Abstract
The angle encompassed between opposing incisors in horses is assumed to decline with age. Previous studies merely consider the overall profile view of clinical crowns presuming a generalized angle, neglecting potential tooth position-dependent differences. Cephalometric measurements from 3D computed tomographic thick-slab reconstructions of single incisors within a global reference frame were used to determine clinical crown interincisal angulation (IIA) of 48 horses. Based on predefined dentoalveolar landmarks, IIA was defined as the angle enclosed by the respective labial axis of the clinical crown (LACC). A measurement repeatability analysis was conducted including a comparison of third incisor teeth IIA with data obtained by cephalometric implementation of previously described landmarks for third incisor teeth (lingual/palatal border). The age-related angle course and differences between tooth positions were investigated considering LACCs of permanent incisors. Determining IIA by LACCs exhibited a high level of reproducibility applying for all tooth positions (mean coefficient of variation = 0.65 %; mean SD ± 0.89°). The comparison method for third incisor teeth revealed two times higher mean dispersion of repeated measurements, P = 0.017. A non-linear model slightly increased predictability of angular changes over time as against linearity assumption. The angle decline was more distinctive in younger horses and appears to approach a final value in older ones. Third incisor teeth exhibited significantly higher angle decline compared to first and second incisor teeth, P < 0.0001. According to the results, age determination of horses using clinical crown IIA is not recommended. Rather, 3D cephalometry may provide a promising tool to determine interdental and dentofacial angles of distinct tooth positions in health and disease.
Highlights
Incisor clinical crowns have been used in many studies to investigate association of positional and morphological dental changes and the age of horses [1,2,3,4,5,6]
Studies reported that based on lateral profile views or photographs in young horses the angle forms a straight or vertical line [4, 5, 7,8,9] and with increasing age the angle becomes more acute [2, 7, 8, 10,11,12], remains obtuse [4, 5] or increases [13]
Exclusion criteria were: (a) horses scanned under general anesthesia, (b) ventral mandibular plane alignment not parallel to the underlying table during scanning, (c) relative horizontal jaw position not centralized, (d) image motion artifacts within the region of interest, (e) incisor or jaw fractures, (f) soft tissue interposition between incisors or (g) incisors not in contact, (h) crib-biting lesions, (i) incisor overbite, (j) overjet or underjet > half of the linguo-/palatolabial width of the occlusal table based on the previous dental examination in unsupported normal head position, (k) excessive diagonal malocclusion, and (l) horses with radiological signs of pathological incisor periodontal lesions
Summary
Incisor clinical crowns have been used in many studies to investigate association of positional and morphological dental changes and the age of horses [1,2,3,4,5,6]. Studies reported that based on lateral profile views or photographs in young horses the angle forms a straight or vertical line [4, 5, 7,8,9] and with increasing age the angle becomes more acute [2, 7, 8, 10,11,12], remains obtuse [4, 5] or increases [13]. Description of methodology, is either subjective, subtotal, or missing
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