[Changes of RGB value in de-mineralized teeth and re-mineralized teeth]

Digital photography, image analysis and tooth-dying were used to detect the change of tooth color RGB value when the ex vivo teeth were de- or re-mineralized.

Thirty-six healthy maxillary deciduous incisors were assigned randomly to 3 groups. 3 mm x 4 mm window was exposed in the center of the labial surfaces for each sample. The windows were dyed using 2% methylene blue then was photographed. The RGB₁ value was measured by image analysis.Then the windows were etched 1 min using 32% phosphoric acid gel. The procedures of tooth-dying, photography repeated in the same way and RGB₂ value was measured. The windows were re-mineralized in artificial saliva 24 h, 48 h, 72 h for group 1, 2 and 3 respectively. Then the windows were dyed and photographed again, RGB₃ value was measured. The RGB value was analyzed using SNK test.

In group 1, the average values for RGB₁, RGB₂, RGB₃ were 54.58±12.66, 24.32±2.4, 29.96±3.32, respectively. In group 2, they were 58.71±5.85, 25.21±2.84, 33.66±4.6, respectively. And in group 3, they were 60.58±8.10, 24.41±2.47, 34.59±3.53, respectively. Within each group, RGB₁, RGB₂, RGB₃ values were statistic different between each other. Between the three groups, RGB₁, RGB₂ values were not significantly different. The difference of RGB₃ value was significant between the group 1 and 2, between the group 1 and 3, while the difference between group 2 and 3 was not significant.

Digital photography, image analysis combined with tooth-dying may recognize the change of tooth color RGB value when the ex vivo teeth were de- or re-mineralized. They may be adopted in teeth de-mineralization and re-mineralization study. Supported by Research Fund of Science and Technology Commission of Shanghai Municipality (Grant No.074119644,08DZ2271100) and Shanghai Leading Academic Discipline Project (Grant No. S30206).