Abstract
Objectives
This study aims to determine dentin bonding durability of universal adhesives using shear bond strength (SBS) tests under various degradation conditions.
Methods
G-Premio Bond (GP, GC), Scotchbond Universal (SU, 3 M ESPE) and All Bond Universal (AB, Bisco) were compared with conventional two-step self-etch adhesive Clearfil SE Bond (SE, Kuraray Noritake Dental). Bonded specimens were divided into three groups of ten, and SBSs with bovine dentin were determined after the following treatments: 1) Storage in distilled water at 37 °C for 24 h followed by 3000, 10,000, 20,000 or 30,000 thermal cycles (TC group), 2) Storage in distilled water at 37 °C for 3 months, 6 months or 1 year (water storage, WS group) and 3) Storage in distilled water at 37 °C for 24 h (control).
Results
SE bonded specimens showed significantly higher SBSs than universal adhesives, regardless of TC or storage periods, although AB specimens showed significantly increased SBSs after 30,000 thermal cycles. In comparisons of universal adhesives under control and degradation conditions, SBS was only reduced in SU after 1 year of WS.
Conclusion
Following exposure of various adhesive systems to degradation conditions of thermal cycling and long term storage, SBS values of adhesive systems varied primarily with degradation period.
Clinical significance
Although universal adhesives have lower SBSs than the two-step self-etch adhesive SE, the present data indicate that the dentin bonding durability of universal adhesives in self-etch mode is sufficient for clinical use.
1
Introduction
In order to assure the long-term stability of resin composite restorations, fillers, resin matrices, initiators of resin composite formation and various other adhesive technologies have been developed . However, degradation of the bond remains inevitable due to biofilm attack, hydrolytic degradation of adhesives, enzymatic degradation by matrix metalloproteinases and adhesive fatigue . Therefore, determinations of the durability of resin composite restorations under intraoral conditions are critical for clinical application.
Bonding performances of resin restorations have been investigated in long-term clinical trials . However, the reported procedures were time-consuming and costly, and case selection, consistency of operators and examiners and numbers of patients are difficult to standardize. In contrast, simulated oral environment testing can be used to rapidly determine relative bonding durability of materials. Specifically, in vitro degradation of restored teeth can be simulated in long-term water storage and thermal cycling experiments, allowing standardization of conditions before and after storage, and assessing degradation using bond strength tests allows easy comparison .
Recently, developments of single-step self-etch adhesives have led to widespread clinical use. The most recently developed self-etch adhesives are referred to as ‘universal’ or ‘multi-mode’ because they can be used with various adherent substrates, including enamel, dentin, metal alloy and ceramics. . Moreover, universal adhesive systems can be applied following phosphoric acid pre-etching using total-etch, selective-etch and self-etch approaches. In addition, in vitro investigations of universal adhesives indicate that initial bonding performances to enamel and dentin without phosphoric acid pre-etching are of similar quality to those of single-step self-etch adhesives. Furthermore, the total-etch approach for universal adhesives increases bond performance with enamel without affecting dentin bonding . However, limited information is available on bond durability of universal adhesives and their reliability remains unclear.
The purpose of this study was to determine the dentin bonding durability of universal adhesives following simulated in vitro degradation. The null hypotheses to be tested were: (1) the dentin bonding durability of universal adhesive would not differ from that of a conventional two-step self-etch adhesive; and (2) different simulated degradation methods would not influence bond strength results.
2
Materials and methods
2.1
Study materials
Adhesive materials ( Table 1 ) included the three universal adhesives G-Premio Bond (GP, GC Corp., Tokyo, Japan), Scotchbond Universal (SU, 3M ESPE, St Paul, MN, USA) and All Bond Universal (AB, Bisco, Schaumburg, IL, USA). The conventional two-step self-etch adhesive Clearfil SE Bond (SE, Kuraray Noritake Dental, Tokyo, Japan) was used as a control. Clearfil AP-X (Kuraray Noritake Dental, Tokyo, Japan) was used as a restorative material for bonding to dentin.
