Influence of the postpolymerization type and time on the flexural strength and dimensional stability of 3D printed interim resins.

STATEMENT OF PROBLEM: The mechanical strength of 3-dimensionally (3D) printed interim resins is unclear but influenced by printing parameters. Evidence regarding standardization of the postpolymerization type and time for 3D printed interim resins is sparse. PURPOSE: The purpose of this in vitro study was to evaluate the influence of postpolymerization type and time on flexural strength and dimensional stability of 3D printed resins for interim restorations. MATERIAL AND METHODS: A total of 288 bars were 3D printed (Form 2; Formlabs, stereolithography-SLA, 50 µm, 30 degrees), (25×2×2 mm; International Organization for Standardization-ISO 4049:2019) abraded and randomly divided into 9 groups (n=30) according to postpolymerization (Ultraviolet device-UV; Microwave with water-MWA; Microwave without water-MW) and time (15, 20, and 30 minutes for UV; and 5, 8, and 10 minutes for MW and MWA). Each bar was then measured with digital calipers at 11 points for length, thickness, and width before and after postpolymerization to analyze dimensional stability. The flexural strength was then measured (σ; 980.6 N, 1 mm/minute) and the fractured surfaces were analyzed with scanning electron microscopy. The σ (MPa) data were evaluated by using a 2-way analysis of variance (ANOVA) and the Tukey honestly significant difference (HSD) pairwise comparisons test (α=.05). Dimensional stability data (mm) were analyzed by using the Kruskal-Wallis test and Dwass-Steel-Critchlow-Fligner multiple comparisons. The Weibull analysis was performed with σ data. RESULTS: The 2-way ANOVA revealed that all factors and their interaction were significant for σ (P<.001). The UV groups presented the highest σ values, being statistically higher than all MW and MWA groups. The Weibull analysis revealed that postpolymerization UV groups found the highest values regarding the characteristic strength, although the MW 8-minute group (13.71) found the highest value for the Weibull modulus. Furthermore, the Kruskal-Wallis test revealed that only the postpolymerization factor was significant for dimensional stability (P<.001). The postpolymerization microwave groups found greater expansion variations at all times, with the MW 8-minute group (0.78 ±0.54) presenting the greatest variation in dimensional stability. CONCLUSIONS: UV was determined to be the most suitable type of postpolymerization for interim printed resin among the postpolymerization methods, regardless of the application time. The postpolymerization MW groups found greater variations in dimensional stability.

Hybrid abutment during prosthetic planning and oral rehabilitation.

INTRODUCTION: The present study aims to describe through a literature review, the characteristics and properties of hybrid abutments, as well as their proper use as a new rehabilitation strategy. EVIDENCE ACQUISITION: A bibliographic search was conducted in the main health databases Pubmed (www.pubmed.gov) and Google Scholar (www.scholar.google.com.br), in which studies published from 2001 to 2020 were collected. Laboratory studies, case reports, systematic and literature reviews were included. Therefore, articles that do not address the characteristics and properties of hybrid abutments were excluded. In addition, studies that did not report the use of hybrid abutments as a new rehabilitation strategy. EVIDENCE SYNTHESIS: According to the inclusion and exclusion criteria, 80 research articles were selected and 20 were excluded, while 25 in vitro, 17 in vivo and 9 in silico studies were reviewed. CONCLUSIONS: The literature demonstrates that hybrid abutments are an excellent alternative in cases of implant-supported rehabilitation, presenting high esthetic results, associated with good soft tissue response, peri implant marginal bone stability and adequate stress distribution during the masticatory loads dissipation.

Effect of neutralization and hydrofluoric acid precipitate remotion on the compressive strength of monolithic lithium disilicate crowns.

