Adequately Prepared? A Study Using an Innovative Computer Application to Measure Clinical Crown Convergence Angles...

This study examined the total occlusal convergence angles created for full coverage crown preparations by students at a UK dental school. Working casts of 82 clinical crown preparations were scanned using a 3D scanner. Stereolithographic files were uploaded to Preppr, a crown preparation analysis application. Mean bucco-lingual convergence angle were 19.6° (+/-11.7) and mesial-distally 17.8° (+/-11.1). Smallest bucco-lingual convergence angles were achieved for canine teeth with the largest on molar teeth. The smallest mesio-distal values were on canine teeth with the largest on molar teeth. Ideal total convergence angles (4-14°) were achieved in 23% of bucco-lingual preparations and 33% of mesio-distal preparation. Results for clinically acceptable angles (10-20°) were 30% and 40% respectively. There were no statistically significant differences between tooth types for mean bucco-lingual values. (p=0.623), mesio-distal mean values were statistically different by tooth type (p=0.003). Mean values for mandibular molars were significantly higher than for maxillary incisors (p=0.001) and mandibular molars had significantly higher values than maxillary canines (p=0.045). Results in this study were comparable to those of other students and qualified clinicians, with a minority of preparation achieving ideal values.