Effects of convergence of the axial walls on the retention of full veneer crowns

Effects of convergence of the axial walls on the retention of full veneer crowns Dr. F. Nejati Danesh* - Dr. M. Savabi ** - Dr. R. Darabi*** *- Assistant Professor of Dental Prosthodontics Dept. - Faculty of Dentistry – Isfahan University of Medical Sciences. **- Assistant Professor of Dental Prosthodontics Dept. Faculty of Dentistry – Isfahan University of Medical Sciences. ***- Resident of Dental Prosthodontics – Faculty of Dentistry – Shahid Beheshti University of Medical Sciences Background and Aim: Full veneer crowns are frequently used for damaged teeth restorations. The function and durability of full veneer crowns are affected by retention. Retention depends on several factors such as convergence angle of the prepared teeth, type of cement, casting frame and so on. The aim of this study was to evaluate the effects of axial walls convergence on the retention of full veneer crowns. Materials and Methods: In this experimental study, 69 brass models with 6˚, 12˚ and 20˚ convergence angles were made. The length of all models was 7mm with diameter of 6mm. Full metal crowns were made and cemented on these models. Then the crowns were detached from dies using an instron testing machine. The applied forced were recorded and data were subjected to ANOVA and Duncan tests for statistical analysis. Results: There were significant differences in the retention of the three different angles of convergence (P<0.0005). The retention decreased to almost one fourth from 6˚ to 20˚. There was also a reverse correlation between the convergence angle and retention. Conclusion: The development of optimal convergence for maximum retention of full veneer crowns in the mouth is difficult, on the other hand convergence is a necessity for work facilitation. Therefore, the development of convergence should be conducted according to its effects on retention and other influencing factors. Key words: Full veneer crown – Crown - Convergence angle.