|Year : 2015 | Volume
| Issue : 3 | Page : 245-249
A comparative effect of various surface chemical treatments on the resin composite-composite repair bond strength
Shaloo Gupta1, Abhishek Parolia2, Ashish Jain3, M Kundabala3, Mandakini Mohan2, Isabel Cristina Celerino de Moraes Porto4
1 Department of Prosthodontics, Manipal College of Dental Sciences, Manipal, Karnataka, India
2 Division of Restorative Dentistry, School of Dentistry, International Medical University, Kuala Lumpur, Malaysia
3 Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Mangalore, Karnataka, India
4 Department of Restorative Dentistry, Federal University of Alagoas, Maceio, Alagoas, Brazil
|Date of Web Publication||9-Jul-2015|
Dr. Abhishek Parolia
School of Dentistry, International Medical University, Bukit Jalil 57000, Kuala Lumpur
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aim: The aim of this in vitro study was an attempt to investigate the effect of different surface treatments on the bond strength between pre-existing composite and repair composite resin. Materials and Methods: Forty acrylic blocks were prepared in a cuboidal mould. In each block, a well of 5 mm diameter and 5 mm depth was prepared to retain the composite resin (Filtek™ Z350, 3M/ESPE). Aging of the composite discs was achieved by storing them in water at 37°C for 1 week, and after that were divided into 5 groups (n = 8) according to surface treatment: Group I- 37% phosphoric acid, Group II-10% hydrofluoric acid, Group III-30% citric acid, Group IV-7% maleic acid and Group V- Adhesive (no etchant). The etched surfaces were rinsed and dried followed by application of bonding agent (Adper™ Single Bond 2. 3M/ESPE). The repair composite was placed on aged composite, light-cured for 40 seconds and stored in water at 37°C for 1 week. Shear bond strength between the aged and the new composite resin was determined with a universal testing machine (crosshead speed of 0.5 mm/min). Statistical Analysis: The compressive shear strengths were compared for differences using ANOVA test followed by Tamhane's T2 post hoc analysis. Results: The surface treatment with 10% hydrofluoric acid showed the maximum bond strength followed by 30% citric acid, 7% maleic acid and 37% phosphoric acid in decreasing order. Conclusion: The use of 10% hydrofluoric acid can be a good alternative for surface treatment in repair of composite resin restoration as compared to commonly used 37% orthophosphoric acid.
Keywords: Composite resins, dental restoration failure, dental restoration repair, operative dentistry
|How to cite this article:|
Gupta S, Parolia A, Jain A, Kundabala M, Mohan M, de Moraes Porto IC. A comparative effect of various surface chemical treatments on the resin composite-composite repair bond strength. J Indian Soc Pedod Prev Dent 2015;33:245-9
|How to cite this URL:|
Gupta S, Parolia A, Jain A, Kundabala M, Mohan M, de Moraes Porto IC. A comparative effect of various surface chemical treatments on the resin composite-composite repair bond strength. J Indian Soc Pedod Prev Dent [serial online] 2015 [cited 2019 May 26];33:245-9. Available from: http://www.jisppd.com/text.asp?2015/33/3/245/160402
| Introduction|| |
Esthetics has become a prime concern among people in recent past. To fulfill these demands, various types of tooth color restorative materials have been tried out. Among these materials, composite resin is the most commonly used nowadays. Composite resins have been introduced into the field of conservative dentistry to minimize the drawbacks of the acrylic resins that replaced silicate cements (the only esthetic materials previously available) in the 1940s. It can be used almost anywhere in the mouth for any kind of restorative procedure. The reason for such expanded usage of these materials relates to improvements in their ability to bond to the tooth structure and their physical properties. Dental composite resin consists of a monomeric matrix resin, silanated inorganic fillers, a polymerization initiator system, inhibitors for storage stability and pigmentation for shading.  Although marked improvements have been noted in terms of physical and mechanical properties during the last 10-20 years, enzymes present in the oral cavity, for instance, can degrade the composite matrix. , Moreover composites are less stable in fluids and their degradation rate is higher in saliva simulating conditions, depending on the chemical nature of the monomers, amount of dimers and oligomers, the degree of cross-linking in the polymerized matrix, and other intraoral impact. , Also, fatigue can accelerate the wear process in composite materials. All these factors result in discoloration, microleakage, wear, ditching at the margins in clinical situations, which in turn, may require repair or replacement of the restoration. ,
Replacement of dental restorations is still common in daily dental practice due to problems like secondary caries, fracture of restoration, fracture of tooth, marginal staining of tooth, marginal defect of the restoration, partial loss of restoration and patient request for esthetics.
