Chemical/molecular structure of the dentin-enamel junction is dependent on the intratooth location

Abstract

The dentin-enamel junction (DEJ) plays an important role in preventing crack propagation from enamel into dentin. This function stems from its complex structure and materials properties that are different from either dentin or enamel. The molecular structural differences in both mineral and organic matrix across the DEJ zone were investigated by two-dimensional confocal Raman microspectroscopic mapping/imaging technique. The intensity ratios of 1450 (CH, matrix)/960 (P-O, mineral) decreased gradually to nearly zero across the DEJ. The width of this transition zone was dependent on the intratooth location, with 12.9 +/- 3.2 microm width at occlusal positions and 6.2 +/- 1.3 microm at cervical positions. The difference in width was significant (P < 0.001). Concurrently, spectral differences in both organic and inorganic matrices across the DEJ were also noted. For example, the ratios of 1243 (amide III)/1450 (CH) within the DEJ were lower than the values in dentin; however, the ratios of 1665 (amide I)/1450 (CH) within the DEJ were higher than those values in dentin. In addition, the ratios of 1070 (carbonate)/960 (phosphate) within the dentin were lower than the values in the DEJ. Raman images indicated that the distribution of the above ratios across the DEJ zone were also different at occlusal and cervical positions. The results suggest 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.

Fig. 1

Representative photograph of a cross-sectional tooth slice illustrating where spectral maps were obtained at the buccal cusp and cervical area. A and B insets indicate buccal and cervical mapping areas.

Fig. 2

Representative Raman spectra of dentin and enamel.

Fig. 3

Representative Raman image of the DEJ based on intensity ratios of 1450/960 at occlusal positions (A) and at cervical positions (B).

Fig. 4

Relative intensity ratios of 1450/960 across the enamel/DEJ/dentin zone at occlusal positions (A) and at cervical positions (B).

Fig. 5

Raman spectra in protein-derived spectral regions from dentin and the DEJ at occlusal positions (A) and at cervical positions (B); representative Raman image of the DEJ based on intensity ratios of amide I/1450 at occlusal positions (C) and at cervical positions (D); representative Raman image of the DEJ based on intensity ratios of amide III/1450 at occlusal positions (E) and at cervical positions (F).

Fig. 6

Raman spectra in mineral-derived spectral regions from dentin and the DEJ at occlusal positions (A); at cervical positions (B); representative Raman image of the DEJ based on intensity ratios of 1070/960 at occlusal positions (C); at cervical positions (D).