Resin bond strength to zirconia: effects of surface treatments and resin cements.

This in vitro study evaluated the effect of surface treatments on the microshear bond strength between zirconia and 2 different resin cements. Thirty sintered zirconia blocks (15.5 × 19.0 × 39.0 mm) were allocated into 10 groups according to 2 factors: surface treatment (control [10% isopropyl alcohol], silica coating, primer, hot etching solution, or glaze) and resin cement (conventional dual-curing [Multilink Automix] or self-adhesive [RelyX U100]). Three cement cylinders (0.7-mm diameter × 1.5-mm height) were made on the surface of each zirconia block. The specimens were stored in water for 6 months at 37°C and then submitted to microshear bond strength tests (n = 9 per surface treatment group). The bond strength data were analyzed statistically with Kruskal-Wallis and Dunn tests (P < 0.05). The contact angle was measured with a goniometer on separate surface-treated disc specimens (n = 2 per group). The greatest mean (SD) bond strength values, regardless of cement type, were reported for the groups with the glaze surface treatment: conventional cement, 13.1 (0.26) MPa; and self-adhesive cement, 20.1 (0.23) MPa. The next greatest mean (SD) values were found in the silica coating groups: conventional cement, 7.94 (0.09) MPa; and self-adhesive cement, 9.8 (0.10) MPa. The self-adhesive cement groups presented the greatest bond strength values, except when the primer surface treatment was applied. The zirconia treated with the hot etching solution presented the greatest mean contact angle, 78.23 (SD 1.34) degrees, and bond strengths that were among the lowest achieved, suggesting that low wettability may have influenced bond strengths.

Influence of insertion techniques for resin cement and mechanical cycling on the bond strength between fiber posts and root dentin.

PURPOSE: To evaluate the effect of the insertion technique for resin cement and mechanical cycling on the bond strength between fiber posts and root dentin. MATERIALS AND METHODS: Sixty-four single-rooted bovine teeth were endodontically prepared to receive glass-fiber posts. The insertion of cement into the root canal was performed using one of the following techniques: POS, insertion with the post; LEN, the use of a lentulo-type drill; EXP, insertion with a straight-tip explorer; or CEN, the use of a Centrix syringe. Half of the specimens were mechanically cycled. All specimens were sectioned into slices of 1.8 mm for the push-out test and 0.5 mm for analysis of the cement layer quality. RESULTS: The insertion technique affected the interaction between factors (bond strength and mechanical cycling; p < 0.0001). Insertion of the Centrix syringe after mechanical cycling showed the highest bond values (13.6 ± 3.2 MPa). Group-to-group comparisons for baseline and cycled conditions indicated that mechanical cycling significantly influenced the bond strength (p < 0.0001) of the POS and CEN groups. The quality of the cement layer did not differ between the techniques when evaluated in the middle (p = 0.0612) and cervical (p = 0.1119) regions, but did differ in the apical region (p = 0.0097), where the CEN group had better layer quality for the two conditions tested (baseline and cycled). CONCLUSION: The use of the Centrix syringe improved the homogeneity of the cement layer, reducing the defects in the layer and increasing adhesive strength values to dentin, even after mechanical cycling.

Preheated Composite as an Alternative for Bonding Feldspathic and Hybrid Ceramics: A Microshear Bond Strength Study.

PURPOSE: To evaluate the bond strength between alternative or conventional luting agents and indirect restorative materials. MATERIALS AND METHODS: Blocks of a polymer-infiltrated ceramic network (PICN, Vita Enamic) and a feldspathic ceramic (FEL, Vita Mark II) were sliced and divided according to the luting agent: resin cement (PICN-RC, FEL-RC), flowable composite (PICN-FC, FEL-FC), or preheated composite (PICN-PH, FEL-PH). The ceramic surfaces were polished, etched with 5% hydrofluoric acid for 60 s, and then a silane layer was applied. Cylinders of the luting agents were built up on the ceramic surfaces. In half the samples, the microshear bond strength (µSBS) was tested after 24 h (baseline). The other half was tested after 5000 thermocycles (5°C-55°C) (aging). The failure modes were determined using a stereomicroscope, and the ceramic surfaces were analyzed using a scanning electron microscope. Data were statistically analyzed with two-way ANOVA. RESULTS: Thermocycling reduced the bond strength values of all experimental groups. Regarding FEL, the preheated composite obtained the highest results. Resin cement showed results similar to the flowable composite at baseline and after aging. The highest results of PICN were obtained from the preheated composite followed by resin cement and flowable composite. Significant differences among the three luting agents were observed before and after aging. The most frequent failures among the experimental groups were adhesive and cohesive in the ceramic. CONCLUSION: Bond strength results indicate that the preheated composite can be an alternative for adhesive cementation when applied on the tested feldspathic ceramic or PICN.

