The purpose of this study is to determine the heritability of occlusal traits in primary dentitions of Brazilian Twins using a twin study design. 16 pairs of monozygotic (MZ) identical twins casts and 19 pairs of dizygotic (DZ) fraternal twins casts were obtained from the University of Pittsburgh. Occlusal traits were measured directly off the casts using an electronic digital caliper calibrated to measure to the nearest 0.01 mm. The occlusal traits investigated include: overjet, overbite, left and right molar sagittal relationship, inter-canine arch breadth, inter-molar arch breadth, maxillary and mandibular arch length. Heritability was computed using a variance component model implemented in the SOLAR (AAVSO, Cambridge, MA, USA) computer analysis package. The heritability estimates were determined to be 84% for overjet, 90% for overbite, 38% to 42% for molar classification, 61% for maxillary inter-canine breadth, 91% for maxillary inter-primary second molar breadth, 95% for maxillary arch length, 82% for mandibular inter-canine breadth, 92% for mandibular inter-primary second molar breadth, and 35% for mandibular arch length. These results indicated a range from moderate to highly heritable genetic influences on phenotypic expression of occlusal traits in the primary dentition.
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