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t es Bond Strength Durability of Direct and Indirect se nz Composite Systems Following Surface Conditioning for Repair Sheila Pestana Passosa/Mutlu Özcanb/Aleska Dias Vanderleia/Fabiola Pessoa Pereira Leitea/ Estevão Tomomitsu Kimparaa/Marco Antonio Bottinoc
Purpose: This study evaluated the effect of surface conditioning methods and thermocycling on the bond strength between a resin composite and an indirect composite system in order to test the repair bond strength. Materials and Methods: Eighteen blocks (5 x 5 x 4 mm) of indirect resin composite (Sinfony) were fabricated according to the manufacturer’s instructions. The specimens were randomly assigned to one of the following two treatment conditions (9 blocks per treatment): (1) 10% hydrofluoric acid (HF) for 90 s (Dentsply) + silanization, (2) silica coating with 30Ìm SiOx particles (CoJet) + silanization. After surface conditioning, the bonding agent was applied (Adper Single Bond) and light polymerized. The composite resin (W3D Master) was condensed and polymerized incrementally to form a block. Following storage in distilled water at 37°C for 24 h, the indirect composite/resin blocks were sectioned in two axes (x and y) with a diamond disk under coolant irrigation to obtain nontrimmed specimens (sticks) with approximately 0.6 mm2 of bonding area. Twelve specimens were obtained per block (N = 216, n = 108 sticks). The specimens from each repaired block were again randomly divided into 2 groups and tested either after storage in water for 24 h or thermocycling (6000 cycles, 5°C to 55°C). The microtensile bond strength test was performed in a universal testing machine (crosshead speed: 1 mm/min). The mean bond strengths of the specimens of each block were statistically analyzed using two-way ANOVA (α = 0.05). Results: Both surface conditioning (p = 0.0001) and storage conditions (p = 0.0001) had a significant effect on the results. After 24 h water storage, silica coating and silanization (method 2) showed significantly higher bond strength results (46.4 ± 13.8 MPa) than that of hydrofluoric acid etching and silanization (method 1) (35.8 ± 9.7 MPa) (p < 0.001). After thermocycling, no significant difference was found between the mean bond strengths obtained with method 1 (34.1 ± 8.9 MPa) and method 2 (31.9 ± 7.9 MPa) (p > 0.05). Conclusion: Although after 24 h of testing, silica coating and silanization performed significantly better in resin-resin repair bond strength, both HF acid gel and silica coating followed by silanization revealed comparable bond strength results after thermocycling for 6000 times. Keywords: hydrofluoric acid, indirect composite, repair, silica coating, microtensile test. J Adhes Dent 2007; 9: 443-447.
Submitted for publication: 08.09.06; accepted for publication: 11.01.07.
T
a PhD student, Department of Dental Materials and Prosthodontics, São Paulo
State University at São José dos Campos, Brazil. b Professor and Research Associate, University Medical Center Groningen, Uni-
versity of Groningen, Department of Dentistry and Dental Hygiene, Clinical Dental Biomaterials, Groningen, The Netherlands. c Professor and Chair, Department of Dental Materials and Prosthodontics, São
Paulo State University at São José dos Campos, Brazil. Reprint requests: Dr. Mutlu Özcan, University Medical Center Groningen, University of Groningen, Department of Dentistry and Dental Hygiene, Clinical Dental Materials, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands. Tel: +31-50-363 85 28, Fax: +31-50-363 26 96. e-mail:
[email protected]
