Comparison of Adhesion Performance of a Self-curing and a Light-curing Universal Adhesive to Various Dental Substrates and CAD/CAM Materials.

PURPOSE: To compare the adhesion of a self-curing (Tokuyama Universal Bond, TUB) and a light-curing (Scotchbond Universal, SBU) universal adhesive to CAD/CAM materials, enamel, and dentin. This study also assessed differences in enamel adhesion between self-etch vs selective etching modes, as well as immediate and long-term adhesion to dentin for both adhesives. MATERIALS AND METHODS: Shear bond strength (SBS) testing was used to assess adhesion to enamel, dentin, Lava Ultimate (LU), Vita Enamic (VE), IPS e.max CAD (LD), IPS e.max ZirCAD (3Y-Zir), and Lava Esthetic (5Y-Zir) (n = 10). Moreover, bonding to enamel in self-etch and selective etching modes (n = 10) as well as immediate and aged resin-dentin bond strength (24 h after bonding, after 100,000 thermal cycles [TC] and long-term storage) was evaluated using the microtensile bond-strength test (n = 30). Failure mode was also determined for the bonding to dentin. Statistical analyses consisted of one-way and two-way ANOVA with appropriate post-hoc Tukey-Kramer or two-sample t-tests, as well as the chi-squared or Fisher's exact test (α = 0.05). RESULTS: TUB and SBU universal adhesives presented similar bonding to LU, VE, 3Y-Zir, and 5Y-Zir. However, SBS for TUB was superior to SBU when bonding to lithium-disilicate glass-ceramic (IPS e.max CAD). SBU showed better adhesion to dentin and enamel when used in the self-etch mode, while TUB promoted strong bond strength to enamel in the selective etching mode. TUB after TC was the only aging condition that yielded a significant reduction in resin-dentin bond strength. CONCLUSION: In-vitro adhesion performance of the self-curing and light-curing universal adhesives varies depending on the dental substrate or CAD/CAM restorative material used for bonding.

Development of a Boron Nitride-Filled Dental Adhesive System.

There is a dearth of adhesive systems capable of forming stable bonds between restorative materials and tooth surfaces. To address the concern, this study determined the effects of using methacrylate-functionalized boron nitride nanosheets (BNNSs) in a polymeric dental adhesive system. The bisphenol A glycidyl dimethacrylate (BisGMA):2 hydroxyethyl methacrylate (HEMA) (60:40) adhesive monomer blend with a photoinitiator was filled with 0 wt% (control), 0.1 wt%, and 1 wt% BNNSs and light cured. Fourier transform infrared spectroscopy was performed to determine the conversion degree of monomer double bonds (DoC). Water absorption and solubility were measured. Flexural strength and Youngs's modulus were evaluated to determine the mechanical properties of the composite adhesive system. Finally, dentin bond strength degradation and fracture mode were quantified with a microtensile bond test to confirm the bonding ability of the developed adhesive system. Results showed that the incorporation of BNNSs increased DoC (9.8% and 5.4% for 0.1 and 1 wt%, respectively), but it did not affect water sorption (101.9-119.72 (µg/mm3)), solubility (2.62-5.54 (µg/mm3)), Young's modulus (529.1-1716.1 MPa), or microtensile bond strength (46.66-54.72 MPa). Further studies are needed with varying BNNS loading percentages from 0.1 wt% to 1 wt% in order to more comprehensively determine the effect of BNNSs on dental adhesives.

Fracture resistance of defective amalgam restorations repaired with a resin-based composite material.