High-Translucency Zirconia Following Chemical Vapor Deposition with SiH4: Evidence of Surface Modifications and Improved Bonding.

PURPOSE: To evaluate the effect of plasma-enhanced chemical vapor deposition (PECVD) with silicon hydride (SiH4) at different times on HT-zirconia surface characteristics and bonding of composite cement before and after thermocycling. MATERIALS AND METHODS: Blocks of HT zirconia were obtained, polished, sintered and divided into five groups, according to PECVD time (n = 31): Zr-30 (30 s), Zr-60 (60 s), Zr-120 (120 s) and Zr-300 (300 s). The control group (Zr-0) did not receive PECVD. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS) in conjunction with field-emission scanning electron microscopy (FE-SEM), x-ray photoelectron spectroscopy (XPS), goniometry, and profilometry tests were used for chemical and topographic characterization. Monobond N silane (Ivoclar Vivadent) was applied to the surface, and a cylinder of composite cement (Variolink N) was made (3 x 3 mm). Half of the specimens of each group were stored for 24 h or subjected to thermocycling (6 x 103 cycles). A shear bond strength (SBS) test was performed. Results were subjected to one-way ANOVA and Tukey's tests (α = 0.05). RESULTS: For experimental groups, XPS showed that formation of Si-O bonds contributed to increased surface free energy (SFE). FE-SEM and EDS showed that the longer the deposition time, the greater the amount of silicon on the surface. Zr-60 and Zr-300 presented higher and lower surface roughnesses, respectively. The silicon penetrated the microstructure, causing higher stress concentrations. The bond strength to composite cement was improved after all PECVD deposition times. CONCLUSION: The PECVD technique with SiH4, associated with chemical treatment with primer based on silane methacrylate, is a solely chemical surface treatment capable of maintaining bonding between composite cement and HT zirconia.

Effect of hydrothermal and mechanical aging on the fatigue performance of high-translucency zirconias.

OBJECTIVES: This study aimed to evaluate the impact of mechanical fatigue cycling using the step-stress approach along with hydrothermaldegradation (134 ºC with a constant pressure of 2 bars for 20 h), and a novel intercalated hydrothermal/fatigue aging protocol on different aspects of the aging resistance of three generations of dental zirconias. METHODS: "Y"Z T (VITA), INCORIS "T"ZI (Dentsply Sirona) and "K"ATANA UTML (Noritake Kuraray) - 1st, 2nd and 3rd generation, respectively-, zirconia disks (N = 153), were divided into 6 groups (n = 3) for monotonic testing and 9 groups (n = 15) for mechanical fatigue testing, according to 3 proposed treatments for each zirconia: CF (control - only mechanical fatigue cycling); AF (aging in hydrothermal reactor at 134 °C for 20 h + mechanical fatigue cycling); AFA (Alternating protocol: 4 steps of 5 h of hydrothermal aging intercalated with mechanical fatigue cycling). Mechanical fatigue aging was performed according to the step-stress approach through biaxial flexural setup (piston-on-3-balls, initial strength: 100 MPa, step: 50 MPa/10,000, frequency: 20 Hz) until failure. Data were analyzed using Kaplan-Meier and Mantel-Cox test (α = 0.05), in addition to Weibull analysis. Fractured disks were analyzed in stereomicroscope, Scanning Electron Microscopy and X-Ray Diffraction. RESULTS: Continuous hydrothermal and mechanical fatigue cycling decreased the fatigue strength of YAF group (516 ± 38 MPa), while the alternating protocol increased it (730 ± 58 MPa). KATANA UTML showed no differences for both treatments and did not undergo t-m phase transformation. The TAF group showed the highest fatigue strength (810 ± 76 MPa) and cycles for failure (147,000.00 cycles). The fracture origin for all specimens was on the tensile side in pre-existing defects. SIGNIFICANCE: INCORIS TZI zirconia had higher fatigue strength and survival rates after hydrothermal and mechanical fatigue aging. Although less resistant, KATANA UTML did not suffer chemical degradation.