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he advancement in filler and polymer technology allowed for the development of resin composites for indirect applications. With the use of indirect resin composites, better proximal contacts, excellent occlusal morphology, good marginal adaptation with lower polymerization shrinkage of resin luting agents, good flexural strength, and easy manipulation and polishing could be achieved.5,16 Although marked improvements have been noted with such materials in terms of physical and mechanical properties during the last 10 to 20 years, and good clinical performance was reported,15 the major problems still seemed to be related to chipping, delamination, or fractures.6 Chipping or delamination of these restorations does not necessarily indicate restoration 443
MATERIALS AND METHODS An acrylic resin template was machined with dimensions of 5 x 5 x 4 mm and impressions were made from this acrylic block with addition silicone putty (Express, 3M ESPE; St Paul, MN, USA; batch #7312) in order to achieve standard molds for the fabrication of 18 indirect resin composite blocks with the same dimensions. Indirect resin composite (Sinfony, 3M ESPE; Seefeld, Germany) was incrementally injected into the mold and light polymerized initially using a hand light unit (XL 3000, 3M ESPE; Seefeld, Germany) (light intensity: 500 mW/cm2). The specimens were further polymerized in a special polymerization device (Visio Beta Vario, 3M ESPE) following the manufacturer’s recommendations. The repair surface (5 x 5 mm) was leveled and polished in a machine using silicone carbide papers in sequence (600, 800, and 1200 grit) under cooling (KG-Sorensen; Barueri, Brazil) and cleaned ultrasonically in distilled water (Vitasonic, Vita Zanhfabrik; Bad Säckingen, Germany) for 10 min. The blocks were then randomly divided into 2 groups (N = 18, 9 per group) and conditioned by one of the following methods: Surface Conditioning Methods Method 1: The resin composite substrates were etched with 10% HF acid gel (Dentsply; Petropolis, Brazil) for 90 s and washed and rinsed thoroughly in accordance with the manufacturer’s recommendations. Method 2: A chairside tribochemical silica coating system was employed using an intraoral chairside air-abrasion de444
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failure, since these fractures may not lead to the need for replacement of the restorations. Repair, as an alternative to complete removal or replacement, would preserve the tooth, as it is often difficult to remove an adhesive restoration without removing an integral part of the tooth.6,8 Several techniques are available in order to improve the bond strength of repair resins to indirect resin composites, such as surface etching with hydrofluoric (HF) acid gel, air abrasion with alumina or silica particles, or utilization of adhesive systems.9 Despite the hazardous effects of HF acid gel, etching the surface of a composite restoration with this acid followed by application of silane coupling agent is a wellknown and recommended method to increase the bond strength. An alternative method to HF acid etching for repair actions is based on airborne particle abrasion using silica particles. In this technique, the surfaces are abraded with silica-coated aluminum oxide particles.13 The pressure of the air abrasion leads to coverage of the restoration surface with silica and alumina particles, making it chemically more reactive to silane coupling agent and the adhesive resin.11 Although repair methods seem to deliver satisfactory results, their long-term clinical durability is not widely documented.12 There is also a need for repair methods to be tested under simulated conditions in in vitro settings. Therefore, the objective of this study was to evaluate the effect of surface conditioning and storage conditions on the bond strength between a direct resin composite and an indirect resin composite system for repair purposes.
