Microstructure of primary tooth dentin.

PURPOSE This study was performed to determine variations in dentin microstructure from primary anterior teeth at specific areas and depths in relation to the dentin enamel junction, (DEJ). METHODS Ten freshly extracted, non-carious primary maxillary anterior teeth were sectioned to provide two 1.0 mm x 1.0 mm matchsticks extending from the DEJ to the pulp chamber--one each from the central and distal regions of each tooth. Slices were prepared at distances of 0.15, 0.8, and 1.45 mm from the DEJ. Following polishing, each slice was examined in a wet scanning election microscope, (SEM) and tubule density, tubular diameter, and peritubular width were determined at nine grid locations. Statistical analyses were carried out using multi-factor ANOVA, Tukey's multiple comparisons, and linear regression to compare rates of change for each parameter. RESULTS Tubule numerical density consistently decreased with distance from the DEJ. Decreases of 11,800 mm2/mm for canine distal matchsticks were significantly greater (P < 0.05) than the rate of 4,400 mm2/mm for canine central matchsticks. Rates for the lateral incisors were not significantly different. Tubule diameters increased with distance from the DEJ at rates of 0.28 micron/mm and 0.39 micron/mm for canines and lateral incisors, respectively, and there was a corresponding decrease in peritubular width. Microcanals or giant dentin tubules, 5-10 microns in diameter were incidently found in varying numbers in the midline of 4 of 20 teeth examined, including central and lateral incisors, but not in canines. CONCLUSIONS The work shows substantial differences in the microstructure of primary dentin as compared to permanent dentin, substantial differences with location, and the relatively common occurrence of microcanals. Therefore, the area of solid dentin that is available for dentin bonding is significantly reduced, accounting for reported differences in bond strength. Such differences may be important factors in tooth sensitivity, susceptibility to trauma, and caries progression.