Effect of universal adhesives and self-etch ceramic primers on bond strength to glass-ceramics: A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

To simplify dental procedures, multicomponent products such as universal adhesives and self-etch ceramic primers have been recommended for glass-ceramic bonding; however, studies have shown a wide range of results.

PURPOSE

The purpose of this systematic review and meta-analysis was to analyze the in vitro bond strength promoted by hydrofluoric acid+silane-containing universal adhesives and a self-etch ceramic primer to glass-ceramics and compare it with that of conventional treatments.

MATERIAL AND METHODS

A systematic search was conducted in the PubMed/Medline, Scopus, LILACS, and ISI Web of Science databases up to April 2021. In vitro studies assessing the resin-mediated bond to glass-ceramics by using a self-etch ceramic primer and hydrofluoric acid+silane-containing universal adhesives and/or compared with traditional hydrofluoric acid+glass-ceramic primers were included. Selection of studies, data extraction, and risk-of-bias analysis were performed. Statistical analysis was performed by using a review management software program using a random effects model (α=.05).

RESULTS

A total of 33 studies were included in the qualitative analysis and 26 studies in the quantitative analysis. Bond strength to lithium disilicate ceramic was higher when a hydrofluoric acid+glass-ceramic primer was used than when using a hydrofluoric acid+silane-containing universal adhesive (P<.05), except when 9% to 10% acid concentration was used in combination with static aging (P=.100). A self-etch ceramic primer promoted bond strength values to lithium disilicate that were similar to those of the hydrofluoric acid+glass-ceramic primer (P>.100).

CONCLUSIONS

Hydrofluoric acid+silane-containing universal adhesive was not as effective as the hydrofluoric acid+glass-ceramic primer in promoting bond strength to glass-ceramic. Bond strength values generated by a self-etch ceramic primer to glass-ceramic were similar to those generated by the conventional treatment.

Bonding effectiveness of tooth-colored materials to resin cement provided by self-etching silane primer after short- and long-term storage

STATEMENT OF PROBLEM

Glass-ceramic materials are typically treated with hydrofluoric acid (HF) and silane to improve their bond to composite resin; however, HF may be harmful to human tissues and the integrity of the material, and its application is a technique-sensitive procedure. A novel self-etching ceramic primer has been introduced with the claim that it can solve those problems. However, independent scientific evidence regarding its performance is scarce.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of self-etching silane primer on glass-ceramic surface roughness and on long-term bonding between glass-ceramic and composite resin cement.

MATERIAL AND METHODS

Plates of 3 materials (n=10), lithium disilicate glass-ceramic (LDC) (IPS e.max CAD), leucite-based glass-ceramic (LEU) (IPS Empress CAD), and resin-modified ceramic (PIC) (VITA ENAMIC), were treated in the following ways: no treatment (C), HF (5%) applied during the recommended time for each material (HF), and self-etching ceramic primer (Monobond Etch & Prime [MBEP]). Surface roughness (Sa) was analyzed with a laser 3D profiler. Ceramic sticks were subjected to (n=20) no treatment (C); treatment with hydrofluoric acid plus silane (HF+S); and treatment with self-etching ceramic primer (MBEP) bonded to prepolymerized composite resin sticks with composite resin cement (Variolink II) and stored for 24 hours and 1 year (n=10). The assemblies were submitted to microtensile bond strength testing (μTBS). Data were analyzed using ANOVA and the Tukey pairwise, post hoc test (α=.05). Failure pattern and surface and interface morphology were assessed using scanning electron microscopy.

