Morphological Characterization of Natural Non-Carious Cervical Lesions

Objectives: This ex vivo study assessed the morphology and angle of natural non-carious cervical lesions (NCCLs), in a sample of previously extracted human premolars.
Methods: 3D scans (Trios4, 3Shape) of a convenience sample of 647 premolars with NCCLs of different severities were analyzed using the Smith and Knight tooth wear index (TWI scores 0-4). TWI visual assessments were conducted by two experienced examiners, who scored the buccal surfaces of the studied teeth by consensus. 3D scans were evaluated using 3Shape TRIOS software, which allowed for 3D rotations and changes in magnification as needed, on a 65-inch high-resolution monitor. NCCLs were classified into flat, cup, wedge-shaped, and striated based on bucco-lingual cross-sections, obtained from the 3D scans. The internal angle between the occlusal and apical walls of NCCLs was measured using ImageJ software (NIH, Bethesda, MD, USA). Data were analyzed using ANOVA with 5% significance level.
Results: TWI scores were distributed as follows: 157 specimens with TWI0 (24.3%), 103 specimens with TWI1 (15.9%), 152 with TWI2 (23.5%%), 104 with TWI3 (16.1%), and 131 with TWI4 (20.2%). Of the specimens with lesions, the mean angle differed significantly among TWI scores (mean±SD): TWI1 (166.7°±9.7), TWI2 (155.3°±15.8), TWI3 (134.3°±24.4), TWI4 (108.7°±27.9) (p<0.001). Significant differences were found in mean angles among morphology classification: flat (158.1°±18.2)>striated (150°±17.1)>cup (127°±26.4)>wedge (94.5°±28.7). The most frequent morphology for each TWI scores were: TWI1-flat (75.7%), TWI2-flat (47.4%), TWI3-cup (42.3%), TWI4-cup (38.9%).
Conclusions: The study found different morphologies and angles of natural NCCLs according to the TWI severity level. Lesion angle decreased with the increase in TWI severity. The most predominant lesion type at lower scores was flat and at higher scores was cup.