The Journal of Adhesive Dentistry, 04/2021

Purpose: To systematically review the literature to evaluate whether the bond strength of resin-based materials to enamel is affected by deproteinizing agents. Materials and Methods: This systematic review and meta-analysis was conducted according to the PRISMA statement. PubMed, ISI Web of Science, Cochrane Library, SciELO, Scopus, LILACS, IBECS, and BVS databases were screened up to December 2020. Eligibility criteria included in vitro studies that reported the effect of a deproteinizing agent applied before or after acid etching on the immediate or long-term bond strength of resin-based materials to enamel. The meta-analysis was carried out using Review Manager (version 5.3.5). A global comparison was performed with the standardized mean difference based on random-effect models at a significance level of α = 0.05. Results: A total of 23 studies were included in the meta-analysis. In all the studies, only the immediate bond strength was evaluated. The bond strength of the materials was improved by the application of NaOCl or papain prior to enamel etching with phosphoric acid (p ≤ 0.006). None of the deproteinizing agents had a significant effect when applied after etching with phosphoric acid (p ≥ 0.27). Conclusions: Based on in vitro studies, deproteinization with sodium hypochlorite or papain-based agents increases the immediate bond strength of resin-based materials to enamel only when used prior to phosphoric-acid etching. Keywords: enamel, sodium hypochlorite, papain, phosphoric etching, deproteinization

Different kinds of interactions between the restorative material and mineralized dental tissues result in secondary caries around dental composites. Of these, the mechanical interactions have to be carefully investigated. Due to the elastic mismatch between dental tissues and the composite restoration, complex stresses and strains develop at their interface. This complex mechanical environment disturbs the demineralization-remineralization equilibrium of dental hard tissues. The fluid flow both over and within enamel and dentin, associated with their complex ultrastructure and mechanical behavior, is a key factor. It is known that external mechanical loading can indirectly promote the dissolution of enamel and dentin through a pumping action of cariogenic fluids in and out of microgaps at the interface between mineralized tissues and composite. Mechanical loading can also directly influence the physicochemical behavior of dental hard tissues by inducing complex strain and stress fields on the crystal scale. It is important to consider both the direct and indirect paths by which mechanical loading can influence the apatite dissolution kinetics. Therefore, a systematic approach should be used to investigate the mechanism of secondary caries formation considering the tooth-composite interface as a unique complex in which each element has an influence on the other. Keywords: secondary caries, dental composites, enamel, dentin, interface

Purpose: Thanks to adhesive techniques and strengthened glass ceramics, ultrathin bonded occlusal veneers have been recently introduced. However, since a universally accepted thickness limit for ultrathin ceramics has yet to be established, their resistance to fracture needs to be better investigated. The purpose of this in vitro study was to evaluate the effect of dentin bonding on the flexural properties (ie, fracture load and flexural strength) of a lithium-disilicate (LD) glass ceramic when used in thicknesses equal to or less than the manufacturer’s recommendations for occlusal restorations. Materials and Methods: A total of 96 dentin slices (2.0 mm thick and 15 mm long) were obtained by sectioning bovine teeth along their long axes. LD slices of different thicknesses (1.5 mm/1.3 mm/1.0 mm/0.8 mm/0.6 mm) and 15 mm in length were cut from CAD/CAM LD blocks (IPS e.max CAD-C16). In each of 5 experimental groups, 16 dentin slices were adhesively luted to 16 LD slices (n = 16) of the same thickness, in order to create 16 bi-layered dentin-LD bonded assemblies. In the control group, the 16 remaining dentin slices were conventionally cemented to 1.5-mm-thick LD slices (n = 16) using a resin-modified glass-ionomer cement (FujiCEM 2). All dentin-LD assemblies were cut perpendicularly to their joint interface, in order to obtain 1-mm-wide, 15-mm-long bi-layered prismatic beams, having the following final thicknesses: for the 5 experimental groups, 2 mm (dentin layer) + 1.5 mm/ 1.3 mm/1.0 mm/0.8 mm/0.6 mm (LD layer); for the control group, 2 mm (dentin layer) + 1.5 mm (LD layer). All prismatic beams were subjected to a three-point bending test (14-mm span, load applied on the LD side). Fracture loads (N) and flexural strengths (MPa) were recorded. Data were analyzed using one-way ANOVA on ranks tests (α = 0.05). The correlations between the recorded flexural strengths and the dentin:LD thickness ratio and between the flexural strength and the luting strategy were also investigated. The failure modes were observed and classified. Results: No statistically significant differences were recorded between the conventionally luted control group (LD thickness 1.5 mm; fracture load 35.26 N; flexural strength 60.44 MPa) and the thinnest adhesively luted experimental group (LD thickness 0.6 mm; fracture load 28.97 N; flexural strength 90.01 MPa) in terms of fracture load and flexural strength. A fracture involving both the dentin and the LD of the bi-layered prismatic beam, but without any debonding between the LD and the dentin substrates of the broken specimen, was the most common failure mode observed on the adhesively luted samples. Conclusion: Compared to conventional cementation, when LD is bonded to dentin, the flexural properties of the whole system are improved, and the two different substrates seem to behave like a single unit. Once adhesively luted, 0.6-mm-thick LD has the same fracture load and flexural strength as that of the conventionally luted 1.5-mm-thick LD. Keywords: dentin, adhesive luting, lithium-disilicate, flexural strength, three-point bending test

