Influence of screw access on the retention of cement-retained implant prostheses.

STATEMENT OF PROBLEM: Many studies have compared cement-retained and screw-retained implant prostheses. One disadvantage of cement-retained crowns is the lack of predictable retrievability, which can be overcome by creating a screw access channel on the occlusal surface. PURPOSE: The purpose of this study was to evaluate the influence of a screw access channel on the retention of cement-retained implant prostheses. MATERIAL AND METHODS: Sixteen cast metal crowns were fabricated and divided into 2 groups of 8 specimens each: a control group (CG) comprising 8 cement-retained prostheses and an experimental group (EG) comprising 8 cement-retained prostheses with a screw access channel. Castings were cemented to abutments with RelyX U100, and the opening screw access channels of EG were filled with photopolymerized composite resin (Filtek Supreme XT). The tensile force required to separate the cemented castings from the abutments was measured after 24 hours of cementation with a universal load-testing machine (EMIC DL 2000). A significance level of 5% (α=.05) was considered statistically significant (Statistical analysis was performed by Kolmogorov-Smirnov non-parametric test and the Student t test). RESULTS: The mean force required to achieve the separation was 191 N for the control group (CG) and 161 N for the experimental group (EG). As shown by the nonparametric Kolmogorov-Smirnov test, the dependent variable followed a normal distribution (P=.923). The Student t test found no statistically significant difference (P=.353) between the groups. CONCLUSIONS: Fabricating cement-retained implant prostheses with screw access does not compromise or reduce the retention of the crowns.

Comparison of fit accuracy between Procera® custom abutments and three implant systems.

BACKGROUND: Although increase of misfit has been reported when associating implant and abutment from different manufacturers, Procera custom abutment has been universally used in clinical practice. PURPOSE: The purpose of this investigation was to compare the vertical gap of zirconia Procera® abutment associated with implants from the same manufacturer (Procera manufacturer) and two other implant systems. MATERIALS AND METHODS: Twenty-four zirconia Procera abutments were produced using computer-assisted design and manufacture and paired with (a) eight MK III, RP 4.1 × 10 mm implants (Nobel Biocare™, Göteborg, Sweden) - GNB group (Nobel Biocare group); (b) eight Try on, 4.1 × 10 mm implants (Sistema de Implantes, São Paulo, Brazil) - ES group (SIN experimental group) ; and (c) eight Master screw, 4.1 × 10 mm implants (Conexão® Sistema de Prótese, São Paulo, Brazil) - EC group (Conexão experimental group). A comparison of the vertical misfit at the implant-abutment interface was taken at six measuring sites on each sample using scanning electron microscopy with a magnification of 408×. One-way analysis of variance was used to test for differences, and Tukey's test was used for pair-wise comparison of groups (α = 0.05). RESULTS: Significant differences relative to average misfit were found when Procera abutments were associated with other implant manufacturers. The ES group and EC group did not differ significantly, but both demonstrated significantly larger average misfit than the GNB group (p = .001). The average misfit was 5.7 µm ± 0.39, 9.53 µm ± 0.52, and 10.62 µm ± 2.16, respectively, for groups GNB, ES, and EC. CONCLUSION: The association of Procera zirconia abutment with other implant systems different from its manufacturer demonstrated significant alteration of vertical misfit at implant-abutment interface.