The Journal of Adhesive Dentistry, 03/2011

Purpose: Single-step self-etching adhesives have been developed as a bonding material that adheres to the tooth surface. The adhesives contain acidic resin monomers that penetrate the dentin but can be neutralized to stop the reaction. This study aimed to improve understanding of the pH changes that occur when self-etching adhesives are mixed with dentin powder. Materials and Methods: Dentin disks obtained from extracted bovine incisors were milled and pulverized into a fine powder. The powder was mixed with diluted self-etching adhesives, and pH changes were measured by a solid-state pH sensor connected to a pH meter at various time points after the start of mixing. Data were analyzed by Tukey's Honestly Significant Difference (HSD) test and Dunnett's test at a significance level of 0.05. Precipitates from the adhesive/ dentin powder mixture were observed by scanning electron microscopy (SEM). Results: The baseline pH values of the self-etching adhesives ranged from 0.97 to 2.83. After mixing with the dentin powder, the pH values significantly increased, ranging from 6.30 to 7.11 at 180 s after mixing. SEM observation revealed products of the reaction between dentin powder and self-etching adhesive which indicate a chemical reaction between the functional monomer and dentin. Conclusion: Dentin has a strong modulation effect against the acidity of self-etching adhesives. Keywords: dentin, functional monomer, pH, self-etching adhesive, insoluble precipitate

Purpose: To evaluate the influence of NaOCl irrigation and water storage on the degradation and microstructure of the resin/dentin interface of primary teeth bonded with three different adhesive systems using the microtensile bond strength test (µTBS) and scanning electron microscopy (SEM). Materials and Methods: Ninety sound primary molars were used. Eighteen groups were formed according to different adhesive systems (Adper Single Bond 2, SB; Clearfil Protect Bond, CP; Adper Prompt L-Pop, APL) with or without 0.5% NaOCl irrigation and water-storage time (24 h, 45 days, 90 days). The middle dentin was exposed. In the NaOCl group, NaOCl irrigation was performed for 30 min, and all groups were restored with composite (Charisma). Sticks with a 1-mm2 cross-sectional area were prepared for the µTBS test. The data were analyzed by ANOVA and Tukey's test (p 0.05). The failure modes, presence or absence of resin tags, and the resin/ dentin interface were evaluated by SEM, and data were analyzed using Cochran-Mantel-Haenszel statistics (p 0.05). Results: The µTBS of APL was significantly lower than the other groups regardless of treatment and storage time. A significant decrease of µTBS values after 90 days of water storage occurred only in the non-NaOCl irrigation groups. After 90 days of storage, resin tags partially disappeared in APL and CP, and in SB, 100% of the resin tags remained. Conclusion: The choice of adhesive system is one of the factors when bonding to primary dentin is considered. In this study, the etch-and-rinse and the two-bottle self-etching adhesive system produced the highest µTBS values irrespective of prior NaOCl irrigation even up to 90 days of water storage. Keywords: microtensile bond strength, NaOCl irrigation, adhesive systems, long-term bonding degradation, primary teeth

Purpose: This study evaluated the effect of cutting initiation location and cutting speed on the bond strength between resin cement and feldspathic ceramic. Materials and Methods: Thirty-six blocks (6.4 x 6.4 x 4.8 mm) of ceramic (Vita VM7) were produced. The ceramic surfaces were etched with 10% hydrofluoric acid gel for 60 s and then silanized. Each ceramic block was placed in a silicon mold with the treated surface exposed. A resin cement (Variolink II) was injected into the mold over the treated surface and polymerized. The resin cement-ceramic blocks were divided into two groups according to experimental conditions: a) cutting initiation location - resin cement, ceramic and interface; and b) cutting speed - 10,000, 15,000, and 20,000 rpm. The specimens were sectioned to achieve non-trimmed bar specimens. The microtensile test was performed in a universal testing machine (1 mm/min). The failure modes were examined using an optical light microscope and SEM. Bond strength results were analyzed using one-way ANOVA and Tukey's test (α = 0.05). Results: Significant influences of cutting speed and initiation location on bond strength (p 0.05) were observed. The highest mean was achieved for specimens cut at 15,000 rpm at the interface (15.12 ± 5.36MPa). The lowest means were obtained for specimens cut at the highest cutting speed in resin cement (8.50 ± 3.27MPa), and cut at the lowest cutting speed in ceramic (8.60 ± 2.65MPa). All groups showed mainly mixed failure (75% to 100%). Conclusion: The cutting speed and initiation location are important factors that should be considered during specimen preparation for microtensile bond strength testing, as both may influence the bond strength results. Keywords: microtensile bond strength test, cutting speed, ceramic

