Adhesion to a Lithium Disilicate Glass Ceramic Etched with Hydrofluoric Acid at Distinct Concentrations

Optimal Hydrofluoric Acid Etching Duration and Impact of Silane/Adhesive on Profilometric Properties and Bonding to Lithium Disilicate Glass Ceramics

OBJECTIVES

This study aimed to assess the surface roughness, surface free energy (SFE), and shear bond strength (SBS) on a lithium disilicate glass-ceramic surface following varying etching protocols (time variation) and application of silane either with or without adhesive material.

METHODS AND MATERIALS

Lithium disilicate glassceramic (LDGC) computer-aided design and computer-aided manufacture (CAD/CAM) blocks were cut using a slow-speed cutting mechanism. CAD/CAM blocks were then evaluated for surface roughness, 6 groups (n=20); SFE,12 groups (n=5); and SBS, 10 groups (n=10). The cut CAD/CAM blocks were randomly allocated to 28 groups. Groups were based on the following: 30 or 90 seconds of etching with 9% hydrofluoric acid (HF); application or absence of silane coupling agent (Sil); and application or absence of adhesive (Adh).The control group (Cont) had untreated surfaces. Unetched surfaces were surveyed with only silane (Sil), only adhesive (Adh), or silane+adhesive (SilAdh). Further etched groups were HF30 with HF for 30 seconds, HF30-Sil, HF30-Adh, and HF30-SilAdh. Alternative 90-second etching times produced similar groups: HF90, HF90-Sil, HF90-Adh, and HF90-SilAdh. A digital profilometer was used to assess the surface roughness of specimens, and two readings were recorded. Sessile drop analysis was used to examine SFE specimens, and the OWRK model was modified to measure liquid surface tension. A universal testing machine (UltraTester, Ultradent Products, Inc, South Jordan, UT, USA) was utilized for the SBS test, with the crosshead speed set at 0.5 mm/min until failure. Representative treated specimens from each group were submitted to surface morphological evaluation and chemical analysis using scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDXS) (n=3). After data collection, evaluation using one- or two-way analysis of variance and the post-hoc Tukey test (α=5%) was conducted.

RESULTS

A longer etching time of 90 seconds produced a rougher surface. After the 90-second etching process, SFE displayed the greatest values; nevertheless, the use of silane did not affect SFE. For every group examined, the application of silane followed by adhesive resulted in an increase in SBS and more stable bonding over time. SEM/EDXS showed that etching times did affect the amount of cerium on the surface and altered surface morphology.

CONCLUSIONS

Higher and more consistent bond strengths have been observed with longer etching periods. Silane and adhesive application on the ceramic surface showed stronger and enhanced bond strength, specifically when longer etching times were employed.

Influence of Varied Silane Commercial Brands and Adhesive Application on Bond Strength and Stability to Lithium Disilicate Glass Ceramic

OBJECTIVES

This study aimed to evaluate the impact of various commercial silane brands with varied chemical compositions with or without the application of an adhesive layer on the microshear bond strength and durability of a resin luting agent to lithium disilicate glass ceramic.

METHODS AND MATERIALS

Lithium disilicate glass ceramic discs (EMX, IPS e.max Press, Ivoclar Vivadent) measuring 10 mm in diameter and 3 mm in thickness were fabricated (n=240). Surfaces were etched using 5% hydrofluoric acid and randomly assigned to 10 groups based on the commercial brand of silane used (n=24): [RP] RelyX Ceramic Primer (3M ESPE); [PS] Prosil (FGM); [SA] Silano (Angelus); [SM] Silano (Maquira); [SU] Silane (Ultradent); [GL] GLUMA Ceramic Primer (Kulzer); [CB] Ceramic Bond (VOCO); [MB] Monobond N (Ivoclar Vivadent); [CP] Clearfil Ceramic Primer (Kuraray); and [DE] 2-step silane (Dentsply Sirona). Half of the EMXs (n=12) received a thin adhesive layer (+) after the silane and prior to resin luting agent, while the other half (n=12) did not receive an adhesive layer (-). For the microshear bond strength test (μSBS), four light-cured resin luting agent cylinders (1 mm in diameter) were created on each EMX surface. Half of these specimens were tested after 24 hours, while the other half were stored in deionized water for 6 months. The μSBS test was conducted using a universal testing machine (DL 500, EMIC) at a crosshead speed of 1 mm/min until failure. The obtained data underwent statistical analysis using analysis of variance (ANOVA) and the Tukey test (α=0.05).

