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Possmann Dias, Dominique (2005): Die Altersschätzung des Pferdes auf Grund morphologischer Veränderungen an den Zähnen: Eine Literaturstudie mit einem Lernprogramm zur Zahnaltersschätzung. Dissertation, LMU München: Tierärztliche Fakultät

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The study presented here is a survey of the current literature about age determination by examing teeth in horses since the publication of PESSINA (1810). The introductory chapter serves to give an overview of the anatomic structure and development of equine teeth. It is followed by a histographic literature summary of dental aging in horses from Greek antiquity to the present. The short introduction about the origin and the appearance of the criteria used for the determination of dental age according to the deciduous and permanent teeth, as well as the age related changes of canine, premolar and molar teeth, will be followed by an overall summary of dental age determination in horses. The majority of the named studies deals with the examination of Warmblood horses, however data from textbooks which do not specify the breed of the horses examined are also included. Following this analysis, the breed-related studies about English Thoroughbred horse, Arab, Trotter, Belgian draft, Ponies, Przewalski horse and donkeys are listed. According to these studies, the most useful and reliable signs to determine dental age in horses are the eruption of the deciduous and permanent incisors. PESSINAS (1810) comments about the change of incisors, according to which the age between 2 – 3 years for I1, 3 – 4 years for I2 and 4 – 5 years for I3, is correct except for some races. The change can be up to half a year late in the Mini-Shetland ponies and between a quarter and half a year in donkeys. In both these races the deciduous teeth also appear later. After the eruption of permanent incisors age determination by dental changes gets increasingly inaccurate. Literature confirms a constant correlation for the dental signs disappearance of cups, dental star, disappearance of marks, changes of shape of occluseal surfaces, direction of upper and lower incisor and changes of the occluseal arrow. Judging these characteristics can, because of high variability, only provide an approximate guess rather than an exact evaluation of the age. On the one hand there are inconsistent time frames given for these criteria, on the other hand there are often discrepancies where revisions are performed. There can be multiple factors responsible for the deviations that affect dental abrasion, the cause and the effect of which are still unknown to a large extend. Numerous studies were able to reveal racial differences but as other factors are often neglected in those studies it is difficult to associate factors and races. A clear connection between breed and the grade of dental shedding could be shown for Arab horses whose adamantine and secondary dentine consists of a harder grade. Therefore the dental wear is slower as in the Trotters and Belgium drafts which have been used for this comparison. The Galvayne´s groove and the hock in the upper corner incisor should have completely lost their meaning for the estimation of age in horses and shell only be mentioned for completeness. A reliable connection between age and appearance of both signs could not be confirmed in the surveyed literature. In conclusion, dental age determination in horses should be considered a method with considerable weaknesses. These shortcomings are inaccuracy and a high margin of error. The fact that it remains the only practible method which can aid in the age determination of an animal and that the obtained information is sufficient in most cases to be used in therapy and prognosis in a patient supports its further use. Considering all the previously mentioned factors it should be mentioned that the determination of the horses’ age is an estimation based on dental markers.