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| Project Details |
| Funding Scheme : | General Research Fund | |||||||||||||||||||||||||||
| Project Number : | 784410 | |||||||||||||||||||||||||||
| Project Title(English) : | Arresting biodegradation of dentin bonded interface | |||||||||||||||||||||||||||
| Project Title(Chinese) : | 停止破壞牙本質粘結界面 | |||||||||||||||||||||||||||
| Principal Investigator(English) : | Prof Yiu, Cynthia Kar Yung | |||||||||||||||||||||||||||
| Principal Investigator(Chinese) : | ||||||||||||||||||||||||||||
| Department : | Faculty of Dentistry | |||||||||||||||||||||||||||
| Institution : | The University of Hong Kong | |||||||||||||||||||||||||||
| E-mail Address : | ckyyiu@hku.hk | |||||||||||||||||||||||||||
| Tel : | 28590252 | |||||||||||||||||||||||||||
| Co - Investigator(s) : |
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| Panel : | Biology & Medicine | |||||||||||||||||||||||||||
| Subject Area : | Medicine, Dentistry & Health | |||||||||||||||||||||||||||
| Exercise Year : | 2010 / 11 | |||||||||||||||||||||||||||
| Fund Approved : | 493,000 | |||||||||||||||||||||||||||
| Project Status : | Completed | |||||||||||||||||||||||||||
| Completion Date : | 29-6-2013 | |||||||||||||||||||||||||||
| Project Objectives : |
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| Abstract as per original application (English/Chinese): |
Background
The advent of dentin adhesives has greatly revolutionized the practice of restorative dentistry. The bonding of composite restorations to coronal dentin, fiber posts and lately root filling materials to root canal dentin can now be achieved via dentin adhesives. Despite the popularity of dentin adhesives, the durability of resin-dentin bonds is still a serious clinical problem. The decline in bond strength with time has been attributed to degradation of the "hybrid layer", which consists of adhesive resin and dentin collagen at the bonded interface.
Key issues
Traditionally, hydrophilic "water-loving" resin monomers are used in dentin adhesives to facilitate bonding to wet dentin, via "water wet-bonding" that prevents collapse of unsupported collagen fibrils and enhances complete penetration of adhesive monomers into demineralized dentin. However, the presence of water in this technique creates a potential for phase separation of hydrophobic "water-hating" and hydrophilic resin monomers, thereby yielding a less than optimum hybrid layer. Under such conditions, resin penetration into demineralized dentin is incomplete and results in exposed collagen fibrils within the hybrid layer, which are prone to attack by the naturally occurring enzymes, matrix metalloproteinase (MMP) 2, 8 and 9 in dentin. Increased water sorption by hydrophilic resin monomers alters the chemistry of the polymer chains (plasticization) and decreases the mechanical properties of dentin adhesives over time.
To extend the longevity of resin-dentin bond, future dentin adhesives should be rendered less hydrophilic. A recently developed “ethanol-wet-bonding” technique allows better infiltration of hydrophobic resin and encapsulation of collagen fibrils. Recent studies have shown that this protocol improves bond durability of hydrophobic adhesives. Alternatively, chlorhexidine (CHX), a potent MMP inhibitor against MMP 2, 8 and 9, can be applied before the dentin adhesives to prevent collagen degradation in the hybrid layer. Therefore, the adjunctive use of ethanol-wet-bonding with CHX for hydrophobic adhesives should be a promising solution to improve the durability of the bonded interface by reducing resin and collagen degradation simultaneously.