| Code | Adhesive (Lot No.) | Main Components | Manufacturer |
|---|---|---|---|
| SU | Scotchbond Universal (41256) | MDP, HEMA, dimethacrylate resins, Vitrebond copolymer, filler, ethanol, water, initiators, silane | 3M ESPE St. Paul, MN, USA |
| GP | G-Premio Bond (1501221) | MDP, 4-MET, MEPS, BHT, acetone,dimethacrylate resins, initiators,water | GC Corp Tokyo, Japan |
| AB | All-Bond Universal (1300008503) | MDP, bis-GMA, HEMA, ethanol, water, initiators | Bisco Inc. Schaumburg, IL, USA |
| SE | Clearfil SE Bond (011613) | Primer: MDP, HEMA, water, initiators Bond: MDP, HEMA, bis-GMA, initiators, microfiller | Kuraray Noritake Dental Tokyo, Japan |
| – | |||
| Resin composite | |||
| Clearfil AP-X (CC0043) |
bis-GMA, TEGDMA,silane barium glass filler, silane silica filler, silanated colloidal silica catalysts, accelerators, CQ, pigments, others | Kuraray Noritake Dental | |
| Filler Load: 84.5% weight | |||
2.2
Specimen preparation
Mandibular bovine incisors were extracted from 2 to 3 year old cattle and were stored frozen for up to 2 weeks for use as human teeth. As a large number of samples were necessary, bovine dentin was used instead of human dentin. Previous research shows that this has little influence on the results . Approximately two-thirds of the apical root structure of each tooth was removed using a diamond impregnated disk with a slow-speed saw (Isomet Low Speed Saw, Buehler, Lake Bluff, IL, USA). Pulp tissues were then removed and labial surfaces were ground with wet 240-grit silicon carbide (SiC) paper (Fuji Star Type DDC, Sankyo Rikagaku Co. Ltd., Saitama, Japan) to create flat dentin surfaces. Teeth were then mounted in self-curing acrylic resin (Tray Resin II, Shofu Inc., Kyoto, Japan) so that the flattened areas were exposed, and temperature rises due to exothermic polymerization reactions of the acrylic resin were moderated by placing specimens under running tap water. Dentin bonding surfaces were next ground flat using a water coolant and a sequence of SiC papers ending with 320-grit (Fuji Star Type DDC), and the dentin surfaces were finally dried with oil-free compressed air.
2.3
Storage conditions and shear bond strength tests
The experimental protocols for the bonding procedures are shown in Table 2 . Ten specimens, each taken from a different tooth, were used. In total three hundred and twenty bovine teeth were used. Adhesives were applied to dentinsurfaces in accordance with the respective manufacturer’s instructions, and specimens were then clamped in an Ultradent Bonding Jig (Ultradent Products Inc., South Jordan, UT, USA) with plastic molds of 2.38-mm internal diameter and 2.0-mm height . Subsequently, resin composites were placed into the mold and were light irradiated for 30 s using a visible-light curing unit (Optilux 501, sds Kerr, Danbry, CT, USA) set at a light irradiance average of 600 mW/cm 2 .
| Adhesive. | Adhesive application protocol. |
|---|---|
| SU | Adhesive was applied to air-dried dentin surfaces with a rubbing action for 20 s, and then medium air pressure was applied to surfaces for 5 s. Light irradiation was then applied for 10 s. |
| GP | Adhesive was applied to air-dried dentin surfaces for 10 s. A strong stream of air was then applied over the liquid adhesive for 5 s or until the adhesive no longer moved and the solvent had completely evaporated. Light irradiation was then applied for 10 s. |
| AB | Adhesive was applied to dentin surfaces with rubbing action for 10–15 s per coat without light curing between coats. A gentle stream of air was then applied over the liquid for at least 10 s. Light irradiation was applied for 10 s. |
| SE | Primer was applied to air-dried dentin surfaces for 20 s followed by medium air pressure to surfaces for 5s. Adhesive was then applied to primed surfaces and was air thinned for 5 s. Light irradiation was applied for 10 s. |
Specimens were subjected to thermal cycling (TC group) or storage in distilled water at 37 °C (water storage, WS group). Bonded specimens of the TC group were stored in distilled water at 37 °C for 24 h and were then treated with 3000, 10,000, 20,000 or 30,000 thermal cycles (TCs) between 5 and 60 °C with a dwell time of 30 s. Specimens of the WS group were stored in distilled water at 37 °C for 3 months, 6 months or 1 year before the shear bond strength (SBS) tests. The storage water was changed weekly, antibiotics were not used. Control specimens were stored in distilled water at 37 °C for 24 h before the SBS tests (control group).
SBSs were determined according to ISO 29022 . Briefly, specimens were loaded to failure at 1.0 mm/min using a universal testing machine (Type 5500R, Instron Corp., Canton, MA, USA), and SBS Values (MPa) obtained. After testing, bonded tooth surfaces and resin composite cylinders were observed under an optical microscope (SZH-131, Olympus Ltd., Tokyo, Japan) at a magnification of ×10, and bond failures were recorded as 1) adhesive failure, 2) cohesive failure in composite, 3) cohesive failure in dentin, or 4) mixed failure .
