Ultrastructure of hypersensitive and non-sensitive dentine. A study on replica models.

Patients with cervical dentine exposures do not always complain of dentine hypersensitivity. The identification of morphological features connected to symptoms is important for both prevention and management of dentine hypersensitivity. The aim of the study was to determine the relationship between the dentine ultrastructure and clinical symptoms in patients with cervical dentine exposures. Replica models for a total of 28 teeth (from 10 patients) with cervical non caroius lesions and dentine exposures were obtained before and after acid etching. The replica models were studied blindly in the scanning electron microscope (SEM). 12 of these were classified clinically as hypersensitive and 16 as non-sensitive. Because of the morphological heterogeneity of all specimens, a grid was used to isolate smaller, more homogeneous areas. 120 (75 non-sensitive and 45 hypersensitive areas) grid areas randomly selected from the 28 dentine surfaces were analyzed. The presence and morphology (amorphous or crystalline) of smear layers and the density and diameter of dentine tubules were recorded. The chi 2 test was used for statistical analysis. In unetched specimens, the surfaces classified as non-sensitive were frequently coated by an amorphous smear layer (88.0%) and occasionally by a crystalline smear layer (2.7%). Only a few and narrow tubules were observed (9.3%). On the other hand, the unetched specimens of the hypersensitive dentine exhibited less frequently (31.3%) an amorphous smear layer. The presence of crystalline smear layer (33.3%), many and wider patent tubules and, sometimes, loss of intertubular dentine manifested as grooves between tubules, were observed (35.6%). The differences were significant (p < .001). In hypersensitive dentine, the acid etching always removed the smear layer whereas removal in non-sensitive dentine was partial or absent. These morphological findings underline the rôle of smear layer in reducing permeability of dentine in patients with dentine sensitivity.