Evaluation of gingival microleakage of class II resin composite restorations with fiber inserts: An in vitro study.

AIMS/
OBJECTIVES: To evaluate the effect of glass and polyethylene fiber inserts and flowable composite as a liner on the microleakage of Class II composite restorations with gingival margins on root surfaces.
MATERIALS AND METHODS: Class II slots were prepared on both the proximal sides of thirty freshly extracted mandibular molars and were divided into six groups, according to the type of fiber insert and use of flowable composite (Filtek Z350) as a liner. Filtek P-60 (3M/ESPE) posterior composite was used to restore all cavities. The specimens were thermocycled and stained with 2% Basic Fuchsin dye, and sectioned to evaluate the dye penetration under Stereomicroscope. Statistical analysis was done using Kruskalwallis test and Mann whitney U test. RESULTS AND
CONCLUSION: This study showed that, fiber insert groups, with or without flowable liner, had reduced microleakage scores as compared to the control groups. However, statistically no significant difference was found between the groups with fiber inserts. Less microleakage was seen in Group IV (With flowable liner and without Fiber inserts) as compared to Group I (Without flowable liner and Fiber inserts).

INTRODUCTION

Light cure composite resins are being widely used for the restoration of posterior teeth. This is not only because of their more favourable esthetic properties, but also due to their adjesion to the dental tissues. Although amalgam has served dentistry for over a century, the clinicians have become more in favour of composites in the recent times. This transition is due to the alleged health concerns and environmental considerations regarding amalgam, the dental professions desire for an adhesive material that demands less invasive cavity preparations, and the patient demand for tooth-coloured restorations even in the posterior teeth.[1] The suitable esthetic posterior restorative materials are competing in the present esthetic era to best suit the above requirements. During recent years, the resin-based composites have been substantially modified to resemble a freshly triturated mass of amalgam in their prepolymerized state, so that they can be condensed into class I and Class II cavities.[2] The newest posterior resin composites show reduced wear rate;[3] however, the marginal adaptation of these restorations particularly in the proximal boxes, has remained unacceptable. Resin composite materials undergo a volumetric polymerization contraction of at least 2.0% which may result in gap formation.[4] Such gaps can result in the passage of salivary fluids along the tooth restoration interface resulting in microleakage.[5] Resin modified glass ionomer cement was placed in the gingival portion of class II composite restorations in an attempt to reduce this microleakage.[6]

Efforts have been made to develop methods to decrease this problem, which include techniques for light polymerization, aimed at reducing the amount of composite volumetric shrinkage, and following strategic incremental placement techniques, which help to reduce the residual stresses at the tooth restoration interface.[7] However, concerns related to the ability of “packable” composites to adequately adapt to internal areas and cavosuface margins have been raised. To solve this problem, using “Flowable” composite as a liner has been suggested. This may also act as a flexible intermediate layer that helps relieve stresses during the polymerization shrinkage of the restorative resin.[8] There is a great deal of stress at the resin dentin layer and the modifications that would reduce or eliminate the interfacial stress concentrations may reduce gap formation and microleakage.[9] Over the last few years new dental materials containing glass, polyethylene, Quartz, carbon or other fibers have been made available which would improve the mechanical properties of the composites and provide wide extended applications for resin composites.[7] Hence, this study is aimed at evaluating the effect of glass and polyethylene fiber placement, and use of flowable composite as a liner, on microleakage in a class II adhesive restoration with gingival margins on the root surface.[10]

MATERIALS AND METHODS

Thirty freshly extracted intact molars (for periodontal reasons) were collected from the Department of Oral surgery. The teeth were cleaned with periodontal scalers. The molars were mounted on Plaster of Paris bases up to 2 mm apical to the cement enamel junction, and stored in distilled water in a refrigerator. Class II slot cavities were made on both the proximal sides of molar using a #245 tungsten carbide bur (SS White, USA) in a water-cooled high-speed air turbine handpiece. The dimensions of the cavities in the gingival floor were as follows: Mesiodistal width=2 mm; buccolingual width=3 mm; gingival floor=1 mm below the cemento enamel junction. The dimensions of the cavities were verified with a periodontal probe. Teeth with prepared cavities were randomly divided into six groups. A universal metal matrix band/retainer (Tofflemire) was placed around each prepared tooth, and was supported externally by applying a low-fusing compound which helped to maintain the adaptation of the band to the cavity margins. Each cavity was cleaned with water spray and was air-dried for five seconds. Bonding agent (Adpersinglebond 2, 3M ESPE) was applied according to the manufacturer instructions. A posterior resin composite (Filtek P60, shade B2, 3M/ESPE) was used to restore all the cavities. The restorations were divided into six groups according to the assigned type of fiber insert and flowable composite (Filtek Z350) as a liner. Cavities without fiber inserts were used as controls.

