Analysis of rotational angle on UCLA-burnout/Co-Cr abutment screws for one-piece-frameworks

OBJECTIVES: The aim is to compare the rotational angle degree of Grade V titanium screws during torque, retorque and detorque steps (Ncm) on one-piece cast frameworks obtained from UCLA burnout/Co-Cr machined collar abutments.

METHODS: Two external hexagonal implants(3.75x13mm) were secured to a metallic base and the wax patterns directly fabricated over them. The UCLA burnout/Co-Cr machined collar abutments were screwed to the implants and joined together with an acrylic resin bar. Ten samples for each abutment type were fabricated. 40 Grade V titanium screws were used in the test. The rotation angle degree was measured with the aid of an device and a computer software, during torque and retorque procedures, being the retorque made 10 minutes after the initial torque, both under 30Ncm. After the retorque procedures, the detorque values were measured. The overall sequence was made three times for each sample. SEM analysis at the implant-abutment interfaces were made before and after the tests(T), as well as on the screw surfaces. The Student's t test was used for between group analyses and the one-way ANOVA test for within group analyses; (P<.05).

RESULTS: During torque, the rotational angle degree was higher for screws used in the UCLA burnout than in the Co-Cr machined collar abutments. During retorque, the angle formed on the screw head was higher for the UCLA burnout than the Co-Cr machined collar abutments, being these differences statistically significant between the first and second screwing. The mean detorque values were higher in the UCLA burnout than in the Co-Cr machined collar screw abutments, but not statistically significant.

CONCLUSIONS:The SEM images demonstrated that the seating surface of the UCLA burnout abutments presented greater irregularities than the Co-Cr machined collar surfaces. Greater deformations were found at the seating abutment screw undersurfaces and in the first apical thread as well.