Abstract
Objectives
To evaluate the influence of different air-blowing durations on the micro-tensile bond strength (μTBS) of five current one-step adhesive systems to dentin.
Methods
One hundred and five caries-free human molars and five current one-step adhesive systems were used: ABU (All Bond Universal, Bisco, Inc.), CUB (CLEARFIL™ Universal Bond, Kuraray), GPB (G-Premio BOND, GC), OBA (OptiBond All-in-one, Kerr) and SBU (Scotchbond Universal, 3M ESPE). The adhesives were applied to 600 SiC paper-flat dentin surfaces according to each manufacturer’s instructions and were air-dried with standard, oil-free air pressure of 0.25 MPa for either 0 s, 5 s, 15 s or 30 s before light-curing. Bond strength to dentin was determined by using μTBS test after 24 h of water storage. The fracture pattern on the dentin surface was analyzed by SEM. The resin–dentin interface of untested specimens was visualized by panoramic SEM image. Data from μTBS were analyzed using two-way ANOVA (adhesive vs. air-blowing time), and Games-Howell (a = 0.05).
Results
Two-way ANOVA revealed a significant effect of materials (p = 0.000) and air-blowing time (p = 0.000) on bond strength to dentin. The interaction between factors was also significantly different (p = 0.000). Maximum bond strength for each system were recorded, OBA/15 s (76.34 ± 19.15 MPa), SBU/15 s (75.18 ± 12.83 MPa), CUB/15 s (68.23 ± 16.36 MPa), GPB/30 s (55.82 ± 12.99 MPa) and ABU/15 s (44.75 ± 8.95 MPa). The maximum bond strength of OBA and SUB were significantly higher than that of GPB and ABU (p < 0.05).
Significance
The bond strength of the current one-step adhesive systems is material-dependent (p = 0.000), and was influenced by air-blowing duration (p = 0.000). For the current one-step adhesive systems, higher bond strengths could be achieved with prolonged air-blowing duration between 15–30 s.
1
Introduction
One step self-etching systems, so-called ‘all-in-one’ system, have been initially advocated about 15 years ago . They became increasingly popular and widely accepted for their distinguishing features; such as, handling convenience, time-saving and user-friendly properties . However, it has been reported that the bond strength of 1-step self-etching systems is lower than that of 2-step and 3-step systems . It appears that the simplified procedures of 1-step self-etching systems did not reduce the technique sensitivity of all-in-one systems, especially considering the air-blowing step .
Adhesive technology is continuously evolving by frequent replacement of commercial adhesive formulations . Currently, as a new branch of 1-step self-etching system, the so-called ‘Universal System’ or ‘Multi-purpose System’ has become commercially available and regains attention from dental clinicians as ‘the eighth generation’ system . These latest systems could not only be used in direct and indirect treatments following manufacturer’s instruction , but also seem to be adequate after short-term clinical evaluation and medium-term clinical evaluation . Taken together the mentioned advantages, universal systems might be a potential brand-new choice for the dentists in daily operative treatment.
In some of the current commercially available universal systems , 10-MDP is included as functional monomer, which has been mainly used as an etching monomer and proven very successful in promoting chemical adhesion to tooth tissue . In previous studies, there were not so many 10-MDP containing 1-step self-etching systems included , because 10-MDP was originally synthesized and patented by Kuraray (Osaka, Japan) and hence was not widely available in the dental market .
Currently, an increased number of new systems, the so called ‘eighth generation’ adhesive system, have a common feature that they are prone to select 10-MDP as their functional monomer, but differ on application procedures, such as: coating manner, waiting time and air-blowing pressure. To ensure the ideal bonding performance could be achieved, detailed information on direction should not be overlooked. In previous studies, it was investigated that bond strength could be influenced by both of air-blowing duration and pressure , because the information on applying process was indefinite in some 1-step self-etching systems’ instruction.
Based on different chemical compositions, universal systems required differently on application process. So far, the influence of different air-blowing durations on bond strength of universal systems has barely been investigated. The aim of this study was to evaluate the influence of different air-blowing durations on μTBS of current one-step adhesive systems. The null hypothesis tested in the present study was that the bonding performance of current one-step adhesive systems is not affected by air-blowing duration.
