Abstract
Aim: To evaluate the presence of failures in prosthetic screws and whether these failures are related to the type of prosthesis, abutment angulation and presence or not of intermediate. Methods: Two-hundred and sixty-seven patients were evaluated at the Federal University of Santa Catarina, totaling 971 external hexagonal implants in place for at least one year. A Tobit regression model for censored variables was used and the explanatory variables were subjected to percentage analysis. Results: The results demonstrated a relationship between the failure in prosthetic screws and the investigated factors with a significance of F=0.003 and p<0.05. The percentage analysis showed that the prosthetic screw failed in 8.82% of 238 unitary prostheses and 10.1% of 773 multiple prostheses. Among 912 abutments, 9.43% failed and in the 59 angled abutments, failures appeared in 15.25%. A total of 200 prostheses were placed over the implant platform and 13% failed. A total of 771 prostheses were made over abutment and 8.95% of these screws failed. Conclusions: Through multiple linear regression it could be concluded that the type of prosthesis showed no significant influence on the prosthetic screw failure, but other variables were related to this mechanical failure. There was a significant relationship among the variables, demonstrating the need for greater attention in choosing the type of prosthesis, the abutment angulation and whether the prosthesis will be placed directly on the implant platform or on the abutment.
Highlights
It is evident that due to the high survival rates that the implant-supported prostheses are fully accepted today as a reliable treatment option for the replacement of single or multiple missing teeth[1]
Some complications are mentioned in several studies including screw loosening and screw, veneer, abutment, framework and implant fractures, and fracture of the luting cement[2]
To reduce some of these complications, internal connection systems were developed to improve the biomechanical properties of implant-abutment joints and have shown significant biomechanical advantages over external-hex connection[2]
Summary
It is evident that due to the high survival rates that the implant-supported prostheses are fully accepted today as a reliable treatment option for the replacement of single or multiple missing teeth[1]. Some complications are mentioned in several studies including screw loosening and screw, veneer, abutment, framework and implant fractures, and fracture of the luting cement[2]. Screw loosening is recognized as one of the most evident complications[3], like fractures of the veneering material[4]. The reasons for screw loosening include fatigue, inadequate tightening torque, inadequate prosthesis fit, poorly machined components, vibrating micro-movement and excessive loading[2,5]. External hexagon connection systems have been considered more prone to screw loosening as a result of their mechanical properties under dynamic load. To reduce some of these complications, internal connection systems were developed to improve the biomechanical properties of implant-abutment joints and have shown significant biomechanical advantages over external-hex connection[2]
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