The effect of filler addition on biaxial flexure strength and modulus of commercial dentin bonding systems

Transcription

1 The effect of filler addition on biaxial flexure strength and modulus of commercial dentin bonding systems Marcelo Giannini, DDS, MSD, PhD 1 /Donald Mettenburg 2 / César Augusto Galvão Arrais, DDS, MSD, PhD 3 / Frederick Allen Rueggeberg, DDS, MSD 4 Objective: To evaluate the effects of filler addition on the biaxial flexural strength and modulus of two commercial adhesive systems. Methods and Materials: The systems were either unfilled (Adper Single Bond [3M ESPE] and Prime & Bond 2.1 [Dentsply]) or filled (Adper Single Bond Plus [3M ESPE] and Prime & Bond NT [Dentsply]). Resin discs of each product (0.6-mm thick and 6.2 mm in diameter) were prepared in Teflon molds (n = 11 each group; 44 in total [au: edit ok?]). The adhesive solutions were light activated with a halogen light-curing unit. The discs were stored dry in the dark 24 hours before biaxial flexural testing in a universal testing machine until fracture (1.27 mm per minute; model 5844, Instron). Data were statistically analyzed by one-way ANOVA and Tukey post-hoc test at a preset alpha of Results: Flexural strength values (MPa) (SD) were Single Bond 62 (16); Single Bond Plus 46 (15); Prime & Bond 59 (13); and Prime & Bond NT 85 (16). The flexural moduli (MPa) (SD) were Single Bond 1,026 (241); Single Bond Plus 1,180 (188); Prime & Bond 744 (146); and Prime & Bond NT 1,539 (267). Based on the results, Prime & Bond NT (filled) exhibited higher flexural strength and modulus than Prime & Bond (unfilled), while no significant difference in both parameters was noted between Single Bond and Single Bond Plus. Conclusion: Filler addition to bonding agents can increase the flexural strength and modulus; however, results are product-dependent. (Quintessence Int 2011;42:xx xxx) Key words: biaxial flexural test, bonding agents, flexural modulus, flexural strength, fillers In addition to resin monomers, organic solvents, and photoinitiators, contemporary adhesive systems may contain filler particles, fluorides, and antibacterial components. 1 Such components were added to the adhesive resin composition in an attempt to improve the durability of 1 Associate Professor, Operative Dentistry Division, Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, São Paulo [au: edit ok?], Brazil. 2 Research Technician III, Dental Materials Section, Department of Oral Rehabilitation, School of Dentistry, Medical College of Georgia, Augusta, Georgia, USA. 3 Assistant Professor, Department of Operative Dentistry, School of Dentistry, University of Guarulhos, Guarulhos, São Paulo, Brazil. 4 Professor and Section Director, Dental Materials Section, Department of Oral Rehabilitation, School of Dentistry, Medical College of Georgia, Augusta, Georgia, USA. Correspondence: Prof Dr Marcelo Giannini, Department of Restorative Dentistry, Piracicaba School of Dentistry, State University of Campinas, Av Limeira, 901, Piracicaba, SP, Brazil giannini@fop.unicamp This study was presented at 85 th International Association for Dental Research in New Orleans, Louisiana, USA (March 21 to 24, 2007). dentin-resin interfaces and, as a result, adhesive restorations. 2 6 During the development of resinbased restorative materials, the addition of filler particles was essential to provide enhanced properties such as fracture and wear resistance, 7,8 so the clinical application of resin composites has become wider. Manufacturers added filler particles to increase adhesive viscosity, which prevents over-thinning of the adhesive layer, resulting in a thicker and more elastic adhesive layer. This thicker layer may relieve the contraction stresses generated by the polymerization of the overlying restorative composite and might also reduce the occlusal stress transferred to the surrounding tooth structure. 1,2,4,9 12 Moreover, similar to all effects observed in resin composites with higher filler content, 7,8 it is reasonable to expect that improvement in the physical properties of dental adhesive systems could be obtained with similar filler addition. VOLUME 42 NUMBER 2 FEBRUARY