However, replacing restorations has many disadvantages such as being time-consuming; unnecessary removal of the healthy tooth structure and damage to the pulpal tissues. ,
Repair as an alternative to complete removal is justifiable because it preserves the tooth structure. It is often difficult to remove an adhesive restoration without removing an integral part of the tooth. However it is not followed widely as the criteria of repairing restorations are still controversial and not widely taught in dental schools. According to a study conducted by Yousef and Khoja  70.7% of the participants were taught the indications for the repair of composite restorations only 43% of them actually repaired restorations. It was also revealed that 30.4% participants did not repair dental restorations as they had no clinical experience; 28.3% performed repairs on their supervisor's recommendation, 18.5% did not perform the procedure due to the lack of evidence and 8.7% due to poor clinical experience.
While the clinical procedures for bonding of resin composites to enamel and dentin as well as to restorative materials such as metal and ceramic are well established, there is still no consensus regarding the most effective protocol for bonding a repair resin composite to an existing composite restoration. A strong and durable composite-to-composite bond is not as difficult to establish as it may appear from the fact that the chemical composition of the resin composite serving as the substrate and the bonded resin composite is basically identical. As a result of the limited number of reactive methacrylate groups after polymerization and water sorption into the preexisting composite, the repair composite cannot effectively bond to aged restorations without adequate surface treatment.  A number of surface treatment protocols have been proposed to improve repair bond strength in between aged and nonaged composite resins, which include grinding, acid etching and sandblasting followed by different types of adhesive treatments, with conflicting results. ,,,, Hence, the aim of this in vitro study was an to investigate the effect of different surface treatments on the bond strength between preexisting composite and repair composite resin.
| Materials and Methods|| |
A block of Filtek™ Z350 composite resin (3M/ESPE, Minnesota, United States of America) was bonded to a newly block of Filtek™ Z350 composite resin (3M/ESPE, Minnesota, United States of America) by application of five different etchants as a surface treatment followed by Adper™ Single Bond 2 adhesive agent (3M/ESPE, Minnesota, United States of America). Each specimen was light-irradiated using a halogen curing light (Spectrum 800, Dentsply DeTrey, Konstanz, Germany) with light output of 500 mW/cm 2 as measured with a curing radiometer (Demetron/Kerr, Danbury, United States of America) was used to cure all specimens.
Preparation of the specimen
A total of 40 acrylic blocks were prepared in stainless steel cuboidal mold of dimension 50 mm in length, 15 mm width, and 10 mm height. The exposed test surfaces of the repair groups were wet-polished with 220, 320 and 400 Carbide polishing paper (Metatech Industrial Consumbles, Maharashtra, India). In each block, a well of 5 mm diameter and 5 mm depth was prepared to retain the composite resin. Each well was filled with composite resin in increments of 1.0 mm thickness and cured for 40 s. Aging of the composite was achieved by storing them in water at 37°C for 1 week. After this 40 wells were divided into five groups (n = 8) and surface treatment was done, as follows:
Group I: Etched with 37% phosphoric acid, Total Etch (Ivoclar Vivadent Inc., Schaan, Liechtenstein) for 60 s.
