The Journal of Adhesive Dentistry, 01/2017

Purpose: To evaluate the in vitro studies conducted in the last six years on new zirconia materials to discover and explore current trends in bonding composite cement to zirconia substrate. Materials and Methods: An in-depth review of the in vitro studies performed between 2010 and 2016 was conducted, focusing on the current trends in surface conditioning methods for zirconia ceramic. PubMed was used for searching the literature. Resin composite bonding to zirconia, zirconia surface coating, and zirconia surface treatment method were the keywords used. Complete scientific articles were reviewed and evaluated for appropriateness. Results: The literature survey showed a variety of surface treatment techniques comprising grit blasting (laboratory or chairside) with or without silica-coated alumina particles, the use of materials containing phosphate monomers, different silanes and primers, laser irradiation, Si vapor-phase deposition, and selective infiltration etching. Conclusions: The problem of composite cement bonding to zirconia has yet to be definitively solved. Nevertheless, the application of phosphate monomer on tribochemically silica-coated zirconia surfaces is currently the least complicated and most efficaceous means of bonding composite cement to zirconia. Selective infiltration etching seems to be a promising technique for establishing a durable bond between composite cement and zirconia, and should be studied further. Keywords: composite cement, shear bond strength, silane primer, tensile bond strength, zirconia

Purpose: To evaluate the effects of tribochemical silica coating and different 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing primers on the shear bond strength (SBS) of orthodontic metal brackets to yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) surfaces. Materials and Methods: One hundred ninety polished Y-TZP specimens were randomly assigned to 19 groups (n = 10): 30 specimens were used for surface analyses after polishing with 600-grit silicon carbide paper, airborneparticle abrasion with 50-μm alumina (A), or tribochemical silica coating (CoJet [C]); 160 specimens were used in SBS testing of orthodontic metal brackets to Y-TZP after alumina airborne-particle abrasion or tribochemical silica coating and application of either ESPE-Sil (S) (ASn, ASa, CSn, CSa), Alloy Primer (AP) (AAPn, AAPa, CAPn, CAPa), Clearfil Ceramic Primer (CP) (ACPn, ACPa, CCPn, CCPa), or Scotchbond Universal (U) (AUn, AUa, CUn, CUa) and either stored in water for 24 h (non-aged, n) or thermocycled 5000 times (aged, a). The surface analyses and SBSs were statistically analyzed with ANOVA and Tukey's tests. Results: Both mechanically treated surfaces had significantly greater surface roughness and surface free energy than did the polished surfaces. The type of primer and aging significantly affected the bond strength. Among the thermocycled specimens, the AAPa, AUa, and CCPa groups showed the greatest SBS. Conclusion: After alumina airborne-particle abrasion, the application of Alloy Primer, Clearfil Ceramic Primer, or Scotchbond Universal provided stable bonding to Y-TZP ceramics. After tribochemical silica coating, however, only Clearfil Ceramic Primer produced a durable bond to Y-TZP ceramics. Keywords: zirconia, bonding, 10-methacryloyloxydecyl dihydrogen phosphate, universal primer

Purpose: To evaluate (1) the initial and long-term microtensile bond strengths of two-step self-etch adhesives with different degrees of conversion (DC); (2) the elastic modulus of the respective adhesive resins; (3) the water sorption of the respective adhesive resins. Materials and Methods: Two two-step self-etch adhesives, Clearfil SE Bond (CSE) and Clearfil SE Bond 2 (CSE2) were used in this study. The DC was determined using ATR/FT-IR with a time-based spectrum analysis. Midcoronal flat dentin surfaces of 24 human molars were prepared with 600-grit SiC paper for microtensile bond strength (µTBS) testing. CSE and CSE2 were applied to the dentin surfaces according to the manufacturer's instructions, followed by composite buildups. The µTBS was measured after water storage for 24 h, 6 months, and 1 year. The elastic modulus (before and after 1 month of water immersion) was determined by the three-point flexural bending test and water sorption values by the water sorption test. Results: CSE2 showed significantly higher DC than CSE. The µTBS of CSE2 was significantly higher than that of CSE in all water storage periods. One-year water storage decreased the µTBS of CSE; however, it did not decrease that of CSE2. Regarding the polymerized adhesive resins, the elastic modulus of CSE2 was significantly higher than that of CSE before and after water immersion (p 0.001), and the water sorption of CSE was higher than that of CSE2. Conclusions: The higher DC of adhesive resins of two-step self-etch adhesives resists water aging and improves the initial bond strengths and durability of the resin-dentin bond. Keywords: two-step self-etch adhesive, degree of conversion, microtensile bond strength, water sorption, elastic modulus

