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J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
J adhesion science technol
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J adhesion science technol

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  • 1. PROOF COVER SHEET Journal acronym: TAST Author(s): Boniek Castillo Dutra Borges Article title: Influence of the preheating of bonding agents on the degree of conversion and bond durability in tridimensional dentin cavities Article no: 736190 Enclosures: 1) Query sheet 2) Article proofs Dear Author, 1. Please check these proofs carefully. It is the responsibility of the corresponding author to check these and approve or amend them. A second proof is not normally provided. Taylor & Francis cannot be held responsible for uncorrected errors, even if introduced during the production process. Once your corrections have been added to the article, it will be considered ready for publication. Please limit changes at this stage to the correction of errors. You should not make insignificant changes, improve prose style, add new material, or delete existing material at this stage. Making a large number of small, non-essential corrections can lead to errors being introduced. We therefore reserve the right not to make such corrections. For detailed guidance on how to check your proofs, please see http://journalauthors.tandf.co.uk/production/checkingproofs.asp 2. Please review the table of contributors below and confirm that the first and last names are structured correctly and that the authors are listed in the correct order of contribution. This check is to ensure that your name will appear correctly online and when the article is indexed. Sequence 1 2 3 4 5 6 7 8 9 Prefix Given name(s) Surname Boniek Castillo Dutra Ana Raquel Rocha Correia Antônio Cavalcanti Charry Alves da Marco Antonio Eduardo José Mario Alexandre Coelho Rodivan Marcos Antônio Japiassú Resende Borges Vilela Silva-Junior Silva-Junior Botelho Souza-Junior Sinhoreti Braz Montes Suffix
  • 2. Queries are marked in the margins of the proofs. AUTHOR QUERIES General query: You have warranted that you have secured the necessary written permission from the appropriate copyright owner for the reproduction of any text, illustration, or other material in your article. (Please see http://journalauthors.tandf.co.uk/preparation/permission.asp.) Please check that any required acknowledgements have been included to reflect this. AQ1 Please provide institutional email address. AQ2 Please provide history date for your article (revised date). AQ3 Please provide the expansion for ‘HEMA and TEGDMA’. AQ4 Please provide the expansion for ‘Bis-GMA’.
  • 3. TAST 736190 Initial CE: VK QA: CS 11 October 2012 Journal of Adhesion Science and Technology Vol. X, No. X, XXXX 2012, XXX–XXX Influence of the preheating of bonding agents on the degree of conversion and bond durability in tridimensional dentin cavities Boniek Castillo Dutra Borgesa*, Ana Raquel Rocha Correia Vilelab, Antônio Cavalcanti Silva-Juniorb, Charry Alves da Silva-Juniorb, Marco Antonio Botelhoa, Eduardo José Souza-Juniorc, Mario Alexandre Coelho Sinhoretic, Rodivan Brazb and Marcos Antônio Japiassú Resende Montesb AQ2 a Laboratory of Nanotechnology, Post-Graduate Program in Biotechnology, Potiguar University (Laureate International Universities), Av. Senador Salgado Filho 1610, Natal 59088-725, Brazil; b Department of Restorative Dentistry, Pernambuco Dental School, Pernambuco University, Camaragibe, Brazil; cDepartment of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil 5 10 (Received 12 August 2012; final version received 29 September 2012) Objectives: The aim of this study was to evaluate the degree of conversion (DC) of dental bonding agents at different temperatures and the bond durability of restorations bonded with preheated dental bonding agents. Materials and methods: Three multistep adhesive systems, including one 3-step etch-and-rinse (Adper Scotchbond Multipurpose Plus) and two 2-step self-etching systems (Clearfil SE Bond; Filtek Low-Shrinkage Adhesive System), were evaluated. Dental bonding agents were preheated at 25, 37, and 60 °C. Barshaped specimens (n = 5) were prepared for DC analysis. Fourier Transform Infrared/Attenuated Total Fluorescence spectra were obtained, and the DC was calculated by comparing the aliphatic bonds/reference peaks of nonpolymerized and polymerized materials. For bond durability analysis, tridimensional dentin cavities were prepared in 180 bovine incisors, which were then restored. Samples were stored in water for 24 h, and half of them were subjected to additional degradation with 10% NaOCl for 5 h. The push-out bond strength test was performed in a universal testing machine until failure. Failure modes were analyzed by scanning electron microscopy. Data were analyzed by analysis of variance (ANOVA) and Tukey’s tests (p < 0.05). Results: Dental bonding agents preheated at 60 °C showed higher DC values than those preheated at 25 and 37 °C. The temperature of the dental bonding agent did not influence the bond durability, although fewer adhesive failures were observed in restorations bonded with dental bonding agents at 60 °C. Conclusion: Although the preheating of dental bonding agents can increase the DC, it may not improve the bond durability of dentin restorations. 