2 Table 1 Composition of adhesive systems used Product (Manufacturer) Adper Single Bond (3M ESPE) Adper Single Bond Plus (3M ESPE) Prime & Bond 2.1 (Dentsply) Prime & Bond NT (Dentsply) Composition manufacturer supplied (Batch number) Unfilled Ethyl alcohol, Bis-GMA, HEMA, copolymer of acrylic and itaconic acids, glycerol 1,3-dimethacrylate, water, diurethane dimethacrylate (2GK) Filled (5 10 wt silane-treated colloidal silica [5 nm]): Ethyl alcohol, Bis-GMA, HEMA, copolymer of acrylic and itaconic acids, glycerol 1,3-dimethacrylate, water, diurethane dimethacrylate (4BR) Unfilled: PENTA, elastomeric dimethacrylate resins, photoinitiators, stabilizers, cetylamine hydrofluoride, acetone (378740) Filled (silicon dioxide [8 nm]): PENTA, TEGDMA, Bis-GMA, Resin R5-62-1, T-resin, D-resin, photoinitiators, stabilizers, cetylamine hydrofluoride, acetone, amorphous ( ) Abbrevs: Bis-GMA: Bisphenol A Diglycidylr Methacrylate; HEMA: 2-Hydroxyethyl Methacrylate; PENTA: Dipentaerythritol Penta Acrylate Monophosphate; TEGDMA: Triethylene Glycol Dimethacrylate. The addition of filler particles to bonding agents is limited by two aspects filler size and content both of which can compromise hybrid layer formation. 1 Filler particle size must be smaller than that of the interfibrillar spaces of demineralized collagen to allow both adhesive monomers and fillers to infiltrate not only into dentin tubules but also into the exposed collagen network. Because filler addition to bonding agents increases it viscosity and reduces its surface wetting capability, only low concentrations of filler (from 3% to 10%) can be added to one-bottle, two-step etch-and-rinse adhesives. 1 The hydrophobic bonding resins, which are commonly present in two-step, self-etching adhesive systems and three-step, etch-and-rinse adhesives, have higher filler content than the adhesive resins from one-bottle, two-step etch-and-rinse and one-step, self-etching adhesive systems, reaching up to 50% by weight. 1,13 The unfilled adhesive layer between the hybrid layer and overlying resin composite restoration presents low tensile strength and elastic modulus. 14,15 Thus, as an analogy with resin composite, it is reasonable that filler addition to adhesive resin systems can improve the physical properties of both the adhesive and hybrid layers. 2,9,11,15,16 However, little is known about the effect of addition of nanosized filler particles, even at low concentrations, on the mechanical properties (flexural strength and flexural modulus) of one-bottle, two-step etch-andrinse adhesives. Therefore, the purpose of this study was to compare the biaxial flexural strength and modulus among representative, commercially available filled adhesive systems and their unfilled counterparts. The hypothesis tested was that both biaxial flexural strength and modulus increase with filler addition, regardless of the product being evaluated. METHODS AND MATERIALS The compositions of the four adhesive systems tested are presented in Table 1. Adhesive systems were classified as either unfilled (Adper Single Bond [3M ESPE] and Prime & Bond 2.1 [Dentsply]) or filled (Adper Single Bond Plus [3M ESPE] and Prime & Bond NT [Dentsply]). Twelve drops of each bonding system component were dispensed into a mixing well and air-dried for 10 seconds to evaporate any organic solvents. The resulting fluid was placed into a Teflon mold resting on a microscope slide and Mylar sheet. After slight overfilling, another Mylar sheet was placed on the top surface, upon which another microscope slide was positioned. Manual pressure was applied to force the fluid to adapt to the mold and remove excess material. Therefore, disc-shaped specimens (0.6- mm thick and 6.2 mm in diameter) were fabricated after 10-second light exposure on both sides with a halogen light-curing 2 VOLUME 42 NUMBER 2 FEBRUARY 2011

3 Table 2 Biaxial flexural strength and moduli (MPa (sd)) of filled and unfilled bonding system. Adhesive systems Flexural strength Flexural modulus Prime & Bond 2.1 (unfilled) 59 (13) b 744 (147) C Prime & Bond NT (filled) 85 (16) a 1539 (267) A Adper Single Bond (unfilled) 62 (16) ab 1026 (241) BC Adper Single Bond Plus (filled) 46 (15) b 1180 (188) AB n = 11 specimens per group. Means having similar letters (lowercase, within flexural strength; uppercase, within flexural modulus) were not statistically different. unit (Optilux 501, Demetron/Kerr) emitting 600 mw/cm 2 as measured using a halogen radiometer (Demetron/Kerr). Eleven adhesive discs were prepared per group and dark-stored dry at room temperature for 24 hours before mechanical testing was performed. After that time, the discs were individually placed into a custommade testing jig and tested in biaxial flexure on a universal testing machine (Instron 5844, Instron) at 1.27 mm per minute until failure occurred (Fig 1). The maximum load was recorded for each specimen, and flexural strength and modulus were automatically calculated with SRS Biaxial Testing Software (Instron). Data were analyzed by one-way analysis of variance (ANOVA) and Tukey post-hoc test (preset alpha of 0.05). not different from the unfilled version of that bonding system, Single Bond (P >.05). No significant difference in flexural strength was noted between Prime & Bond 2.1 (unfilled) and either unfilled Adper Single Bond or its filled version, Adper Single Bond Plus. The flexural modulus of Prime & Bond NT (filled) was higher than that of unfilled adhesives (Adper Single Bond and Prime & Bond 2.1) (P <.05), while Adper Single