Rehardening of caries-like lesions in root surfaces by saliva substitutes

Objective: This study sought to evaluate whether root dentine caries‐like lesions could be remineralised by saliva substitutes. Methods: Root dentine slabs (3 × 3 × 2 mm) were cut from bovine incisors, ground flat, polished and pre‐tested for Knoop microhardness (KHN) at five locations spaced 500 μm apart and 500 μm from the left edge of each sectioned piece. After 60 out of the 100 slabs had been selected based upon their KHN values, specimens were coated with wax except for their outer surface. Specimens were then cycled through a highly cariogenic challenge model to induce caries‐like lesions, whose formation was confirmed by KHN measurements located 500 μm from the right edge of the specimen. According to a randomised complete block design, the experimental units (n = 15) were exposed to 1.5 ml of saliva substitutes, based on either mucin (MC) or carboxymethylcellulose (CM), to natural human saliva (HS) or to 100% relative humidity (RH) over 20 days. Remineralisation was verified by KHN measurements located 1000 μm apart from the right edge of the specimen. Results: Analysis of variance indicated a significant (p < 0.0001) difference among the KHN values attained by the carious root dentine after exposure to the remineralising agents. Tukey's test ascertained that remineralisation was greatest with MC, intermediate with CM and least with HS, but rehardening did not reach the pre‐caries lesion formation values. Conclusion: Saliva substitutes may provide partial remineralisation to preformed caries‐like lesions in root dentine.