How mechanical stresses modulate enamel demineralization in non-carious cervical lesions?

To introduce an experimental non-carious cervical lesion (NCCL) model for studying the influence of presence and type of stress (tension or compression) on acid effects involved in NCCL formation on the enamel near the cement-enamel junction (CEJ).

108 bovine incisors were cut into 18 × 3×3 mm³ beams, with a notch in the cervical region to generate a standardized area of stress concentration. Half of the specimens were immersed in distilled water and the other half in acetic acid solution (pH 4.5) for 72h. Each group was divided into three subgroups. Two subgroups underwent 800gf static loading, with the specimen positioned in a bending jig with the buccocervical region under either tension or compression. The load was applied simultaneously to immersion (in water or in acid). The third subgroup was not subjected to loading. Transversal and longitudinal 0.05 mm plates of the specimens were analyzed under a light microscope (40, 100 and 200×) to measure the enamel demineralization depth and to assess the presence of cracks, fractures and gaps at the enamel-dentin junction. The demineralization depth data were submitted to ANOVA and Tukey's test at a 5% significance level.

Enamel demineralization depth (μm) was higher under tension (158±19 in transversal sections and 229±32 in longitudinal sections) than under compression (transversal: 129±16 and longitudinal: 167±10) or unstressed condition (transversal: 138±21 and longitudinal: 187±21). Specimens immersed in acid and subjected to tensile stress presented enamel micro fractures and wider gaps in the dentin-enamel junction.

Enamel demineralization was significantly higher in the presence of tensile stress, due to wider gaps between dentin and enamel, stress corrosion cracking and increased enamel permeability to acid.