| Objective:The occurrence of early caries is mainly caused by the acid effect of cariogenic bacteria, which lead to the imbalance of enamel demineralization and remineralization, and finally cause demineralization of the local enamel. So the quantitative research on early enamel demineralization is the necessary mean for accurately quantitative diagnosis of early caries. In this paper, we carried out quantitative research on the early artificial demineralization of bovine enamel in vitro by Optical Coherence Tomography(OCT), and verified its accuracy by Atomic Absorption Spectrometry(AAS), which measured the amount of calcium loss of different time- demineralization domains. We explored a new method of quantitative detection of early enamel demineralization, and provided scientific basis and experimental data for accurately quantitative detection of early caries with OCT in stomatologyical practice.MethodsThe samples of bovine permanent teeth were from the Teeth Bank in the Research Center of Tianjin Stomatological Hospital, and collected within two weeks. The root and pulp of bovine permanent teeth were removed, and the crowns were remained. The following experiments and data analysis were mainly carried out and completed in the Centre.1. Establish artificial gradient early demineralization model of bovine enamel:Ten crowns of bovine permanent teeth with no chalk, pigmentation and cracked changes were selected. Gradient demineralized domains of different time periods(24h,48h,72h,96h) were prepared as the experimental windows on the smooth surface of each permanent bovine tooth by chemical demineralization solution method, and the normal enamel tissue as control windows. The chemical demineralized solutions of experimental windows with different time periods of demineralization were collected and stored.2. Scan with OCT system:The experimental windows and control windows on the bovine enamel surface were scanned by the OCT system along the short axis of each tooth. Five two-dimensional OCT images with the interval of 1500 micron were obtained from each bovine permanent tooth. 3. Calculate the gray scale of OCT images in different-time demineralized experimental windows:â‘ Determine the depth of demineralization in different degree of demineralization experimental windows:The average gray of OCT images was analyzed by Matlab software. The average gray of different degrees of demineralized experimental windows was compared with the normal control windows to determine the depth of demineralization.â‘¡Calculate the gray scale variation within a specific range of different degree of demineralization experimental windows on OCT images: The gray values of demineralization experimental windows, which were obtained through the average gray value of the specific range of different degrees of demineralized domain multiplied by the volume of the domain, were subtracted by the gray values of the normal enamel in the same range.4. Measure the dissolution of calcium of each experimental window in the chemical demineralized solution:The calcium content in chemical demineralization solution of different degrees of demineralized experimental windows were measured by AAS, and then were subtracted by calcium content in the initial chemical demineralized solution. The dissolution of calcium of each experimental window (the amount of calcium loss in experimental window with different degrees of demineralization) was obtained.5. Correlation research on the gray scale variation and the amount of calcium loss in the demineralized experimental windows:The gray scale variation and the amount of calcium loss in the demineralized experimental windows were analyzed using Pearson Correlation Analysis.Results:1. The morphological evaluation on early artificial gradient demineralized model of bovine enamel:The early artificial gradient demineralized model of bovine enamel was observed. There was no significant difference between the demineralized windows of 24h and the normal windows, while the chalk changes occurred in other demineralized windows and became more severe and enlarged; as the demineralized time increased. In the OCT images, all of the demineralized windows could be discriminated with the normal windows clearly. As the demineralized time increased, the gray scale of demineralized windows increased.2. The gray scale variation in OCT images of different degree of demineralized experimental windows:The gray scale variation of different degree of demineralized domains in the OCT images were statistically different by ANOVA (P<0.05). According to pairwise comparisons, we recognized that the gray scale variation of different degrees of demineralized experimental windows increased as the demineralized time increased.3. The amount of calcium loss of the artificial model of early bovine enamel demineralization:The amount of calcium loss of the artificial model of early bovine enamel demineralization were statistically different by ANOVA (P<0.05). According to pairwise comparisons, we recognized that the amount of calcium loss of different degrees of demineralized experimental windows increased as the demineralized time increased.4. The correlation of the gray scale variation and the amount of calcium loss of different degrees of demineralized experimental windows:The result suggested that the amount of calcium loss were positively correlated with the values of the gray scale of the different degrees of demineralized experimental windows. This confirmed that the gray scale variation of different degrees of demineralized experimental windows increased as the amount of calcium loss increased.Conclusion1. The gray scale variation in the OCT images of different degrees of demineralized experimental windows was used as an index to detect the degree of demineralization quantitatively. We explored a new index for OCT to detect and analyze early demineralization of bovine enamel quantitatively.2. The correlation of the gray scale variation in the OCT images of demineralized domains and the amount of calcium loss was confirmed.3. Early demineralization of bovine enamel could be detected sensitively and noninvasively with OCT. The gray scale variation on the OCT image would be hopefully used as a new mothod of accurately quantitative diagnosis of early enamel caries after the experimental errors were corrected and the analysis means was improved. |
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