Purpose: To compare the effect of different methods of cleaning residual composite cement from the surface of lithium-disilicate glass-ceramic on its bond strength. Materials and Methods: Blocks of lithium-silicate glass-ceramic (e.max CAD) were coated with composite cement. Blocks in a positive control (CO+) group received no cement; negative controls (CO-) received composite cement. After water storage (24 h), specimens were cleaned as follows (n = 20/group): BUR: grinding with a fine-grit diamond bur (20 s); ALUM: air abrasion with 50-µm alumina (10 s); GLASS: air abrasion with 50-µm glass beads (10 s); FURN: firing in ceramic furnace and cleaning with ethanol; SULF: immersion in sulfonic acid solution (1 h); HYFL: no additional treatment. All specimens were etched with hydrofluoric acid, aside from the CO- group, and treated with silane. A 1.5-mm diameter cement-filled tube was affixed to the specimens and light polymerized. Specimens were stored in 37°C water for 24 h (n = 10) or 90 days (n = 10). Shear bond strength was tested. Two-way ANOVA and post-hoc Tukey tests were performed. Specimens from each group were examined with SEM. Results: Bond strength significantly differed according to surface cleaning method (p < 0.01) and storage time (p < 0.01), but their interaction was not significant (p = 0.264). Longer storage time decreased the bond strength. BUR, ALUM, GLASS, and FURN did not differ statistically significantly from CO+, but were significantly greater than CO-. SULF and HYFL did not differ statistically significantly from CO- and were significantly lower than CO+. Conclusions: Cleaning composite cement with BUR, ALUM, GLASS, and FURN restored bond strengths to that of the positive control. However, only GLASS and FURN did not roughen the surface of the underlying lithium-silicate glass-ceramic.

Purpose: The effect of surface moisture on bur-cut dentin on the microtensile bond strength (μTBS) of universal adhesives with various contents of 2-hydroxyethyl methacrylate (HEMA) and methacrylamide monomers was evaluated. Materials and Methods: Flat mid-coronal dentin surfaces of human molars were exposed, and a standardized smear layer was prepared using a fine-grit diamond bur. The surfaces were either left wet or air dried for 10 s before bonding with Clearfil Universal Bond Quick (UBQ), experimental UBQ without an amide monomer (UBQexp), Scotchbond Universal (SBU), Prime&Bond Universal (PBU), or BeautiBond Universal (BBU). The specimens were built up with resin composite, sectioned into sticks and subjected to the μTBS test after 24 h or 10,000 thermal cycles. The μTBS data were analyzed using three-way ANOVA followed by pairwise comparisons with Bonferroni’s correction (α = 0.05). Results: The level of dentin moisture did not significantly affect μTBS of UBQ and BBU (p > 0.05). HEMA-containing UBQ, UBQexp, and SBU exhibited higher μTBS to dry dentin, while HEMA-free PBU and BBU showed higher μTBS to wet dentin. Thermocycling significantly decreased the μTBS of UBQexp (p < 0.01) and BBU (p < 0.001) irrespective of dentin moisture level, while SBU was significantly affected only on dry dentin (p < 0.001). Thermocycling had no significant effect on UBQ and PBU containing methacrylamide monomers (p > 0.05). Conclusion: Dry surfaces enabled obtaining optimal bonding for HEMA-containing adhesives to bur-cut dentin, while wet surfaces enabled optimal bonding for HEMA-free adhesives. Methacrylamide monomers could contribute to the improvement of the initial and long-term bonding performance of universal adhesives to bur-cut dentin. Keywords: bond strength, dentin moisture, hydrophilic monomer, thermocycling, universal adhesives, diamond bur

