Final Colour of Ultratranslucent Multilayered Zirconia Veneers, Effect of Thickness, and Resin Cement Shade.

Background: Aesthetic restorations should be able to mimic the natural colour depth of teeth, affected by several factors including material properties. There is a lack of information regarding the effect of cement shade and material thickness on the final colour of ultratranslucent multilayered zirconia veneers. Objectives: This study evaluated the effect of ceramic thickness and resin cement shade on the final colour of different layers of ultratranslucent multilayered (UTML) zirconia veneers. Methods: This in vitro study produced 90 rectangular-shaped specimens with nonsintered Katana UTML monolithic zirconia (Kuraray Noritake Dental, Tokyo, Japan), shade A1 blocks. Ceramic samples were prepared in two groups of 0.7 mm and 0.5 mm thicknesses, 45 of each (a: 8 × 11 × 0.5 mm; b: 8 × 11 × 0.7 mm). Specimens of each thickness were further divided into 5 groups: universal, clear, brown, white, and opaque (n = 9). Each adhesive resin cement (Panavia V5) was applied between the ceramic samples and composite substrate. The colour values were measured using a spectrophotometer in baseline and after resin cement application according to the CIELab system. For all samples, ΔE00 values were obtained. Data were evaluated with SPSS 25 using the three-way ANOVA test (p < 0.05). Results: The factors of cement shade, ceramic thickness, and ceramic layers have statistically significant effect on ΔE00 values (p < 0.001). The results showed lower ΔE00 values with thicker ceramic veneers. Tukey test results showed that the opaque and brown shade had a significantly greater ΔE00 values comparing to universal (p = 0.004), clear, and white shades (p < 0.001). Conclusion: The colour change was greater in lower ceramic thickness. Different shades of resin cement and layers of UTML zirconia differently affected the final colour.

Effect of accelerated aging and double application on the dentin bond strength of universal adhesive system.

BACKGROUND: Despite the many advantages of simplified adhesive systems, there are concerns about the durability of the adhesive layer over time. The aim was to investigate the effects of various aging methods and double application of an adhesive layer on the bond strength of the universal adhesive system using etch-and-rinse (ER) and self-etch (SE) strategies. MATERIALS AND METHODS: In this in vitro study, the occlusal enamel of 120 extracted, intact human third molars was removed to expose the dentin. Then, the samples were randomly divided into four groups of thirty according to All-Bond Universal (ABU) adhesive application strategy (ER and SE) and the number of adhesive layers (1 or 2). Then, each group was subdivided into three subgroups of ten according to aging method (control, thermal cycling, and 10% sodium hypochlorite [NaOCl]). The shear bond strength was measured at the strain rate of 0.5 mm/min. Data were analyzed using three-way ANOVA and Tukey's post hoc tests (P < 0.05). RESULTS: The effect of adhesive application strategy (P < 0.001) and aging method (P < 0.001) on the bond strength was statistically significant, but the effect of the double application was not statistically significant (P > 0.05). In addition, the interactive effect of adhesive application strategy-aging method was significant (P = 0.005). CONCLUSION: Using ABU with ER strategy leads to higher dentin bond strength compared to the SE method in the control and thermal cycling groups. However, no significant differences were observed between ER and SE strategies after aging with the NaOCl. Furthermore, the double application might not have any effect on the bond strength and durability.

Effect of curing method and thermocycling on flexural strength and microhardness of a new composite resin with alkaline filler.

BACKGROUND: Cention N has been introduced as an alternative material for amalgam. The purpose was to investigate the flexural strength and microhardness of this material in self-cure and dual-cure modes before and after thermocycling. MATERIALS AND METHODS: In this experimental study, 40 samples of Cention N were prepared in order to determine and compare the microhardness. Half of the samples were set by self-cure method and the other half with dual-cure method. The Vickers microhardness test was performed once after 24 h and again after 10000 thermocyclings. Three-point flexural test was used to determine and compare the flexural strength of 52 rod-shaped samples. Half of the samples were set by self-cure method and the other half with dual-cure method. Among 26 samples in each group, 13 samples were randomly selected and three-point flexural test was performed after 24 h and for another 13 samples after 10,000 thermocyclings. Data were analyzed using two-way ANOVA and paired samples t-test (P < 0.05). RESULTS: There was a statistically significant difference between the mean of microhardness values in two curing methods (P < 0.001) and in two storage conditions (P < 0.001). The mean of dual-cure microhardness (100.99 ± 7.22) was higher than that of self-cure (64.61 ± 12.51) and the mean value associated with pre-thermocycling (89.75 ± 15.84) was higher than that of the post-thermocycling (76.44 ± 23.56). There was no statistically significant difference between the mean flexural strength in the two curing methods (self-cure [72.85 ± 16.26], dual cure [79.87 ± 23.07]; [P > 0.05]). However, the mean flexural strength without thermocycling (85.98 ± 21.74) was higher than that of the thermocycled group (64.24 ± 6.40) (P < 0.001). CONCLUSION: The microhardness of Cention N in dual-cure mode was higher than that of self-cure mode, but the flexural strength of dual-cure was not significantly different from that of self-cure. Thermocycling had a significant effect on the microhardness and flexural strength.

