[Fitting method and characteristics of upper occlusal plane based on three-dimensional fusion imaging]

To explore a method for accurately fitting the upper occlusal plane, and investigate its morphological and positional characteristics in different skeletal type groups based on the fusion images from cone beam computed tomography (CBCT) and digital dental cast models.

Fifteen patients were selected from each of the skeletal Class Ⅰ & normodivergent, Class Ⅱ & hyperdivergent, and Class Ⅲ & hypodivergent. Their CBCT and dental cast models before treatment were integrated and fused, and then the landmarks of the fused models were obtained. Divided into left and right sides, the upper anterior and posterior occlusal planes were fitted separately using buccal landmarks, lingual landmarks, both buccal and lingual landmarks, and clinical crown centers in the median sagittal plane. Indicators reflecting the morphological and positional characteristics of the upper occlusal plane were mea-sured. Analysis of variance (ANOVA) or non-parametric test was employed to compare the differences in the indicators of the upper occlusal planes fitted using the four methods, as well as differences among three different skeletal type samples. Multiple comparisons were also conducted. Pearson's correlation coefficient was used to analyze the relationship between the indicators of the upper occlusal planes and skeletal types.

There were statistically significant differences in the intersection angles between the upper posterior occlusal planes and the palatal plane obtained using the four different fitting methods (F=7.05, P=0.002), as well as in the intersection angles between the anterior occlusal planes and the palatal plane (F=85.56, P < 0.001). There were also statistically significant differences in the intersection angles between the anterior and posterior occlusal planes (F=40.08, P < 0.001). Regardless of which of the four methods was used, the intersection angles between the upper anterior and posterior occlusal planes and the palatal plane, respectively, showed statistically significant differences (P < 0.001), among the three skeletal type samples. Only the intersection angles between the anterior and posterior occlusal planes individually fitted by clinical crown centers, exhibited a statistically significant negative correlation with the ANB (A point-nasion-B point) angle, mandibular plane angle, and palatomandibular plane angle (P < 0.05).

There were significant differences in the intersection angles of the upper anterior and posterior occlusal planes fitted with different landmarks with the palatal plane, respectively, and in the intersection angles between the anterior and posterior occlusal planes. From skeletal class Ⅲ & hypodivergent to Class Ⅰ & normodivergent and then to Class Ⅱ & hyperdivergent, the degree of forward and downward inclination of the upper posterior occlusal planes increased, while the degree of forward and upward inclination of the upper anterior occlusal planes decreased in sequence; the upper occlusal planes individually fitted by clinical crown centers were more sensitive to skeletal type differences and more accurately reflected the influence of facial skeletal types.