Reproducibility of the digital palate in forensic investigations: a two-year retrospective cohort study on twins

Abstract

The palatal scans of the same individuals were compared after two years to assess forensic reproducibility. The effect of orthodontic treatment, the comparison area and the digitization approach were investigated. The palate was scanned three times in 20 pairs of monozygotic twins with an intraoral scanner (IOS), to assess repeatability. The same subjects were re-scanned two years later, with two different IOSs. An elastic impression and a plaster model were also made and scanned with a laboratory scanner (indirect digitization). Mean absolute distance between scans was compared after best-fit alignment. Scans from the two sessions were compared to evaluate the combined effect of aging, orthodontic treatment and different digitization methods (forensic reproducibility). Additionally, the scans of different digitization methods from the second session were compared (technical reproducibility). The between-siblings difference was compared in the two sessions, to evaluate the effect of aging on palatal morphology. The anterior palatal area showed significantly better repeatability and forensic reproducibility than the whole palate (p<0.001), but orthodontic treatment had no effect. Indirect digitization produced lower forensic and technical reproducibility than IOSs. For IOSs, repeatability (22µm) was significantly (p<0.001) better than either forensic (75-77µm) or technical reproducibility (37µm). No significant changes were observed from the first to the second session in the between-sibling comparison. The closest between-sibling value (239µm) considerably exceeded the highest forensic reproducibility value (141µm). Reproducibility is acceptable between the different IOSs, even after two years, but is poor between IOS and indirect digitization. The anterior palate is relatively stable in young adults. Intraoral scanning of the anterior palatal area has superior reproducibility, regardless of the IOS brand. Therefore, the IOS method could be suitable for identifying humans through anterior palatal morphology. However, the digitization of elastic impressions or plaster models had low reproducibility, preventing their application for forensic purposes.