|Year : 2015 | Volume
| Issue : 2 | Page : 49-53
Status of self-etch adhesives for bonding to pulp chamber dentin
Muhammet Kerim Ayar
Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey
|Date of Web Publication||8-May-2015|
Muhammet Kerim Ayar
Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon 61080
Source of Support: None, Conflict of Interest: None
Purpose: Present study investigated microtensile bond strengths (μTBS) of four one-step self-etch dental adhesive systems, two two-step self-etch adhesive systems and one three-step etch-and-rinse adhesive system to pulp chamber dentin. Materials and Methods: The μTBS of seven current adhesives, including one three-step etch-and-rinse (Optibond FL, Kerr, USA), two two-step self-etch (Clearfil SE Bond, Kuraray, Japan; AdheSE, Ivoclar, Liechtenstein) and four one-step self-etch adhesives (Clearfil S3 Bond, Kuraray, Japan; Optibond all-in-one, Kerr, USA; iBond, Heraeus Kulzer, Germany; L-POP, 3M ESPE, Germany) were determined. Adhesives were applied to pulp chamber dentin according to their respective manufacturer's instructions, then μTBS tests were performed. Results: μTBS varied from 29.99 ± 7.82 to 38.15 ± 10.38 MPa. Highest μTBS mean was obtained with Optibond FL and lowest iBond, Heraeus Kulzer, Germany. There were no significant differences among all adhesives. Conclusion: Bonding effectiveness of one-step self-etch adhesive systems to pulp chamber dentin was comparable to two-step self-etch and three-step etch-and-rinse adhesive systems.
Keywords: Dentin bonding agents, microtensile bond strength test, one-step self-etch adhesives, pulp chamber dentin
|How to cite this article:|
Ayar MK. Status of self-etch adhesives for bonding to pulp chamber dentin. J Res Dent 2015;3:49-53
| Introduction|| |
Coronal restoration of endodontically treated teeth using resin composite restoratives in association with adhesive resin systems has become a common procedure in the clinics as these adhesive restorations permit a more conservative way to post and core restorations.  In addition, restoration of endodontically treated teeth using adhesive procedures offerssome advantages; (I) adhesive resin materials allow to carrying of functional stresses across the resin-dentin/enamel interfaces to the tooth tissues, with the potential to strengthen weakened tooth structure, (II) formation of resin-diffused collagen layer also called dentinal hybrid layer across resin-dentin interfaces can also seal dentin from oral fluids, thus reduce coronal microleakage. ,,
Although it is claimed that resin adhesive systems may be used in the pulp chamber to seal the root canal to prevent microleakage of oral fluids and microorganism,  resin adhesive systems evolved significantly towards to being more user-friendly and less technique sensitive during last decade.  Contemporary dental adhesives can be divided two main categories either an etch-and-rinse adhesives or a self-etch adhesives. Self-etch adhesives do not require a separate etching step unlike to etch-and-rinse adhesives. They contain acidic monomers that simultaneously etch and prime dental hard tissues. The latest generation of self-etch adhesive are most simple-to-use one-step adhesives.  These adhesives are further classified into two subcategories either mixing before applying to substrate or applying substrate from one bottle directly. First type is called all-in-one one-step self-etch adhesives, while latter type is called one-bottle one-step self-etch adhesives.  The latter type presents the true one-bottle one-step dental adhesive systems in the market.
Despite that one-step self-etch adhesives are considered as most user-friendly adhesives, it should be noted that, three-step etch-and-rinse adhesive (Optibond FL, Kerr, USA) in etch-and-rinse adhesives, and two-step self-etch adhesive (Clearfil SE Bond, Kuraray, JAPAN) in self-etch adhesives consistently exhibit superior performance in laboratory and clinical studies when bonding to bur cut enamel and dentin, thus being considered as a goldstandard.  However, bonding effectiveness of resin adhesive systems, especially one-step self-etch adhesives to pulp chamber dentin remains not-well investigated, despite distinct surface morphology of pulp chamber dentin compared to bur-cut dentin.
Prepared dentin surface using either diamond bur or abrasive papers are covered with smear layers with varying thickness which are supposed to exhibit a challenge against to bonding effectiveness of self-etch adhesive with mild pH. , Unlike to prepared dentin surfaces, pulp chamber dentin is generally not prepared during endodontic treatment and remains smear layer-free. , Although dentin is very complex and challenging tissue as a bonding substrate, pulp chamber dentin may be considered as more favorable bonding substrate for one-step self-etch adhesives, as these adhesives have generally mild pH.
