Abstract
Objective
This study evaluated the effects of surface preparation and the application time of adhesives on the resin–dentine bond strengths with universal adhesives.
Methods
Sixty molars were cut to exposed mid-coronal dentine and divided into 12 groups ( n = 5) based on three factors; (1) adhesive: G-Premio Bond (GP, GC Corp., Tokyo, Japan), Clearfil Universal Bond (CU, Kuraray Noritake Dental Inc., Okayama, Japan) and Scotchbond Universal Adhesive (SB, 3M ESPE, St. Paul, MN, USA); (2) smear layer preparation: SiC paper ground dentine or bur-cut dentine; (3) application time: shortened time or as manufacturer’s instruction. Fifteen resin–dentine sticks per group were processed for microtensile bond strength test (μTBS) according to non-trimming technique (1 mm 2 ) after storage in distilled water (37 °C) for 24 h. Data were analyzed by three-way ANOVA and Dunnett T3 tests ( α = 0.05). Fractured surfaces were observed under scanning electron microscope (SEM). Another 12 teeth were prepared and cut into slices for SEM examination of bonded interfaces.
Results
μTBS were higher when bonded to SiC-ground dentine according to manufacturer’s instruction. Bonding to bur-cut dentine resulted in significantly lower μTBS ( p < 0.000). Shortening the application time resulted in significantly lower bond strength for CU on SiC and GP on bur-cut dentine. SEM of fractured surfaces revealed areas with a large amount of porosities at the adhesive resin interface. This was more pronounced when adhesives were bonded with a reduced application time and on bur cut dentine.
Clinical significance
The performance of universal adhesives can be compromised on bur cut dentine and when applied with a reduced application time.
1
Introduction
All-in-one self-etching adhesives have become popular in dentistry because of their advantages such as less technique sensitivity and user-friendliness . However, there are still concerns about the effectiveness of 1-step adhesives when bonding to uncut enamel , to different smear layer preparation and their long-term durability .
Recently, universal adhesives have been introduced to the market. They are principle 1-step self-etching adhesives that can be applied in either self-etching mode or etch-and-rinse mode . Similar to the mildly acidic self-etching adhesives, there are concerns regarding the effect of smear layer on their bonding performance . Most of the studies that have evaluated the effect of smear layer preparation on the bond strength of adhesives used only different SiC-paper grits, which can be regarded as not clinically relevant . Furthermore, the study from Oliveira et al. reported that the loosely organized smear layer produced by SiC papers was easier for self-etching primer to penetrate when compared to those of diamond burs.
To overcome the infiltration-impairing effect of smear layer, prolonged application time has been suggested as an option to increase bond strength . Although, the bond strength improvement might be system-specific . However, contrary to the suggestive findings referred above, the newly developed product from GC Corp., G-Premio Bond claims that high bond strength can be achieved even when applied with shortened application time (optional manufacturer’s instructions). Although shorter application time may be clinically appealing, the procedure may carry negative consequences to adhesive infiltration and solvent evaporation. Since one product has adopted such optional reduced application time, it becomes interesting to test if such approach can also be applied to other adhesives; and whether the type of smear layer plays a role on the adhesive effectiveness at different application times.
Therefore, the aim of this study was to evaluate the effects of adhesive application time and dentine surface preparation on resin–dentine microtensile bond strength (μTBS) of three universal adhesives. The null hypotheses tested were that (1) there is no effect of application time and, (2) there is no effect of surface preparation on the bond strength.
2
Materials and methods
2.1
Tooth selection and preparation
Seventy-two extracted non-carious human third molars were used in this study. They were stored in an aqueous solution of 0.5% chloramine-T at 4 °C and used within 6 months after extraction. The teeth were collected under a protocol reviewed and approved by the university ethical committee (#2013-7). The teeth were abraded to expose mid-coronal dentine with a gypsum model trimmer under water coolant. A light microscope was used to confirm that no enamel remained on the dentine surface.