2
Materials and methods
2.1
Teeth used
One hundred extracted caries-free human molars were used in this study to test 5 different current one-step adhesive systems. Each set consists of 20 teeth, which were further divided into 4 groups with 5 teeth in each. The teeth were collected under a protocol reviewed and approved by the institutional review board of China Medical University, Shenyang, China. The teeth were stored at 4 °C in an aqueous solution of 0.5% Chloramine-T and used within 3 months after extraction. Flat dentin surfaces were obtained by removing the coronal enamel of each tooth in a gypsum model trimmer with water coolant, leaving the surrounding enamel. After that, the dentin surfaces were ground with 600-grit SiC paper for 60 s under continuous water-cooling to produce a standardized smear layer prior to bonding.
2.2
Adhesives
Five commercially available current one-step adhesive systems were applied in this experiment: ABU (All Bond Universal, Bisco, Inc.), CUB (CLEARFIL™ Universal Bond, Kuraray), GPB (G-Premio BOND, GC), OBA (OptiBond All-in-one, Kerr) and SBU (Scotchbond Universal, 3M ESPE). Table 1 shows the chemical compositions and the respective manufacturer’s instructions for application of these 5 adhesives. Among these systems, only OBA does not contain 10-MDP, OBA was selected as a control group from former all-in-one systems. The adhesive procedures in the present study, except for the air-blowing duration, followed the respective manufacturer’s application guide. Dentin surface in the 4 subgroups consisting of 5 teeth per adhesive were air-blown for either 0 s, 5 s, 15 s, or 30 s, respectively, before light-curing. The maximum air-blowing pressure was adjusted to be 0.25 MPa, and the air syringe head was positioned vertically to the dentin surface at a distance of 15 mm. All systems selected in the present study were applied only as one-step self-etch materials. The same operator performed all steps.
| Materials & lot no. | Chemical formulation & pH | Manufactures’ instruction |
|---|---|---|
| All Bond Universal | 10-MDP, Bis-GMA, HEMA, ethanol, water, initiators. | 1. Dispense 1–2 drops of bond into a clean well. |
| Lot no. 1300008729 (Bisco, Inc.) | pH = 3.2 | 2. Apply two separate coats of bond, scrubbing the preparation with a micro-brush for 10–15 s per coat. Do not light cure between coats. |
| 3. Evaporate excess solvent by thoroughly air-drying with an air syringe for at least 10s, there should be no visible movement of the adhesive. | ||
| 4. Light cure for 10 s. | ||
| CLEARFIL Universal Bond | 10-MDP, Bis-GMA, HEMA, ethanol, water, Silane coupling agent, fillers, Initiators. | 1. Dispense the bond into a dispensing dish |
| Lot no. 1L0003 (Kuraray) | pH = 2.3 | 2. Apply bond to the dentin surface and rub it in for 10 s. |
| 3. Dry the dentin surface sufficiently by blowing mild air for more than 5 s until bond does not move. | ||
| 4. Light cure for 10 s. | ||
| G-Premio BOND | 10-MDP, Acetone, dimethacrylate component, photoinitiator, butylated hydroxytoluene. | 1. Prior to dispensing, shake the bottle of G-Premio BOND thoroughly. Dispense a few drops into a clean dispensing dish. |
| Lot no. 1411061G (GC) | pH = 1.5 | 2. Immediately apply to the prepared enamel and dentin surfaces using the disposable applicator. |
| 3. Leave undisturbed for 10 s after the end of application. | ||
| 4. Dry thoroughly for 5 seconds with oil free air under maximum air pressure. | ||
| 5. Light-cure for 10 s | ||
| OptiBond All-in-one | GPDM, mono and dysfunctional methacrylate monomers, water, acetone, ethanol, CQ, filler sodium hexafluorosilicates and ytterbium fluoride. | 1. Shake bottle briefly |
| Lot no. 5538778 (Kerr) | pH = 2.5 | 2. Dispense 2–3 drops into a clean well. |
| 3. Apply the adhesive on dentin with applicator brush and scrub the surface for 20 s. | ||
| 4. Repeat Step3 again. | ||
| 5. Dry the adhesive with gentle air first and then medium air for at least 5 s with oil-free air. | ||
| 6. Light cure for 10 s. | ||
| Scotchbond Universal | 10-MDP, HEMA, ethanol, water, dimethacrylate resins, methacrylate-modified polyalkenoic acid copolymer, polyacrylic acid copolymer, silane, fillers, initiators. | 1. Apply the adhesive to the prepared tooth and rub it in for 20 s. |
| Lot no. 572054 (3M ESPE) | pH = 2.7 | 2. Gently air dry the adhesive for approximately 5 s to evaporate the solvent. |
| 3. Light cure for 10 s. | ||
All bonded surfaces were built-up with resin composite (Clearfil AP-X, Kuraray Medical Inc.; Okayama Japan, Shade A3, Lots: BH0052) in increments to a thickness of 5 mm. Each incremental layer was light cured (PENCURE 2000, J. MORITA MFG. CROP) for 20 s, the light output intensity was properly controlled to be more than 2000 mW/cm 2 . The bonded teeth were stored in distilled water at 37 °C for 24 h.
