Ana Maria Estivalete Marchionatti

Does air particle abrasion affect the flexural strength and phase transformation of Y-TZP? A systematic review and meta-analysis

OBJECTIVES A systematic review was conducted to assess the effects of air-particle abrasion procedures on the mechanical strength and phase transformation of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). DATA This report followed the PRISMA Statement. From 1013 eligible studies, 78 were selected for full-text analysis, from which 37 were excluded. The 41 remaining papers were included for the systematic review; hand-searching yielded three papers. The review comprised a total of 44 studies; 21 were included in the meta-analysis. SOURCES Searches were performed with no publication year limit through November 2015 in PubMed/MEDLINE, Web of Science (Core Collection) and Scopus databases. STUDY SELECTION In vitro studies evaluating the effect of air-particle abrasion protocols on the mechanical strength and/or phase transformation of Y-TZP zirconia specimens, immediately or after aging. For the meta-analysis, flexural strength data of air-particle abrasion vs. control (nonabraded) were globally and subgroup analyzed. Subgroup analyses assessed blasting parameters (particle size, pressure, or time duration) and the effect of aging. Statistical analyses were conducted using RevMan 5.1 (Cochrane Collaboration, Copenhagen, Denmark). Comparisons were performed with random-effect models at a 5% significance level. Phase transformation data were included only in the systematic review, as insufficient data were available for meta-analysis. CONCLUSIONS Airborne-particle abrasion improved flexural strength of Y-TZP, regardless of abrasion parameters and the presence or lack of aging (p≤0.05). Phase transformation tended to be increased by air abrasion immediately or with up to 2h of aging. However, after aging for 12h or more, the abraded Y-TZP showed less monoclinic content than the control.

Influence of periodontal ligament simulation on bond strength and fracture resistance of roots restored with fiber posts

Objective Considering that periodontal ligament simulation may influence the stress distribution over teeth restored with intraradicular retainers, this study aimed to assess the combined effect of mechanical cycling and periodontal ligament simulation on both the bond strength between fiber posts and root dentin and the fracture resistance of teeth restored using glass fiber posts. Material and Methods Ninety roots were randomly distributed into 3 groups (n=10) (C-MC: control; P-MC: polyether; AS-MC: addition silicone) to test bond strength and 6 groups (n=10) (C: control; P: polyether; AS: addition silicone, without mechanical cycling, and C-MC, P-MC and AS-MC with mechanical cycling) to test fracture strength, according to the material used to simulate the periodontal ligament. For the bond strength test, fiber posts were cemented, cores were built, mechanical cycling was applied (2×106 cycles, 88 N, 2.2 Hz, and 45º incline), and the teeth cut into 3 slices (2 mm), which were then subjected to the push-out test at 1 mm/min. For the fracture strength test, fiber posts were cemented, cores were built, and half of the groups received mechanical cycling, followed by the compressive strength (45° to the long axis and 1 mm/min) performed on all groups. Results Periodontal ligament simulation did not affect the bond strength (p=0.244) between post and dentin. Simulation of periodontal ligament (p=0.153) and application of mechanical cycling (p=0.97) did not affect fracture resistance. Conclusions The materials used to simulate the periodontal ligament did not affect fracture or bond strength, therefore periodontal ligament simulation using the tested materials could be considered optional in the conditions of the study.

Color stability of ceramic laminate veneers cemented with light-polymerizing and dual-polymerizing luting agent: A split-mouth randomized clinical trial

Statement of problem The color stability of luting agents influences the esthetics of ceramic laminate veneers. Clinical studies that have evaluated the color changes of veneers cemented to enamel with light‐ and dual‐polymerizing resin cement are lacking. Purpose The purpose of this split‐mouth randomized clinical trial was to evaluate the color change and marginal discoloration of dual‐ and light‐polymerizing cement used for cementation of ceramic laminate veneers. Material and methods In 10 participants, 0.3‐mm‐thick ceramic laminate veneers were cemented on the buccal surface of the second premolars without tooth preparation. A randomized application of light‐polymerized cement was used on one side and a dual‐polymerized cement on the contralateral side. The operator and participants were blinded to the activation mode. Color was evaluated by a blinded evaluator with a spectrophotometer at 24 hours and at 2, 6, 12, and 24 months after cementation. The CIELab (&Dgr;E*ab) and CIEDE2000 (&Dgr;E*00) formulas were used to quantify color alteration, and &Dgr;a*, &Dgr;b*, and &Dgr;L* were calculated between the first and subsequent measurements. US Public Health Service guidelines were used to evaluate the marginal discoloration. Results Wilcoxon tests did not show a statistical difference in &Dgr;E*ab and &Dgr;E*00 between the groups (P>.05). At 24 months, the median &Dgr;E*ab was 2.31 (interquartile ranges [IQR]: 3.34) for the light‐polymerizing mode and 1.57 (IQR: 0.41) for the dual‐polymerizing mode, while the median &Dgr;E*00 was 1.65 for the light‐polymerizing mode (IQR: 2.34) and 1.18 for the dual‐polymerizing mode (IQR: 0.25). The thresholds for clinically acceptable color changes &Dgr;E*ab>3.46 and &Dgr;E*00>2.25 were found for both curing modes. Marginal discoloration was observed from the 2‐year assessment. Conclusions The color stability of ceramic laminate veneers was similar for both of the polymerizing modes for all evaluated periods. Marginal discoloration increased over a 2‐year period for both the light‐ and the dual‐polymerizing modes.

