The Journal of Adhesive Dentistry, 03/2014

Purpose: While it has been shown that no method produces specimens with exactly the same cross-sectional bonded area (BA), BA variations within and between studies are a well-known covariate in microtensile test results. However, no method has yet been described to accurately account for its influence. A procedure is presented that allows controlling for variations of BA effects on results. Further, a proposal for reporting is presented which enables results of different studies to be compared. Materials and Methods: Partially using the results of the report in which the microtensile test was originally described, 144 both general (caused by differences in BA) and specific (due to a material's performance differences and intrinsic biological variability of specimens) variabilities were separated through linear regression of microtensile (MPa) to BA (mm2) pooled results. Comparing the specific variability of specimens - the residuals to the regression line - of groups allowed assessing differences between groups. Results: A means comparison of residuals showed that specific differences were significant (t-test, p = 0.0004). The null hypothesis could be rejected: materials' performances were different. This could not be determined in the original report, since BA variability was very high. A proposal for reporting of results to facilitate their clinical interpretation and comparison between studies is presented. Conclusion: Controlling for general variability caused by differences in BA size allows precise comparison of microtensile tests results. Keywords: microtensile bond strength, bonded area, dental adhesion, dentin, enamel

Purpose: To evaluate the mechanical and physical properties of experimental HEMA-containing and HEMA-free resin adhesives. Materials and Methods: Experimental HEMA-free adhesives containing alternative dimethacrylates (bis-EMA 10 [B10], bis-EMA 30 [B30], PEG 400 [P400], PEG 1000 [P1000], PEG 400 UDMA [UP400]) were formulated and compared with a HEMA-containing adhesive (control). The adhesives were characterized by rheological analysis, polymerization kinetics (PK), water sorption (WS), and solubility (SL) tests. Flexural strength (FS) and flexural modulus (E) tests were performed under dry or wet conditions (distilled water or 70% ethanol solution). One-way and two-way ANOVA as well as Tukey's test were used to evaluate differences between groups (p 0.05). Results: The control group showed the lowest viscosity and was the only one with a degree of conversion lower than 50%. The control and the P1000 adhesive showed the statistically significantly highest WS (p 0.05). The control and the UP400 adhesive showed the highest FS and E, and the dry-stored specimens showed more improved mechanical strength than did the wet-stored specimens (p 0.05). Conclusion: The physicomechanical properties of some of the HEMA-free adhesives were substantially improved when compared with those of the control, indicating that they could be potential monomers for the development of HEMA-free adhesive systems. Keywords: dental adhesives, HEMA, hydrophilicity, cross linking, FTIR, mechanical properties

Purpose: This study evaluated the effects of light exposure times on water sorption, solubility, and polymer cross-linking density of simplified etch-and-rinse adhesives. Materials and Methods: Four commercial adhesives (XP Bond, Adper Single Bond 2, Tetric N-Bond, and Ambar) were selected, and resin disks 5 mm in diameter and 1.0 mm thick were prepared and light cured for 20, 40, or 80 s using an LED light-curing unit at 1200 mW/cm2. Water sorption and solubility were evaluated over a 28-day period. For polymer cross-linking density, additional specimens were prepared and their Knoop hardness measured before and after immersion in 100% ethanol. The data from each test were evaluated using a two-way ANOVA and Tukey's test (α = 0.05). Results: The XP Bond adhesive showed higher water sorption (similar to Adper Single Bond 2) and solubility (p 0.05) than did the other materials. Prolonged exposure times did not reduce the water sorption but did reduce the solubility of all tested materials (p 0.05). For Ambar, the increase in the exposure time resulted in a significantly lower percent reduction in hardness. Conclusion: Water sorption, solubility, and cross-linking density of the materials selected in this study seem to be mainly influenced by the adhesive composition. Prolonged light exposure times reduced the solubility of the materials. Keywords: adhesives systems, water sorption, solubility, polymerization time

Purpose: To evaluate the influence of shortening the etching time on the bond degradation of one etch-and-rinse and one two-step self-etching adhesive system to sound (SD) and caries-affected (CAD) dentin of deciduous teeth. Materials and Methods: Flat dentin surfaces from 48 deciduous molars were assigned to 8 groups according to substrate (SD and CAD, pH cycling for 14 days), adhesive system (Adper Single Bond 2 [SB] and Clearfil SE Bond [CSEB]), and etching time (recommended by manufacturers and half the recommended etching time). Composite buildups were constructed and sectioned to obtain bonded sticks (0.8 mm2) to be subjected to microtensile testing immediately or after 12 months of water aging. Two sticks from each tooth at each time were immersed in silver nitrate solution to qualitatively assess nanoleakage. The microtensile bond strength (μTBS) values of each adhesive were submitted to three-way repeated measures ANOVA and Tukey's post-hoc tests (α = 0.05). Results: The etching time influenced the bond strength only for SB. The highest μTBS values and lowest silver nitrate uptake were observed when half the recommended acid-etching time was used, regardless of substrate. Water storage for 12 months reduced bond strengths, except to CSEB bonded to SD. The μTBS values obtained for CAD were lower than for SD, irrespective of adhesive system. Nanoleakage was more pronounced in CAD. Conclusion: The effect of shortening the etching time is material dependent and results in better bond stability for sound and caries-affected dentin of deciduous teeth when an etch-and-rinse adhesive system is employed. Keywords: deciduous teeth, caries-affected dentin, etching time, microtensile testing, nanoleakage, deterioration

