How do different intraoral scanners and milling machines affect the fit and fatigue behavior of lithium disilicate and resin composite endocrowns?

The aim of this in vitro study was to evaluate the effect of the combinations of two different intraoral scanners (IOS), two milling machines, and two restorative materials on the marginal/internal fit and fatigue behavior of endocrowns produced by CAD-CAM. Eight groups (n= 10) were considered through the combination of TRIOS 3 (TR) or Primescan (PS) IOS; 4-axes (CR; CEREC MC XL) or 5-axes (PM; PrograMill PM7) milling machines; and lithium disilicate (LD; IPS e.max CAD) or resin composite (RC; Tetric CAD) restorative materials. Specific surface treatments were applied to each material, and the bonding to its corresponding Endocrown-shaped fiberglass-reinforced epoxy resin preparations was performed (Variolink Esthetic DC). Computed microtomography (µCT) was performed to assess the marginal/internal fit, as well as a mechanical fatigue test (20 Hz, initial load = 100 N/5000 cycles; step-size = 50 N/10,000 cycles until a threshold of 1500 N, then, the step-size was increased if needed to 100 N/10,000 cycles until failure or a threshold of 2800 N) to evaluate the restorations long-term behavior. Complementary analysis of the fracture features and surface topography in scanning electron microscopy was performed. Three-way ANOVA and Kaplan-Meier test (α = 0.05) were performed for marginal/internal fit, and fatigue behavior data, respectively. PS scanner, CR milling machine, and RC endocrowns resulted in a better marginal fit compared to their counterparts. Still, the PM machine resulted in a better pulpal space fit compared to the CR milling machine. Regardless of the scanner and milling machine, RC endocrowns exhibited superior fatigue behavior than LD ones. LD endocrowns presented margin chipping regardless of the milling machine used. Despite minor differences in terms of fit, the 'IOS' and 'milling machine' factors did not impair the fatigue behavior of endocrowns. Resin-composite restorations resulted in a higher survival rate compared to glass-ceramic ones, independently of the digital devices used in the workflow.

Influence of CAD-CAM milling strategies on the outcome of indirect restorations: A scoping review.

STATEMENT OF PROBLEM: The influence of computer-aided manufacturing (CAM) parameters and settings on the outcomes of milled indirect restorations is poorly understood. PURPOSE: The purpose of this scoping review was to summarize the current CAM systems, parameters, and setting changes, and their effects on different outcomes of milled indirect restorations and aspects related to their manufacture. MATERIAL AND METHODS: The protocol of this review is available online (https://osf.io/x28ps/). Studies that used at least 2 different parameters (CAM units, number of axes, digital spacers, or protocols with different rotatory instruments, grit-sizes, milling speed, or others) for milling indirect restorations were included. A structured search up to July 2023 was performed by 2 independent reviewers for articles written in English in LILACS, MEDLINE via PubMed, EMBASE, Web of Science, and Scopus. RESULTS: Of 1546 studies identified, 22 were included in the review. Discrepancies were found between the planned and actual measured cement space, with a decreasing linear relationship impacting restoration adaptation at different points. The CEREC MC XL milling machine was the most used system in the included studies, with variations in bur types, milling modes, and number of burs uses affecting internal fit and surface trueness. The results demonstrated the better adaptation of restorations made with 5-axis over 3-axis milling machines. Lithium disilicate and zirconia were the most commonly used materials, and crowns and inlays were popular designs. Marginal and internal adaptation were the primary outcomes assessed using the various techniques. CONCLUSIONS: The study presented a comprehensive exploration of CAM systems and parameters, and their influence on indirect restorations. The planned cement space was not properly reproduced by the milling. Bur characteristics can affect restoration fit and trueness. The 5-axis units seem to result in better-adapted restorations compared with 3- and 4-axis units.

Conventional-, bulk-fill- or flowable-resin composites as prosthetic core build-up: Influence on the load-bearing capacity under fatigue of bonded leucite-reinforced glass-ceramic.

This study aimed to evaluate the fatigue performance of simplified ceramic restorations (leucite-reinforced glass ceramic) adhesively cemented onto substrates of different resin composites. Three options from the same commercial line were selected (Tetric N-Line, Ivoclar), classified as Conventional (CRC), Bulk-fill (BRC) and Flowable (FRC), which were used to make discs using a cylindrical metallic device (n = 19; Ø = 10 mm, thickness = 2.0 mm). A total of 57 discs (Ø = 10 mm, thickness = 1.0 mm) were made from CAD/CAM prefabricated blocks of a leucite reinforced glass-ceramic (Empress CAD, Ivoclar) to simulate a monolithic restoration, then were randomly distributed to be bonded on 19 discs of each three different resin composite substrates (CRC; BRC; or FRC) with a dual resin cement (Multilink N; Ivoclar). The samples were subjected to a compression test with a hemispherical stainless-steel piston (Ø = 40 mm) at a monotonic regimen (n = 4; 1 mm/min loading rate and 500 kgf loading cell until fracture). The cyclic fatigue test was performed underwater at a frequency of 20 Hz (n = 15). The first step was applied using 200N for 5000 cycles, followed by increments of 50N at each step of 10,000 until failure. The outcome considered for both tests was the occurrence of radial crack. Specific statistical tests (α = 0.05) were performed for monotonic (One-way ANOVA; Tukey's test) and fatigue data (Kaplan-Meier test; Log-rank test). Fractography of fractured samples were also performed. The FRC group had the lowest failure load in both test regimes (p < 0.05; monotonic: 726.64N; fatigue: 716.67N). There were no differences between the CRC and BRC groups (p > 0.05; monotonic: 989.30 and 990.11N; fatigue: 810.00 and 833.33N, respectively). The same result was obtained considering cycles for fatigue failure (FRC < CRC=BRC). Leucite glass-ceramic bonded to substrates made of flowable resin composite behaves worse mechanically than bonding to conventional or bulk-fill resin composite substrates.