15 20 25 30 Keywords: preheating; degree of conversion; failure analysis; in vitro; stress Introduction One of the major concerns in adhesive dentistry is the durability of bonds to dentin, because the bonding is established on a complex hydrated biological composite structure [1]. AQ1 Although 3-step etch-and-rinse and 2-step self-etching adhesives have shown better results *Corresponding author. Email: boniek.castillo@gmail.com ISSN 0169-4243 print/ISSN 1568-5616 online Ó 2012 Taylor & Francis http://dx.doi.org/10.1080/01694243.2012.736190 http://www.tandfonline.com 35
  • 4. TAST 736190 2 5 10 15 20 25 30 Initial CE: VK QA: CS 11 October 2012 B.C.D. Borges et al. than their simplified versions [2], continuous degradation of the resin–dentin bond has been observed for both materials in vivo [3,4]. Thus, efforts should be made to improve the dentin bond durability of these dental adhesive systems. The degree of conversion (DC) of the adhesive system and stress at the adhesive interface due to composite shrinkage fundamentally impact the bond stability over time. The presence of large amounts of unreacted monomer can expedite water absorption and compromise the integrity of the hybrid and adhesive layers [5]. As the composite cures, an increase in stiffness, due to volumetric changes that are confined by the cavity walls, results in stresses that challenge the bond integrity between the composite restoration and the tooth, particularly in high C-factor cavities [6]. Thus, obtaining a high DC with low stress levels at the adhesive interface during composite polymerization could improve the dentin bond stability in high C-factor cavities. A relatively recent method to increase the DC of resin-based dental materials is to preheat the materials before photoactivation. Although preheating composite resins up to 68 °C reportedly increases the DC [7–10], few studies have evaluated the DC values of preheated dental bonding agents. Silorane-based low-shrinkage restoratives have been developed to overcome the drawbacks associated with the polymerization-related shrinkage of traditional methacrylate-based composite resins. In this technique, a 2-step self-etching adhesive system is used to bond the silorane-based composite to dental tissues. However, no study has evaluated the bond durability of restorations in high C-factor dentin cavities when the bonding agent is preheated before polymerization. This study aimed to evaluate: (I) the DC of preheated dental bonding agents and (II) the bond durability of restorations in high C-factor dentin cavities bonded with preheated dental bonding agents and filled with methacrylate- or silorane-based composite resins. The hypotheses tested were as follows: (I) higher temperature would favor increased DC of the bonding agents and (II) the bond durability of restorations bonded with preheated bonding agents would be higher. Materials and methods 35 40 Experimental design This study tested: (1) the DC of preheated dental bonding agents and (2) the bond durability of restorations in high C-factor dentin cavities bonded with preheated dental bonding agents and filled with composite resins. The multistep adhesive systems utilized in this study were Adper Scotchbond Multipurpose Plus (MP) (3M ESPE, St. Paul, MN, USA), Clearfil SE Bond (SE) (Kuraray Osaka, Japan), and Filtek Low-Shrinkage (LS) (3M ESPE). The DC was evaluated with three different bonding agents (in MP, SE, and LS) at three different temperatures (25, 37, and 60 °C). The push-out bond durability was evaluated with three different adhesive systems (MP, SE, and LS) at three different temperatures of the bonding agents (25, 37, and 60 °C) and with two different aging methods (short-time water storage with or without subsequent chemical degradation by sodium hypochlorite). The compositions, manufacturers, and batch numbers of the materials are shown in Table 1. Preheating of the bonding agents 45 One bottle of each dental bonding agent was kept in an oven (incubator) at 25, 37, or 60 °C for 2 h before starting the adhesive procedure [11]. One bottle of each dental bonding agent from the same batch number was used for each temperature, which was checked with a thermometer before the restorative procedure.
