The Journal of Adhesive Dentistry, 03/2012

Purpose: To evaluate the morphological changes in the acid-base resistant zone (ABRZ) at the resin/dentin interface after long-term storage in water. Materials and Methods: Two-step self-etching adhesive systems, Clearfil SE Bond (SE) and Clearfil Protect Bond (PB) (Kuraray Medical) were used. Human dentin disk sandwiches with resin composite were prepared, sectioned, and embedded in epoxy resin. The specimens were stored in water for 1 day, 1, 3 or 6 months, and then subjected to demineralizing solution and 5% NaOCl. The specimens were finally sectioned again, polished, argon-ion etched, and observed with SEM. Results: The outer lesion (OL) thickness at 1 day ranged from 10 to 15 µm but increased to approximately 30 µm after 6 months, suggesting gradual loss of dentin stored in water. A lower electron density was noted in the adhesives at the locations that were exposed to water. The ABRZs were observed clearly in all groups; the thickness of the ABRZ at the mid-point of the OL gradually decreased with time for SE. For PB, the thickness was stable up to 1 month, but decreased after 3 months. The bottom of the ABRZ in SE formed a right angle with dentin; in contrast, in PB, it sloped down toward dentin with a broadening bottom. Conclusions: Water storage resulted in changes both in the dentin substrate and the adhesive layer. An ABRZ was observed beneath the hybrid layer after long-term storage in water in both SE and PB. The ABRZ was thicker and relatively more stable in PB, probably due to fluoride release. Keywords: fluoride, acid-base resistant zone, recurrent caries, hybrid layer, self-etching adhesive system

Purpose: Using atomic force microscopy (AFM), the purpose was to investigate the effect of phosphoric acid (H3PO4) concentration and etching duration on surface roughness (Ra) and micromorphology of enamel and dentin substrates of uremic patients receiving hemodialysis. Materials and Methods: Sixty-three enamel and dentin slabs were prepared from 42 sound natural molars collected from uremic patients under hemodialysis and mechanically polished up to 4000-grit roughness. Nine slabs of each substrate were not etched (control group). The remaining slabs were divided into two experimental groups (n = 27) according to etchant concentration (37% or 42%). In each group, 9 specimens were etched for 15, 30, and 60 s. The surface morphology of the control and test specimens was examined by AFM operated in "contact" mode. The obtained Ra was subjected to statistical analysis. Results: Statistical analysis showed that increasing the duration of acid application (irrespective of acid concentration and type of substrate) significantly increased the amount of Ra. H3PO4 at a concentration of 42% was more effective at producing Ra than was H3PO4 at 37% for all 3 application times. The Ra quantity produced by H3PO4 at 42% was time specific, with 15 s being significantly less effective than 30 or 60 s. However, 60 s was significantly better than 30. Conclusion: The findings of this study support the use of 42% H3PO4 for etching uremic hard tooth tissues for 60 s. Keywords: uremia, etchant concentration, etching duration, enamel and dentin, surface roughness

Purpose: To examine the influence of operator experience level on shear bond strength (SBS) of a self-etching adhesive (Clearfil SE Bond [CSE], Kuraray) and an etch-and-rinse adhesive (Single Bond [SB], 3M ESPE). Materials and Methods: Flat dentin surfaces were created on 120 extracted human third molars. Bonding agents and composite resin were applied and light cured according to manufacturers' directions (n = 15). Four operators with different levels of experience in operative dentistry performed the same specimen preparation steps independently: group 1: specialist in operative dentistry; group 2: post-graduate student; group 3: undergraduate dental student; group 4: private general practitioner. Specimens were stored in distilled water for 24 h at 37°C before SBS testing. Statistical analyses were carried out with Mann-Whitney U- and Kruskall-Wallis tests. Results: For CSE, mean SBS and standard deviations were: (1) 54.4 ± 15.6a, (2) 55.3 ± 7.6a, (3) 49.4 ± 10.5ab, (4) 41.6 ± 13.1b. For SB, they were: (1) 28.6 ± 10.3c, (2) 32.7 ± 11.2c, (3) 17.5 ± 5.6d, (4) 24.4 ± 9.5cd. Groups with the same superscript letters are not significantly different. CSE showed higher bond strengths than SB in all groups (p 0.05). There was no significant difference in mean bond strengths between groups 1 and 2 for each adhesive (p > 0.05). Depending on the adhesives, groups 3 and 4 were significantly different from groups 1 and 2, but not different from each other. Conclusion: Operator experience influences dentin bond strength values of dentin adhesives. An increased level of experience with a specific adhesive system and the associated application procedures correlates with higher SBSs. Keywords: dentin bond strength, operator experience, etch-and-rinse, self-etching

