Influence of dentin permeability and thickness on LED light propagation

Objective: To evaluate the influence of dentin permeability and thickness on transdentinal LED light propagation. Methods: Initially, 45 dentin discs with 0.5 mm thickness were obtained from intact human teeth and individually submitted to a first transdentinal power loss measurement after LED irradiation (630 nm). Then, the discs were conditioned with 0.5M EDTA for 60 s, submitted to hydraulic conductance test and irradiated again to determine if the presence of smear layer influences LED light propagation through dentin (power loss). In the second part, 42 additional dentin discs were divided into three groups according to their thicknesses (0.2 mm, 0.5 mm, and 1.0 mm). Following EDTA dentin conditioning, the transdentinal light propagation was measured after LED irradiation with wavelengths of 450 nm, 630 nm and 850 nm. Power loss was calculated by subtracting the power measured direct from the light source and that registered when the dentin discs were interposed between the light and the potentiometer. Data were submitted to Wilcoxon and ANOVA complemented by Tukey tests at 5% level of significance. Results: There was a weak correlation between dentin permeability and power loss (Spearman, r_S=0.19). The transdentinal propagation of LED light significantly increased after EDTA conditioning. Overall, irradiation at all wavelengths resulted in progressive increase in power loss as dentin thickness increased except for LED irradiation at 850 nm. For that wavelength, no statistically significant difference was seen between 0.5- and 1.0-mm dentin discs. The wavelength of 850nm allowed greater LED light propagation through dentin irrespective of the dentin thickness. Conclusion: Dentin permeability did not play a significant role in LED light propagation through dentin, while it was positively influenced by the smear layer removal. Both wavelength and dentin disc thickness affected power loss during transdentinal irradiation.

(FAPESP: 2009/03615-0 M; 2010/50798-0)