RESULTS

There was significant influence of the silane commercial brand on bond strength. Notably, "universal primers" yielded lower bond strength results compared to "pure" silane solutions. Water storage had a detrimental effect on microshear bond strength for certain silane commercial brands. Additionally, the application of an adhesive layer negatively impacted bond strength results for all silanes.

CONCLUSIONS

This study confirms the importance of both silane commercial brand and chemical composition in relation to bond strength of resin luting agents to lithium disilicate glass ceramic. Furthermore, the application of an adhesive layer may have an adverse effect on bond stability over time.

Effects of Hydrofluoric Acid Concentrations, Commercial Brands, and Adhesive Application on the Bond Strength of a Resin Luting Agent to Lithium Disilicate Glass Ceramic

OBJECTIVES

To evaluate the surface topography/roughness and bond strength of a resin luting agent to a lithium disilicate glass ceramic after etching with different concentrations of hydrofluoric acid (HF) and commercial brands.

METHODS

For bond strength evaluation, 260 lithium disilicate glass ceramic (EMX) discs were randomly distributed into 13 groups based on concentrations of HF and commercial brands (n=20): 5% and 10%, Lysanda (LY5 and LY10); 5% and 10%, Maquira (MA5 and MA10); 5% and 10%, FGM (FG5 and FG10); 4.8%, Ivoclar Vivadent (IV5); 5% and 10%, PHS do Brasil (PH5 and PH10); 5% and 10%, BM4 (BM5 and BM10); 9%, Ultradent Inc (UL10); and Dentsply (DE10). A further random distribution (n=10) was made based on the application (+) or absence (-) of an adhesive layer. Resin luting agent cylinders (1 mm in diameter) were added on EMX surfaces, light-cured, and stored for 24 hours in deionized water at 37°C. On a universal testing machine (DL 500, EMIC), specimens were submitted to a microshear bond strength test at a crosshead speed of 1 mm/min until failure. A representative etched EMX disc from each group underwent surface topography analysis using field-emission scanning electron microscopy (n=1), and five (n=5) etched EMX discs from each group were tested for surface roughness. Data were statistically analyzed using analysis of variance and Tukey test (α=0.05).

RESULTS

A less conditioned and smoother surface was observed for 5% HF compared to 10%. Additionally, commercial brands of HF were shown to affect bond strength. When the adhesive layer was not used (-), a 10% concentration promoted higher bond strengths to EMX. However, when adhesive was applied (+), the concentrations of HF and commercial brands had no effect on bond strength results.

CONCLUSIONS

A 10% concentration of HF results in higher bond strength than a 5% concentration. If an adhesive layer is applied, neither this distinction nor the influence of commercial brands is 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.

Adhesion to lithium disilicate glass-ceramics after aging: Resin viscosity and ceramic surface treatment effects

OBJECTIVE

To evaluate the influence of intaglio ceramic surface treatments, resin cement viscosities, and storage regimens on the microshear bond strength of lithium disilicate ceramic. In addition, to investigate the dynamic viscosity of the resin-based luting agents.

MATERIALS AND METHODS

Ceramic slices were randomly allocated into eight groups (n = 19) considering three factors: ceramic surface treatment (hydrofluoric acid followed by silane, HF; or self-etching ceramic primer, E&P), resin cement viscosity (high, HIGH; or low, LOW) and storage regimen (baseline or aging). Surface treatments were performed, resin cement cylinders were built and microshear bond strength tests (μSBS, wire-loop method, speed: 1.0 mm/min) were run according to the storage factor. Failure mode, topographic and dynamic viscosity (37 °C; shear rate of 1.0-100 s^-1) of resin cement components (base, high and low catalyst) were also performed.

RESULTS

Resin cement viscosity and the association among ceramic surface treatment, resin cement viscosity, and storage regimen were statistically significant factors (p < 0.05). Worse behavior was identified for the E&P_HIGH group compared to the E&P_LOW and HF_LOW in the baseline condition. After aging, the HF_HIGH group (16.78 MPa) presented the worst result among the aged groups (21.44-25.25 MPa). Most of the failures were adhesive. Surface micrographs revealed a distinct pattern after etching, more aggressive by HF and milder by E&P. High viscosity catalyst is 5.3 and 8.5-fold more viscous than the base and low viscosity catalyst, respectively (high > base > low).

