Dentin comparison in primary and permanent molars under transmitted and polarised light microscopy: an in vitro study

Dentin is the fundamental substrate of restorative dentistry and its properties and characteristics are key determinants of nearly all restorative, preventive and disease processes of the teeth. The intrinsic permeability of dentin is responsible for permitting bacterial or chemical substances to diffuse across the dentin and irritate the pulpal and periradicular tissues. Improved understanding of the dentin structure and nature will have important consequences for today's dental procedures. The aims of the study were to observe the direction of dentinal tubules, interglobular dentin, incremental lines of dentin and the dead tracts.

A total of 30 teeth (15 primary and 15 permanent molars), unrestored, noncarious, hypoplastic extracted molars were used. Longitudinal ground sections of teeth were obtained using hard tissue microtome.

Examination of ground sections of the primary teeth dentin showed "s"-shaped curvature in four (26.7%) specimens and a straight course of dentinal tubules in 11 (73.3%) specimens out of 15 teeth examined whereas in permanent teeth, all 15 (100%) specimens showed an "s"-shaped curvature. These results are statistically highly significant (P < 0.001).

Dentinal tubules followed an "s"-shaped course in all the 15 (100%) permanent molars and in four (26.7%) primary molars. There was no significant difference in the occurrence of interglobular dentin of primary and permanent molars. But, they were at angles in the primary teeth.