Thickness of Enamel at the Base of Pits and Fissures in Human Molars and Bicuspids

¹ Eastman Dental Dispensary, Rochester, New York

The pattern of distribution of deeply invaginated pit and fissure areas and the enamel thickness at the base of these areas in a pooled sample of 40 upper and lower first and second molars and 12 upper first and second bicuspids was investigated, using 1,312 undecalcified semiserial sections and a graphical reconstruction technique, as follows: (a) imaginary planes of section which followed the fissure area of each tooth were drawn on co-ordinate paper, from measurements obtained from enlarged tracings [see figure in the PDF file] of each of the 1,312 sections; (b) from these planes and their associated sections, three graphs were drawn for each of the 52 teeth, representing true enamel thickness, probe enamel thickness, and ideal enamel thickness, along the length of each fissure; (c) these individual graphs were combined to construct average curves, which showed the distribution of enamel thickness along the length of a fissure.

In all but one of the 52 teeth examined, the presence of deeply invaginated fissure areas was noted. Although there was no fixed relationship between tooth morphology and distribution of these areas, they were present to about the same extent in the molar and upper bicuspid teeth sectioned. The use of a dental probe to gauge the thickness of enamel in such areas is bound to give the clinician a misleading impresion, since the thickness estimate could be optimistic by a factor of six times in the molars and five times in the bicuspids.

The contour of the occlusal opening of the fissure corresponded to the contour of the underlying dentinoenamel junction but not to the contour of the enamel surface along the fissure base.

This study shows that areas of deep invagination in the enamel are much more prevalent than was hitherto suspected. If a tooth has an occlusal surface containing pits and/or fissures which will admit even the point of a probe, there is every likelihood that such a tooth will contain some areas of deeply invaginated enamel. Our investigations of these areas lead us to the conclusion that the presence of these areas in teeth is normal and tends to discount the contention that they are structural malformations or the result of some hypoplastic condition or developmental anomaly.

The fact that teeth can be free of caries despite the presence of these areas is worthy of further investigation of possible factors responsible for this apparent immunity. Furthermore, the widespread existence of these areas, coupled with the high and early incidence of decay in the pit and fissure areas of posterior teeth, suggests the need for research to develop materials which could be applied dirctly to the natural fissure, to seal over these ubiquitous food traps, somewhat along the lines of Hyatt's original suggestion but without the operative work involved.