BACKGROUND: The cleaning protocol for the ceramic surface after acid etching resulted in a decrease in bond strength and flexural strength of a glass ceramic. This study aims to evaluate the effect of different ceramic surface treatments after hydrofluoric acid etching (HF) on the compressive strength of monolithic lithium disilicate crowns. METHODS: Forty (40) human third molars received conventional full coverage preparation. After performing digital impressions of teeth preparations, ceramic blocks were machined using a CAD/CAM system in order to obtain the crowns. The crowns were distributed in 4 groups as ceramic surface treatment (N.=10): (HF) - 4.9% HF for 20s + air-water spray for 30s; (HFN) - HF + neutralizing agent for 5 min (N); (HFU) - HF + ultrasonic bath for 5 min (U); e (HFNU) - HF + N + U. SEM and EDS analysis was performed in each group in order to characterize the ceramic surface and to verify the chemical element distribution after HF cleaning protocols. A silane layer was applied (for 60s), and crowns were then cemented with dual resin cement. A compressive load was applied on the middle of the occlusal crown surface with a crosshead speed of 1 mm/min until fracture. Data were analyzed using ANOVA and Tukey test (α=0.05). RESULTS: Fluoride ions were found in samples of all postetching cleaning protocols. The mean value (Kgf) was: HF =169.92±21.37; HFN =187.34±34.79; HFU =166.63±40.22 and HFNU=175.26±40.22. The ceramic surface treatment after HF etching did not significantly influence (P>0.05) the compressive strength of the tested ceramic crowns. CONCLUSIONS: Surface treatments with neutralizing agent associated with the ultrasonic bath as the pre-cementation protocol was the most efficient protocol in eliminating the precipitate deposited on the porosities created by acid etching.

Influence of different post-endodontic restorations on the fatigue survival and biomechanical behavior of central incisors.

PURPOSE: To evaluate the influence of different post-endodontic techniques on the fatigue survival and biomechanical behavior of crowned restored central incisors. METHODS: The crowns of 69 bovine incisors were cut, and the roots were treated endodontically and assigned randomly into three groups (n=23): resin composite buildup (BUP), glass fiber post-retained resin composite buildup (GFP), and cast post-and-core (CPC). They received full crown preparation with 2 mm ferrule, and a leucite-reinforced ceramic crown was cemented adhesively. Three specimens from each group were tested monotonically. The remaining specimens were subjected to the stepwise stress fatigue test until fracture or suspension after 1.5 x 106 cycles in a chewing simulator. The load and step at which each specimen failed were analyzed by Kaplan-Meier and Mantel-Cox (log-rank test) statistics, followed by multiple pairwise comparisons, at 5% significance level. The three groups tested (BUP, GFP, and CPC) were 3D modeled (Rhinoceros 4.0) and the maximum principal stress (MPa) criteria were used to calculate the results using FEA. RESULTS: There was no statistical difference between the treatments regarding the load or the number of cycles (Mantel-Cox log-rank test for trend, X²= 0.015, df=1, P= 0.901, X²=3.171, df=1, P= 0.995). Crown cracks were the predominant failure mode, and oblique root fractures were only observed in groups GFP and CPC. In endodontically treated incisors with a 2-mm ferrule, the post-endodontic treatment had no significant effect on fatigue survival. Non-restorable fractures only occurred in teeth restored with posts. CLINICAL SIGNIFICANCE: Although the clinical significance of laboratory studies has some limitations, this study suggests that composite buildups without posts may be an option for restoring endodontically treated incisors with 2 mm ferrule height.

Durability of staining and glazing on a hybrid ceramics after the three-body wear.

Hybrid ceramic is a promising material for monolithic restorations that could require an individualization through the extrinsic staining to improve aesthetics. Due to the possibilities to treat this ceramic prior to staining, this study evaluated the wear resistance of surface treatments prior to staining and glazing a hybrid ceramic. Thirty-two specimens (Vita Enamic) were divided into 8 groups according to the surface treatment prior to the staining (Polishing: Pol, Acid etching: Ac, Sandblasting with Al2O3: Sd or Self-etching silane: Ses) and glaze application (with: gl or without: gl). The specimens were submitted to the ACTA wear machine simulating the presence of food bolus and antagonist. The wear rate of the stain was determined after 7 intervals of 20,000 cycles, using a profilometer. The surface before and after staining, and after wear were inspected using Scanning Electron Microscopy (SEM). The rates were analyzed using three-way ANOVA and Tukey test. The wear was affected by surface treatment, glaze application and number of cycles (p < 0.001). 100% of the staining was removed after 20,000 cycles for Pol, 40,000 for Pol + gl, 60,000 for Ses + gl, 80,000 for Ac, 100,000 for Sd and Ses, 120,000 for Ac + gl and 140,000 for Sd + gl. SEM showed similar worn surfaces. Sandblasting followed by glaze application was the most durable treatment to maintain the external staining on the hybrid ceramic surface when subjected to three-body wear.

Survival Probability, Weibull Characteristics, Stress Distribution, and Fractographic Analysis of Polymer-Infiltrated Ceramic Network Restorations Cemented on a Chairside Titanium Base: An In Vitro and In Silico Study.

