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    Effect of post-restoration on stresses in premolars with endodontic-periodontal lesion: an FEA study
    (TAYLOR & FRANCIS LTD, 2017) Belli, Sema; Eraslan, Oguz; Hakki, Sema Sezgin; Eskitascioglu, Murat; Eskitascioglu, Guercan
    Aim: This finite elemental stress analysis (FEA) study was aimed to test the effect of fiber and metal posts on stress distribution in premolar teeth with endodontic-periodontal (EP) lesion. Methodology: Three FEA models representing different EP lesions (primary endodontic disease (PED), PED with periodontal involvement and true-combined) were created. Tooth-model without EP lesion was used as control. The root-canals were assumed as root-filled, restored using glass-fiber or metal posts, resin composite build-up, and ceramic crown. A 300 N load was applied from the palatal surface of the crown with a 135 degrees angle. The SolidWorks/Cosmosworks structural analysis program was used for FEA analysis. Results were presented by considering von Mises criteria. Results: Maximum stress values for PED, PED with periodontal-involvement and true-combined lesions were 2.26, 1.25, 0.74 MPa for glass-fiber post; 2.08, 1.51, 1.18 MPa for metal post, respectively. If there is PED, fiber-post gave an advantage to the tooth at core structure and coronal third of the root. Metal post kept the stress inside its body however caused small, high stress concentrated areas at cervical. When there is PED with periodontal-involvement, metal post forwarded less stress toward the apical while fiber-post saved the coronal structure. In true-combined lesion model, metal post kept the stresses within its body and forwarded less stress toward the remaining root structure and periodontium. Conclusion: EP lesions have an effect on stress distribution therefore the post material selection should be done based on the severity of the lesion. Metal posts might be preferrable since it forwards less stress toward the surrounding periodontal tissues during wound healing.
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    A Study on Dimensional and Marginal Gap Changes Through Application of Different Sintering Methods and Veneer Firings on Zirconia Crowns
    (Selçuk Üniversitesi, 2021) Aydogdu, Hasan Murat; Eskitascioglu, Murat
    Background: The marginal fit of dental restorations is a vital factor for long-term success. The veneering process of zirconia, which involves multiple firings at high temperatures, has shown to affect the marginal fit of zirconia cores. The aim of this study is to observe dimensional and marginal gap changes during veneer firing of zirconia frameworks sintered with different procedures. Methods: 30 Y-TZP ((inCoris ZI, Sirona, Bensheim, Germany) crown frameworks sintered with three different durations of 8 hours, 2 hours and 10 minutes. Occlusal and buccal dimensional measurements based on reference points measured with toolmaker’s microscope. Frameworks subjected to veneer firings without application of veneering material to observe the effect of firing process only. All dimensional and marginal gap measurements were repeated and after veneer firings. Data were analysed with one-way ANOVA and paired t test. Results: No significant differences observed between the sintering shrinkage of three groups. Marginal gaps decreased after veneer firings for all groups and the decrease was significant for 2 hour and 10-minute sintering groups (p <.05). The occlusal surface dimensional changes were negative which indicates shrinkage; again, buccal surface was positive which indicates enlargement. No significant differences between the three groups regarding surface dimensions were detected. Conclusion: For all three sintering groups, veneer firing caused distortion on zirconia structures in the form of shrinkage in occlusal surfaces and enlargement in buccal surfaces, whereas marginal gap values decreased after firing in all groups.