BACKGROUND: Repair is used to increase the longevity of defective restorations, such as large amalgams. The aim of this study was to investigate the fracture resistance and fracture modes of mesio-occlusodistal (MOD) amalgam molar restorations with extensive cuspal fracture repaired or replaced using a bulk-fill resin-based composite material. METHODS: Amalgam restorations were placed in 84 permanent extracted molars and randomly assigned (n = 14) to groups: (1) MOD amalgam, (2) composite repair of 1-cusp fracture and adjacent proximal box, (3) composite repair of 1-cusp fracture, (4) composite repair of 2-cusp fracture, (5) replacement of 1-cusp defect and existing MOD amalgam, (6) replacement of 2-cusp defect and MOD amalgam. Each molar was prepared to simulate the assigned fracture and either repaired or replaced. Specimens were aged and then loaded to fracture. Fracture resistance and fracture modes were recorded. RESULTS: The authors found significant differences (P < .001) between group 4 (1,652.3 N) and groups 5 (3,095.0 N), 1 (2,669.8 N), 6 (2,658.6 N), and 2 (2,442.9 N) as well as between group 3 (2,133.5 N) and group 5 (3,095.0 N). The results of the Fisher exact test showed differences among groups (P < .001), with group 5 having the highest number of nonrestorable fractures as well as higher fracture resistance on average. CONCLUSIONS: Composite material is a viable option for the repair and replacement of cuspal defects, especially in the case of a 1-cusp fracture and 1-cusp fracture involving the adjacent proximal box. PRACTICAL IMPLICATIONS: Within the limitations of this study, the repair of cusp fractures in existing MOD amalgam-restored molars is an appropriate treatment option, although replacement of the defect and existing restoration with resin-based composite will withstand higher forces.

The Effect of Sintering on Zirconia Manufactured via Suspension-Enclosing Projection Stereolithography for Dental Applications: An In Vitro Study.

BACKGROUND: Zirconia is a widely used material in the dental industry due to its excellent mechanical and aesthetic properties. Recently, a new 3D printing process called suspension-enclosing projection stereolithography (SEPS) was introduced to fabricate zirconia dental restorations. However, the effect of the sintering time and temperature on the properties of zirconia produced via SEPS has not been fully investigated. METHODS: Zirconia slurries were prepared with varying percentages of zirconia powders and 3D printing resins, and 5Y-TZP (5 mol% yttria-stabilized zirconia) (n = 40) and 3Y-TZP (3 mol% yttria-stabilized zirconia) (n = 40) bar specimens were fabricated via SEPS manufacturing. The specimens were sintered at different temperatures and dwell times, and their flexural strength, density, and phase composition were measured. The viscosity of the slurries was also measured. Statistical analysis was performed using Welch's ANOVA and Kruskal-Wallis tests to evaluate the impact of the sintering conditions. RESULTS: Significant differences in flexural strength (p < 0.01) were observed between the 5Y-TZP samples, with those sintered at 1530 °C for 120 min showing an average strength of 268.34 ± 44.66 MPa, compared to 174.16 ± 42.29 MPa for those sintered at 1450 °C for 120 min. In terms of density, significant differences (p < 0.01) were noted for the 3Y-TZP specimens, with an average density of 6.66 ± 0.49 g/cm3 for samples sintered at 1530 °C for 120 min, versus 5.75 ± 0.55 g/cm3 for those sintered at 1530 °C for 10 min. X-ray diffraction confirmed the presence of a predominantly tetragonal phase in both materials. CONCLUSIONS: Zirconia printed via SEPS manufacturing can be sintered at a higher temperature with shorter dwell times, thereby producing high density samples. Different sintering conditions can be used to fully sinter 3D-printed zirconia for potential dental applications.

Fatigue bond strength of dental adhesive systems: Historical background of test methodology, clinical considerations and future perspectives.

Numerous laboratory evaluations have been conducted since Dr. Rafael Bowen introduced a method for determining the bond strengths of adhesive systems to dental substrates in 1965. Most of the past studies have been conducted using static bond strength tests, such as shear and tensile bond strength testing with either macro or micro sized specimens. These static bond strength tests are conducted using a monotonically increasing load in which stress is applied continuously until failure occurs. Although the type of stress that develops in static bond strength tests is not typically encountered in clinical situations, over the years clinicians have based their choice of adhesive systems for use in daily practice on the results of such tests. However, some well-known researchers have reported that the results obtained from static bond strength testing may have limited clinical relevance and should not be used only by themselves to make recommendations for clinical use. In clinical situations, restorations undergo cyclic stress during mastication at stress levels well below the breaking stress used in static bond strength tests. Thus, dynamic bond strength tests, using cyclic loading, should be more clinically relevant than static bond strength tests. Over 15 years, a testing method designed to assess fatigue bond strengths of dental adhesive systems has been developed through inter-collegial and international collaborative efforts. This review discusses the development of fatigue bond strength testing methodology, provides both a historical perspective and current information regarding available testing data for all categories of adhesive systems to enamel and dentin and perspectives on the future development of both adhesive systems and testing methods.

