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Evaluation of compatibility between different
types of adhesives and dual-cured resin cement
Article in The journal of adhesive dentistry · February 2002
Source: PubMed
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Vol 4, No 4, 2002 271
Evaluation of Compatibility Between
Different Types of Adhesives and
Dual-cured Resin Cement
Eduardo B. Francoa^ /Lawrence G. Lopes b/Paulo H. P. D’alpinob^ / José C. Pereira a^ /Rafael F. L. Mondellic/Maria F. L. Navarro d
a (^) Associate Professor, Department of Operative Dentistry, Endodon- tics and Dental Materials, Bauru Dental School, University of São Paulo, SP, Brazil. b (^) PhD student, Department of Operative Dentistry, Endodontics and Dental Materials, Bauru Dental School, University of São Paulo, SP, Brazil. c (^) Assistant Professor, Department of Operative Dentistry, Endodon- tics and Dental Materials, Bauru Dental School, University of São Paulo, SP, Brazil. d (^) Professor, Chief of the Department of Operative Dentistry, Endo- dontics and Dental Materials, Bauru Dental School, University of São Paulo, SP, Brazil.
Purpose: The objective of this in vitro study was to evaluate the bonding compatibility between different adhesives and a dual-cured resin cement, using a conventional tensile bond test. Materials and Methods: The adhesives used were: Prime & Bond (PB) (Dentsply) (PB), Scotchbond Multi Purpose (SB) (3M), and the activator Self Cure (SC) (Dentsply). The dual-curing resin cement used was Enforce (EF) (Dentsply). Six groups with five specimens in each were tested: G1: EF/PB/EF (light cured); G2: EF/SB/EF (light cured); G3: EF/PB+SC/EF (light cured); G4: EF/PB+SC/EF (only chemically cured); G5: EF/EF (light cured); G6: EF/EF (only chemically cured). The resin cement was applied in two stainless steel molds with a cone-shaped perforation measuring 4 mm in diameter and 1 mm in thickness, and the adhesive was applied between them. Ten minutes after specimens were cured, the tensile strength was measured in a universal testing machine at a crosshead speed of 0.5 mm/min. Results: The mean values (MPa) ± SD obtained in each experimental group were: G1: 1.4 ± 0.2; G2: 1.3 ± 0.2; G3: 1.2 ± 0.4; G4: 0.8 ± 0.2; G5: 1.2 ± 0.1; G6: 0.7 ± 0.1. The results were statistically evaluated using nonparametric Kruskal-Wallis and Dunn tests (p ≤ 0.05). Statistically significant differ- ences among groups were found only between G1 and G4, and G1 and G6. Conclusion: There was no incompatibility among the different adhesives used with dual-cured resin ce- ment. The lowest tensile bond strength values occurred in the absence of photoactivation.
J Adhes Dent 2002; 4: 271–275. Submitted for publication: 02.04.02; accepted for publication: 23.07.02.
Reprint requests: Dr. Eduardo B. Franco, Department of Operative Dentistry, Endodontics and Dental Materials, Bauru Dental School, University of São Paulo. Al. Octávio Pinheiro Brizola 9-75, 17012901, Bauru-SP, Brazil. Tel: +55-14-235-8265, Fax: +55-14-235-8325. e-mail: ebfranco@fob.usp.br
ne of the main objectives of dental research is to develop adhesives which are universally ap- plicable. Factors such as time and simplification of the clinical steps have led to an increased use of the simplified-step adhesives in association with resin materials. The conventional (three-step) and simplified-step adhesives are presently the most common of the ad- hesive systems currently on the market. In the former, an acid is applied separately to enamel and dentin. Thereafter, the primer – which contains hy- drophilic resin (HEMA) and solvents (ethanol, ace- tone, or water) – is applied to the dentin. Subse- quently, the adhesive, which contains resin mono- mers (bis-GMA and UDMA), is applied to both enam- el and dentin. The one-bottle adhesive systems con-
O
Vol 4, No 4, 2002 273
mold. The adhesive was applied over the cement sur- face of the first mold and photocured for 20 s. The resin cement was then applied into the second mold and photocured for 40 s to produce a layered spec- imen of resin cement/adhesive/resin cement (Fig 1 ) with an hourglass shape. For group 3, a dual adhe- sive was obtained by mixing similar proportions of Prime & Bond 2.1 and Self Cure activator. For group 4, the application of the materials was the same; however, the resin cement and the adhesive were not photocured. To ensure that the chemical curing reac- tion was completed in the first part of the resin ce- ment, 5 min were allowed to elapse before adhesive application. The same time was allowed before the second application of the resin cement. For groups 5 and 6, only the luting cement was applied into the two molds, without application of the adhesive be- tween them. These last two groups served to estab- lish the cohesive strength of the resin cement. Tensile strength was measured in a universal testing machine (Kratos, São Paulo, Brazil). The two molds with the cement/adhesive/cement speci- men were adapted and fixed to the device that was attached to a load cell and base (Fig 2). The tensile test was performed 10 min after application of the luting cement at a crosshead speed of 0.5 mm/min until fracture. To improve the interpretation of the data, the acidity (pH) of the adhesives was measured. Three ml of each adhesive was dispensed into clean glass vials and stirred for 30 s. The pH values of the adhesives were measured at ambient tempera- ture (22 to 25°C) using a digital pH meter (Micronal B371, São Paulo, Brazil).
