Endodontic Dentistry: Analysis of Dentinal Stress and Strain Development during Shaping of Curved Root Canals.

BACKGROUND: Endodontic shaping causes stress and strain in the root canal dentin. Dentin microcracks have the potential to be later followed by root fractures occurring under the occlusal load. The aim of our research was to theoretically determine the values of such dentinal states of stress and strain during the endodontic shaping of curved root canals using finite element analysis (FEA). METHODS: To highlight the stress concentrations in dentin, two geometric models were created considering the volume of the curved dental root and the contact between the endodontic file and the root canal walls. The application of forces with different values was simulated both on a uniform curved root canal and on a root canal with an apical third curvature of 25° as they would be applied during the preparation of a root canal. RESULTS: In the case of the first model, which was acted upon with a force of 5 N, the deformations of the root canal appeared along the entire working length, reaching the highest values in the apical third of the root, although there were no geometric changes in the shape of the root canal. Regarding the second root model, with an apical third curvature of 25°, although the applied force was 2 N, the deformations were accompanied by geometric changes in the shape of the root, especially in the upper part of the apical third. At a higher force of 7 N exerted on the endodontic file, the geometric shape changed, and the deformation reached extreme critical values. The resulting tensile stresses appearing in the experimental structure varied similarly to the deformations. CONCLUSIONS: Significant stress and strain can develop, especially in the apical third of curved root canals during their shaping, and the risk of cracks is higher for endodontically treated teeth presenting severe curvatures in the apical third of the root.

Influence of the Thermal Environment on Occupational Health and Safety in Automotive Industry: A Case Study.

Considering thermal environment aspects have a major impact not only on occupational health and safety (OH&S) performance but also on the productivity and satisfaction of the workers, the aim of the case study was to assess the thermal comfort of a group of 33 workers in an automotive industry company, starting with collecting data about the thermal environment from different workplaces, continuing with the analytical determination and interpretation of thermal comfort using the calculation of the Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) indices, according to provisions of the standard ISO 7730:2005, and comparing the results with the subjective perception of the workers revealed by applying individual questionnaires. The results of the study represent an important input element for establishing the preventive and protective measures for the analysed workplaces in correlation with the measures addressing other specific risks and, also, could serve as a model for extending and applying to other similar workplaces in future studies. Moreover, the mathematical model and the software instrument used for this study case could be used in further similar studies on larger groups of workers and in any industrial domain.

Microscopic morphological changes of the tooth surface in relation to fixed orthodontic treatment.

Orthodontic treatment has, as any other medical intervention, in addition to its benefits, side effects, some of them being perceived as unavoidable. The aim of this case series was to microscopically evaluate the changes of the tooth surface in relation to fixed orthodontic treatment. A case series study was implemented by the usage of four extracted first maxillary premolars, from patients with previous orthodontic treatment, of 12 and 23 months. Analysis was performed using the high precision stereomicroscope (Axiovert, Carl Zeiss, Germany), at magnifications from 10× to 50×. The tooth surface corresponding to the bracket bonding area registered numerous disorderly grooves and cracks, with various directions and depths, and was flattened, having lower convexity compared to teeth surfaces where brackets were not bonded. Root resorption lacunae were more frequently observed in teeth under orthodontic treatment, these having various depths, and sizes considerably larger than those observed in teeth without orthodontic treatment. Following orthodontic treatment, teeth exhibit changes that can be perceived as being directly linked to this medical intervention. These teeth changes usually have low or moderate severity, which can be influenced at some degree by the clinical conduct of the orthodontic treatment. The stereomicroscope proved to be a high sensitivity tool for the analysis of morphological changes of teeth in relation to the fixed orthodontic treatment.