Purpose: 1. To evaluate the effect of tooth age on the microtensile bond strengths (µTBS) of various adhesive systems to dentin; 2. To evaluate the effect of different etching times on the microtensile bond strengths of different adhesive systems to young vs mature dentin. Materials and Methods: One hundred twenty intact human teeth were mechanically ground to expose midcoronal dentin and were randomly assigned to three groups (n = 40) according to subjects' age in years: 15 to 25, 35 to 45, and >= 55. Within each group, specimens were further randomized into 8 subgroups according to adhesive (etch-and-rinse 3- and 2-step; self-etching 2- and 1-step) and etching time (manufacturer instructions vs extended). Resin composite was applied to the treated surfaces, and after 24 h, all specimens were processed for microtensile bond strength testing. Data were analyzed by factorial ANOVA and Tukey's test (p = 0.05). Results: µTBS values ranged from 10.9 MPa (2-step self-etching, extended etching time, age group 15 to 25) to 50.7 MPa (1-step self-etching, extended etching time, age group >= 55). With only one exception, tooth age and etching time had no significant effect on the bond strengths of the adhesives to dentin. The 2-step self-etching system had lower bond strengths than the other systems, regardless of etching time or tooth age. Conclusion: Tooth age and etching time did not affect the dentin bond strengths of the adhesives tested. Keywords: dentin bonding, dentin age, adhesive application time, etching time, microtensile test

Purpose: To evaluate the effects of increasing thermocycling regimens on bond strength and nanoleakage of an etch-and-rinse adhesive. Materials and Methods: Adper Single Bond (3M ESPE) was used for bonding resin composite to human enamel and dentin. Specimens were stored in water (37°C, 24 h) and subjected to thermocycling (5°C and 55°C) in five groups: 1. control (no thermal cycling), 2. 100, 3. 500, 4. 2000, or 5. 10,000 cycles. The microshear bond test was performed at a crosshead speed of 1 mm/min (n = 16). Nanoleakage specimens were immersed in silver nitrate and FE-SEM micrographs were digitally analyzed to calculate silver penetration in three samples. Results: The mean bond strength to enamel was not significantly affected by thermocycling. However, artificial aging decreased dentin bond strength in groups 4 and 5 compared to control. Weibull analysis indicated that the characteristic strength decreased gradually with aging in both substrates. All groups exhibited some nanoleakage, and a significant increase in silver penetration compared to the control was observed in enamel and dentin groups 2 to 5. Conclusion: A nanoleakage increase was detected in an earlier stage of aging than when a significant drop in bond strength was observed, with the dentin bond being more susceptible to deterioration. Keywords: dental adhesive, thermocycling, nanoleakage, bond strength

