Dent Mater 8:74-78, March, 1992
In vitro bond strengths of three current dentin adhesives
to primary and permanent teeth S. Bordin-Aykroyd 1, J. Sefton 25, E.H. Davies 2 Departments of Children's Dentistry,2Biomaterials, The Institute of Dental Surgery, London, England 3Nowat Amerlite DiagnosticsLimited, Pollards WoodLaboratory, Bucks, England Abstract. The in vitro shear bond strengths of three chemically different dentin bonding agents were tested between both permanent and deciduous dentin and their respective anterior composite filling materials. Theeffectofthepost-mortemageoftheteeth on bond strength was evaluated by comparison of fresh (extracted within 24 h) and old (extracted within 10 d) teeth. The results indicated that these materials bonded more strongly to the dentin of permanent than to deciduous teeth (8.8 + 4.9 M N/m 2vs. 6.2 + 4.8 M N/m2). The intermaterial comparison indicated that the bondstodentinwerestrongestforScotchbond2(12.3 +4.4 MN/m 2) followed by Tenure (6.9 + 3.3 MN/m 2) and then Gluma (3.3 + 1.7 MN/m2). Both the above findings were shown to be statistically significant. The effect of time lapse after extraction of the teeth was not statistically significant. Recent advances in preventive and conservative dentistry and the development of adhesive restorative materials have led to the theoretical reduction ofmicroleakage and marginal staining. To be effective, a dental bonding agent needs to achieve a strong and immediate bond between the tooth and restorative material. With composites, dentin bonding agents must resist the polymerization contraction forces so that microscopic gaps can be minimized. Suitable adhesion between restorative materials and tooth tissue was first achieved by Buonocore in 1955, using phosphoric acid in the acid-etch technique to create micromechanical retention of resins to enamel. However, conditioning of dentin with this strong mineral acid has been shown to result in a non-retentive, weak, sponge-like structure consisting mainly of collagen (Hoppenbrouwers et al., 1974; Torney, 1978; Stanford, 1985) and also to cause pulpal irritation (Stanley et al., 1975). Thus, much research has been conducted into the development of conditioners and adhesives for forming a suitable bond between dentin and composite restorative materials. Most commercial dentin bonding systems rely on conditioning the dentin with an acidic solution, which exposes the tubules and decalcifies the dentin. There is much speculation as to the bonding mechanism of the adhesives, but evidence suggests that there is mechanical retention due to infiltration of monomers into the surface zone of demineralized dentin (Erickson, 1989). The chemical composition and morphology of the conditioned dentin should therefore be of paramount importance for adhesion. So far, comparative studies on dentin bonding agents ofthe current "third generation" have investigated applications in the permanent dentition (Eliades et al., 1985; Cooleyand Dodge, 1989). Enamel of primary teeth has a reduced calcification
74 Bordin-Aykroyd et aL/Adhesives on primary and permanent dentin
compared with enamel of permanent teeth. Some chemical and morphological differences between permanent and deciduous dentin also seem to exist (Hirayama et al., 1986). This investigation assesses three chemically different dentin adhesive systems by measuring the in vitro shear bond strengths between dentin and anterior composite restorative materials, on both deciduous and permanent teeth.
MATERIALS AND METHODS The systems investigated were three currently commercially available dentin bonding agents--Scotchbond 2, Gluma, and Tenure--which were used with their appropriate photopolymerizable microfilled anterior composite systems--Silux Plus, Pekalux, and Perfection, respectively. The details of material compositions and information on the manufacturers are given in Table 1. Application techniques for each of the adhesive systems are summarized in Table 2. One hundred forty-five extracted non-carious or minimally carious human teeth (76 deciduous and 69 permanent) were used in this study. Within each group, two subgroups were created, one where the specimens were "fresh" (tested within 24 h of extraction), the other where the teeth were "old" (tested within 10 d of extraction). These subgroups were then further divided into three groups for each material, with a minimum of 10 teeth in each group. The teeth were stored in distilled water at 4°C until use. Individual teeth were prepared by flat wet-grinding of the occlusal surface by means of a water-cooled Knuth Rotor Grinder with 80-grit silicon carbide paper. Final polishing of the dentin surface was carried out with 500-grit paper. Care was taken to ensure that a sound dentin surface with a minimum diameter of 3.5 mm was available for adhesion testing. Each specimen was mounted in a plasticine block and, after being washed and dried, was treated according to the manufacturer's instructions (Table 2). Following the application of the dentin bonding agent, the appropriate composite was added to the surface by packing the material into a copper cylinder with an internal diameter of 3 mm and a height of 2 mm. The composite was cured with a standard light source of 450-470 nm (Elipar Uvio-Visio Universal, ESPE GmbH, Oberbay, Germany) held close to the surface. A 60 s exposure was used to ensure thorough polymerization. The restored teeth were removed from the plasticine, immersed in distilled water, and stored in an incubator at 37°C for 7 d. Prior to being tested, the teeth were mounted in plaster using ring molds 2.5 cm in diameter and 1.5 cm deep. The shear bond strength was tested by means of a wireloop shearing jig in the tensile mode of an Instron Universal