Purpose: The pretreatment of glass-ceramic before adhesive cementation can be performed with hydrofluoric acid (HF)/silanization (S) or with an ammonium polyfluoride-containing primer (APF). It can be modified by application of a silane-containing universal adhesive (UA) and/or additional silanization. The aim of this study was to evaluate the bond strength of composite cements to two different glass ceramics after different pretreatments and aging. Materials and Methods: Disks of leucite-reinforced glass-ceramic or lithium-disilicate glass-ceramic were pretreated with HF+S, HF+UA, HF+S+UA, APF, or APF+S, bonded in pairs with composite cement and sectioned into microsticks (n = 96/group). The microtensile bond strength was determined either after 24 h (n = 48) or after aging for 6 months in water (n = 48). Fracture patterns were analyzed at 50X magnification. Statistical evaluation was performed using the Kruskal-Wallis test, pairwise comparisons with Bonferroni’s correction, and the chi-squared test (p < 0.05). Results: Pretreatment with HF+UA or APF led to significantly lower bond strength compared to HF+S. Additional silanization after application of UA or APF resulted in a significant increase in bond strength. After aging, HF+UA groups showed significantly lower bond strengths, independent of additive silanization. Aging did not affect APF-pretreated leucite-reinforced glass-ceramic; for lithium-disilicate glass-ceramic, the bond strength dropped significantly. Additional silanization improved aging resistance for the respective groups. Conclusion: Bond strength and its long-term stability depend on the ceramic used and on the pretreatment. An ammonium polyfluoride-containing primer seems to be a promising option compared to conventional pretreatment with hydrofluoric acid. Additive silanization improves the long-term stability of the microtensile bond strength. Keywords: Monobond Etch & Prime, ammoniumpolyfluoride, hydrofluoric acid, universal adhesive, silane, glass ceramic, microtensile bond strength test

Purpose: To evaluate the effect of different concentrations of ethylene-diamine-tetra acetic acid (EDTA) on bond strength (BS) and nanoleakage (NL) of fiber posts bonded into root canals. Materials and Methods: Seventy-two single roots were endodontically treated and divided into six groups (n = 12), according to the combination of the following factors: surface treatment (no irrigation [control], 17% EDTA, or 24% EDTA), and composite cement applied with an adhesive used in a self-etch mode (Single Bond Universal/RelyX Ultimate [SB], 3M Oral Care; Ambar Universal/Allcem [AM], FGM). After fiber post cementation, six 1-mm-thick disks were obtained for each root. Push-out bond strength (BS) was evaluated using 8 specimens per group, and the other 4 specimens were used to examine nanoleakage (NL). Data from BS and NL of each adhesive were evaluated by two-way ANOVA (surface treatment vs root region) and Tukey’s test (α = 0.05). Results: The application of 17% and 24% EDTA did not influence the bond strengths of either adhesive. In general, the application of 17% and 24% EDTA increased NL values for both adhesives. Conclusion: Pre-treatment with different concentrations of EDTA was not able to improve the adhesion of fiber posts into root canals with universal adhesives. Keywords: adhesive, bond strength, fiber posts, root dentin

Purpose: This study evaluated whether active application of self-etching adhesives would influence their microtensile bond strength (µTBS) to dentin cut with burs of different grit sizes. Materials and Methods: Eighty-four human premolars were divided into 12 groups according to 1) two dentin surface preparations with either superfine- or regular-grit diamond burs; 2) three adhesives – Clearfil SE Bond 2 (SE2), Scotchbond Universal (SBU, 3M Oral Care) and G-Premio Bond (GPB, GC); and 3) two application modes of each adhesive (active or passive). Six bonded teeth per group were sectioned into sticks for µTBS testing. Statistical analyses were performed using 3-way ANOVA followed by Duncan’s test (p < 0.05). Additional teeth were prepared to observe the interaction between the dentin smear layer obtained from each bur with adhesives under different application modes using transmission electron microscopy (TEM). Results: Active application significantly increased the dentin bond strength of SE2, irrespective of the kind of bur used (p < 0.05). The highest bond strength of SBU was observed when bonded to superfine-grit diamond bur-cut dentin with the active application. There was, however, no influence of the tested factors on GPB group (p > 0.05). TEM observation showed that active application promoted dentin smear layer dissolution in all adhesive groups. Conclusions: Bond strengths of self-etching adhesives to dentin are influenced by bur-cut smear layers and mainly by application mode of adhesive materials. Active application improves µTBS of self-etching adhesives by enhancing smear layer modification and resin penetration into bur-cut dentin. Keywords: active application, adhesion to dentin, diamond bur, microtensile bond strength, self-etching adhesives, smear layer, transmission electron microscopy