Different techniques are available to manufacture polymer-infiltrated ceramic restorations cemented on a chairside titanium base. To compare the influence of these techniques in the mechanical response, 75 implant-supported crowns were divided in three groups: CME (crown cemented on a mesostructure), a two-piece prosthetic solution consisting of a crown and hybrid abutment; MC (monolithic crown), a one-piece prosthetic solution consisting of a crown; and MP (monolithic crown with perforation), a one-piece prosthetic solution consisting of a crown with a screw access hole. All specimens were stepwise fatigued (50 N in each 20,000 cycles until 1200 N and 350,000 cycles). The failed crowns were inspected under scanning electron microscopy. The finite element method was applied to analyze mechanical behavior under 300 N axial load. Log-Rank (p = 0.17) and Wilcoxon (p = 0.11) tests revealed similar survival probability at 300 and 900 N. Higher stress concentration was observed in the crowns' emergence profiles. The MP and CME techniques showed similar survival and can be applied to manufacture an implant-supported crown. In all groups, the stress concentration associated with fractographic analysis suggests that the region of the emergence profile should always be evaluated due to the high prevalence of failures in this area.

Three-body wear effect on different CAD/CAM ceramics staining durability.

Regardless the materials properties, the vast majority of ceramic restorations could require an individualization through the extrinsic staining to improve aesthetics. This study aimed to compare the staining wear durability of different monolithic ceramics. Specimens of high translucent zirconia (YZHT), zirconia reinforced lithium silicate (ZLS), hybrid ceramic (HC) and feldspathic ceramic (FLD) were divided in five groups according to each material staining technique. The ZLS ceramic was tested with stained prior (ZLS1) and after crystallization (ZLS2). All specimens were extrinsically characterized, i.e. stained, and crystallized or sintered in specific ovens, according to the manufacturer's recommendation. The specimens were submitted to three-body wear tests in ACTA wear machine, simulating the presence of food bolus and antagonist (pH 7, 15 N, 1 Hz). The wear rate of the stain surface was determined after 5 intervals of 200,000 cycles, using a profilometer. The ceramic surface before and after staining, and after wear were inspected by Scanning Electron Microscopy (SEM). The wear rates were analyzed using two-way ANOVA and post-hoc Tukey test. The wear rates of the staining were affected by ceramic and the number of cycles (P < 0.001). 100% of staining was removed after 200,000 cycles for HC, and after 600,000 cycles for YZHT and ZLS1. Staining of ZLS2 and FLD remained on ceramic surface even after 1,000,000 cycles. Furthermore, FLD showed a significant higher staining durability than ZLS2. SEM revealed different surface morphologies for each group with and without staining and after the wear test. Ceramics with fired staining showed higher durability compared to the polymerized one. The feldspar ceramic presented superior staining durability, followed by zirconia reinforced lithium silicate and high translucent zirconia. The conventional two steps staining technique showed improved durability for zirconia reinforced lithium silicate.

Silica coating followed by heat-treatment of MDP-primer for resin bond stability to yttria-stabilized zirconia polycrystals.

This study evaluated the influence of silica coating, primer type and its heat treatment on bond strength durability between resin cement and an yttrium-stabilized polycrystalline tetragonal zirconia (Y-TZP). Eighty (80) Y-TZP blocks were allocated into 16 groups considering four factors: silica coating (without and with); type of primer (RelyX Ceramic Primer, a silane-based primer; Single Bond Universal, a universal MDP-based primer); heat treatment of the primer (without and with); aging (without and with). After zirconia treatments, resin cement cylinders (RelyX ARC) (n = 20; N = 320) were built. Half of the samples were tested after 24 h, and another half were subjected to aging (thermocycling 5-55°C/5.000, and storage in water for 6 months). Shear bond strength test and failure analysis were performed. Bond strength data were submitted to four-way ANOVA and Tukey test (p = 0.05). All factors were statistically significant (p < 0.001) for bond strength (MPa): silica coating (7.3 ± 5.9) > no-treatment (3.6 ± 4.3); universal primer (6.7 ± 4.8) > silane (4.2 ± 5.8); heat-treatment (6.5 ± 6.3) > no-heating (4.4 ± 4.3); no-aging (8.2 ± 5) > aging (2.7 ± 4.4). Tukey test revealed that the association of silica coating + universal primer + heat-treatment promoted higher and stable resin bond strength. Silica coating, universal adhesive application and heat treatment improve/increase durability and bond strength of zirconia. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 104-111, 2019.

Do Mechanical Advantages Exist in Relining Fiber Posts with Composite Prior to its Cementation?