vo rbe ha lte n n vice (Micro-Etcher, Danville; San Ramon, CA, USA) filled with
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ss(CoJete nz CoJet-Sand (30-Ìm Al2O3 particles coated with silica) Sand, CoJet system, 3M ESPE; Seefeld, Germany; batch #142820) perpendicular to the surface from a distance of approximately 10 mm for a period of 4 s at 2.8 bar pressure. The conditioned substrates were then coated with a 3-methacryloxypropyltrimethoxysilane coupling agent, γMPS (ESPE-Sil, 3M ESPE; Seefeld, Germany) and allowed to react for 5 min. Bonding Procedure The conditioned resin blocks were coated with a thin layer of adhesive resin and air thinned following the manufacturer’s instructions (Adper Single Bond, 3M ESPE; Seefeld, Germany; batch #5EK). Then resin composite was packed (W3D-Master, Wilcos, Petrópolis, RJ, Brazil; batch #006/03) in approximately 2 mm increments and each layer was light polymerized for 40 s (XL 3000, 3M ESPE; Seefeld, Germany) (light output: 500 mW/cm2) to obtain blocks with a height of ca 5 mm. After completion of the indirect resin composite/repair resin composite assemblies, the specimens were stored in distilled water at 37°C for 1 week until preparation of specimens for the microtensile test. The specimens from each repaired block were tested either after storage in water for 24 h or thermocycling (6000 cycles 5°C to 55°C, dwell time: 30 s, transfer time from one bath to the other: 2 s) (Nova Etica; São Paolo, Brazil). Production of Specimens for Microtensile Test Composite blocks were sectioned using a diamond disk (Microdont; São Paulo, Brazil, n. 34570) at low speed under water cooling in a sectioning machine.1 Initially, the blocks were fixated with cyanoacrylate adhesive gel (Super Bonder Gel, Loctite; São Paulo, Brazil) on a metallic base that was attached to the sectioning machine. The blocks were positioned as perpendicularly as possible in relation to the diamond disk of the machine. The first section, measuring approximately 0.5 mm, was discarded in case of the possibility of excess or absence of adhesive at the interface that might alter the results. Thereafter, four sections measuring 0.8 ± 0.1 mm in thickness were achieved. Each section was rotated 90 degrees and once again fixated to the metallic base. The first section was discarded (0.5 mm) due to the aforementioned reasons. Subsequently, four other sections were obtained, also measuring 0.8 ± 0.1 mm in thickness. This process was followed for the other three sections, and thus only the central specimens were used for the experiments. Twelve specimens were obtained from each block. The rectangular beam specimens had a non-machined (nontrimmed) adhesive zone with a bonded area measuring approximately 0.6 mm2 and ca 0.8 mm length. The specimen preparation has previously been described in detail elsewhere.17 Microtensile Bond Strength Test Keeping the adhesive zone free, each specimen was fixated with cyanoacrylate gel (Super Bonder Gel, Loctite) to the rods of a device adapted for this test. The specimens were posiThe Journal of Adhesive Dentistry
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Table 1 Results of two-way analysis of variance for the experimental conditions Source of variation
df
Surface conditioning Storage Interaction Error Total
1 1 1 217 220
SS
MS
F
3590.20 2218.30 978.80 22922.80
3590.16 2218.35 978.65 105.64
33.99 21.00 9.26
80
70
70
60
60
50
50
a 40 P 30 M
a 40 P M 30
P
0.0001 0.0001 0.0026
10
10 0
e ss e n z
20
20
0
without HF
with
without with Cojet
without HF
with
without with Cojet
Fig 1 The mean microtensile bond strength values (MPa) for the two surface conditioning methods and the storage conditions (with and without thermocycling) in dispersion diagram (dot plot).
Fig 2 The mean microtensile bond strength values (MPa) and standard deviations for the two surface conditioning method with and without thermocycling.
tioned parallel to the long axis of the device in order to reduce the bending stresses. The device was fixated in the universal testing machine (EMIC DL-1000, EMIC; São José dos Pinhais, Brazil) as parallel as possible in relation to application of the tensile load, and testing was performed at a crosshead speed of 1 mm/min. The bond strength was calculated according to the formula R=F/A, where “R” is the strength (MPa), “F” is the load required for rupture of the specimen (N) and “A” is the interface area of the specimen (mm2), measured with a digital caliper before the test.
RESULTS
Topographic Analysis of Conditioned Indirect Resin Composite Surface Additional indirect resin composite specimens (n = 4) were conditioned using the two surface conditioning methods in order to observe the topographic surface changes under a scanning electron microscope (DSM 962, Zeiss; Jena, Germany). Statistical Analysis The means of each group were analyzed by two-way analysis of variance (ANOVA), with microtensile bond strength as the dependent variable and the surface conditioning methods and storage conditions as the independent factors (Statistix 8.0 for Windows, Analytical Software; Tallahassee, FL, USA). P values less than 0.05 were considered to be statistically significant in all tests.