Purpose: To evaluate the light transmission characteristics of different types, shades, and thicknesses of novel CAD/CAM materials and their effect on the degree of conversion (DC) of a dual-curing resin cement. Materials and Methods: Square specimens (12 × 12 mm2) of three CAD/CAM materials - GC Cerasmart, Lava Ultimate, Vita Enamic - of different thicknesses (1.00, 1.50, and 2.00 mm, n = 5 per thickness) were irradiated with an LED unit. The amount of transmitted light was quantified. Thereafter, the DC% of the dual-curing resin cement (RelyX Ultimate) was recorded after 15 min using Fourier transform infrared spectroscopy. Statistical analysis was performed using two-way ANOVA followed by the Tukey's HSD post-hoc test at a significance level of p 0.05. Regression analysis was performed to investigate the correlation between the DC and radiant energy, and the DC and thickness. Results: Although the type and shade of CAD/CAM material significantly affect transmitted light irradiation (p 0.0001), degrees of conversion are similar when the CAD/CAM material or material shade were taken into consideration (p > 0.05). Conversely, material thickness significantly affected light transmission (p 0.0001) and DC (p 0.0001). Multiple effects of material, shade, and thickness did not significantly affect the evaluated parameters (p = 0.638 for light irradiation; p = 0.637 for DC). Linear regression analysis showed a correlation between delivered energy and DC% results of the Vita Enamic (R² = 0.4169, p 0.0001). Conclusion: Reduced light transmission in 2-mm-thick specimens of all CAD/CAM materials indicates that proper curing of the cement beneath CAD/CAM materials should be ensured. Keywords: hybrid nanoceramic, polymer infiltrated ceramic, resin nanoceramic, light transmission, degree of conversion

Purpose: To determine whether an experimental thermally deposited siloxane-methacrylate coating for use in industrial scale applications would improve the bond strength of resin-based materials to glass fiber posts (GFPs) without affecting their mechanical properties. Materials and Methods: An experimental 5% (w/v) solution of methacryloxypropyltrimethoxysilane was prepared. Two types of GFPs (Exacto, Angelus; White Post DC, FGM) were divided into the following groups: S: silane; SA: silane and adhesive; HS: 35% H₂O₂ and silane; HSA: 35% H₂O₂, silane and adhesive; Exp: siloxane-methacrylate coating (Si-O) via post immersion in experimental solution followed by heating; Exp-S: silane after Si-O treatment; Exp-A: adhesive after Si-O treatment; and Exp-SA: silane and adhesive after Si-O treatment. The posts were positioned in a mold to allow insertion of a dual-curing resin core, serially sectioned into beams, and subjected to microtensile bond strength (μTSB) testing. The three-point bending test and SEM/EDX analysis were used to assess the mechanical and surface properties of untreated GFPs that were etched with H₂O₂ or treated with Si-O. Results: Surface treatments affected the μTSB only for the Exacto GFPs. The highest μTBS (MPa) was observed in Exp-S and Exp-SA groups, whereas H₂O₂ etching resulted in intermediate values. The mechanical properties were not affected by surface treatments. Exacto GFPs had significantly higher flexural strength (σ_f) and flexural modulus (E_f) than did the White Post DC GFPs, but the latter were significantly stiffer (S) than Exacto, regardless of the surface treatment tested. H₂O₂ promoted morphological changes in post surfaces. The experimental treatment promoted deposition of Si onto the post surface, improving bond strengths of Exacto posts. Conclusion: The proposed novel coating technique is a viable procedure for fiber post manufacturers to improve the μTSB of resin-based materials. Keywords: bond strength, fiber post, hydrogen peroxide etching, silane

