Unilateral misfit effect on retention screw preload of implant-supported crowns

Objectives: Evaluate the effect of unilateral misfit at different levels on a crown-implant-retention screw system of implant-supported crowns fabricated with UCLA Co-Cr/plastic sleeve abutments. Methods: Hexed UCLA Co-Cr/plastic sleeve abutments were cast in Co-Cr alloy to fabricate 48 metallic crowns divided into four groups (n=12). In group A (control group) the crowns did not present misfit, but in groups B, C and D the crowns were fabricated with unilateral misfit of 50µm, 100µm and 200µm respectively. The crowns were attached by titanium retention screw with 30N/cm to external hexagonal osseointegrated implants embedded in acrylic resin. After 2 minutes the retention screw of each replica was submitted to detorque evaluation by an analogic torque gauge. Three retention screws were used to perform destorque evaluation at each replica and the procedure was repeated twice with each screw. So, each group was submitted to 72 detorque measurements. Data were evaluated by ANOVA and Tukey test (p<0.05). Results: All groups exhibited a significant decrease (p<0.05) in preload and the lowest decrease occurred in group A. Groups B, C and D were statistically significant different from group A (p<0.05), but there was no statistically significant difference between groups B and D (p>0.05). Conclusions: Crowns with unilateral misfit presented higher preload decrease than crowns completely fitted to osseointegrated implants.

Financial support: FAPESP (grant number 05/56804-4)