Thesis
Dentoalveolar variation in mandibular arches of individuals with orofacial clefts and unaffected relatives
University of Iowa
Master of Science (MS), University of Iowa
Spring 2021
DOI: 10.17077/etd.006024
Abstract
IntroductionIndividuals born with cleft lip/palate (CL/P) exhibit a broad phenotypic spectrum including abnormalities in craniofacial growth, dental anomalies, and malalignment of teeth and jaws, which can exist with varying degrees of severity. Because CL/P is inherited in a multifactorial way, with contributions from both genetic and environmental factors, phenotypes of unaffected family members (UFM), who presumably carry greater genetic risk, have been investigated in order to better understand the genetic basis and phenotypic spectrum of CL/P. Previous studies have evaluated cephalometric features, facial shapes, and dental morphology of unaffected relatives. The present study uses geometric shape analysis of landmarks from digital models of dental arches to compare mandibular arch shape differences between individuals with clefts, UFM, and controls.
Materials and Methods
Landmarks were placed along gingival margins, incisal edges and cusp tips of digitized mandibular dental casts of 1747 individuals comprised of individuals with a non-syndromic cleft (n=71), their unaffected family members (UFM) (n=481), and controls without a known family history of clefting (n=1195). A Procrustes fit procedure was done on the three-dimensional landmarks to allow shapes to be compared. Mahalanobis and Procrustes distances were measured between groups for both an anterior arch (canine to canine) comparison and a full arch (first molar to first molar) comparison. The full arch analysis employed 80 landmarks, and the anterior arch analysis employed 40 landmarks. A permutation test with 10,000 iterations was used to determine significance. Canonical variate analysis was used to characterize shape differences between groups. In addition to the case-UFM-control comparisons, the same techniques were used to evaluate differences in arch shape comparing different types of clefts to one another and to a control group with no clefts that included both controls and UFM.
Results
Significant shape differences were found in both Mahalanobis and Procrustes distances between cases, controls, and UFM with the greatest differences being those between cases and UFM. In both the full-arch and anterior-arch canonical variate analysis, variation was separated into two components: the first separated individuals with clefts from controls and UFM, and the second separated UFM from controls. Mandibles of individuals with clefts were largely separated from controls and UFM in ways that can be described as Class III dentoalveolar compensations, having upright incisors, lingually inclined molars, less anterior arch projection and squarer arches. They also exhibited shorter teeth, in general. UFM differed from controls in a way that was distinct. They had incisors with retruded gingival margins, and taller teeth with more open incisal embrasures. When comparing mandibles of individuals with different cleft types to one another and to controls, no differences were found between different cleft types. The only significant mandibular shape differences found were those between cleft and non-cleft individuals.
Conclusions
There are significant differences in mandibular arch shapes between individuals with clefts, UFM – who have increased genetic risk of clefting, and controls. Mandibular arches of individuals with clefts are highly variable but tend to exhibit proportionately shorter teeth and dental compensations associated with Class III malocclusion. Arches of UFM show more subtle shape differences than cases when compared to controls, but tend to have taller teeth, more open incisal embrasures, and incisors that are retrusive at the level of the gingival margins. While we hypothesized that mandibular shape differences might be expressed along a spectrum, with cleft individuals representing one extreme, controls representing the other, and UFM taking an intermediate position, we did not find this. Rather, individuals with clefts and UFM each differ from controls in distinct ways, demonstrating that there does not appear to be a gradual spectrum of expression of mandibular shape variation that correlates with genetic risk. Significant differences in mandibular arch shape were detected between each cleft type and controls, although not consistently. We were unable to detect differences in mandibular arch shape between the different types of clefts.
Details
- Title: Subtitle
- Dentoalveolar variation in mandibular arches of individuals with orofacial clefts and unaffected relatives
- Creators
- Mitchell C Hemann
- Contributors
- Lina M Moreno Uribe (Advisor)Steven Miller (Committee Member)Shankar Rengasamy Venugopalan (Committee Member)Brian Howe (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Orthodontics
- Date degree season
- Spring 2021
- DOI
- 10.17077/etd.006024
- Publisher
- University of Iowa
- Number of pages
- xii, 75 pages
- Copyright
- Copyright 2021 Mitchell C Hemann
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 67-75).
- Public Abstract (ETD)
Individuals born with cleft lip/palate (CL/P) exhibit a broad spectrum of traits including dental anomalies and malalignment of teeth and jaws, which can exist with varying degrees of severity. Work has been done to describe these and other qualities to expand the understanding of the condition and better treat these individuals who often require numerous medical interventions.
CL/P is inherited in a multifactorial way, including both genetic and environmental factors. Because of the genetic component, studies have investigated how unaffected relatives of individuals with clefts (UFM), who carry greater genetic risk, are different from the general population. Studies have investigated dental, skeletal, and facial characteristics and have combined these with genetic studies, in an attempt to understand the genetic underpinnings of CL/P and to further describe the subtle ways the condition can be expressed.
The present study uses geometric shape analysis of over 1,700 digital models of dental arches to compare mandibular arch shape differences between individuals with clefts, UFM, and controls. Shape differences were found between all three groups. Rather than there being a single spectrum of mandibular shape differences, we found that cleft individuals and UFM are each different from controls in unique ways. Mandibular arches of UFM did not represent a milder version of how cleft individuals differ from controls. We also compared individuals with different types of clefts to one another, but did not find significant differences between groups.
- Academic Unit
- Orthodontics; Craniofacial Anomalies Research Center
- Record Identifier
- 9984097278102771
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