  • 5. Batch number 3-step etch-andrinse adhesive system 2-step self-etching adhesive system 2-step self-etching adhesive system Dimethacrylatebased composite resin Silorane-based composite resin Adper Scotchbond Multipurpose Plus (3M ESPE, St. Paul, MN, USA) Clearfil SE Bond (Kuraray, Tokyo, Japan) Filtek Low-Shrinkage Adhesive System (3M ESPE, St. Paul, MN, USA) Filtek Z250 (3M ESPE, St. Paul, MN, USA) Filtek Low-Shrinkage Composite (3M ESPE, St. Paul, MN, USA) Initial Notes: HR: bonding agent; HEMA: 2-hydroxyethyl methacrylate; Bis-GMA: bisphenol-glycidyl methacrylate; 10-MDP: 10-methacryloyloxydecyl dihydrogen phosphate; TEGDMA: triethylene glycol dimethacrylate; UDMA: diurethane dimethacrylate; TMPTMA: trimethylolpropane trimethacrylate; and Bis-EMA: bisphenol A polyethylene glycol diether dimethacrylate. Silane-treated quartz (60–70), 3,4-epoxycyclohexylcyclopolymethylsiloxane (5–15), Bis-3,4-epoxycyclohexylethyl-phenyl-methylsilane (5–15), yttrium trifluoride (5–15), products (<26) Silane-treated silica (75–85), Bis-EMA (1–10), UDMA (1–10), Bis-GMA (1–10), TEGDMA (<5) 9N115915BR N139697 Primer: HEMA (15–25), Bis-GMA (15–25), phosphoric acidmethacryloxyhexylesters (5–15), ethanol (10–15), water (10–15), silane-treated silica (8–12), 1,6-hexanediol dimethacrylate (5–10), (dimethylamino)ethyl methacrylate (<5), copolymer of acrylic and itaconic acid (<5), phosphine oxide (<5), camphorquinone (<5) HR: substituted dimethacrylate (70–80), silane treated silica (5–10), TEGDMA (5–10), phosphoric acids-6methacryloxy-hexylesters (<5), 1,6-hexanediol dimethacrylate (<3), camphorquinone (<3) Primer: HEMA (10–30), 10-MDP (np), hydrophilic dimethacrylate (np), water (np), accelerators (np), dyes (np), camphorquinone (np) HR: Bis-GMA (25–45), HEMA (20–40), 10-MDP (np), hydrophilic dimethacrylate (np), colloidal silica (np), initiators (np), accelerators (np), dyes (np), camphorquinone (np) Etchant: water (55–65), phosphoric acid (30–40), synthetic amorphous silica (5–10) Primer: ethyl alcohol (70–80), water (20–30), methacryloxypropyltrimethoxysilane (<2) HR: Bis-GMA (60–70), HEMA (30–40) Composition (% by weight) – np: not provided by the manufacturer Primer: N130675 HR: N137817 Primer: 00896A HR: 01321A Etchant: 9NL Primer: N124653 HR: N195685 Type Materials used in this study. Material (Manufacturer) Table 1. TAST 736190 CE: VK QA: CS 11 October 2012 Journal of Adhesion Science and Technology 3
  • 6. TAST 736190 4 Initial CE: VK QA: CS 11 October 2012 B.C.D. Borges et al. Degree of conversion analysis 5 10 15 The DC was analyzed by Fourier Transform Infrared/Attenuated Total Reflectance (Spectrum 100, PerkinElmer, Shelton, USA) at 24 °C under 64% relative humidity. Silicon molds (1 mm  1 mm  7 mm) were filled with one drop (10 μL) of the dental bonding agents at each temperature (n = 5). A Mylar strip was placed on the mold to cover the dental bonding agents. The specimens were photoactivated for 10 s with a high-radiance light-emitting diode (LED) unit (Coltolux, Coltène/Whaledent, Allstätten, Switzerland) at 1264 mW/cm2. The specimens were carefully removed from the silicon molds and stored dry in dark receptacles at 37 °C for 24 h. The absorption spectra of nonpolymerized and polymerized bonding agents were obtained from the region between 4000 and 650 cmÀ1 with 32 scans at 4 cmÀ1. The DC (%) was calculated with the following equation: DC (%) = 100  [1 À (R polymerized/R nonpolymerized)], where R represents the ratio between the absorbance peaks at 1638 and 1608 cmÀ1. The final DC values were analyzed by two-way analysis of variance (ANOVA) (dental bonding agent  temperature of the dental bonding agent), followed by Tukey’s test (p < 0.05). Push-out bond strength analysis 20 25 