Three-dimensional anatomy of equine incisors: tooth length, enamel cover and age related changes

Abstract

BackgroundEquine incisors are subjected to continuous occlusal wear causing multiple, age related changes of the extragingival crown. It is assumed that the occlusal wear is compensated by continued tooth elongation at the apical ends of the teeth. In this study, μCT-datasets offered the opportunity to analyze the three-dimensional appearance of the extra- and intraalveolar parts of the enamel containing dental crown as well as of the enamel-free dental root. Multiple morphometric measurements elucidated age related, morphological changes within the intraalveolar part of the incisors.ResultsEquine incisors possess a unique enamel cover displaying large indentations on the mesial and distal sides. After eruption tooth elongation at the apical end outbalances occlusal wear for two to four years resulting in increasing incisor length in this period of time. Remarkably, this maximum length is maintained for about ten years, up to a tooth age of 13 to 15 years post eruption. Variances in the total length of individual teeth are related to different Triadan positions (central-, middle- and corner incisors) as well as to the upper and lower arcades.ConclusionEquine incisors are able to fully compensate occlusal wear for a limited period of time. However, after this ability ceases, it is expected that a diminished intraalveolar tooth length will cause massive changes in periodontal biomechanics. The time point of these morphodynamic and biomechanical changes (13 to 15 years post eruption) occurs in coincidence with the onset of a recently described destructive disease of equine incisor (equine odontoclastic tooth resorption and hypercementosis) in aged horses. However, further biomechanical, cell biological and microbiological investigations are needed to elucidate a correlation between age related changes of incisor morphology and this disease.

Radiological prevalence of equine odontoclastic tooth resorption and hypercementosis

“…The still very high prevalence of EOTRH in our study is comparable to that of FORL in cats [11,12,15], but different than the very low prevalence of MIRR in humans [14]. The total length of normal incisor teeth begins to decrease when the occlusal wear continues while elongation ceases from a tooth age of 13-15 years post-eruption [16]. Although, occlusal wear and excessive mechanical stress of the periodontal ligament in the ageing incisors are currently considered important factors initiating the disease [6][7][8]16,17].…”

“…These findings suggest that the observations made by Schrock et al [16] might not be a necessary precondition, but rather a predisposing factor. These findings suggest that the observations made by Schrock et al [16] might not be a necessary precondition, but rather a predisposing factor.…”

“…The aetiology of EOTRH is still unknown. Considering that in the fairly comprehensible time frame in which the equine incisors begin to be exposed to fundamental biomechanical changes within the periodontal ligament, it might be expected that no horse younger than 15 years has any radiological signs of the disease, if these changes are a necessary precondition for the onset of EOTRH as suggested by Schrock et al [16]. The total length of normal incisor teeth begins to decrease when the occlusal wear continues while elongation ceases from a tooth age of 13-15 years post-eruption [16].…”

“…However, it seems to have a correlation with the tooth age and is considered to be multifactorial [6,16,17]. However, it seems to have a correlation with the tooth age and is considered to be multifactorial [6,16,17].…”

Equine dental and periodontal anatomy: A tutorial review

“…It has recently been shown that the shape of incisor pulp canals ranges from tubular to mesiodistally flattened (Schrock et al . ). These canals are mostly unbranched in the upper incisors, but small side branches are present in the apical aspect of the pulp canal of the lower incisors (Schrock et al .…”