Erica C. Teixeira

Effect of calcium hydroxide intracanal dressing on the bond strength of a resin-based endodontic sealer

The aim of this in vitro study was to evaluate the bond strength of Epiphany resin-based sealer to dentin walls after placement of calcium hydroxide [Ca(OH)2] dressings. Fifteen extracted single-rooted human teeth were instrumented using 2.5% NaOCl + EDTA as irrigants. The teeth were randomly assigned to 3 groups (n=5), according to the intracanal dressing: G1= Ca(OH)2 + saline; G2= Ca(OH)2 + 2% chlorhexidine gluconate (CHX) gel; and G3= saline (control). After 10 days of storage in 100% humidity at 37 degrees C, the dressings were removed and the root canals were filled with Epiphany sealer. After additional 48 h of storage, the specimens were sectioned transversally into 2-mm-thick discs. Push-out tests were performed (1 mm/min, Instron 4411) and the maximum loads at failure were recorded in MPa. One-way ANOVA and Newman-Keuls tests showed a statistically significant decrease in bond strength when a Ca(OH)2 dressing was used before root canal filling with Epiphany (G1= 10.18 +/- 1.99 and G2= 9.98 +/- 2.97) compared to the control group (13.82 +/- 3.9) (p< 0.05). It may be concluded that the use of Ca(OH)2 as an intracanal dressing material affected the adhesion of Epiphany to the root canal walls, but even though the values were within the acceptable range found in the literature.

Influence of post-bleaching time intervals on dentin bond strength

It has been reported that bond strength of resin to tooth structure can be reduced when the bonding procedure is carried out immediately after the bleaching treatment. This study evaluated the effect of bleaching of non-vital teeth bleaching on the shear bond strength (SBS) of composite resin/bovine dentin interface and the influence of delaying the bonding procedures for different time intervals following internal bleaching. According to a randomized block design, composite resin cylinders (Z100/Single bond - 3M) were bonded to the flattened dentin surface of two hundred and fifty-six teeth which had previously been subjected to four different treatments: SPH - sodium perborate + 30% hydrogen peroxide; SPW - sodium perborate + distilled water; CP - 37% carbamide peroxide; and CON - distilled water (control), each one followed by storage in artificial saliva for 0 (baseline), 7, 14, and 21 days after bleaching (n = 16). The bleaching agents in the pulp chambers were replaced every 7 days, over 4 weeks. The SBS test of the blocks was done using a universal testing machine. The ANOVA showed that there was no significant interaction between time and bleaching agents, and that the factor time was not statistically significant (p > 0.05). For the factor bleaching treatment, the Students t-test showed that [CON = CP] > [SPW = SPH]. The bleaching of non-vital teeth affected the resin/dentin SBS values when sodium perborate mixed with 30% hydrogen peroxide or water was used, independently of the elapsed time following the bleaching treatment.

Bond strength of different endodontic sealers to dentin: push-out test

Objective The aim of this in vitro study was to evaluate the bond strength of different root canal sealers to dentin. Material and Methods Forty extracted single-rooted human teeth were examined and the coronal and middle thirds of the canals were prepared with a 1.50 mm post drill (FibreKor Post System, Pentron). The teeth were allocated in two experimental groups, irrigated with 2.5% NaOCl+17% EDTA or saline solution (control group) and instrumented using Race rotary files (FKG) to a size #40 at the working length. Then, the groups were divided into four subgroups and filled with Epiphany sealer (Group 1), EndoREZ (Group 2), AH26 (Group 3) and Grossmans Sealer (Group 4). After 2 weeks of storage in 100% humidity at 37ºC, all teeth were sectioned transversally into 2-mm-thick discs. Push-out tests were performed at a cross-head speed of 1 mm/min using a universal testing machine. The maximum load at failure was recorded and expressed in MPa. Results Means (±SD) in root canals irrigated with 2.5% NaOCl and 17% EDTA were: G1 (21.6±6.0), G2 (15.2±3.7), G3 (14.6±4.5) and G4 (11.7±4.1).Two-way ANOVA and Tukeys test showed the highest bond strength for the Epiphanys group (p< 0.01) when compared to the other tested sealers. Saline solution decreased the values of bond-strength (p<0.05) for all sealers. Conclusion Epiphany sealer presented higher bond strength values to dentin in both irrigating protocols, and the use of 2.5% NaOCl and 17% EDTA increased the bond strength values for all sealers.