Repair versus replacement of defective direct restorations: A cross-sectional study among US dentists.

BACKGROUND: Repair increases the longevity of restorations and is well-accepted by patients. In this study, the authors assessed the acceptance of dental restoration repair by dentists and determined the main variables of repair versus replacement of defective restorations. METHODS: A 15-item questionnaire was developed and distributed electronically to the American Dental Association Clinical Evaluators panel members (n = 785) during a 2-week period in 2019. Descriptive, bivariate, and multivariable analyses were conducted. RESULTS: Of the 387 respondents, 83.7% stated that they repair defective restorations, and 16% stated that they always replace them. Reasons to forego a restoration repair among dentists who perform repairs included defect size and carious lesion extension (42%) and negative personal experience or lack of success (37.9%). However, the latter was considerably higher for dentists who do not perform repairs (60.7%). The most commonly cited patient-related reason and tooth condition to repair restorations were limited patient finances (67%) and noncarious marginal defects (86%), respectively. Neither sex nor age group was significantly associated with the practice of restoration repair (P = .925 and P = .369, respectively). However, sole proprietors were more likely to perform repairs than those in an employee, associate, or contractor practice setting (P = .008). The most significant reason to forego restoration was negative experience or lack of success (P = .002). CONCLUSIONS: Restoration repair is considered a treatment option for managing defective restorations. Negative personal experience or lack of success and practice setting influenced the dentists' decision to repair or replace a defective restoration. PRACTICAL IMPLICATIONS: Understanding dentists' clinical challenges and practice environment is necessary when advocating for this approach.

Bonding and wear properties of self-adhesive flowable restorative materials.

The purpose of this study was to evaluate the bonding and wear properties of self-adhesive flowable restorative materials. Five self-adhesive flowable restorative materials were used. The study parameters were: (i) shear bond strengths; (ii) microleakage; (iii) occlusal wear; and (iv) qualitative evaluation of the bonding interface. The range of shear bond strengths of the materials was as follows: 7.4-12.2 MPa to ground enamel, 22.5-32.5 MPa to etched enamel, and 1.3-4.2 MPa to dentin. The microleakage scores of the materials did not show any statistically significant differences regardless of the presence or absence of etching. The wear facets on the materials showed 0.099-0.447 mm3 of volume loss and 148.6-365.3 µm maximum depth, with statistically significant differences between materials. Scanning electron microscopic images of the interfaces of the materials showed good adaptation regardless of substrate. The bonding and wear properties of self-adhesive flowable restorative materials were still limited and showed lower values than previously reported results for nanofilled composites with an adhesive system. Selective enamel etching can improve the bonding performance of these materials.

Dental adhesive microtensile bond strength following a biofilm-based in vitro aging model.

OBJECTIVE: Laboratory tests are routinely used to test bonding properties of dental adhesives. Various aging methods that simulate the oral environment are used to complement these tests for assessment of adhesive bond durability. However, most of these methods challenge hydrolytic and mechanical stability of the adhesive- enamel/dentin interface, and not the biostability of dental adhesives. To compare resin-dentin microtensile bond strength (µTBS) after a 15-day Streptococcus mutans (SM) or Streptococcus sobrinus (SS) bacterial exposure to the 6-month water storage (WS) ISO 11405 type 3 test. METHODOLOGY: A total of 31 molars were flattened and their exposed dentin was restored with Optibond-FL adhesive system and Z-100 dental composite. Each restored molar was sectioned and trimmed into four dumbbell-shaped specimens, and randomly distributed based on the following aging conditions: A) 6 months of WS (n=31), B) 5.5 months of WS + 15 days of a SM-biofilm challenge (n=31), C) 15 days of a SM-biofilm challenge (n=31) and D) 15 days of a SS-biofilm challenge (n=31). µTBS were determined and the failure modes were classified using light microscopy. RESULTS: Statistical analyses showed that each type of aging condition affected µTBS (p<0.0001). For Group A (49.7±15.5MPa), the mean µTBS was significantly greater than in Groups B (19.3±6.3MPa), C (19.9±5.9MPa) and D (23.6±7.9MPa). For Group D, the mean µTBS was also significantly greater than for Groups B and C, but no difference was observed between Groups B and C. CONCLUSION: A Streptococcus mutans- or Streptococcus sobrinus-based biofilm challenge for 15 days resulted in a significantly lower µTBS than did the ISO 11405 recommended 6 months of water storage. This type of biofilm-based aging model seems to be a practical method for testing biostability of resin-dentin bonding.