Interfacial Fracture Energy Between New Translucent Zirconias and a Resin Cement.

PURPOSE: To determine the interfacial fracture energy (IFE) and stress distribution of Brazil-nut-shaped specimens made of translucent zirconia and resin cement. MATERIALS AND METHODS: Three types of translucent zirconia were used: 3Y-TZP (high, Vita YZ HT), 4Y-TZP (super, Vita YZ ST), and 5Y-TZP (extra, Vita YZ XT). The adhesive surfaces were air abraded and 10-MDP-based resin cement was used. The cemented Brazil-nut-shaped specimens, with an elliptical defect in the center (as in real Brazil nuts), were thermally aged (5°C-55°C; 40,000 cycles). The IFE test was conducted with a piston to apply compression on the specimen, while the adhesive interface was positioned at four different angles (0, 10, 20, and 30 degrees) to measure the IFE during tensile, shear, and mixed failure modes. All adhesive interfaces were observed to determine failure patterns. The finite element analysis (FEA) was used to calculate tensile and shear stress distributions according to inclinations. Statistical analysis was conducted using the Kruskal-Wallis and Dunn's post-hoc tests (95%), as well as the Mann-Whitney test (95%) was applied to compare each group regarding the aging factor. RESULTS: According to Kruskal-Wallis and Dunn's post-hoc tests, there were no statistically significant differences between non-aged (p > 0.05) and aged materials (p > 0.05). However, there was a significant difference between aged and non-aged materials for all inclinations (p < 0.05) (Mann-Whitney test). According to the FEA, the compressive loading of Brazil-nut-shaped specimens at different angles showed a predominance of tensile stress at 0 degrees and shear stress at 30 degrees. CONCLUSION: The IFE under predominantly shear stresses is higher than when specimens are subjected only to tensile stresses, which allows the interpretation that failures in the oral environmental will probably occur preferentially under tensile stresses, because less energy is needed. All translucent zirconia bonded to resin cement has similar IFE, and thermal aging negatively affects these bonding interfaces.

Silica infiltration on translucent zirconia restorations: Effects on the antagonist wear and survivability.

OBJECTIVE: To assess potential antagonist wear and survival probability of silica-infiltrated zirconia compared to glass-graded, glazed, and polished zirconia. METHODS: Table top restorations made of 3Y-TZP (3Y), 5Y-PSZ (5Y), and lithium disilicate (LD) were bonded onto epoxy resin preparations. Each zirconia was divided into five groups according to the surface treatment: polishing; glaze; polishing-glaze; glass infiltration; and silica infiltration. The LD restorations received a glaze layer. Specimens were subjected to sliding fatigue wear using a steatite antagonist (1.25 ×106 cycles, 200 N). The presence of cracks, fractures, and/or debonding was checked every one/third of the total number of cycles was completed. Roughness, microstructural, Scanning electron microscopy, wear and residual stress analyses were conducted. Kaplan-Meier, Mantel-Cox (log-rank) and ANOVA tests were performed for statistical analyses. RESULTS: The survival probability was different among the groups. Silica infiltration and polishing-glaze led to lower volume loss than glaze and glass-infiltration. Difference was observed for roughness among the zirconia and surface treatment, while lithium disilicate presented similar roughness compared to both glazed zirconia. Scanning electron microscopy revealed the removal of the surface treatment after sliding fatigue wear in all groups. Compressive stress was detected on 3Y surfaces, while tensile stress was observed on 5Y. SIGNIFICANCE: 3Y and 5Y zirconia behaved similarly regarding antagonist wear, presenting higher antagonist wear than the glass ceramic. Silica-infiltrated and polished-glazed zirconia produced lower antagonist volume loss than glazed and glass-infiltrated zirconia. Silica-infiltrated 3Y and lithium disilicate restorations were the only groups to show survival probabilities lower than 85%.

Feldspathic and Lithium Disilicate Onlays with a 2-Year Follow-Up: Split-Mouth Randomized Clinical Trial.