RESULTS

Only individual factors resulted in statistically significant differences for both variables (material: P<.001; surface treatment: P=.020), interaction (P=.570). HF group (0.49 ±0.11 μm) showed statistically higher roughness values (P≤.05) than control groups (0.44 ±0.97 μm), while MBEP (0.48 ±0.11 μm) was comparable with both. HF produced greater surface alterations than MBEP and C. PIC (0.60 ±0.051 μm) exhibited significantly higher roughness values (P≤.05) than LDC (0.37 ±0.07 μm) and LEU (0.45 ±0.04). Regarding μTBS, the general mean of PIC (24.6 ±10.1 MPa) was higher (P≤.05) than LEUs (14.7 ±6.7 MPa) and LDCs (13.1 ±4.8 MPa), while treatment groups HF+S (17.9 ±10.0 MPa) and MBEP (20.5 ±9.7 MPa) produced higher μTBS values than control groups (14.2 ±5.5 MPa). Adhesive failure was associated with low μTBS values and aged specimens, while cohesive failure within the composite resin-cement layer and mixed failures were associated with higher μTBS values. Interface debonding was detected in C groups for LDC and LEU. PIC exhibited better interface stability.

CONCLUSIONS

MBEP produced smoother surfaces than HF. HF+S and MBEP significantly improved ceramic and composite resin cement bonding.

Bond Strength of CAD/CAM Restorative Materials Treated with Different Surface Etching Protocols

PURPOSE

To evaluate the effect of different surface treatments on the surface morphology of CAD/CAM ceramics and on their bond strength to cement.

MATERIALS AND METHODS

Sixty cubic sections were cut from each of three materials (lithium disilicate glass-ceramic [DL], leucite-based glass-ceramic [LC], resin-matrix ceramic composite [RMCC]) and were treated as follows (n = 10): 1. no treatment (C); 2. 5% hydrofluoric acid applied for 20 s plus silane (HF5% 20 s); 3. 5% hydrofluoric acid applied for 60 s plus silane (HF5% 60 s); 4. 10% hydrofluoric acid applied for 20 s plus silane (HF10% 20 s); 5. 10% hydrofluoric acid applied for 60 s plus silane (HF10% 60 s); 6. Self-etching ceramic primer (MBEP). Ceramic cubes were bonded to pre-polymerized composite resin cubes with a composite cement. Each set was cut into stick-shaped specimens (1 ± 0.3 mm2). After 24-h water storage, microtensile bond strength (µTBS) was measured. Data were analyzed using two-way ANOVA and Tukey's test (α = 0.05). Failure pattern and surface morphology were assessed using scanning electron microscopy (SEM).

RESULTS

Both factors significantly influenced µTBS, while no interaction between factors was found. RMCC presented statistically higher µTBS values than LC and DL, while the surface treatments HF5% 20 s, HF5% 60 s, HF10% 20 s, HF10% 60 s and MBEP, did not show statistical differences between them, although they resulted in statistically significantly higher bond strengths than did C groups. A high number of pre-test failures were detected in the control groups for all materials. MBEP produced less extensive surface alterations than did all HF treatments.

CONCLUSION

All of the hydrofluoric acid treatments tested showed similar cement-ceramic bonding efficacy. The self-etching ceramic primer produced less surface alterations and comparable bonding efficacy compared to separate hydrofluoric acid/silane primer application.

Effect of light absence or attenuation on biaxial flexural strength of dual-polymerized resin cements after short- and long-term storage

OBJECTIVE

To evaluate whether biaxial flexural strength (BFS) of dual resin cements is affected by light absence or attenuation, storage time, or cements' chemical nature.

MATERIALS AND METHODS

One hundred and twenty disk-shaped specimens were made from each cement (non-self-adhesive cement and self-adhesive cement) using Teflon molds on a controlled temperature surface (35°C). Specimens were polymerized as follows (N = 30): self-cured, directly light-cured, light-cured at a distance of 6 mm between the light tip and the specimen, and through a 6-mm thick composite resin barrier (indirectly light-cured). Each group was divided (N = 10) for storage purposes (15 minutes, 24 hours, and 6 months). Specimens were placed into a biaxial-flexure jig and a vertical load was applied until failure. The BFS values were subjected to generalized linear models statistical analysis and Weibull distributions (α = 0.05).

RESULTS

After 15 minutes aging, neither material achieved enough polymerization to perform the BFS test when polymerized using the self-curing mode. The self-adhesive product demonstrated much lower variation in strength with storage time than did the non-self-curing cement.

CONCLUSIONS

Attenuated/light-curing reduced BFS values only for 15-minutes storage period for both materials. Flexural strength of the self-adhesive cement was less affected by light absence/attenuation and storage time.

