|Year : 2012 | Volume
| Issue : 2 | Page : 98-103
Evaluation of the influence of flowable liner and two different adhesive systems on the microleakage of packable composite resin
Muliya Vidya Saraswathi, George Jacob, Nidambur Vasudev Ballal
Department of Conservative Dentistry & Endodontics, Manipal College of Dental Sciences, Manipal, Manipal University, Karnataka, India
|Date of Web Publication||4-Sep-2012|
Muliya Vidya Saraswathi
Department of Conservative Dentistry & Endodontics, Manipal College of Dental Sciences, Manipal, Manipal University, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aim: The aim of the study was to evaluate the microleakage of a packable resin composite using two adhesive systems (self-etch and total-etch) with and without a flowable liner. Materials and Methods: Class II cavities were prepared on 50 human molars, with standardized dimensions. The teeth were divided into five groups. In group I, the cavities were total-etched with phosphoric acid and bonded with an Adper single bond and then restored with a packable resin composite. In group II, the cavities were total-etched, bonded with an Adper single bond and a flowable resin composite was placed as a liner and restored with a packable resin composite. In group III, self-etching adhesive was used instead of total-etch and a procedure similar to group II was performed. In group IV, a procedure similar to group III was performed, except with the placement of a flowable resin composite liner. Group V served as a control where neither adhesive nor a flowable liner was used. All the samples were placed in a dye for 24 hours and examined for leakage. Results: Packable resin composite, when used alone with self-etch adhesive, demonstrated minimum microleakage when compared to the total-etch system (P = 0.30). The lining of class II cavities with a flowable resin composite, followed by packable restoration, demonstrated higher leakage values than when the packable resin composite was used alone (P = 0.001). Conclusion: The use of a self-etch adhesive system was superior to the total-etch system when the cavities were restored with a combination of a flowable resin composite liner, overlaid with a packable resin composite.
Clinical Relevance to Interdisciplinary Dentistry
- A flowable resin composite can be used as a liner material between dentin and a packable resin composite to reduce microleakage.
- Use of a proper adhesive system is one of the key factors in reducing microleakage in packable composite resin.
Keywords: Dentin bonding agent, flowable resin composite, polymerization shrinkage
|How to cite this article:|
Saraswathi MV, Jacob G, Ballal NV. Evaluation of the influence of flowable liner and two different adhesive systems on the microleakage of packable composite resin. J Interdiscip Dentistry 2012;2:98-103
|How to cite this URL:|
Saraswathi MV, Jacob G, Ballal NV. Evaluation of the influence of flowable liner and two different adhesive systems on the microleakage of packable composite resin. J Interdiscip Dentistry [serial online] 2012 [cited 2019 Dec 16];2:98-103. Available from: http://www.jidonline.com/text.asp?2012/2/2/98/100601
| Introduction|| |
Silver amalgam has remained the material of choice for more than a century, even after the advent of esthetic restorative materials for posterior restorations. , Resin-based composites were advocated as a viable alternative, because they were mercury-free, thermally non-conductive, esthetic, and could bond to the tooth readily, with the use of adhesive systems. ,, Even though the wear resistance of contemporary resin-based composites have improved significantly and good proximal contact and contour can be achieved, polymerization shrinkage remains the biggest challenge in direct resin-based composite restorations. 
If the adhesive bond of the resin composite to the tooth structure is insufficient, shrinkage of the resin composite pulls it away from the cavity walls, resulting in the formation of a gap. This allows for microleakage, staining, sensitivity, and / or recurrent decay. , If the bond to the tooth structure is strong enough as the resin composite shrinks, stress is applied to the tooth, which may result in fractured cusps, movement of cusps, and / or postoperative sensitivity. 
A new type of resin composite termed as a 'packable resin composite' claims to have better physical properties, particularly in the restoration of posterior teeth. , Manufacturers claim that increased stiffness of the packable resin composites compared to traditional resin composites, provides sufficient resistance to the condensation forces and facilitates establishing of proximal contacts.  However, concern regarding the ability of these stiffer materials to adequately adapt to the internal areas and cavosurface margins, particularly at the cervical level, has been raised. 
