Three-dimensional Analysis of Dental Arch Dimensions in Hypodontia and Controls

Objectives: To develop and validate a new 3D methodology for dental arch measurement; to compare dental arch dimensions in hypodontia patients with matched controls; to assess sexual dimorphism of arches in hypodontia.
Methods: The sample was 137 patients, 69 with mild and moderate hypodontia and 68 controls matched for age, sex and ethnicity. Maxillary and mandibular dental casts were scanned using an Amann Girrbach Ceramill Map400 3D scanner to produce a stereolithographic image. Measurements for intercanine (IC) width, intermolar (IM) width and arch length (AL) were recorded. MeshLab software was used for linear point-to-point measurements to record IC and IM widths. Custom software was designed for the arch length measurements. Arch length was recorded from the distal of the first molar through the ideal mesio-distal contact points to the distal of the contralateral first molar. Intra- and inter-operator reproducibility were assessed for all measurements. Validation of the 3D measurements was also undertaken by comparison with 2D calliper measurements. Intra-class correlation coefficients ranged from of 0.80 to 0.95. Measurements were analysed using linear-mixed effects models.
Results: Results showed statistically significant reductions in IC (p<0.0001), IM (p<0.05) and AL (p<0.02), in the maxillary arch in hypodontia compared with controls. No significance differences were seen in the mandibular arches. Male controls had larger and wider arches than female controls (p<0.0001) but this difference was less when comparing hypodontia males with hypodontia females (p=0.05).
Conclusions: A new method of analysing dental arches in 3D has been developed which can be further advanced with the application of geometric morphometrics. Hypodontia patients had statistically significant differences in arch dimensions compared with the control group. Hypodontia affected maxillary arch morphology to a greater extent than the mandibular arch. The extent of the phenotypic change is greater in males with hypodontia.