The reliability and validation of a 2D image analysis system when applied to the measurement of twin study model samples

Abstract

This study aimed to investigate dental fluctuating asymmetry of tooth dimensions in monozygotic (MZ) co-twins as a measure of how dental development is affected by epigenetic and environmental factors. The mesiodistal (MD), buccolingual (BL) dimensions of the central incisor, lateral incisor, second premolar and first molar in each of the four quadrants, on 20 sets of study models of MZ twin pairs were determined manually and two dimensional (2D) image analysis. The extent of asymmetry was assessed by determining intra-class correlation coefficients (ICCC’s) between pairs of antimeric teeth between individuals, then the fluctuating asymmetry (FA) between twin pairs determined. Intra-operator repeatability for 2D measurement was substantial or excellent. Differences were detected between left and right antimeres for all the four measurements, and these differences were not the same for both twins in a pair. 2D image analysis facilitated the additional measurements of surface area and perimeter. Asymmetry between twin pairs for each tooth type followed a pattern fitting with the morphogenetic field theory with the key teeth showing the least asymmetry (upper centrals, upper sixes, lower laterals, lower sixes) and the variable teeth showing the most asymmetry (upper laterals, upper fives and lower sixes). The MD dimension also followed this trend.