Relationship between analysis of laser speckle image and Knoop hardness on softening enamel

- Laser speckle images provide access to enamel hardness loss.
- Initial caries lesion can be diagnosed by laser images.
- It is a nondestructive method to infer tooth hardness.

BackgroundIn this study is presented the correlation between laser speckle images and enamel hardness loss.MethodsIn order to shift the enamel hardness, a dental demineralization model was applied to 32 samples of vestibular bovine teeth. After they were cleaned, cut and polished, the samples were divided into 4 groups and immersed in 30 ml of a cola-based soft drink for 10, 20, 30 and 40 min twice a day for 7 consecutive days with half the surface protected by two layers of nail polish. Each sample was analyzed by Knoop hardness and laser speckle imaging.ResultsPearson's correlation analysis demonstrated that the laser speckle image technique presents a strong correlation with the hardness loss of the enamel (r = 0.7085, p < 0.0001). This finding is corroborated by Blend & Altman analysis, in which the data presented a constant behavior throughout the whole interval. For both analyses, more than 95% of the data is within the confidence interval, as expected.ConclusionThis work demonstrates, for the first time to our knowledge, an empirical model for correlating laser speckle images with the loss of tooth enamel hardness.