Occlusal Angles of Equine Incisors

The angulation of equine incisors is frequently used as a parameter for dental corrections. However, the term incisor angle is only vaguely defined, and no studies exist presenting a series of reliable measurements in individual incisors of multiple horses. The aim of this study was to establish an exact method to determine incisor angles and to test whether clinically accessible landmarks (facial crest and bars) are suitable to estimate incisor angles. Eighteen horses were used to create 3-dimensional (3D) reconstructions of the skulls from computed tomography (CT) data sets. Reference planes (median and transverse plane) were calculated using defined anatomical landmarks. Subsequently, occlusal planes for incisors and for incisor quadrants were calculated. Occlusal table angles were measured in relation to the reference planes. For each incisor, sagittal and transverse angles were measured. Mean values of individual incisor angles ranged from 3.5° to 6.8° (transverse angle) and from 32.6° to 44.9° (sagittal angle). No significant differences were detected in mean between the left and the right side when teeth in same Triadan positions were compared. However, in individual horses, marked differences between the left and the right side of the jaws occurred. Mandibular incisors showed significantly steeper sagittal angles than maxillary incisors. Furthermore, angles of opposing incisors were correlated with each other. The facial crest and the upper jaw bars featured a curved shape and were therefore of limited use to estimate the angulation of the upper incisors. In contrast, the lower jaw bars were suitable to determine the angulations of lower incisors.