The Journal of Adhesive Dentistry, 05/2017

Purpose: To formulate adhesive resins with 2 wt% of hydroxyapatite (HAp), α-tricalcium phosphate (α-TCP), or octacalcium phosphate (OCP) and to compare these groups with an unfilled adhesive regarding the degree of conversion, polymerization rate, microshear bond strength and mineral deposition. Materials and Methods: The experimental adhesive resin was formulated mixing 66.6 wt% bisphenol A glycol dimethacrylate (bis-GMA), 33.3 wt% 2-hydroxyethyl methacrylate (HEMA), and a photoinitiator system. OCP, α-TCP, or HAp were added in concentrations of 2 wt% to the adhesive, and a group without additional filler was used as the control. Calcium-phosphate particle sizes were determined using a laser-diffraction particle-size analyzer. The degree of conversion (DC) of the adhesives was determined with FTIR-ATR. The polymerization rate (Rp) was determined using differential scanning calorimetry equipped with a photocalorimetric accessory. Adhesive bonding was evaluated using the microshear bond strength test in sound bovine mandibular incisors. Mineral deposition in human third molars affected by caries was evaluated using micro-Raman spectroscopy after selective removal of carious dentin. Data were analyzed by one-way ANOVA and Tukey's test (α = 0.05). Results: HAp presented the highest mean particle size (26.7 nm), while that of α-TCP was 6.03 nm and OCP was 4.94 nm. The DC of all groups was above 50%. The OCP group showed the fastest Rp, with no difference from the control group (p > 0.05). The α-TCP group presented the highest microshear bond strength (p = 0.005) and mineral deposition at the interface. Conclusion: Incorporation of α-TCP nanofiller into adhesive resins can improve bond strengths and may be a promising strategy to achieve therapeutic remineralization at the composite-dentin interface. Keywords: tooth remineralization, dentin bonding agents, dental caries, hydroxyapatite

Purpose: To evaluate the effect of dentin moisture and application mode of universal adhesives on bond strength (BS) and nanoleakage (NL) of fiber posts bonded to root dentin. Materials and Methods: The roots of 96 extracted human canines were treated endodontically, and the fiber posts were cemented according to the combination of the following factors: dentin moisture (dry and wet), cementation system [Single Bond Universal/RelyX ARC (SBU) and Prime&Bond elect/Enforce (PBE)], and adhesive application [active (A) and passive (P)] in accordance with the manufacturer's instructions. After one week, the specimens were transversely sectioned into six 1-mm-thick disks. From each group, 8 specimens were subjected to the push-out BS test and the other 4 specimens underwent NL analysis. For both tests, the data were subjected to 3-way repeated measures ANOVA and Tukey's tests (α = 0.05). Results: For BS and NL, the cross-product interaction of all factors was significant (p < 0.05). Lower BS was observed under P application independent of the dentin moisture; for A application, SBU showed higher BS than did PBE in both moisture conditions. Nanoleakage was present in all groups and ranged from 22.9% to 36%. Conclusion: The active application of universal adhesives improves the adhesion in fiber post cementation, independent of dentin moisture condition. Keywords: fiber posts, root dentin, push-out bond strength, silver nitrate

