| Abstract|| |
Purpose: The aim of this study was to evaluate the tensile bond strength (TBS) of repairs in recent fillings of methacrylate- (MBC) or silorane-based composites (SBC) subsequent to different surface treatments.
Materials and Methods: Fifty slabs of Filtek P60 (3M ESPE, St Paul, USA) and Filtek P90 (3M ESPE) were stored for 10 days in distilled water at 37°C. The surface of adhesion was abraded with a 600-grit silicone paper and repaired using each respective composite: G1, no treatment (control); G2, application of adhesive; G3, application of silane and adhesive; G4, sandblasting (Al2O3) and adhesive; and G5, sandblasting (Al2O3), silane, and adhesive. Further 10 slabs of each composite were also evaluated for cohesive strength (G6). After 30 days immersion in distilled water at 37°C, the TBS was determined.
Results: TBS results were higher for MBC than for SBC (P = 0.00012). The experimental groups were similar for SBC and the TBS was 27% of its cohesive strength. For P60, sandblasting significantly improved the TBS compared to other groups. With MBC, G4 and G5, the TBS was approximately 47% of its cohesive strength.
Conclusion: Sandblasting (Al2O3) improves the repair-strength of MBC, whilst for the SBC all treatments succeed. MBC presents higher repair strength than SBC.
Keywords: Composite resin; dental restoration permanent; dental restoration repair
|How to cite this article:|
Kaneko M, Caldas RA, Feitosa VP, Xediek Consani RL, Schneider LJ, Bacchi A. Influence of surface treatments to repair recent fillings of silorane-and methacrylate-based composites. J Conserv Dent 2015;18:242-6
|How to cite this URL:|
Kaneko M, Caldas RA, Feitosa VP, Xediek Consani RL, Schneider LJ, Bacchi A. Influence of surface treatments to repair recent fillings of silorane-and methacrylate-based composites. J Conserv Dent [serial online] 2015 [cited 2020 May 25];18:242-6. Available from: http://www.jcd.org.in/text.asp?2015/18/3/242/157265
| Introduction|| |
Resin-based composites are still extensively and successfully used as restorative materials in the clinical practice. However, a recent silorane-based composite (SBC) has been developed in order to overcome the effects of polymerization contraction. This material uses a ring-opening polymerization instead of traditional free radical polymerization of methacrylate monomers. , It has also been demonstrated that SBCs present lower water solubility and sorption than methacrylate-based composites (MBCs). 
Although resin composites have been notably improved, they have a limited lifetime in the oral environment. The occurrence of premature fractures of recent fillings, the need to contour and re-contour, as in the cases of deficient contact point, infra occlusion or inadequate anatomy, requires the addition of more resin composite to the initial restoration. Such procedures are suitable for composite repairs. This avoids weakening of the tooth structure by removal of the entire filling with bursfavoring the minimally invasive dentistry. ,
For repair procedures, the reactivity of "old" material is lower than during the initial incremental technique.  For MBCs, oxygen present in the air creates a superficial thin inhibited layer which provides "adhesion" for the following increment. However, this uncured layer is not present during the repair procedures, even within a short period after the first placement of the filling. In siloranes, the adhesion of successive composite layers occurs due to a surficial reactivity of the material, which decreases after aging.  Moreover, the oral environment might readily lead to chemical degradation, wear, water sorption, and leaching of unreacted monomers jeopardizing the reparability of resin composites. , Thus, alternative surface treatments should be adopted to improve the adhesion of the repair composite.
Mechanical and chemical methods are traditionally employed as surface treatments. The mechanical methods aim to remove the superficial composite layer exposed to the oral environment, increasing surface roughening and exposing the filler particles.  For this procedure, methods as air abrasion and rotating burs are largely used.  Among the chemical methods, adhesive resins and silanes are the most undertaken due to their bonding capability with organic matrix and inorganic fillers.  However, it was recently observed that there is not a protocol of repair applicable for all the composites.  Indeed, the different repair techniques deserve more investigation for different resin composites such as siloranes and methacrylates.
The aim of this study was to evaluate the effect of different surface treatments on the tensile bond strength (TBS) of repairs in MBC or SBC when problems in recent fillings have to be contoured. The null hypotheses were that (I) repairs realized in MBC do not present different TBSs than those in SBC; and (II) the surface treatments are ineffective in increasing the repair strength.
| Materials and Methods|| |
Preparation of the repaired specimens
Resin composites (Filtek P60 or P90, 3M ESPE, St. Paul, USA) were packed into half hour-glass shaped silicone molds (6.5 mm length × 2 mm thickness with 6 mm width at one extremity and 3 mm width at the other extremity corresponding to the central portion of the hour-glass shaped specimen) and light-cured in 2 mm increments for 40 s each with a LED light-curing unit at 800 mW/cm 2 (Ultra-Lume LED 5, Ultradent, South Jordan, USA). The slabs were stored in distilled water for 10 days at 37°C in order to simulate an early repair procedure. The water bath was changed twice within this period. Fifty replicates were prepared for each resin composite.