30 35 40 45 50 Samples were prepared according to a previously described method for the push-out bond strength test [12]. Figure 1 is a schematic representation of sample preparation and methods utilized in this study. A total of 180 bovine incisors, free from cracks and structural defects, were selected. The teeth were disinfected in a 0.1% aqueous solution of thymol at 40 °C for no longer than 1 week. The roots were removed with a water-cooled diamond saw (South Bay Technology, San Clement, CA) coupled to a precision cutting machine (Isomet 1000; Buehler, Lake Forest, IL). The buccal aspect of the crown was wet-ground with 400- and 600-grit SiC abrasive papers in a polishing machine (Labopol-21, Struers, Copenhagen, Denmark) in order to obtain flat dentin surfaces. Standardized conical cavities (2 mm top diameter  1.5 mm bottom diameter  2 mm height) were prepared with conical diamond burs at high-speed, under air–water cooling. A custom-made preparation device allowed the cavity dimensions to be standardized. The burs were replaced after every five preparations. To expose the bottom surface of the cavities, the lingual surfaces were ground in accordance to the procedure described for flattening the buccal aspects. In this manner, a cavity with a C-factor magnitude of 2.2 was obtained [13]. The prepared specimens were assigned to 18 groups (n = 10), according to the factors under study (dental adhesive system  temperature of the dental bonding agent  aging method). The adhesive systems were applied, according to the manufacturers’ instructions, as follows: MP: Dentin was etched with 35% phosphoric acid (Scotchbond Etchant, 3M ESPE) for 15 s and thoroughly washed in water for 30 s. Excess water was blot-dried with absorbent paper, leaving the dentin surface visibly moist (wet-bonding). One coat of the primer was applied to the dentin and air dried for 10 s at 20 cm. One coat of the bonding agent was applied and light cured for 10 s with a Coltolux LED at 1264 mW/cm2. SE: One coat of the self-etching primer was applied to the dentin with slight agitation for 20 s and air dried for 10 s at 20 cm. One coat of the bonding agent was applied and light cured for 10 s with a Coltolux LED at 1264 mW/cm2. LS: One coat of the self-etch primer was applied to the dentin with slight agitation for 15 s, air dried for 10 s at 20 cm, and light cured for 10 s with a Coltolux LED at 1264 mW/ cm2. The bonding agent was applied and light cured for 10 s. After application of the adhesive systems, the specimens were placed onto a glass slab. The restorative procedures were performed with the composites, which were bulk-inserted
  • 7. TAST 736190 Initial Journal of Adhesion Science and Technology CE: VK QA: CS 11 October 2012 5 Figure 1. Schematic representation of sample preparation and methods. To test each adhesive system in each one of the three temperatures (25, 37, and 60 °C), 20 bovine incisors were used. The roots were removed with a diamond saw. The buccal aspect of the crown was wet-ground with SiC abrasive papers in a polishing machine to obtain flat dentin surfaces. Standardized conical cavities (2 mm top diameter  1.5 mm bottom diameter  2 mm height) were prepared with conical diamond burs, and their lingual faces were ground. The adhesive systems were applied following the manufacturers’ directions. The teeth were restored with composite resin and the buccal and lingual aspects of the restorations were finished with abrasive papers coupled to a polishing machine. The samples were stored in distilled water at 37 °C for 24 h. Half of them were subjected to further chemical degradation with 10% NaOCl for 5 h before initiating the push-out bond strength test in a universal testing machine.
