Award Date

December 2016

Degree Type


Degree Name

Master of Science (MS)


Dental Medicine

First Committee Member

Ronald Lemon

Second Committee Member

Stanley Nelson

Third Committee Member

Tanya Al-Talib

Fourth Committee Member

Edward Herschaft

Fifth Committee Member

James Mah

Sixth Committee Member

Debra Martin

Number of Pages



Background: The collum angle is an angular measurement of the difference between the longitudinal axis of the crown and the longitudinal axis of the root. The aim of this study was to determine the mean collum angles for all maxillary and mandibular anterior teeth. In addition, the collum angles of different molar and skeletal classifications were compared for each anterior tooth.

Methods: Based on patient records obtained from the University of Nevada, Las Vegas Department of Orthodontics and Dentofacial Orthopedics, 326 CBCT scans were selected and divided into four molar and skeletal classifications. The patients were divided into Class I, Class II division 1, Class II division 2, and Class III molar and skeletal classifications. For the molar classifications, each side of a patient’s mouth was considered a different sample, whereas in the skeletal classifications, both sides were classified in the same way. After the exclusion criteria, the total sample size used in this study was 652. The collum angles of all anterior teeth were then measured using the angular measurement tool built into Invivo 5.4.5’s software.

Results: The mean collum angles for the maxillary central incisors, lateral incisors and canines were 4.13± 6.17 degrees, 6.20±6.53 degrees and 1.11± 6.82 degrees, respectively. For the mandibular arch, the mean collum angle for the central incisors was 5.94±3.71 degrees. The mean collum angles for the mandibular lateral incisors and canines were 6.49±4.32 degrees and 7.82±4.73 degrees. A one sample t-test indicated that all of the collum angles in the anterior teeth were significantly different from zero. An analysis of variance (ANOVA) in conjunction with a Bonferonni post-hoc test was conducted between the molar and skeletal classifications. In the comparison with molar classifications, the maxillary central and lateral incisors were significantly different in the Class II div 2 malocclusion when compared to all other molar classifications. The Class II div 2 collum angle for the maxillary central incisor was 7.86±6.10 degrees, whereas the collum angle for the maxillary lateral incisor was 2.47±6.14 degrees. A similar result was seen in the comparison with skeletal classifications. The Class II div 2 maxillary central incisor had a mean collum angle of 8.91±5.98 degrees whereas the maxillary lateral had a mean collum angle of 1.82±7.15 degrees. A mean comparison between the skeletal and molar classifications indicated that the mean collum angles were not significantly different between the different types of classifications.

Conclusions: The mean collum angles found in anterior teeth were significantly different from zero. When comparing these collum angles between different molar malocclusions, the Class II div 2 maxillary central incisors had significantly larger collum angles, while the maxillary lateral incisors had significantly smaller collum angles. The larger collum angle found in Class II div 2 maxillary centrals may possibly be an etiological factor in the development of a deep bite. In addition, larger collum angles may limit biomechanical movements during orthodontic treatment. In particular, attention must be given to root proximity to the cortical plate. Extrusive, intrusive and torquing forces must be carefully examined in teeth with large collum angles in order to prevent root resorption, dehiscences and alveolar perforation during fixed appliance therapy.


Collum angle; crown to root angle; dental anatomy; orthodontics; torque


Biology | Dentistry