The slabs of each material were randomly divided into five groups (n = 10), the surface of adhesion abraded for10 s with a 600-grit silicone paper to remove the superficial layer, ultrasonically cleaned (Vitasonic, Vita Zahnfabrik, Bad Säckingen, Germany) for 10 min in distilled water, and repaired with the respective composite, following the surface treatments: G1, no treatment (control); G2, application of adhesive; G3, application of silane and adhesive; G4, sandblasting (Al 2 O 3 ) and adhesive; and G5, sandblasting (Al 2 O 3 ), silane, and adhesive.
The application of the materials was as follows:
Airabrasion with 50 µm particles of aluminum oxide for 20 s at 2.8 bar pressure at a distance of 10 mm perpendicularly to the specimen surface. The slabs were ultrasonically cleaned as previously mentioned.
Application of the solution and airblast for 30s.
Adper single bond 2
Application of a thin layer for 10 s on Filtek P60 specimens, gentle airblast to evaporate the solvent, and light curing for 20s.
P90 adhesive bond
Application of a thin layer for 10 s on Filtek P90 specimens, airthinning, and light-curing for 20s.
The slabs were placed in an hour-glass shaped mold (13 mm length × 2 mm thickness with 6 mm width at the extremities and 3 mm width at the central portion) so that the remaining part of the shape could be filled with fresh composite, following the same procedure described to make the first set of slabs. The last layer was cured for 40 s through a glass slide pressed on top of the two halves of the hour-glass.
Specimen preparation for cohesive strength
The above mentioned hour-glass shaped silicone molds were completely filled with fresh resin composite following the same incremental technique and curing time of the repairs. Ten slabs of each composite were fabricated for the cohesive strength evaluation. They were also stored in distilled water at 37°C for 30 days before the tensile strength assessment.
The dimensions of the central portion of the hour glass shaped specimens were obtained with a digital caliper, and the TBS was calculated by dividing the force to fracture (Kgf) by the area of the constriction (mm 2 ). 
After 1 month storage in distilled water at 37°C, each slab was fixed with cyanoacrylate glue gel (Super Bonder Gel, Loctite Ltda., Sao Paulo, Brazil) to a device adapted to a universal testing machine (Instron 4411, Instron Corporation, Canton, USA) parallel to the long axis of the device, and tested in tension at 0.5 mm/min as the speed.
After TBS evaluation, the fractured specimens were evaluated using a stereomicroscope (Leica Microsystems GmbH, Wetzlar, Germany) at ×30 magnification for analysis of the mode of failure of the fractured surfaces, which was classified as adhesive, cohesive, or mixed. Representative fractured specimens were mounted on aluminum stubs, coated with gold, and examined by scanning electron microscopy (SEM; JSM-5600 LV, JEOL; Tokyo, Japan) operated at 15 kV.
Data was explored using Statistical Package for Social Sciences (SPSS)® software (version 20; IBM, Armonk, NY, USA). The bond strength data were submitted to two-way analysis of variance (ANOVA) (resin composites and surface treatments) and the mean values were compared by Tukey's test, at 5 % significance level.
| Results|| |
The outcomes of tensile repair strengths are depicted in [Table 1]. Between the resin composites, considering the mean values of all groups, the MBC presented overall statistically higher results than the SBC (P = 0.00012). The comparison between the two composites for each surface treatment showed higher values for the MBC; however, only the treatment with airabrasion + adhesive (P60: 24.23 ± 7.93 MPa) and airabrasion + silane + adhesive (P60: 28.36 ± 6.98 MPa) were statistically different from the former (12.78 ± 4.21 MPa) and the latter (14.27 ± 4.99 MPa) treatments with P90.
|Table 1: Mean and standard deviation values of tensile bond strength (MPa)|
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Regarding surface treatments, statistical significant difference was also observed (P = 0.00001). The higher repair bond strengths for the MBC were observed with aluminum oxide airabrasion (G4 and G5) which presented statistically different from other treatments (G1-G3). The repaired group with the highest values (G5; airabrasion, silane, and adhesive application) achieved approximately 47% of the cohesive strength of the material (G6, mean 60.86MPa). With the SBC, only G1 (no treatment as control) presented statistically lower TBS among the repaired groups and all experimental treatments (G1-G5) provided similar results. The surface treatments attained27% of the cohesive strength of P90 (G6: 54.90 ± 12.07 MPa). The interaction between the two factors (composite and surface treatment) demonstrated to be statistically significant (P = 0.02669).
