Abnormal-Shaped Prisms in the Lingual Enamel of Human Permanent Incisor Teeth

Abstract

The tangentially polished surfaces of the outer enamel under the projections of the marginal ridges and the basal tubercle in the lingual side of maxillary incisor teeth, extracted from elderly periodontic patients, were observed by scanning electron microscopy after EDTA etching. In general, EDTA selectively erodes the prism sheath regions; however, our observations reversed this. It indicates that the prism sheath regions may have been penetrated by organic materials with minerals derived from saliva due to an exposure of the old teeth to the oral cavities for a longer duration since eruption and also the attrition for a longer period. The etched surfaces more or less showed a disordered orientation of enamel prisms. At the junctions of such disorders, there were scattered abnormal-shaped prisms including a spiral, a circle, and double borders. Moreover, the 'inner' prism-like sheaths of the double bordered prisms occasionally showed a circle or a dotted remnant other than an arcade, whereas the circular prisms frequently contained an arcade, a spiral, or a smaller circle in the 'outer' sheaths. These abnormal-shaped prisms are probably formed by the prism orientation disorders following the variable morphological changes of Tomes' processes during the formation of their enamel projections.