Patterns of morphological integration in the dental arches of individuals with malocclusion.

OBJECTIVES: In humans, there is a large range of variation in the form of the maxillary and mandibular dental arches. This variation can manifest as either prognathism or retrognathism in either or both arches, which can cause malocclusion and lead to abnormal masticatory function. This study aims to identify aspects of variation and morphological integration existing in the dental arches of individuals with different types of malocclusion. METHODS: Coordinate landmark data were collected along the gingival margins of 397 scanned dental casts and then analyzed using geometric morphometric techniques to explore arch form variation and patterns of morphological integration within each malocclusion type. RESULTS: Significant differences were identified between Class II forms (increased projection of upper arch relative to the lower arch) and Class III forms (lower arch projection beyond the upper arch) in symmetrical shape variation, including anteroposterior arch discrepancies and abnormal anterior arch divergence or convergence. Partial least squares analysis demonstrated that Class III dental arches have higher levels of covariance between upper and lower arches (RV = 0.91) compared to the dental arches of Class II (RV = 0.78) and Class I (RV = 0.73). These high levels of covariance, however, are on the lower end of the overall range of possible masticatory blocks, indicating weaker than expected levels of integration. CONCLUSIONS: This study provides evidence for patterns of variation in dental arch shape found in individuals with Class II and Class III malocclusions. Moreover, differences in integration found between malocclusion types have ramifications for how such conditions should be studied and treated. Am. J. Hum. Biol. 28:879-889, 2016. © 2016Wiley Periodicals, Inc.

Phenotypic diversity in white adults with moderate to severe Class II malocclusion.

INTRODUCTION: Class II malocclusion affects about 15% of the population in the United States and is characterized by a convex profile and occlusal disharmonies. The specific etiologic mechanisms resulting in the range of Class II dentoskeletal combinations observed are not yet understood. Most studies describing Class II phenotypic diversity have used moderate sample sizes or focused on younger patients who later in life might outgrow their Class II discrepancies; such a focus might also preclude the visualization of adult Class II features. The majority have used simple correlation methods resulting in phenotypes that might not be generalizable to different samples and thus might not be suitable for studies of malocclusion etiology. The purpose of this study was to address these knowledge gaps by capturing the maximum phenotypic variations in a large sample of white Class II subjects selected with strict eligibility criteria and rigorously standardized multivariate reduction analyses. METHODS: Sixty-three lateral cephalometric variables were measured from the pretreatment records of 309 white Class II adults (82 male, 227 female; ages, 16-60 years). Principal component analysis and cluster analysis were used to generate comprehensive phenotypes to identify the most homogeneous groups of subjects, reducing heterogeneity and improving the power of future malocclusion etiology studies. RESULTS: Principal component analysis resulted in 7 principal components that accounted for 81% of the variation. The first 3 components represented variation on mandibular rotation, maxillary incisor angulation, and mandibular length. The cluster analysis identified 5 distinct Class II phenotypes. CONCLUSIONS: A comprehensive spectrum of Class II phenotypic definitions was obtained that can be generalized to other samples to advance our efforts for identifying the etiologic factors underlying Class II malocclusion.

Phenotypic diversity in white adults with moderate to severe Class III malocclusion.

INTRODUCTION: Class III malocclusion is characterized by a composite of dentoskeletal patterns that lead to the forward positioning of the mandibular teeth in relation to the maxillary teeth and a concave profile. Environmental and genetic factors are associated with this condition, which affects 1% of the population in the United States and imposes significant esthetic and functional burdens on affected persons. The purpose of this study was to capture the phenotypic variation in a large sample of white adults with Class III malocclusion using multivariate reduction methods. METHODS: Sixty-three lateral cephalometric variables were measured from the pretreatment records of 292 white subjects with Class II malocclusion (126 male, 166 female; ages, 16-57 years). Principal component analysis and cluster analysis were used to capture the phenotypic variation and identify the most homogeneous groups of subjects to reduce genetic heterogeneity. RESULTS: Principal component analysis resulted in 6 principal components that accounted for 81.2% of the variation. The first 3 components represented variation in mandibular horizontal and vertical positions, maxillary horizontal position, and mandibular incisor angulation. The cluster model identified 5 distinct subphenotypes of Class III malocclusion. CONCLUSIONS: A spectrum of phenotypic definitions was obtained replicating results of previous studies and supporting the validity of these phenotypic measures in future research of the genetic and environmental etiologies of Class III malocclusion.

Patient preferences regarding 1-visit versus 2-visit root canal therapy.

INTRODUCTION: Patient preferences should be taken into account by clinicians when treatment planning. The purposes of this study were to describe the number of visits patients preferred when undergoing root canal therapy (RCT) and to assess whether their preferences were related to hypothetical treatment success rates. METHODS: Self-administered questionnaires were mailed to 351 consecutive patients scheduled for initial RCT appointments in the University of Iowa College of Dentistry's graduate or faculty endodontic clinic. The questionnaires ascertained demographic information; preferences for 1-visit versus 2-visit RCT given different hypothetical success rate scenarios for the 2 approaches, as well as patient dental history. Univariate frequency distributions were generated, and relationships between hypothetical success rates and patient preferences were evaluated. RESULTS: Questionnaires were returned by 124 patients (35% response). Given equal success rates, 78% of respondents preferred 1-visit RCT, compared with 7% who preferred 2-visit RCT and 16% who would follow their dentist's recommendation. As success rates for 2-visit RCT went from equal to 5% better to 10% better to 20% better compared with 1-visit RCT, the proportion of respondents who preferred 2-visit RCT increased from 7% to 34% to 46% to 65%, respectively. Regardless of success rates, approximately 5% of respondents said they would prefer 2-visit RCT, and 20% would do whatever their dentist recommended. CONCLUSIONS: Although most respondents preferred 1-visit RCT regardless of success rates, many would prefer 2-visit RCT if its success rate were greater than that of 1-visit RCT. This finding confirms the importance of discussing success rates and considering patients' wishes when treatment planning.