevençäo do câncer bucal no município de Bauru, através do auto-exame / Oral cancer prevention through self-examination programme in Bauru - Säo Paulo

No município de Bauru, realizou-se um trabalho sobre prevençäo de câncer bucal, o qual constou de palestras e apresentaçäo de "posters" sobre câncer bucal e de como fazer o auto-exame da boca para detecçäo precoce de lesöes bucais. Após as palestras, os pacientes foram examinados nos Postos de Saúde de cada bairro visitado; ao final do estudo, observou-se que várias lesöes da mucosa bucal foram detectadas nos pacientes examinados, o que evidenciou a necessidade de o paciente fazer periodicamente um auto-exame da boca e que todo programa de saúde bucal deva incluir o diagnóstico precoce do câncer bucal