Prescribing practices for antibiotic prophylaxis in patients with prosthetic joints.

AIMS: With the increasing number of patients with prosthetic joints, recommendations for antibiotic prophylaxis (AP) prior to dental procedures to prevent prosthetic joint infections (PJI) have changed. METHODS AND RESULTS: This survey evaluated dentists' AP practices for patients with prosthetic joints undergoing dental procedures and their familiarity with the American Dental Association Guidelines (ADA CPG) and American Academy of Orthopaedic Surgeons Appropriate Use Criteria (AAOS AUC). Dentists' attitudes about antibiotic resistance, medical-legal aspects, and adverse effects to using AP were examined. Dentists (n = 574) were familiar (51.2%) with ADA CPG and with the AAOS AUC (25.8%). Familiarity varied according to years since graduation. Female dentists (63.5%) were more likely to be very familiar with the ADA CPG than male dentists (49.5%). Overall, 65.4% of respondents believed that AP is not effective in the prevention of PJI, and 19.4% believed there is enough evidence to support AP. For a healthy patient, 28.9% of dentists would never recommend AP, 44.9% would recommend AP within the first two years since prosthetic joint replacement. CONCLUSIONS: Dentists' recommendations for the use of AP varied depending on different factors, including health status of the patient, dental procedure, time elapsed since joint surgery, suggesting that adherence to the ADA CPG and AUC is still challenging.

The effect of aging methods on the fracture toughness and physical stability of an oxirane/acrylate, ormocer, and Bis-GMA-based resin composites.

PURPOSE: To determine the effect of aging methods on the fracture toughness of a conventional Bis-GMA-based resin composite (Filtek Supreme), an ormocer-based resin composite (Admira), and an experimental hydrophobic oxirane/acrylate interpenetrating network resin system (OASys)-based composite. METHODS: A 25 × 5 × 2.8-mm stainless-steel mold with 2.5 mm single-edge center notch, following ASTM standards [E399-90], was used to fabricate 135 specimens (n = 15) of the composite materials and randomly distributed into groups. For the baseline group, specimens were fabricated and then tested after 24-h storage in water. For the biofilm challenge, specimens were randomly placed in a six-well tissue culture plate and kept at 37 °C with bacterial growth media (Brain Heart Infusion (BHI); Streptococcus mutans) changed daily for 15 days. For the water storage challenge, specimens were kept in 5 ml of deionized distilled autoclaved water for 30 days at 37 °C. µCT evaluation by scanning the specimens was performed before and after the proposed challenge. Fracture toughness (KIc) testing was carried out following the challenges. RESULTS: µCT surface area and volume analyses showed no significant changes regardless of the materials tested or the challenge. Filtek and Admira fracture toughness was significantly lower after the biofilm and water storage challenges. OASys mean fracture toughness values after water aging were significantly higher than that of baseline. Toughness values for OASys composites after biofilm aging were not statistically different when compared to either water or baseline values. CONCLUSION: The fracture toughness of Bis-GMA and ormocer-based dental resin composites significantly decreased under water and bacterial biofilm assault. However, such degradation in fracture toughness was not visible in OASys-based composites. CLINICAL SIGNIFICANCE: Current commercial dental composites are affected by the oral environment, which might contribute to the long-term performance of these materials.

