Microhardness measurements of teeth from German Shepherd dogs as an alternative method for age estimation

Introduction and Aims For age estimation of animals, the teeth are usually evaluated for the degree of abrasion and for radiological alterations. The aim of the present study was to measure the microhardness of enamel and dentin of extracted teeth from a certain dog breed and relate it to the known age of the animals. Material and methods From the macerated skulls of six German Shepherd dogs, euthanized at the age of 1.5, 2, 5, 8.5, 10 and 12 years, the canine tooth (C) from the left lower jaw, and the premolar (P4) from the right upper jaw were extracted. The teeth were resin-embedded without decalcification, and surface-polished 350 μm thick sections were cut in horizontal plane (C) and in axial plane (P4). Using the Vickers method, three microhardness measurements, respectively, were performed in the superficial, middle and deep zone of enamel and dentin in comparable regions at the mid-crown and above the neck of the teeth. The significance of the measured HV-values in relation localisation and age of the animals was statistically evaluated. Results The microhardness of the enamel ranged from 212 to 436 HV, and for dentin from 42 to 111 HV, resulting in higher values for the P4 in all animals. In the enamel of the canines, the mid-crown HV-values were significantly higher than above the neck, but always decreasing from the enamel surface to the enamel-dentin border. The dentin microhardness of the mid-crown was also significantly higher than above the neck. In the three younger dogs, the highest dentin HV-values were measured at the enamel-dentin border, while in the older dogs, microhardness significantly increased in the deep zone near the pulpal cavity. In the P4 enamel was significantly harder above the neck than at the middle of the crown, also with decreasing values from superficial to deep zone. At the tip of the P4 crown, enamel microhardness was also higher than at mid-crown. In the dentin of the P4 crown-tip the higest HV-values were measured, and in the P4 of all ages the dentin microhardness decreases from the enamel-dentin border towards the pulpal cavity. In the enamel regions of higher microhardness in both teeth of the German Shepherd dog a different pattern of enamel prisms was observed, similar to the highly specialized enamel of hyenas. With increasing age the microhardness of enamel in both teeth increased significantly (p≤0.05), while the increase in microhardness of dentin was not significant. Conclusions The measurement of microhardness proved to be a suitable method to show not only regional, apparently loading-dependent differences of HV-values in enamel and dentin, but also a significant relation to the age of German Shepherd dogs. Thus, measuring microhardness in teeth appears to be a new method for age estimation in animals which can be applied to teeth extracted in vivo or post mortem.