Objective and quantitative assessment of caries lesion activity

Evaluate the ability of objectively measured specular reflection, roughness, and fluorescence change during dehydration to assess caries lesion activity.

One hundred ninety-five ground/polished 3 × 3 × 2 mm sound human enamel specimens were divided into three groups and demineralized using a multispecies microbial caries model for 3, 6, or 9 days; and then remineralized with 1100 ppm-F as NaF solution for 10 days using a pH-cyclic model. Reflection (amplitude: %), roughness (Ra: μm), fluorescence change during dehydration (ΔQ: %×mm²), and microfocus computed tomography [μ-CT: lesion volume (μm³)] were measured for sound, demineralized and remineralized enamel. The surface was hydrated and fluorescence images were acquired at 1 s intervals for 10 s (ΔQ₁₀). During image acquisition, surface was dehydrated with continuous compressed air. Changes-in-ΔQ per second (ΔQ_D: %×mm²/sec) at 5 (ΔQ_D5) and 10 s (ΔQ_D10) were obtained.

Reflection decreased from sound to demineralized groups (p < 0.0001); remineralized groups were higher than demineralized groups (p < 0.001), but not different from sound (p > 0.32). Roughness increased from sound to demineralized groups (p < 0.0001) and remineralized groups were also higher than sound (p < 0.0001). ΔQ₁₀, ΔQ_D5 and ΔQ_D10 increased from sound to demineralized groups (p < 0.0001), and remineralized groups decreased compared to demineralized groups (p < 0.05), but was higher than sound (p < 0.0001). The correlations of μ-CT with reflection, roughness, and ΔQ₁₀ were -0.63, 0.71, and 0.82, respectively (p < 0.0001).

Reflection, roughness and ΔQ could distinguish between sound and demineralized enamel. Reflection and ΔQ were able to distinguish between demineralized and remineralized enamel.

Determination of caries activity, whether a lesion is active or inactive, is an essential and critical component of caries diagnosis. However, especially for enamel lesions, it is difficult to estimate without longitudinal follow-up. Reflection, roughness and fluorescence change during dehydration have the potential to measure caries lesion activity at a-single-appointment.