Correlation Between Colour of Defect and Enamel Breakdown in First Permanent Molars With Molar Incisor Hypomineralisation (MIH) (MIH)

Aim of the study is the correlation between the colour of the enamel defect and enamel breakdown in young first permanent molars. Children diagnosed with MIH from the onset of eruption of the first permanent molar, matched by age with children with sound first permanent molars are investigated. Children screened by the school dental services of Basel-Stadt as well children attending the department of children and adolescents (KJZM) of the University Centre for Dental Medicine in Basel (UZB), diagnosed with MIH on one or more first permanent molars receive a letter of information- invitation to be seen in the department of children and adolescents (KJZM). The control group consists of fit and healthy children 5-8 years old, who attend the department of children and adolescents (KJZM-UZB) for their regular dental check-ups. A written informed consent will be obtained from the parents/legal guardians.

Colour definition:

The exact colour determination of the teeth will be carried out as follows: the teeth are photographed with a canon SLR camera. (Canon EOS 80D; Canon inc. Japan), a ringflash (Macro Ring Lite MR-14EXII; Canon) and a macro lens (EF-S 60mm 1:2:8 USM; Canon) will be used. All camera settings (1/250, aperture F20, iso-sensitivity 100 and a fixed white balance AWBW (white priority), flash intensity +/-0) and the tooth-lens distances (25 cm) are standardized by one operator (VM, SR). A colour reference card (grey card) is photographed together with the tooth of interest in order to identify and equalize the colour deviations. The resulting photo will be uploaded to the Adobe Photoshop 6 and the values of the RGB code (0-255 for each of the three colours) will be determined. The tolerance range is set to +/- 10. If the 3 colours are within the tolerance, the photo can be used to determine the colour of the tooth to be examined. The darkest part of the tooth is then determined. The degree of darkness is indicated by a number between zero and one hundred, where L=100 is white and L=0 is black (Wiedrichs et al. 2023).

Degree of enamel loss will be investigated and measured as follows:

The teeth will be scanned using the iTero 5D Plus intraoral scanner in the first appointment and then at 3, 6 and 9 months. The obtained stl file is optimised for the subsequent digital superimposition procedures. The distances between surface points of the two digital models (initial scan vs scan at 3months, initial scan vs scan at 6 months and initial scan vs scan at 9 months) will be converted to root mean square (RMS) values that assess the mean value of errors in the comparison of two datasets with an identical coordinate system. The RMS values represent the data of trueness or loss of enamel. The results of deviation analysis will be complemented by visualisation of the 3D colour-coded maps in which the yellow-to-red fields indicate that distance values are greater than the positive limits while turquoise-to-dark blue fields indicate that distance values are smaller than the negative limits. The range of tolerance (green color) is set at ± 0.05 mm, which means that the software report surface differences in the color-coded maps only beyond this range.