2.4
Scanning electron microscopy (SEM) observations
Interfaces between restoratives and dentin and representative fracture sites after SBS tests were observed using field-emission electron scanning microscopy (SEM, ERA-8800FE, Elionix Ltd., Tokyo, Japan). Prior to ultrastructure observations of restorative–dentin interfaces, bonded specimens were embedded in epoxy resin (Epon 812, Nisshin EM, Tokyo, Japan) and were then longitudinally sectioned using a diamond saw (Isomet Low Speed Saw). Sectioned surfaces were then polished to a high gloss using abrasive discs (Fuji Star Type DDC, Sankyo Rikagaku Co. Ltd, Saitama, Japan) followed by a series of diamond pastes down to particle sizes of 0.25 μm (DP-Paste, Struers, Ballerup, Denmark). Fracture sites from each storage condition were prepared directly for scanning electron microscopy (SEM), and SEM specimens were then dehydrated in ascending grades of tert-butyl alcoholand were next then transferred to a critical-point dryer (Model ID-3, Elionix, Tokyo, Japan) for 30 min. Resin–dentin interfaces were then subjected to argon-ion beam etching (EIS-200ER, Elionix) for 40 s with the ion beam directed perpendicular to polished surfaces. Finally, all SEM specimens were coated with a thin film of gold (Quick Coater, Type SC-701, Sanyu Denchi Inc, Tokyo, Japan) and observations were performed under an operating voltage of 10 kV .
2.5
Statistical analysis
A two way analysis of variance (ANOVA) followed by Tukey’s honestly significant difference (HSD) test (α = 0.05) was used for separate analyses of the SBS data for the TC group and WS group, to determine the influence of the adhesive type, and of TC cycles or WS period. Statistical analyses were performed using Sigma Plot software (Ver. 11.0; SPSS Inc., Chicago, IL, USA).
2
Materials and methods
2.1
Study materials
Adhesive materials ( Table 1 ) included the three universal adhesives G-Premio Bond (GP, GC Corp., Tokyo, Japan), Scotchbond Universal (SU, 3M ESPE, St Paul, MN, USA) and All Bond Universal (AB, Bisco, Schaumburg, IL, USA). The conventional two-step self-etch adhesive Clearfil SE Bond (SE, Kuraray Noritake Dental, Tokyo, Japan) was used as a control. Clearfil AP-X (Kuraray Noritake Dental, Tokyo, Japan) was used as a restorative material for bonding to dentin.
| Code | Adhesive (Lot No.) | Main Components | Manufacturer |
|---|---|---|---|
| SU | Scotchbond Universal (41256) | MDP, HEMA, dimethacrylate resins, Vitrebond copolymer, filler, ethanol, water, initiators, silane | 3M ESPE St. Paul, MN, USA |
| GP | G-Premio Bond (1501221) | MDP, 4-MET, MEPS, BHT, acetone,dimethacrylate resins, initiators,water | GC Corp Tokyo, Japan |
| AB | All-Bond Universal (1300008503) | MDP, bis-GMA, HEMA, ethanol, water, initiators | Bisco Inc. Schaumburg, IL, USA |
| SE | Clearfil SE Bond (011613) | Primer: MDP, HEMA, water, initiators Bond: MDP, HEMA, bis-GMA, initiators, microfiller | Kuraray Noritake Dental Tokyo, Japan |
| – | |||
| Resin composite | |||
| Clearfil AP-X (CC0043) |
bis-GMA, TEGDMA,silane barium glass filler, silane silica filler, silanated colloidal silica catalysts, accelerators, CQ, pigments, others | Kuraray Noritake Dental | |
| Filler Load: 84.5% weight | |||
2.2
Specimen preparation
Mandibular bovine incisors were extracted from 2 to 3 year old cattle and were stored frozen for up to 2 weeks for use as human teeth. As a large number of samples were necessary, bovine dentin was used instead of human dentin. Previous research shows that this has little influence on the results . Approximately two-thirds of the apical root structure of each tooth was removed using a diamond impregnated disk with a slow-speed saw (Isomet Low Speed Saw, Buehler, Lake Bluff, IL, USA). Pulp tissues were then removed and labial surfaces were ground with wet 240-grit silicon carbide (SiC) paper (Fuji Star Type DDC, Sankyo Rikagaku Co. Ltd., Saitama, Japan) to create flat dentin surfaces. Teeth were then mounted in self-curing acrylic resin (Tray Resin II, Shofu Inc., Kyoto, Japan) so that the flattened areas were exposed, and temperature rises due to exothermic polymerization reactions of the acrylic resin were moderated by placing specimens under running tap water. Dentin bonding surfaces were next ground flat using a water coolant and a sequence of SiC papers ending with 320-grit (Fuji Star Type DDC), and the dentin surfaces were finally dried with oil-free compressed air.
2.3
Storage conditions and shear bond strength tests
The experimental protocols for the bonding procedures are shown in Table 2 . Ten specimens, each taken from a different tooth, were used. In total three hundred and twenty bovine teeth were used. Adhesives were applied to dentinsurfaces in accordance with the respective manufacturer’s instructions, and specimens were then clamped in an Ultradent Bonding Jig (Ultradent Products Inc., South Jordan, UT, USA) with plastic molds of 2.38-mm internal diameter and 2.0-mm height . Subsequently, resin composites were placed into the mold and were light irradiated for 30 s using a visible-light curing unit (Optilux 501, sds Kerr, Danbry, CT, USA) set at a light irradiance average of 600 mW/cm 2 .
