Reliability and reproducibility of a conversion factor for grayscale values obtained from CBCTS assessed at various anatomical regions- A retrospective study

Background: Bone density assessment in dental practice is required for dental implant planning and placement, Orthodontic tooth movement, and establishing mid palatal suture maturation. Establishing a linear relationship between grayscale values and Hounsfield units (HUs) in softwares can improve the ease of diagnosis and treatment planning. Aim: To determine a conversion factor and test its reliability and reproducibility for grayscales values to HUs obtained in Cone-beam computed tomography (CBCT) s at various anatomical regions using Galileos Sirona CBCT Viewer Software and Philips DICOM Viewer. Methods: Eighty-seven (87) CBCTs were included in this retrospective study and 343 sites were assessed across different anatomical regions. Sites assessed were isolated in both softwares at identical locations. Grids were used for standardizing reference planes at different anatomical sites. Reference landmarks were isolated 1) between anterior interdental regions 2) between posterior interdental regions, and 3) at radio-opaque regions. Grayscale value was divided with HU to obtain conversion factors at different sites, which was the primary outcome of the study. The reproducibility of the factor obtained was also assessed to improve its clinical correlation. Results: In anterior interdental regions, grayscale values were 7.6 times greater than HUs. In posterior interdental regions, gray scale values were 4.5 times greater than HUs. The reliability of values obtained was verified using Kappa's correlation test. In radio-opaque regions, grayscale values were 1.4 times greater than HUs and highly reliable (r = 0.972). Conclusion: In well-exposed regions, a defined conversion factor can be established between grayscale values and HUs in Galileos Software. This factor determined is highly reproducible and reliable in radio-opaque regions, and adequately reliable in anterior and posterior interdental regions.