Zirconia–parylene multilayer thin films for enhanced fracture resistance of dental ceramics

Abstract Recent research has shown that the application of specific thin films can enhance the material properties of a laminate construct. In this study, the effect of different mono/multilayered films on the strength of a ceramic specimen is demonstrated. It is well established that cracks can initiate and/or propagate from the internal surfaces of all-ceramic dental restorations. Modifying that surface by thin-film deposition might help increase clinical longevity and applicability. Specimens were divided into the following groups according to different surface treatments received: uncoated (control group), 10 μm yttria-stabilized zirconia (YSZ) thin film, 10 μm parylene thin film, 9.75 μm YSZ + 0.25 μm parylene film, and a multilayered film (five layers of 1.25 μm YSZ + 0.75 μm parylene). Depositions were performed using a radio-frequency magnetron sputter system (working pressure 15 mT, 150 °C, 30:1 Ar/O2 gas ratio) to produce the YSZ layers, and a vapour deposition process was used to produce the parylene layers. Flexural strength measurements were carried out by three-point bending (span = 10 mm) in a servo-electric material testing system in deioinized (DI) water (37 °C). The results showed that the strength of the specimen significantly increased with the deposition of all types of coating, showing the greatest increase with the multilayered film (∼32 per cent). It is hypothesized that a multilayer thin film (brittle/ductile) can promote crack deflection, causing strength enhancement of the brittle construct.

Dynamic fatigue behavior of dental porcelain modified by surface deposition of a YSZ thin film.

PURPOSE The objective of this study was to evaluate the basic fatigue parameters of a dental porcelain modified by deposition of a yttria-stabilized zirconia (YSZ) thin film and to compare the data to that of an unmodified control. METHODS Two hundred bars (2 x 2 x 15 mm(3)) were cut from ProCAD blocks. Specimens were wet-polished with 1200-grit SiC abrasive. One surface of each bar was sandblasted with 50 microm Al2O3 abrasive (50 psi). Half the specimens were further modified through deposition of a 3-microm YSZ thin film on the sandblasted surface. Depositions were performed using an radio frequency magnetron sputter system (working pressure of 15 mT, 150 degrees C, 30:1 Ar:O2 gas ratio). Specimens were tested at different stressing rates: 5.0, 0.1, and 0.01 MPa/s (n = 25/group) in deionized water (37 degrees C), and inert strength was determined in air (25 degrees C, 70 MPa/s). All strength measurements were carried out by three-point bending (span = 10 mm) in a servo-electric test system. RESULTS The mean flexural strength values (MPa) and standard deviation for the uncoated sandblasted group were: 98.6 (5.5), 90.7 (5.9), and 84.2 (8.5), and for the sandblasted + YSZ thin film group: 125 (9.4), 119.3 (7.8), and 102.8 (7.0), for the highest to the lowest stressing rates, respectively. The fatigue parameters n and lnB were calculated by linear regression of dynamic fatigue data. For the uncoated group, n = 38 and lnB = 4.7 MPa(2)/s, and for the coated group, n = 33 and lnB = 10.8 MPa(2)/s. Weibull analysis was also performed showing that the characteristic parameter (sigma(o)) was 113.3 and 125.7 MPa for the uncoated and coated group, respectively. CONCLUSIONS There was an increase in strength for specimens modified by application of a YSZ thin film. It is hypothesized that thin-film application modifies flaws or residual surface stress states.