In order to improve cavity wall adaptation and reduce microleakage, flowable resin composite was suggested as an intermediate restorative material, between the dentin and the packable resin composite. Due to its low viscosity, increased elasticity, and wettability, the flowable resin composite may be useful in absorbing the stress caused by polymerization shrinkage.  The handling characteristics and a syringe delivery system make flowable resin composites an ideal choice for use as a liner at the cementum margins of the proximal box. Several studies have investigated the influence of a flowable resin composite on the marginal sealing of class II resin composite restorations, with conflicting results. ,,, Another potent factor for microleakage may be the type of adhesive system used in the bonding of the restorative material. Self-etch systems, composed of aqueous mixtures of acidic functional monomers, generally phosphoric acid, do not require a separate acid-etch technique and the subsequent rinsing procedures.  An additional advantage of the self-etch system includes reduced technique sensitivity; with moist bonding not necessarily being required, as with the total-etch systems.
Dentin bonding has always remained a challenge due to the complex composition of dentin and the histological nature associated with dentin. Fifth generation bonding agents have been introduced with the idea of simplifying dentin treatment and bonding, with the use of only one bottle. However, these systems require prior acid etching and multiple applications of the adhesive.  Although technological advances have been made in materials and techniques in adhesive dentistry, microleakage occurs with all restorations.
Hence, the aim of this study was to evaluate the microleakage of packable resin composite resin using two adhesive systems (self-etch and total-etch), with and without a flowable liner.
| Materials and Methods|| |
Fifty extracted non-carious, non-restored human molars, from persons in the age group of 20 - 50 years, were used for this study. Ethical clearance was obtained from the Institutional Review Board. The soft tissues on the root surface of the teeth were cleaned with a soft brush. The teeth were then stored in 0.2% sodium azide at 4 0 C until use.
Class II cavities (box only) were prepared on the mesial surface of the teeth with a straight fissure diamond point (Horico, Germany) using a high speed turbine under a water coolant. The cavities were prepared following the standardized dimensions. The buccolingual width and the axial depth of the cavity was 2 mm. The cervical margin of the proximal box was located 1 mm coronal to the cementoenamel junction. The buccal and lingual walls of the preparations were approximately parallel and connected to the gingival wall, with rounded internal line angles. A William's graduated probe was used to gauge the depth of all the cavities
Following cavity preparation the teeth were rinsed with water and dried. The teeth were randomly divided into five groups (n = 10).
Group I : The cavities were total-etched with 36% phosphoric acid gel (Ivoclar Vivadent, Mumbai, India) for 15 seconds, rinsed with water for 10 seconds, and air dried for 2 seconds. Two layers of Adper single bond 2 (3M ESPE, Seefeld, Germany) was applied onto the cavity surface, gently air dried, and lightly cured for 15 seconds, using a LED curing light (Fast cure, DP Corp., Florida, USA). A Tofflemire matrix and retainer was placed around the tooth and held by finger pressure against the gingival margin of the cavity so that the preparation would not be overfilled at the gingival margin. This also allowed the light to be directed only in the apical direction, when curing the resin composite.
The Filtek P60 packable resin composite (3M ESPE, Seefeld, Germany) was then placed in increments of 1 mm, which was judged using a William graduated probe, and each increment was light cured for 20 seconds.
Group II : A procedure, similar to the one used for group I, was performed until the application of the bonding agent. This was followed by placement of 1 mm increment of flowable resin composite Filtek Z350 (3M ESPE, Seefeld, Germany) on the gingival seat and axial wall. The depth of the increment was judged by placing a groove on the delivery needle. The flowable resin composite was light cured for 20 seconds and the packable resin composite was placed incrementally and light cured for 20 seconds, similar to group I.
Group III : Two layers of single step self-etching adhesive, Adper Prompt (3M ESPE, Seefeld, Germany) was directly applied to all the 10 specimens. The adhesive was brushed onto the cavity surfaces for 15 seconds and light cured for 10 seconds. The packable resin composite was then placed in increments and each increment was light cured for 20 seconds similar to group I.
Group IV : Adper prompt single step self-etch adhesive was applied onto the tooth surface as in group III and this was followed by the placement of flowable resin composite in 1 mm increment and light cured for 20 seconds. Packable resin composite was then placed in 1 mm increments and each increment was light cured for 20 seconds.
Group V : This group served as the negative control. No adhesive or flowable resin composite was used and the cavity was restored with packable resin composite.
The margins of all the restorations were finished with Sof Lex disks (3M ESPE, USA). Following restoration, the teeth from all groups were stored in distilled water. The specimens were then thermally cycled between 5°C, 37°C, and 60 0 C for 1500 cycles, with a 30 second dwell time, and a 10 second transfer time.