PURPOSE: To evaluate two different techniques for glass fiber-reinforced resin post (FRC) insertion by assessing the stress distribution under polymerization shrinkage or masticatory loading and measuring the pull-out bond strength to dentin. MATERIALS AND METHODS: A model of an endodontically treated maxillary central incisor was used for three-dimensional simulation with two conditions: conventionally cemented (FRC) and relined (RFRC). The volumetric solids were exported to analysis software (ANSYS 17.2, ANSYS) in STEP (Standard for the Exchange of Product Data) format. All contacts were considered perfectly bonded between the geometries. Numerical models received a load of 100 N (45 degrees) on the lingual surface. The composite cement polymerization shrinkage was simulated by thermal analogy to obtain Von Mises, maximum principal stress, and shear stress. For in vitro evaluation, a pull-out bond strength test (n = 20/N = 40) was performed (50 Kgf, 1 mm/min) after mechanical cycling (in water at 37°C, 84 N, 2 bar, 45 degrees, 106 cycles, 4 Hz), and failure analysis was subsequently performed. The results were analyzed using one-way ANOVA and Tukey's test (α < 0.05). RESULTS: The FRC group showed more stress concentration in the cement layer. The RFRC group [(32 ± 13); (288 ± 129)] presented better performance than the FRC group [(6 ± 7); (152 ± 87)] for stress distribution and bond strength (p < 0.05). Adhesive and mixed failures occurred in both groups. CONCLUSION: Relined fiberglass posts reduced the stress generated by polymerization shrinkage and showed greater bond strength to dentin.

The Influence of Ceramic Re-pressing on Surface Properties, Bond Strength, and Color Stability of Leucite Ceramic.

PURPOSE: To evaluate the influence of recycling a pressed ceramic material on surface properties, color stability and bond strength to composite cement. MATERIALS AND METHODS: Forty-eight (48) ingots from a heat-pressed ceramic (PM9, Vita Zahnfabrik) were fabricated through the lost-wax technique and then polished with SiC sandpaper to standardize the dimensions (diameter: 12 mm; length: 4 mm). Leftover material from processing the pressed groups was retrieved and used to repeat heat pressing for the re-pressed groups. The ingots were randomly divided into 3 groups according to the number of injections - one, two, or three times. Ra, Rz, and RSm surface roughness parameters were evaluated through a contact rugosimeter. Topography was analyzed using SEM and the chemical constituents using EDS (energy dispersive spectroscopy). Color stability was evaluated according to CIE-Lab parameters to determine color variation (∆E). Composite ingots with the same dimensions were cemented over each ceramic, then this set was cut into sticks with a 1-mm2 cross-sectional area. Half of the sticks were submitted to microtensile bond strength (µTBS) testing after 24 h. The other half was tested after thermocycling (5000 cycles, 5°C-55°C) and storage in water at 37°C for 6 months. RESULTS: One-way ANOVA showed that the number of injections influenced both Rz and RSm roughness parameters (p = 0.00), but not Ra (p = 0.97). One injection exhibited higher (Rz) and grooves with less space between them (RSm) compared to the other groups. For color stability, the values of L*, a*, and b* were influenced by the number of injections (p = 0.00). ∆E = 5 was found for 2 injections and ∆E = 3 for 3 injections, using a control group as reference. One-way ANOVA showed that the number of injections significantly influenced wettability values: 1inj (63 ± 5.3)A > 2inj (49 ± 8.2)B > 3inj (45.8 ± 15.8)B. However, the evaluated factor did not influence the bond strength of non-aged groups. Furthermore, aged groups showed that 1inj (21 ± 37)a presented higher mean values than 2inj (10 ± 8)b or 3inj (12 ± 10.)b. CONCLUSION: Re-pressing the evaluated ceramic improves roughness and wettability, but compromises the color stability and decreases bond strengths after long-term aging.

Fracture Strength, Failure Types, and Weibull Characteristics of Three-Unit Zirconia Fixed Dental Prostheses After Cyclic Loading: Effects of Veneering and Air-Abrasion Protocols.