The present study was a prospective, controlled, randomized, clinical short-term trial aiming to evaluate the clinical performance of adhesively luted, lithium disilicate and feldspathic glass-ceramics onlays over a period up to 2 years. A total of 11 patients (7 female, 4 male; age range: 18-60 years, mean age: 39 years) were selected for this study. Each patient received a maximum of two restorations per group in a split-mouth-design. LD: Eleven onlays, performed with lithium disilicate-based ceramic (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein), and FP: Eleven onlays, performed with feldspathic ceramic (Vita Mark II, Vita Zanhfabrik, Bad Säckingen). Recalls were performed at 2 weeks (baseline = R1), 1 year (R2) and 2 years (R3) after the cementation by three calibrated blinded independent investigators using mirrors, magnifying eyeglasses, probes and bitewing radiographs. The postoperative sensitivity, secondary caries, marginal integrity, marginal discoloration, color match, surface roughness, tooth integrity, and restoration integrity were evaluated. The Friedman test was used to determine if there was a statistically significant difference in time-to-time comparison of the parameters in the ceramics restorations. A total of 95.4% of the restorations were clinically acceptable at the 2-year recall, without a difference for any evaluation parameter for both ceramic materials. Based on the 2-year data, the CAD-CAM onlays manufactured with feldspathic and lithium-disilicate based ceramics showed similar clinical performance.

Effect of glazing application side and mechanical cycling on the biaxial flexural strength and Weibull characteristics of a Y-TZP ceramic.

OBJECTIVE: Glaze application on monolithic zirconia (Y-TZP) can be a practical approach to improve the mechanical properties of this material. Our study evaluated the effect of glazing side and mechanical cycling on the biaxial flexure strength (BFS) of a Y-TZP. METHODOLOGY: Eighty sintered Y-TZP discs (Ø:12 mm; thickness: 1.2 mm - ISO 6872) were produced and randomly assigned into eight groups (n=10), according to the factors "glazing side" (control - no glazing; GT - glaze on tensile side; GC - glaze on compression side; GTC - glaze on both sides) and "mechanical aging" (non-aged and aged, A - mechanical cycling: 1.2×106, 84 N, 3 Hz, under water at 37°C). Specimens were subjected to BFS test (1 mm/min; 1,000 Kgf load cell) and fractured surfaces were analyzed by stereomicroscopy and SEM. Hsueh's rigorous solutions were used to estimate the stress at failure of glazed specimens. Two-way ANOVA, Tukey's test (5%), and Weibull analysis were performed. RESULTS: The "glazing side", "mechanical aging" and the interaction of the factors were significant (p<0.05). Groups GC (1157.9±146.9 MPa), GT (1156.1±195.3 MPa), GTC (986.0±187.4 MPa) and GTC-A (1131.9±128.9 MPa) presented higher BFS than control groups (Tukey, 5%). Hsueh's rigorous solutions showed that the maximum tensile stress was presented in the bottom of zirconia layer, at the zirconia/glaze interface. Weibull characteristic strength (σo) of the GC was higher than all groups (p<0.05), except to GT, GTC-A and GTC, which were similar among them. The fractography showed initiation of failures from zirconia the tensile side regardless of the side of glaze application and fatigue. CONCLUSION: Glazing zirconia applied on both tensile and compression sides improves the flexural strength of Y-TZP, regardless the mechanical aging.

Impact of Acid Concentration and Firing on the Long-term Bond Strength of a Zirconia-Lithium Silicate Ceramic Following Adhesive Cementation.