Thus, in the current study, the bonding effectiveness of four one-step self-etch adhesive systems to pulp chamber dentin in comparison to two two-step self-etch and one three-step etch-and-rinse adhesive systems was investigated. The null hypothesis was that microtensile bond strength (μTBS) of adhesive resin to pulp chamber dentin was not affected by different adhesive systems.
| Materials and methods|| |
In the present study, seven dental adhesive systems were tested as follows; one three-step etch-and-rinse adhesive system (Optibond FL, Kerr, Orange, CA, USA), two two-step self-etch adhesives (Clearfil SE Bond, Kuraray, Osaka, Japan; AdheSE, Ivoclar, Vivadent, Schaan, Liechtenstein), and four one-step self-etch adhesive systems (Clearfil S3 Bond, Kuraray, Osaka, Japan; Optibond all-in-one, Kerr, Orange, CA, USA; iBond, Heraeus Kulzer, Hanau, Germany; L-POP, 3M ESPE, Seefeld, Germany). Brand names, chemical compositions, manufacturer instructions of respective adhesive systems were presented in the [Table 1].
|Table 1: Chemical compositions and application instructions of respective manufacturers of dental adhesive systems tested in the present study |
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Thirty bovine incisors which were stored in the 0.02% sodium azide solution prior to usage at room temperature were used to prepare pulp chamber dentin specimens to be bonded. Corresponding procedure was shown in the [Figure 1]. Namely, two sections which were perpendicular to long axis of tooth were performed using low-speed diamond saw under water cooling. The first section was performed at 5 mm above enamel-cement border, the other one was performed at 1 mm under enamel-cement border. Then, obtained crown segments with 6 mm heights were sectioned into halves using low-speed diamond saw. Pulp tissue remnants were carefully removed from pulp chamber surfaces with spoon-shaped excavator. Pulp chamber surfaces were examined using stereomicroscopy at × 40 magnification to avoid pulp calcifications and cracks. Exposed root dentin surfaces left after sectioning were covered with nail polish to demarcate pulp chamber dentin to be bonded.
|Figure 1: Schematic presentation of specimen preparation for microtensile bond strength test for bonding to bovine pulp chamber dentin|
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Randomly selected 35 pulp chamber dentin specimens were divided into seven groups randomly (n = 5). Each adhesive system was applied to pulp chamber dentin according to respective manufacturer instructions [Table 1]. After adhesive procedures, resin composite (Valux Plus, 3M ESPE, St Paul, MN, USA) build-ups in three layers up to a height of 4 mm, were done on the surfaces. Each increment layer was cured for 20 s using the Elipar Freelight LED light (3M ESPE, St Paul, MN, USA).
Following storing all bonded teeth in distilled water at 37°C for 24 h before μTBS test, resin-dentin sticks with approximately 0.8 × 0.8 mm 2 dimensions were obtained using diamond saw under copious water (Micracut 125, Metkon, Bursa, Turkey) running at 300 rpm. Four of obtained resin-dentin sticks were selected to test, randomly, yielding 20 sticks for each group. Then, the specimens were fixed to jig with cyanoacrylate glue (Pattex, Henkel, Dusseldorf, Germany) and forced in tension at a crosshead speed of 1 mm/min using Bisco microtensile testing machine. The μTBS was derived by dividing the enforced force at the time of fracture by the bond area (mm 2 ). The mode of failure was determined by stereomicroscope under × 40 magnification (Meade Bresser Biolux, Meade Bresser, Rhede, Germany), and recorded as "adhesive" or "cohesive" neither dentin nor resin and "mix" failures include more than one of the dentin and resin parts.
One-way analysis of variance (ANOVA) was used to determine effects of independent variable (dental adhesive systems) on dependent variable (μTBS mean). P - value was set at 0.05.
| Results|| |
Mean μTBS values of seven dental adhesive systems were presented in the [Table 2]. Mean μTBS values ranged from 29.99 ± 7.82 to 38.15 ± 10.38 MPa. The lowest mean μTBS value was obtained from iBond, a one-step self-etch adhesive, while the highest mean μTBS value was obtained from Optibond FL, a three-step etch-and-rinse adhesive. There was no significant difference among all groups (P > 0.05). Mix and adhesive failures were dominant in each groups [Table 2].
|Table 2: Mean microtensile bond strength (μTBS) values (n=20) and failure modes |
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| Discussion|| |
In the present study, the bonding effectiveness of four one-step self-etch dental adhesive systems to pulp chamber dentin in comparison to two two-step self-etch and one three-step etch-and-rinse adhesive systems was assessed. The null hypothesis was that the μTBS of adhesive resin to pulp chamber dentin was not affected by different adhesive systems was accepted since all adhesive systems exhibited similar bond strength means [Table 2]. However, in the previous studies on the bonding effectiveness of contemporary dental adhesive systems to bur-cut dentin, significant differences among different adhesive systems, that is, three-step etch-and-rinse adhesives vs one-step self-etch adhesives were frequently revealed. ,,,,, Generally, three-step etch-and-rinse adhesive (Optibond FL) and then two-step self-etch adhesive (Clearfil SE Bond) produce high bond strengths in the laboratory studies. , Therefore, these adhesives are accepted as a gold standard when bonding to bur-cut dentin in respective bonding strategies, that is, etch-and-rinse and self-etch.  Although recent clinical studies revealed similar clinical success using one-step self-etching adhesive with these gold standard adhesives, , laboratory studies indicates frequently lower bonding effectiveness of one-step self-etch adhesives when bonding to bur-cut dentin. ,,, Despite that, in the current study, one-step self-etch adhesives showed comparable bond strength to those of three-step etch-and-rinse and two-step etch-and-rinse adhesives when bonding to pulp chamber dentin. Morphological and surface property differences between bur-cut dentin and pulp chamber dentin may arise this difference.
