Basic Research—Technology
The Evaluation of Bond Strength of a Composite and a Compomer to White Mineral Trioxide Aggregate with Two Different Bonding Systems Emine ¸Sen Tunç, DDS, PhD,* Is¸ıl ¸Sarog˘lu Sönmez, DDS, PhD,† ¸Sule Bayrak, DDS, PhD,* and Türkan Eg˘ilmez, DDS* Abstract The purpose of this study was to evaluate the bond strength of a resin composite and a polyacid modified composite or “compomer” to white mineral trioxide aggregate (WMTA) with two different bonding systems (total-etch one bottle and self-etch one step). Forty specimens of WMTA were prepared and divided into four groups. In group one, Single Bond (3M/ESPE, St Paul, MN) and Z250 (3M/ESPE) were placed over WMTA. In group two, Prompt L-Pop (3M Dental Products, St Paul, MN) and Z250 were applied. In group three, Single Bond was applied with Dyract AP (Dentsply DeTrey, Konstanz, Germany), and, in group four, Prompt L-Pop was applied with Dyract AP. The shear bond strength was measured, and the fractured surfaces were examined. The results of the shear bond strength tests were analyzed by one-way analysis of variance test. The results of this study have suggested that the total-etch one-bottle adhesive system mediated a stronger bond to WMTA for both the resin composite and the compomer investigated. The placement of composite (Z250) and compomer materials (Dyract AP), used with total-etch one-bottle adhesive (Single Bond), over WMTA as final restoration may be appropriate. (J Endod 2008;34:603– 605)
Key Words Compomer, composite resin, shear bond strength, white mineral trioxide aggregate
From the *Department of Pediatric Dentistry, University of Ondokuz Mayıs, Samsun, Turkey; and †Department of Pediatric Dentistry, Faculty of Dentistry, University of Kırıkkale, Kırıkkale, Turkey. Address requests for reprints to Dr Is¸ıl S¸arog˘lu Sönmez, Kırıkkale U¨niversitesi, Dis¸ Hekimlig˘i Fakültesi, Pedodonti ABD, Kırıkkale, Turkey. E-mail address: isilsaroglu@yahoo.com. 0099-2399/$0 - see front matter Copyright © 2008 by the American Association of Endodontists. doi:10.1016/j.joen.2008.02.026
M
ineral trioxide aggregate (MTA) is a biocompatible material with numerous exciting clinical applications in endodontics (1-3). MTA is a powder consisting of fine hydrophilic particles of tricalcium aluminate, tricalcium silicate, and tricalcium oxide. It also contains small amounts of other mineral oxides, which modify its chemical and physical properties (4, 5). In the presence of moisture, MTA sets into a hard mass by forming calcium hydroxide and silicate hydrate gel (6). It is available commercially as ProRoot MTA (Dentsply; Tulsa Dental, Tulsa, OK) and has been proposed as a potential material for furcation repair, internal resorption treatment, pulpotomy procedures, and capping of pulps with reversible pulpitis (2, 4, 7–12). As the use of MTA in vital pulp therapy has gained popularity, the material that would be placed over MTA as final restoration is an important matter. The potential of restorative materials to attach to MTA is not well known. Until the initiation of this study, there were no published reports documenting the bond strength between MTA and restorative materials. The aim of this study was to measure the bond strength of a frequently used resin composite (Z250; 3M/ESPE, St Paul, MN) and a polyacid modified composite resin or “compomer” (Dyract AP; Dentsply DeTrey, Konstanz, Germany) when bonded to white MTA (WMTA) with two different bonding systems (one bottle total etch and one step self-etch).
Materials and Methods Forty specimens of WMTA (Dentsply, Tulsa Dental) were prepared by using cylindrical acryl blocks. The blocks had central hole measuring 4 mm in diameter and 2 mm in depth. WMTA was mixed according to the manufacturer’s instructions. The acrylic blocks were filled with WMTA and covered with a wet cotton pellet and temporary filling material (Cavit; ESPE America, Inc, Norristown, PA). Then, the specimens were stored at 37°C with 100% humidity for 48 hours to encourage setting. After the removal of the temporary material, the WMTA surface was not rinsed or polished. Specimens were divided into 4 groups of 10 specimens.
