ABSTRACT
Objective: Despite the high strength of zirconia restorations, aging in the oral environment and masticatory loading may result in transformation of tetragonal to monoclinic phase and decrease their strength. Statements in this regard are controversial. This study sought to compare the flexural strength [FS] of Zirkonzahn [ZirkonZahn, Cercon, Ceramill] and Mamut [Dubai Medical Equipment LLC, Dubai, UAE] zirconia ceramics and assess the effect of thermal and mechanical aging on their FS
Methods: In this in vitro experimental study, 40 bar-shaped specimens measuring 20×5×2 mm were cut from Zirkonzahn and Mamut zirconia blocks and polished. Specimens in the aging groups were subjected to thermocycling [12,000 cycles, 5-55[degree sign], dwell time of 20 seconds]. Next, they were subjected to mechanical stress in a chewing simulator [40,000 cycles, 200N force]. The three-point flexural strength [TPFS] was determined in megapascal [MPa] using a Universal Testing Machine at a crosshead speed of 0.5 mm/min. Data was analyzed using two-way ANOVA
Results: The mean and standard deviation [SD] of TPFS of Zirkonzahn and Mamut specimens in the no aging group was 809.57 [205.95] and 708.53 [158.72] MPa, respectively. These values were 810.53 [158.96] and 839.06 [217.49] MPa for the Zirkonzahn and Mamut specimens subjected to aging, respectively. Type of zirconia [Zirkonzahn or Mamut] and exposure to aging process [p=0.27] had no significant effect on TPFS of specimens
Conclusion: Within the limitations of this study, the results showed that the process of aging did not decrease the TPFS of Zirkonzahn and Mamut specimens. Thus, these ceramics may be successfully used in the clinical setting
ABSTRACT
PURPOSE: Heat of composite polymerization (HP) indicates setting efficacy and temperature increase of composite in clinical procedures. The purpose of this in vitro experimental study was to evaluate the effects of 5 temperatures on HP of two new composites. MATERIALS AND METHODS: From each material (Core Max II [CM] and King Dental [KD]), 5 groups of 5 specimens each were prepared and their total HPs (J/gr) were measured and recorded, at one of the constant temperatures 0degrees C, 15degrees C, 23degrees C, 37degrees C and 60degrees C (2 x 5 x 5 specimens) using a differential scanning calorimetry (DSC) analyzer. The data were analyzed using a two-way ANOVA, a Tukey's test, an independent-samples t-test, and a linear regression analysis (alpha=0.05). RESULTS: No polymerization reactions occurred at 0degrees C; then this temperature was excluded from statistical analyses. The mean HP of the remaining 20 KD specimens was 20.5 +/- 14.9 J/gr, while it was 40.7 +/- 12.9 J/gr for CM. The independent-samples t-test showed that there were significant differences between the HP of the two materials at the temperatures 15degrees C (P=.0001), 23degrees C (P=.0163), 37degrees C (P=.0039), and 60degrees C (P=.0106). Linear regression analysis showed statistically significant correlations between environment temperatures and HP of CM (R2=0.777). CONCLUSION: Using CM is advantageous over conventional composite because of its better polymerization capacity. However due to its high HP, further studies should assess its temperature increase in vivo. Preheating KD is recommended. Refrigerating composites can negatively affect their polymerization potential.