CONCLUSION

Differences in filler content can impact the resin viscosity of the material (more fillers increase the viscosity), which in turn can influence the bond strength of a lithium disilicate ceramic, depending on the surface treatment and storage regimen.

Comparison of the Micro-Shear Bond Strength of Resin Cements to CAD/CAM Glass Ceramics with Various Surface Treatments

This study aimed to compare the effect of acid etching, sandblasting, or silica coating on the micro-shear bond strength of dual-cured resin cements to computer-aided design and computer-aided manufacturing (CAD/CAM) glass ceramic materials. Feldspathic, lithium disilicate, and zirconia-reinforced CAD/CAM ceramics were divided into four groups: control group (C), no surface treatment; hydrofluoric (HF) group, 5% HF acid-etched; sandblasting (SB) group, abraded with 50 µm aluminum oxide (Al₂O₃) particles; silica-coated (CJ) group, abraded with 30 µm silica-modified Al₂O₃ particles. Roughness values were obtained by using a profilometer. The cements were condensed on the surface-treated specimens and a micro-shear bond test was conducted. The ceramic material (p < 0.001) and surface treatment type (p < 0.001) significantly affected the micro-shear bond strength values. HF acid etching can be recommended for the surface pretreatment of feldspathic, lithium disilicate, and zirconia-reinforced CAD/CAM ceramics. Better bond strengths can be obtained with HF acid etching than with sandblasting and silica coating.

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.

Influence of Fit-checking Material and Cleaning Protocols on the Bond Strength of Lithium Disilicate Glass-ceramics

Objectives

To evaluate the bond strength of a resin luting agent to a lithium disilicate glass-ceramic after the use of different fit-checking materials and cleaning protocols.

Methods and Materials

Two hundred and forty-two (242) ceramic specimens were etched with 5% hydrofluoric acid for 20 seconds and distributed into 22 groups (n=10), in total. Four (4) groups were created based on fit-checking material and that had no following cleaning protocol: no fit-checking material used (control group); articulating paper; articulating spray; and fit-checker liquid. For each fit-checking material (3), 6 cleaning protocols were tested creating an additional 18 groups (n=10): air/water spray; 70% alcohol (ethanol); acetone; 35% phosphoric acid; 5% hydrofluoric acid; and a commercially available cleaning paste (Ivoclean, Ivoclar Vivadent). Silane and bonding resin were applied to all ceramic surfaces. Resin luting agent cylinders (1 mm in diameter) were created using silicone matrices, light-cured, and specimens were stored in deionized water at 37°C for 24 hours. Microshear bond strength test (μSBS) was performed on a universal testing machine (DL 500, EMIC) at a crosshead speed of 1 mm/min until failure. Results were statistically analyzed using ANOVA and Tukey’s test (α=0.05).

Results

Articulating paper and fit-checker liquid, when not properly removed, negatively affected the bond strength (p&lt;0.05). None of the tested cleaning protocols were effective for articulating paper (p&lt;0.05). There was no significant difference in bond strength after the cleaning protocols between articulating spray and fit-checker liquid when compared to the control group (no contamination) (p&gt;0.05).

Conclusion

The cleaning protocols tested can effectively restore the bond strength of resin luting agents to lithium disilicate ceramics that were exposed to articulating spray or fit-checker liquid. The use of articulating paper is not recommended for fit-checking indirect lithium disilicate restorations.

Current Protocols for Resin-Bonded Dental Ceramics

Resin-bonded ceramic restorations are common treatment options. Clinical longevity of resin-bonded ceramic restorations depends on the quality and durability of the resin-ceramic bond. The type and composition of the specific ceramic determines the selection of the most effective bonding protocol. Such protocol typically includes a surface pretreatment step followed by application of a priming agent. Understanding of fundamental ceramic properties and chemical compositions enables the clinician to make proper material selection decisions for clinically successful and long-lasting restorations. Based on research accrued over the past decades, this article reviews and discusses current resin-bonding protocols to most commonly used dental ceramics.

Adhesive application after ceramic surface treatment is detrimental to load-bearing capacity under fatigue of a lithium disilicate glass-ceramic

OBJECTIVE

To evaluate whether an adhesive application after surface treatment on a lithium disilicate ceramic (LD) has an influence on its load-bearing capacity under fatigue.

