Molecular Structure of the Dentin-Enamel Junction Using Confocal Raman Microscopy

Objective: The dentin-enamel junction (DEJ) plays an important role to prevent crack propagation from enamel to dentin. This function stems from its complex structure which is different from either dentin or enamel. The molecular structural differences in both inorganic and organic matrices across the DEJ zone were investigated using 2-dimensional confocal Raman microspectroscopic mapping/imaging technique. Methods: Five extracted human third molars were cut bucco-lingually to get 2-3 mm thick slices using a water-cooled diamond saw. The slices with exposing DEJ were further polished with 600 grit sandpaper. Raman spectra were acquired at positions corresponding to 1 micron intervals across the dentin-enamel junction using the computer controlled x-y-z stage with a minimum step width of 50 nm. Results: The ratios of 1450(CH, matrix)/960(P-O, mineral) decreased gradually to nearly zero across the dentin-enamel junction. The width of this transition zone was dependent on the intratooth location, which was 12.94±3.28 microns at occlusal positions, 6.20±1.23 microns at cervical positions. The difference in width was significant (P<0.001). The spectral differences in both organic and inorganic matrices across the DEJ were also noted. For example, the ratios of 1243(amide III)/1450 (CH) were 0.56±0.06 within the DEJ, lower than the values (0.81 ± 0.02) in dentin. However, the ratios (1.17±0.08) of 1665(amide I)/1450(CH) within the DEJ were higher than those values (1.00± 0.02) in dentin (P<0.01). Conclusions: The results indicated that the intratooth-location-dependent structure of the DEJ may be related to its function. Micro-Raman spectroscopic/imaging analysis of the DEJ provides a powerful means of identifying the functional width and molecular structural differences across the DEJ. Supported by NIH K25 DE015281, R03 DE15735 and K23 DE01623.