The Journal of Adhesive Dentistry, 02/2021

Purpose: The goals of this review are (1) to describe the evidence behind the use of ceramics vs composite resin to restore teeth with anterior veneers using a minimally-invasive strategy; and (2) to discuss the choice of materials and techniques for anterior veneer restorations. Overview: In recent years new adhesive restorative materials and techniques have been introduced in dentistry, including nanofilled composite resins for direct restorations, new ceramic materials that combine esthetics and strength, and polymer/ceramic materials for indirect restorations that are fabricated chairside using CAD/CAM technology, allowing the dentist to design, mill, and cement the restoration in one session. In spite of the novelty and new technology behind the introduction of new materials, the available evidence that backs some of these materials does not justify their use over similar materials or techniques that have been used by dentists for some years. Notwithstanding the success of laminate veneers and the popularity of new materials and digital techniques, the classical direct composite resin veneer is still very popular among clinicians and taught in dental schools and continuing education courses. Direct composite resin veneers are usually more affordable than indirect veneers, less invasive of the tooth structure, and easier to repair. Current composite resin materials can be finished to a tooth-like appearance, but they are susceptible to alterations of the surface gloss and potential discoloration of the composite resin. On the other hand, the preparation for indirect veneers is generally more invasive and the respective restorations are more difficult to repair. In addition, the esthetic outcome of bonded ceramic restorations still depends on the clinical behavior of the dentin adhesive and resin luting cement used to bond the restoration to the tooth structure. Conclusions: The ultimate goals of any restorative treatment are to restore function and esthetics, prevent recurrent caries lesions and bacterial leakage into the pulp space, save tooth structure, and promote the well-being of our patients. The armamentarium of new dental materials for esthetic clinical procedures has increased exponentially in the last few years. The use of different materials and techniques for anterior veneer restorations must be based on sound evidence rather than on the marketing hype or testimonials. Keywords: adhesion, ceramics, clinical, composite resin, MID, restorative materials, veneers

Purpose: To evaluate the influence of different surface treatments of two CAD/CAM glass ceramics on surface topography, shear bond strength of composite cement, flexural strength, and elastic modulus. Materials and Methods: Two ceramics were evaluated: lithium-disilicate (LDS) and zirconia-reinforced lithium silicate (ZLS) glass ceramics. Glass ceramics were sintered and the surfaces were sandblasted (SBL) or etched with 9% hydrofluoric acid for 10 s (HF10), 20 s (HF20) or 30 s (HF30). The treated surfaces were analyzed using scanning electron microscopy (n = 3) to evaluate the etching pattern. For bond strength testing, ceramic samples were silanized after treatments and an adhesive was applied to the surface. Afterwards, a silicone mold was used to build composite-cement cylinders, which were tested after 24 h or one year of water storage (n = 10). Flexural strength and modulus were assessed using a 3-point bending test (n = 15). The data were subjected to statistical analysis at a pre-set α = 0.05. Results: SBL and HF resulted in different surface topographies. Increased HF etching time influenced the surface dissolution level and exposition of crystals for LDS, while no effect of etching time was observed for ZLS. After one year, the bond strength to LDS significantly decreased, regardless of treatments. For ZLS, HF10 and HF20 showed stable bond strengths over time. SBL yielded the lowest bond strength for both ceramics and statistically significantly reduced the flexural strength of ZLS. The flexural strength and elastic modulus of ceramics were not affected by different etching times. Conclusion: Bonding stability depended on the glass ceramic and the pretreatment method employed. HF etching did not change the mechanical properties of the ceramics and is indicated as a ceramic treatment for bonding. Keywords: ceramics, bond strength, flexural strength, flexural modulus, hydrofluoric acid etching