  • 8. TAST 736190 6 5 10 15 20 25 CE: VK QA: CS 11 October 2012 Initial B.C.D. Borges et al. into the cavity from its wider side. For MP and SE, a methacrylate-based composite resin was used (Filtek Z250, 3M ESPE). For LS, the LS composite resin (Filtek Low-Shrinkage, 3M ESPE) was used. Photoactivation was performed with a Coltolux LED at 1264 mW/cm2 for 20 s. The light tip was positioned directly on the restoration, which had been previously covered with a Mylar strip. The restorations were finished with abrasive cups and diamond pastes on the buccal and lingual aspects. The samples were stored in distilled water at 37 °C for 24 h. Half of them were subjected to further chemical degradation with 10% NaOCl for 5 h [14]. The push-out test was performed in a universal testing machine (model 4411, Instron, Canton, MA, USA). An acrylic device with a central orifice was adapted to the base of the machine. Each specimen was placed in the device with the top of its cavity against the acrylic surface. The bottom surface of the restoration was loaded with a 1 mm diameter cylindrical plunger, at a cross-head speed of 0.5 mm/min, until failure of the tooth–composite bond occurred in the lateral walls of the cavity. The plunger tip was positioned so that it touched only the filling material, without stressing the surrounding walls. The load required for failure was recorded by the testing machine, along with the area of each cavity (transformed into MPa). The data for the bond strength were analyzed by three-way ANOVA (dental adhesive system  temperature of the dental bonding agent  aging method), followed by Tukey’s test (p < 0.05). Failure modes The fractured specimens were cut in half with a water-cooled low-speed diamond saw (Isomet 1000, Buehler, Lake Bluff, IL, USA) to obtain two specimens. Both specimens were fixed to aluminum stubs, with the fractured interfaces facing upward. Specimens were sputter-coated with gold (SDC 050 Suptter Coater, Baltec) and evaluated by scanning electronic microscopy (JEOL, JSM 5600LV, Tokyo, Japan) to determine the failure mode. The failure modes were defined as adhesive failure, cohesive failure in composite, and mixed failure (adhesive and cohesive in composite). The data for the failure modes were analyzed by Kruskal–Wallis (p < 0.05). Results Dc 30 For the DC, differences among dental bonding agents and among temperatures of the dental bonding agents were observed (p < 0.01). Multiple comparisons are shown in Table 2. All of the dental bonding agents presented higher mean DC values when they were preheated at 60 °C. The bonding agent of the LS dental adhesive system presented the lowest mean DC value at all temperatures. Table 2. DC of the preheated bonding agents. Temperature Bonding agent MP SE LS 25 °C 37 °C 60 °C 83.0 (0.4) Ba 83.7 (1.8) Ba 75.7 (1.5) Bb 82.4 (0.7) Ba 84.3 (1.5) Ba 76.6 (1.8) Bb 89.1 (1.1) Aa 91.6 (1.6) Aa 82.5 (0.6) Ab Notes: Data are shown as means (standard deviations). Different uppercase letters in rows and lowercase letters in columns indicate statistically significant differences (p < 0.05).