Purpose: The use of bovine teeth as a substitute for human enamel has been proposed for dental studies. The aim of this study was to determine the shear bond strength and Adhesive Remnant Index (ARI) of deciduous and permanent bovine teeth. Materials and Methods: Twenty deciduous and 20 permanent extracted bovine teeth were embedded in resin blocks. Stainless steel conventional orthodontic brackets were bonded to the teeth using an orthodontic adhesive. All samples were tested in shear mode on a testing machine. ARI scores were then recorded. Statistical analysis was performed to determine significant differences in bond strength and ARI scores. Results: The bond strength of permanent bovine teeth was significantly higher (p = 0.0010) than that of the deciduous teeth. ARI scores showed no significant differences (p = 0.74). Conclusion: Deciduous teeth show lower shear bond strength than permanent teeth. Keywords: deciduous bovine teeth, permanent bovine teeth, shear bond strength

Purpose: This study evaluated the efficacy of the union between two new self-etching self-adhesive resin cements and enamel using the microtensile bond strength test. Materials and Methods: Buccal enamel of 80 bovine teeth was submitted to finishing and polishing with metallographic paper to a refinement of #600, in order to obtain a 5-mm2 flat area. Blocks (2 x 4 x 4 mm) of laboratory composite resin were cemented to enamel according to different protocols: (1) untreated enamel + RelyX Unicem cement (RX group); (2) untreated enamel + Bifix SE cement (BF group); (3) enamel acid etching and application of resin adhesive Single Bond + RelyX Unicem (RXA group); (4) enamel acid etching and application of resin adhesive Solobond M + Bifix SE (BFA group). After 7 days of storage in distillated water at 37°C, the blocks were sectioned for obtaining microbar specimens with an adhesive area of 1 mm2 (n = 120). Specimens were submitted to the microtensile bond strength test at a crosshead speed of 0.5 mm/min. The results (in MPa) were analyzed statistically by ANOVA and Tukey's test. Results: Enamel pre-treatment with phosphoric acid and resin adhesive (27.9 and 30.3 for RXA and BFA groups) significantly improved (p = 0.05) the adhesion of both cements to enamel compared to the union achieved with as-polished enamel (9.9 and 6.0 for RX and BF). Conclusion: Enamel pre-treatment with acid etching and the application of resin adhesive significantly improved the bond efficacy of both luting agents compared to the union achieved with as-polished enamel. Keywords: enamel, acid etching, adhesives, luting agents, tensile bond strength

Purpose: This study evaluated the effect of prolonged polymerization times on the microtensile resin-dentin bond strength (µTBS), degree of conversion of adhesive films (DC) and silver nitrate uptake (SNU) for an ethanol/water- (Adper Single Bond 2, [SB]) and an acetone-based (One Step Plus, [OS]) etch-and-rinse adhesive. Materials and Methods: Thirty caries-free extracted molars were included in this study. The occlusal enamel of all teeth was removed by wet grinding the occlusal enamel on 180-grit SiC paper. Adhesives were applied according to the manufacturer's instructions, but they were light cured for 10, 20 and 40 s at 600mW/cm2. Bonded sticks (0.6 mm2) were tested in tension (0.5 mm/min). Two bonded sticks from each tooth were immersed in an ammoniacal solution of silver nitrate (24 h), photodeveloped (8 h), and analyzed by SEM. The DC of the adhesives was evaluated under Fourier Transformed Infra-Red spectroscopy (FTIR). Data for each property were analyzed by two-way ANOVA and Tukey's test (α = 0.05). Results: Statistically higher µTBS and DC were observed for SB and OS when both adhesives were light cured for 40 s in comparison with 10 s. For OS, the µTBS in the 20- and 40-s groups did not differ statistically, while for SB it did. Higher prolonged exposure times did not prevent nanoleakage within the hybrid layer for all groups regardless of the adhesive. Conclusion: This study supports the hypothesis that exposure times longer than those recommended can improve the degree of conversion of adhesive films and the immediate resin-dentin bonds. The prolonged curing times (20 and 40 s) for polymerization of simplified adhesives resulted in an increase in the degree of conversion of the adhesive films and resin-dentin bond strengths but did not reduce the nanoleakage within the hybrid layer. Keywords: dentin adhesives, bond strength, degree of conversion, exposure time