2.3
Micro-tensile 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 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 calculated by division of the applied force (N) at the time of fracture by the bonded area (mm 2 ), and data were analyzed by two-way ANOVA and Tukey’s test (a = 0.05).
2.4
Failure mode analysis
The fractured specimens were mounted on an aluminum stub, then coated with Pt–Pd for 120 s. The fracture modes were determined using a scanning electron microscope (SEM, S-4000, Hitachi, Tokyo, Japan) at an accelerating voltage of 10 kV. Fractured and specific features on dentin surfaces were further examined at lower magnification of 3000× . Fracture mode categories were classified into three groups: A: cohesive failure within dentin or composite resin; B: adhesive failure; C: failure at dentin or resin.
2.5
Panoramic SEM observation of the resin–dentin interface
In order to investigate the typical morphology of the resin–dentin interface of each system, 5 additional resin-bonded specimens from maximum bond strength group of each system were sectioned perpendicularly to the adhesive interface with an Isomet saw to obtain two slabs of 2 mm thickness. The sectioned surfaces were sequentially polished with 600-, 800-, and 1000-grit silicon carbide papers under running water. This was followed by polishing sequentially with 6-, 3-, 1-μm diamond pastes (DP-Paste, Struers, Denmark), and by cleaning with an ultrasonic device after each diamond paste polish. After polishing, the specimens were immersed in 1 M hydrochloric acid for 30 s and 5% sodium hypochlorite for 5 min, followed by rinsing with water. After naturally drying in the laboratory over night, the specimens were sputter-coated with Pt–Pd for 120 s. The resin–dentin interfaces were then analyzed in a scanning electron microscope (SEM, S-4000, Hitachi, Tokyo, Japan). Panoramic SEM images were seamlessly connected by Adobe Photoshop CS4 (Version:11.0.27) from three independent sequential photographs from each resin-adhesive-dentin interface.
2
Materials and methods
2.1
Teeth used
One hundred extracted caries-free human molars were used in this study to test 5 different current one-step adhesive systems. Each set consists of 20 teeth, which were further divided into 4 groups with 5 teeth in each. The teeth were collected under a protocol reviewed and approved by the institutional review board of China Medical University, Shenyang, China. The teeth were stored at 4 °C in an aqueous solution of 0.5% Chloramine-T and used within 3 months after extraction. Flat dentin surfaces were obtained by removing the coronal enamel of each tooth in a gypsum model trimmer with water coolant, leaving the surrounding enamel. After that, the dentin surfaces were ground with 600-grit SiC paper for 60 s under continuous water-cooling to produce a standardized smear layer prior to bonding.
2.2
Adhesives
Five commercially available current one-step adhesive systems were applied in this experiment: ABU (All Bond Universal, Bisco, Inc.), CUB (CLEARFIL™ Universal Bond, Kuraray), GPB (G-Premio BOND, GC), OBA (OptiBond All-in-one, Kerr) and SBU (Scotchbond Universal, 3M ESPE). Table 1 shows the chemical compositions and the respective manufacturer’s instructions for application of these 5 adhesives. Among these systems, only OBA does not contain 10-MDP, OBA was selected as a control group from former all-in-one systems. The adhesive procedures in the present study, except for the air-blowing duration, followed the respective manufacturer’s application guide. Dentin surface in the 4 subgroups consisting of 5 teeth per adhesive were air-blown for either 0 s, 5 s, 15 s, or 30 s, respectively, before light-curing. The maximum air-blowing pressure was adjusted to be 0.25 MPa, and the air syringe head was positioned vertically to the dentin surface at a distance of 15 mm. All systems selected in the present study were applied only as one-step self-etch materials. The same operator performed all steps.
