|Year : 2013 | Volume
| Issue : 3 | Page : 81-85
Microtensile bond strength of three adhesive systems to different dentin tissues
Bilinç Bulucu1, Cemal Yesilyurt2, Davut Çelik3, Gunes Bulut Eyuboglu2, Cemile Kedici Alp2, Hikmet Aydemir4
1 Department of Restorative Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey
2 Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey
3 Department of Endodontics, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey
4 Department of Endodontics, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey
|Date of Web Publication||25-Sep-2013|
Cemile Kedici Alp
Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, 61080, Trabzon,
Source of Support: None, Conflict of Interest: None
Purpose: The aim of this in vitro study was to determine the micro-tensile bond strengths (mTBS) of three adhesive systems (Prime&Bond NT, Clearfil SE Bond, G Bond) to four different dentin structures; bovine dentin and unerupted, sound, caries affected human dentins. Materials and Methods: Flat bovine molar, unerupted, sound and caries affected human molar dentin structures were obtained at the occlusal surfaces of the extracted teeth. Final surface grindings were performed using 600-grit Silicon carbide paper. Three adhesive systems (Prime&Bond NT, Clearfil SE Bond, G Bond) were used to bond composite resin (P60, 3M ESPE) to the prepared dentin surfaces. After 24 h distilled-water storage, the bonded specimens were cross-sectioned (0.8 ± 0.2 mm 2 ) and subjected to a (μTBS) test. One-way analysis of variance multiple comparison test were used to statistically analyze the mean bond strength data α =0.05. Results: There was statistically significant difference in mTBS among the dentin types (P < 0.0005). Mean bond strength to sound human and bovine dentin was significantly higher than to caries-affected dentin and dentin of unerupted human teeth (P < 0.05). Statistically similar bond strength was obtained with Prime&Bond NT and Clearfil SE Bond while G-Bond showed the lowest bond strengths. Conclusion: The type of dentin structure has an important effect on the mTBS values of adhesive systems.
Keywords: Bovine teeth, caries affected dentin, dentin adhesives, micro-tensile test
|How to cite this article:|
Bulucu B, Yesilyurt C, Çelik D, Eyuboglu GB, Alp CK, Aydemir H. Microtensile bond strength of three adhesive systems to different dentin tissues. J Res Dent 2013;1:81-5
|How to cite this URL:|
Bulucu B, Yesilyurt C, Çelik D, Eyuboglu GB, Alp CK, Aydemir H. Microtensile bond strength of three adhesive systems to different dentin tissues. J Res Dent [serial online] 2013 [cited 2019 Apr 19];1:81-5. Available from: http://www.jresdent.org/text.asp?2013/1/3/81/118900
| Introduction|| |
A truly adhesive bond between a restorative material and the natural tooth structure is one of the main goals of dental materials.  Dentin microstructure and properties are the fundamental substrate of restorative dentistry. , Biological and clinical factors such as tubule orientation, sclerotic and carious dentin can also affect dentin bonding. , Although bond strength measurements of hard tooth tissue are of clinical interest, standardization of the bonding substrate is very difficult to achieve. 
Many factors can influence the bonding performance of adhesive systems to dentin. Wide variations in bond strength data have been reported, probably due to differences in protocol like; the testing procedures, the handling of the materials, tooth substrate, dentin substrate, tooth age, bonding techniques and methods employed. ,,
The situation for clinical dentin bonding is more complex because morphology of the dentin varies depending upon location in the tooth, depth,  caries,  age,  history and other factors. , Therefore; differences in the results are due not to the performance of the adhesive, but to variations in the dentin structure.  The morphologic and structural variation of the dentin with location also affects bond strength. ,
Only a small number of investigations pay attention to exact determination to the type of dentin structure are available in the literature.  Laboratory studies are usually performed on extracted human teeth and in some cases bovine teeth.  Because of difficulty in obtaining large numbers of intact extracted human teeth for laboratory studies, investigators have evaluated bovine teeth as possible substitutes for human teeth. ,
Variations in species need consideration because the use of animal dentin may have advantages such as greater availability and the ability to make direct in vivo and in vitro comparisons. However, the structure may differ from human dentin. 
Researchers are studying to find the answer of the significant difference in the bond strength. Is it due to dentin type or adhesive system? Studies revealed that bond strength to dentin depends upon the adhesive system used, the location and type of the dentin. ,, Of course, it would be difficult, expensive and time consuming to evaluate every adhesive system available and to include all possible variables in dentin type. Therefore, to find the most suitable dentin substrate for in vitro bond studies is important and may be helpful to standardize the dentin surface.