PURPOSE: To evaluate the effect of different firing stages (without firing, additional crystallization and glaze firings), hydrofluoric acid (HF) concentrations (5% and 10%), and thermocycling on the bond strength between resin cement and a zirconia-lithium silicate (ZLS) ceramic. MATERIALS AND METHODS: ZLS ceramic (Celtra Duo, Dentsply Sirona) blocks were cut into smaller blocks and divided into 12 groups (N = 72), according to the HF concentration used, firing stage, and thermocycling (n = 6). All specimens were silanized (Monobond N, Ivoclar) and cemented with resin cement (Multilink N, Ivoclar) onto blocks of composite resin (Filtek Z250 XT, 3M). The specimens were immersed in distilled water for 24 h. The blocks were cut into sticks and tested immediately or thermocycled for 10,000 cycles in water (5°C-55°C). Microtensile bond strength (µTBS) testing was then performed in a universal testing machine (0.5 mm/min, 50 kgf load cell). The failure modes of the sticks were examined using SEM and classified as adhesive, predominantly adhesive, or cohesive. Fracture surfaces were topographically evaluated using SEM. The 5% and 10% HF groups were analyzed separately and the data submitted to two-way ANOVA and Tukey's test (p < 0.05). Additional samples were used for SEM topographic analysis of representative ceramic surfaces. RESULTS: The most frequent types of failure were predominantly adhesive between cement and ceramic and adhesive (cement completely covered the composite). Statistically significant differences were found only for the thermocycling factor (p < 0.05) for both HF concentrations. However, for the 10% HF groups, a marked decrease in µTBS was observed after firing and thermocycling. SEM showed superficial irregularities on ZLS without etching, partial and total dissolution of the vitreous matrix and exposure of the crystals using 5% and 10% HF, respectively. CONCLUSION: The crystallization and glaze firings of ZLS ceramics conditioned with 5% HF promoted bond strength maintenance after thermocycling. Thermocycling decreased the bond strength in all groups, but mainly for fired ZLS conditioned with 10% HF.

In vitro wear of a zirconium-reinforced lithium silicate ceramic against different restorative materials.

It is important to predict the wear behavior of a material as well as its potential to wear antagonized restorative materials. Thus, this study investigated the performance of zirconia-reinforced lithium silicate (ZLS) after wear with different antagonists. Thirty discs of ZLS were made and divided into three groups according to the antagonist (n = 10). Ten cylinders of each antagonist were also made. The parameters for the simulation of wear were: 30N, horizontal movement of 6 mm, and 1.7 Hz, totaling 300,000 cycles, in distilled water. Wear measurements (volume losses (mm3)) on the ZLS and antagonists were performed by digital optical profilometry or an analytical balance. Hardness of all materials was also measured, whereas roughness and Scanning Electron Microscopy (SEM) were only accessed for the ZLS. The wear and hardness values were subjected to one-way ANOVA and the Tukey Test (95%), while the roughness data was analyzed with paired T-test (95%). The hardness means of all materials were statistically different (zirconia > steatite = ZLS > acrylic resin) (p = 0.0001). Zirconia and steatite severely worn ZLS and only acrylic resin worn surfaces could be measured for roughness, which was significantly higher after wear (p = 0.007). SEM showed the ZLS's wear tracks when worn by steatite and zirconia. It was possible to observe differences of ZLS wear patterns depending on the antagonist and quantify the volumes worn with steatite (17.61 ±â€¯2.65) and zirconia (41.98 ±â€¯19.45), which were significantly different (p = 0.001). Acrylic resin promoted a superficial wear on ZLS that could not be quantified. In terms of the antagonists' materials, zirconia presented significantly different less volume loss compared to acrylic resin and steatite (p = 0.000). It can be concluded that zirconia caused more wear on ZLS than steatite and acrylic resin.

Reinforced Glass-ceramics: Parametric Inspection of Three-Dimensional Wear and Volumetric Loss after Chewing Simulation.

The aim of this study was to investigate the three-dimensional wear, volumetric loss and surface roughness after chewing simulation of two glass ceramics. Lithium disilicate (LD, Emax CAD, Ivoclar) and Zirconia reinforced lithium silicate (ZLS, Vita Suprinity, Vita Zhanfabrick) discs (n=20/g) were scanned to obtain stereolithography (STL) files for each sample. All discs were submitted to chewing simulation with sliding configuration (30 N, 300,000 cycles, 6 mm and 1.7 Hz) with steatite as antagonist. The samples were then scanned again and the volume loss and the deepest defect depth was measured using the superimposed file from the baseline using three-dimensional digital parametric inspection software (GOM Inspect, Braunschweig, Germany). Surface roughness (Ra and Rz) was analyzed with a contact profilometer. Data were analyzed by one-way ANOVA and Tukey test (α=0.5%). ANOVA showed significant differences among the groups. Considering the ceramic volume loss, wear depth defect length and Rz roughness, LD (-22.09±5.57%; 0.80±0.06 µm; 3.08±1.02 µm) showed higher mean values than ZLS (-15.67±4.51%; 0.56±0.09 µm; 1.51±0.90 µm). Ra mean values were similar for both materials (p=0.064). All discs exhibited slight surface scratches along with the sliding direction with pitted wear patterns, while large cracks were observed on wear traces. These same areas can be identified in blue, overlapping the STL files before and after chewing simulation in inspection software. The linear reduction generated by sliding contact shows a graph with a similar wear pattern shape. ZLS was more resistant to wear than LD, with less volume loss and shallower surface defects.