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No pretest failures were experienced throughout the experimental procedures. Two-way ANOVA revealed a significant influence of the storage conditions (p = 0.0001) and the surface conditioning methods (p = 0.0001) on the test results. Interaction between factors was also significant (p = 0.0026) (Table 1). Means and standard deviations are presented in Fig 1. After 24-h water storage, silica coating and silanization (method 2) showed significantly higher bond strength results (46.4 ± 13.8 MPa) than that of hydrofluoric acid etching and silanization (method 1) (35.8 ± 9.7 MPa) (p < 0.001). After thermocycling, however, no significant difference was found between the mean bond strengths obtained with method 1 (31.9 ± 7.9 MPa) and method 2 (34.1 ± 8.9 MPa) (p > 0.05) (Fig 2). SEM analysis at 5000X magnification, complementary to the microtensile bond strength tests, revealed that HF acid gel dissolved the fillers of the substrate and produced porous, irregular surfaces (Fig 3a). On the other hand, the silica-coated specimens exhibited a rough surface covered with abundant sand particles (Fig 3b).
DISCUSSION According to Crispin,3 indirect resins are more easily repaired than ceramics, because of the similarity between 445
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*
Figs 3a Representative SEM image (5000X magnification) of a hydrofluoric acid etched specimen (Sinfony). Note that the acid treatment dissolved the filler components of the substrates (*).
Fig 3b Representative SEM image (5000X magnification) of a silica coated specimen. Note that the surfaces are covered with abundant sand particles even after air drying (←).
substrates. In a previous study by Özcan et al,10 three surface treatments, namely, hydrofluoric acid application and air abrasion with alumina (50 μm) or silica particles (30 μm), for various indirect resins were employed for repair purposes. It was reported that the bond strength varied according to the type of resin and conditioning method investigated when the shear bond test was used, with the results being more favorable for silica coating and silanization than for hydrofluoric acid etching and silanization. Although SEM findings were similar to those of that study, in this study, neither surface conditioning method showed significant differences after thermocycling for the substrate material tested. However, interaction terms were significant; therefore, it was not possible to draw a conclusion on the main effect. The mean bond strength results with both methods, and particularly with HF acid gel application and silanization (31.9 ± 7.9 MPa), were higher than those of Özcan et al10 (5.2 ± 1.2 MPa), although the monomer matrices of the indirect composite substrate material (HEMA and octahydro-4,7-methano-1H-indenediyl)bis(methylene)-diacrylate) and the repair resin (bisGMA) used in this study were similar. Several factors may have contributed to the differences in the results, one of which could be the testing methodology. The shear test is not considered an ideal mechanical test, since it often leads to nonuniform distribution of the stresses at the adhesive area. In this kind of test, maximum tensile forces occur close to the load application area, thereby affecting the substrate more than the adhesive interface itself.4 The microtensile test, suggested by Sano et al,14 assesses the bond strength of specimens with reduced areas of adhesive joint, where fractures occur basically at the adhesive interface. For these reasons, in this study a microtensile test was used. Therefore, the results of mechanical tests
should be evaluated with caution, because discrepancies may simply be due to the differences between test methods. The hazardous and extremely caustic effects to soft tissues make the clinical use of HF acid gels a controversial affair, due to its rapid vaporization and the danger of inhalation. Although no clinical incidence report exists in the dental literature regarding harmful consequences of HF acid gel use, caution should be exercised during handling this material. Considering the possible hazardous effects and the nonsignificant differences between hydrofluoric acid etching and silica coating, clinicians should consider the use of the latter for safer applications. However, after both conditioning methods, silane application is