Purpose: To compare the dentin microtensile bond strength (µTBS) and the Knoop hardness of bulk-fill and conventional restorative composites in box-shaped Class I cavities using different insertion techniques. Materials and Methods: Forty box-shaped Class I preparatons 4 mm deep were performed in the pulp chamber of sound human third molars. The restorations were made using either a conventional microhybrid (Z250, 3M ESPE) or bulk-fill (Tetric EvoCeram Bulk-fill, TCBF) composite using two incremental thicknesses: 2 mm or 4 mm (n = 10). After 24-h water storage, the restorations were sectioned. The first slice (0.7 mm thick) taken from a proximal surface was submitted to the Knoop hardness (KHN) test at five depths from the occlusal cavosurface to the pulpal line angle. Sticks were fabricated from the remaining sections and tested for dentin microtensile bond strength (µTBS). Means were analyzed using two-way ANOVA and Tukey's test (p < 0.05). Results: Higher (p < 0.05) µTBS resulted when both composites were restored with 2-mm increments, with no significant difference between materials (p > 0.05). Higher (p < 0.05) KHN means were found when 2-mm increments were used, with no significant differences (p > 0.05) between the materials. When the teeth were restored with one bulk increment (4 mm), the deeper layers presented lower KHN means (p < 0.05) starting at 2 mm for Z250 and 3 mm for TCBF. Conclusion: The 2-mm increment restorations in box-shaped cavities yielded higher µTBS and microhardness for conventional and bulk-fill composites. Keywords: bond strength, bulk-fill composites, hardness, restorative dental composites

Purpose: To examine the effect of mechanical fatigue on the bond strength of resin composite cemented to silica-coated yttria-tetragonal zirconia polycrystal ceramic (Y-TZP). Materials and Methods: Ten Y-TZP blocks were polished down to 600-grit silicon carbide paper. Specimens were silica coated by airborne-particle abrasion with 30-μm silica-modified Al2O3 particles. Blocks were cleaned in an ultrasonic bath, and a dental adhesive was applied and light cured for 20 s. Pre-cured composite blocks were luted to treated Y-TZP surfaces with a dual-curing resin cement. Half of the samples (n = 5) were subjected to mechanical fatigue before trimming (fatigue group) and the other half tested 24 h after bonding procedures (control group). Forty-five beam-shaped samples with an approximately 1 mm2 cross-sectional area were prepared for each group and tested in microtensile mode at 0.5 mm/min. Fractographic analysis was performed by optical and scanning electron microscopy. Only specimens that failed at the interface area were considered for statistical analysis. Weibull distribution (95% confidence bounds) was used to determine the characteristic strength (σ0 in MPa) and Weibull modulus (m) for each group. Probability of survival was calculated over the range of loads until specimens failed. Results: The control group showed σ0 = 45.91 MPa and m = 7.98, and the fatigue group σ0 = 43.94 MPa and m = 6.44 (p > 0.05). The probability of survival did not differ significantly between groups. Conclusions: Fatigue did not affect the bond strength between silica-treated Y-TZP intaglio surfaces and composite cement under these experimental conditions. Keywords: zirconia, silica coating, microtensile bond strength, mechanical fatigue, Weibull

Purpose: To investigate the bonding efficacy of a multimode adhesive to plasma-treated and -untreated (control) dentin using a mini-interfacial fracture toughness (mini-iFT) test. Materials and Methods: Twenty human molars were used in a split-tooth design (n = 10). The adhesive Scotchbond Universal (SBU; 3M ESPE) was applied in etch-and-rinse (E&R) and self-etch (SE) modes. Mid-coronal dentin was exposed and covered with a standardized smear layer ground to 320 grit. One half of each dentin surface received 15 s of non-thermal atmospheric plasma (NTAP), while the other half was covered with a metallic barrier and kept untreated. Following the E&R mode, dentin was plasma treated immediately after phosphoric acid etching. SBU and a resin-based composite were applied to dentin following the manufacturer's instructions. Six mini-iFT specimens were prepared per tooth (1.5 x 2.0 x 16 to 18 mm), and a single notch was prepared at the adhesive-dentin interface using a 150-μm diamond blade under water cooling. Half of the mini-iFT specimens were immediately loaded until failure in a 4-point bending test, while the other half were first stored in distilled water for 6 months. After testing, the exact dimensions of the notch were measured with a measuring optical microscope, from which ΚIc was determined. Results: Three-way ANOVA revealed higher mini-iFT for SBU applied in E&R than SE mode for both storage times, irrespective of NTAP treatment. Conclusion: Overall, mini-iFT did not decrease for any of the experimental groups upon 6-month aging, while plasma treatment did not show a direct beneficial effect on mini-iFT of SBU applied in either E&R or SE mode. Keywords: plasma, dentin, bonding, interface, multimode adhesive, fracture toughness