Dental adhesive microtensile bond strength following a biofilm-based in vitro aging model

Abstract Laboratory tests are routinely used to test bonding properties of dental adhesives. Various aging methods that simulate the oral environment are used to complement these tests for assessment of adhesive bond durability. However, most of these methods challenge hydrolytic and mechanical stability of the adhesive- enamel/dentin interface, and not the biostability of dental adhesives. Objective To compare resin-dentin microtensile bond strength (μTBS) after a 15-day Streptococcus mutans (SM) or Streptococcus sobrinus (SS) bacterial exposure to the 6-month water storage (WS) ISO 11405 type 3 test. Methodology A total of 31 molars were flattened and their exposed dentin was restored with Optibond-FL adhesive system and Z-100 dental composite. Each restored molar was sectioned and trimmed into four dumbbell-shaped specimens, and randomly distributed based on the following aging conditions: A) 6 months of WS (n=31), B) 5.5 months of WS + 15 days of a SM-biofilm challenge (n=31), C) 15 days of a SM-biofilm challenge (n=31) and D) 15 days of a SS-biofilm challenge (n=31). μTBS were determined and the failure modes were classified using light microscopy. Results Statistical analyses showed that each type of aging condition affected μTBS (p<0.0001). For Group A (49.7±15.5MPa), the mean μTBS was significantly greater than in Groups B (19.3±6.3MPa), C (19.9±5.9MPa) and D (23.6±7.9MPa). For Group D, the mean μTBS was also significantly greater than for Groups B and C, but no difference was observed between Groups B and C. Conclusion A Streptococcus mutans- or Streptococcus sobrinus-based biofilm challenge for 15 days resulted in a significantly lower μTBS than did the ISO 11405 recommended 6 months of water storage. This type of biofilm-based aging model seems to be a practical method for testing biostability of resin-dentin bonding.

An Overview of Dental Adhesive Systems and the Dynamic Tooth-Adhesive Interface.

From the conception of resin-enamel adhesion to today's 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.

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.

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 Titankeramik's 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 manufacturer's 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 Tukey's 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.

The effect of surface treatment of the interfacial surface on fatigue-related microtensile bond strength of milled zirconia to veneering porcelain.

PURPOSE: The success of zirconia-reinforced all-ceramic crowns depends on the formation of a stable bond between the zirconia core and the veneering porcelain. The purpose of this study was to test the effects of liner application and airborne particle abrasion of a postsintered Y-TZP core on the bond strength between the zirconia core and veneering porcelain with or without cyclic loading. MATERIALS AND METHODS: Kavo Everest® Y-TZP blank disks were sintered and divided into three treatment groups: airborne particle abrasion, IPS e.max® Ceram Zirliner application, or no surface treatment. The disks were then veneered with IPS e.max® ZirPress veneering porcelain. Half the veneered disks from each group were cyclically loaded. This created six experimental groups: three surface treatment groups cyclically loaded and three not loaded. The disks were then sectioned into microbars for microtensile bond strength (MTBS) testing (40 specimens per group). Specimens were luted to a fixture mount and loaded to failure using a universal testing machine (MTS Insight). The maximum force was measured and bond strength computed. Data were analyzed with a two-way ANOVA and Tukey's HSD test (α= 0.05). RESULTS: Airborne particle abrasion significantly decreased MTBS values (p= 0.043), and ZirLiner application did not have a significant effect on MTBS values compared to control. Cyclic loading did not have a significant effect on MTBS values. The predominant failure mode in all groups was mixed. CONCLUSIONS: Airborne particle abrasion of the interfacial surface of the Everest® Y-TZP core significantly decreased the MTBS to ZirPress veneering porcelain when compared to no interfacial surface treatment. Application of ZirLiner to the interfacial surface of the Everest® Y-TZP core did not significantly increase or decrease the MTBS to ZirPress veneering porcelain, compared to the other surface treatments. Cyclic loading did not affect bond strengths in any of the groups, regardless of surface treatment. Neither cyclic loading nor surface treatment affected the failure mode of the specimens.

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.

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.

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 percent 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 percent chlorhexidine gluconate (CHX) gel; and G3= saline (control). After 10 days of storage in 100 percent humidity at 37ºC, 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.