Fracture pattern analysis of the repaired slabs
The spreading on the mode of failure is depicted in [Figure 1]a (for P60) and 1B (for P90). The control group (G1) of both composites presented 100% adhesive failure. The MBC presented predominantly cohesive fractures after airabrasion + adhesive (G4:70%) and airabrasion + silane + adhesive (G5:80%), while for G3 (silane + adhesive) predominated adhesive (50%) and cohesive (40%) fractures. It was observed in G2 (only adhesive application) predominance of mixed (50%) and cohesive (40%) fractures. With the SBC, the predominant failure patterns were adhesive and mixedfor all surface treatments (G2-G5).
|Figure 1: (a) Failure patterns for repairs in themethacrylate-based composite groups. (b) Failure patterns for repairs in thesilorane-based composite groups|
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Representative SEM images of the failure pattern are shown in [Figure 2]. Mixed fractures were reported showing three types of failures that occurred among the materials.
|Figure 2: Representative mixed failures for (a) silorane-based composite and (b) methacrylate-based composite. The images present areas of adhesive debonding exposing the composite resin repaired substrate (CR-S), areas that show fracture of the adhesive bonding agent (AD) and also regions where the composite resin filling (CR-F) used as restorative repair had a cohesive failure|
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| Discussion|| |
The first null hypothesis was rejected as the statistical analysis presented significant differences on the TBSs between the repaired MBC and SBC. The second hypothesis must be also rejected as the surface treatments induced striking improvements to the repair strength of both composites in comparison with the group with no treatment. The present outcomes highlighted that the overall repair strengths after surface treatments for MBC are higher than those for the SBC. Yet, the highest repair TBS with surface treatedP60 achieved 47% of the cohesive strength, whilst for P90, the maximum repair strength reached 27% of the cohesive strength. Such percentages reinforce the higher reparability of methacrylates in comparison with siloranes. There pair procedure is affected by the degree of degradation of the aged composite fillings which is related to the microstructural characteristics and the material's composition.  With methacrylates, the leaching of componentsmay reduce the number of unreacted monomers available for further reaction with the repair composite and adhesive resins. ,, The lower repair potential of silorane resin can be explained by the lower reactivity of silorane groups after polymerization. These polymerize through a cationic mechanism and are less available for additional reaction than other resin composites.  Moreover, the nature of cationic polymerization involves neutralization of available reactive species in presence of water. Indeed, this allied with slower polymerization of silorane molecules contribute to a decrease in reactivity over time.
Furthermore, the MBC P60 has ceramic fillers in 80-90 w%, whilst the silorane-based P90 has quartz fillers in 70-80 w%. Therefore, we may speculate that the surface treatment with silane might be more effective with the MBC due to the higher content of fillers. Moreover, the silorane-based matrix requires a silorane-modified silane molecule to react with the silorane monomers. This modified silane is not commercially available and was not used. In addition, the higher percentage of organic matrix in P90 may increase the negative role of monomeric reactivity/availability for siloranes in comparison with methacrylates which was aforementioned.
There was a correlation between the surface treatments and the category of resin composite. While with the SBC, the surface treatments attained similar repair strengths, with the methacrylate composite the repair strength increased after the airabrasion and adhesive application irrespective of the use of silane. This findingis in agreement with a previous report that revealed that there is not an optimal surface treatment for all types of composites; thus, the knowledge of the material composition is crucial for the repair success,  once the microstructure influences the mechanical behavior of the repairs. 
Regarding the chemical treatment of the composite repairs, silanes and unfilled resins are traditionally used as coupling agents between the filler particles , and the organic matrix acting as a bridge between the aged and the fresh composite.  In the present study, the use of silane in combination with the adhesive did not lead to more effective repair bond strength in both composites, which is in agreement with previous investigations. ,],[ This circumstance has been attributed to the thick interfacial layer caused by the simultaneous use of the silane and adhesive, which would be more vulnerable to failure. , The mechanical treatments have been employed to increase the surface roughness besides to eliminate the surficial layer possibly deteriorated by the oral fluids and bacteria. Sandblasting with aluminum oxide leads to increased repair bond strength. However, in the present study, improvement of TBS by using sandblasting was only observed with MBC repairs.
The control group (G1) of both composites presented 100% of adhesive failures due to the absence of any surface treatment which jeopardizes the bonding of the repair composite. With P60, cohesive fractures were predominant in G4 and G5, highlighting adequate repair of bond strength with such treatments. The mode of failure of SBC repairs after the all surface treatments was similar [Figure 1]b] and indeed is correlated with the similarity observed on the TBS outcomes for these groups.
| Conclusion|| |
Within the limitations of this in vitro study, it can be concluded that:
- For recent fillings the surface treatments improve the repair bond strength in comparison with no treatment for both composites and attained approximately 27% of the cohesive strength of the SBC;
- Sandblasting (Al 2 O 3 ), silane, and adhesive application increase the repair bond strength of MBC and lead to repair of bond strengths by approximately 47% of the cohesive strength.
- Repairs undertaken with MBC present higher overall repair ability potential than those with SBC.
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Dr. Ataís Bacchi
Piracicaba Dental School, University of Campinas - Prosthodontics and Periodontics, Av. Limeira, 901 Piracicaba, São Paulo - 13414-903
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]