Purpose: To investigate the effect of a universal adhesive on the bond strength of composite cements to a polymer-infiltrated ceramic network. Materials and Methods: Shear bond strength to a polymer-infiltrated ceramic network (Vita Enamic) and to its polymer and ceramic components was assessed on polished surfaces using either a conventional dual-curing resin (RelyX Ultimate) or self-adhesive composite cement (RelyX Unicem 2 Automix). Substrate surfaces were either not pretreated or a silane coupling agent (Vitasil), a universal adhesive (Scotchbond Universal Adhesive), or both were applied. Further, the shear bond strength to polymer-infiltrated ceramic network was evaluated after etching with 5% hydrofluoric acid (Vita Ceramics Etch) of 0, 15, 30, 60 or 120 s without or with application of silane, universal adhesive, or both (n = 10). Statistical analysis was performed using the Kruskal-Wallis test (p < 0.05) followed by post-hoc comparisons with Bonferroni correction. Results: No bond (0 MPa) was formed to the polished polymer-infiltrated ceramic network or to its components for either cement. Application of silane resulted in low mean bond strengths (4 to 5 MPa) to the ceramic. The universal adhesive bonded mainly to the polymer part of the polymer-infiltrated ceramic network. The best bonding performance for both cements was achieved when silane and universal adhesive were applied on the polymer-infiltrated ceramic network. Etching for 30 s or 60 s resulted in the highest mean shear bond strengths for all pretreatment groups (p < 0.05). Conclusion: The best bonding performance of the self-adhesive dual-curing composite cement RelyX Unicem 2 Automix was found on the HF-etched polymer-infiltrated ceramic network. The conventional dual-curing composite cement RelyX Ultimate with Scotchbond Universal Adhesive may bond chemically to the polymer part of the polymer-infiltrated ceramic network. To achieve the highest bond strengths for both cements, the polymer-infiltrated ceramic network should be etched for 30 to 60 s, followed by the application of silane and universal adhesive. Keywords: shear bond strength, polymer-infiltrated ceramic, universal adhesive, silane, hydrofluoric acid etching

Purpose: To investigate the effects of room-temperature etching with hydrofluoric acid (HF) in the presence and absence of ultrasonic irradiation on the bonding of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) to resin. Materials and Methods: Y-TZP specimens were etched with 40% HF at room temperature for different time periods (2, 5, 10, 15, 30, 60, and 90 min) with and without ultrasonic exposure. The surface roughness, micromorphology, dimensions, and phases of the treated Y-TZP specimens were evaluated by atomic force microscopy (AFM), scanning electron microscopy (SEM), digital caliper measurement, and x-ray diffraction, respectively. The HF etching conditions that resulted in the most drastic Y-TZP surface morphology and highest roughness values were used to prepare specimens for shear bond strength (SBS) testing; the effect of thermocycling on SBS was also examined. Alumina-sandblasted Y-TZP specimens were used as the control. Results: The Y-TZP surfaces etched with HF without ultrasonic exposure for 30, 60, and 90 min and those surfaces ultrasonically etched with HF for 10 and 15 min were severely etched, although their dimensions were not changed by etching. Monoclinic-phase zirconia was observed only in the alumina-sandblasted Y-TZP specimens. Surface roughening from HF etching for 30 min and ultrasonic etching for 10 min resulted in higher mean SBS compared to roughening with alumina sandblasting. Conclusion: Ultrasonic etching with 40% HF at room temperature for 10 min may be used as an alternative roughening method for improving the bonding of Y-TZP. Keywords: hydrofluoric acid etching, surface roughening, adhesion, zirconia, bonding, ultrasonic exposure