JABFM eISSN 2280-8000
J Appl Biomater Funct Mater 2016; 00(00): 000-000 DOI: 10.5301/jabfm.5000261
Original Article
Comparison of shear bond strength of universal adhesives on etched and nonetched enamel Riccardo Beltrami1, Marco Chiesa2, Andrea Scribante2, Jessica Allegretti2, Claudio Poggio2 1 2
Statistics Section, Department of Brain and Behavioral Sciences, University of Pavia, Pavia - Italy Dentistry Section, Department of Clinical-Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia - Italy
Abstract Background: The purpose of this study was to evaluate the effect of surface pretreatment with 37% phosphoric acid on the enamel bond strength of different universal adhesives. Methods: One hundred and sixty bovine permanent mandibular incisors freshly extracted were used as a substitute for human teeth. The materials tested in this study included 6 universal adhesives, and 2 self-etch adhesives as control. The teeth were assigned into 2 groups: In the first group, etching was performed using 37% phosphoric acid for 30 seconds. In the second group, no pretreatment agent was applied. After adhesive application, a nanohybrid composite resin was inserted into the enamel surface by packing the material into cylindrical-shaped plastic matrices. After storing, the specimens were placed in a universal testing machine. The normality of the data was calculated using the Kolmogorov-Smirnov test. Analysis of variance (ANOVA) was applied to determine whether significant differences in debond strength values existed among the various groups. Results: Groups with phosphoric acid pretreatment showed significantly higher shear bond strength values than groups with no enamel pretreatment (p0.05). Conclusions: All adhesives provide similar bond strength values when enamel pretreatment is applied even if compositions are different. Bond strength values are lower than promised by manufacturers. Keywords: Enamel, Shear bond strength, Universal adhesives
Introduction The contemporary adhesive systems can be classified, on the basis of underlying adhesion strategy to interact with enamel and dentin substrates, into etch-and-rinse and self-etch adhesives (1). While the etch-and-rinse approach requires a separate acid-etch step to promote dentin and enamel demineralization before monomer infiltration, demineralization and infiltration occur simultaneously in the self-etch approach (2) and the washing process is removed (1, 3). The main disadvantage of etch-and-rinse adhesives is their susceptibility to the complete filling of the interfibrillar Accepted: November 2, 2015 Published online: Corresponding author: Claudio Poggio Department of Clinical-Surgical Diagnostic and Pediatric Sciences Section of Dentistry Policlinico “San Matteo” Piazzale Golgi 3 27100 Pavia, Italy
[email protected]
© 2016 Wichtig Publishing
spaces by resin monomers thus resulting in areas of exposed demineralized enamel and dentin within the bonded interface (4-8). This incomplete infiltration of resin monomers network may lead to interfacial hydrolysis (9, 10) and postoperative sensitivity (3, 11). Self-etch adhesives incorporate the partially dissolved smear layer, resin, collagen and mineral into the hybrid layer and the superficial portion of the resin tags which may prevent postoperative sensitivity. Their use on dentinal tissue is therefore preferred. However, their etching agents are not as effective as phosphoric acid, and lower enamel bond strengths have been registered (12). Thus, when only enamel is exposed, self-etch adhesives can not ensure adequate enamel shear bond strength both for dental restorations both for bonding orthodontic brackets. To overcome this limitation, enamel acid pretreatment and consequent washing have been recommended prior to the application of self-etch adhesives (13, 14). Facing these technical limitations, in order to simplify adhesive procedures and shorten the application time, new single-stage self-etching adhesive systems have been introduced with improved chemical structure and different application patterns (15, 16). These systems combine acid primer and bond in the same solution which should be applied in 1 step (17, 18). Micromechanical retention provided by resin monomers interlocked in the created porosities is the principal mechanism of adhesion (19),
Shear bond strength of universal adhesives
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although the hybrid layer has a submicron thickness (20). Self-etch adhesives contain specific monomers characterized by at least 1 polymerizable group and a functional group, which have different purposes, such as wetting and demineralizing the substrate (21, 22). Many universal adhesives have been launched, but few in vitro and clinical studies support and compare the effectiveness of adhesion. Each self-etching adhesive system may have different ingredients which can affect the performance of adhesion (23). The aim of this in vitro laboratory study was to predict the performance of these products both on etched and intact enamel in a short period of time using a shear bond strength test. We used bovine teeth. Although it is preferable to use extracted human teeth for bonding research (24), it has become increasingly difficult to obtain such samples for laboratory studies in Italy. Bovine teeth have the advantage that bovine enamel is similar to human enamel thus allowing large samples for in vitro studies on enamel bonding (25). Bovine teeth also have large, flat surfaces and are unlikely to have undergone prior caries challenges that could affect the test result. The mineral distribution within the carious lesions in bovine teeth is reportedly similar to that found in human teeth, and the structural changes that occur in human and bovine teeth are also similar (26). The null hypothesis tested was that there would be no differences between the bond strength of 7 different 1-step self-etch adhesives and a conventional self-etch adhesive, whether they were applied on etched enamel or on intact enamel surfaces.