Purpose: To evaluate the hydrolytic stability of three one-step self-etching adhesives (1-SEAs) bonded to dentin through bond strength testing and ultra-morphological interfacial analysis before and after long-term thermocycling. Materials and Methods: Eighteen flattened mid-coronal dentin surfaces of extracted human molars were subjected to bonding treatment using three 1-SEAs (Clearfil S3 Bond, Kuraray (S3), G-Bond, GC (GB), Absolute, Dentsply-Sankin (AB)), after which the bonded surfaces were built up with composite. After storage overnight at 37°C, the specimens were sectioned into slabs and further trimmed into an hourglass shape with an interface area of approximately 1 mm2. The specimens were left untouched (control) or were thermocycled for 100,000 cycles. The microtensile bond strength (µTBS) was measured and the ultrastructure of the adhesive/dentin interface characterized using transmission electron microscopy (TEM). Results: Long-term thermocycling significantly decreased the µTBS of all one-step adhesives tested (p 0.05, oneway ANOVA and Games-Howell test). TEM revealed a similar interfacial ultrastructure before and after thermocycling for S3. For GB, many voids were observed at the interface after 100,000 thermocycles. Regarding AB, collagen fibrils could no longer be clearly observed upon staining, while the adjacent unaffected dentin was rich in voids. Conclusion: The bond strength and ultramorphological data demonstrated that the bond of 1-SEAs to dentin degrades with time, although the degree of degradation is obviously material dependent. Keywords: one-step self-etching adhesives, bonding effectiveness, thermal cycles, dentin

Purpose: To evaluate interface degradation leading to marginal microleakeage in Class II restorations that had received an application of surface sealant at the tooth/restoration interface or not. Materials and Methods: Eighty bovine incisors were used, and the teeth were split obliquely, 10 mm from the amelodentinal proximal junction, and finished with water abrasive papers to obtain a smooth, flat incisal surface. Cavities were made to simulate Class II preparations (8 mm high, 4 mm wide and 1.5 mm deep), and the restorations were performed with a composite resin. Teeth were then randomly allocated into 8 groups according to the surface sealant (none, Fortify, Single Bond 2, or Scothbond MP Plus) and aging process (none or thermocycling and storage for 6 months). Microleakage was then evaluated using a dye penetration method immediately after the restoration or after aging. The samples were triturated and assessed by spectrophotometer. Results: Microleakage was statistically similar in all groups when assessed immediately after the restorative procedure. After aging, teeth sealed with Fortify presented better results than the other groups. Conclusion: Aging causes interface degradation and increased microleakage. Surface sealant can reduce these effects and decrease microleakage in Class II restorations. Keywords: composite resin, surface sealants, microleakage, degradation

Purpose: Selective infiltration etching is a newly developed surface treatment used to modify the surface of zirconiabased materials, rendering it ready for bonding with resin cements. The aim of this study was to evaluate zirconia/resin bond strength and durability using the new technique. Materials and Methods: Zirconia disks received one of the following surface treatments: selective infiltration etching or airborne-particle abrasion with 50-µm aluminum oxide particles, while as-sintered surfaces served as control. The zirconia disks were bonded to pre-aged composite resin disks using a light-polymerized adhesive resin (Panavia F 2.0). Zirconia resin bond strength was evaluated using the microtensile bond strength test (MTBS) and the test was repeated after each of the following intervals of accelerated artificial aging: thermocycling (10,000 cycles between 5°C and 55°C), 4 weeks, 26 weeks, 52 weeks, and 104 weeks of water storage (37°C ). A repeated measures ANOVA and Bonferroni post-hoc tests were used to analyze the data (n = 18, α = 0.05). Results: There were significant differences in the MTBS values between the three test groups at each of the test intervals (p 0.001). After 2 years of artificial aging, all specimens of the control group demonstrated spontaneous failure, while significant reduction in the bond strength of the particle-abraded groups was observed (21.3 MPa). The bond strength of the selective infiltration etched group was relatively stable (44.1 MPa) after completion of artificial aging. Conclusion: Within the limitations of this study, micromechanical retention and adhesion promoters are prerequisites for establishing a strong and durable bond to zirconia-based materials. Keywords: selective infiltration etching, zirconia resin bond, MTBS

Purpose: To evaluate the bond strength of indirect restorations to dentin using self-adhesive cements with and without the application of adhesive systems. Material and Methods: Seventy-two bovine incisors were used, in which the buccal surfaces were ground down to expose an area of dentin measuring a minimum of 4 x 4 mm. The indirect resin composite Resilab was used to make 72 blocks, which were cemented onto the dentin surface of the teeth and divided into 4 groups (n = 18): group 1: self-adhesive resin cement BiFix SE, applied according to manufacturer's recommendations; group 2: self-adhesive resin cement RelyX Unicem, used according to manufacturer's recommendations; group 3: etch-and-rinse Solobond M adhesive system + BiFix SE; group 4: etch-and-rinse Single Bond 2 adhesive system + RelyX Unicem. The specimens were sectioned into sticks and subjected to microtensile testing in a universal testing machine (EMIC DL- 200MF). Data were subjected to one-way ANOVA and Tukey's test (α = 5%). Results: The mean values (± standard deviation) obtained for the groups were: group 1: 15.28 (± 8.17)a, group 2: 14.60 (± 5.21)a, group 3: 39.20 (± 9.98)c, group 4: 27.59 (± 6.57)b. Different letters indicate significant differences (ANOVA; p = 0.0000). Conclusion: The application of adhesive systems before self-adhesive cements significantly increased the bond strength to dentin. In group 2, RelyX Unicem associated with the adhesive system Single Bond 2 showed significantly lower mean tensile bond strengths than group 3 (BiFix SE associated with the etch-and-rinse Solobond M adhesive system). Keywords: dentin, strength, self-adhesive cements

