Study on the influence of leucine-rich amelogenin peptide (LRAP) on the remineralization of enamel defects via micro-focus x-ray computed tomography and nanoindentation

Regeneration of severely damaged enamel (e.g. deep demineralized lesions) is currently not possible, because the structural units of enamel crystal construction are removed after its maturation. The aim of this in vitro study was to evaluate the effect of surface impregnation by leucine-rich amelogenin peptide (LRAP) on the remineralization of eroded enamel using micro-focus x-ray computed tomography (mu CT). Fifteen bovine enamel blocks were embedded in resin and three zones (sound, demineralization, and remineralization) were defined on each specimen. Lesions were prepared by immersing the samples in demineralization solution for 7 d. The samples were soaked in distilled water or 60 or 120 mu g mL(-1) solution of LRAP in water for 30 min. After the surface treatment, specimens were incubated in artificial saliva for either 5 or 10 d at 37 degrees C. The amount of mineral gain (d Delta Z%) and the relative changes in the lesion depth (dLD%), obtained from mu CT, were used to evaluate the effect of LRAP on the remineralization of lesions. The effects of LRAP on cross-sectional integrated hardness Delta INH were studied after 10 d using nanoindentation. ANOVA test was used to determine the effect of time and/or LRAP concentration on d Delta Z%, dLD% and Delta INH mean values. Tukey's analysis was used for multiple comparison testing (alpha = 0.05). Analysis of mu CT data showed significant effect of time and LRAP concentration on the d Delta Z% (p = 0.013, p = 0.003) and the dLD% (p < 0.001, p = 0.002) mean values. The nanoindentation hardness was significantly improved by 120 mu g mL(-1) LRAP (p = 0.02). Also, the peptide treatment affected the mineral distribution throughout the lesion by inhibiting of superficial deposition. This study showed that the treatment of eroded lesions in enamel by LRAP can improve and regulate the pattern of remineralization in vitro.