Methods One hundred and sixty bovine permanent mandibular incisors freshly extracted and stored in a solution of 0.1% (wt/vol) thymol were used as a substitute for human teeth
(26, 27). The criteria for tooth selection included intact buccal enamel with no crack caused by extraction. The teeth were cleansed of soft tissue and embedded in self-curing, fast- setting acrylic resin (Rapid Repair, DeguDent GmbH, Hanau, Germany). Specially fabricated cuboidal Teflon mold was filled with the acrylic resin and allowed to cure, thus encasing each specimen while allowing the buccal surface of enamel to be exposed. Each tooth was oriented so that its labial surface was parallel to the shearing force. The buccal enamel surface of all specimens was flattened with aluminum oxide disks of sequentially decreasing granulation (400, 600, 1200 grit) with copious water coolant to obtain flat enamel/dentin surfaces (28). This process standardizes the orientation of enamel prisms and removes the outer hypermineralized and acid-resistant enamel. It is also consistent with clinical practice when the outer 0.5 mm of labial enamel is removed during beveling or for veneering (29). The materials tested in this study included 6 universal adhesives (Futurabond M+ by Voco, Scotchbond Universal by 3M ESPE, Adhese Universal by Ivoclar Vivadent, Clearfil Universal Bond by Kuraray, GBU-500 by GC Corporation and Peak Universal Bond by Ultradent) and 2 self-etch adhesives (Clearfil SE Bond 2 by Kuraray and OptiBond XTR by Kerr) as control. The specifications of all adhesive systems are listed in Table I. The adhesive systems were applied to the demarcated bonding area, following each manufacturer’s instructions. Before application of the adhesive systems, the labial surface of each incisor was cleaned for 10 seconds with a mixture of water and fluoride-free pumice in a rubber-polishing cup with a low-speed handpiece. The enamel surface was rinsed with water to remove pumice or debris and then dried with an oilfree air stream.
TABLE I - Adhesive systems used in study Adhesive
Manufacturer
Batch number Composition
pH Application protocol
Futurabond M+ Voco, Cuxhaven, 1442146 Germany
2-Hydroxyethyl methacrylate (10%-25%), BIS-GMA (10%-25%), ethanol (10%-25%), acidic adhesive monomer (2.5%-5%), Urethane dimethacrylate (2.5%-5%), catalyst, pyrogenic silicic acids.
Scotchbond Universal DCA
3M ESPE, St. Paul, MN, USA
547836
MDP phosphate monomer, dimethacrylate resins, HEMA, Vitrebond™ copolymer, filler, ethanol, water, initiators, silane.
2.7 1. Apply for 10 seconds 2. Dry for 5 seconds 3. Light for 10 seconds
Adhese Universal
Ivoclar Vivadent AG, Schaan, Liechtenstein
T02458
2-Hydroxyethyl methacrylate (10%-25%), BIS-GMA (10%-25%), ethanol (10%-25%), decamethylendimethacrylate (3%-10%), methacrylated phosphoric acid ester (3%-10%), camphorquinone (1%-2.5%), 2-dimethylaminoethyl methacrylate (1%-2.5%).
ND 1. Apply for 10 seconds 2. Dry for 5 seconds 3. Light for 10 seconds
Bisphenol A diglycidylmethacrylate (15%-35%), 2-hydroxyethyl methacrylate (10%-35%), ethanol (
