Year : 2009 | Volume
: 20 | Issue : 2 | Page : 180--184
Effect of repeated use on dentin bond strength of two adhesive systems: All-in-one and one-bottle
Fershteh Shafiei1, Mahtab Memarpour2,
1 Department of Operative Dentistry , Dental Faculty, Shiraz University of Medical Sciences, Shiraz, Iran
2 Department of Pediatric Dentistry, Dental Faculty, Shiraz University of Medical Sciences, Shiraz, Iran
Department of Pediatric Dentistry, Dental Faculty, Shiraz University of Medical Sciences, Shiraz
Aims: To compare the effects of repeated use of two one-bottle adhesives with that of two all- in- one adhesives (with acetone solvent) on bond strength to dentin.
Materials and Methods: A flat dentin surface was prepared on 120 bovine incisors using 600- grit abrasive pape. The teeth were randomly assigned into 12 equal groups. The four adhesive systems [Prime and Bond NT (P&B NT), One-Step Plus (OS), iBond (iB), and G-Bond (GB)] were used at baseline, after the lid of the container had been opened 30 times, and after it had been opened 60 times. Before each use of the adhesives, the lids of the containers were left open for 1 min. The resin composites were applied on the dentin in a cylindrical split mold. After thermocycling, shear bond strength test was performed with a universal testing machine at 1 mm/min. We used Kruskal-Wallis and Dunn tests for statistical analysis.
Results: There was no statistically significant difference among bond strength (MPa) of the groups of P&B NT (31.9 ± 4.6, 31.8 ± 6.5, 26.1 ± 6.7) and OS (33.2 ± 5.1, 30.9 ± 7, 29.3 ± 5.9), respectively (P > 0.05). The mean of the bond strength of iB and GB after 60 times (15.3 ± 4.1 and 12.2 ± 3.9, respectively) was significantly lower than that of iB and GB at baseline (23.5 ± 4.8 and 22.2 ± 4.5, respectively) (P < 0.05).
Conclusions: Repeated use (60 times) of the all-in-one adhesive led to a decline in the dentin bond strength. To avoid this problem it would be advisable to have containers with smaller amounts of adhesive or perhaps those with only a singe dose.
|How to cite this article:|
Shafiei F, Memarpour M. Effect of repeated use on dentin bond strength of two adhesive systems: All-in-one and one-bottle.Indian J Dent Res 2009;20:180-184
|How to cite this URL:|
Shafiei F, Memarpour M. Effect of repeated use on dentin bond strength of two adhesive systems: All-in-one and one-bottle. Indian J Dent Res [serial online] 2009 [cited 2020 Sep 25 ];20:180-184
Available from: http://www.ijdr.in/text.asp?2009/20/2/180/52897
Achieving effective bonding to dental substrates is a major goal in restorative dentistry. Following acid etching, enamel shows predictable and high bond strength but the development of a strong and durable bond to dentin substrate remains a challenge.  Many factors account for this difference between the enamel and dentin. Their dissimilar structural composition is the primary factor. Micromechanical retention within the demineralized dentin surface through the formation of a resin-reinforced hybrid layer is generally believed to be the mechanism by which adhesive resin bonds to dentin. , With the introduction of the enamel/dentin adhesive system in the past decade, the stages of application have been simplified. The fifth-generation (one-bottle) adhesives are used by combining primer and adhesive resin in a single bottle on moist dentin in a single step (wet-bonding). , In most of these systems, resin monomers have been dissolved in an organic solvent (acetone or ethanol) which has a 'water chasing effect.' These solvents lower the surface tension of water and replace it within the collagen network of demineralized dentin. This results in enhancement of the removal of water from the collagen surface. Ultimately, the solvent within the demineralized dentin can be exchanged for the adhesive resin by increasing the vapor pressure of water. These solvents may also promote the penetration of the bonding agents into the demineralized collagen-rich dentin surface by lowering the viscosity of the solution. ,, After etching of the dentin and rinsing, the presence of some water in the collagen network is mandatory since acetone-based adhesives cannot penetrate into the collapsed collagen network after it has fully drie. Appropriate wetness of the dentin in these systems and technique sensitivity of these adhesives are always an important consideration. ,,
Self-etch adhesives were introduced in order to simplify the bonding steps. In some of these so-called all-in-one adhesive systems, the three steps of etching, priming, and resin bonding have been combined. Application of the acidic primer provides both demineralization of dentin and penetration of the adhesive.  Water is the main component of these adhesives since it produces acidic "H+ ions . In some of these systems, ethanol and/or acetone is also present to promote the solubility of the resin monomers. , Acetone (boiling point: 65.5°C) has a relatively high vapor pressure. Some studies have reported a reduction in the bond strength of acetone-based adhesives after repeated opening of the container, which has been considered to be due to the loss of acetone by evaporation from the container. , The present study was carried out to evaluate how repeated opening of adhesive bottles during their clinical use affected bond strength to dentin. We studied two types of simplified adhesives: Two fifth-generation (one-bottle) adhesives (Prime & Bond NT and One-Step Plus) and two seventh-generation (single-component all-in-one) adhesives (iBond and GBond).