compulsory. Clinically, for invisible repair procedures, a bevel should be created by a carbide bur or other ultrasonic oscillating devices. Additionally, non-contaminated surfaces should be achieved using prophylaxis paste and rubber cups. While hydrofluoric acid is considered hazardous, silica coating requires additional equipment in the dental practice, compared to simply drilling the surface and applying an intermediate adhesive resin. However, this approach has recently been shown to create almost exclusively adhesive failures between the substrate and the adherend, implying the necessity of silica coating and silanization that almost exclusively resulted in cohesive failures in the substrate.2
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CONCLUSIONS When repaired specimens were not thermocycled, silica coating and silanization showed significantly higher bond strength results than that of hydrofluoric acid etching and silanization. After thermocycling (6000 cycles), however, no The Journal of Adhesive Dentistry
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REFERENCES 1. Andreatta Filho OD, Galhano G, Bottino MA, Camargo FP, Valandro LF, Nishioka RS. Evaluation of the bond strength between an aluminous ceramic and a resin cement: Effect of thermo-cycling. Braz Dent Sci 2003;6:32-39. 2. Brendeke J, Özcan M. Effect of aging and adhesion mediums on the adhesion of particulate filler composites to composites. J Adhes Dent 2007;9:399-406. 3. Crispin BJ. Indirect composite restorations: alternative of replacement for ceramic? Compendium 2002;23:611-624. 4. Della Bona A, Van Noort R. Shear vs. Tensile bond strength of resin composite bonded to ceramic. J Dent Res 1995;74:1591-1596. 5. Duke ES. The introduction of a new class of composite resin: ceromers. Compendium 1999;20:246-247. 6. Kukrer D, Gemalmaz D, Kuybulu EO, Bozkurt FO. A prospective clinical study of ceromer inlays: results up to 53 months. Int J Prosthodont 2004;17:17-23. 7. Mjör IA, Gordan VV. Failure, repair, refurbishing and longevity of restorations. Oper Dent 2002;27:528-534. 8. Özcan M, Niedermeier W. Clinical study on the reasons for and location of failures of metal-ceramic restorations and survival of repairs. Int J Prosthodont 2002;15:299-302. 9. Özcan M. Evaluation of alternative intraoral repair techniques for fractured ceramic-fused-to-metal restorations. J Oral Rehabil 2003;30:194-203. 10. Özcan M, Alander P, Vallitu PK, Huysmans MC, Kalk W. Effect of three surface conditioning methods to improve bond strength of particulate filler resin composites. J Mater Sci Mater Med 2005;16:21-27.
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significant differences were found between the two repair methods.
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n tPK. Effect of Özcan M, Lassila L, Raadschelders J, Matinlinna JP, Vallittu e[abstract some parameters on silica-deposition on a zirconia ceramic ss e n z 63114]. J Dent Res 2005;84.
12. Özcan M. Longevity of repaired composite and metal-ceramic restorations:3.5 year clinical study [abstract 0076]. J Dent Res 2006;85. 13. Peutzfeldt A, Asmussen E. Silicoating. Evaluation of a new method of bonding composite resin to metal. Scand J Dent Res 1988;96:171-176. 14. Sano H, Shono T, Sonoda H, Takatsu T, Ciucchi B, Carvalho RM. Relationship between surface area for adhesion and tensile bond strength-evaluation of a micro-tensile bond test. Dent Mater 1994;10:236-240. 15. Scherrer SS, Wiskott AH, Coto-Hunziker V, Belser UC. Monotonic flexure and fatigue strength of composites for provisional and definitive restorations. J Prosthet Dent 2003;89:6:579-588. 16. Touati B, Aidan N. Second generation laboratory composite resins for indirect restorations. J Esthetic Dent 1997;9:108-118. 17. Valandro LF, Özcan M, Bottino MC, Bottino MA, Scotti R, Bona AD. Bond strength of a resin cement to high-alumina and zirconia-reinforced ceramics: the effect of surface conditioning. J Adhes Dent 2006;8:175-181.
Clinical relevance: Both silica coating plus silanization and hydrofluoric acid etching plus silanization could be advised for the repair of the indirect resin composite and repair resin combination tested in this study. However, clinicians may consider choosing silica coating and silanization, due to the hazardous effects of hydrofluoric acid gel.
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