The restored teeth were then cleaned with pumice water slurry and dried. The apices, crown, and root were covered with two coats of nail varnish, except 1 mm around the margin of the restoration. After the nail varnish had dried, the specimens were immersed in 2% Rhodamine B dye (Reached Laboratory Chemicals Pvt., Ltd., Chennai, India) for 24 hours. On removal from the dye, the teeth were rinsed thoroughly and stored in distilled water. Then, each tooth was sectioned mesiodistally across the center of the restoration using a diamond disk (Horico, Germany). The sectioned teeth were examined under a stereo microscope at 15x magnification and the amount of dye leakage was measured using a micrometer placed in the optical eye piece.
Score 0 - no dye penetration
Score 1 - dye penetration till 0.5 mm of the gingival seat
Score 2 - dye penetration till 1 mm of the gingival seat
Score 3 - dye penetration till 1.5 mm of the gingival seat
Score 4 - dye penetration till 2 mm of gingival seat and involving the axial wall
The results were analyzed using the Chi Square test and the intergroup comparison was done by the Mann Whitney U test.
| Results|| |
Mean dye leakage measurements of various groups are presented in [Table 1].
|Table 1: Mean and standard deviation of dye leakage of various experimental groups|
Click here to view
A statistically significant difference existed in the microleakage between groups I and II, with the latter showing more dye penetration (P = 0.001). When groups I and III were compared, there was a significant difference between them. Group III exhibited significantly less leakage (P = 0.30) than group I. When comparing group I and IV, group IV showed higher dye leakage than group I, but it was not statistically significant (P = 0.104). On comparing groups I and V, there was a very significant difference in group V, which showed a higher degree of leakage (P = 0.001). When groups II and III were compared, a highly significant difference was seen, with group II exhibiting more leakage (P = 0.001). A similar result was found when groups II and IV were compared, with group II exhibiting more leakage (P = 0.005). However, when group II was compared with group V, group V showed significantly more leakage (P = 0.001). When group III was compared with group IV, a highly significant difference was observed, with group IV exhibiting maximum leakage (P = 0.001).
| Discussion|| |
Composite resin restorations, especially as a substitute for the amalgam has become a routine procedure in dental offices in recent years.  Despite the advances that have been made, many clinical and material limitations have restricted the universal use of resin composite resins as posterior restoration.  Packable or 'condensable' resin composites were introduced with the expectation that they would be handled and condensed like amalgam, thereby improving proximal contacts. 
The quest for simplification of the chairside adhesion procedure has probably played a pivotal role in the evolution of self-etch systems.  This kind of adhesion reduces the technique sensitivity, because there is no need for a separate etching procedure and no rinsing is required, hence, there is no risk of desiccating the dentin surface.  Also the important advantage of the self-etch approach is that infiltration of the resin occurs simultaneously with the self-etching process. 
The self-etch adhesive Adper Prompt, used in this study belongs to the category of a strong self-etch adhesive with a pH of 0.35±0.01.  Of the ten commercially available strong self-etch systems today, Adper prompt is reported to have the least pH. 
The current investigation evaluated microleakage at the gingival margin of a class II cavity. Several previous studies have demonstrated that in class II cavities, gingival margins are potentially a greater source of microleakage as compared to the occlusal margin. ,, To obtain good interproximal contact, the use of a metallic matrix has been advocated and thus a resin composite can only be light cured from the occlusal surface. As a result, polymerization shrinkage is directed away from the gingival margin of the preparation.  However, in a study by Versluis et al., they found that shrinkage vectors were determined mainly by the boundary conditions, while they were only slightly affected by the position of the light.  To simulate clinical conditions, a metallic matrix band was used and an incremental technique was employed for the placement of packable resin composite. , In the present study, a flowable resin composite was placed in an increment of 1 mm, which was in agreement with Malmstrom et al., wherein, they concluded that microleakage was significantly more when the thickness of the flowable resin composite was placed in an increment less than 1 mm. 
The light-emitting diode (LED) curing light was used in this study, as it had distinct advantages over the conventional halogen light curing units. LEDs had a lifetime of more than 10,000 hours and underwent little degradation of light output over time. Their efficiency was ten times that of the halogen light cure units. This would enhance the effectiveness of polymerizing the resin composite resins. ,
All specimens in this study were thermocycled through 1500 cycles between the temperatures of 5˚C, 37˚C and 55˚C. Wahab et al., evaluated whether thermocycling affected the microleakage values of several commercially available resin composites. They found that it significantly increased the marginal gaps, which added more clinical relevance to an in vitro study. 