METHODS

LD discs (Ø= 10 mm; thickness= 1 mm) were allocated into 8 groups (n= 15), considering 3 factors: "ceramic surface treatment" - HF: hydrofluoric acid + universal primer application; or MEP: single-component ceramic primer; "adhesive application" - with or without; and "aging protocol" - baseline: 24 h to 7 days; or aging: 180 days of storage + 25,000 thermal cycles. The LD discs were adhesively bonded to glass fiber-reinforced epoxy resin discs (Ø= 10 mm; thickness= 2 mm) and stored according to the condition and each group. Cyclic fatigue testing (initial load= 100 N; step size= 100 N until600 N and after step size= 25 N to failure; 10,000 cycles/step; 20 Hz frequency) was performed. Fractographic and adhesive interface analyzes were also performed. The collected data were then analyzed by Kaplan Meier and Mantel-Cox tests and One-way ANOVA.

RESULTS

The adhesive application in the baseline condition had no influence on the load-bearing capacity under fatigue when the HF surface treatment was performed, however, adhesive application for the MEP treatment led to worse results than without it. The adhesive application in the aged condition showed worse fatigue outcomes for both treatments. All specimens presented radial cracks. MEP treatment followed by adhesive application presented the thickest luting layer.

CONCLUSION

The adhesive application after surface treatments of a lithium disilicate glass-ceramic is detrimental to its load-bearing capacity under fatigue when adhesively luted onto a supporting substrate.

Evaluation of Cleaning Methods on Lithium Disilicate Glass Ceramic Surfaces After Organic Contamination

The purposes of this study were to 1) evaluate the effectiveness of different cleaning methods from a previously etched and silanized lithium disilicate glass ceramic (EMX) surface after contact with organic fluids (saliva or human blood) and 2) assess the effect of applying a new silane layer after the cleaning methods on the microshear bond strength (mSBS) of resin cement to EMX. EMX discs were etched with 5% hydrofluoric acid (HF) and properly silanized. Three control groups were created (n=10): control (without contamination), saliva positive, and human blood positive. Later, after new contaminations, the samples were distributed into four groups according to the cleaning method (n=20): air–water spray (AWS), 35% phosphoric acid, 70% alcohol, or Ivoclean cleaning paste. After the cleaning methods, subgroups were submitted to a new silane layer application, or not (n=10). All samples received a thin layer of a bonding agent and, subsequently, three light-cured resin cement cylinders were prepared on each EMX surface for the mSBS test. This test was performed on a universal testing machine at a vertical speed of 1 mm/minute until rupture. Contaminated and cleaned silanized EMX surfaces were assessed by scanning electron microscopy (SEM) (n=1). The noncontaminated control group showed an average mSBS of 18.7 MPa, and the positive saliva and human blood control groups yielded a 34% and 42% reduction in bond strength, respectively, compared to the uncontaminated control (p&lt;0.05). For saliva-contaminated surfaces, all cleaning methods were effective and not different from one another or the control group (p&gt;0.05). However, for human blood contamination, only Ivoclean cleaning paste was effective in restoring μSBS to uncontaminated control group levels (p&gt;0.05). SEM images showed a clean surface (ie, with no contaminant residues) after the cleaning methods, regardless of the organic contaminant type. All the assessed cleaning methods were effective in removing saliva from the silanized EMX surface; however, only Ivoclean was able to restore the adhesion quality when the silanized EMX surface was contaminated with human blood.

Increasing Acid Concentration, Time and Using a Two-Part Silane Potentiates Bond Strength of Lithium Disilicate-Reinforced Glass Ceramic to Resin Composite: An Exploratory Laboratory Study

There is still a lack of consensus concerning the recommended etching concentration, application time and type of silane when bonding lithium disilicate-reinforced glass ceramics manufactured by CAD/CAM. The purpose of this study was thus to conduct an in vitro study which investigates the influence of hydrofluoric acid (HF) concentration, etching time and silane type on the microtensile bond strength (μTBS) of lithium disilicate to resin composites. Thirty-nine IPS e.max CAD blocks were randomly divided between thirteen groups (n = 3). The variables were HF concentration (9.5 or 4.9%), etching time (20 or 60 s) and silane type (Bis-Silane, Monobond Plus and ESPE Sil Silane). The blocks were cut into beams, aged for 10,000 cycles in a thermocycler and submitted to tensile stress to determine μTBS. A control group featuring the Monobond Etch & Prime (MEP) agent that combines etching/silanisation into a simultaneous process was also added. This group was discarded from the analysis due to only having pre-test failures. The data were analysed using a three-way ANOVA (α = 0.05). The HF concentration, etching time and silane type significantly influenced μTBS (p < 0.001). Significant interactions between time and silane type (p = 0.004), HF concentration and silane type (p < 0.001) and among the three factors (p < 0.001) were noted. Etching lithium disilicate with 9.5% HF (60 s), followed by the application of Bis-Silane, resulted in the highest μTBS (16.6 ± 9.0 MPa). The highest concentration and etching time under study, combined with a two-part silane, resulted in the highest bond strength, while the application of MEP showed a complete pre-test failure.

