Towards Synetic Superimposition of Dental 3D Data

Accurate quantification of dental morphology is an important component of studies investigating the causes of variation in dental development e.g. using monozygotic twin pairs. However, superimposition of 3D dental images using "best fit" non-linear methods to identify differences between co-twins produces inconsistent results. Therefore, we have developed a new approach, "Synetic superimposition", to allow regions of difference in dental crowns to be both identified and quantified. This method minimises the least squares calculations for registration of surface data into full 3D voxel datasets. Diffusion based registration is then used to superimpose an image of one twin on that of the co-twin.

Objective: To assess the reliability of obtaining 3D laser scanned images of individual teeth using dental study models of monozygotic twins, as an initial step in validating the application of Synetic Superimposition.

Methods: 3D scans of dental study models were produced using an Optix 400s profile laser scanner. Two operators each produced two sets of scans of 20 maxillary models for reliability calculations. Each operator then produced two separate sets of measurements detailed in Table 1. Fleiss' intra-class correlation coefficient was calculated to give estimates of intra- and inter-operator reliability. The variables chosen represented direct measurements between two points and also across the surface of the crown (denoted by ‘a').

Results: The reliability of the 3D images created by two operators ranged from good to

excellent (Table 1).

Conclusions: This approach to producing 3D scans of dental study models has proven to be repeatable and reproducible for several measurement variables. These 3D laser scans will form the datasets to enable further development of the Synetic superimposition methodology. Further reliability tests will be undertaken of the superimposed image comparisons.

Table 1. Intra and inter-operator reliability based on ICCC values

MD = mesio-distal, LL = labio-lingual, IG=inciso-gingival, SA = surface area.