Bond Plus (filled) showed greater stiffness than Prime & Bond 2.1 (unfilled) (P <.05). No significant difference in flexural modulus was observed between the two filled adhesive systems (P >.05) or the unfilled bonding agents (P >.05). Fig 1 The test setup. The arrow indicates the adhesive disc placed into a custom-made testing jig. RESULTS Biaxial flexural strength and moduli values are presented in Table 2. Statistically significant differences were found among products for flexural strength (P <.0001) and modulus (P =.002). Prime & Bond NT (filled) exhibited higher flexural strength and modulus than its unfilled counterpart, Prime & Bond 2.1 (P <.05), while the presence of fillers resulted in no significant difference regarding flexural strength and modulus for Adper Single Bond system (P >.05). The filled bonding agent Prime & Bond NT had higher flexural strength than the filled version of the competitive product Single Bond Plus (P <.05), but was DISCUSSION The research hypothesis was only partially confirmed in the current study, since only one of the evaluated products demonstrated significant improvement in strength and modulus with filler addition. Prime & Bond NT, which contains 8 nm amorphous silicon dioxide particles, showed higher flexural strength than its unfilled version. Nanofiller technology is supposed to strengthen both the adhesive and hybrid layers into which the system infiltrates, so improved marginal integrity and an increase in bond strength should be expected. In addition to advanced filler incorporation, the composition of this product includes other resin monomers VOLUME 42 NUMBER 2 FEBRUARY

4 designed to better infiltrate the demineralized dentin surface and to form a strong, crosslinked polymer network. 4,13 On the other hand, the only difference noted between the filled version (Adper Single Bond Plus) and unfilled version (Adper Single Bond) is the presence of filler particles consisting of 5% to 10% wt, 5 nm spherical silica particles. The presence of fillers did not lead to significant differences in flexural strength on Adper Single Bond. However, the association between fillers and enhanced resin formulation significantly increased the strength and modulus of Prime & Bond. The addition of filler particles increases adhesive viscosity, which is important for clinicians since filled adhesive yields a thicker layer after air-thinning. This thicker layer minimizes the effect of oxygen inhibition on polymerization, as the depth of inhibition is related to both filler presence and system viscosity. 17 Furthermore, because of its inherently lower elastic modulus compared to that of resin composite restorative materials, an adhesive layer composed of filled bonding agent may also provide relief of contraction stresses generated during polymerization of the restorative resin composite or under oclusal loading. 12,18 20 Enhancement in the physical properties of bonding systems has conflicting aspects. In contrast to the increase in flexural strength, the increase in flexural modulus due to filler addition may provide less stress relief. Because of their enhanced properties, filled adhesive resins may create a polymer layer that is not as elastic as previous unfilled resins. 12,18 20 On the other hand, filler addition results in higher flexural strength than that observed in unfilled systems. Thus, there seems to be potentially beneficial and detrimental effects simultaneously with respect to filler addition on adhesive resin composition. This study used four one-bottle, twostep etch-and-rinse adhesives (two filled and two unfilled) from two manufacturers. To analyze the influence of filler particles, the materials from the same company should have apparently similar monomeric composition. These onebottle adhesives were selected among several adhesive systems with different compositions and approaches for bonding. Thus, care must be taken when comparing the mechanical properties of these bonding agents to those of others, because flexural strength and modulus of adhesives are highly dependent on the composition of each product. While the effects of fillers on the mechanical properties of contemporary restorative composites have been well established, 8,18,19 results of flexural strength and modulus for adhesive systems are not abundant in dental literature. 1 Etch-and-rinse adhesives create a bonded interface in dentin represented by the hybrid layer formation. The hybrid layer consists of the infiltration of resin monomers into demineralized dentin around the collagen fibrils and polymerization of adhesive monomer in situ. 1,2,4,13,14 In this study, only the adhesive resin specimens were tested, so further studies are required to determine the effects of such fillers on some mechanical properties, such as flexural strength and modulus, of the hybrid layer, which is composed not only of adhesive resin but also collagen fibrils from demineralized dentin matrix. With the tendency toward filler addition in contemporary bonding agents, clinicians need to be aware that the results of enhanced properties may be productdependent. 