  • 9. TAST 736190 CE: VK QA: CS 11 October 2012 Initial Journal of Adhesion Science and Technology 7 Push-out bond strength 5 The push-out bond strength values showed differences in the dental bonding agent  temperature of the dental bonding agent  aging method interaction (p = 0.02). Multiple comparisons are shown in Table 3. After storage for 24 h in water, the prepolymerization temperatures of the dental bonding agents influenced the bond strength values only for LS. Tooth restorations bonded with preheated dental bonding agents at 60 °C presented the highest bond strength values. LS showed the highest bond strength compared to the other restorative systems, regardless of the temperature of the dental bonding agent. MP and SE showed bonding stability after 10% NaOCl degradation at all temperatures of the bonding agent. LS showed bonding stability when the bonding agent was preheated at 25 or 37 °C. 10 Failure modes 15 The frequencies of the failure modes are shown in Table 4. There were no statistically significant differences among the temperatures for each adhesive system. Discussion The first hypothesis tested in this study was validated, since dental bonding agents preheated at 60 °C showed increased DC. However, since higher temperature of the bonding agents did not provided increased bond durability of restorations, the second hypothesis tested was rejected. The dental bonding agents are a solvent-free mixture of monomers, which are polymerized after photoactivation. All of the bonding agents showed significantly increased DC values when they were preheated at 60 °C. Improved monomer conversion of resin-based materials in response to increased prepolymerization temperature can occur for many reasons. The viscosity of the material is decreased with increasing temperature, which enhances radical mobility [7]. The higher the curing temperature (below the glass transition temperature), the greater the collision of nonreactive groups with free radicals [8]. Temperatures of 25, 37, and 60 °C were chosen to simulate room temperature, body temperature, and properly heated materials, respectively. Only samples that were preheated at 60 °C displayed improved DC values, presumably because this temperature provided greater radical mobility and collision of the nonreactive groups with free radicals. This is in agreement with previous studies investigating composite resins, which obtained increased DC for preheated materials [7–10]. Table 3. Push-out bond strength of dentin cavities restored with preheated 358 bonding agents, according to aging method. Temperature Aging method Bonding agent 25 °C 37 °C 60 °C 24 h water storage MP SE LS 10.1 (3.8) Ab 10.8 (3.4) Aab 15.2 (3.5) ABa 7.1 (4.0) Ab 11.3 (2.1) Aab 13.5 (1.8) Ba 9.9 (6.6) Ab 11.1 (4.7) Ab 17.1 (3.8) Aa 24 h water and 5 h 10% NaOCl degradation MP SE LS 7.1 (2.5) Aa 8.6 (3.6) Aa 11.8 (5.7) Aa 7.0 (4.1) Aa 7.8 (2.8) Aa 13.3 (5.3) Aa 9.6 (3.5) Aa 9.3 (3.5) Aa 11.4 (4.4)⁄ Aa Notes: Data are shown as means (standard deviations). ⁄Different from 24 h water storage by ANOVA for the same bonding agent and temperature (p < 0.05). Different uppercase letters in rows and lowercase letters in columns indicate statistically significant differences (p < 0.05). 20 25 30
  • 10. TAST 736190 8 CE: VK QA: CS 11 October 2012 Initial B.C.D. Borges et al. Table 4. Frequency of the failure modes. Aging method 24 h water storage Temperature of the bonding agent A MP 25 °C 37 °C 60 °C 25 °C 37 °C 60 °C 25 °C 37 °C 60 °C 10 5 7 9 7 5 4 5 1 – – 1 – – – – – 3 – 5 2 1 3 5 6 5 6 25 °C 37 °C 60 °C 25 °C 37 °C 60 °C 25 °C 37 °C 60 °C 8 7 6 10 6 5 9 7 6 – – – – – – – – – 2 3 4 – 4 5 1 3 4 SE LS 24 h water storage and 5 h 10% NaOCl degradation Failure modes Adhesive systems MP SE LS CC M p ns ns ns ns ns ns Notes: A: adhesive failure; CC: cohesive failure in composite; M: mixed (adhesive and cohesive in composite). ns: p > 0.05. Regardless of the prepolymerization temperature, the dental bonding agent of the LS adhesive system showed the lowest DC values, whereas those of MP and SE were similar. The different DC values for the three materials can be attributed to differences in their chemiAQ3 cal compositions. HEMA and TEGDMA are diluent monomers that are frequently added to AQ4 Bis-GMA mixtures to reduce resin viscosity and increase monomer mobility. These conditions favor the kinetics of monomer conversion [15]. The bonding agents of MP and SE 10 contain higher amounts of HEMA/TEGDMA monomers than does LS, which is probably why the LS bonding agent showed a lower DC value. The LS bonding agent showed the lowest DC. However, teeth restored with the LS system showed the highest immediate bond strengths. In contrast with all other adhesive systems tested, the self-etching/primer agent of the LS system must be photoactivated. The polymeriz15 able, self-etching primer of the LS adhesive system may mimic a 1-step self-etching adhesive, because it contains the