Biomechanical evaluation of equine masticatory action: position and curvature of equine cheek teeth and age-related changes.

The equine cheek tooth battery is part of a very dynamic system. The aim of this study was to investigate whether the curvature and position of the teeth are also involved in such dynamical processes. The alveolar crest was labelled with a radiodense marker (48 cadaver heads, 15 skulls) and laterolateral radiographs were taken. Then a geometrical method was elaborated to determine a cheek tooth's curvature and its position by means of specific angles. This method respects the remarkable changes of the equine dentition throughout life by considering two items: (1) the alveolar crest was taken as a constant landmark, (2) the central axis of the curved dental crown was determined by calculation of a linear regression equation. This equation considered several geometrically determined points on the curved dental crown which had been marked in the radiographs. Our study yielded the following results: Mandibular cheek teeth became more curved with age, but their positions (represented by the so-called mesio-occlusal angle between tooth and alveolar crest) did not change significantly. In maxillary cheek teeth, however, the mesio-occlusal angle became larger with age (indication of change of dental position), while their curvature did not change. Even though changes of the dental position were not always statistically significant, they are discussed as being biologically/functionally relevant. The mandibular anticlinal tooth, i.e. the tooth positioned at a mesio-occlusal angle of about 90 degrees, was not in contact with the maxillary anticlinal tooth. Interestingly, the maxillary anticlinal tooth is known to cause most clinical dental problems.