The Wear Performance of Glazed and Polished Full Contour Zirconia.

This study evaluated the influence of zirconia surface finishes on the wear of an enamel analogue. 40 zirconia discs were divided into four groups: control (without finish); glazed; polished; polished and glazed. All samples were subjected to wear against steatite antagonists. The specimens underwent roughness, topographic, scanning electron microscopy (SEM) and wettability analyses. Quantitative wear measurements were performed on both steatites and discs. To measure wear of steatites the weight before and after the test and the diameter after the test were used. Profilometer measurements were performed to determine the wear on discs. Roughness, volumetric wear and mass loss were analyzed using the Kruskal-Wallis and Dunn tests (5%), while contact angle values were analyzed with One-way ANOVA and Tukey tests (5%). The polished group had the lowest roughness means, being statistically different from the other groups (p-value=0.0001). The glazed group presented the lowest steatite volumetric wear (p-value=0.0001), but not statistically different from the polished and glazed group, whereas these groups presented the highest zirconia volumetric wear, with statistically different (p-value=0.0002) compared to the others. SEM showed irregularities on the control groups surface, grooves on the polished group, and a homogeneous surface for the glazed group with a few pores. All groups presented contact angles lower than 90 degrees, characterizing hydrophilic surfaces. It can be concluded that just glazed zirconia caused less wear on the antagonist when compared to no finish and polished zirconia.

Fatigue Failure Load of Resin-bonded Simplified Lithium Disilicate Glass-Ceramic Restorations: Effect of Ceramic Conditioning Methods.

PURPOSE: To evaluate the influence of different ceramic surface conditioning methods on the fatigue failure load of adhesively cemented simplified lithium-disilicate glass-ceramic restorations. MATERIALS AND METHODS: Ceramic (IPS e.max CAD, Ivoclar Vivadent) (Ø = 10 mm; thickness = 1.2 mm) and epoxy resin (Ø = 10 mm; thickness = 2.3 mm) disks were produced. The ceramic bonding surfaces were treated as follows: no etching and MPS-silane primer application only (MN); etching with 10% hydrofluoric acid (HF) for 20 s followed by primer application (HF + MN); HF + universal multimode adhesive application (HF + SU); etching with a one-step etching primer (ME&P); HF + primer + conventional adhesive (HF + MN + PAB). The epoxy resin disks were etched with 10% HF for 20 s followed by a coat of bonding agent (Multilink Primer A+B). Pairs of ceramic/epoxy resin disks were cemented with composite cement (Multilink N, Ivoclar Vivadent). The mean fatigue failure load was determined by the staircase method (100,000 cycles at 20 Hz frequency; initial load = 1435 N; step size = 72 N). RESULTS: ME&P had the highest fatigue failure load, followed by HF etched groups, while the non-etched condition (MN group) had the lowest. All samples presented radial cracks originating from defects at the conditioned ceramic surface (interface). CONCLUSION: The simultaneous physicochemical conditioning with one-step self-etching ceramic primer promoted the best fatigue behavior results of the glass-ceramic restorations. It might indicate that this one-step conditioning reduces the number of flaws at the ceramic surface due to the slighter surface alterations than those produced by hydrofluoric acid etching, improving the fatigue behavior.

Failure Probability, Stress Distribution and Fracture Analysis of Experimental Screw for Micro Conical Abutment.

The aim of this study was to evaluate the failure probability of two types of abutment screws after compressive load and to analyze the stress distribution with finite element method. Sixty (60) single-tooth implant restorations were assembled on titanium implants (e-fix, A.S. Technology - Titanium Fix). The groups were divided into Conventional screw (Screw neck 1.5 ø mm) and Experimental screw (Screw neck constricted with 1.2 ø mm). Specimens were subjected to single load to failure with compressive test according ISO 14801. The fractured specimens were subjected to stereomicroscopy for measurement of remaining screws inside the implant and characterization of fracture origin. Representative specimens were analyzed by scanning electronic microscopy. For finite element method (FEM), an identical 3D model of the two in vitro test groups were used with similar conditions (30º, 100 N load). The stress in the abutment screw was analyzed by von-Mises criteria. The results of strength means were 4132.5 ± 76 MPa and 4528.2 ± 127.2 for conventional and experimental groups, respectively. During microscopy, the mean (mm) of the remaining screw piece inside the implants were 0.97 ± 0.23 and 1.32 ± 0.12 for conventional and experimental groups, respectively. In FEM, the conventional group showed stress concentered in an unfavorable region (peak of 39.23 MPa), while the experimental group showed more stress areas but less concentration than the conventional group (36.6 MPa). In using the tested experimental geometry, the abutment screw can have its strength improved, and the origin of failure can be more favorable to clinical resolution.