Impact of try-in paste removal on the fatigue behavior of bonded lithium disilicate ceramics.

This in vitro study assessed the effectiveness of three cleaning protocols (air-water spray, 37% phosphoric acid, or Ivoclean) on lithium disilicate restorations' fatigue behavior after try-in paste application, compared to a clean condition. Lithium disilicate discs (IPS e.max CAD, Ivoclar) with Ø-= 12 mm and 1 mm thickness were prepared from prefabricated CAD-CAM blocks, polished, subjected to CAD-CAM milling topography simulation and crystallization. After, etching with 5% hydrofluoric acid and the application of try-in paste (Variolink try-in paste shade white; load of 2.5 N for 5 min) was performed. Discs that received try-in paste were divided into three groups according to the removal protocol: SPRAY - air-water spray for 30 s; HPO - active application of 37% phosphoric acid for 60 s; IVOC - application of Ivoclean for 20 s. Control group (CTRL group) did not receive the try-in paste application. Half of the specimens (n= 15) were tested in the baseline condition (24 h up to 7 days), and the others underwent 25,000 thermal cycles (5 - 55 °C) + 210 days of distilled water storage (37 °C). Additional specimens (n= 3) underwent monotonic testing (1 mm/min). Fatigue testing involved a cyclic fatigue approach (20 Hz, initial load = 100 N - 5000 cycles, step size = 50 N - 10,000 cycles) until a visible crack appeared. Fractographic and topographic analyses were performed. Fatigue data were statistically analyzed with two-way ANOVA, Kaplan-Meier log-rank (Mantel-Cox), and independent t-test (α= 0.05). In the baseline condition, the IVOC group resulted in a superior fatigue behavior compared to the CTRL and SPRAY groups, but similar to the HPO group. The HPO and SPRAY presented a similar fatigue behavior to the CTRL group. It was noticed a decrease in fatigue behavior after aging, which resulted in all the cleaning protocols leading to similar fatigue behavior compared to the CTRL group. On the SPRAY group surface, try-in pastes remnants were noticed. In summary, despite a detrimental impact at baseline conditions, all tested cleaning protocols seem proper to remove the try-in paste from the ceramic's surface in the long-term evaluation.

Characteristic fatigue strength and reliability of dental glass-ceramics: Effect of distinct surface treatments - Hydrofluoric acid etching and silane treatment vs one-step self-etching ceramic primer.

The aim of this study was to mechanically characterize through flexural fatigue test two CAD-CAM glass-ceramics according to distinct surface etching protocols. To do so, feldspathic (FELD) and lithium disilicate (LD) glass ceramics were subjected to different surface treatments: (1) control - no treatment (Ctrl); (2) conventional protocol etching with 5% hydrofluoric acid followed by silane coupling agent application (HF + SIL; Monobond N, Ivoclar); or (3) using a self-etching ceramic primer (E&P; Monobond Etch & Prime, Ivoclar). Ceramic discs (N = 120; Ø = 12 mm; thickness = 1.2 mm) were produced from CAD-CAM blocks, with 60 being from FELD (VITABLOCS Mark II, Vita Zahnfabrik) and 60 from LD (IPS e.max CAD, Ivoclar). Next, 20 disks of each ceramic were allocated into three groups: Ctrl, HF + SIL, or E&P. Surface roughness data were collected on all samples before and after surface treatments (except for Ctrl). Cyclic fatigue (n = 15) biaxial flexural strength tests were performed by the piston-on-three-balls geometry (ISO 6872) considering the test parameters established from a monotonic test (n = 5). The monotonic test was carried out at a 1 mm/min loading rate and 500 kgf loading cell until fracture to obtain the failure data. The cyclic fatigue test was executed underwater at a frequency up to 20 Hz, with the first stress being 25% of the monotonic test for 5000 cycles, followed by increments of 5% of the monotonic test at each step of 10,000 cycles until failure (fracture). Complementary fractography, topography and Atomic Force Microscopy (AFM) analyses were performed. Characteristic Fatigue Strength (CFS) and Weibull modulus were analyzed by Weibull analysis using the fatigue test data. Roughness and complementary analysis data were analyzed by one-way ANOVA. The statistical results exhibited similar CFS among Ctrl, HF + SIL and E&P for both glass-ceramics. The survival analysis corroborates the findings, however the Weibull modulus pointed out superior structural reliability of FELD treated with the E&P group compared to HF + SIL. According to the complementary analyses, HF + SIL exhibited a higher surface area than E&P and Ctrl for FELD (p = 0.001). Roughness showed statistically significant differences among conditions for FELD (E&P < Ctrl = HF + SIL; p < 0.05) and no difference for LD (p > 0.05). Therefore, the CFS were not influenced by any condition evaluated for FELD and LD glass-ceramics; however, superior structural reliability (higher Weibull modulus) for the feldspathic ceramic treated with the E&P was observed.

