Cephalometric variability among siblings
Marcks, Katharine Luskin
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OBJECTIVE: To determine whether multiple siblings in a family resemble one another in terms of their craniofacial characteristics. METHODS: This pilot study was conducted retrospectively using the Forsyth Twin sample. 32 families were included, each with at least 4 siblings who had lateral cephalometric radiographs taken after skeletal maturity was documented, for a total of 142 subjects. Headfilms were digitized and skeletal landmarks located to allow measurement of 6 parameters indicating sagittal jaw relationships and vertical status. Dixon’s Q test was applied to identify any outliers in a family for a given parameter. Manhattan distance quantified similarity among siblings per parameter. Scatter plots visually displayed subject’s measure relative to the mean and standard deviation of each parameter to assess clinical relevance. RESULTS: 11 families (34.4%) had no outliers on any of the 6 parameters, 13 families (40.6%) had outliers on only 1 parameter, and 8 families (25%) had outliers on at least 2 parameters. Our analyses identified 29 individuals with at least one outlying measure (20.4%). Of those, only 2 individuals (1.4%) were significantly different from their siblings for more than 1 measurement. Although the majority of the families did not demonstrate a statistical outlier for any given measurement, the ranges were clinically relevant as they might lead to differing orthodontic treatment plans. CONCLUSIONS: Although families are generally not statistically dissimilar in their craniofacial characteristics as measured on cephalometric radiographs, measurements from siblings cannot be used to predict the measurements of another sibling in a clinically meaningful way.