2.2
Adhesives and bonding procedures
The teeth were randomly assigned into 12 experimental conditions ( n = 5 to μTBS; n = 1 to interfacial structure observation) according to: dentine surface preparation (SiC-prepared dentine vs bur-cut dentine) and adhesive application time (manufacturer’s instruction vs shortened). These variables were tested for three adhesive systems: G-Premio Bond [GP, GC Corp., Tokyo, Japan], Clearfil Universal Bond [CU, Kuraray Noritake Dental Inc., Okayama, Japan], and Scotchbond Universal Adhesive [SB, 3M ESPE, St. Paul, MN, USA]. Details of the variables and products can be found in Table 1 .
| Adhesive (batch number) | pH a | Composition | Manufacturers’ instruction |
|---|---|---|---|
| Clearfil Universal Bond (000002) |
2.3 | 10-MDP, Bis-GMA, HEMA, ethanol, hydrophilic aliphatic dimethacrylate, colloidal silica, dl-camphorquinone, silane coupling agent and water | 1. Apply the adhesive to the dentine surface with the applicator brush and rub it in for 10 s |
| 2. Dry the dentine surface sufficientlyby blowing mild air for more than 5 s until the adhesive does not move | |||
| 3. Light cure for 10 s | |||
| G-Premio Bond b (1411061G) |
1.5 | 10-MDP, 4-META, 10-methacryoyloxydecyl dihydrogen thiophosphate, methacrylate adic ester, distilled water, acetone, photo initiators, silica fine powder | 1. Apply using a microbrush |
| 2. Leave undisturbed for 10 s after application | |||
| 3. Dry thoroughly for 5 s with oil free air under maximumair pressure | |||
| 4. Light cure for 10 s | |||
| Scotchbond Universal (572054) |
2.7 | 10-MDP, HEMA, silane, dimethacrylate resins, Vitrebond™ copolymer, filler, ethanol, water, initiators | 1. Apply the adhesive on the surface and rub it in for 20 s |
| 2. Gently air-dry theadhesive for approximately 5 s for the solvent to evaporate | |||
| 3. Light cure for 10 s |
a The pH for SB and CU was obtained from Ref. . For GP it was informed by the manufacturer.
b The shortened application time is an optional application mode suggested by the manufacturer.
Occlusal dentine surfaces were prepared by using either 600-grit SiC paper (Sankyo-Rikagaku Co., Saitama, Japan) or tapered regular grit diamond bur (diamond point FG, #103R, Shofu, Kyoto, Japan). For SiC paper preparation, the surfaces were manually polished for 60 s under running water using a 600-grit SiC paper. In case of diamond bur, dentine surfaces were ground with the bur in a high-speed handpiece with copious water spray for 5 light-pressure strokes per tooth in order to make a uniform surface. For each surface preparation, half of the teeth received the adhesives applied according to manufacturer’s instruction, and the other half received the adhesives applied under the shortened time. Each adhesive was dropped directly from the bottle on dentine, air dried immediately and then light cured. Two 2mm-thick layers of resin composite (Clearfil AP-X, Kuraray Noritake Dental Inc., Tokyo, Japan) were built-up on the bonded surface. Each layer was light cured for 20 s operating using a light curing device (Optilux 401, Demetron/Kerr, Orange, CA, USA) at ≥550 mW/cm 2 .
2.3
Microtensile bond strength (μTBS) test
After storage in 37 °C water for 24 h, each bonded tooth was sectioned into beams (cross-sectional area approximately 1 mm 2 ) using an Isomet diamond saw (Isomet 1000, Buehler, Lake Bluff, Illinois, USA). For each tooth ( n = 5), three beams from the central area were randomly selected for μTBS, therefore resulting in a total of 15 beams to be tested. The remainder of the beams was stored for longer-term testing. The beams were fixed to a Ciucchi’s jig with cyanoacrylate glue (Model Repair 2 Blue, Dentsply-Sankin, Otahara, Japan) and subjected to a tensile force at a crosshead speed of 1 mm/min in a desktop testing apparatus (EZ test, Shimadzu, Kyoto, Japan). μTBS was expressed in MPa, and data were analyzed by three-way ANOVA and Dunnett T3 tests ( α = 0.05).