Evaluation paste removal method and bond strength between resin cement and lithium disilicate ceramic: An in vitro study.

STATEMENT OF PROBLEM: After the use of evaluation paste, residue can remain on the bonding surface. However, how adhesion to lithium disilicate ceramic is affected is unclear. PURPOSE: The purpose of this in vitro study was to determine the effectiveness of lithium disilicate cleaning after contamination with an evaluation paste and before the application of a resin cement. MATERIAL AND METHODS: Rectangular lithium disilicate (IPS e.max CAD) specimens were obtained with a simulated milled surface, crystallized, etched with 5% hydrofluoric (HF) acid, and contaminated with an evaluation paste. The cleaning methods tested were air-water spray (SPRAY), 37% phosphoric acid (HPO), ultrasonic bath (ULT), cleaning paste (IVOC), and a conventional surface treatment (HF + silane-HF+SIL). The control (CTRL) group was not contaminated. After silane had been applied, resin cement cylinders were fabricated and light polymerized. Half of the cylinders (n=56) were tested for microshear bond strength at baseline (24 hours), and the other half after 210 days of water storage and 25 000 thermal cycles. Surface roughness, failure analysis, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were performed. Statistical analysis was performed with the Kruskal-Wallis and Mann-Whitney tests for surface roughness and the 2-way ANOVA and Bonferroni post hoc tests for bond strength (α=.05). RESULTS: At baseline, only SPRAY did not restore the bond strength compared with CTRL. After aging, the bond strengths of SPRAY and IVOC were lower than of CTRL (P<.05); no significant difference was found between CTRL, HPO, ULT, and HF+SIL (P>.05). EDS demonstrated the presence of carbon in the SPRAY and ULT groups, probably remnants of the evaluation paste. SEM analysis identified such remnants in the SPRAY group only. CONCLUSIONS: For optimal bond strength between lithium disilicate and resin cement after evaluation paste use, cleaning the ceramic surface with 37% phosphoric acid, ultrasonic bath, or with hydrofluoric acid worked best.

Survival rate and treatment success of glass fiber posts cemented with two adhesive cementation strategies after up to 106 months: a randomized clinical trial.

OBJECTIVES: The objective of this study is to evaluate the longevity of two fiber post cementation strategies in a prospective, multicenter, non-inferiority, double-blind randomized controlled trial. METHODS: A total of 152 teeth, with adequate endodontic treatment and loss of coronal structure and bilateral simultaneous posterior occlusal contacts, were randomly allocated to receive glass fiber posts cemented with a conventional cementation strategy (CRC group: adhesive system + resin cement) (Adper Single Bond + RelyX ARC; 3 M-ESPE) or a self-adhesive cementation strategy (SRC group: self-adhesive resin cement; RelyX U100/U200; 3 M-ESPE). The patients were recalled annually for clinical and radiographical evaluation with a 93% recall rate (142 teeth, with 74 at CR groups and 68 at SRC group). The primary outcome was survival rate, considering the fiber post debonding (loss of retention). The secondary outcome included the success rate of the prosthetic treatment with crown debonding, post fracture, and tooth loss (not related to post failure). Both outcomes were evaluated annually. The Kaplan-Meier method and Cox regression with 95% confidence interval were used for the statistical analysis. RESULTS: For the primary outcome (failures directly related to fiber posts cementation strategy), there were 4 fiber post debondings (2 per group), 8 root fractures (3 for SRC group and 5 for CRC group), and one mixed failure (debonding combined with root fracture for CRC), with both strategies presenting similar survival rates (p = 0.331), with 88.9% for the CRC group and 90.9% for the SRC group. For the secondary outcome (failures not related to fiber post cementation strategies), there were 8 crown debondings, 3 post fractures, and 3 tooth losses, with no statistically difference between groups (p = 0.701), with 77% for SRC and 82% for CRC. CONCLUSION: Fiber post cementation strategies with conventional or self-adhesive resin cement presents similar tooth survival and success rates. TRIAL REGISTRATION: NCT01461239 CLINICAL RELEVANCE: Both adhesive cementation strategies led to high survival and success rates and are indicated for fiber post cementation, even after a long follow-up period (up to 106 months).

Resin cement coating reverts the machining damage on the flexural fatigue strength of lithium disilicate glass-ceramic.