The required connector dimension for zirconia fixed dental prostheses (FDPs) may be a clinical limitation due to limited space in the occlusogingival direction. Using no veneering in the gingival regions of the pontics and connectors may solve this problem. This study evaluated the mechanical durability of zirconia FDPs with and without veneering in the gingival area of the connectors and pontics and subsequent air abrasion of this region with different protocols. Models were made of resin abutments (diameter = 6 or 8 mm, height = 6 mm, 6 degrees convergence) and embedded in polyurethane resin (distance = 11 mm). Zirconia frameworks were milled and randomly distributed by veneering (veneering of the entire framework [VEN] or no veneering at gingival regions of the pontic and connector [NVEN]) and by air-abrasion (Al2O3/SiO2, 30 µm; or 45 µm Al2O3. FDPs were adhesively cemented and subjected to mechanical cycling (1,200,000 cycles, 200 N, 4 Hz, with water cooling). Specimens were tested until fracture (1 mm/min), and failure modes were classified. Data (N) were subjected to one-way analysis of variance in two sets, Tukey test (α = .05) and Weibull analysis. While veneering did not significantly affect the results (VEN: 1,958 ± 299 N; NVEN: 1,788 ± 152 N; P = .094), air abrasion did (P = .006), with the worst results for the groups conditioned with 45 µm Al2O3 (SiO2: 1,748 ± 273 N; Al2O3: 1,512 ± 174 N). The NVEN group demonstrated the highest Weibull modulus (12.8) compared with the other groups (5.3-7.2). Fractures commonly initiated from the gingival side of the connector. Veneering of the gingival region of the connectors and pontics in zirconia FDPs did not diminish the fracture strength, but air-abrasion of this area with 45 µm Al2O3 decreased the results.

Extended glaze firing improves flexural strength of a glass ceramic.

OBJECTIVE: To investigate the effect of firing protocols on flexural strength, surface roughness, and crystalline structure of a leucite-based glass ceramic. METHODS: Discs produced by automated machining were distributed into five groups (n=30) according to the applied firing protocols, conducted above (790°C) or below (575°C) the ceramic transition temperature (Tg) (625±20°C): C - control, no heat treatment; G790 - glaze firing (790°C) for 1.5 min (manufacturer-recommended); G790-SC - G790 modified by slow cooling; EGF790-SC - extended G790 for 15 min, with slow cooling; and EF575-SC - extended firing below Tg at 575°C for 15 min, with slow cooling. Discs were subjected to biaxial flexural tests and results were assessed using Weibull analysis. Surface roughness was measured before and after treatments. One specimen from each group was used for X-ray diffraction (XRD). RESULTS: Highest values of characteristic strength (σ0) were obtained for EGF790-SC (211.7MPa). Regimens EF575-SC, G790-SC, and G790 produced σ0 values (167.9, 157.7, and 153.7MPa, respectively) lower than the control (C) (187.7MPa). The Weibull modulus (m) was statistically similar between groups. All treatments reduced the mean roughness (Ra) of the specimens. Extended cycles (EGF790-SC, EF575-SC) decreased the mean amplitude (Rz). XRD revealed no crystalline phase transformation and slight changes in size of leucite crystallites. SIGNIFICANCE: Increased values of fracture strength and decreased surface roughness for a leucite-reinforced glass ceramic are achieved by extended glaze firing after machining. Crystalline structure is not modified. Glaze cycles, manufacturer-recommended or modified by slow cooling, and firing below Tg, significantly reduce fracture strength.

Hard machining, glaze firing and hydrofluoric acid etching: Do these procedures affect the flexural strength of a leucite glass-ceramic?

OBJECTIVE: To evaluate the effects of hard machining, glaze firing and hydrofluoric acid etching on the biaxial flexural strength and roughness of a CAD/CAM leucite glass-ceramic; to investigate if ceramic post-machining surface roughness is influenced by the machining order and by the pair of burs used for it. METHODS: A hundred forty four discs were machined by six nominally identical pairs of burs and divided into groups (n=24): (1) machining-M, (2) machining and glaze firing-MG, (3) machining and hydrofluoric acid etching-MA, (4) machining, glaze firing and hydrofluoric acid etching-MGA, (5) machining followed by polishing, as a control-MP, (6) machining, polishing and hydrofluoric acid etching-MPA. The roughness after each treatment (Ra and Rz) was measured. The discs were submitted to a piston-on-three ball flexure test (ISO 6872/2008) and strength data analyzed through Weibull statistics (95% CI). RESULTS: M resulted in lower characteristic strength (σ0) (128.2MPa) than MP (177.2MPa). The glaze firing reduced σ0 (109MPa), without affecting roughness. Hydrofluoric acid etching increased the roughness without affecting σ0. Spearman's coefficient (rs) indicated strong and significant correlation between machining order and roughness (rsRa=-0.66; rsRz=-0.73). The ceramic post-machining surface roughness differed significantly according to the pair of burs employed (p<0.05). SIGNIFICANCE: hard machining and glaze firing reduced the leucite ceramic strength, while hydrofluoric acid etching did not affect the strength. Variability in the roughness might be expected after machining, since it was influenced by the machining order and by the bur pairing.