Effect of different loading pistons on stress distribution of a CAD/CAM silica-based ceramic: CAD-FEA modeling and fatigue survival analysis.

PURPOSE: This study evaluated the effect of different loading pistons, made of various materials and with different elastic moduli acting as antagonist material, on stress distribution and fatigue behavior of a CAD/CAM silica-based ceramic. MATERIALS AND METHODS: Discs of CAD/CAM made silica-based ceramic (N = 60) (VITA MARK II) were divided into six groups (n = 10 per group), according to the test method (M: Monotonic; F: Fatigue) and the antagonist piston material (T: Tungsten; S: Steel; G: Epoxy resin). FT, FS and FG combinations were submitted to mechanical cycling (2 × 106 cycles, 4 Hz, 45 N). The bending stress after fatigue were also valuated using Weibull analysis and the parameters η (eta), ß (beta) and the mean time to failure (MTTF) were calculated. Fractographic analysis and Finite Element Analysis (FEA) were performed. Data were analyzed using ANOVA and Tukey's tests (alpha=0.05). RESULTS: MG presented significantly less bending strength (MPa) (75.6) compared to MT (87.8) and MS (84.4) (p < 0.05). Six specimens from FT (MMTF: 8.3 × 106; ß:0.60; η:5.6 × 106), four from FS (MMTF: 1.9 × 106; ß:1.2; η:2.0 × 106) and one from FG (MMTF: 1.3 × 106; ß:0.48; η:0.64 × 106) survived the fatigue test. The stress peak on the tensile surface of S was similar to that of T and both were less than that of G. The failure origins were on the tensile surface. CONCLUSION: The epoxy resin pistons were able to decrease the bending stress, and life expectancy (faster failure) of a silica-based ceramic compared to tungsten and steel.

Bond strength between a polymer-infiltrated ceramic network and a composite for repair: effect of several ceramic surface treatments.

The effects of several ceramic surface treatments on bond strength of a polymer-infiltrated ceramic network and resin composite as repair material were evaluated. CAD-CAM blocks of a polymer-infiltrated ceramic network (Vita Enamic) were sliced and subjected to aging process, followed by embedding in acrylic resin. The bonding/repair area was treated as follows (n = 30): C- without treatment; UA- universal adhesive application; FM- 10% hydrofluoric acid and silane application; OM-airborne-particle abrasion with aluminum oxide and silane application; RP- tribochemical silica coating; and CA- surface grinding and application of universal adhesive. Composite resin cylinders were made on the treated surface. Specimens from each group were assigned randomly to two subgroups (n = 15) considering storage condition: Baseline (shear tests after 48 hours) or Storage (tests after 6 months under distilled water). The treated surfaces were analyzed by goniometry, roughness, and SEM. Two-way ANOVA and 1-way ANOVA were applied to analyze the bond data and roughness / contact angle data, respectively, followed by Tukey's test (α = 5%). Surface treatments and storage conditions affected bond strengths (p < 0.01). Surface grinding (CA) followed by universal adhesive promoted the highest value of bond strength (14.5 ± 4.8 MPa for baseline, 8.5 ± 3.4 MPa for storage) and the roughest ceramic surface. Grinding with silicon carbide paper (simulating diamond bur) followed by the application of a universal adhesive system is the best option for repairing fractures of the polymer-infiltrated ceramic network.

Can heat-pressed feldspathic ceramic be submitted to multiple heat-pressing?

