Abstract
The retention of indirect dental restorations is of concern for clinicians as it influences the success of clinical outcomes. Retention and resistance are dependent on many factors including the convergence angles of the opposing axial wall tapers. Adequate axial wall taper is important in crown preparation to improve physical retention and increase resistance of the restoration. Aims and objectives To determine and compare the convergence angles (CA) of KaVo® teeth prepared for full coverage crown restorations by fourth year dental students in a preclinical fixed prosthodontics module in a five year dentistry training programme. Methodology Crown preparations produced by fourth year dental students at Sefako Makgatho Health Sciences University (SMU), South Africa, over a period of 3 years were included in this study. These preparations were digitally captured using CAD-CAM imaging technology. The images were analysed in ImageJ® software to determine the mesio-distal convergence angles. Statistical analysis was undertaken using SPSS ver. 27 for Windows. Results The overall mean convergence angle of 15.38° ± 6.68° was computed for n=75 crown preparations. ANOVA revealed a significant difference (p<0.05) in the CA among the three cohorts (2017: 16.87° ± 6.94°; 2018: 17.23° ± 6.13°; 2019: 12.02° ± 5.86°). A reasonable proportion of dental students n=25 (33%) achieved the recommended CA of 6° to 12°.ConclusionThis study indicates that with objective evaluation tools, it is possible to improve on the intended guidelines for crown preparations during undergraduate teaching and training in pre-clinical Fixed Prosthodontics.
Highlights
The retention of indirect dental restorations is of concern for clinicians as it influences the success of clinical outcomes
This study indicates that with objective evaluation tools, it is possible to improve on the intended guidelines for crown preparations during undergraduate teaching and training in pre-clinical Fixed Prosthodontics
The overall mean convergence angle of 15.38° ± 6.68° was computed for n=75 crown preparations
Summary
The retention of indirect dental restorations is of concern for clinicians as it influences the success of clinical outcomes. Retention and resistance are dependent on many factors including the convergence angles of the opposing axial wall tapers. The concept of retention and resistance form is of vital clinical concern because of the vectoring of occlusal forces that may be directed in both a lateral and/or apical directions during oral functioning.[1] Retention is the ability of a restoration to withstand removal forces along the long axis.[2] The term resistance form refers to the features of a tooth preparation that enhances the stability and durability of a restoration that affords it to resist dislodgment along an axis other than the path of placement.[3] The angle formed by the intersection of the mesial and distal axial wall tapers is routinely referred to as the convergence angle (CA) of a tooth preparation, and is the measurement of the combined taper of opposing axial walls. Retention and resistance dependent factors related to tooth preparation for full coverage restorations (FCR), include ensuring maximal cervical-occlusal height, appropriate surface texture of the preparation and most importantly, an acceptable CA.[4, 5] It is generally recognised that the smaller the convergence angle, the better the retention, and the greater longevity of the restoration.[6]
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