Increasing Enamel Cariostatic Effect by Heat Therapy of Organic Matrix

Objective: Heating tooth enamel to attain cariostatic effect by laser is thought to be clinically detrimental due to potential pulpal damage caused by the increased temperatures. Although enamel organic matrix may be physico-chemically modified to block enamel diffusion using low-energy laser or heating, the underlying cariostatic mechanisms remained to be fully elucidated. Method: Seven human molars were collected, cleaned and cut into halves. One half of each tooth was randomly selected for organic matrix (OM) extraction while the other half used as the matched control. Each tooth half was sectioned and randomly selected to undergo heating at different temperatures including 100, 200, 300, 400 degree Celsius. Birefringence of the tooth sections were quantified before and after heating with polarized light microscope. Each tooth section was then cut into coronal and cervical segments, with diffusion coefficient of the coronal segments quantified using Fluorescence Recovery after Photo Bleaching (FRAP) technique coupled with confocal microscopy. After incubation of the unvarnished window on cervical enamel segments in caries-inducing demineralization solution, lesion depth was measured with polarized light microscopy. Additional cervical segments were gold-coated prior to imaging with Field Emission Scanning Electron Microscope (FESEM). Data analysis was performed using 2-sample t-tests. Result: Maximal cariostatic effects of heated OM were demonstrated with 32 ± 10% (p<0.05), 27 ± 1% (p<0.05) and 10 ± 1% (p=0.03) reduction in lesion depth (at 300 °C), diffusion coefficient (at 400 °C) and birefringence (at 400 °C), respectively, against corresponding OM extracted controls. The SEM micrographs revealed the blocking of diffusion pathways in the inter-prismatic spaces. Conclusion: Heating enamel with intact organic matrix at the temperature range of 300~400°C may render maximal cariostatic effects and the “organic blocking theory” may be one of the major mechanism involved in the laser-induced caries prevention.