Comparison of the microstructure of crown and root dentin by a scanning electron microscopic study

Background/purpose: Detailed information of the dentin microstructure is essential in order to interpret data from investigations on dentin adhesive materials. Most studies of dentin microstructure focused on the crown dentin, and few compared microstructures of the crown and root dentin. The purpose was to compare the density and diameter of dentinal tubules and the thickness of peritubular dentin at the crown, and coronal and middle root. Materials and methods: Ten caries-free human lower first molars were sectioned into four parts as the chamber roof, chamber wall, coronal root, and middle root. After being immersed in 5.25% NaOCl solution for 30 minutes, sectioned surfaces were examined under a scanning electron microscope. Data of tubule density, diameter, and peritubular dentin thickness in the inner, middle and outer portions were collected. Friedman's nonparametric related sample test and Wilcoxon nonparametric signed rank post hoc test were used for data analyses. Results: Tubule densities of the inner and middle dentin of the root were significantly lower than that of the crown. Peritubular dentin width in the chamber roof was significantly higher than those in other areas of the tooth. Conclusion: Our findings show that the proportion of the tubular area is lower, and there is less peritubular dentin in the root dentin than in crown dentin. To achieve good bonding of resin to root dentin, it is potentially beneficial to focus on improving the quality of the hybrid layer rather than that of resin tags.