Effects of aging procedures on the topographic surface, structural stability, and mechanical strength of a ZrO2-based dental ceramic.

OBJECTIVE: To determine the effects of different aging methods on the degradation and flexural strength of yttria-stabilized tetragonal zirconia (Y-TZP) METHODS: Sixty disc-shaped specimens (∅, 12mm; thickness, 1.6mm) of zirconia (Vita InCeram 2000 YZ Cubes, VITA Zahnfabrik) were prepared (ISO 6872) and randomly divided into five groups, according to the aging procedures (n=10): (C) control; (M) mechanical cycling (15,000,000 cycles/3.8Hz/200N); (T) thermal cycling (6,000 cycles/5-55°C/30s); (TM) thermomechanical cycling (1,200,000 cycles/3.8Hz/200N with temperature range from 5°C to 55°C for 60s each); (AUT) 12h in autoclave at 134°C/2bars; and (STO) storage in distilled water (37°C/400 days). After the aging procedures, the monoclinic phase percentages were evaluated by X-ray diffraction (XRD), and topographic surface analysis was performed by 3D profilometry. The specimens were then subjected to biaxial flexure testing (1mm/min, load 100kgf, in water). The biaxial flexural strength data (MPa) were analyzed by 1-way ANOVA and Tukey's test (α=0.05). The data for monoclinic phase percentage and profilometry (Ra) were analyzed by Kruskal-Wallis and Dunn's tests. RESULTS: ANOVA revealed that flexural strength was affected by the aging procedures (p=0.002). The M (781.6MPa) and TM (771.3MPa) groups presented lower values of flexural strength than did C (955MPa), AUT (955.8MPa), T (960.8MPa) and STO (910.4MPa). The monoclinic phase percentage was significantly higher only for STO (12.22%) and AUT (29.97%) when compared with that of the control group (Kruskal-Wallis test, p=0.004). In addition, the surface roughnesses were similar among the groups (p=0.165). SIGNIFICANCE: Water storage for 400 days and autoclave aging procedures induced higher phase transformation from tetragonal to monoclinic; however, they did not affect the flexural strength of Y-TZP ceramic, which decreased only after mechanical and thermomechanical cycling.

Influence of air-particle deposition protocols on the surface topography and adhesion of resin cement to zirconia.

OBJECTIVES: This study evaluated the influence of air-particle abrasion protocols on the surface roughness (SR) of zirconia and the shear bond strength (SBS) of dual-polymerized resin cement to this ceramic. MATERIALS AND METHODS: Sintered zirconia blocks (n = 115) (Lava, 3M ESPE) were embedded in acrylic resin and polished. The specimens were divided according to the 'particle type' (Al: 110 µm Al2O3; Si: 110 µm SiO2) and 'pressure' factors (2.5 or 3.5 bar) (n = 3 per group): (a) Control (no air-abrasion); (b) Al2.5; (c) Si2.5; (d) Al3.5; (e) Si3.5. SR (Ra) was measured 3-times from each specimen after 20 s of air-abrasion (distance: 10 mm) using a digital optical profilometer. Surface topography was evaluated under SEM analyses. For the SBS test, 'particle type', 'pressure' and 'thermocycling' (TC) factors were considered (n = 10; n = 10 per group): Control (no air-abrasion); Al2.5; Si2.5; Al3.5; Si3.5; ControlTC; Al2.5TC; Si2.5TC; Al3.5TC; Si3.5TC. After silane application, resin cement (Panavia F2.0) was bonded and polymerized. Specimens were thermocycled (6.000 cycles, 5-55°C) and subjected to SBS (1 mm/min). Data were analyzed using ANOVA, Tukey's and Dunnett tests (5%). RESULTS: 'Particle' (p = 0.0001) and 'pressure' (p = 0.0001) factors significantly affected the SR. All protocols significantly increased the SR (Al2.5: 0.45 ± 0.02; Si2.5: 0.39 ± 0.01; Al3.5: 0.80 ± 0.01; Si3.5: 0.64 ± 0.01 µm) compared to the control group (0.16 ± 0.01 µm). For SBS, only 'particle' factor significantly affected the results (p = 0.015). The SiO2 groups presented significantly higher SBS results than Al2O3 (Al2.5: 4.78 ± 1.86; Si2.5: 7.17 ± 2.62; Al3.5: 4.97 ± 3.74; Si3.5: 9.14 ± 4.09 MPa) and the control group (3.67 ± 3.0 MPa). All TC specimens presented spontaneous debondings. SEM analysis showed that Al2O3 created damage in zirconia in the form of grooves, different from those observed with SiO2 groups. CONCLUSIONS: Air-abrasion with 110 µm Al2O3 resulted in higher roughness, but air-abrasion protocols with SiO2 promoted better adhesion.

