Microscopic examination of the horse teeth and their surrounding tissues. Part II: Histology of the cheek teeth

In the 2nd part of the microscopic examination of equine teeth, the histology of the cheek teeth together with their neighbouring tissues is presented. On 3 in situ perfusion fixed horses heads aged 5, 2 and 13 years the cheek teeth P4 and M1, in particular, were examined and resulted in unchanged normal findings. The selection concerned teeth that were frequently diseased. The age groups were the 5-year-old horse after permanent teeth replacement, the 2-year-old horse before replacement and the 13-year-old horse at an age when the longitudinal growth of the teeth is considered complete. In the 2-year-old horse, the wolf tooth (P1) and the subsequent P2 were also examined. In addition, the apical stages of development on the permanent teeth and decay processes on the deciduous teeth could also be recorded. On the cheek teeth embedded in methyl methacrylate (MMA) without decalcification, series of longitudinal sections were taken from one half of the jaw and series of cross-sections from the crown to the apical root were taken from the other half of the jaw and stained with Giemsa. The cross-sections of the molars showed the shape of the enamel folds and the ear-like shape of the enamel cups together with their inner lining by cementum. The longitudinal sections also revealed the depth of the enamel cups and the enamel folds. In the caudal half of the cheek teeth, longitudinal sections showed the division of the pulp cavities into pulp grains and, towards coronal, the storage of secondary dentin. On the cross-sections, the division of the pulp cavity into mostly 5 pulp grains or pulp horns could be demonstrated towards apical. In general, it was possible to show all the hard tissues of the molars from dentin to enamel and cementum without loss of substance in their respective localisation. In the enamel cups of the molars, the inner part was often not completely filled with cementum; the possible cavities are usually in connection with the oral cavity, whose fluids and food residues can also lead to degradation processes of the hard tissues of the enamel cups. In the vicinity of the molars, the gums, the periodontium and the jaw bones could be seen in their natural position. In the upper jaw, the hard palate with the palatal artery, parts of the nasal cavity as well as the maxillary sinus and the infraorbital nerve could also be shown; in the lower jaw, the inferior alveolar nerve of the mandibular nerve was shown in its canal. The periodontium was also predominantly around 500 mu m thick on the molars. Apart from the Sharpey's fibres pulling towards the cementum apically, the periodontium contained mainly circularly running fibre bundles. The adjacent jaw bone in the upper jaw as well as in the lower jaw consists mainly of thin bone bellicles, which are only around 200 mu m wide. The mass of these bone tufts seems to give the molars enough support to withstand the chewing pressure. A "lamina dura" of the jaw bone in the vicinity of the molars could not be detected. The peripherally located compacta was clearly stronger in the mandible than in the bones of the maxilla. The topographical histology of the molars, similar to the histology of the incisors with their surrounding tissues, is intended to provide dental professionals with a more in-depth anatomical orientation.