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.

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.

Two-Year Follow-Up of Self-Etching Ceramic Primer as Surface Treatment for Feldspathic Veneers: A Clinical Case Review

The two-step approach of applying hydrofluoric acid followed by silane is deemed the goldstandard surface treatment protocol before bonding to glass ceramics. Given hydrofluoric acid is a toxic conditioning agent and with the intention to simplify this step, the dental company Ivoclar Vivadent (Schaan, Lietchtenstein) released a self-etching ceramic primer, Monobond Etch & Prime in 2015, claiming that hydrofluoric acid and silane application would no longer be required prior to luting glass ceramics. Therefore, this clinical case report and retrospective analysis describes the replacement of unsatisfactory anterior veneers due to clinical failures for new feldspathic glass ceramic veneers, using the aforementioned self-etching ceramic primer. After two years, feldspathic glass ceramics presented satisfying clinical performance with absence of debonding, tooth sensitivity, recurrent carious lesions, or marginal infiltration.

Effect of milling, fitting adjustments, and hydrofluoric acid etching on the strength and roughness of CAD-CAM glass-ceramics: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Whether procedures performed before the cementation of computer-aided design and computer-aided manufacturing (CAD-CAM) glass-ceramic restorations, including milling, fitting adjustment, and hydrofluoric acid etching introduce defects on the ceramic surface that affect the mechanical and surface properties is unclear.

PURPOSE

A systematic review and meta-analysis were conducted to assess the effect of milling, fitting adjustments, and hydrofluoric acid etching (HF) on the flexural strength and roughness (Ra) of CAD-CAM glass-ceramics.

MATERIAL AND METHODS

Literature searches were performed up to June 2020 in the PubMed/MEDLINE, Web of Science, and Scopus databases, with no publication year or language limits. The focused question was "Do milling, fitting adjustments, and hydrofluoric acid etching affect the flexural strength and roughness of CAD-CAM glass-ceramics?" For the meta-analysis, flexural strength and Ra data on milling, fitting adjustment, and HF etching versus control (polishing) were analyzed globally. A subgroup analysis assessed the effect of etching parameters (HF concentration and time) on the flexural strength and roughness of CAD-CAM glass-ceramics with different microstructures. Comparisons were performed with random-effect models at 5% significance.

RESULTS

Fourteen studies from 2764 potentially relevant records were included in the qualitative syntheses, and 12 in the meta-analysis. Milling and fitting adjustments increased roughness and reduced the flexural strength of CAD-CAM glass-ceramics. The effect of HF etching was dependent on the glass-ceramic microstructure, HF concentration, and etching time. For feldspathic- and leucite-reinforced ceramics, HF 5% applied for between 30 and 120 seconds increased roughness without affecting flexural strength. For lithium disilicate glass-ceramics, HF concentrations greater than 4.9% used for 20 seconds or more reduced the strength without affecting the surface roughness.

CONCLUSIONS

The flexural strength of CAD-CAM glass-ceramic is reduced by grinding procedures such as milling and fitting adjustment. Ceramic microstructure, HF concentration, and etching time determined the effect of hydrofluoric acid etching on the flexural strength and surface roughness of glass-ceramic materials.

