Raman spectroscopic study of noncarious cervical lesions

The surface of noncarious cervical lesions (NCCLs) consists of sclerosed dentin. This type of dentin may affect the ability of adhesive restorative materials to bond well to its surface, but little information exists on the chemical nature of this dentin surface and how it may be affected during acidic treatment. The inorganic part of normal dentin and dentin from NCCLs before and after acid conditioning with phosphoric acid or polyacrylic acid was investigated. Ten premolars with NCCLs and four human third molars (control) were used. Replicas of NCCLs were examined using scanning electron microscopy (SEM). Surfaces and longitudinal sections of four NCCLs and control dentin discs were analyzed using Raman spectroscopy. The discs and NCCLs were sectioned, and treated with 35% phosphoric acid or 20% polyacrylic acid/3% aluminum chloride, and Raman spectra obtained. The area under phosphate ν₁ of the dentin spectrum was computed to obtain a ratio with the area under the second-order spectrum of a silicon phonon comparative standard. Mean phosphate ν₁ and silicon phonon ratios from normal dentin and NCCLs were compared using a linear model with repeated measurements and Tukey’s pairwise tests. Mean ratios from different locations of the NCCLs were compared using one-way analysis of variance (ANOVA) and Tukey’s pairwise tests. SEM micrographs of NCCL surfaces showed variation from relatively smooth with no dentinal tubule openings to surfaces with occluded tubules. The mean phosphate ν₁ and silicon phonon ratios for NCCLs were higher than those of normal dentin in all treatment groups (P < 0.05). Ratios from the untreated specimens were higher than those of the polyacrylic acid-treated specimens, and those for the phosphoric acid-treated group were the lowest (P < 0.05). The ratios obtained for the surfaces of NCCLs were higher than those halfway towards the pulp, and those adjacent to the pulp were the lowest (P < 0.05).