CLINICAL SIGNIFICANCE

Biaxial flexural strength of a self-adhesive resin cement is less sensitive to variation in light application and storage time than is a non-self-adhesive cement.

Depth of cure of bulk fill resin composites: A systematic review

OBJECTIVE

To evaluate scientific evidence regarding depth of cure of bulk-fill resin composites (BFRCs) and related factors.

MATERIAL AND METHODS

PubMed/Medline, Embase, Scopus, and ISI Web of Science databases were accessed from October 2016 to May 2017. Investigations published in English language, assessing depth of cure of BFRCs by microhardness test and/or degree of conversion (DC) were included. Studies using exclusively ISO 4049, employing specimens deepness less than 4 mm, as well as those not reporting exposure time and/or irradiance from light curing units (LCUs) were excluded.

RESULTS

In total, 742 studies were found from which 33 were included. From 21 studies evaluating BFRCs microhardness, 10 showed acceptable bottom/top ratios (≥0.8) for all tested materials. However, material-dependent results and non-satisfactory bottom/top microhardness ratios (<0.8) were reported in 9 and 2 investigations, respectively. From 19 studies that assessed DC, 11 showed acceptable results (≥50%) for all tested BFRCs, while 8 studies reported material-dependent outcomes. Overall, irradiance from LCUs ranged from 650 to 1330 mW/cm² and exposure time from 5 to 60 seconds. Favorable depth of cure results were observed with the use of LCUs emitting irradiance ≥1000 mW/cm² and exposure times ≥20 seconds.

CONCLUSIONS

High depth of cure rates by BFRCs, depends on some factors as material, irradiance and exposure time. Polywave LCUs were useful but not essential on polymerizing alternative photoinitiator-containing BFRC.

CLINICAL SIGNIFICANCE

LED curing devices (polywave or monowave) displaying an irradiance ≥1000 mW/cm² and 20 seconds of exposure time are imperative to accomplish successful polymerization of most BFRCs.

Impact of Silane-containing Universal Adhesive on the Biaxial Flexural Strength of a Resin Cement/Glass-ceramic System

The aim of this study was to determine whether using a silane-containing universal adhesive as a silane primer in glass-ceramic/resin cement systems affects biaxial flexural strength (BFS) and bonded interface integrity after loading. Glass-ceramic (IPS e.max CAD, Ivoclar/Vivadent, Schaan, Liechtenstein) disc-shaped specimens (6.5±0.1mm in diameter, 0.5±0.1mm thick) were etched with 5% hydrofluoric acid (HF) for 20 seconds and divided into four groups of 30 specimens, to be treated as follows: 1) One bottle silane primer (RCP); 2) Separate application of silane and adhesive (RCP+SB); 3) Silane-containing universal adhesive (SBU); 4) No treatment (C). After silanization, all specimens were resin cement- coated and polymerized for 40 seconds. Each specimen layer was measured, as well as each assembly's thickness, using a digital caliper and scanning electron microscope (SEM). Specimens were stored for 24 hours and submitted to a BFS test (1.27 mm/min). BFS values were calculated using the bilayer disc-specimen solution. Bonded interfaces were analyzed on fractured fragments using SEM. One-way ANOVA and Tukey tests (α=0.05) were applied, as well as the Weibull analysis. Factor "silane treatment" was statistically significant ( p<0.0001). RCP+SB (372.2±29.4 MPa) and RCP (364.2±29.5 MPa) produced significantly higher BFS than did the C (320.7±36.3 MPa) or SBU (338.0±27.1 MPa) groups. No differences were found in the Weibull modulus ( m: RCP: 10.1-17.3; RCP+SB: 10.1-17.0; SBU: 12.3-22.4; C: 7.4-12.9). Bonded interface analysis exhibited ceramic-cement separation (SBU, C) and voids within the resin cement layer (all groups). Neither the ceramic/cement system's BFS nor its bonded interface stability were improved by SBU after loading.

