Assessment of structural changes in translucency and opacity of tooth enamel against a direct demineralization process: An in vitro study

Objective: The objective of this study was to assess in vitro the structural changes in translucency and opacity of tooth enamel following a direct demineralization process. Materials and Methods: This experimental in vitro study evaluated 45 thirds (cervical, middle, and occlusal) of the tooth enamel surface of premolar teeth extracted from young adults divided into three groups of 15 specimens each: Group 1 (solution based on calcium, phosphorus, and fluorine), Group 2 (orthophosphoric acid 37%), and control group (distilled water). All underwent optical macroscopic examination with ×3 magnification to determine the initial translucency according to the variation of the medium in their intercrystalline spaces, and Thylstrup and Fejerskov Index was used. The experimental groups were then subjected to an artificial caries process during which the specimens were placed in an inorganic and organic solution of calcium, phosphorus, and fluorine at 37°C for 90 days with the acidic solution at pH 5 and the neutral solution at pH 7. The control specimens were placed in distilled water. Finally, all the specimens were assessed by polarization microscopy. Results: In relation to the occlusal third, the highest proportion in Groups 1 and 2 was in Grades 2 and 3 (80%). A significant association was only observed between the experimental groups in the degree of translucency in the occlusal third (P = 0.002), whereas no association was found in relation to the degree of opacity in the middle and cervical thirds in either study group (P 0.05). Conclusion: The resistance of enamel hydroxyapatite crystals increases from occlusal to cervical due to the greater presence of aprismatic enamel in the cervical horizontal third.