Purpose: This study evaluated the effect of the design of the light-curing unit (LCU) and mouth opening on the properties of bulk-fill resin-based composites (RBCs). Materials and Methods: Eighty molars received a mesio-occlusal-distal preparation and were restored using two different bulk-fill RBCs, Opus Bulk Fill APS (FGM) and Filtek Bulk Fill One (3M Oral Care), using two different designs of LCU, straight (Valo Cordless [Ultradent]) and angled (Radii-Cal [SDI]). Two mouth openings of 25 and 45 mm at the incisors were used. Forty samples were sectioned mesiodistally. One half was immersed in tetrahydrofuran to examine the effect of the solvent on the RBCs (SE), and the other half to measure the degree of conversion (DC) in proximal and occlusal boxes using Fourier Transform Infrared spectroscopy. The other 40 samples were subjected to thermomechanical fatigue and immersed in silver nitrate to examine the gingival margin integrity (GMI) using SEM. The irradiance (mW/cm2) and emission spectrum (mW/cm2/nm) from the LCUs were measured using a MARC Resin Calibrator (BlueLight Analytics). DC data were analyzed by 3-way ANOVA and Tukey’s test; SE and GMI were analyzed by an ANOVA on Ranks and Dunn test (α = 0.05). Results: The DC values were similar in the occlusal and proximal boxes when using Valo Cordless, irrespective of RBC and the mouth opening used. Lower DC values were measured in proximal boxes when using Radii-Cal. The mouth opening had a greater effect on the irradiance delivered by Radii-Cal. Radii-Cal with 25-mm mouth opening had greater SE and GMI values, whereas the SE and GMI values obtained with Valo Cordless were unaffected by mouth opening. Conclusion: The choice of LCU did not influence the properties of tested bulk-fill RBCs when the 45-mm mouth opening was used. However, when using the 25-mm mouth opening, the choice of LCU did influence the properties of the RBCs. Keywords: bulk-fill resin composites, composite resin polymerization, light-curing units, light curing, mouth opening access, posterior composite resin restorations

Purpose: To evaluate the effect of different etching times of a self-etching ceramic primer on the microshear bond strength (µSBS) and topographic surface pattern of a lithium-disilicate glass-ceramic. Materials and Methods: Ceramic slices were subjected to an in-lab simulation of CAD/CAM milling and randomly allocated to 10 groups (n = 35) considering two factors: “surface treatment” in 5 levels – one control group (5% hydrofluoric acid + silane application [HF5+SIL]), and 4 experimental groups using ceramic etching/primer (Monobond Etch & Prime, E&P) with different passive application times (40 s, 2 min, 5 min, or 10 min); and “aging” factor in 2 levels – short-term (after 24 h), or long-term (storage for 180 days + 12,000 thermal cycles). Composite cement cylinders were built and µSBS tests were run in a universal testing machine. The failure patterns were categorized, and complementary analyses with SEM and Atomic Force Microscopy (AFM) were performed. Results: The groups showed statistically similar bond strengths in the short term (range 22.4 to 25.1 MPa). However, only the E&P 20s+40s (19.3 MPa) and E&P 20s+5min (21.5 MPa) groups maintained stable bond strength in the long term, and HF5+SIL (17.1 MPa) presented statistically significantly lower values than did E&P 20s+5min. The failure pattern was predominantly adhesive. The increased application time of the ceramic primer promoted greater dissolution of the glass matrix; thus, the E&P 20s+10min group presented the most complex surface characteristics in the fractal dimension analysis. Conclusion: The self-etching ceramic primer can be used as an alternative to classical conditioning with HF plus silane, promoting stable bond strength for etching times of 40 s or 5 min of passive application. Keywords: adhesion, CAD/CAM, fractal dimension, glass ceramic, surface treatments, topographical changes

Purpose: To investigate the impact of pretreatment and conditioning on shear bond strength (SBS), surface free energy (SFE) and surface roughness (SR) between polyetheretherketone (PEEK) and cold-cured polymethylmethacrylate (PMMA). Materials and Methods: PEEK substrates (Dentokeep PEEK Disc, nt-trading) were air abraded with Al2O3 particles of different grain sizes applied with varying pressure at 1) 0.2 MPa – 50 µm Al2O3; 2) 0.4 MPa – 50 µm Al2O3; 3) 0.2 MPa – 110 µm Al2O3; 4) 0.4 MPa – 110 µm Al2O3; or 5) without air abrasion (n = 172/group). Surface properties were quantified using SFE and SR (n = 10/group), and scanning electron microscope imaging (n = 2/group). Substrates were conditioned with a) Visio.link (VL, Bredent); b) Scotchbond Universal (SU, 3M Oral Care); c) Bonding Fluid (BF, Schütz Dental); or d) without conditioning (WC; n = 40/subgroup) and bonded to the polymer (Futura Jet, Schütz Dental). SBS and fracture types were determined before and after 10,000 thermal cycles (n = 20/subgroup). Univariate ANOVA, Kruskal-Wallis test, Mann-Whitney U-test, Kaplan-Meier survival estimates, and Weibull distribution were computed (p < 0.05). Ciba-Geigy tables and the chi-squared test were used to analyze fracture type distributions. Results: An increase in particle size and pressure resulted in similar or increased SBS, Weibull characteristic strength, and Weibull moduli (p < 0.001 – 0.046). The lowest results were observed for the control group (without air abrasion), while pretreatment with 0.4 MPa – 110 µm Al2O3 presented the highest values (p < 0.001). In comparison with the other conditioning procedures, VL showed high (p < 0.001 – 0.03), and SU and WC low SBS (p < 0.001 – 0.006). Although it did not influence SFE, an increase in particle size and pressure led to an increased SR (p < 0.001). Conclusion: Pretreatment with 0.4 MPa – 110 µm Al2O3 can be recommended to increase bonding properties between PEEK and PMMA. Application of adhesives such as VL can enhance SBS further. Keywords: PEEK, polymethylmethacrylate acrylic denture polymer, bonding, shear bond strength, air-particle abrasion, adhesive