This study evaluated the effect of resin cement coating with high and low viscosities on the flexural fatigue strength of machined lithium disilicate glass-ceramic. Discs (IPS e.max CAD; Ivoclar Vivadent) were prepared and divided according to the surface condition (machining [M]-CEREC inLab; and polishing [P]-laboratory procedures), resin cement coating (with or without), and cement viscosity (high [H] and low [L]). The ceramic bonding surface was etched/primed by a one-step primer application followed by resin cement application (Variolink N base + high or low viscosity catalyst; Ivoclar Vivadent). Biaxial flexural fatigue strength was evaluated on a piston-on-three-ball set by the step-test method (n = 15) (initial stress: 60 MPa; incremental steps: 20 MPa; 10,000 cycles/step, at 20 Hz). Weibull statistics were used for fatigue data. Contact angle, topographic, and fractographic analysis were also performed. Machining produced statistically lower contact angle than polishing and a significant detrimental effect on the fatigue behavior (σ0 M = 247.2 [246.9-268.3]; σ0 P = 337.4 [297.8-382.4]). Machined groups followed by resin cement coating (σ0 MH = 297.9 [276.0-321.5]; σ0 Ml = 301.2 [277.1-327.4]) behaved similarly to the polished and coated groups (σ0 PH = 342.0 [308.9-378.5]; σ0 PL = 357.3 [324.7-393.1]), irrespective of the cement viscosity. Therefore, cement coating has able to revert the detrimental effects of the machining on the fatigue strength of lithium disilicate glass-ceramic. High and low viscosity cements behaved similarly in the improvement of CAD-CAM lithium disilicate fatigue strength.

A brief review on fatigue test of ceramic and some related matters in Dentistry.

The characteristics of dental ceramics have been extensively studied over the years to provide highly qualified materials for use in prosthetic restorations. The ability to adhere to dental substrates, outstanding aesthetics (translucency, color, and substrate masking ability) and improved mechanical properties provide these materials with optical features and high strength to withstand masticatory stimuli. Different classifications are adopted, and it is generally considered that glass-ceramics have better optical characteristics due to the high glass content, and polycrystalline ceramics have superior strength favored by their densified and organized crystals, hampering crack growth. This knowledge was largely built-up during years of scientific research through different testing methodologies, but mainly employing static loads. It is important to not only take into account the intensity of loads that these materials will be exposed to, but also the effect of the intermittence of cyclic load application leading to mechanical fatigue and the influence of factors related to the crack origin and their propagation under this condition. Furthermore, the bonding surface of ceramic restorations requires surface treatments that improve the bond strength to luting agents; however, these treatments require caution because of their potential to produce defects and affect the structural behavior. Moreover, ceramic restorations often require internal adjustments for proper seating or external adjustments for fitting the occlusal contact with the antagonist. In this sense, finishing/polishing protocols may alter the defect population, as luting agents may also interact by filling in the superficial defects on the restoration intaglio surface. Thus, the balance among all these factors will define the performance of a restorative setup, as well as the posterior exposure to the humid environment and the masticatory stimuli (cyclical loading), which may favor developing slow and subcritical growth of cracks in ceramic materials and the degradation of the bond interface. Therefore, it is essential that the concepts which explain the fatigue mechanism are understood, as well as the crack propagation and failure patterns of restorative ceramic materials.

Longevity of metal-ceramic single crowns cemented onto resin composite prosthetic cores with self-adhesive resin cement: an update of a prospective analysis with up to 106 months of follow-up.

OBJECTIVES: To evaluate the longevity of metal-ceramic single crowns cemented onto resin composite prosthetic cores using a self-adhesive resin cement in a prospective clinical descriptive study. METHODS: A total of 152 teeth were endodontically treated and received resin composite prosthetic cores and metal-ceramic crowns cemented with a self-adhesive resin cement. The patients included in the sample were recalled for clinical and radiography evaluation in an up-to-106-month period after the final cementation procedures, with an average of 62 months of follow-up. 91.5% of the sample (142 teeth) were evaluated regarding the treatment survival rate, analyzed considering the loss of crown retention (crown debonding) and tooth loss as the primary outcome. In addition, post debonding, and root fracture occurrences were also recorded as secondary outcomes to evaluate the success rate of the prosthetic treatment. The aesthetic parameters were also evaluated according to the FDI criteria. The Kaplan-Meier method and Cox regression with 95% confidence interval were applied for the statistical analysis. RESULTS: Regarding the primary outcome, the metal-ceramic crowns cemented with self-adhesive resin cement presented a high survival rate (91.5%), with 8 crown debondings and 3 tooth losses (1 due to caries and 2 due to periodontal disease) occurring after the evaluation period. For secondary outcomes, 9 root fractures and 4 post debondings occurred, generating a success rate of 72%. All crowns had a score 1 on the FDI criteria, indicating that they were clinically excellent or very good regarding the aesthetic parameters. CONCLUSION: The metal-ceramic crowns luted with a self-adhesive resin cement presented a survival rate of 91.5% after an average of 62 months of follow-up. Furthermore, the restorations remained aesthetically satisfactory over time, without changes that would indicate prosthetic retreatment. A success rate of 72% was obtained considering the secondary outcome, mainly related to intraradicular retainer failures (root fractures or post debonding). CLINICAL SIGNIFICANCE: The self-adhesive resin cement is clinically indicated for cementation of metal-ceramic crowns onto resin composite prosthetic cores.

