Complementary Microscopic Studies of the Peritubular-Intertubular Human Dentin Region

Objective: To investigate the differences in structure, composition and mechanical properties between Peritubular Dentin (PTD) and Intertubular Dentin (ITD) using confocal Raman microscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Scanning Acoustic Microscopy (SAM). Methods: The dentin beams from the central part of human third molars were fractured to expose tubules. The planes of the observed surfaces were carefully selected to be perpendicular to the direction of the tubules. Raman mappings/images as well as SEM images were collected from these surfaces. SAM images were obtained from the above specimens after polishing. Real-time AFM images were collected from the specimens fractured along the direction of the dentin tubules in the EDTA solution. Results: It was found that PTD was highly mineralized with the mineral/matrix ratios 2–2.5 times higher than those of ITD. Although Raman peak contour in the amide regions was similar, the ratios of 1243 (amide III)/1450 (CH) within the ITD (~1.5) were higher than the values (~1.29) in PTD. In addition, ITD contained more proline and hydroxyproline than PTD. By real-time AFM, in-situ observation of the PTD and ITD junction in the EDTA solution revealed that there was a gap region between ITD and PTD where underwent fast demineralization, and dentin collagen fibrils were observed to cross this region from ITD to PTD. Furthermore, the results from acoustic impedance images using SAM verified the existence of the gap region between ITD and PTD. Conclusion: The compositional and structural differences at the molecular level and high spatial resolution were revealed between peritubular and intertubular dentin. Comprehensive high resolution microscopic analyses of the PTD/ITD provide powerful means of identifying the structural differences across the junction zone. The information obtained is critical in understanding the formation and function of peritubular dentin. Supported by NIH/NIDCR DE015281.