GP2d - Cranial Base Shape Is Significantly Associated With the Skeletal Malocclusion Phenotype

Abstract: The cranial base plays a crucial role in craniofacial development by serving as a structural foundation and growth center for the face and skull. Abnormalities in the cranial base can lead to craniofacial disorders. The results of previous studies regarding the association of the cranial base morphology with the development of the maxilla and mandible, and ultimately the skeletal malocclusion, have been controversial, with most of these studies conducted using data derived from two-dimensional (2D) images such as lateral cephalograms. The aim of this study is to clarify the role of the cranial base in the development of skeletal malocclusion with the use of data derived from 3D imaging with the use of quantitative shape analyses.
Cone-beam computed tomography (CBCT) images from a curated normative dataset of 306 de-identified individuals with Class I (N–f100), Class II (N f100) and Class III (N–f106) malocclusion, were analyzed in 3D with a use of a validated set of 43 anatomical landmarks by trained intercalibrated observers (mean age 24.5 years, 167 females). Two Class III subgroups were created based on what was the main deformity in the initial diagnosis: Class IIIA/Maxillary Hypoplasia (N–f29), Class IIIB/Mandibular Hyperplasia (N–f78). The Cartesian landmark coordinates were exported for analysis. Principal Component Analysis (PCA) was used to explore the overall shape variation between skeletal classes. Canonical Variate Analysis (CVA) was also conducted including only the coordinates of the cranial base landmarks to compare the shape between the three skeletal Classes. 3D plots were generated for visualization of the PCA and CVA results. Pre- and post-operative CBCTs from N– 31 orthognathic surgery patients (N–f28 Class III, N–f3 Class II; N–f19 one jaw cases; N –f12 two-jaw cases) were analyzed and then projected to the normative database PCA plot to assess their pre- and post-surgical classification in order to further evaluate the contribution of the cranial base in the skeletal malocclusion phenotype. All participants had been consented onto IRB-approved protocols.
The 3 skeletal classes clearly clustered on the complete skull PCA, which explained almost 40% of the overall shape variation. The results of the CVA analysis which explained 100% of the morphological variation indicate morphological differences of the cranial base shape between the skeletal Classes, with a clear difference between Class III and the other two Classes. In all 28 Class III surgical cases and in 2 out of 3 Class II cases, the postoperative craniofacial shape remained within the original skeletal malocclusion cluster, despite the orthognathic surgical correction and the achievement of Class I jaw relationships.
The overall craniofacial shape clearly segregates into the three skeletal malocclusion types. The cranial base shape plays a significant role as the orthognathic surgery correction to Class I did not move the patients to the Class I cluster; instead, the patients remained in the original skeletal malocclusion cluster despite surgery. The decoding of the integration between the modules of the skull will be a key element in the deeper understanding of the craniofacial development in dentofacial deformities, thereby accurately establishing craniofacial growth prediction models.

References:
1. Lieberman DE, Hallgrímsson B, Liu W, Parsons TE, Jamniczky HA. Spatial packing, cranial base angulation, and craniofacial shape variation in the mammalian skull: testing a new model using mice. Journal of Anatomy. 2008;212(6):720-35.
2. Baccetti T, Reyes BC, McNamara JA, Jr. Craniofacial changes in Class III malocclusion as related to skeletal and dental maturation. Am J Orthod Dentofacial Orthop. 2007;132(2):171.e1-.e12.
Figure 1. a. Visualization of the results of the CVA with the use of a 3D plot. Class IIIA and IIIB groups extend in a different direction from the Class I and II groups across the PC1 axis, which explains most of the morphological differences. b. Wireframes comparing each skeletal malocclusion Class (II, IIIA, IIIB) with the mean Class I cranial base shape. Class IIIA subjects are more similar morphologically to the Class I group’s cranial base angulation, in comparison to the Class IIIB subjects who present with a more acute cranial base angle. Both Class III groups present a wider cranial base width in comparison to the Class I group. The Class II group presents with the opposite trends, with a more obtuse and narrower cranial base angle in comparison to the orthognathic subjects. Figure 2. a. Preoperative and postoperative clinical profile photos and CBCT volume renderings of a double jaw orthognathic surgery case. b. PCA 3D plot of the normative cohort where the subject’s preoperative and postoperative CBCTs are projected. The preoperative CBCT’s position in the plot is closer to the Class IIIC subgroup, which agrees with her clinical diagnosis. Her postoperative CBCT is still projected within the Class IIIC subgroup cluster, despite the extensive surgical correction. This indicates that the shape of the cranial base, which remains intact, defines the classification of the subject to a significant extent.