Stresses in Implant-Supported Fixed Complete Dentures with Different Screw-Tightening Sequences and Torque Application Modes.

PURPOSE: To compare the effects of different screw-tightening sequences and torque applications on stresses in implant-supported fixed complete dentures supported by five abutments. MATERIALS AND METHODS: Strain gauges fixed to the abutments were used to test the sequences 2-4-3-1-5; 1-2-3-4-5; 3-2-4-1-5; and 2-5-4-1-3 with direct 10-Ncm torque or progressive torque (5 + 10 Ncm). Data were analyzed using analysis of variance and standardized effect size. RESULTS: No effects of tightening sequence or torque application were found except for the sequence 3-2-4-1-5 and some small to moderate effect sizes. CONCLUSION: Screw-tightening sequences and torque application modes have only a marginal effect on residual stresses.

Evaluation of the accuracy of 3 transfer techniques for implant-supported prostheses with multiple abutments.

PURPOSE: This study evaluated the deformation of a metallic framework connected to 15 stone casts fabricated using 3 transfer techniques to determine the most accurate impression procedure. MATERIALS AND METHODS: Five stone casts were made from polyether impressions of an epoxy resin master model for each transfer technique. Group 1 samples were created by the direct splinted technique (square transfer copings splinted with carbon steel pins and autopolymerizing acrylic resin, custom tray); group 2 samples were made by the direct nonsplinted technique (square transfer copings, custom tray); and group 3 samples were fabricated using the indirect technique (tapered transfer copings, custom tray). Sixteen strain gauges were fixed on the framework to measure the degree of framework deformation for each stone cast. Pairs of strain gauges placed opposite each other constituted 1 channel to read deformation (half Wheatstone bridge). Deformation readings were collected at the 4 segments between abutments in 4 directions (anterior, posterior, superior, and inferior). Deformation data were analyzed using analysis of variance and the Tukey test at the .05 and .01 levels of significance. RESULTS: Group 1 samples allowed the most accurate reproduction of analog position compared to the samples made using the other techniques. No significant difference was found between the direct nonsplinted (group 2) and indirect (group 3) techniques. DISCUSSION: Although some studies have evaluated transfer techniques with similar methodology, this study demonstrated the most suitable strain gauge setup to record framework deformations in all directions and simultaneously offset the effects of temperature variation. CONCLUSIONS: The direct splinted technique was the most accurate transfer method for multiple abutments compared to direct nonsplinted and indirect techniques.