Purpose: The aim of this study was to compare microshear bond strength (µSBS) of different adhesives to normal dentin (ND) and caries-affected dentin (AD) as differentiated using the dye permeability test. Materials and Methods: One hundred freshly extracted carious teeth were ground to expose normal and cariesaffected dentin. Differentiation between both substrates was carried out using microhardness and a new dye permeability method. Ground teeth were divided into 5 groups according to the adhesive tested; Clearfil SE Bond (SE), Clearfil DC Bond (DC) (Kuraray), Bond Force (BF) (Tokuyama), AdheseOne (AH) (Ivoclar), Adper Prompt-L-pop (PR) (3M ESPE). Adhesives were applied to selected substrate, and composite cylinders (0.9 mm diameter x 0.7 mm length) were formed. After 24 h, specimens were subjected to microshear testing at a crosshead speed of 0.5 mm/min. Failure modes were determined using a stereomicroscope at 40X magnification. Data were analyzed using Kruskal-Wallis and Mann-Whitney U-tests. Results: Normal dentin was permeable for the dye, while caries-affected dentin was impermeable. Vickers hardness numbers (VHN) for normal and caries-affected dentin were 63.98 ± 3.24 and 62.40 ± 3.49 respectively, which were not significantly different (p > 0.05). µSBS values were: SE-ND = 22.34 ± 6.4, SE-AD = 18.70 ± 4.0, BF-ND = 24.52 ± 4.9, BF-AD = 18.31 ± 4.9, DC-ND = 24.49 ± 8.0, DC-AD = 18.97 ± 9.4, AH-ND = 17.21 ± 6.8, AH-AD = 17.03 ± 10.3, PR-ND = 13.67 ± 4.4, PR-AD = 7.31 ± 2.4 MPa. A statistically significant difference was found among the adhesive systems to both normal (p 0.01) and caries-affected dentin (p 0.001). However, µSBS of SE, DC, and AH adhesives to normal dentin were not significantly different from those of caries-affected dentin (p > 0.05). Conclusions: The permeability test was an effective tool to differentiate between normal and caries-affected dentin. Some adhesive systems showed no significant difference in their bond to normal or affected dentin. Keywords: microshear, adhesion, self-adhesives, caries-affected, dentin, staining of caries-affected dentin

Purpose: This study evaluated the effects of peripheral enamel margins on the long-term bond strength (µTBS) and nanoleakage in resin/dentin interfaces produced by self-adhesive and conventional resin cements. Materials and Methods: Five self-adhesive [RelyX-Unicem (UN), RelyX-U100 (UC), GCem (GC), Maxcem (MC), Set (SET)] and 2 conventional resin cements [RelyX-ARC(RX), Panavia F(PF)] were used. An additional group included the use of a two-step self-etching adhesive (SE Bond) with Panavia F (PS). One hundred ninety-two molars were assigned to 8 groups according to luting material. Five-mm-thick composite disks were cemented and assigned to 3 subgroups according to water-exposure condition (n = 6): 24-h peripheral exposure (24h-PE-enamel margins), or 1 year of peripheral (1yr-PE) or direct exposure (1yr-DE-dentin margin). Restored teeth were sectioned into beams and tested in tension at 1 mm/min. Data were analyzed by two-way ANOVA and Tukey's test. Two additional specimens in each group were prepared for nanoleakage evaluation. Nanoleakage patterns were observed under SEM/TEM. Results: Except for RX, no significant reduction in µTBS was observed between 24h-PE and 1yr-PE. 1yr-DE reduced µTBS for RX, PF, GC, MC, and SET. No significant reduction in µTBS was observed for PS, UC, and UN after 1 year. After 1yr-DE, RX and PS presented the highest µTBS, and SET and MC the lowest. Nanoleakage was reduced when there was a peripheral enamel margin. SET and MC presented more silver deposition than other groups. Conclusion: The presence of a peripheral enamel margin reduced the degradation rate in resin/dentin interfaces for most materials. The µTBS values produced by the multi-step luting agents RX and PS were significantly higher than those observed for self-adhesive cement. Keywords: self-adhesive cements, resin cements, TEM, SEM, nanoleakage, microtensile bond strength