TABLE 1: MATERIALSUSED Components Presentation Chemical Composition Batch No. SCOTCHBOND 2/SILUX PLUS SYSTEM, 3M Health Care Dental Products, Loughborough, UK. Scotch Prep dentin primer 1 part liquid aq. solution of maleic acid and hydroxyethylmethacrylate(HEMA) 8AA Scotchbond 2 light cure dental adhesive 1 part liquid HEMA, bis-GMAviscosity modifier, photoinitiator 8AA Silux Plus 1 part paste Microfill anterior composite acrylate resin (Universal shade) 8BH1 TENURE/PERFECTION SYSTEM, DenMatCorporation, Thornton Heath, UK. Tenure dentin conditioner 1 part liquid acidified aqueous solution of aluminum oxalate 291014 Tenure solution 2 parts liquid acetone solutions of PMDM + NTG-GMA A: 461010, B: 462012 Visar Seal 1 part liquid low-viscositybis-GMA resin 139098 Perfection 1 part paste microfill anterior composite acrylate resin (extra-light& Opaque shades) 287011 GLUMA/PEKALUXSYSTEM, Bayer Dental, Newbury, UK. Gluma 2 cleanser 1 part liquid aq. solution of EDTA (0.5 M, pH 7.4) 1957D Gluma 3 primer 1 part liquid aq. solution of glutaraldehyde (5%) + HEMA (35%) 1967D Gluma 4 sealer 1 part liquid polyfunctional methacrylic esters (98%) 2050D Pekalux 1 part paste polyfunctional methacrylate microfill anterior composite (universal shade) 2036D
testing machine (Instron Ltd., High Wycombe, UK) at a crosshead speed of 0.5 mm/min. The "bond strengths" were recorded for all specimens, and the mean for each subgroup was calculated. RESULTS The individual shear bond strengths are shown in the incidence plot of data (Fig. 1) and the mean values in Table 3. Intermaterial Comparison. Scotchbond 2 generally showed bond strengths (12.3 _+ 4.4 MN/m 2) higher than those of Tenure (6.9 _+3.3 MN/m2), which in turn were higher than those of Gluma (3.3 _+1.7 MN/m2). A Tukey's test on these pooled results confirmed these observations (p < 0.05) by the lack of overlap between the calculated intervals (Fig. 2). However, the distribution of the entire data and the subgroups was not normal, and the variance between the materials not homogenous. The data were therefore transformed to normality and the variance stabilized by a power (1/3) transformation for the different materials, ages, types of teeth, and Student t tests were carried out among the subgroups (Mabotho, 1990). These statistical analyses (Table 3) also confirmed that there was a significant difference (p< 0.0001) when materials were compared (S>T, S>G, T>G). Permanent and Deciduous Comparison. Permanent teeth showed a higher mean bond strength for all materials tested (8.8 _+4.9 MN/m 2) than the deciduous teeth (6.2 _ 4.8 MN/m2); these differences were significant (p < 0.001). Fresh and Old Comparison. Only small differences between the mean values of fresh and old teeth could be observed for each material. Fresh teeth showed a slightly higher mean shear bond strength (8.2 _+5.5 MN/m 2) than old teeth (6.9 _ 4.4 MN/m2), though not statistically significant (p > 0.1). Examination of the fractured surfaces revealed that most failures occurred at the dentin/adhesive interface. However, subgroups with the highest mean bond strengths showed an increased incidence of failure at the adhesive/composite interface. Failures within the dentin for Scotchbond 2 on deciduous teeth, and within the composite for Tenure were also noted. Statistical treatment of these observations by a forward stepwise selection ofvariables into a logistic model showed that the probability of the failure occurring at the interface is directly dependent on the force required and the material, but not on the age or type of tooth (Mabotho, 1990).
TABLE 2: APPLICATIONTECHNIQUES Procedure Time (s) SCOTCHBOND 2/SILUX PLUS SYSTEM (t) Apply primer with agitation 60 (2) Dry (until dull and dry appearance) 5 (3) Apply dental adhesive uniformly 5 (4) Gently air-thin, where necessary 5 (5) Cure 20 (6) Check adhesive coating with probe 5 (7) Apply composite and polymerize Total application time for Scotchbond 2 adhesive 100 TENURE/PERFECTION SYSTEM (1) Apply conditioner 30-60 (2) Rinse 15 (3) Dry 5 (4) Mix and apply liquids A & B 5 (5) Allow to dry 10-20 (6) Re-apply liquids A & B 5 (7) Allow to dry 10-20 (8) Appy Visar Seal 5 (9) Air-thin until uniform layer 5 (10) Cure 20 (11) Apply composite and polymerize Total applicationtime for Tenure adhesive 110-160 GLUMA/PEKALUXSYSTEM (1) Apply cleanser 30 (2) Rinse 15 (3) Dry 5 (4) Apply primer 5 (5) Leave 30 (6) Dry 5 (7) Apply sealer 5 (8) Air-thin to uniform layer 5 (9) Apply composite and polymerize Total application time for Gluma adhesive 100
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