Translucency and masking ability of a translucent zirconia with different thicknesses over dark backgrounds / Translucidez e capacidade de mascaramento de uma zircônia translúcida com diferentes espessuras sobre substratos escuros

ABSTRACT Objectives: To evaluate the translucency, contrast ratio and masking ability of a translucent zirconia with different thicknesses. Methods: Disc shaped specimens (n= 3) with 10 mm (Ø) x 1.5 mm, 1 mm and 0.7 mm (thickness) were manufactured simulating all-ceramic simplified restorations. Substrate discs (n= 2; Ø: 10 mm; thickness: 2 mm) were simulated with composite resin shades: A2 (positive control) and C4; and metal alloys: silver (Ni-Cr) and golden (Cu-Al). Optical properties of the 9 translucent zirconia specimens placed on the 3 different substrates were analyzed by a spectrophotometer. The color variation (ΔE00) between each ceramic structure over the positive control substrate (A2) and over the dark backgrounds (C4, silvery, golden) were obtained as to their ceramic masking ability and subjected to non-parametric Kruskal Wallis test (5%). The translucency parameter (TP00) and contrast ratio (CR) of the different thicknesses of the ceramic discs were also collected and analyzed by one-way ANOVA and the Tukey test (5%). Results: The translucent zirconia showed greater opacity in the thickness of 1.5 mm, although it was not statistically different between 0.7 and 1.0 mm. All dark backgrounds significantly affected the final color of the simplified restoration in all evaluated thicknesses. However, the increase in ceramic thickness showed a decrease in ΔE00 values for all substrates. Conclusion: The translucent zirconia was not able to mask the dark substrates, independent of the evaluated thickness.

RESUMO Objetivos: Avaliar a translucidez, razão de contraste e capacidade de mascaramento de uma zircônia translúcida com diferentes espessuras. Métodos: Espécimes em forma de disco (n= 3) com 10 mm (Ø) x 1,5 mm, 1 mm e 0,7 mm (espessura) foram confeccionados simulando restaurações simplificadas em cerâmica pura. Discos de substrato (n= 2; Ø: 10 mm; espessura: 2 mm) foram simulados com as cores de resina composta: A2 (controle positivo) e C4; e ligas metálicas: prata (Ni-Cr) e ouro (Cu-Al). As propriedades ópticas dos 9 espécimes de zircônia translúcida posicionados nos 3 substratos diferentes foram analisadas por um espectrofotômetro. A variação de cor (ΔE00) entre cada espécime cerâmico sobre o substrato controle positivo (A2) e sobre os fundos escuros (C4, prateado, dourado) foi calculada quanto à capacidade de mascaramento da cerâmica e submetida ao teste não paramétrico de Kruskal Wallis (5%). O parâmetro de translucidez (TP00) e a razão de contraste (CR) das diferentes espessuras dos discos cerâmicos também foram coletados e analisados por ANOVA de uma via e teste de Tukey (5%). Resultados: A zircônia translúcida apresentou maior opacidade na espessura de 1,5 mm, embora não tenha sido estatisticamente diferente entre 0,7 e 1,0 mm. Todos os fundos escuros afetaram significativamente a cor final da restauração simplificada em todas as espessuras avaliadas. No entanto, o aumento da espessura da cerâmica mostrou uma diminuição nos valores de ΔE00 para todos os substratos. Conclusão: A zircônia translúcida não foi capaz de mascarar os substratos escuros, independente da espessura avaliada.

Cyclic fatigue vs static loading for shear bond strength test of lithium disilicate and dentin substrates: A comparison of resin cement viscosities.

OBJECTIVE: To explore the effect of resin cement viscosities on the shear bond strength under static and fatigue load of lithium disilicate and dentin substrates. METHODS: Bonded tri-layer samples (lithium disilicate ceramic cylinder, resin cement, and substrate - ceramic or dentin) was performed considering 2 factors (n = 15): "resin cement viscosity" (high, HV; or low, LV) and "loading mode" (static, s-SBS; or fatigue shear bond strength, f-SBS). The specimens were subjected to s-SBS (1 mm/min, 1 kN load cell) and f-SBS (cyclic fatigue, initial load: 10 N; step-size: 5 N; 10,000 cycles/step; underwater). Failure mode, topography, and finite element analysis (FEA) were performed. RESULTS: The resin cement viscosity did not influence the s-SBS and f-SBS of lithium disilicate substrate; however, it affected the bond strength to dentin, with HV presenting the worst fatigue behavior (f-SBS = 6.89 MPa). Cyclic loading in shear testing induced a notorious detrimental effect with a relevant decrease (16-56 %) in bond strength and survival rates, except for dentin substrate and LV. Most failures were adhesive. A distinct pattern comparing the disilicate and dentin was identified and FEA demonstrated that there was a stress concentration on the top of the cement layer. SIGNIFICANCE: Cyclic fatigue loading in shear testing has detrimental effects on the adhesive behavior and survival probabilities of bonded lithium disilicate sets, regardless of resin cement viscosity. In contrast, resin cement viscosity affects the bond strength and the survival rates of dentin substrate submitted to cyclic loading mode, in which a low viscosity results in better performance.

In-lab simulation of CAD/CAM grinding and intaglio surface treatments of 4YSZ monolithic restorations: Effect on its load-bearing capacity under fatigue.

