Development of an experimental model for assessment of palatal tissue decomposition by intraoral scanner

Abstract

Intraoral scanning of the palate is considered reliable for human identification; however, its accuracy on postmortem tissue remains dubious. This study aimed to investigate the effect of tissue decomposition on the precision of the intraoral scanner and the deviation of the scan. Ten fresh lamb (Ovies aries) maxillae were either unwashed or washed, selected, and stored at 20.5 °C and 80 % humidity for 20 days. Each palate was scanned three times a day with an Emerald S intraoral scanner. The anterior rugae area was cropped for analysis. The three scans of each day for each lamb were digitally aligned using the iterative closest point algorithm to ensure precision. The day one mesh was compared to each subsequent day to assess the postmortem scan deterioration, and a quadratic curve was fitted to the data. The mesh from different lambs was compared on day one to calculate the differences between the lambs. The length, location, and value of the largest curvatures of five randomly chosen rugae on each specimen were determined. A supervised machine learning procedure using linear discriminant classification assessed the specificity and sensitivity of singular ruga discrimination. Precision was significantly lower (p < 0.001) in the unwashed group (0.025 mm) compared to the washed group (0.013 mm), but the postmortem days had no effect. The deviation curve for the unwashed samples had a significantly higher quadratic term (p < 0.05) compared to the washed sample, indicating a slightly greater deterioration after day 11. The least difference between lambs was 0.484 mm. The deterioration curves crossed the minimum value on day 6 in both groups. The sensitivity of rugae detection was 0.89 on day one and decreased to 0.69 on day 20; the specificity ranged from 0.59 to 0.66. Intraoral scanning is an accurate approach for postmortem palatal imaging. Superimposition of the anterior palatal scan can accurately distinguish between lambs for up to six days. Nevertheless, deteriorated rugae can still be distinguished with moderate accuracy for up to 20 days.

Keywords: Forensic dentistry; Identification; Intraoral scanner; Palate; Postmortem; Tissue decomposition.