Group II: Etched with 10% hydrofluoric acid, Porcelain Etch Gel (Pulpdent Corp., Massachusetts, United States of America) for 60 s.
Group III: Etched with 30% citric acid for 60 s (the citric acid formulation was prepared by Manipal Pharmacy, Mangalore, Karnataka, India).
Group IV: Etched with 7% maleic acid for 60 s (the maleic acid formulation was prepared by Manipal Pharmacy, Mangalore, Karnataka, India).
Group V: Control, no etching.
The etched surfaces of preexisting composite resin were rinsed with a jet of water and dried using an air spray. This was followed by application of a layer of Adper™ Single Bond 2 adhesive system (3M/ESPE, Minnesota, United States of America). The surfaces were then light-cured for 20 s with the same light curing the source. The repair of Filtek™ Z350 composite resin (3M/ESPE, Minnesota, United States of America) was placed on aged composite using split mold (5 mm diameter) and light-cured for 40 s. The blocks were again stored in water at 37°C for 1 week to simulate the oral environment and shear bond strength measurements were made.
Shear bond strength test
Shear bond strength test was done by a universal testing machine, Instron Model 4411 (Instron Corp., Massachusetts, United States of America) with a crosshead speed of 0.5 mm/min. A stainless steel blade 1 mm thickness with 45° inclination at the tip was adapted at the interface of the aged and new composite cylinders. The direction of the force was perpendicular to the long axis of specimens. The shear bond strength value was calculated in Megapascal (Mpa).
The normality of the distribution was assessed by Shapiro-Wilk's W-test. Compressive shear bond strengths values were analyzed using analysis of variance F-test, followed by Tamhane's T2 test for pairwise comparisons between the means, at a significance level of 0.05. Statistical Package for the Social Sciences (SPSS) software, version 17.0 (SPSS, Chicago, IL, United States of America) was used for all statistical analyzes.
| Results|| |
The shear bond strengths of control and all the acids used except maleic acid group showed normal distribution. All five groups showed significant variation between shear bond strengths with F = 5.111 and (P = 0.003) as indicated in [Table 1]. The results of the shear bond strengths for different surface treatments and control groups are shown in [Table 2]. Among the five groups used, hydrofluoric acid showed the maximum bond strength with a mean of 16.94 Mpa, followed by citric acid 14.29 Mpa, maleic acid 10.63 Mpa and phosphoric acid 10.57 Mpa in decreasing order. The's T2 post hoc analysis showed that the significant difference was observed in between hydrofluoric acid and the control group (P < 0.05) indicating its superiority to other etchants used. The specimens treated with citric acid, maleic acid, and phosphoric acid did not show any significant difference from the control group (P > 0.05). There were no significant differences among all specimens treated with different acids [Table 2].
|Table 1: Variation between shear strengths of the five groups using ANOVA|
Click here to view
| Discussion|| |
Establishing a strong and durable composite-to-composite bond is not as trivial as it may appear from the aspect that the chemical composition of the resin composite serving as the substrate and the bonded resin composite is basically identical.  Thus repairing the composite restoration rather than replacing the whole restoration, which involves destroying the remaining healthy tooth structure, is a more suitable treatment option. It is considered minimal invasive and cost effective treatment, which not only prolongs the service life of aged composite restorations, but also is more acceptable to the patients. 
In the present study, composite resin was repaired with the same type of composite resin using different etchants. It is known that in repair of composite resin restoration, the new composite resin cannot effectively bond to the aged, polished composite resin because of the limited number of reactive methacrylate groups left in the preexisting composite resin after polymerization and water sorption. Therefore, to achieve the better outcome it is essential to roughen this polished surface of preexisting composite resin by using adequate surface treatment. 