None of the systems in use is consistent in the results they produce. One possible reason for the highly variable results is the difference in the physical and chemical structure of individual teeth.  Studies usually compare one , or two  type of dentin in a study. No single study has compared the bond strengths of newer adhesive systems to bovine dentin and unerupted, sound and caries affected human dentin.
The objective of the current study was to compare the micro-tensile bond strength (mTBS) to bovine dentin and unerupted, sound and caries affected human dentin of three adhesive systems; Prime&Bond NT (total-etch), Clearfil SE Bond (two step self-etch), G Bond (one step self-etch).
The hypothesis to be tested that bond strength values of adhesive systems can differ due to the type of dentin.
| Materials and Methods|| |
In this study, four groups were arranged according to dentin type. The groups were as; bovine molars and unerupted human third molars sound and caries affected human molars. Each group was consisted of 15 teeth. Totally 60 teeth were used. All teeth were stored at 4°C in physiological saline, in which several crystals of thymol were added.
After removal of the occlusal enamel with a diamond disc (Buehler, USA) grinding was finally performed with 600-grit Silicon carbide paper under running water according to the combined criteria of visual examination.
In order to obtain caries-affected dentin, grinding was performed using the combined criteria of visual examination and staining with a caries detector solution. (Snoop, Pulpdent Corp., MA02471, USA). , That is, the dentin was hard to an explorer and no longer stained bright red with the caries detector dye.
Bonding procedure and bond strength testing
The teeth were, then, randomly divided into three adhesive groups (Prime&Bond NT, Clearfil SE Bond, G Bond), each containing five teeth.
Adhesive systems were applied following the manufacturers' recommendations [Table 1]. After adhesive application, a resin composite crown was built up using three layers of a hybrid resin-based composite (Filtek P60, 3M ESPE, Dental Products, St Paul, MN, USA) to a height of approximately 5 mm, curing each layer for 20 s with a light-emitting diode (ELİPAR, 3 M ESPE,).
After, 1 day of storage in distilled-water at 37°C, the resin-bonded teeth were sectioned in the Z and Y-axis; parallel to the longitudinal tooth axis, by using a low speed diamond saw (Micracut 125, Metkon Ins., Ltd., Bursa, Turkey) under water lubrication thereby obtaining stick shape specimens, with approximately 0.8 ± 0.2 mm 2 of bonding area.
The specimens were attached to a table-top material tester (Dillon, Tronix Inc., MN 56031 Instron Drive Fairmont, USA) with a cyanoacrylate adhesive (Zapit, DVA, Corona, USA) and individually fractured on micro-tensile test (Bisco Inc., Schaumburg, USA) at a crosshead speed of 1 mm/min. The bond strength data was expressed in megapascal (MPa) after measuring the cross-sectional area at the site of fracture with a digital caliper (Mitutoyo, Tokyo, Japan).
One-way analysis of variance (ANOVA) (Bonferroni as Post-hoc) multiple comparison test were used to statistically analyze the mean bond strength data. Statistical significance was established at α = 0.05.
| Results|| |
The results of mTBS test are presented in [Table 2]. The ANOVA indicated a significant difference among the four-dentin type (P < 0.0005). There was no statistically significant difference between sound and bovine dentin (P > 0.05). Bond strength to sound and bovine dentin was significantly higher than to caries-affected dentin and unerupted teeth (P < 0.05). In addition, there was no statistically significant difference between caries-affected dentin and unerupted teeth (P > 0.05). On statistically report, similar bond strengths were obtained with Prime&Bond NT and Clearfil SE Bond while G-Bond showed the lowest strengths [Graph 1] [Additional file 1].
|Table 2: Mean micro-tensile bond strength (MPa) and standard deviation of adhesive systems' to dentin types |
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Fractured specimens were observed under an optical microscope (SZ-PT Olympus, Japan) to determine the type of fracture after micro-tensile test. The results are presented in [Table 3]. Failures after testing mostly occurred between the adhesive layer and dentin. A few specimens, however, showed cohesive failures in composite or in dentin.
|Table 3: Failure modes for the adhesives in dentin of sound teeth, bovine teeth, caries-affected teeth and unerupted teeth |
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| Discussion|| |
Laboratory studies usually evaluate the performance of dentin bonding restorative systems in the clinical situation.  It is impossible to compare the laboratory results of bond strength studies because of the tremendous variations in the test methodologies employed.  No guidelines are available for the bond strength of adhesive systems for in vitro studies. 
One of the factors that can influence bond strength is the nature of the substrate.  As current bonding systems are susceptible to the different substrates, care should be taken when choosing dentin-bonding systems, to the various dentin substrates.  Dentin is a complex hydrated biological composite structure for which only limited structure property relationships are available.  It has a heterogeneous composition, with approximately 30% by volume organic matter and consequently low surface energy.  The key problem remains in our lack of detailed understanding of dentin itself. 
