A LIGHT-MICROSCOPIC AND ULTRASTRUCTURAL EXAMINATION OF CALCIFIED DENTAL-TISSUES OF HORSES .2. ULTRASTRUCTURAL ENAMEL FINDINGS

Ultrastructural examinations defined 3 equine enamel types termed equi ne (Eq.) Types 1, 2 and 3 enamel, according to the transverse appearan ces of their enamel prisms and the amount and appearance of their inte rprismatic enamel. Eq. Type I enamel contained alternating rows of ova l shaped prisms and thick interprismatic enamel plates, and was found adjacent to the amelodentinal junction, Eq. Type 2 enamel consisted of circular, 'keyhole' to 'horseshoe' shaped prisms with little or no in terprismatic enamel and was located adjacent to the amelocemental junc tion. Eq. Type 3 enamel was composed of rounded prisms surrounded by l arge amounts of interprismatic enamel and was inconsistently present i n a thin layer at the amelodentinal and amelocemental junctions. Prism decussation was seen in the thickest peripheral enamel of the upper c heek teeth but was present throughout incisor enamel therefore making incisors highly resistant to cracking. Scanning electron microscopic e xamination showed enamel crystals to be cylindrical shaped on transver se section; however, on transmission electron microscopic examination these crystals had shapes, ranging from near oval to rectangular and f ormed small subunits, with crystals diverging from each other at vario us angles.