OBJECTIVES: To evaluate the effect of in-lab simulation of CAD/CAM grinding and intaglio surface treatments on the surface characteristics (topography and roughness) and fatigue behavior of adhesively luted 4YSZ simplified restorations. METHODS: Ceramic discs (Ø = 10 mm, thickness = 1 mm) were randomly allocated into 6 groups considering: "In-lab simulation of CAD/CAM grinding" (ground or polished) and "intaglio surface treatments": Ctrl (without surface treatment), AlOx (aluminum oxide air abrasion) or GLZ (glaze spray application). The surface roughness of all samples was measured, the treated discs received a ceramic primer, were luted with resin cement onto a dentin analogue material (woven glass-reinforced epoxy resin) and tested under a cyclic fatigue test (step-stress approach, n = 15; 1.4 Hz, 10,000 cycles/step, step-size of 100N starting at 200N until failure). A complementary analysis was performed to corroborate the findings in the fatigue test that the glaze fill defects increase the mechanical properties of the ceramic. To do so, bars (n= 10; 1.0 × 1.0 × 12 mm; considering the groups: N-ID: non-indented; ID: indented; ID-GLZ: indented plus glaze spray application) were indented in a vickers hardness tester to produce a crack pattern, treated with glaze or not, and then submitted to flexural strength tests (FS). Fractographic and topographic analysis were performed. RESULTS: In-lab simulation of CAD/CAM grinding decreased the fatigue failure load of the 4YSZ ceramic when comparing polished and ground groups, regardless of surface treatment. GLZ induced better fatigue performance compared to the air abrasion, regardless of the grinding condition (ground or polished surface). The results of the flexural strength test corroborated the findings in the fatigue test, as the ID-GLZ group presented superior FS than the ID group, however both had inferior FS than N-ID. There is an inverse association between roughness and fatigue failure load, as the higher the surface roughness, the lower the fatigue failure load. Failures in the fatigue and flexural strength tests started from the face subjected to tensile stresses. CONCLUSION: In-lab simulation of CAD/CAM grinding had a detrimental effect on the fatigue behavior of 4YSZ and glaze spray induced better 4YSZ performance compared to the air abrasion. The intaglio surface treatments differently influenced the 4YSZ fatigue performance, however, only glaze spray can reverse the damage caused by the grinding.

Mechanical characterization of a multi-layered zirconia: Flexural strength, hardness, and fracture toughness of the different layers.

This study compared the flexural strength under monotonic (static - sσ) and cyclic load application (fatigue - fσ), hardness (H) and fracture toughness (KIC) of different layers of a multi-layered zirconia (IPS e.max ZirCAD MT Multi, Ivoclar). Each layer was sectioned, classified into three groups according to yttria content (4-YSZ, 4/5-YSZ and 5-YSZ), and shaped on samples for flexural strength and fracture toughness tests (bars: 1.0 × 1.0 × 11 mm); and Vickers hardness test (plates: 1.5 × 4.0 × 5.0 mm). Flexural strength under monotonic load application (sσ; n = 10) was obtained through two different devices (three-point-bending and ball-in-hole device) and fatigue flexural strength (fσ; n = 15; initial load: 10 N; step-size: 5 N; 10,000 cycles/step) was assessed using a ball-in-hole device under cyclic load application. Vickers hardness test (n = 5), fracture toughness test (n = 10), and additional analyzes (Finite Element Analysis - FEA, Energy-dispersive X-ray spectroscopy - EDS and Scanning Electron Microscopy - SEM) were also performed. No differences were found between the different devices in the monotonic flexural strength test, and FEA showed similar tensile stress distribution for the two devices. 4-YSZ showed higher values of flexural strength under monotonic and cyclic load application modes (sσ = 1114.73 MPa; fσ = 798.84 MPa), and fracture toughness (KIC = 3.90 MPa√m). 4/5-YSZ had an intermediate sσ; however, fσ was similar to 5-YSZ (404.00-429.36 MPa) and KIC similar to 4-YSZ (KIC = 3.66 MPa√m). No statistical differences were found for hardness and Weibull modulus for fatigue flexural strength data. The amount of yttria in the layer compositions increased from 4-YSZ to 5-YSZ, and larger zirconia crystals were observed in the topographic images of 5-YSZ. Failures in the flexural strength and toughness tests started from the face subjected to tensile stress. Different layers of the multi-layered zirconia blank presented distinct mechanical properties. 4-YSZ (cervical layer) presented the highest flexural strength under monotonic and cyclic loads (fatigue), and higher fracture toughness even similar to the transition layer (4/5-YSZ). Hardness was similar between the layers. The ball-in-hole device performed similarly to the three-point bending device and can be used as an alternative to the traditional method.

Thickness and internal adjustment of monolithic resin composite milled crowns: Effect on the load-bearing capacity under fatigue.