2.4
Fracture mode analysis
The fractured specimens were mounted on an aluminum stub, then coated with Pt-Pd for 150 s. The fracture modes were determined using a scanning electron microscope (SEM, S-4000, Hitachi, Tokyo, Japan) at an accelerating voltage of 10 kV. Surfaces were examined at lower magnification to categorize the mode of fractured and specific features were further examined at 3000× and 10,000×. Fracture mode categories were classified into four groups : A, adhesive failure; CD, cohesive failure within dentine; CC, cohesive failure within composite resin; or M, mixed failure.
2.5
Interfacial structure observation
One tooth per group was bonded in the same way as described for μTBS test. The teeth were cut parallel to the long axis into slabs. Two slabs from central part were selected and prepared for SEM observation by following a protocol described by Ting et al. . All slabs were serially polished with the series of SiC papers and diamond pastes. After that, treated with 5% HCl for 30s followed by NaOCl for 5 min. Then, the slabs were left to air dry for 24 h. Finally, they were sputter-coated with Pt-Pd for 150 s and then examined at 3000× magnification.
2
Materials and methods
2.1
Tooth selection and preparation
Seventy-two extracted non-carious human third molars were used in this study. They were stored in an aqueous solution of 0.5% chloramine-T at 4 °C and used within 6 months after extraction. The teeth were collected under a protocol reviewed and approved by the university ethical committee (#2013-7). The teeth were abraded to expose mid-coronal dentine with a gypsum model trimmer under water coolant. A light microscope was used to confirm that no enamel remained on the dentine surface.
2.2
Adhesives and bonding procedures
The teeth were randomly assigned into 12 experimental conditions ( n = 5 to μTBS; n = 1 to interfacial structure observation) according to: dentine surface preparation (SiC-prepared dentine vs bur-cut dentine) and adhesive application time (manufacturer’s instruction vs shortened). These variables were tested for three adhesive systems: G-Premio Bond [GP, GC Corp., Tokyo, Japan], Clearfil Universal Bond [CU, Kuraray Noritake Dental Inc., Okayama, Japan], and Scotchbond Universal Adhesive [SB, 3M ESPE, St. Paul, MN, USA]. Details of the variables and products can be found in Table 1 .
| Adhesive (batch number) | pH a | Composition | Manufacturers’ instruction |
|---|---|---|---|
| Clearfil Universal Bond (000002) |
2.3 | 10-MDP, Bis-GMA, HEMA, ethanol, hydrophilic aliphatic dimethacrylate, colloidal silica, dl-camphorquinone, silane coupling agent and water | 1. Apply the adhesive to the dentine surface with the applicator brush and rub it in for 10 s |
| 2. Dry the dentine surface sufficientlyby blowing mild air for more than 5 s until the adhesive does not move | |||
| 3. Light cure for 10 s | |||
| G-Premio Bond b (1411061G) |
1.5 | 10-MDP, 4-META, 10-methacryoyloxydecyl dihydrogen thiophosphate, methacrylate adic ester, distilled water, acetone, photo initiators, silica fine powder | 1. Apply using a microbrush |
| 2. Leave undisturbed for 10 s after application | |||
| 3. Dry thoroughly for 5 s with oil free air under maximumair pressure | |||
| 4. Light cure for 10 s | |||
| Scotchbond Universal (572054) |
2.7 | 10-MDP, HEMA, silane, dimethacrylate resins, Vitrebond™ copolymer, filler, ethanol, water, initiators | 1. Apply the adhesive on the surface and rub it in for 20 s |
| 2. Gently air-dry theadhesive for approximately 5 s for the solvent to evaporate | |||
| 3. Light cure for 10 s |
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