Purpose: To evaluate both the immediate and water-stored repair tensile bond strength (TBS) of a nanohybrid resin composite using different bonding protocols. Materials and Methods: One hundred sixty half hourglass-shaped slabs were prepared. Eighty half-slabs were wet ground immediately after light curing using high-speed abrasive burs, while the other half-slabs were stored in water for one month (delayed) and then wet ground for repair. Each set of the 80 repaired slabs was split into two groups to be tested for TBS after 24 h or 1 month of water storage. For all repaired slabs, either immediate or delayed, four bonding procedures were used involving wet and dry bonding with a 3-step etch-and-rinse adhesive with or without silane pretreatment. TBS tests were performed at a crosshead speed of 0.5 mm/min. To determine the cohesive strength of the resin composite itself, which served as the reference, additional whole slabs were prepared and tested in tension after a 24-h (n = 10) and a 1-month storage period (n = 10). Failure modes were evaluated using a stereomicroscope at 40X magnification. Three-way ANOVA was run to test the effect of water storage, testing time, bonding protocols, and their interactions on the repair TBS, which was given as a percentage of the reference values. Results: For the immediate repair groups, the repair TBS ranged from 40% to 61.9% after 24-h storage and from 26% to 53.1% after 1-month water storage compared to the TBS of the whole slabs. For the delayed repair group, the repaired TBS ranged from 47.2% to 63.6% for the 24-h repairs and from 32.2% to 44.2% for the test groups stored in water for 1 month. Three-way ANOVA revealed that water storage had no significant effect on the repair TBS (p = 0.619). Both testing time and bonding protocols had a significant effect on the repair TBS (p = 0.001). The interactions between the independent variables (water storage, testing time, and bonding protocols) had no significant effect (p = 0.067). Conclusion: The repair bond strength was consistently and highly significantly less than the cohesive strength of the composite. A delay of 1 month before carrying out the repair had no effect on the bond strength, irrespective of the bonding procedure used. Silane treatment did not improve the repair bond strength. In all instances, except for the immediate wet bonding plus silane procedure and delayed dry bonding, the bond strength of the repairs significantly dropped after 1 month of storage in water. Keywords: nanohybrid composite, tensile bond strength, immediate and delayed repair

Purpose: To evaluate in vitro the effect of using a universal primer on the resin bond strength to ceramics (silicate and zirconia) and two noble alloys for metal-ceramic restorations. Materials and Methods: Disk-like specimens made of four dental restoration materials (silicate ceramic, zirconia ceramic, gold-based alloy and palladium-based alloy) were ground with abrasive paper, prepared for bonding (silicate ceramic: etching with 5% hydrofluoric acid for 60 s; the other materials: air abrasion with 50-µm Al2O3 at 2.5 bar) and ultrasonically cleaned in 96% isopropanol. Eight specimens of each material were primed with a universal primer, 8 specimens were primed with a well-established material-specific method (silicate ceramic: silanization; zirconia ceramic: phosphate monomer-containing primer; alloys: sulfuric monomer-containing primer). Plexiglas tubes filled with a composite resin were bonded to the specimens using an alignment apparatus and a composite luting resin. After storage in 37°C tap water for three days, or 167 days with additional thermocycling, tensile bond strength (TBS) was measured in a universal testing machine at a crosshead speed of 2 mm/min. Results: After 167 days of storage, median TBS values for each material were (well-established method/universal primer) 40 MPa/37 MPa (silicate ceramic), 41 MPa/41 MPa (zirconia ceramic), 20 MPa/17 MPa (gold-based alloy), and 20 MPa/19 MPa (palladium-based alloy). Statistical analysis revealed no statistically significant differences among control groups and test groups. Conclusion: The universal primer seems to be a promising alternative compared to using three different primers for alloys, silicate and zirconia ceramics. Keywords: tensile bond strength, primer, zirconia ceramic, alloys, silicate ceramic

Purpose: To evaluate the effects of acidic functional monomers on the bond strength and durability of an acrylic resin joined to Ti-6Al-7Nb alloy and component metals. Materials and Methods: Disk specimens of two different sizes (10 and 8 mm in diameter and 2.5 mm in thickness) were prepared from uncast Ti-6Al-7Nb alloy, titanium, aluminum, and niobium. The specimens were ground with abrasive paper and divided into 8 groups: unprimed control, primed with Acryl Bond, Alloy Primer, All Bond II Primer B, Estenia Opaque Primer, M.L. Primer, MR. Bond, and Super-Bond Liquid. The disks were bonded with tri-n-butylborane (TBB)-initiated acrylic resin, and shear bond strengths were determined both before and after thermocycling. Results: The Alloy Primer and Estenia Opaque Primer agents, which contain a hydrophobic phosphate monomer (MDP), and Super-Bond Liquid demonstrated a durable bond with Ti-6Al-7Nb alloy. MDP was also effective in bonding Ti, Al, and Nb. Conclusion: The two primers containing MDP were effective for treating Ti-6Al-7Nb alloy and Ti. Al and Nb showed bonding behavior similar to Ti-6Al-7Nb alloy and Ti when the two metals were treated with acidic primers and bonded with the TBB-initiated acrylic resin. Keywords: niobium, phosphate, Ti-6Al-7Nb alloy, titanium