A method for testing bond strengths has been developed by Sano et al. called the mTBS test.  This technique allows the use of smaller, uniform dentin samples. With this method, less number of teeth is required.
Bouillaguet et al. reported that the most convenient source of human teeth is unerupted, young third molars, which mainly consist of highly permeable dentin.  In this study, low bond strength values were observed in unerupted teeth group. A probable explanation for this is that an unerupted tooth has not encounter with thermal changes, loading and dentinal changes with advancing age. Therefore, while using these types of teeth it must be kept in mind that unerupted teeth may not represent the in vivo conditions correctly.
In general, human and bovine teeth have been reported in the literature for dentinal adhesion testing. , The difference in behavior between human and bovine dentin may be due to the magnitude of the biological spreading in bovine material. In bovine dentin, the relaxation of microhardness indentations shows a trend, similar to the behavior in human dentin.  Bovine teeth are larger and may be an alternative substrate for human dentin in bond strength testing. , The collagenous matrix of bovine dentin is mainly Type I collagen, the same as human dentin.  Retief showed that the tubular distribution in bovine dentin is more compact than in human dentin.  However, they have never been considered as a perfect substitute for human dentin in adhesive studies.  Schilke et al. reported no significant difference between human and bovine in the superficial layer, but decreased bond strength in accordance with the depth of dentin due to the lower density of dentinal tubules.  Some previous investigations have found no differences on the efficiency of adhesives bonded onto bovine.  The bond strength values found in this study was much greater and similar for sound human teeth and bovine teeth than to caries affected and unerupted human teeth. Hence, bovine teeth can be used as a substitute for sound human teeth.
Within the limitations of this study, it was observed that the type of dentin affects the bond strength of adhesive systems. Prime&Bond NT were showed similar bond strengths to sound human dentin and bovine dentin. However, the same adhesive system showed statistically lower bond strength to caries affected and unerupted dentin. This situation was also observed in other tested adhesive systems.
Current dentin adhesive strategies have been principally focused on the normal composition and structure of unaffected dentin. However, sound teeth are not representative of the dentin restored clinically, namely dentin affected by advancing caries or other pathologic conditions. 
Caries affected dentin is not normal dentin, because the tubules are occluded with mineral crystals, but it is free of bacteria.  The remaining mineral phase in the caries affected intertubuler dentin may be very different from that of normal dentin.  Caries affected dentin appears demineralized and the lower calcium and phosphate content can adversely affect adhesion.  Bonding to caries affected dentin shows different bonding characteristics compared with bonding to normal dentin, such as reduced permeability and decreased intrinsic water content.  This can probably explain the low bond strength of caries affected groups in the present study.
Hardness values for caries affected dentin was found to be approximately half that of normal dentin. The repeated cycles of demineralization and remineralization that occur during the development of carious lesions may produce larger crystals of calcium phosphate in forms that are less soluble in acidic conditions than is normal apatite. Thus, stronger acids may be required to dissolve the mineral phase of caries affected dentin enough to obtain sufficient resin infiltration for high resin bond strengths.  Therefore, the differences of the bond strength values may also be material dependent. Nakajima et al. reported lower bond strength to caries affected dentin than to normal dentin when using self-etching primer.  In this study, Prime&Bond NT showed the highest bond strength in caries affected dentin. Teeth were acid etched with the phosphoric acid. This procedure removes the smear layer.
Manufacturers have introduced one-step adhesive systems to simplify clinical procedures.  G Bond, which is one-step adhesive system, showed the lowest bond values in all groups. Acid, primer and adhesive are in one bottle in G Bond. Therefore, its use is practical, but bond strength is not high as Clearfil SE Bond and Prime&Bond NT. G Bond's pH value is high. Therefore, it has low acidic value and cannot demineralize the dentin as needed. Caries affected dentin may require more acidic content adhesive material.
With the improvements of adhesive materials, there is increasing incidence of cohesive failures of dentin during testing.  In this study, adhesive failures were observed to be prevalent.
Although bond strength measurements to these types of hard tooth tissue are of clinical interest, standardization of the bonding substrate is still very difficult to achieve. Bovine dentin and sound human dentin show higher bond strength values than to caries affected and unerupted teeth. The results of this study, however, were limited to three adhesive systems. Further investigations will be necessary to verify other dentin adhesives on bond strength of different dentin type.
| Conclusion|| |
- The type of dentin plays an important role to bonding performance of adhesive resin systems
- Adhesive systems chemical composition can also affect the bonding mechanism performance
- Caries affected dentin and unerupted dentin can show low bond strength values for adhesive systems in in vitro studies.
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[Table 1], [Table 2], [Table 3]