Efeito de Diferentes Protocolos de Condicionamento Ácido na Microestrutura Tridimensional de Materiais Cerâmicos CAD/CAM

O objetivo foi avaliar o efeito de diferentes protocolos de condicionamento ácido em diferentes propriedades estruturais de materiais cerâmicos CAD/CAM. Foram avaliados três materiais: LE (IPS Empress-Ivoclar), DL (IPS e.max-Ivoclar) e CI (Enamic-VITA). Foram obtidos 60 blocos (3x3x2mm), polidos (SiC 600), divididos em 6 grupos (n10) e tratados com diferentes protocolos de condicionamento: 1.Controle (C) 2.Ácido fluorídrico (HF) 5%, 20 segundos (s) (HF5%20s) 3.HF5%60s 4.HF10%20s 5.HF10%60s 6.Monobond Etch&Prime (MBEP). Foram avaliadas rugosidade (microscópio, Lext OLS 4000, Olympus), proporções dos elementos Si/K (LE e DL) e Si/C (CI), morfologia e profundidade de condicionamento (microscópio eletrônico de varredura, JSM 5600 LV JEOL). Todas as variáveis foram submetidas ao teste ANOVA de um fator e ao teste de Tukey (a0,05). Para LE, só os tratamentos com HF10% produziram valores de rugosidade e proporção Si/K diferentes ao C. Para DL e CI, os grupos HF5%60s e HF10% produziram valores de rugosidade maiores ao C. Para CI, todos os tratamentos (exceto MBEP) produziram taxas Si/C menores ao C. Todos os tratamentos (exceto MBEP) produziram profundidade de condicionamento maior ao C nos 3 materiais, a maior foi produzida por HF10%60s (LE:403,2±11,4µm DL:617,4±75,7µm CI:291,6±6,5µm). HF10% produziu padrões de condicionamento mais agressivos. Os tratamentos MBEP e HF5%20s, produziram as menores alterações estruturais. O condicionamento com HF produz um padrão irregular e tridimensional, dependente da concentração/tempo de aplicação. Apoio: CAPES, CNPq.Palavras-chave: Cerâmicas. Ácido Fluorídrico. Microscopia Eletrônica.

Short- and Long-Term Bond Strength Between Resin Cement and Glass-Ceramic Using a Silane-Containing Universal Adhesive

This study aimed to evaluate the effect of various silane-containing solutions on bonding between resin cement and glass ceramic after 24 hours and after six months of water storage. Glass-ceramic plaques (IPS e.max CAD) were sandblasted with aluminum oxide, etched with 10% hydrofluoric acid (HF), and divided into five “silane treatment” groups: RelyX Ceramic Primer (RCP), RelyX Ceramic Primer and Single Bond Plus (RCP+SB), Scotchbond Universal (SBU), Clearfil Ceramic Primer (CP), and no solution (HF-only control). Each group was divided into two “storage time” subgroups: 24 hours or six months in 37°C water. Eighteen resin cement cylinders (RelyX Ultimate) were bonded to each treatment group substrate (n=18) and then subjected to microshear testing. Failure mode was analyzed using scanning electron microscopy. Debond data were analyzed using a two-way analysis of variance and the Tukey post hoc test (α=0.05) as well as Weibull distributions. The factors “silane treatment,” “storage time,” (p&lt;0.0001), and their interaction were statistically significant (p&lt;0.0010). Group means (MPa±SD), RCP (24 hours: 27.2±3.1; six months: 18.0±4.9), and HF-only control (24 hours: 21.1±3.4; six months: 15.7±5.8) showed a reduced bond strength after six months of water storage, while RCP + SB (24 hours: 23.4±4.4; six months: 22.2±5.4), SBU (24 hours: 18.8±3.0; six months: 17.2±3.6), and CP (24 hours: 21.7±4.3; six months: 17.4±4.8) remained constant. Weibull analysis revealed that more reliable bond strengths were obtained after six months for SBU and RCP + SB. Evaluation by scanning electron microscopy revealed that all groups demonstrated hydrolytic degradation at six months of storage, but RCP + SB and SBU indicated less. Use of a separate application of silane and adhesive system improved short and long-term ceramic/resin cement bond strength.