Geometric Morphometric Analyses of Dental Arch Asymmetry

Growth of bilateral structures is not a standard phenotypic finding in humans during development. Dental arch asymmetry is a common finding in orthodontically untreated children as well as in subjects with congenital malformations, finger sucking, extractions, interproximal caries and other extrinsic factors. Full asymmetry of an organism consists of two components: directional asymmetry (DA) and fluctuating asymmetry (FA). As a sensitive indicator of the organism's ability to cope with the stresses during ontogeny, one would expect FA of the dental arch in an inbred Adriatic island population to increase with the level of inbreeding, and to be higher than in an outbred sample from a panmictic population. Two hundred and fifty five dental casts of children from the island of Hvar, Croatia, with various inbreeding estimated from different endogamy levels. Dental casts from a panmictic population from Zagreb, Croatia formed the control group. The tree dimensional coordinates of 26 dental arch landmarks were digitized with Polhemus Fastrac. For the decomposition of the original forms into DA and FA, the Procrustes asymmetry assessment was applied. FA was higher in the island sample than in control group and increasing FA with the endogamy level. There was no significant DA in the Zagreb sample and likewise in the upper jaw of the outbred island group, but significant DA in both jaws of the inbred population. The endogamous groups were consistently different in conformation of left and right side while the reference sample did not exhibit DA. These results suggest an environmental as well as a genetic influence on dental arch asymmetry, and while the lower jaw expresses these two stresses almost additively, the upper jaw appears to be better buffered.