Purpose: To evaluate the effect of water storage and cyclic loading on the microtensile bond strength (μTBS) and fracture pattern of adhesives to dentin. Materials and Methods: Midcoronal dentin surfaces (n = 36) were prepared and composite restorations were built up using two adhesives (self-etch and etch-and-rinse). The specimens were randomly divided into 3 groups according to the aging conditions (n = 6): 1. control: storage in water for 24 h (CO); 2. water storage: storage in water for 6 months (WS); 3. mechanical loading: 750,000 mechanical cycles (ML) using the Rub&Roll loading device. Specimens were sections into beams and the μTBS was tested. Fracture patterns were analyzed using stereomicroscopy and fractographic analysis was performed using SEM. μTBS data (n = 53-72 specimens) were subjected to two-way ANOVA and Tukey's post-hoc test. The chi-squared test was used to compare the distribution of failure modes (p 0.05). Results: Aging conditions and adhesives significantly affected μTBS (p 0.01). The CO group showed no difference between materials and had highest μTBS. After WS, the self-etch adhesive showed higher μTBS than did the etchand- rinse adhesive. ML resulted in lower μTBS for both adhesives. Materials (p 0.01) and aging (p 0.01) significantly influenced the distribution of failure modes. SEM analysis showed that specimens submitted to WS or ML showed features of degradation and fatigue at the fractured interface, depending on the adhesive. Conclusion: Mechanical loading had a negative effect on the bonding efficacy of both adhesives and influenced the fracture pattern, with specimens presenting a different fracture surface from that observed in water-stored specimens. Keywords: microtensile bond strength, mechanical load, fracture pattern, adhesive, aging, water storage, dental adhesive, self-etch

Purpose: To assess the immediate and six-month microshear bond strength (µSBS) of a universal adhesive applied using different etching strategies on sound and eroded dentin. Materials and Methods: Eighty bovine incisors were polished to obtain flat buccal dentin. Forty teeth were submitted to a pH-cycling model to simulate artificial erosion (3x/day cola drink for 7 days). Teeth from both dentin conditions (sound and eroded) were randomly assigned to four groups according to the adhesive and etching approach: a universal adhesive in self-etch and etch-and-rinse modes (Scotchbond Universal Adhesive), and as controls a two-step etch-and-rinse adhesive (Adper Single Bond Plus), and a two-step self-etch adhesive (Clearfil SE Bond). Four composite restorations (Z250) were built up on each dentin surface, using the area delimitation technique. Half of the specimens were evaluated in the µSBS test after 24 h of water storage, and the other half were evaluated six months later. Data (MPa) were analyzed with three-way repeated measures ANOVA and Tukey's post-hoc tests (? = 0.05). Results: The µSBS values of all adhesives significantly decreased after six months of aging (p = 0.01). Lower µSBS values were obtained in eroded dentin (p = 0.04). The universal adhesive showed similar µSBS to the self-etch adhesive used as control, irrespective of the etching strategy. However, Scotchbond Universal Adhesive applied in self-etch mode performed better than the control etch-and-rinse adhesive (p = 0.02). Conclusion: The universal adhesive does not provide the same bonding efficacy on eroded dentin as on sound dentin, and its performance does not depend on the etching mode. Keywords: dentin bonding agents, microshear, erosion tooth wear, degradation, one-step adhesive

Purpose: To assess the fracture resistance (FR) and cusp deflection (CD) of lined or non-lined composite (CO) and glass hybrid (GH) restorations over residual demineralized dentin. Materials and Methods: In 48 extracted human premolars, artificial residual demineralized dentin was induced on pulpo-axial walls of standardized cavities. Various restorations were placed over this demineralized dentin: an experimental GH, a composite restoration (OptiBond FL+Tetric EvoCeram) without lining, or composite restorations with non-setting (Hypocal) or setting (Dycal) calcium hydroxide lining. After thermomechanical cycling, groups (n = 12) were compared regarding their CD and FR. Results: CD did not differ significantly between groups. FR was significantly lower in teeth restored with GH (median: 238 N; 25th/75th percentiles: 191/287 N) than in those restored with lined or non-lined composites (median range: 517-569 N; p 0.05/Mann-Whitney), which did not differ significantly from each other (p > 0.05). Conclusion: Within the conditions of this in vitro study, CH lining of pulpo-axial walls had only limited impact on CD and FR. GH showed the lowest FR and might not be optimal for restoring deep or extended cavitated lesions. Keywords: calcium hydroxide, caries, glass-ionomer cements, composite restorations, selective excavation