RESULTS
The mean tensile strengths (MPa) and standard de- viations for the different groups are summarized in Table 2. The pH value of each adhesive is also shown in Table 2. The data were analyzed with the nonparametric tests Kruskal-Wallis (one-way) and Dunn for individual comparisons (p ≤ 0.05). No significant differences were detected among the studied groups, except between group 1 (EF/PB/EF, light cured) and group 4 (EF/PB + SC/EF, chemically cured). Although there was also a significant difference between group 1 (EF/PB/EF, light cured) and group 6 (EF, chemically cured), it was not relevant to the analysis, since no adhesives were applied in group 6.
DISCUSSION
When the simplified-step adhesives are used in association with resin materials which contain ele- ments responsible for the chemical curing reac- tion, there is an interaction of the residual acidic monomers from the adhesive inhibition layer with the binary peroxide-amine system, inhibiting the adhesive process. 6,10,13^ The results of this study showed that the different adhesives had no influ- ence on tensile bond strength when used in asso- ciation with the dual-cured resin cement. Yamauchi^14 and Tay et al^13 state that the residual acidic monomers cured poorly in the presence of the peroxide/amine system. The dual-cured resin cement contains components responsible for physical and chemical polymerization.4, In the present study, Prime & Bond 2.1 had the lowest pH (2.1); however, it demonstrated the high- est mean tensile strength. This can be explained by the fast curing reaction induced by photopolymer- ization. Thus, direct contact of the peroxide/amine system with the acidic layer formed over the adhe- sive was prohibited. The reaction begun by immedi- ate photopolymerization had a protective function. A recent study demonstrated that the photopoly- merization of the dual-cured resin cements promot- ed a quick initial hardening.^7 Schiltz et al,^11 using a dual-cured resin cement (Duo-Link, Bisco), reported that the bond strength
Fig 1 Molds with the finished specimen (resin cement/ adhesive/resin cement).
274 The Journal of Adhesive Dentistry
was inversely proportional to the interval between the application of the cement and photopolymer- ization. They stated that the reaction between acid- ic monomers and tertiary amine occurs slowly. For this reason, group 4 was included in this study, and the chemically-cured material was allowed 5 min of contact in the first and second stages of specimen preparation in order to permit a possible interaction between acidic monomers and tertiary amine. Although there was a decrease in the bond- ing strength in this group (0.8 MPa), this finding was not due to the acid-base interaction; rather, it might be related to the absence of the photopoly- merization, reducing the degree of conversion. This was observed in group 6 (0.7 MPa), where the co- hesive strength of the resin cement cured only by chemical reaction was measured. In accordance with this speculation, Breeding et al 1 reported that if a dual-cured cement is cured only chemically, there will be a low degree of conversion and conse- quently low hardness value. However, the associa- tion of the two activation modes, physical and chemical, leads to a higher degree of hardness.
Adhesive acidity did not influence results in group 4, probably because the mixture of Prime & Bond 2.1 with Self Cure activator raised the pH from 2. to 4.6 (Table 2). In these experiments, the specimens were tested 10 min after completion, since the intent was to evaluate only the direct influence of the pH on ten- sile bond strength with dual-cured resin cement, dis- regarding others factors that could potentially affect the interpretation of the results, such as water stor- age or thermal cycling. This methodology allowed the direct evaluation of the compatibility between different adhesives and dual-cured resin cement. In other research carried out by this group (un- published data) using the same methodology, in which a chemically-cured composite (Adaptic, Dentsply) was used with several adhesives such as Prime&Bond, there was a total absence of compat- ibility between them (0 MPa). Even though the pH of adhesives did not influence the bonding strength values with the dual-cured resin cement used in this study, it would seem important for clinicians to avoid the combination of products from different
Table 2 Means and standard deviations in MPa of the tensile strength test and pH values of the different adhesives Groups⇒ G1 G2 G3 G4 G5 G
Means ± SD 1.4 ± 0.2 1.3 ± 0.2 1.2 ± 0.4 0.8 ± 0.2 1.2 ± 0.1 0.7 ± 0. pH PB 2.1 SB 6.2 PB+SC 4.6 PB+SC 4.6 – –
Fig 2a (left) The specimen adapted and fixed to the device that is attached to the load cell.
Fig 2b (right) Specimen mounted in the base of the universal testing machine.
