ABSTRACT
Marginal adaptation is important for long-term success of full-coverage restorations. Thickness of core is one of the important factors influencing the marginal integrity. Thus, the aim of this study was to evaluate the effect of different thicknesses of zirconia core on marginal adaptation of all-ceramic restorations. In this single blind in vitro study, a standard brass die 7 mm in length and 5 mm in diameter was prepared with a classic chamfer finish line with 0.8 mm depth and 10 degrees of wall taper. Copings were made using the CAD / CAM system. We had three groups of 10 samples each. Group 1 with a zirconia thickness of 3.0 mm, group 2 with a thickness of 0.5 mm and group 3 with a thickness of 0.7 mm. Copings were then placed on the die and randomly numbered. The vertical gap in the margin was measured at 10 points using scanning electron microscopy [SEM]. Data were collected. The mean and standard deviation values were calculated and ANOVA was used for the comparison of the three groups. Tukey's test was also applied. The gap in 0.3, 0.5 and 0.7 mm thicknesses of zirconia before porcelain firing was 89.21 +/- 28.90, 79.55 +/- 39.32 and 40.813 +/- 10.3 micro, respectively. The difference in marginal gap between the three groups was statistically significant [P=0.001]. Tukey's test failed to find a significant difference in marginal gap between 0.3 and 0.5 mm thicknesses [P=0.006]. But, the difference between 0.3 and 0.7 mm [P=0.001] and also 0.5 and 0.7 mm [P=0.001] was statistically significant. Based on the results, by increasing the thickness of the zirconia core marginal gap decreases in all ceramic restorations
ABSTRACT
Fractured ceramic crowns can sometimes be repaired with composite resin. The aim of the current study was to determine the shear bond strength of composite to Feld spathic porcelain after CO[2] and Er:YAG laser porcelain surface preparation. In this in-vitro study, 36 Feldspathic porcelain blocksmeasuring 1*10*10 mm were divided into 3 groups of 12. Porcelain surfaces in the first and second groups were treated with 1.8W CO[2] laser and 5W Er:YAG laser irradiation, respectively. Third group specimens were subjected to 9.5% hydrofluoric acid surface conditioning. All groups received application of silane and adhesive after wards. A composite cylinder with 3.5 mm diameter and 5 mm height was bonded to specimens. In order to evaluate the shear bond strength, a Universal Testing Machine with crosshead speed of 1 mm/min was used. Statistical analysis was performed using one-way ANOVA and Tukey's HSD test and P<0.05 was considered statistically significant. The mean shear bond strength values [MPa] were 13.03 +/- 2.57%, 12.02 +/- 3.4 and 19.23 +/- 4.62, for the first, second and third groups respectively. One-way ANOVA revealed a statistically significant difference in this respect between the three groups [P< 0.001]. Tukey's HSD test demonstrated significant differences between the first and third groups [P= 0.000] as well as the second and third groups [P=0.000]. However, no significant difference was detected between the first and second groups [P =0.778]. Considering the study results, CO[2] or Er:YAG laser irradiation is not suggested as an appropriate alternative to hydrofluoric acid for surface preparation of Feld spathic porcelain
ABSTRACT
Intrapulpal posts are used as retention for reconstructing of missed crown. Today fiber posts eliminated most of disadvantages of metal posts. The purpose of this study is a comparison of stress distribution in these types of posts [casting and Quartz fiber post] on root canals of teeth with photo elastic method. In this experimental study Quartz fiber and casting posts with length of 15mm and diameter of 0.9mm were used. Four epoxy resin models [10x20x40mm] were made that two of them include casting posts and two other include Quartz fiber posts. Then, cores were prepared for each model. Vertical force of 100N and oblique force with 30' and 150 N were applied on cores and isochromatic fringe patterns around post were recorded in the field of Polariscope. In the vertical loads the minimum cervical stress was observed in casting post that was 1.22 [in Quartz fiber post it was 2.65] But in apical region maximum stress was recorded in casting post that was 1.63 [in Quartz fiber post it was 1.38]. In the oblique load, casting post showd 1.39 stress in cervical that was the minimum [in Quartz fiber post it was 2.35] and in the apical region, casting post showed the maximum stress that was 1.68 [in Quarts fiber post it was 1] display more critical stress pattern [1.63]. In the vertical and oblique loads casting posts shows the maximum stress in the apical region that makes the worse fracture in tooth that couldn't be prepared but in Quartz fiber post maximum stress was in cervical region so it is more repairable