Influence of Veneering Fabrication Techniques and Gas-Phase Fluorination on Bond Strength between Zirconia and Veneering Ceramics

PURPOSE Porcelain chipping has been one of the main problems of porcelain-fused-to-zirconia restorations. This study evaluates the bond strengths of layered, pressed, and adhesively bonded porcelain to yttria-stabilized zirconia substrates that have undergone traditional preparation or gas-phase fluorination. MATERIALS AND METHODS A three-point bending test was used to evaluate the bond strength of the porcelain and zirconia interface. Sixty-six specimens were prepared (n = 11) following ISO 9693 and loaded until failure using an Instron testing machine. One-half of the zirconia substrates received gas phase fluorination treatment before veneering application. Three porcelain veneering methods were evaluated: layered, pressed, and adhesively bonded porcelain. Bond strength results were interpreted using a two-way ANOVA and a Bonferroni multiple comparisons test. Statistical significance was set at α = 0.05. RESULTS ANOVA revealed a statistically significant effect of the veneering fabrication methods. No main effect was observed regarding the surface treatment to the zirconia. There was a significant effect related to the veneering method used to apply porcelain to zirconia. For untreated zirconia, layered porcelain had a significantly higher flexural strength compared to pressed or bonded, while pressed and bonded porcelains were not significantly different from one another. For zirconia specimens receiving fluorination treatment, both layered and pressed porcelains had significantly higher bond strengths than adhesively bonded porcelain. In addition, fluorinated pressed porcelain was not statistically different from the control layered or fluorinated layered porcelain. CONCLUSION The choice of veneering fabrication technique was critical when evaluating the zirconia to porcelain interfacial bond strength. Bonded porcelain to zirconia had a lower flexural strength than layered or pressed porcelain, regardless of zirconia surface treatment. In addition, fluorination had an effect on the bond strength of pressed porcelain.

An Overview of Dental Adhesive Systems and the Dynamic Tooth–Adhesive Interface

From the conception of resin-enamel adhesion to todays contemporary dental adhesive systems, clinicians are no longer afraid of exploring the many advantages brought by adhesive restorative concepts. To maximize the performance of adhesive-based restorative procedures, practitioners must be familiar with the mechanism of adhesion, clinical indications, proper handling, the inherent limitations of the materials and the biological challenges. This review provides an overview of the current status of restorative dental adhesives, their mechanism of adhesion, mechanisms of degradation of dental adhesive interfaces, how to maximize performance, and future trends in adhesive dentistry.

Effect of Bonding Agent Application Method on Titanium-Ceramic Bond Strength

PURPOSE Although milled titanium may be used as a substructure in fixed and implant prosthodontics, the application of the veneering porcelain presents particular challenges compared to traditional alloys. To address these challenges, some Ti ceramic systems incorporate the application of a bonding agent prior to the opaque layer. Vita Titankeramiks bonding agent is available as a powder, paste, and spray-on formulation. We examined the effect of these three application methods on the bond strength. MATERIALS AND METHODS Four titanium bars were milled from each of 11 wafers cut from grade II Ti using the Kavo Everest milling unit and a custom-designed milling toolpath. An experienced technician prepared the 25 × 3 × 0.5 mm(3) metal bars and applied bonding agent using one of three application methods, and then applied opaque, dentin, and enamel porcelains according to manufacturers instructions to a 8 × 3 × 1 mm(3) porcelain. A control group received no bonding agent prior to porcelain application. The four groups (n = 11) were blindly tested for differences in bond strength using a universal testing machine in a three-point bend test configuration, based on ISO 9693-1:2012. RESULTS The average (SD) bond strengths for the control, powder, paste, and spray-on groups, respectively, were: 24.8 (2.6), 24.6 (2.6), 25.3 (4.0), and 24.1 (3.9) MPa. One-way ANOVA and Tukeys multiple comparison tests were performed between all groups. There were no statistically significant differences among groups (p = 0.951). CONCLUSION Titanium-porcelain bond strength was not affected by the use of a bonding agent or its application method when tested by ISO 9693-1 standard.