As the bond strength of composite to the etched enamel has been reported to be about 15-30 Mpa, hence the repair bond strength of composite resin restoration should not be less than this value.  According to Brosh et al.  the bonding of old and new composite resin, occur by three distinct means, that is, chemical bonding with the organic matrix, chemical bonding with exposed filler particles and through micromechanical retention to the treated surface. As it is known that a strong chemical bond to resin matrix of an aged composite is questionable and in order to improve repair bond strength, different surface treatments have to be used such as silica coating, phosphoric acid etching followed by an adhesive, hydrofluoric acid etching, abrasion, and sandblasting.  Sandblasting and etching with hydrofluoric acid are reliable methods to bond composite to porcelain. , However, studies on the repair strength of composite resins using different etching agents are very few. This study compared different etchants such as 10% hydrofluoric acid, 30% citric acid, 7% maleic acid and 37% phosphoric acid and it was revealed that hydrofluoric acid provided the best repair bond strength among these etchants. Hydrofluoric acid being a strong acid etches amorphous SiO 2 , quartz or glasses and commonly used to etch ceramic dental restorations to improve bonding in their repair.  It reacts with and remove, the glassy matrix that contains silica. This leaves the crystalline phase exposed and thus increases the surface roughness. This process also results in enhanced wettability and surface energy on the ceramic surface allowing greater penetration of the resin cement tags. This results in increased bond strength between the ceramic and cement. The same applies to composite, which has silica as filler. Commonly used 37% phosphoric acid is not as efficient in removing silica as hydrofluoric acid.  Thus, it was justifiable to use hydrofluoric acid for repair of composite resin. It results in a better bond strength if used at the desired concentration that is 4-10% hydrofluoric acid. The results of the present study is in disagreement with the study done by Lucena-Martín et al.,  in which the application of hydrofluoric acid as a surface treatment in the repair of composite resin has shown lower shear bond strength. This could be due to the duration of the application of hydrofluoric acid on the surface. In the present study hydrofluoric acid was used for 1 min on the substrate and that seems to favor the high bond strength with the new composite resin while Lucena-Martín et al. applied hydrofluoric acid for 2 min. However, hydrofluoric acid is contraindicated on dentin because it blocks the dentinal tubules by forming star-like structures, which in turn degrades the bond strength of composite resin to the tooth structure. ,
Potential hazards of hydrofluoric acid known from other applications than dentistry should be considered also in dental applications. Hydrofluoric acid can be harmful due to its ability to readily penetrate skin tissues (often without causing an external burn). The damage is directly related to the concentration of the acid and the duration of contact. Erythema and pain may be delayed up to 24 h in exposure to dilute hydrofluoric acid solutions (<20%). In high concentration (>21%) it can cause extensive internal tissue damage, as well as alter blood calcium levels (due to the formation of CaF 2 ), which can lead to dangerous heart arrhythmias.  But, a concentration range of 4-10% can be used safely for dental procedures such as intraoral repair, provided caution is taken to use appropriate barrier techniques, viscous hydrofluoric acid gel formulations, and continual visual observation during the application period. , Other etchants such as 30% citric acid, 7% maleic acid and 37% phosphoric acid have also been used in the past with varied results. ,,, The results of this study showed that the synergic effect between chemical surface treatment with the most commonly used etchant that is, 37% phosphoric acid and dentin bond agent exhibited significantly less bond strength as compared to etchants like 7% maleic acid and 30% citric acid. This finding agrees with previous study that phosphoric acid group reached the lower MPa values.  It could be possibly due to the insufficient amount of residual monomers left in aged composite, required to promote a strong chemical bond by participating in the chemical reaction with the new composite resin, thus a greater surface roughness is required to increase micromechanical retention that phosphoric acid was not able to provide. 
| Conclusion|| |
To repair a composite resin restoration, 10% hydrofluoric acid can be a good alternative for surface treatment as compared to commonly used 37% orthophosphoric acid. However, proper protocol entails the application of an adhesive agent following the acid etching procedure as the latter alone cannot produce an effective bond of aged composite to repair composite.
| Acknowledgment|| |
This study was supported by 3M ESPE, India.
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[Table 1], [Table 2]