Effect of Different Fiber Reinforcement Strategies on the Fracture Strength of Composite Resin Restored Endodontically Treated Premolars

Objective: To compare the effect of three different fiber reinforcement strategies on the fracture strength of composite resin restored endodontically treated premolars. Material and Methods: Seventy-two sound human premolars extracted for orthodontic reasons were divided into 6 groups (n=12) after endodontic treatment. Group 1: intact teeth (positive control); Group 2: endodontically treated teeth without restoration (negative control); Group 3: composite resin restoration; Group 4: placement of fibers at occlusal position; Group 5: splinting the buccal and palatal walls with horizontal fiber posts; Group 6: placement of fibers at the occlusal position after splinting the buccal and palatal walls with horizontal fiber posts. Then fracture strength was measured at a crosshead speed of 0.5 mm/min in a universal testing machine. Data were analyzed using one-way ANOVA and post hoc Tukey tests at α=0.05. Results: There were significant differences between the negative and positive control groups (p<0.001) and between the negative control group and all the other study groups (p<0.001). However, there were no statistically significant differences between the positive control group and all the experimental groups and between the experimental groups (p>0.05). Conclusion: Fiber insertion had no additional reinforcing effect on the fracture strength following composite resin restoration.

Effect of three different mouthrinses on microleakage of composite resin restorations with two adhesive systems after bleaching with 10% carbamide peroxide.

AIM: The aim was to evaluate the effects of Oral-B (OB), Listerine (LN) and Rembrandt Plus (RM) mouthrinses on microleakage of composite resin restorations bonded with two adhesive systems after bleaching with 10% carbamide peroxide. MATERIALS AND METHODS: A total of 60 Cl V cavities were prepared on human premolars. The occlusal and gingival margins were placed 1 mm occlusal to and apical to CEJ respectively. The teeth were randomly divided into two groups based on the adhesive system used: Excite (EX) and Clearfil SE Bond (CSE) groups. After composite resin restoration of cavities, thermocycling and bleaching with 10% carbamide peroxide for 2 hours daily for 14 days, the teeth in each adhesive group were further subdivided into three subgroups and were immersed for 12 hours in the three OB, RM and LN mouthrinses. The teeth were then placed in 2% basic fuschin for 24 hours. After dissecting the teeth, microleakage was evaluated under a stereomicroscope at 16×. Data was analyzed with multifactor ANOVA and Bonferroni test at p < 0.05. RESULTS: Microleakage with EX was significantly higher than that with CSE (p = 0.009). Microleakage at gingival margins was significantly higher than that at occlusal margins (p = 0.15). Microleakage with OB was higher than that with LN (p = 0.02). However, there were no significant differences in microleakage between LN and RM (p = 1) and between RM and OB (p = 0.15). In addition, with the EX adhesive system, microleakage with OB was higher than that with LN and RM (p = 0.02). CONCLUSION: In the present study, microleakage of composite resin restorations was influenced by the type of the adhesive system, mouthrinse type and the location of the cavity margin. CLINICAL SIGNIFICANCE: Use of some mouthrinses, such as OB after bleaching can increase postrestoration microleakage of resin composite restorations bonded with etch-and-rinse adhesive systems.

The effect of marginal ridge thickness on the fracture resistance of endodontically-treated, composite restored maxillary premolars.

This study evaluated the effect of varying thicknesses of marginal ridge on the fracture resistance of endodontically-treated maxillary premolars restored with composite. Ninety non-carious maxillary premolars, extracted for orthodontic reasons, were selected for this experimental in vitro study. The teeth were randomly assigned to six groups (n=15). Group 1 received no preparation. In groups 2 through 6, the premolars were root filled and DO preparations were created, while MOD preparations were also created for group 2. The condition of the boxes was: the gingival seat was 1.5 mm above the CEJ and the buccolingual dimensions were 3.5 mm in gingival and 3 mm in occlusal. In groups 3 through 6, the dimensions of the mesial marginal ridge were measured using a digital caliper as follows: 2 mm, 1.5 mm, 1 mm and 0.5 mm, respectively. All samples in groups 2 through 6 were restored with a dentin bonding system (DBS: Single Bond, 3M) and resin composite (Z 250, 3M). Subsequently, premolars from all six groups were subjected to a thermocycling regimen of 500 cycles between 5 degrees C and 55oC water baths. Dwell time was 30 seconds, with a 10-second transfer time between baths. The premolars were submitted to axial compression up to failure at a 45 degrees angle to the palatal cusp in Universal Test Equipment (Tinius Olsen, Ltd, H5K-S model). The mean load necessary to fracture the samples was recorded in newtons (N), and data were subjected to analysis of variance (ANOVA) and LSD post-hoc test. According to these results, the mean loads necessary to fracture the samples in each group were (in N): group 1: 732 +/- 239, group 2:489 +/- 149, group 3: 723 +/- 147, group 4: 696 +/- 118, group 5: 654 +/- 183 and group 6: 506 +/- 192). Differences between group 1 and groups 2 and 6, and also differences between groups 3, 4 and 5 compared with group 2 and 6 were statistically significant (p < 0.05).