Maxillary central incisor crown-root relationships in class I normal occlusions and class III open and deep malocclusions

Introduction: The purpose of this study were several: (1) examine a new measurement for the angle of the maxillary central incisor called labial crown-root angle (LCRA) and correlate it with the accepted existing measurement, collum angle (CA), for different types of dental malocclusions; (2) establish average values for CA and LCRA for different types of dental malocclusions and compare them; (3) compare the amount of overbite and values for CA and LCRA for different dental malocclusions. Methods: 46 Class I samples, 20 Class III open bite samples and 22 Class III deep bite samples who met the criteria were examined using x-rays. Results: A strong correlation was found between CA and LCRA for all samples. The mean CA and LCRA for the Class III deep bite group was significantly different from the Class I normal core, Class I expanded and Class III open bite groups. There was no significant correlation between CA or LCRA and overbite within Class III open and Class III deep bite groups. Conclusions: LCRA and CA were highly correlated in Class III patients. Patients with Class III deep bites had statistically higher average CA and LCRA compared to Class I normal occlusions and Class III open bite malocclusions. There was no significant correlation between the measures for overbite and either CA or LCRA values in Class III patients. This information will help orthodontists identify and better treat patients with higher CA and LCRA values. We recommend LCRA as a better method of measuring the crown-root angle.