Date of Award



Department of Orthodontics

First Advisor

Marie M. Tolarová


Background and purpose: In recent years, questions regarding the genetic and environmental factors affecting variation in human craniofacial morphology have received increasing attention. Medical and clinical genetic research using family studies has proven foundational for our understanding of which genes affect craniofacial variation. On the other hand, cephalometricbased studies showed a relationship between the cranial base and midface characteristics among individuals with different skeletal pattern of malocclusion. The purpose of our pilot study was to analyze specific variants of facial genes that were suggested to be associated with cranial base width and depth in Class II and Class I malocclusions. Methods: Patient data (extraoral photographs, intraoral photographs, and iCAT CBCT images obtained as part of patients’ routine orthodontic examinations) was collected for patients who had come to the Orthodontic Clinic, Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, CA, from July 2019 to July 2021. For 72 patients who met the inclusion criteria for Class I or Class II groups in our study, saliva samples were collected, and DNA was isolated and analyzed using rtPCR genotyping for the following single-nucleotide gene polymorphisms (SNPs): rs79272428 (A>G), rs17106852 (A>G), rs12786942 (A>T) and rs6555969 (C>T). Results: We observed differences between Class I and Class II malocclusions in genotype proportions and allele frequencies in gene variants rs6555969 (C>T) and rs12786942. Genotype 4 CT (rs6555969) was found in a higher frequency in the Class I group generally and in the phenotypic Cluster 1. There were no differences observed for other gene variants studied. Regarding the cranial base characteristics, Asian patients had shorter and more acute cranial base. In Hispanic patients, there was a significant difference (P<0.005) between Class I and Class II patients regarding the cranial base width. Conclusions: The aim of our study was to determine genotypic differences between Class I and Class II malocclusion groups and to study genotypic associations with phenotypic clusters. We showed genotypic and phenotypic cluster differences between Class I and Class II groups. These differences were not statistically significant, probably, due to a small size of the studied groups. However, in this pilot study, we found trends, on which we will focus in our future study using a larger sample.