Group One The WMTA surface was etched for 15 seconds with 37.5% phosphoric acid etching gel (Kerr, Karlsruhe, Germany), rinsed with water for 10 seconds, and excess water was removed by blotting with absorbent paper, leaving the surface visibly moist dried. Single Bond (3M/ESPE) was then applied in 2 consecutive coats, gently air dried with oil-free compressed air from an air syringe for 5 seconds to evaporate the solvent (keeping the air syringe 2 cm from the surface), and light cured for 10 seconds. Resin composite Z250 was applied into a cylindrical shaped plastic matrix with an internal diameter of 2 mm and height of 2 mm and then light cured with a light-emitting diode light-curing unit (Elipar Freelight II, 3M ESPE) with the intensity at 1,200 mV/cm2 for 20 seconds. Group Two The WMTA surface was dried for 10 seconds (keeping the air syringe 2 cm from the surface) to ensure a dry surface. Prompt L-Pop (3M Dental Products, St Paul, MN) was applied with scrubbing for 15 seconds. Then, the surface was gently air dried with
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Basic Research—Technology TABLE 1. Mean Shear Bond Strength Values n
10
Single bond
Prompt L-Pop
Z250 Dyract
13.22a " 1.22 15.09a " 2.74
10.73b " 1.67 5.44c " 0.86
Groups identified by different superscript letters were significantly different at p
0.05.
an air syringe for 5 seconds and light cured for 10 seconds. Z250 was applied as in group one.
Group Three The same procedures were performed as in group one, but compomer material Dyract AP was placed over Single Bond instead of Z250. Group Four The same procedures were performed as in group two, and Dyract AP was placed over Prompt L-Pop. The polymerized specimens were stored in 100% relative humidity at 37°C for 24 hours. For shear bond strength testing, the samples were secured in a holder placed on the platen of the testing machine and then sheared with a knife-edge blade on a universal testing machine (Lloyd LRX; Lloyd Instruments, Fareham, Hants, UK) at a cross-head speed of 1.0 mm/min. Shear bond strength in MPa was calculated from the peak load at failure divided by the specimen surface area. The mean bond strengths of each group were compared by using one-way analysis of variance. Significance was set at the 5% level. Post hoc comparisons were made by using the Scheffé test.
Results The mean values and standard deviations of shear bond strengths are given in Table 1. When the adhesive systems were compared, Single Bond presented significantly higher bond strength values than Prompt L-Pop in both Z250 and Dyract AP groups (p 0.05). When comparing the restorative materials, the difference between Single Bond applied with Dyract AP (15.09 MPa) was not statistically significant (p ! 0.05) from Single Bond applied with Z250 (13.22 MPa). The lowest bond strength means was observed with Prompt LPop when applied with Dyract AP, and the difference between this group and the other three groups was statistically significant (p 0.05).
Discussion A clinical trial is the most valid way to evaluate the quality and efficacy of adhesion of materials. However, long-term clinical trials are difficult to perform (13). The most common method to evaluate adhesive properties of restorative materials is bond strength assessment. This has become a well-recognized method to analyze an important part of the in vitro performance of materials (14, 15). So the shear bond strength test has been used in this study to evaluate the adhesive properties of WMTA to composite and compomer restorative materials. The bond strength between two materials is of importance for the quality of the fillings. It has been estimated that bond strengths of 17 to 20 MPa may be required to resist contraction forces sufficiently to produce gap-free restoration margins (16, 17). Despite the improvements of compomer materials, the dentin bond strength of these materials remains inferior to resin composites (18 –20). In the present study, the difference between the resin composite and compomer materials was not significant (p ! 0.05) when applied with the total-etch one bottle adhesive system (Single Bond). When used with the one step self-etch adhesive system (Prompt L-Pop), compomer material showed significantly (p 0.05) lower bond strength values than the composite material. 604
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Self-etch systems contain a simultaneously acidic and hydrophilic monomer and do not need to be rinsed away after etching. By decreasing the time and steps required for placement, they have a simplified application method and they are less technique sensitive (20, 21). However there is controversy concerning the efficacy of self-etch systems. Some investigations show that they provide dentin bond strengths comparable with those obtained with the total-etch technique (14, 22–24), whereas others have observed significantly lower bond strengths (25– 28). In the present study, the total-etch one-bottle bonding system (Singlebond) showed significantly (p 0.05) higher bond strengths in both composite and compomer materials compared with the one-step self-etch bonding system (Prompt L-Pop) when bonded to WMTA. The following reasons have been advocated to account for the suboptimal performance of self-etching primers: (1) the combination of acidic hydrophilic and hydrophobic monomers into a single step may compromise polymerization of the adhesive, (2) the inherent low strength of the adhesive polymer, and (3) the lower degree of polymerization of the resin monomer because of a major solvent/oxygen inhibition effect during light activation of these materials (14). Also, one of the explanations of this low bond strength might be the incompatibility between the adhesive and the restorative material. The present results have shown that the total-etch one-bottle adhesive system (Single Bond) bonded to WMTA significantly more strongly than the self-etch one-step adhesive system (Prompt L-Pop) in both composite (Z250) and compomer (Dyract) materials. However, there are a number of different bonding materials, resin composites, and compomers available on the market. Because of the variations in the composition of different dentin adhesives, resin composites, and compomers, different results could be achieved. Further investigations with different materials are required.
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