Purpose: To investigate the influence of cyclic impact load and the number of load cycles on compressive shear bond strength under the three different cements. Materials and Methods: The following materials were used: Super Bond C&B (SB) and Panavia Fluoro Cement (PF) as adhesive resin cements, Fuji Luting (FL) as a resin-modified glass-ionomer cement, and zirconium dioxide ceramics as adherend. Before the shear bond test, three different impact loading conditions (compressive direction, shear direction, and no impact) and the number of load cycles (1 to 106 cycles), were performed. A total of 189 specimens (n = 3/group) were randomly assigned to groups and tested. A cyclic impact test was performed by applying a load of 98N at a distance of 40 mm and a loading cycle frequency of 1 Hz. All results were statistically analyzed with two-way ANOVA and Tukey's multiple comparison test. Results: Shear bond strengths of SB, PF, and FL subjected to no cyclic impact load were 21.6 to 53.8 MPa in SB, 27.0 to 63.6 MPa in PF, and 20.0 to 35.9 MPa in FL. The shear bond strength of SB and PF increased to a certain degree from one to 105 cycles, while FL did likewise from one to 104 cycles. Conclusion: The shear bond strengths of SB, PF, and FL were greatest without cyclic impact, followed by compressive and then shear cyclic impact. Keywords: zirconium dioxide, shear bond strength, cyclic impact load, adhesive cement, fatigue, prosthetic dentistry

Purpose: To determine, by means of a non-destructive experimental procedure, the effectiveness of adhesive restorations in reducing the cuspal deflection of endodontically treated premolars, with or without root canal fiber posts. Materials and Methods: The cuspal deflection of ten sound, intact maxillary premolars was evaluated. A loading device induced deformation by axial force (ranging from 98 to 294 N) applied on the occlusal surface of teeth while laser sensors registered the amount of deflection. Once tested, teeth were endodontically treated and the marginal ridges were removed. The teeth were randomly divided into two groups and restored with: group 1) dual curing adhesive, flowable composite, and microhybrid composite; group 2) the same materials associated with root canal glass fiber post and composite cement. The cuspal deflection test was repeated with the same protocol after restorative procedures, allowing a direct comparison of the same samples. Statistical analysis was performed using ANOVA at a significance level of 0.05. Results: Different average cuspal deflection was detected in the two groups: composite resin with post insertion resulted in lower deformation compared with composite alone. Mean deflection ranged from 3.43 to 12.17 µm in intact teeth, from 14.42 to 26.93 µm in group 1, and from 15.35 to 20.39 µm in group 2. ANOVA found significant differences (p = 0.02). Conclusion: Bonded composite restorations with fiber posts may be more effective than composite alone in reducing the cuspal deflection in endodontically treated premolars in which the marginal ridges have been lost. Keywords: fiber post, cuspal deflection, resin-based composite (RBC) restoration

Purpose: To test in vitro the shear bond strength of resin teeth to an acrylic resin denture base given different ridgelap surface treatments. Materials and Methods: Ninety rectangular dies were made with wax and traditionally invested in metallic or plastic flasks. The stone molds were covered with silicone, in which were included an acrylic molar with a wax stick fixed on the ridge lap surface. After deflasking, the wax sticks were removed, the teeth were cleaned with detergent, the ridge lap surface was submitted to different treatments (unmodified, bur-cut grooves, aluminum oxide particle sandblasting, monomer swelling, and primer swelling), and the teeth were replaced in the silicone molds. Metallic flasks were placed in a thermopolymerizing unit to polymerize heat-curing denture-base polymer, and plastic flasks were placed in a domestic microwave oven at 900 W to polymerize microwaveable denture base polymer. After deflasking, the specimens were submitted to the shear bond test in an Instron machine at a cross-speed of 1 mm/min. Results were submitted to ANOVA and Tukey's test (5%). Results: Shear bond strength values were influenced by the ridge-lap surface treatments only in the microwaved polymer. Sandblasting + monomer swelling and sandblasting + primer swelling interactions yielded lower strengths for microwaved polymer. Only the unmodified surfaces presented a significant difference when the resins were compared, where the microwaved polymer showed a higher value. Conclusion: Different tooth ridge-lap surface treatments promoted different strengths of the tooth/resin bond. Keywords: adhesive treatment, ridge lap surface, denture base, shear bond strength