Aims and significance
The proposed project aims to evaluate the effect of ethanol-wet-bonding and CHX in arresting bond degradation. We plan to use this novel bonding technique in two different dentin substrates: coronal and root canal dentin. The effectiveness of the new technique will be evaluated quantitatively using bond strength testing and nanoleakage, and qualitatively using transmission electron microscopy. Our findings will improve adhesion and restoration technology, as well as the longevity of a wide spectrum of esthetic bonded dental restorations. 牙本質粘接劑的出現徹底改變牙科修復技術. 可是,樹脂牙本質粘接的耐用性仍然是一個大問題. 為了延長樹脂牙本質粘結的壽命，未來牙本質粘合劑應用少親水性樹脂.“乙醇濕粘結”技術已被證明可以更好地滲透疏水性樹脂和包蓋混合層的膠原蛋白. 洗必泰（放線菌酮）是一種有效的蛋白酶抑製劑, 在牙本質粘合劑應用前使用洗必泰, 已被證明可以防止混合層的膠原蛋白分解.因此,放線菌酮的應用加“乙醇濕粘結”技術應可以減少膠原的降解, 提高結合界面的耐久性. 擬議項目的目的是評估“乙醇濕粘結”技術與放線菌酮停止破壞牙本質粘結界面成效. |
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| Realisation of objectives: | Objective 1: To evaluate the effect of ethanol-wet bonding (EWB) with or without chlorhexidine (CHX) on the bond durability of hydrophobic adhesives to normal and caries-affected dentin The first objective is 100% completed. Dentine surfaces of molars were etched after caries removal and randomly allocated to four groups. In Groups 1 and 2, dentine surfaces were saturated with either 2 ml of 100% ethanol or 2 ml of ethanol with 2% CHX for 60 s. In Groups 3 and 4, dentine surfaces were saturated with either 15 µL of distilled water or 15 µL of distilled water with 2% CHX for 60 s. Two coats of primer, followed by neat resin were applied and light-cured for 40 s. Resin composite build-ups were placed and bonded specimens were sectioned for bond strength testing after 24 h and 12 months’ storage in artificial saliva. Bond strength data were analyzed using 3-way ANOVA and SNK tests. Interfacial nanoleakage was evaluated using a field-emission scanning electron microscopy and data were analyzed using Kruskal-Wallis test. Objective 2: To examine the effect of EWB with or without CHX on the bond durability of fiber post luted to intra-radicular dentin with hydrophobic adhesives The second objective is 100% completed. Ninety-six extracted human teeth with a single root and root canal were prepared for post placement after endodontic treatment. The teeth were randomly divided into four groups after etching and rinsing for rewetting: Group 1: water-wet bonding, Group 2: water-wet bonding with CHX, Group 3: ethanol-wet bonding and Group 4: ethanol-wet bonding with CHX. Teeth in Groups 1 and 2 were treated with either distilled water or distilled water with 2% CHX for 60 s; while teeth in Groups 3 and 4 were treated with either 100% ethanol or 100% ethanol with 2% CHX. Two coats of primer, followed by neat resin were applied and light-cured for 40 s. Fiber posts were luted to bonded root dentine using dual-cure resin cement. Bonded roots were subjected to push-out bond strength testing and interfacial nanoleakage evaluation after 24 h, 6 and 12 months’ of storage. Data were analyzed using 3-way ANOVA and SNK tests. | |||||||||||||||||||||||||||
| Summary of objectives addressed: |
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| Research Outcome | ||||||||||||||||||||||||||||
| Major findings and research outcome: | Objective 1 (1) Adjunctive application of chlorhexidine (CHX) and ethanol-wet bonding (EWB) on durability of bonds to sound and caries-affected dentine. Major research outcome: After 12 months of ageing in artificial saliva, the adjunctive application of CHX with EWB preserved the bond strength of hydrophobic adhesive to both sound dentine (SD) and caries-affected dentine (CAD). Conversely, the adjunctive application of CHX with water-wet bonding (WWB) similarly preserved the bond strength of hydrophobic adhesive to SD after 12 months. Incorporation of CHX to EWB with hydrophobic adhesive enhances the success rate of aesthetic bonded restorations. Research output: A manuscript has been provisionally accepted for publication at Journal of Dentistry and a revised version has been submitted (Part C 8 No.1). Conferences abstract: Three abstracts presented (Part C 9 No. 1, 2, 7, 8). 