Influence of Low-Pressure Plasma on the Surface Properties of CAD-CAM Leucite-Reinforced Feldspar and Resin Matrix Ceramics

The introduction of new ceramic materials for dental restorations is currently a reality; however, little information is available on their surface treatment for the bonding process. Furthermore, surface treatment with plasma on ceramic materials has been recently introduced, although not many studies are available. The aim of this study was to evaluate the surface properties of a leucite-reinforced feldspar ceramic (LIC) and resin matrix ceramic (RMC) after low-pressure plasma treatment. From each material, 48 discs were prepared and subject to surface treatment. The LIC group was treated by hydrofluoric acid (HF) (LIC-HF), plasma with oxygen (LIC-O2), and plasma with argon (LIC-Ar). The RMC group was treated by sandblasting with alumina (RMC-SB), plasma with oxygen (RMC-O2), and plasma with argon (RMC-Ar). The groups whose surfaces were not subjected to treatment were considered as the control group. Surface wettability and roughness was analyzed. The results showed significant differences among the treatments for both ceramics regarding wettability and roughness. Plasma treatments increased the wettability and had a very low effect on the roughness. Plasma treatments achieved similar values for both surface properties in each ceramic group with no differences between both treatments. Plasma treatment seems to be a promising alternative for ceramic surface treatments since it increased the surface energy of the ceramics analyzed and hardly affects the roughness. Further studies are necessary to evaluate the effect of plasma treatment on the bond strength of ceramics.

Fatigue performance of fully-stabilized zirconia polycrystals monolithic restorations: The effects of surface treatments at the bonding surface

This study evaluated the distinct conditioning effect of the intaglio surface of bonded fully-stabilized zirconia (FSZ) simplified restorations on the mechanical fatigue behavior of the set prior to and after aging. Ceramic disc shaped specimens (Ø= 10 mm and 1 mm thick) were randomly allocated into 14 groups considering: "surface treatments" (Ctrl: no-treatment; PM: universal primer; GLZ: low-fusing porcelain glaze; SNF: 5 nm SiO₂ nanofilm deposition; AlOx: air-abrasion with aluminum oxide; SiC: air-abrasion with silica-coated aluminum oxide; 7%Si: air-abrasion with 7% silica-coated aluminum oxide); and "aging" (baseline: 24 h at 37 °C in water; or aged: 90 days at 37 °C in water + 12,000 thermal cycles). The discs were treated, luted with resin cement onto the dentin analog, subjected to aging or not, and then tested under a step-stress fatigue test at 20 Hz, 10,000 cycles/step, step-size of 100N starting at 200N, and proceeding until failure detection. Fractographic, topographic, surface roughness, contact angle, and atomic force microscopy analyzes were performed. The surface treatments at baseline led to statistically similar fatigue failure loads (953N-1313N), except for GLZ (1313N), which was significantly higher than 7%Si (953 N). Meanwhile, Ctrl had 40% pre-test failures (debonding) after aging, and therefore the worst fatigue performance (notable decrease in fatigue results), while all the other groups presented superior and statistically similar fatigue behavior (973-1271N). In fact, when considering baseline Vs aging conditions, stable fatigue results could only be noted when using surface treatments. In conclusion, internal surface treatments of FSZ ceramic restorations are mandatory for fatigue behavior stability after aging the restorative set, while non-treatment induced unstable results.

Fatigue performance of adhesively luted glass or polycrystalline CAD-CAM monolithic crowns

STATEMENT OF PROBLEM

Data comparing the fatigue performance of adhesively luted glass or polycrystalline ceramic systems for computer-aided design and computer-aided manufacturing (CAD-CAM) are scarce.

PURPOSE

The purpose of this in vitro study was to evaluate and compare the fatigue performance of monolithic crowns manufactured from glass or polycrystalline CAD-CAM ceramic systems adhesively luted to a dentin analog.

MATERIALS AND METHODS

Fifty-four pairs of standardized preparations of dentin analog (NEMA Grade G10) and simplified ceramic crowns of 1.5-mm thickness were obtained with 3 ceramic materials: lithium disilicate (LD) glass-ceramic (IPS e.max CAD); zirconia-reinforced lithium silicate (ZLS) glass-ceramic (Vita Suprinity); and translucent yttrium fully stabilized polycrystalline zirconia (Trans YZ) (Prettau Anterior). The simplified crowns (n=15) were adhesively cemented onto the preparations and subjected to step-stress fatigue test (initial load of 400 N, 20 Hz, 10 000 cycles, followed by 100-N increment steps until failure). Collected data (fatigue failure load [FFL] and cycles for failure [CFF]) were submitted to survival analysis with the Kaplan-Meier and Mantel-Cox post hoc tests (α=.05) and to Weibull analysis (Weibull modulus and its respective 95% confidence interval). Failed crowns were submitted to fractography analysis. The surface characteristics of the internal surface (roughness, fractal dimension) of additional crowns were accessed, and the occlusal cement thickness obtained in each luted system was measured.

