The effects of different root canal irrigation protocols and artificial aging procedures on the bond strength between dentin and hybrid ceramic posts.

The purpose of this study is to investigate the effects of different root canal irrigation protocols applied to the dentin and artificial aging procedures on the micro pushout bond strength (mPBS) between dentin and hybrid ceramic posts. Seventy-five single-rooted mandibular premolar teeth were divided into 5 groups (Gr1-5). 50 of the teeth were used for the mPBS tests (n = 10), whereas 25 were used for the smear layer examinations (n = 5). Post space were prepared and irrigated with different irrigation-protocols in each group. (Gr1:[SS], Gr2:[NaOCl] + SS, Gr3:[EDTA] + NaOCl + SS, Gr4:[MA] + NaOCl + SS, Gr5:[Ch] + NaOCl + SS). Post and core pattern were fabricated with pattern resin and a fiber post, after scanning, the posts were milled with Vita Enamic resin ceramic block, and cemented. After 7 days the roots were sliced at thicknesses of 1 mm; half of them were subjected to mPBS test, while the other half were tested after undergoing mechanical cycling for artificial aging. For data analysis, the Shapiro-Wilk test was utilized to test normal distributions, 3-way analysis of variance was used to compare mPBS, and Tukey's HSD test was conducted for multiple comparisons. SEM analysis was performed for examination of failure modes and smear layer removal. Different root canal irrigation protocols affected mPBS significantly. While Gr4 had the highest mPBS, Gr1 had the lowest. Regarding to different zones, the highest mPBS was in coronal zone, and the lowest one was in the apical zone. The aging procedure also led to a statistically-significant decrease in mPBS. Most frequent failure modes were cohesive failure in dentin and mixed failure. Irrigation with 7%MA (Gr4) showed better performance than 17% EDTA (Gr3) in smear layer removal, especially at the apical zone of the tooth. This is critical for the success of root canal treatment and increased the mPBS to a higher extent in all zones of the tooth.

Effect of Repeated Firings and Thickness on Optical Properties of Variable Preshaded and Shaded Novel Translucent Zirconia Blocks.

Objective: The purpose of this study was to examine the optical properties of translucent zirconia with different thickness during multiple firings. Materials and Methods: Three different types of translucent zirconia (Vita YZ HT (HT), Vita YZ ST (ST), Vita YZ XT (XT)) with thickness of 0.5, 1, and 1.5 mm were used in the study. 180 disk-shaped specimens (n = 10) were prepared from preshaded and nonshaded blocks. The coloring liquid (A2, Vita Shade Liquid) was applied with a synthetic nylon brush in the nonshaded group. Then, the specimens were then subjected to 1, 3, and 5 firing times. After consecutive firings, color differences (ΔE) and translucency parameter (TP) were measured. Statistical analysis was carried out by using repeated measure ANOVA followed by Tukey test. Results: ANOVA analysis reveals that TP and ΔE were significantly affected by the repeated firings. The highest TP was seen in 0.5 mm XT specimen. For all specimens, TP decreases from 1st to 3rd firing cycles, despite TP increases from 3rd to 5th firing cycles. Although there is a significant change in TP values in 0.5 mm thickness, there is no significant change between firing cycles for 1 and 1.5 mm thickness specimens. The highest ΔE value was observed for shaded specimens between 1st and 5th firings. ΔE values were not significantly different between 1 and 3 firings. Conclusions: Changes in thickness and repeated firings of zirconia specimens affected final color and translucency of zirconia specimens. HT blocks are more affected by consecutive firings than ST and XT blocks. ΔE increased as the thicknesses decreased for both types of translucent zirconia specimens tested.

Effect of Veneering and Hydrothermal Aging on the Translucency of Newly Introduced Extra Translucent and High Translucent Zirconia with Different Thicknesses.

PURPOSE: The purpose of this study was to evaluate the effect of veneering and aging on the translucency of newly introduced extra and high translucent zirconia with different thickness. MATERIALS AND METHODS: One hundred forty disk-shaped specimens were fabricated from two translucent zirconia blocks (VITA YZ XT and VITA YZ HT), and they are milled with CAD/CAM system. Then, specimens were divided into nonveneered (XT, HT) and veneered groups (XTV, HTV). Nonveneered groups were prepared with four different thicknesses (0.5-1-1.5-2 mm). Veneered groups were divided into three subgroups (n = 10) for veneering with base dentin ceramic with thicknesses of 0.5 + 0.5, 0.5 + 1, and 0.5 + 1.5 mm. A spectrophotometer was used to calculate the translucency parameter (TP) and contrast ratio (CR) of all specimens before and after aging. Statistical analysis was performed using 3-way ANOVA and Tukey HSD tests (p < 0.05). RESULTS: TP values were significantly affected by thickness of specimens (p < 0.001). VITA YZ XT was significantly found more translucent than VITA YZ HT. The highest translucency was observed in the XT-0.5 mm group. There is no significant difference between translucency of the veneered and nonveneered groups in the same thickness for XT. On the contrary, veneering significantly affected translucency of HT. TP values significantly decreased after aging for all groups. After aging, translucency value difference before and after aging was the highest in the XT-0.5 mm group whereas the HTV-2 mm group showed the lowest difference after aging. TP decreased significantly as thickness of specimen increases regardless of the material type. Extra translucent and nonveneered zirconia groups are more prone to hydrothermal aging. CONCLUSIONS: The translucency parameter of zirconia ceramics was significantly influenced by both material type and veneering. Also, extra translucent and nonveneered zirconia groups are more susceptible to hydrothermal aging.

Effect of coloring and sintering on the translucency and biaxial strength of monolithic zirconia.

STATEMENT OF PROBLEM: The influences of coloring and sintering procedures on the optical and mechanical properties of monolithic zirconia have not been thoroughly investigated. PURPOSE: The purpose of this in vitro study was to investigate the effects of the coloring procedure and of varying final sintering temperatures on the translucency parameter (TP) and biaxial flexural strength (BFS) of monolithic zirconia. MATERIAL AND METHODS: Disk-shaped specimens (N=210) of 2 different monolithic zirconia brands (Vita YZ HTWhite [VYZa]; Vita YZ HTColor A2 [VYZb]; Prettau Zirkonzahn [PZ]; Prettau Anterior Zirkonzahn [PZA]) with a diameter of 15 mm and a thickness of 1.0 ±0.05 mm were prepared. Half of the specimens prepared from noncolored blocks (VYZa, PZ, and PZA) received coloring liquid application. Then, the specimens were divided into 3 subgroups (n=10) according to the final sintering temperatures (1350°C, 1450°C, and 1600°C). The TP was determined by using a reflection spectrophotometer, and the BFS was tested with the piston-on-3-ball method in a universal testing machine. Data were statistically analyzed by multivariate multiple regression and Bonferroni tests (α=.05). RESULTS: Significant differences were obtained among the groups based on the results of the TP and BFS (P<.05). The TP was affected by the changes in final sintering temperature. The varying final sintering temperatures demonstrated no significant effect on the BFS, except in group PZ (noncolored) that produced lower BFS when sintered at 1350°C than the subgroups sintered at 1450°C and 1600°C (P<.05). Coloring liquid application significantly decreased the TP of VYZa (sintered at 1350°C) but produced no significant effect on the groups PZ and PZA. Additionally, the coloring procedure had no significant effect on the BFS of tested materials (VYZa, PZ, and PZA) (P>.05). CONCLUSIONS: Increased sintering temperature leads to increased translucency with minimal impact on the BFS. The coloring procedure should be considered at the time of material selection to avoid possible reduction in translucency.