There are several methods to detect microleakage. These include the use of dyes, bacterial leakage, radioactive tracers, scanning electron microscopy, and fluid filtration. ,,,, Dye leakage has the advantage of being detectable in dilute concentrations, it is inexpensive, requires no special equipment, and is non-toxic. Several dye penetration studies have been performed using methylene blue, India ink, basic fuschin, crystal violet, and fluorescin.  The current study has utilized the Rhodamine B dye to evaluate microleakage, because it presents greater diffusion on human dentin. This advantage of the dye relates to its molecular size, which is as low as 10 A 0 or 1 nm, which is smaller than the diameter of a dentinal tubule, and can thus penetrate through even the smallest of gaps; between the restoration tooth interfaces. According to Azoubel and Veeck, Rhodamine B dye must be used in leakage studies because of small particle size and ease of visualization. 
The results of the present study found that, Group III (self-etch adhesive followed by packable resin composite) demonstrated the lowest mean leakage values among all. This could be attributed to the thickness of the hybrid layer formed with a self-etch adhesive. In a scanning electron microscope (SEM) study, on comparing the hybrid layer thickness of 10 self-etch adhesive agents, it was found that the Adper Prompt displayed a total thickness of 6 micrometers (μ). The tags were found to be numerous, reaching up to 80 μ into the dentin. This thickness of 6 μ was higher than what had been previously reported for a single bond by other authors.  Their values ranged from 2.5 μ to 4.9 μ. , These parameters, with respect to hybrid layer formation, supported our observation of the least microleakage with a self-etch agent. 
However, in the present study, as the cervical margin of the class II cavity was present in the enamel, the self-etch adhesive was able to resist the interfacial gap formation at the cervical area better than the total-etch adhesive. Even though the data suggested that self-etch adhesives generally demonstrated poorer bonding to enamel, , there was an equal body of data pertaining to Adper Prompt that supported the view that self-etch adhesives showed better sealing of the enamel margin. ,
A recent study characterized the micro morphological pattern obtained by etching with 35% phosphoric acid as well as Adper Prompt, using a SEM. Statistically no difference was found among etching and the resin infiltration pattern produced by total-etch or self-etch resin. 
It was also found that when the flowable resin composite was placed under a packable resin composite, consistently more leakage was seen. Even though few studies , have reported the additional use of a flowable resin composite liner in a class II cavity, there is a plethora of scientific peer-reviewed literature that points to the contrary. Flowable resin composite resins exhibit lower filler loading (60 - 70% by wt and 46 - 70% by volume) and a greater proportion of resin matrix than packable resins. The greater proportion of resin matrix in flowable composite resins may contribute to its high polymerization shrinkage. When the overlying packable resin composite is light irradiated, the contraction stress generated as a result of the curing process pulls the lining material away from the tooth wall. Thus, the increased polymerization shrinkage of the flowable liner may cause a greater leakage seen with this material, under packable composite resin. ,,
Enamel micro fractures are known to occur at the gingival margin by occlusal to the cement enamel junction. Belli and others have demonstrated that such enamel fractures are cohesive in nature, indicating a good adhesion between a flowable resin composite and the enamel, yet resulting in the fracture of thin enamel, because of high polymerization contraction stresses.  This would in turn appear as microleakage. In this study, we did find increased microleakage between the flowable liner and the tooth structure. Whether such microleakage was attributable to a cohesive enamel fracture or an adhesive fracture between the flowable liner and the tooth structure was not within the scope of this study.
The packable resins alone, when used either with the self-etch or the total-etch adhesives, had a superlative performance. This might be attributed to its higher filler content. In view of its better adaptation as well as higher bond strength, the results of the present study, demonstrating the low leakage values with P60, are validated.
Even though this in vitro study has contributed to the understanding of packable and flowable resin composite resins as well as the etch-and-rinse and self-etch adhesives, with respect to marginal leakage, the results can only be validated through a longitudinally followed, randomized, controlled clinical trial, which explains the behavior of these materials when in function within the stomatognathic system.
| Conclusion|| |
From the present in vitro study it was concluded that packable resin composite when used alone with self-etch adhesive, demonstrated minimum microleakage when compared to the total-etch system. The lining of class II cavities with a flowable resin composite, followed by packable restoration, demonstrated higher leakage values than when a packable resin composite was used alone. The use of a self-etch adhesive system was superior to the total-etch system when the cavities were restored with a combination of a flowable resin composite liner and overlaid with packable resin composite.
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