OBJECTIVES: To evaluate the fatigue failure load (FFL), cycles for fatigue failure (CFF) and survival rates of different occlusal thicknesses of resin composite simplified crowns with internal adjustments (IA) or without as control (C). METHODS: 30 monolithic simplified crowns of CAD/CAM resin composite (Tetric CAD, Ivoclar) were milled in three different occlusal thicknesses (0.5 mm, 1.0 mm, and 1.5 mm). Half of the crowns were submitted to restricted adjustment with diamond burs on the crown's inner surface and half remained milled without internal adjustment. The samples were treated and adhesively luted onto a prosthetic preparation made of epoxy resin reinforced by glass-fiber substrate. The sets were subjected to a fatigue test (cyclic fatigue: initial load of 200 N; step-size of 50 N; 10,000 cycles/step; 20 Hz; maximum load: 2800 N).Microscopic analysis of tested representative samples was performed. The fatigue data were statistically analyzed (α= 0.05) and the micrograpic images were qualitatively evaluated. RESULTS: All specimens from groups 1.0C and 1.5C survived the cyclic loads, while all 0.5C samples failed during the test. The 1.0IA and 1.5IA crowns showed no statistical difference for FFL (2530 N= 2670 N) and CFF (471,000 cycles= 499,000 cycles) between them, and they were both statistically superior to the 0.5IA (FFL= 1812.50 N; CFF= 327,500 cycles). The 1.0 mm and 1.5 mm crowns presented superior fatigue behavior (2530 N-2800 N) compared to the 0.5 mm crowns (1812 N-2140 N), whether internal adjustment was performed or not. A statistically significant difference was found for FFL and CFF of 0.5 mm crowns with and without internal adjustment, with a deleterious impact of the adjustment for both parameters (FFL and CFF: 0.5C > 0.5IA). SIGNIFICANCE: Resin composite milled crowns can bear high cyclic fatigue loads despite thickness, although thicker crowns had better mechanical behavior; however, the internal adjustment in the composite resin crown leads to a detrimental effect on its fatigue behavior, which presents a risk of mechanical failure due to premature fatigue.

Is the application of a silane-based coupling agent necessary to stabilize the fatigue performance of bonded simplified lithium disilicate restorations?

This study evaluated the influence of ceramic surface conditioning and storage regimen (baseline vs. aging) on the fatigue performance of simplified lithium disilicate glass-ceramic restorations. A total of 90 ceramic discs (Ø= 10 mm; thickness= 1.0 mm) were allocated into 6 groups (n= 15), considering 2 factors: "ceramic surface treatment" - CA (only silane-based coupling agent, Monobond N), HF (5% hydrofluoric acid etching), or HF+CA (5% HF acid etching plus silane-based coupling agent); and "storage regimen" - baseline (24 hours - 5 days of distilled water at 37 °C), or long-term aging (180 days of distilled water at 37 °C + 25,000 thermal cycles). After intaglio ceramic conditioning, adhesive bonding (Multilink N) was performed onto epoxy resin discs (Ø= 10 mm; thickness= 2.5 mm) and the bonded sets were subjected to step-stress fatigue tests (initial load: 200 N; step-size: 50 N; 10,000 cycles per step; 20 Hz). Fatigue data were analyzed using Kaplan-Meier and Weibull statistical analyses. Fractography and topography analyses were also conducted. The fatigue findings demonstrated that the performance among groups for both baseline and aging conditions maintained a tendency: the CA groups had the worst behavior (baseline: 893 N/143,667 cycles; aging: 639 N/84,179 cycles), while the surface etching with HF (baseline: 1247 N/214,333 cycles; aging: 816.67 N/128,333 cycles) and HF+CA groups (baseline: 1290 N/222,333 cycles; aging: 900 N/145,000 cycles) had no statistically significant difference between them. The aging protocol reduced the performance of all groups. The groups with better fatigue performance (HF and HF+CA) did not have statistical differences regarding structural reliability (Weibull modulus). Most failures were radial cracks from the cementation interface, except for CA aging specimens, with 27% failing from debonding. The HF etching led to noteworthy surface topographical alterations. Micromechanical interlocking resulting from HF acid etching remained prevalent in the fatigue behavior. Thus, the silane-based coupling agent (Monobond N) does not need to be applied after HF etching in terms of fatigue behavior outcomes.

Fatigue behavior and stress distribution of molars restored with MOD inlays with and without deep margin elevation.

OBJECTIVES: This study evaluated the effect of deep margin elevation (DME) and restorative materials (leucite-reinforced glass-ceramics [C] vs. indirect resin composite [R]) on the fatigue behavior and stress distribution of maxillary molars with 2-mm deep proximal margins restored with MOD inlay. METHODS: Fifty-two extracted human third molars were randomly assigned into four groups (n = 13): C; DME + C; R; and DME + R. Inlays were fabricated in CAD-CAM and bonded to all teeth. The fatigue behavior was assessed with the stepwise stress test (10,000 cycles/step; step = 50 N; 20 Hz; initial load = 200 N). Fatigue failure loads and the number of cycles were analyzed with 2-way ANOVA and Tukey's test (p < 0.05) and Kaplan-Meier survival plots. The stress distribution was assessed with finite element analysis. The models were considered isotropic, linear, and homogeneous, and presented bonded contacts. A tripod axial load (400 N) was applied to the occlusal surface. The stress distribution was analyzed with the maximum principal stress criterion. RESULTS: For fatigue, there was no difference for DME factor (p > 0.05). For the material factor, the load and number of cycles for failure were statistically higher in the R groups (p < 0.05). The finite element analysis showed that resin composite inlays concentrated more stress in the tooth structure, while ceramic inlays concentrated more stress in the restoration. Non-reparable failures were more frequent in the resin composite inlays groups. CONCLUSIONS: DME was not negative for fatigue and biomechanical behaviors. Resin composite inlays were more resistant to the fatigue test, although the failure mode was more aggressive. CLINICAL SIGNIFICANCE: DME does not impair mechanical behavior. Resin composite inlays failed at higher loads but with a more aggressive failure mode.