Materials and Methods
Using 600-grit silicon carbide paper, flat middle dentin surfaces were prepared on 120 extracted intact bovine lower incisors. The specimens were mounted in acrylic molds and randomly separated into 12 equal groups of 10 teeth each. Four adhesive systems [Table 1], Prime & Bond NT (Dentsply De Trey, Germany), One-Step Plus (Bisco Inc., Schaumburg, Il, USA), iBond (Heraeus-Kulzer, Hanau, Germany), and G-Bond (GC Co., Japan) were used at baseline in groups 1, 2, 3, and 4 according to the manufacturer's instructions; these formed the control groups. In groups 5, 6, 7, and 8, the same adhesives were used, but from containers that had been used 30 times previously. Thirty times of adhesive use was simulated by opening the container three times a day, on 5 days every week, for two continuous weeks (except during the weekends, when the adhesives were kept refrigerated). At each simulated use of the adhesive, the lid of container was kept opened for 1 min; the adhesive was picked up from the bottle using a small disposable brush (in the cases of P & B NT, OS, GB) or a little drop of adhesive (in the case of iB) which was transferred to small glass container. In groups 9, 10, 11, and 12, the same adhesives were applied from containers that had been used 60 imes previously. Sixty times of adhesive use was simulated, as described before, over a period of 4 weeks.
After the bonding procedure, the respective resin composites (Spectrum TPH, AElite, Charisma, and Gradia) were applied using a cylindrical split mold. All the specimens were stored in distilled water for 24 h at room temperature and then thermocycled for 500 cycles at 5°C and 55°C. Dwell time in each bath was 20 s and the transfer time was 10 s. The specimens were loaded to failure in a universal testing machine (Instron, model 4302, Germany) with a crosshead speed of 1 mm/min. Shear bond strength (SBS) was recorded in MPa and the data were analyzed with Kruskal-Wallis and by Dunn's multiple comparison tests with a significance level of 0.05. Finally, stereomicroscopic observation (×20) determined the mode of failures that occurred during debonding.
Mean SBS values (in MPa) are shown in [Table 2]. There was no statistically significant difference among SBS of the groups of P&B NT (31.9 ± 4.6, 31.8 ± 6.5, 26.1 ± 6.7) and OS (33.2 ± 5.1, 30.9 ± 7, 29.3 ± 5.9), respectively P > 0.05, while SBS of iB and GB after 60 times, (15.3 ± 4.1, 12.2 ± 3.9) were lower than their control groups at baseline (23.5 ± 4.8, 22.2 ± 4.5) significantly (P 0.05). Each group of P&B NT and OS showed significantly higher bond strength when compared with similar group of iB and GB (P  As Reis et al. reported, a significant reduction in the bond strength to dentin occurred by elimination of the organic solvent (acetone or ethanol) in two bonding systems (P&B 2.1 and Single Bond). This reduction was attributed to incomplete penetration of monomer into demineralized dentin. Also, incomplete water displacement could have resulted in dilution of the water-soluble components of resin, with reduction in the degree of polymerization and bond strength.  However, Cho and Dickness  reported an increase in bond strength to dentin by lowering the acetone content in an experimental adhesive. They reported that lower acetone concentration, as could result from solvent evaporation during clinical use of acetone-based adhesive, can improve the integrity of the dentin-adhesive bond. In the present study, bond strength to dentin of P&B NT and OS at baseline, after 2 weeks (30 times of use), and after 4 weeks (60 times of use), remained largely unchanged.In contrast, Perdigao et al. reported a significant decrease in bond strength with the One-Step system (with acetone as solvent) when they compared the SBS to dentin at baseline and after 3 weeks (30 times of use). However, they did not observe any difference in the bond strength under similar conditions in the other three adhesive systems they tested, which had ethanol, ethanol and water, or water as solvents. They attributed this decrease in bond strength with repeated use of the acetone-based One-Step adhesive to evaporation of the solvent.  The reason for the difference between their study and ours may be related to the difference in the way repeated clinical use of the adhesive was simulated. In the study by Perdigao et al., each time the bottle's lid was removed, the bottle was squeezed a little so that the adhesive was only evident at the orifice of the bottle during the 1-min period. But in the present study, for a better simulation of the clinical situation, in this 1-min opening of the bottle's lid, the adhesive was removed up for one clinical use. With our technique, any evaporation of the solvent was probably accompanied by a decrease in adhesive content also. Consequently, the ratio of the solvent to the other components did not change sufficiently enough to affect the bond strength negatively. In addition, the design of the bottle containing adhesive was such that there was minimum evaporation of the solvent during clinical use. Reis et al. reported that when a bottle of P&B 2.1 was opened at an ambient temperature of 22°C, there was a small weight reduction over time of about 0.08%, 0.15%, and 0.22% after 1 min, after 2 h, and after 48 h, respectively. This shows that even when the bottle is left open, not much is lost to evaporation.  Additionally, in our study, to prevent phase separation we ensured that the bottle was shaken well before it was opened each time. This shaking of the bottle is important, especially in the case of P&B NT and OS, both of which contain filler particles. As pointed out by Nicholls, the liquids in the bottles have different densities and are not chemically bonded to one another and therefore phase separation can occur. This means that the liquids separate, according to their densities, into different layers within the bottle. Thus, when the bottle is left undisturbed for 1-2 h, the solvent is separates from the resin. It is because of this that shaking of the adhesive bottle before use has been recommended.  In the undisturbed bottle, phase separation results in the less dense acetone layer coming to lie above the adhesive layer. In our study, by shaking the bottle before opening it, we prevented this separation and thus reduced the evaporation of acetone.