Purpose: To compare microtensile bond strength (μTBS) and interfacial morphology of a new one-step multimode adhesive with a two-step self-etching adhesive and two etch-and-rinse adhesives systems on enamel. Materials and Methods: Thirty human third molars were sectioned to obtain two enamel fragments. For μTBS, 48 enamel surfaces were ground using 600-grit SiC paper and randomly assigned into 6 groups (n = 8): nonetched Scotchbond Universal [SBU]; etched SBU [SBU-et]; non-etched Clearfil SE Bond [CSE]; etched CSE [CSE-et]; Scotchbond Multi-Purpose [SBMP]; Excite [EX]. The etched specimens were conditioned with 37% phosphoric acid for 30 s, each adhesive system was applied according to manufacturers' instructions, and composite resin blocks (Filtek Supreme Plus, 3M ESPE) were incrementally built up. Specimens were sectioned into beams with a cross-sectional area of 0.8-mm2 and tested under tension (1 mm/min). The data were analyzed with oneway ANOVA and Fisher's PLSD (α = 0.05). For interface analysis, two samples from each group were embedded in epoxy resin, polished, and then observed using scanning electron microscopy (SEM). Results: The μTBS values (in MPa) and the standard deviations were: SBU = 27.4 (8.5); SBU-et = 33.6 (9.3); CSE = 28.5 (8.3); CSE-et = 34.2 (9.0); SBMP = 30.4 (11.0); EX = 23.3 (8.2). CSE-et and SBU-et presented the highest bond strength values, followed by SBMP, CSE, and SBU which did not differ significantly from each other. EX showed the statistically significantly lowest bond strength values. SEM images of interfaces from etched samples showed long adhesive-resin tags penetrating into demineralized enamel. Conclusions: Preliminary etching of enamel significantly increased bond strength for the new one-step multimode adhesive SBU and two-step self-etching adhesive CSE. Keywords: self-etching adhesive, etch-and-rinse adhesive, phosphoric acid, interface, functional monomer, scanning electron microscopy

Purpose: To compare the mean shear bond strength (SBS) and failure mode of a resin-modified glass-ionomer luting cement (RM-GIC) to five different metals using unsupported and supported cement specimens with different placement of the shear load. Materials and Methods: A RM-GIC was bonded to five metals using "unsupported" and "supported" techniques at a SBS-specimen diameter of 2.36 mm. The bond was stressed to failure using shear knife and wire loop debonding protocols. For the shear knife method, the distance of the shear force from the interface was 0 mm or 0.3 mm. Failure analysis was assessed by stereomicroscope and SEM. Results: Two-way ANOVA and post-hoc Tukey's test revealed a significant difference between the unsupported and supported mean SBS. The SBS of supported specimens, where the shear force was applied to the mold that enclosed the specimens, were in most cases statistically significantly higher (p 0.05) than specimens that were not supported. The mean bond strengths of RM-GIC ranged from 4.5 ± 2.3 MPa to 27.4 ± 3.7 MPa. Analysis of the failure mode showed significant differences (p 0.001) for the test methods except for adhesion to gold-based metal. The adhesive failure mode was between 91% and 97% for supported specimens and between 47% and 63% for unsupported specimens. Conclusion: Within the limits of this study, supported specimens exhibited higher mean SBS than unsupported specimens. The method of debonding had a significant effect on the mean SBS for RM-GIC bonded to metal. Mold-supported specimens had a higher incidence of adhesive failure than unsupported cement specimens. Keywords: shear bond strength, adhesive, resin-modified glass ionomer, metal

Purpose: To evaluate the shear bond strength (SBS) to zirconia ceramics using different associations of primers and resin cements. Materials and Methods: Two blocks of LAVA zirconia (3Y-TZP) were randomly submitted to an application of three different commercially available primers: Alloy Primer (AP), Z-Prime Plus (ZP), and Signum Zirconia Bond (SZB). Nonprimed specimens were considered controls. After treatment, the 80 specimens (5 mm × 5 mm × 2 mm) were randomly cemented with one of the resin cements: Panavia F, Multilink, seT, and NX3. For cementation, cylinders of resin cement were built on the ceramic surfaces using the SDI SBS apparatus. The specimens were submitted to the SBS test. Fractured surfaces were observed under stereomicroscopy to determine the failure mode, and mean bond strength values were analyzed using the Kruskal-Wallis and Mann-Whitney tests (α = 0.05). Results: Signum Zirconia Bond had the highest SBS compared to all other primers and the control group, regardless of the resin cement used. The highest values were obtained when associating Panavia F with Signum Zirconia Bond. Alloy Primer increased bonding values when associated with seT cement only. When no primer was used, no statistical difference was observed among resin cements. All specimens fractured due to adhesive failure. Conclusion: Signum Zirconia Bond is capable of increasing bonding values of resin cements to zirconia ceramics. Its association with Panavia F shows enhanced results when considering short-term adhesion to zirconia. Keywords: primers, resin cement, shear bond strength, zirconia

