Novel method of constructing a stable reference frame for 3-dimensional cephalometric analysis.

INTRODUCTION: Three-dimensional (3D) cephalometric analysis has provided the ability to overcome the limitations of 2-dimensional cephalometrics. However, there is no international standard method for 3D cephalometric analysis yet. Determining the position of the midsagittal plane (MSP) practically is the most important step when constructing a 3D cephalometric reference frame. Recent studies have used several approaches to construct the MSP. In this study, we aimed to determine the true MSP of the skull to establish a stable reference frame for 3D cephalometric analysis.

METHODS: Cone-beam computed tomography data of 12 adult patients were divided into 2 groups: symmetry (n = 6) and asymmetry (n = 6). The anterior cranial base region model and its mirror model were registered and used to determine the MSP to prevent any influence of the degree of symmetry on the registration of other parts of the skull, particularly for subjects with severe facial or cranial asymmetry. Intraclass correlation coefficients were used to assess intraexaminer and interexaminer reliabilities of the x, y, and z coordinates of all landmarks measured by 2 investigators.

RESULTS: The intraclass correlation coefficient values were greater than 0.9, indicating almost perfect agreement.

CONCLUSIONS: The candidate reference planes constructed using this novel method were thought to be reliable for 3D cephalometric analysis and may expand its clinical applicability in patients with cranial asymmetry.