Low-temperature degradation of a Y-TZP ceramic after surface treatments.

The purpose of this study was to evaluate the influence of zirconia surface treatments on low-temperature degradation (LTD). Disc-shaped specimens were subjected to one of four surface treatments, denoted as C (control-no surface treatment), Si (air abrasion with 30 µm silica-modified alumina particles), Al (air abrasion with 30 µm alumina particles), and Gr (grinding with 120 grit diamond discs). Half of the samples were submitted to autoclave treatment for 12 h (127°C, 1.5 bar). Samples were characterized by x-ray diffraction and profilometer analysis and were subjected to biaxial flexural strength test. All of the groups exhibited an increase in the amount of monoclinic phase (m-phase) after LTD. The t→m transformation was remarkable for the specimens from the C group, which also exhibited a significant increase in strength. The Gr group also exhibited an increase in strength but lower initial roughness, which probably suppressed LTD on the zirconia surface. The specimens subjected to air abrasion exhibited higher initial amounts of m-phase and a small increase in m-phase after LTD; the strength was not affected in these groups. The effects of LTD were different with each surface treatment applied. Apparently, LTD may be suppressed by smoother surfaces or the presence of an initial amount of m-phase on zirconia surface.

The impact of hydrofluoric acid etching followed by unfilled resin on the biaxial strength of a glass-ceramic.

OBJECTIVES: To evaluate the null hypotheses that hydrofluoric (HF) acid etching time would neither decrease the biaxial flexural strength of a glass-based veneering ceramic nor enhance it after silane and unfilled resin (UR) applications. METHODS: Disc-shaped IPS e.max ZirPress specimens were allocated into 12 groups: G1-control (no-etching), G2-30 s, G3-60 s, G4-90 s, G5-120 s, G6-60 s+60 s. Groups (G7-G12) were treated in the same fashion as G1-G6, but followed by silane and UR applications. Surface morphology and roughness (Ra and Rq) of the ceramics were assessed by means of scanning electron microscopy (SEM) and profilometry, respectively. Flexural strength was determined by biaxial testing. Data were analyzed by two-way ANOVA and the Sidak test (α=0.05). Weibull statistics were estimated and finite element analysis (FEA) was carried out to verify the stress concentration end areas of fracture. RESULTS: The interaction (etching time vs. surface treatment) was significant for Ra (p=0.008) and Rq (0.0075). Resin-treated groups presented significantly lower Ra and Rq than non-treated groups, except for the 60s group (p<0.005). SEM revealed that etching affected the ceramic microstructure and that the UR was able to penetrate into the irregularities. A significant effect of etching time (p=0.029) on flexural strength was seen. G7-G12 presented higher strength than G1-G6 (p<0.0001). None of experimental groups failed to show 95% confidence intervals of σ0 and m overlapped. FEA showed lower stress concentration after resin treatment. SIGNIFICANCE: HF acid etching time did not show a damaging effect on the ceramic flexural strength. Moreover, the flexural strength could be enhanced after UR treatment.

Effects of thickness, processing technique, and cooling rate protocol on the flexural strength of a bilayer ceramic system.