RESULTS

Trans YZ crowns presented the highest values of FFL, CFF, and survival rates, followed by ZLS and LD (mean FFL: 1740 N>1187 N>987 N; mean CFF: 149 000>92 613>73 667). Weibull modulus and cement thickness were similar for all tested materials. LD presented the roughest internal surface, followed by ZLS (mean Ra: 226 nm>169 nm>93 nm). The LD and ZLS internal surfaces also showed higher fractal dimension, pointing to a more complex surface topography (mean fractal dimension: 2.242=2.238>2.147).

CONCLUSIONS

CAD-CAM monolithic crowns of Trans YZ show the best fatigue performance. In addition, ZLS crowns also showed better performance than LD crowns.

Effect of Hydrofluoric Acid Concentration and Thermal Cycling on the Bond Strength of Brackets to Ceramic

This study to evaluate the effects of different hydrofluoric acid (HF) concentrations and thermal cycling on the shear bond strength (SBS) of brackets to ceramic. Cylinders of ceramic were divided into 10 groups (n=15), according to HF concentrations: 1-1%;2-2.5%;3-5%;4-7.5%;5-10% (storage 24 h); 6-1%;7-2.5%;8-5%;9-7.5%; and, 10-10% (thermal cycling). All cylinders were etched for 60s and received one layer of silane. Metallic brackets were bonded to the cylinders using Transbond-XT, light activated for 40 s, using a LED (Radii Plus) and stored in deionized water at 37o C for 24h. The groups 6 to 10 were submitted to thermal cycling (7,000 cycles - 5o/55oC). SBS was performed in an Instron at crosshead speed of 1.0 mm/min. Data were submitted to two-way ANOVA and Tukey's post-hoc test (α=0.05). The Adhesive Remaining Index (ARI) was evaluated at 40x magnification. The different HF acid concentrations influenced on the SBS of the brackets to ceramic (p<0.05). The thermal cycling decreased the SBS of the brackets to ceramic for all acid concentrations (p<0.05). The ARI showed a predominance of scores 0 for all groups, with an increase in scores 1, 2 and 3 for the group storage for 24 h. In conclusion, the different HF acid concentrations 5.0%, 7.5% and 10% influenced on the SBS of brackets to ceramic. The thermal cycling decreased significantly the SBS of brackets to ceramic.

HF etching of CAD/CAM materials: influence of HF concentration and etching time on shear bond strength

Background

The required pretreatment of CAD/CAM ceramic materials before resin composite cement application varies among studies. The aim of the present study was to evaluate the effect of hydrofluoric acid concentration and etching time on the shear bond strength (SBS) of two adhesive and two self-adhesive resin composite cements to different CAD/CAM ceramic materials.

Methods

SBS of two adhesive (Panavia V5, Kuraray, [PV5]; Vita Adiva F-Cem, Vita Zahnfabrik, [VAF]) and two self-adhesive (RelyX Unicem 2 Automix, 3 M Espe, [RUN]; Vita Adiva S-Cem, Vita, [VAS]) cements to four different CAD/CAM materials (Vitablocs Mark II, Vita, [VM]; Vita Enamic, Vita, [VE]; e.max CAD, Ivoclar Vivadent, [EC]; Vita Suprinity PC, Vita, [VS]) was measured. The effect of the surface pretreatment by using two different hydrofluoric acid products (HF5% Vita Ceramics Etch, Vita and HF9% buffered, Ultradent Porcelain Etch, Ultradent Products) were assessed at etching times of 0 s, 5 s, 15 s, 30s and 60s for each cement and restorative material combination (n = 10 per group, total n = 1440).

Results

Significant effects were found for the etching time and cement for all materials with highest shear bond strength for etching times of 60s = 30s = 15 s ≥ 5 s > 0 s and for RUN>PV5 = VAF > VAS (p < 0.05). Etching with HF5% for 5 s to 15 s resulted in higher SBS values, while no differences were observed between HF5% and HF9% buffered when the substrates were etched for 30s to 60s (p < 0.05).

Conclusions

Within the limitations of this study the recommended surface pretreatment of silicate ceramics is HF etching with concentrations of 5% or 9% for 15 s to 60s to achieve highest shear bond strength while the glassy matrix is sufficiently dissolved. The tested resin composite cements can be applied with all tested materials and suggested for clinical application.