1 Enhanced product performance has significant clinical impact, as it has the potential to reduce microleakage 21 and improve the microstructure and strength of bonding agents to dentin, 2,9,11,15,16,22 leading to more durable composite resin restorations. 10 However, the literature indicates that such benefits may not be obtained solely with filler addition, 23,24 as the monomer composition also determines the clinical performance of adhesive systems. 4 VOLUME 42 NUMBER 2 FEBRUARY 2011

5 CONCLUSION The results suggest that filler addition to bonding agents can enhance flexural strength and modulus, but such effects are product-dependent. ACKNOWLEDGMENTS This study was supported by grants from FAEPEX (#21/06), CNPq (#301769/2004-4), and CAPES BEX-0184/05-5, as well as The Medical College of Georgia. REFERENCES 1. Van Landuyt KL, Snauwaert J, De Munck J, et al. Systematic review of the chemical composition of contemporary dental adhesives. Biomaterials 2007; 28: Perdigão J, Baratieri LN, Lopes M. Laboratory evaluation and clinical application of a new one-bottle adhesive. J Esthet Dent 1999;11: Frankenberger R, Lopes M, Perdigao J, Ambrose WW, Rosa BT. The use of flowable composites as filled adhesives. Dent Mater 2002;18: Tay FR, Moulding KM, Pashley DH. Distribution of nanofillers from a simplified-step adhesive in acidconditioned dentin. J Adhes Dent 1999;1: Imazato S, Kinomoto Y, Tarumi H, Ebisu S, Tay FR. Antibacterial activity and bonding characteristics of an adhesive resin containing antibacterial monomer MDPB. Dent Mater 2003;19: Hara AT, Queiroz CS, Freitas PM, Giannini M, Serra MC, Cury JA. Fluoride release and secondary caries inhibition by adhesive systems on root dentine. Eur J Oral Sci 2005;113: Darvell BW, Clark RK. The physical mechanisms of complete denture retention. Br Dent J 2000;189: Kim KH, Ong JL, Okuno O. The effect of filler loading and morphology on the mechanical properties of contemporary composites. J Prosthet Dent 2002;87: Fanning DE, Wakefield CW, Robbins JW, Bagley AL. Effect of a filled adhesive on bond strength in three dentinal bonding systems. Gen Dent 1995;43: Boghosian A. Clinical evaluation of a filled adhesive system in Class 5 restorations. Compend Contin Educ Dent 1996;17: , Youssef JA, Turbino ML, Youssef MN, Matson E. [Bond strength to dentin of resin composites associated with filled and unfilled adhesive systems]. Pesqui Odontol Bras 2001;15: Pongprueksa P, Kuphasuk W, Senawongse P. Effect of elastic cavity wall and occlusal loading on microleakage and dentin bond strength. Oper Dent 2007; 32: Perdigão J, Lambrechts P, van Meerbeek B, Tome AR, Vanherle G, Lopes AB. Morphological field emission-sem study of the effect of six phosphoric acid etching agents on human dentin. Dent Mater 1996;12: Bae JH, Cho BH, Kim JS, et al. Adhesive layer properties as a determinant of dentin bond strength. J Biomed Mater Res B Appl Biomater 2005;74: Kim JS, Cho BH, Lee IB, et al. Effect of the hydrophilic nanofiller loading on the mechanical properties and the microtensile bond strength of an ethanol-based one-bottle dentin adhesive. J Biomed Mater Res B Appl Biomater 2005;72: Miyazaki M, Ando S, Hinoura K, Onose H, Moore BK. Influence of filler addition to bonding agents on shear bond strength to bovine dentin. Dent Mater 1995;11: Rueggeberg FA, Margeson DH. The effect of oxygen inhibition on an unfilled/filled composite system. J Dent Res 1990;69: Kemp-Scholte CM, Davidson CL. Marginal integrity related to bond strength and strain capacity of composite resin restorative systems. J Prosthet Dent 1990;64: Kemp-Scholte CM, Davidson CL. Complete marginal seal of Class V resin composite restorations effected by increased flexibility. J Dent Res 1990;69: Montes MA, de Goes MF, da Cunha MR, Soares AB. A morphological and tensile bond strength evaluation of an unfilled adhesive with low-viscosity composites and a filled adhesive in one and two coats. J Dent 2001;29: Harada TS, Pazinatto FB, Wang L, Atta MT. Effect of the number of coats of simplified adhesive systems on microleakage of dentin-bordered composite restorations. J Contemp Dent Pract 2006;7: Lee SY, Greener EH, Covey DA, Menis DL. Effects of food/oral simulating fluids on microstructure and strength of dentine bonding agents. J Oral Rehabil 1996;23: Braga RR, Cesar PF, Gonzaga CC. Tensile bond strength of filled and unfilled adhesives to dentin. Am J Dent 2000;13: Swift EJ Jr, Perdigao J, Heymann HO, et al. Eighteenmonth clinical evaluation of a filled and unfilled dentin adhesive. J Dent 2001;29:1 6. VOLUME 42 NUMBER 2 FEBRUARY