Nanomechanical and Chemical Characterization of Teeth With Noncarious Cervical Lesions

Objectives: Noncarious cervical lesions (NCCLs) are a common dental condition, not initiated by bacteria that results in continuous damage of the tooth structure. This study investigated changes in composition and nanomechanical properties of NCCL-affected enamel and dentin.
Methods: Extracted sound and affected teeth with severe NCCLs were cut in the long axis. Chemical characterization using Raman spectroscopy was performed on one half of each tooth, while the other half was used for evaluation of the nanomechanical properties (reduced elastic modulus – Er and creep). For spectra collection, a Raman microspectrometer (Renishaw) was used with 50Χ microscope objective and 785 nm laser. Raman signal was collected (5 scans for each area), baseline corrected and smoothened (Savitzky-Golay filter). The relative peak intensities and area were used to calculate the ratios: mineral quality (ratio of carbonate to phosphate 1070 cm^-1/958 cm^-1); dentin’s mineral to matrix (958 cm^-1/1451 cm^-1), collagen posttranslational modifications (Amide I 1656 cm^-1/CH₂ scissoring 1451 cm^-1). The nanoindentation was done in a triboindenter (Bruker) with a berkovich tip with segments of 5s loading, 15s holding at maximum load of 1000μN and 5s unloading. Ten indentations spaced 5 μm from each other, were done in both dentin and enamel of each sound and affected tooth along the cervical area (near the cementoenamel junction). Data was statistically analyzed by One-way Anova and Tukey’s (α=0.05).
Results: Reduced mineral quality ratio was observed in the NCCL teeth enamel (p=0.004). In the NCCL-affected dentin, there was increased collagen posttranslational modification (p=0.01), representative of increased cross-links. There was no significant difference in the mineral to matrix ratio between sound and NCCL-affected dentin (p=0.223). In enamel, increased Er (p<0.001) and reduced creep (p<0.001) were observed in the NCCL teeth. Whereas, reduced Er (p=0.004) and increased creep (p<0.001) were observed in the NCCL dentin.
Conclusions: In the NCCL-affected areas, collagen posttranslational modifications and decreased nanomechanical properties are indicative of chemical and mechanical changes within the affected dentin area, these may play significant roles in lesion progression.