Aim: To compare the levels, causes and the impact of stress from cohort of fifthyear dental students in the Faculties of Dental Medicine in Plovdiv, Bulgaria and Montpellier, France. Materials and methods: The questionnaire we used comprised the modified version of the 56-item Dental Environment Stress (DES) questionnaire. It was completed by fifth-year undergraduate dental students in both faculties in 2011 and 2016, totaling 335 dental students. A five-point Likert scale was used to record the responses from the subjects. Statistical analysis was performed with STATA version 14.1 (StataCorp, College Station, USA) specialized software. Results: The mean age of studied population was not significantly different between 2011 and 2016 (p=0.08). The common stress value per student was 1.74 (CI: 1.64; 1.84, range: 0.12; 4.50). It was higher in Plovdiv (1.79±0.81) than in Montpellier (1.63±0.66); it was statistically higher for girls (1.94±0.70) than for boys (1.49±0.77), and decreased between 2011 and 2016. A significant overall effect of the common mean stress was influenced by the town (p=0.008), year of study (p=0.003), gender (p=0.0001) and accommodation (p=0.01) of the student. Conclusion: Academicals and clinical factors of stress are prevailing stressors during education. The challenge is now to decrease the influence of both, without altering the quality of dental education. Regular discussions and debriefs about the clinical cases before and after clinical activity. Alternative methods of education and examination, such as interactive methods, could be considered in order to reduce the stress of theoretical exams.

AIM: The aim of the present work was to study the size of cavity wall deformation in eight class I and II defects after composite restoration. MATERIALS AND METHODS: 1. Creating a geometric model - data on the size of the left maxillary second premolar were obtained from a routine craniofacial scanning of a 20-yearold patient with a 2,5 Dental CT scanner (General Electric), with high resolution and 0.625mm-thin slices. The contour of each of the 33 cross-sections of tooth 25 was delineated using graphics software (CorelDraw 7.0) and transferred to a specialized product for engineering design (SolidWorks Offi ce Premium 2010, SolidWorks Corp. USA). The pulp cavity and periodontal ligament were created in the same manner and were integrated in the premolar body; 2. Generation of a fi nite element method - the geometric model was exported to specialized software for analysis by the fi nite element method - COSMOSWorks 2010, which automatically builds a 3D fi nite elements mesh. Based on the generated model, eight additional models of class I and II cavities with different geometries, adhesive layer and nanofi lled composite restorations were constructed. The polymerization shrinkage was modelled by thermal deformation, with a negative temperature difference (cooling), corresponding to the actual volume shrinkage of the composite materials by 2.1%. RESULTS: In models A and B, the maximum cavity wall displacement was small - 0.014 mm and 0.015 mm, respectively. In models A1, B1, C1 and C, the displacement was at the expense of large deformation of the dental tissues. The maximum cavity wall displacements were 0.020 mm, 0.026 mm, 0.020 mm, 0.035 mm, respectively. The least cavity wall displacement was in models A2 and B2 with 0.008 mm and 0.017 mm, respectively. CONCLUSIONS: The least displacement resulting from cavity wall deformation is found in patient-friendly class I and II preparations. Preservation of the dental tissues reduces the risk of mechanical pressure on the dentinal lymph and the likelihood of post-operative sensitivity.

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The immune response is a complex, dynamic and strongly individual biologic network that plays an essential role in the pathogenesis of chronic apical and marginal periodontitis. Recent research in the field of periodontology has indicated that the major determinant of susceptibility to disease is the nature of the immunoinflammatory response as marginal periodontal tissue damage is thought to be primarily mediated by the host reaction. Whether the same rules apply for the development of apical periodontitis, however, remains largely unexplored. This review aims to draw parallels between the pathogenesis of chronic periodontitis of endodontic and marginal origin, outline the evidence for the destructive role of immune response in chronic marginal periodontitis and raise questions about its role in chronic apical periodontitis. It would be worthy to further explore the impact of the immune system on the characteristics and progress of these diseases and transfer some of the scientific models from the field of periodontology to the field of endodontics. Research in this area could lead to a more comprehensive understanding of the dynamics of apical and marginal periodontitis and lay the foundation of new personalized treatment strategies.