1 Faculty Research Seminar delivered 17 Oct 2011. (2) A new method of evaluation of fracture patterns following microtensile bond strength testing using polarized light microscopy Major research outcome: The results of EDX mapping and SEM observation showed that the use of polarized light microscopy is a simple, viable method for differentiation between the resin-covered and dentin surfaces for determining fracture pattern analysis after bond testing. Research output: A manuscript has been accepted for publication at Journal of Adhesive Dentistry (Part C item 3). (3) Effect of solvent on the inhibition of matrix metalloproteinases (MMP) by chlorhexidine Major findings and research outcome: CHX solvated in ethanol and acetone had greater inhibitory effect on soluble and matrix-bound MMPs than in water. Conferences abstract: One abstract presented (Part C 9 No. 6). For Objective 2 (1) Effect of chlorhexidine and ethanol-wet bonding with hydrophobic adhesive to intraradicular dentine Major research outcome: After 12 months of ageing in artificial saliva, EWB groups showed significantly higher bond strength than WWB groups for all three root regions tested. The bond strengths of the EWB groups were not affected by ageing in artificial saliva. However, the addition of CHX to EWB did not further improve the bond strength of fiber post to intraradicular dentine, when compared to EWB alone. EWB with a hydrophobic adhesive alone could improve the bond durability of fiber post to intraradicular dentine and therefore would increase the success rate of post and core restorations of endodontically treated teeth. Research output: A manuscript has been published at Journal of Dentistry (Part C item 2). Conference abstract: Three abstracts presented (Part C 9 No.3, 4 & 5). | |||||||||||||||||||||||||||
| Potential for further development of the research and the proposed course of action: |
It has been shown in our in vitro study that ethanol-wet bonding (EWB) + chlorhexidine (CHX) improved resin-dentin bond durability in both sound and caries-affected coronal dentin, while EWB alone could improve the bond durability of fiber post to intraradicular dentine. Future studies should investigate the effects of EWB with or without CHX on vital pulp so that this beneficial bonding technique can be applied clinically to enhance the longevity of esthetic tooth colored restorations as well as post and core restorations of endodontically treated teeth. Because of the electrostatic binding nature of CHX, another possible direction of research will be to prolong the action of MMP inhibitor in the hybrid layer. Further studies should investigate the effect of incorporation of methacrylate-based, matrix metalloproteinases inhibitory monomers into experimental adhesives on preventing bond degradation. | |||||||||||||||||||||||||||
| Layman's Summary of Completion Report: | Despite the popular usage of dentin adhesives, durability of resin-dentin bonds is still a major clinical problem. To extend the longevity of resin-dentin bond, future dentin adhesives should be rendered less hydrophilic as increased water sorption by hydrophilic resin monomers causes plasticization of the polymer chains and decreases the mechanical properties of dentin adhesives over time. The ethanol wet bonding (EWB) technique allowed better infiltration of hydrophobic resin and encapsulation of collagen fibrils. Conversely, chlorhexidine (CHX), a potent matrix metalloproteinases inhibitor, has been shown to prevent collagen degradation in the hybrid layer. Hence, the adjunctive application of EWB and CHX with hydrophobic adhesives should be a promising solution to improve the durability of the bonded interface by reducing collagen and resin degradation simultaneously. Findings of our study showed that EWB + CHX improved the stability resin-dentin bond over time in both sound and caries-affected coronal dentin, while EWB alone could improve the bond durability of fiber post to intraradicular dentine. The results of our project established a solid foundation for further in vivo investigation of this beneficial bonding technique clinically to improve the longevity of a wide spectrum of bonded restorations for our patients. | |||||||||||||||||||||||||||
| Research Output | ||||||||||||||||||||||||||||
| Peer-reviewed journal publication(s) arising directly from this research project : (* denotes the corresponding author) |
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| Recognized international conference(s) in which paper(s) related to this research project was/were delivered : |
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| Other impact (e.g. award of patents or prizes, collaboration with other research institutions, technology transfer, etc.): |
In this research project, we have collaborated with Prof Franklin Tay (Department of Endodontics, School of Dentistry, Georgia Regents University, Augusta, GA, USA) and Prof Nigel King (Paediatric Dentistry, School of Dentistry, University of Western Australia, Oral Health Centre of WA, Australia. They have provided expert advice on the design of the experimental studies. | |||||||||||||||||||||||||||
| SCREEN ID: SCRRM00542 |