The aim of this study was to determine if multiple processing (heat-pressing) of a dental ceramic influences flexural strength, hardness, and microstructure. Ninety bar-shaped specimens (15 mm × 4 mm × 2 mm) of a pressed ceramic (Vita PM9) were fabricated and randomly divided into 6 groups (n = 15) according to the factors "number of pressings" (C1, C2, and C3, fired 1, 2, and 3 times, respectively) and "mechanical cycling" (M). Half of the specimens were mechanically cycled (106 cycles, 45 N, 3.4 Hz, in water) and all specimens were tested for 3-point bending (0.5 mm/min, load 1000 kgf) and Vickers hardness (19.6 N for 20 s). X-ray diffraction was used to characterize the phases and scanning electron microscopy to characterize the microstructure. The flexural strength data was statistically analyzed with Weibull analysis, ANOVA, and Tukey test. Hardness data was evaluated by 2-way ANOVA and Fisher test. All tests were performed with a significance level of 0.05. Two-way ANOVA revealed that neither "number of pressings" (p=0.085) or "mechanical cycling" (0.055) significantly affected flexural strength. But Weibull analysis showed significant difference for Weibull moduli and characteristic strength between groups. For hardness, a statistical difference was seen for the interaction "Number of pressings * Mechanical cycling", (p = 0.016). Hardness decreased in the following order: C1 (775±17.2), CM3 (751±101), CM2 (735±45), C3 (701±82), CM1 (671±82), and C2 (663±92). Fewer defects were observed with an increased number of firings. Therefore, the possibility of recycling PM9 ceramic does not interfere in the evaluated mechanical properties and improves microstructure.

Effect of ceramic thickness, grinding, and aging on the mechanical behavior of a polycrystalline zirconia.

Monolithic restorations of Y-TZP have been recommended as a restorative alternative on prosthetic dentistry as it allows a substantial reduction of ceramic thickness, which means a greater preservation of tooth structure. However, the influence of grinding and aging when using a thinner layer of the material is unclear. This investigation aimed to evaluate and compare the effects of ceramic thickness (0.5 mm and 1.0 mm), grinding and aging (low-temperature degradation) on the mechanical behavior and surface characteristics of a full-contour Y-TZP ceramic. Y-TZP disc-shaped specimens (15 mm diameter) were manufactured with both thicknesses and randomly assigned into 4 groups considering the factors 'grinding with diamond bur' and 'aging in autoclave'. Surface topography (roughness, 3D profilometry and SEM), phase transformation, flexural strength and structural reliability (Weibull) analyses were executed. Grinding affected the surface topography, while aging did not promote any effect. An increase in m-phase content was observed after grinding and aging, although different susceptibilities were observed. Regardless of zirconia's thickness, no deleterious effect of grinding or aging on the mechanical properties was observed. Thus, in our testing assembly, reducing the thickness of the Y-TZP ceramic did not alter its response to grinding and low temperature degradation and did not impair its mechanical performance.

Effects of porcelain thickness on the flexural strength and crack propagation in a bilayered zirconia system.

OBJECTIVE: This study evaluated the influence of porcelain (VM9, VITA Zahnfabrik, Germany) thickness on the flexural strength and crack propagation in bilayered zirconia systems (YZ, VITA Zahnfabrik, Germany). MATERIAL AND METHODS: Thirty zirconia bars (20.0x4.0x1.0 mm) and six zirconia blocks (12.0x7.5x1.2 mm) were prepared and veneered with porcelain with different thickness: 1 mm, 2 mm, or 3 mm. The bars of each experimental group (n=10) were subjected to four-point flexural strength testing. In each ceramic block, a Vickers indentation was created under a load of 10 kgf for 10 seconds, for the propagation of cracks. RESULTS: The results of flexural strength were evaluated by One-way ANOVA and Tukey's test, with a significance level of 5%. The factor "thickness of the porcelain" was statistically significant (p=0.001) and the l-mm group presented the highest values of flexural strength. The cracks were predominant among the bending specimens with 1 and 2 mm of porcelain, and catastrophic failures were found in 50% of 3-mm-thick porcelain. After the indentation of blocks, the most severe defects were observed in blocks with 3-mm-thick porcelain. CONCLUSION: The smallest (1 mm) thickness of porcelain on the zirconia infrastructure presented higher values of flexural strength. Better resistance to defect propagation was observed near the porcelain/ zirconia interface for all groups. Higher flexural strength was found for a thinner porcelain layer in a bilayered zirconia system. The damage caused by a Vickers indentation near and far the interface with the zirconia shows that the stress profiles are different.