Spectrophotometric analysis of dental bleaching after bonding and debonding of orthodontic brackets.

INTRODUCTION: The aim of this study was to evaluate the bleaching effect after aging simulation in teeth submitted to bonding and debonding of orthodontic brackets. MATERIALS AND METHODS: For this study, 90 human premolars were selected, and randomly divided into 6 groups: control, bleaching, and other 4 groups submitted to bleaching after bonding and debonding brackets using different methods. Color measurement of sample through the CIE L*a*b* system was performed in three moments: T1 - after brackets debonding, T2 - after staining cycling, and T3 - after bleaching. For evaluation of results among the components L*, a* and b*, the two criteria analysis of variance and the multiple comparison Tukey test (p < 0.05) were used. RESULTS: Statistically significant difference was observed among the groups submitted to brackets bonding and debonding through self-conditioning adhesive system and tungsten drill, also the control and bleaching groups between the moments T1 e T2. CONCLUSION: Bonding and debonding brackets methods tested in this study showed influence on the sample color change, and after the tooth bleaching process, only the group without brackets previous bonding achieved the color value presented before the staining and aging of samples in the brackets absence.

Influence of surface treatment of resin composite substrate on the load-bearing capacity under fatigue of lithium disilicate monolithic simplified restorations.

This study evaluated the influence of surface treatments of resin composite substrate on the fatigue behavior of adhesively cemented lithium disilicate glass-ceramic simplified restorations. CAD/CAM lithium disilicate ceramic blocks were shaped into discs (N = 60, Ø = 10 mm; thickness = 1.0 mm). Resin composite discs (N = 60, Ø = 10 mm, thickness = 2 mm) were allocated into four groups considering the "surface treatment" factor: Ctrl - no surface treatment; Bur - grinding with coarse diamond bur (#3101G, KG Sorensen); PA - etching with 37% phosphoric acid (15 s); AA - air abrasion with alumina particles (45 µm, 10 mm distance, 2.8 bars, 10 s). The surface topography, the roughness, the fractal dimension (estimated by the box-counting method) and the contact angle analyses were performed after the surface treatments. The lithium disilicate discs were etched (5% hydrofluoric acid, 20 s), silanized and adhesively cemented (Multilink N, Ivoclar Vivadent) on the resin composite discs. The samples (bonded restoration set) were subjected to a step-stress fatigue test at 20 Hz, 10,000 cycles/step with a step-size of 100 N applied on the ceramic surface, having ceramic up and resin composite down. Fractographic analysis was performed. The fatigue data (Fatigue Failure Load - FFL; and Cycles for Failure - CFF) were analyzed by Kaplan Meier with Mantel-Cox log-rank post-hoc tests (α = 0.05). No statistical difference for fatigue performance could be found among the groups (FFL means: 820-867 N; CFF means: 53,195-61,090 cycles). The bur group showed higher surface roughness and contact angle values. The PA group has the highest average fractal dimension. Therefore, the resin composite surface treatment induces topographical changes, however, it has no effect on the fatigue behavior of lithium disilicate restorations.

Grinding and polishing of the inner surface of monolithic simplified restorations made of zirconia polycrystals and lithium disilicate glass-ceramic: Effects on the load-bearing capacity under fatigue of the bonded restorations.

This study evaluated the effect of grinding and polishing the inner surface of monolithic discs made of zirconia polycrystals (ZR) and lithium disilicate glass-ceramic (LD) on the load-bearing capacity under fatigue of the restorations bonded onto a dentin analogue material (epoxy resin). ZR and LD ceramic discs (10 mm in diameter, 1 mm in thickness) were produced and randomly allocated into 10 groups considering the internal adjustment approach: Ctrl - No adjustment; F - Grinding with fine diamond bur (46 µm); F + Pol - Grinding with fine diamond bur followed by polishing with 2 tips (finisher and polisher); FF - Grinding with extrafine diamond bur (30 µm); FF + Pol - Grinding with extrafine diamond bur followed by polishing. In addition, discs (10 mm in diameter, 2.5 mm in thickness) of fiber reinforced epoxy resin were produced. Afterwards, the intaglio surface of the ZR discs were air-abraded with 45 µm alumina particles for 10 s, the LD and resin epoxy discs were etched with hydrofluoric acid (5%/20 s and 10%/60 s, respectively), and the treated discs were primed as recommended. Each ceramic disc was luted onto the epoxy resin disc with resin cement. Then, the samples were tested under a step-stress fatigue test (20 Hz, 10,000 cycles/step, step-size of 100 N starting at 200 N, and proceeding until failure detection). Fractographic, topographic and surface roughness analysis were also performed. The adjustments (grinding with or without polishing) (ZR: 733-880 N; LD: 1040-1106 N) triggered a detrimental effect on the fatigue behavior in both ceramics compared with the absence of treatment (control group; ZR: 973 N; LD: 1406 N). The polishing step had no effect on fatigue findings. Thus, grinding the inner surface of the tested ceramics should be avoided wherever possible to prevent introducing damage and its detrimental effects on the fatigue behavior.