Does veneering technique affect the flexural strength or load-to-failure of bilayer Y-TZP? A systematic review and meta-analysis

Statement of problem. Causes of failures of bilayer yttria‐stabilized tetragonal zirconia polycrystal (Y‐TZP) restorations include the processing technique and the properties of the veneer ceramic. The effect of the veneering method on the mechanical behavior of veneered Y‐TZP remains unclear. Purpose. The purpose of this systematic review was to assess the effect of the veneering method on the flexural strength and failure load of bilayer Y‐TZP. Material and methods. This study followed the Preferred Reporting Items for the Systematic Reviews and Meta‐Analyses (PRISMA) statement. Searches were performed through August 2017 in PubMed/MEDLINE, Web of Science (Core Collection), Scopus, and Embase, with no year or language limit, targeting in vitro studies evaluating the effect of the veneering technique on the flexural strength and load‐to‐failure of bilayer Y‐TZP immediately or after aging. Statistical analyses were conducted using an appropriate software. Comparisons were drawn with random effect models (&agr;=.05). Results. From 3242 identified studies, 241 were selected for full‐text analysis; from these, 33 studies were included. Manual searching yielded no additional papers. The meta‐analysis consisted of 32 studies. Meta‐analysis was performed separately for flexural strength and failure load data to compare the hand‐layered method (control) with pressed, fused, and cemented veneering techniques. The cemented and fused methods were analyzed using subgroups depending on the veneering material being examined (predominantly glass–ceramics and particle‐filled glass–ceramics), and the results were compared with those of the hand‐layered method. The pressed group presented flexural strength (7 studies) (P=.150) and failure load (19 studies) (P=.140) values that were similar to those of the hand‐layered group. Subgroup analysis revealed that the fused group with particle‐filled glass–ceramics (7 studies) produced higher load‐to‐failure (P=.006) values than the hand‐layered group. Subgroup analyses showed a statistical difference that favored the hand‐layered over the cemented method, with predominantly glass–ceramic materials (5 studies) (P=.002). Conclusions. The fused technique with particle‐filled glass–ceramics seems more appropriate for the veneering of Y‐TZP, with improved failure load, than the hand‐layered method with predominantly glass–ceramic materials. The use of predominantly glass–ceramics for the cemented method is not recommended as failure load was lower than for the hand‐layered group. Pressed veneers showed failure load and flexural strength values similar to those of the the hand‐layered technique.

Influence of elastic modulus of intraradicular posts on the fracture load of roots restored with full crowns

Objective: This study aimed to evaluate the fracture load and displacement of roots restored with posts of different elastic modulus. Material and method: Thirty-six replicas of epoxy resin mixed with glass microfibers were made from an endodontically-treated human premolar root prepared to a length of 12 mm with a custom drill, leaving the apical 4 mm unprepared. Replicas were randomly restored with (n = 12): FP-LM (fiber post with low elastic modulus– 50 GPa), FP-HM (fiber post with high elastic modulus – 67 GPa) and MP (metallic post – 208 GPa), using self-curing adhesive and dual resin cement. Cores were built up with composite resin and metallic crowns were cemented in all the roots with self-adhesive resin cement with self-curing mode. Specimens were subjected to a fracture load test (45° inclination/0.5 mm/min) and displacement was registered at 100 N. Result: One-way ANOVA showed that elastic modulus of the post did not affect the fracture load means (p = 0.203) (FP-LM: 237.4 ± 65.11 N; FP-HM: 236.7 ± 92.85 N; MP: 295.8 ± 108.7 N) but was statistically significant for the displacement (p < 0.00): Tukey’s test showed that FP-LM displacement mean (0.81 ± 0.15 mm) was significantly higher than those for FP-HM (0.46 ± 0.26 mm; p = 0.00) and MP (0.62 ± 0.07 mm; p = 0.04). Conclusion: Posts with different elastic modulus exhibit similar fracture loads, but a lower displacement is achieved when fiber posts with a high elastic modulus and metallic posts are used. Descriptors: Compressive strength; intraradicular posts; dental materials; dental prosthesis. Rev Odontol UNESP. 2017 July-Aug; 46(4): 232-237 Influence of elastic modulus of intraradicular posts... 233