UCSF

Background and Objective: The purpose of the study is to evaluate the utility of the palatal plane in both 2D and 3D. The first aim is to study and compare the correlation between the sella nasion-to-mandibular plane angle (SN-MP), to the palatal plane-to-mandibular plane angle (PP-MP), and open bite tendency. The second aim is to develop a method of identifying the palatal plane, mandibular plane, and associated landmarks in 3D on CBCT. The third aim is to test and compare the reliability of landmarks identification involved in palatal plane, mandibular plane, and associated measurements in 3D and 2D. The last aim is to evaluate the difference between the palatal and mandibular plane associated measurements identified from the 3D CBCT analysis and 2D lateral cephalographs.

Materials and Methods: Aim 1: 50 subjects in permanent dentition were randomly chosen at UCSF. Their lateral cephalographs were collected to measure and compare the correlation between SN-MP, PP-MP, and overbite. Aim 2: A protocol was developed to use a hybrid between volumetric rendering and multi-planar reconstruction to trace palatal plane, mandibular plane, and associated measurements in 3D using Anatomage Invivo5. Aim 3: Precision of the landmarks were compared between 3D tracing on CBCT and 2D lateral cephalographs, both overall as well as per individual axis. Aim 4: associated measurements, PP-MP, U1-PP, and L1-MP, were measured and compared between 3D and 2D tracings.

Results: There was a strong correlation between SN-MP and PP-MP (R= 0.859) and no significant difference between SN-MP to open bite and PP-MP to open bite. Generally, landmark identification was significantly more precise in 3D tracing than 2D tracing (0.549mm vs 1.440mm). In 3D, tracing was more precise in Y-axis than X-axis (0.168mm vs 0.367mm), whereas in 2D, it was more precise in X-axis than in Y-axis (0.640mm vs 0.823mm). Incisor crown tips ranked high on precision ranking in both 3D and 2D. and PNS ranked low in both 3D and 2D, while root apices ranked higher on 3D than in 2D. U1-PP measurements in 3D were significantly lower than that of 2D (-3.73 degrees), L1-MP measurements in 3D were significantly higher than that of 2D (+2.35 degrees), but PP-MP measurements did not significantly differ between 3D and 2D.

Conclusions: PP-MP, similar to SN-MP, is valuable in evaluating vertical jaw relationship and open bite tendencies. Overall, landmark identification in 3D is significantly more reliable and precise than in 2D. However, the patterns of precision differ between different landmarks and different axes. Measurements such as U1-PP and L1-MP significantly differ when measured in 3D compared to 2D.