Purpose: To evaluate the effect of inclusion of two dimethyl sulfoxide (DMSO) concentrations in simplified etch-and-rinse adhesives on dentin bonding durability after three years of water storage. Materials and Methods: Forty-two caries-free third molars were divided into six experimental groups (n = 7) according to the following factors: 1) adhesive (Adper Single Bond 2 [SB], 3M Oral Care; Prime&Bond 2.1 [PB], Dentsply Sirona); 2) concentration of DMSO (control group: 0.0% DMSO; addition of 0.2% DMSO [0.2] and 2% DMSO [2.0]). After completing restoration, specimens were stored in water (37ºC) for 24 h, sectioned into adhesive-dentin sticks (0.8 mm2), tested for microtensile bond strength (µTBS) at 0.5 mm/min, and examined for nanoleakage (NL) using SEM immediately thereafter or after three years of water storage. Data were subjected to a three-way repeated-measures ANOVA and Tukey’s test (α = 0.05) for each property evaluated. Results: After three years of water storage, for both adhesives, the incorporation of 2% DMSO maintained the µTBS when compared to immediate µTBS (p > 0.05). In general, SB resulted in a statistically significantly higher mean of µTBS compared to PB, independent of the DMSO concentration after water storage (p < 0.05). Furthermore, the amount of NL was lower and practically limited to the hybrid layer given the concentrations of 0.2% and 2% DMSO for both tested adhesives after three years. Conclusion: The incorporation of DMSO in simplified etch-and-rinse adhesives maintains the long-term stability of the dentin bond. Keywords: DMSO, bond strength, nanoleakage, hybrid layer, longevity

Purpose: To investigate the effects of root canal irrigants, dentin surface treatment, and timing of the restoration on the microtensile bond strength (μTBS) of a universal adhesive to deep coronal dentin. Materials and Methods: Ninety (90) intact molars were grouped according to the irrigation protocol: group 0 (saline, control group); group 1: 5.25% sodium hypochlorite (NaOCl), 17% ethylenediaminetetraacetic acid (EDTA) followed by 5.25% NaOCl; group 2: 18% etidronic acid (HEDP) + 5.25% NaOCl in a single mixture. Groups 1 and 2 were divided into 2 subgroups (n = = 10) according to the time of restoration: immediate (subgroup A) and after 7 days (subgroup B). Four other groups (n = 10) were created according to the dentin surface pretreatment and received an immediate restoration: group 3: 5.25% NaOCl – 17% EDTA and AH Plus Cleaner; group 4: 5.25% NaOCl – 17% EDTA and 100% ethanol; group 5: 5.25% NaOCl + 18% HEDP and AH Plus Cleaner; group 6: 5.25% NaOCl + 18% HEDP and 100% ethanol. μTBS testing was carried out for each subgroup and interfaces were analyzed through SEM. The μTBS was analyzed with Welch statistics and the post-hoc Games-Howell test for multiple comparisons (p < 0.05). Results: Statistically significant differences were observed between test groups and control groups (p < 0.001), except for group 3 (p = 0.349). No significant differences were recorded between groups 1A (27.5 ± 8.7 MPa), 2A (32.6 ± 14.5 MPa) and 3 (27.3 ± 14.3 MPa). Group 6 (48.6 ± 11.6 MPa) exhibited the highest μTBS among all tested groups. For groups 1 and 2, significantly higher values were recorded for subgroups 1B (39.3 ± 7.6 MPa) and 2B (43.8 ± 8.3 MPa) compared to subgroups 1A (27.5 ± 8.7 MPa) and 2A (32.6 ± 14.5 MPa). Conclusion: When using NaOCl as root canal irrigant, it is advisable to delay the placement of a post-endodontic-treatment restoration. Keywords: delayed restoration, endodontics, etidronic acid, microtensile, root canal irrigation, universal adhesives