External cervical root resorption. A multimodular analysis.

The research work focuses on the important topic of external cervical tooth resorption (ECR). ECR is a clinical condition that can result in tooth loss. The main outcome of this work is given hereafter.

A multimodular methodology combining histological analysis and advanced 3D imaging is needed in order to investigate and understand ECR cases. In particular, histology can provide information on cellular and tissue structures, whereas 3D imaging gives a 3D visualization of the resorption pattern at the tissue level.

Based on this approach, it was found that ECR was a very dynamic and complex process, whereas its nature is observed to be both destructive and reparative. The progression pattern is consisted of three stages, namely initiation, progression and repair. At the initiation phase, local destruction/disruption of the normal PDL architecture and cementum took place. In the resorption stage, ECR invaded the tooth structure by destroying cementum, dentin and enamel. At the reparative stage, repair took place by formation of bone-like tissue, which substituted the resorbed tooth structure. Resorption and repair can progress in parallel at the same time at different areas of the same tooth.

A similar ECR pattern (three stages) was observed in endodontically treated teeth. However, the absence of the pulp and the Pericanalar Resorption Resistant Sheet (PRRS) possibly accelerated the invasive actions of the clastic cells, whereas the reparative areas were more limited.

Descriptive analysis of potential predisposing factors showed that in the majority of the examined clinical cases, more than one potential predisposing factor was identified, indicating that ECR is multifactorial. In addition, some combinations of potential predisposing factors such as orthodontics with extraction of a neighbouring tooth, orthodontics with traumatic injury and orthodontics with parafunctional habits have a much higher frequency of appearance than others. This indicates a synergism between the factors.

In addition, gender does not seem to be related to ECR. On the other hand tooth position seems to play a vital role, as a much higher occurrence was observed at the maxillary central incisor, in comparison to other tooth types.

Finally, hypoxia was suggested as the main stimulating factor (driving force) of ECR, since it can regulate clastic cells formation, migration and activation. However, during the reparative stage the circadian rhythm and piezoelectricity might also have a contributing role.