The identification of possible reference planes on a CBCT scan taken with a small FOV—an observational analytical study

Unlike a CBCT scan which has a large field of view (FOV), a scan with a small FOV may not involve the base of the skull. Therefore, routinely used reference planes may not be available to evaluate treatment outcome. The present study was undertaken to determine if the palatal plane and a molar occlusal plane may be used as reference planes to measure the change in the axial inclination of the maxillary central incisor and the maxillary first permanent molar towards the end of orthodontic treatment on a CBCT scan captured with a small FOV.A lateral cephalogram and a CBCT scan with a small FOV were taken for fifteen young adults prior to, and six months after, mini-implant supported, distal movement of the maxillary arch. CBCT multi-planar slices were sequentially viewed to obtain an image that contained the entire length of the maxillary central incisor and the maxillary first permanent molar in the tangential view. The axial inclination of the maxillary central incisor and the maxillary first permanent molar was measured from the palatal plane and the molar occlusal plane on both sides. The same parameters were evaluated on the lateral cephalogram using the palatal plane as a reference. An independent t test (p = 0.05) was conducted to compare the results. A Bland–Altman plot with linear regression was constructed to measure accuracy, method agreement and reliability.There was no statistically significant difference when a change in the axial inclination of the maxillary central incisor and the maxillary first permanent molar was measured using the two reference planes. The change in axial inclination of the maxillary central incisor and maxillary first permanent molar had a 95% confidence interval of -1.82 to 4.19 and -4.48 to 3.05 and a p-value of 0.425 and 0.701 on the right side, respectively, and a 95% confidence interval of -1.76 to 4.79 and -4.41 to 2.79 and p-value of 0.350 and 0.650 on the left side.The molar occlusal plane and the palatal plane may be used as reference planes for measuring change in the axial inclination of the maxillary central incisor and the first permanent molar in a CBCT scan taken with a small FOV.