Scanning electron microscopy (SEM) and macroscopic analysis of immature human permanent molar immersion in hydrochloric acid (HCL, 38%).

Recent literature indicates the destruction of human remains using hydrochloric acid (HCl, 38%) is often attempted to obscure the identity of victims or as a disposal method. Dentition are informative in an investigation where acid is used as a means of body disposal, as teeth are more likely to survive intact. Importantly, researchers studying acid immersion have not observed immature dentition, nor have they analyzed immature acid-treated teeth using scanning electron microscopy (SEM). This study analyzes the effects of HCl on immature human molars, with two goals: understanding the timing and nature of physical changes to immature molars caused by HCl immersion, and aiding in the identification and age determination of dental tissues partially or nearly completely destroyed using HCl. Our results indicated that immature human molars immersed in HCl follow a pattern of physical changes and decrease in weight as they dissolve similar to mature molars, although the timing of dissolution is affected by their smaller size and incompletely developed roots in a predictable way. With less root material present and an open root tip, we observed that HCl can more quickly penetrate the pulp cavity of immature molars. The mobile SEM images indicated immature and mature molars immersed in HCl exhibit similar changes at the microscopic level. Immature molars treated with HCl for over 18 h exhibited cracking features similar to those visible on mature molars that were difficult to differentiate from similar features on untreated teeth (both mature and immature) when images were taken at 3,000x or less. The appearance of features such as peeling layers and lamination at high magnification (6000x) were visible on both acid-treated mature and immature molars, but were not visible on untreated molars at the same level of magnification. By observing changes in the enamel and pulp cavity, it was possible to determine whether third molars were immature until approximately 18 h immersed in acid. At 42 h, it was no longer possible to determine whether the molars were immature. However, they were still easily identifiable as human teeth. In situations where teeth may no longer be identifiable macroscopically, we found that the laminating and peeling features observed on high magnification SEM imagery can be useful in characterizing acid treatment even on very small fragments of dental remains, potentially allowing investigators to determine if acid was used as a disposal method.