OBJECTIVE: To determine whether the thickness, processing technique, and cooling protocol of veneer ceramic influence the flexural strength of a bilayer ceramic system. MATERIALS AND METHODS: Sixty-four bar-shaped specimens (20mm×4mm×1mm) of yttria-stabilized tetragonal zirconia (Vita In-Ceram YZ, Vita) were fabricated (ISO 6872) and randomly divided into 8 groups (n=8) according to the factors "processing technique" (P - PM9 and V - VM9), "thickness" (1mm and 3mm), and "cooling protocol" (S - slow and F - fast). The veneer ceramics were applied only over one side of the bar-shaped specimens. All specimens were mechanically cycled (2×10(6) cycles, 84N, 3.4Hz, in water), with the veneer ceramic under tension. Then, the specimens were tested in 4-point bending (1mm/min, load 100kgf, in water), also with the veneer ceramic under tension, and the maximum load was recorded at first sign of fracture. The flexural strength (σ) was calculated, and the mode of failure was determined by stereomicroscopy (30×). The data (MPa) were analyzed statistically by 3-way ANOVA and Tukey's test (α=0.05). RESULTS: ANOVA revealed that the factor "thickness" (p=0.0001) was statistically significant, unlike the factors "processing technique" (p=0.6025) and "cooling protocol" (p=0.4199). The predominant mode of failure was cracking. SIGNIFICANCE: The thickness of the veneer ceramic has an influence on the mechanical strength of the bilayer ceramic system, regardless of processing technique and cooling protocol of the veneer ceramic.

Air-particle abrasion on zirconia ceramic using different protocols: effects on biaxial flexural strength after cyclic loading, phase transformation and surface topography.

This study evaluated the effect of different air-particle abrasion protocols on the biaxial flexural strength and structural stability of zirconia ceramics. Zirconia ceramic specimens (ISO 6872) (Lava, 3M ESPE) were obtained (N=336). The specimens (N=118, n=20 per group) were randomly assigned to one of the air-abrasion protocols: Gr1: Control (as-sintered); Gr2: 50 µm Al2O3 (2.5 bar); Gr3: 50 µm Al2O3 (3.5 bar); Gr4: 110 µm Al2O3(2.5 bar); Gr5: 110 µm Al2O3 (3.5 bar); Gr6: 30 µm SiO2 (2.5 bar) (CoJet); Gr7: 30 µm SiO2(3.5 bar); Gr8: 110 µm SiO2 (2.5 bar) (Rocatec Plus); and Gr9: 110 µm SiO2 (3.5 bar) (duration: 20 s, distance: 10 mm). While half of the specimens were tested immediately, the other half was subjected to cyclic loading in water (100,000 cycles; 50 N, 4 Hz, 37 °°C) prior to biaxial flexural strength test (ISO 6872). Phase transformation (t→m), relative amount of transformed monoclinic zirconia (FM), transformed zone depth (TZD) and surface roughness were measured. Particle type (p=0.2746), pressure (p=0.5084) and cyclic loading (p=0.1610) did not influence the flexural strength. Except for the air-abraded group with 110 µm Al2O3 at 3.5 bar, all air-abrasion protocols increased the biaxial flexural strength (MPa) (Controlnon-aged: 1,030 ± 153, Controlaged: 1,138 ± 138; Experimentalnon-aged: 1,307 ± 184-1,554 ± 124; Experimentalaged: 1,308 ± 118-1,451 ± 135) in both non-aged and aged conditions, respectively. Surface roughness (Ra) was the highest with 110 µm Al2O3(0.84 µm. FM values ranged from 0% to 27.21%, higher value for the Rocatec Plus (110 µm SiO2) and 110 µm Al2O3 groups at 3.5 bar pressure. TZD ranged between 0 and 1.43 µm, with the highest values for Rocatec Plus and 110 µm Al2O3 groups at 3.5 bar pressure.

Zirconia-porcelain bonding: effect of multiple firings on microtensile bond strength.

PURPOSE: To determine the bond strength between zirconia and porcelain with varying numbers of veneer firing cycles. MATERIALS AND METHODS: Fifty specimens of zirconia veneered with feldspathic ceramic were submitted to one (1-firing), two (2-firings), three (3-firings), four (4-firings), or five (5-firings) firing cycles to sinter the porcelain. After the respective number of firings, the specimens were embedded into acrylic resin and sectioned into bars with a 1-mm2 cross-sectional area. The microbars were bonded to a special device and attached to a universal testing machine (Emic DL 1000). Microtensile bond strength testing (MTBS) was performed at 0.5 mm/min. The maximum load for fracture was recorded (N) and the microtensile bond strength was calculated in MPa. Data were analyzed using one-way ANOVA and Tukey's test (α = 0.05). The Weibull modulus and characteristic strength was also calculated for each experimental group. RESULTS: Specimens submitted to a single firing cycle presented the lowest bond strength values (14.1 MPa), two firing cycles provided intermediate bond strength values (15 MPa) and the other groups presented equivalently high values (18.1 - 18.4 MPa). The Weibull modulus did not change between the groups. CONCLUSION: More than three firing cycles of a veneer ceramic provided higher bond strengths between zirconia and the veneering ceramic.