Purpose: To evaluate the fracture resistance (FR) and bond strength (BS) after mechanical fatigue (MF) of flared root canals restored with different restorative techniques for fiber post cementation. Materials and Methods: The root canals of 84 single-rooted premolars were endodontically treated and prepared in order to simulate an oversized root canal, except for the positive control group (PC), in which a prefabricated fiber post (PFP) with a diameter compatible with the post cavity was cemented. In the oversized root canals, alternative restorative techniques for post cementation were tested, as follows: NC: negative control (PFP with a diameter smaller than that of the root canal); AP: PFP + accessory posts; RR: root reinforcement with composite resin; DAP: direct anatomical post; IAP: indirect anatomical post. After the luting procedures using Excite DSC and Variolink II, indirect composite crowns were cemented on composite resin cores and the specimens were mechanically fatigued (1.2 x 106 cycles, 40 N). From each group, 8 specimens were subjected to the push-out BS test and the others 6 specimens to the FR test. For both tests, the data were subjected to ANOVA and Scheffe's tests (α = 0.05). Results: In terms of FR, all alternative techniques showed intermediate performance, being similar to both control groups. In terms of BS, only the groups DAP and IAP were similar to the well-adapted condition (positive control group). Conclusion: The use of DAP and IAP should be the first choice for fiber post cementation in oversized root canals. Keywords: bond strength, fiber posts, fracture resistance, resin cements, root dentin, weakened roots

Purpose: To evaluate the effect of QMix and other conventional endodontic irrigants on the micropush-out bond strength of Biodentine (BD) and white mineral trioxide aggregate (WMTA). Materials and Methods: One hundred eighty midroot dentin slices with a thickness of 1.0 mm were prepared. BD and WMTA were placed inside the lumens of the root slices (n = 90). Then the specimens of each material were divided into 6 groups (n = 15) according to irrigation solution (saline, 5.25% NaOCl, 2% CHX, 17% EDTA, or QMix) immersed in the same for 30 min. For the control group, a wet cotton pellet was placed over the specimen. After that, the micropush-out bond strength was determined using a universal testing machine, and the bond failure mode was determined using a stereomicroscope. The morphological microstructures of specimens were evaluated with scanning electron microscopy (SEM). Data were analyzed using ANOVA and Tukey's post-hoc test. Results: BD revealed higher bond strength than WMTA (p 0.05). WMTA was significantly affected after exposure to 2% CHX solution. QMix irrigant did not compromise the bond strength of BD or WMTA. Most failures for BD were cohesive, while for WMTA, adhesive failures were the predominant type. A substantial change in the microstructure of BD and WMTA occurred after exposure to different irrigation solutions. Conclusions: QMix did not affect the bond strength of BD or WMTA. BD showed higher resistance than WMTA to dislodgement forces from root dentin. Keywords: Biodentine, white mineral trioxide aggregate, micropush-out, perforation repair, QMix

Purpose: To evaluate and compare the 3-year clinical performance of a silorane-based composite with that of a methacrylate-based composite in Class II restorations. Materials and Methods: Seventy-eight patients, each with two class II restorations under occlusion, were enrolled in this study. One hundred fifty-six restorations were placed, 50% for each material: a silorane-based composite, Filtek P90/ P90 System Adhesive and a methacrylate-based resin composite, Quixfil/ Prime &Bond NT. A single operator placed all restorations according to the manufacturers' instructions. Immediately after placement, the restorations were finished/polished. Clinical evaluation was performed at baseline and at yearly intervals after placement by two other independent examiners using slightly modified USPHS criteria. The changes in the USPHS parameters during the three-year period were analyzed with the Friedman test. The baseline scores were compared with those at the recall visits using the Wilcoxon signed rank test. The level of significance was set at p 0.05. Results: All restorations were evaluated at 3 years. Post-operative sensitivity was observed in 6 patients (2 Filtek P90, 4 Quixfil) between 1 and 3 weeks. Seven failed restorations (4.5%) were observed during the follow up: 4 in the Filtek P90 (5.1%) and 3 in the Quixfil group (3.8%). This resulted in non-significantly different annual failure rates of 1.7% and 1.2%, respectively. Fracture of restoration was the main reason for failure. Conclusion: After 3 years, no significant difference was seen in overall clinical effectiveness between the silorane- based and methacrylate-based composite restorative systems. Keywords: silorane composite, methacrylate composite, posterior restorations, clinical performance