EXPERIMENTAL COMPARISON OF THE DEGREE OF FIXING SCREW TIGHTENING FOR FULL ZIRCONIA CROWNS SUPPORTED BY STRAIGHT IMPLANTS, STRAIGHT IMPLANTS WITH ANGLED ABUTMENTS, AND ANGLED IMPLANTS WITH DIFFERENT PLATFORM INCLINATIONS. IN VITRO STUDY

Abstract

ABSTRACT
 Background: Success of immediate implant placement in the area of maxillary central incisor greatly depends on the degree of tightening of the fixing screw of the fully zirconia crowns. For treatment of this kind, clinicians use implants of various designs and implants with angled abutments to bypass anatomical limitations, achieve primary implant stability, and fabricate a screw-retained crown. However, the crown fabricated for the implant placed can experience non-axial loads during occlusion, which can lead to screw loosening and adversely affect treatment success, especially in the early post-operative period.
 
 Objective: to perform a comparative analysis of the effect of cyclic loading on the reliability of the fixing screw in full zirconia crowns supported by angled implants with platform inclination of 12, 24, 36, by straight implants and straight implants with angled abutments.
 
 Materials and methods: the degree of the prosthetic screw tightening was studied in 30 samples, 6 groups of 5 implants (straight implants, straight implants with standard 17 angled abutments and 12 custom abutments, angled implants with platform inclination of 12, 24, and 36. A full zirconia crown of maxillary central incisor was fabricated and fixed on every implant and subsequently exposed to cyclic loading up to 1*106 cycles. Afterwards, the maximum unscrewing torque was determined for each group. Statistical analysis was carried out.
 
 Results: the minimum values of the maximum torque were 20.8040.01 N/cm for the group of straight implants with 17 angled abutments, and the maximum values for the group of straight implants were 22.820.04 N/cm. There was no significant difference in values between the straight and angled implant groups. However, the values in these groups were higher compared to the groups of implants with angled abutments.
 Conclusion: the study showed that fixing screws are more reliable in crowns supported by straight implants and angled implants with different platform inclinations. Therefore, these implants are the most preferred option for immediate implant placement in the anterior region.