Gallo et al. did not report any significant decrease in SBS to dentin when there was delayed (by 10 min) application of P&B 2.1 as compared to the SBS achieved with immediate use; however, there was a trend toward lower bond strength with delayed application. As their study was performed in a closed environment (temperature of 22°C and humidity of 60% ± 5%), they noticed that increased airflow could also affect the bond strength of the adhesive by increasing evaporation of the solvent.  Our study was carried out in conditions similar to that of Gallo et al.'s study. We too found no significant change in the bond strength. It seems that a change in the surrounding environment (increased airflow or temperature) and also increasing the number of times that the adhesive bottle is opened can lead to decrease in bond strength. No significant difference in bond strength to dentin after 30 times of use of iB and GB was observed; However, after 60 times of use, the bond strength decreased significantly. To explain this difference, as in the case of P&B NT and OS, it is possible that the design of the adhesive bottles and the method adopted for removing the adhesive from the bottle at each use (e.g., whether the bottle was shaken before being opened) may have prevented evaporation of acetone to some extent during the first 30 times of use. However, by the time the bottle had been opened 60 times, the loss of acetone had reached a critical level, sufficient to affect bond strength. This difference, which was not observed with P&B NT and OS, may be related to the differences in the way iB and GB systems function. These adhesives are one-step self-etch systems (all-in-one) in which etching, priming, and bonding are provided with application of one solution of iB or GB. Even a little alteration in the components of these mixtures may lower their bonding ability. Van Landyut et al. called these 'difficult' mixtures; they are a complex mixture of hydrophilic and hydrophobic monomers with a relatively high concentration of solvent and water for keeping them in solution.  All-in-one adhesives contain hydroyethyl methacrylate (HEMA) which keeps water.By elimination of HEMA from iB and GB formulation, water was separated from other components during evaporation of acetone. This phase separation can have an effect in decreasing the efficiency of these adhesive systems. , On the other hand, this phase separation may occur in the adhesive inside the bottle during evaporation of acetone from bottles containing iB and GB before application of adhesive on the dentin. This leads to a decrease of bond strength after 60 times of clinical use.
Another finding of this study was that the primary bond strengths of P&B NT and OS were significantly higher than those of iB and GB, which agrees with the results of many other researches. ,,, Generally, one-step self-etch system or an all-in-one system have weaker bonding ability in comparison with other bonding systems (e.g., two-step etch and rinse). This is due to many factors; for example, 1) acidic, hydrophilic and hydrophobic monomers, organic solvent, and water are placed together in one or two bottles and this state affects the function and efficiency of these components adversely; 2) high concentration of the solvent; 3) insufficient thickness of the adhesive layer (because of the high water content and low viscosity), may result that the whole of adhesive layer thickness include oxygen inhibited layer during light curing; 4) possibility of some residual solvent (water), leading to interference with resin polymerization; 5) the high hydrophilicity after polymerization, making them act like permeable membranes; and 6) during solvent evaporation, the monomer-water ratio may change, which could result in phase separation and the formation of water blisters. ,,,,
In one-component one-step self-etch adhesives, the solvent and functional monomers usually make up almost 50% of the adhesive. So the concentration of hydrophobic cross-linking monomers is drastically reduced. Since the mechanical strength of the adhesive is mainly provided by the polymerization of cross-linking monomers, relatively less hydrophobic monomers are available on the tooth surface after application of these adhesives; this impairs the bond strength. , On the other hand, P&B NT and OS can be effective in protecting the integrity of the hybrid layer and can resist polymerization shrinkage stress because they form the appropriate adhesive layer and have filler particles.This characteristic of the adhesive layer of P&B NT and OS,act as stress absorbing layer and improve the bond strength. ,,
The results of this study show that when using all-in-one adhesives with acetone as the solvent, immediate recapping of the bottle is necessary after each use because evaporation of even a little acetone can lead to decrease of bond strength to dentin. Due to the relatively low primary bond strength of these adhesives, this decrease could be critical. Thus more attention needs to be paid to prevention of acetone evaporation during clinical use of adhesive. It would be better if manufacturers market acetone-based all-in-one adhesives in small bottles containing less material and/or even single-dose bottles. In this study, repeated use did not affect bonding efficiency of two one-bottle systems.
The authors would like to thank Dr. D. Mehrabani of the Center for Development of Clinical Studies of Nemazee Hospital for editorial assistance.
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