It is well-known that thick of smear layers on the dentin surfaces created during cavity preparation using different burs in the clinic or during surface preparation using abrasive papers in the laboratory studies effect bonding effectiveness of self-etch adhesives to dentin. ,, It must be considered that self-etch adhesives with milder pH exhibit incomplete smear layer dissolution and/or encapsulation.  When the self-etch adhesive does not etch deeply enough, the adhesive will be not able to establish a firm bond with the underlying sound dentin, then failure is likely to occur at the transition between the smear layer and the intact dentin, due to the rather weak bond of the smear layer to the underlying dentin.  Conversely to bur-cut dentin, pulp chamber dentin surfaces are free of smear layers as a surface property , unless it is not prepared during endodontic treatment, therefore it may be considered as a favorable substrate for self-etch adhesives with mild pH. As pulp chamber dentin surfaces are free of smear layer, self-etch adhesives with mild pH may able to etch profoundly enough intact dentin and encapsulate exposed collagen fibrils, thus provide high retention for resin composite after polymerization.
The current study is one of the few studies to investigate the bond strength of one-step self-etch adhesive systems to pulp chamber dentin and findings encourage using of one-step self-etch adhesives in association with light-curing resin composite restoratives for coronal restorations of endodontically treated teeth. In the previous studies, Clearfil SE Bond, a two-step self-etch adhesive and Adper Prompt L-POP, an all-in-one one-step self-etch adhesive,  Clearfil SE Bond and Clearfil S3 Bond, a one-step self-etch adhesive  showed similar bond strengths, respectively, as being in correlation with findings of the present study [Table 2].
In case of etch-and-rinse adhesive tested in the current study, to the best knowledge of the author, Optibond FL, which is gold standard adhesive in bonding to bur-cut dentin has not been used in any study on bonding to pulp chamber dentin, thus direct literature comparison cannot be performed. Meanwhile that, some previous reports suggested that etch-and-rinse adhesives result significantly lower bond strengths to pulp chamber dentin when compared to self-etching adhesives, that is, Clearfil SE Bond , and Clearfil S3 Bond,  while some reports provided contrary findings.  However, when bonding to bur-cut dentin, evenly high bond strengths of Optibond FL were attributed to high filler loading of adhesive resin.  The same explanation may be attributed to high bond strength of Optibond FL to pulp chamber dentin in the current study.
High immediate bond strength of adhesive systems is necessary to achieve adequate sealing of resin-tooth interfaces, since polymerization stress occur due to polymerization shrinkage of resin composite may produce gaps along interfaces if bond strength of adhesive resin is not able to compensate it. It is reported that polymerization stress might reach to 20 MPa in Class V cavities and also reported this as the bond strength required for producing gap free margins.  In this context, it can be concluded that bonding effectiveness of all tested adhesives in the current study to pulp chamber dentin were enough to achieve successful sealing of adhesive-tooth interfaces. However, it must be noted that polymerization stress occurs in the pulp chamber should be higher than that occurs in Class V cavities. Nevertheless, if composite resin is placed using appropriate layering techniques, polymerization stress might be minimized. 
Retention of resin composite restoration of teeth received root canal therapy may be exclusively determined by ability of adhesive resin to bond to pulp chamber dentin if cavity walls are too divergent and lack of self-retentive cavity configuration.  This implies that providing high bond strength is an important criteria in selection of adhesive system for restoration of endodontically treated teeth.
It may be noted that being user-friendly and less technique sensitive are also secondary exclusive criteria in selection of adhesive system. In this context, one-step self-etch adhesives are most preferable adhesive systems among tested adhesives, since they do not require separate etching, priming steps that are considerably technique sensitive procedures during resin bonding. Etching, priming, and bonding steps are accomplished simultaneously, when one drop of one-step self-etch adhesive solution from one bottle is applied onto substrate surface in one step. Therefore, overall bonding procedure becomes simpler and takes less time. 
| Conclusion|| |
It seems that bonding effectiveness of current dental adhesive systems to pulp chamber dentin were enough to resist against to polymerization stress occurs during polymerization of resin composite restoratives. One-step self-etch adhesives, which are accepted as most user-friendly adhesive systems, may be considered as an alternative resin bonding approach when bonding to pulp chamber dentin to simply bonding procedures.
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[Table 1], [Table 2]