O objetivo desse estudo in vitro foi avaliar a resistência de união do cimento resinoso Epiphany™ às paredes dentinárias após aplicação de pastas de hidróxido de cálcio [Ca(OH)2]. Quinze dentes humanos uniradiculares foram igualmente instrumentados sob irrigação com as soluções de NaOCl 2,5 por cento + EDTA. Os dentes foram divididos em três grupos (n=5) e tratados com diferentes pastas de Ca(OH)2: G1= Ca(OH)2 + soro fisiológico; G2= Ca(OH)2 + 2 por cento CHX e G3= tratado apenas com soro fisiológico (grupo controle). Após 10 dias de armazenamento a 37°C e 100 por cento de umidade, as medicações foram removidas e os dentes obturados com o cimento Epiphany. Passadas 48 horas de armazenamento adicional, as amostras foram seccionadas tranversalmente em discos de 2 mm de espessura. Os testes de resistência de união (push-out) foram realizados em máquina de ensaio mecânico (1 mm/min) e os resultados expressos em MPa. Os testes de ANOVA e Newman-Keuls mostraram um significante decréscimo nos valores de resistência de união quando as pastas de Ca(OH)2 foram utilizadas (10,18 ± 1,99 e 9,98 ± 2,97) em comparação ao grupo controle (13,82 ± 3,9) (p<0,05). Pode-se concluir que o uso do Ca(OH)2 como medicação intracanal diminuiu a adesão do cimento Epiphany™ às paredes dos canais radiculares, embora os valores de resistência de união estejam dentro das médias aceitáveis encontradas na literatura.

Effect of YSZ thin film coating thickness on the strength of a ceramic substrate.

Although ceramics are used for many different biomedical applications they are brittle materials that can be compromised by surface defects when under stress. The objective of this study was to evaluate the effect of surface modification with an yttria-stabilized zirconia (YSZ) thin film coating on the strength of a machinable dental ceramic. Fifty bars (2 mm x 2 mm x 15 mm) were cut from ProCAD (Ivoclar-Vivadent) blocks. Specimens were wet-polished through 1200-grit SiC abrasive. One surface of each bar was sandblasted with 50 microm Al(2)O(3) abrasive (0.34 MPa). Specimens were further modified through the deposition of a sputtered YSZ thin film on the sandblasted surface. Different thin film thicknesses were evaluated: 1, 3, 5, and 7 microm. Depositions were performed using a radio frequency magnetron sputter system (working pressure of 15 mT, 150 degrees C, 30:1 Ar/O(2) gas ratio). Flexural strength measurements were carried out by three-point bending (span = 10 mm) in a servo-electric material testing system in DI water (37 degrees C). The results showed that the strength of porcelain significantly increased with the deposition of a 3-microm YSZ thick coating. A nonlinear relationship was observed between film thickness and strength. Strengthening of porcelain is shown through the application of a sputtered YSZ thin film. It is presumed that the strengthening mechanism is due to modification of surface flaws and/or surface residual stress by the applied thin film.

Dynamic fatigue and strength characterization of three ceramic materials.

Fracture strength and fatigue parameters of three ceramic materials submitted to dynamic fatigue were evaluated. A machinable leucite-reinforced dental ceramic, aluminum oxide, and yttria-stabilized zirconia (YSZ) were tested. The inert strength of the materials was determined in air (25 degrees C) at stressing rates of 70, 250, 400 MPa/s for Porcelain, Alumina and YSZ respectively. The data was analyzed using a two-parameter Weibull distribution. The Weibull modulus (m) and the characteristic of fracture (sigma0) parameters were determined for each material. Specimens were also tested in 3-point bending at different stressing rates in distilled/deionized water at 37 degrees C (dynamic fatigue) in order to calculate the fatigue parameters n and ln B. The strength for each material was characterized using Strength-Probability-Time (SPT) diagrams for 1 day, 1 year and 10 years. YSZ showed a high-fracture strength sigma0 (1,459 MPa) at a failure probability of 63.2% and high resistance to subcritical crack growth. YSZ and alumina showed better resistance to slow crack growth than porcelain, indicating less susceptibility to strength degradation by stress corrosion. Lifetime predictions after 10 years indicate a reduction of 50%, 36% and 29% in strength for porcelain, alumina and YSZ respectively. YSZ seems to be a very promising material for long-term dental and biomedical applications.