three cardinal steps for bonding (i.e. etching, priming, and bonding), leading to the proper impregnation of the dentin substrate and optimal polymerization [16]. In fact, the DC of the primer layer is even higher than the DC of the adhesive layer in dentin interfaces bonded with the LS adhesive system [16]. Moreover, because the bond strength was 20 evaluated in high C-factor dentin cavities, the low shrinkage rates of the LS composite [17] might be related to the improved bond integrity, due to the low stress levels generated in the adhesive interface. Both of these attributes likely contributed to increase the immediate bond strength of samples restored with the Filtek low-shrinkage composite restorative. Despite the bonding agents preheated at 60 °C had higher DC values than those preheated 25 at 25 and 37 °C, an increase in the immediate bond strength was only observed for LS restorations bonded with the bonding agent preheated at 60 °C. Most likely, the combination of the increased DC of the bonding agent with the low stress levels in the adhesive interface provided the higher immediate bond strength for these samples. On the other hand, whereas 5
  • 11. TAST 736190 Initial CE: VK QA: CS 11 October 2012 Journal of Adhesion Science and Technology 9 the bonding agents of MP and SE showed higher DC values when they were preheated at 60 °C, the higher stress levels generated by the polymerization-induced shrinkage of the traditional methacrylate-based composite resin could have decreased the immediate bond strength of these samples. The temperatures of the dental bonding agents provided statistically similar failure modes for restorations with the same dental adhesive system. Moreover, most of the tested conditions showed statistically similar bond durability of the dentin restorations. In fact, the 3-step etch-and-rinse and 2-step self-etching adhesive systems have been shown to display satisfactory short-time dentin bond stability [12]. Use of 10% NaOCl as an aging method can induce oxidation, leading to the fragmentation of resin unprotected collagen fibrils and affecting the bond integrity [5]. Moreover, 10% NaOCl can promote resin dissolution at the hybrid layer of adhesive systems [18], decreasing bond integrity. A demineralized dentin zone that is insufficiently infiltrated by resin at the bottom of the hybrid layer is classically related to etch-and-rinse adhesive systems. Nevertheless, collagen fibers that are incompletely coated by resin have also been observed beneath the hybrid layer in self-etching adhesive systems [16]. Thus, all of the adhesive systems tested in this study could have been exposed to both of these scenarios under 10% NaOCl use. The improved DC of the LS dental bonding agent preheated at 60 °C was not sufficient to prevent NaOCl degradation of the adhesive interface. Polymers with high crosslink densities (CLDs) are morphologically more compact than those with a linear character and are more resistant to solvent degradation and liquid absorption [19]. Resin-based polymer networks with different DC values can present similar CLDs [20]. It is likely that the LS dental bonding agent preheated at 60 °C presented an extremely high DC, but a low CLD. This scenario would favor, to some extent, the increased absorption of NaOCl and resin degradation, leading to decreased bond integrity. Different methods, such as the shear and tensile bond strengths, have been used to measure dentin bond integrity. One disadvantage of these methodologies is that they are generally performed on flat surfaces. In such situations, the C-factor is very low and the shrinkage stress is not directed at the bonding interface [13]. For these reasons, the push-out bond strength test was employed in the present study. The advantage of using the push-out test is that the bond strength can be evaluated in a high C-factor cavity (2.2), such as Class V cavities, with high stress generation directed to the bonding area [11]. The entire bonding area was subjected to the compressive force at the same time, allowing the shear bond strength to be evaluated in the cavity. The method also provides a better estimation of the bond strength than does the conventional shear test, because fracture occurs in parallel (not transverse) with the dentin bonding interface, thereby simulating the clinical condition [21]. 5 10 15 20 25 30 35 Conclusion 40 The dental bonding agents tested showed higher DC values when they were preheated at 60 ° C. However, the increased prepolymerization temperature of the dental bonding agents did not lead to enhanced bond durability in high C-factor dentin cavities. Therefore, increasing of the DC of dental bonding agents is not sufficient to improve the bond durability of the dentin restorations. 45 Acknowledgements The authors are grateful to KG Sorensen for providing them with their burs and polishing materials.
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