The groups were divided as follows:

Group 1- with packable composite (Filtek P-60) (Control);

Group 2- Packable composite with glass fiber inserts (ever stick net, Stick Tech, Finland);

Group 3- Packable composite with polyethylene fiber inserts (Ribbond THM);

Group 4- Packable composite with Flowable composite (Filtek Z 350) as a liner;

Group 5- Packable composite with Flowable composite as a liner and glass fiber inserts;

Group 6- Packable composite with Flowable composite as a liner and polyethylene fiber inserts.

An approximate 2 mm layer of P-60 was carefully adapted onto the gingival floor and light-polymerized for 40 seconds. The remaining cavity portion was filled by horizontal incremental placement technique. For fiber inserts group, less than 1 mm thick amount of resin composite was first placed on the gingival floor [Figure 1]. Following this, a 3 mm piece of fiber insert was placed onto the composite increment and condensed through it, to adapt it against the gingival floor. Light-polymerization followed for 40 seconds from the occlusal cavity. Rest of the cavity was filled with horizontal placement technique. Only the occlusal surfaces were then finished (Shofu Composite Finishing Kit) and Polished (Shofu, Super-Snap Rainbow Technique Kit). The specimens were stored in distilled water at 37°C for two weeks which were later subjected to 500 thermocycles between 5°C and 55°C in water baths, with a 30-second dwell time. Apical foramina of the teeth were sealed with yellow sticky wax. Two layers of nail varnish were applied on the tooth surfaces, leaving the varnish coat as 1 mm short of the gingival margins of the restoration. The teeth were immersed in a 2% basic fuchsin dye for 24 hours at 37° C, after which they were rinsed with tap water for five minutes. Each tooth was then sectioned mesiodistally with diamond discs. The section with the deepest dye penetration was selected to represent the tooth. The extent of dye penetration was determined by examination under the stereo microscope according to a five-point scale, as elaborated below:

Figure 1

Schematic representation of the restoration of the cavities with fiber in combination with composite resin

0=No dye penetration;

1=Dye penetration less than half of the gingival wall;

2=Dye penetration along the gingival wall;

3=Dye penetration along the gingival wall and less than half of the axial wall;

4=Dye penetration along the gingival and axial wall.

Data was statistically analyzed with non-parametric Kruskal-Wallis test and Mann-Whitney U test.

RESULTS

The means and standard deviations of microleakage scores of all the groups is presented in Table 1. In general, the fiber inserts group had less microleakage as compared to the control groups. Test of significance of these mean scores between different study groups by Kruskal-Wallis analysis of variance (ANOVA) showed that there was statistically high significant difference (P=0.002). Analysis with the Mann-Whitney U test showed significant differences in mean microleakage scores between controls with P<0.05 (Group I and Group IV), and between Group I and the group with Fiber inserts with P<0.01. However, there was no statistically significant difference in the mean microleakage scores between the fiber inserts group (P>0.05).

Table 1

Microleakage score distribution seen in the study for the different groups

DISCUSSION

Marginal microleakage is one of the major disadvantages of resin composite restorations. The main thrust of research has been directed towards means to reduce or eliminate this disadvantage. Bowen RL postulated that, if the total amount of composite material used to restore a Class II cavity could be reduced, the overall amount of polymerization shrinkage would be proportionately reduced.[11] Introduction of fibers into the composite resin during restoration is a step towards the postulate of Bowen. Fiber inserts placed at the gingival margins of Class II composite restorations enhance the quality of the marginal area in two ways:[7]

Fibers replace part of the composite.

The fibers resist the pulling away of the initial increment of composite from the margins towards the curing light.

Fibernet are silanized E-glass fiberspreimpregnated with resin, whereas Ribbond THM consist of cold plasma-treated polyethylene fibers, and are made from a higher concentration of small diameter fibers.[11] Kolbeck stated that the reinforcing effect of glass fibers was more effective than that of polyethylene fibers, and this was attributed to the difficulty in obtaining good adhesion between polyethylene fibers and resin matrix.[12] Further, glass fibers are light conducting.[13] However, statistically no significant difference wasfound in microleakage scores between the two different fibers, thus supporting the findings of Hamza et al. Placing a layer of flowable composite as a liner under packable composite helped in reducing the microleakage.[14] Flowable composites have low viscosity, increased elasticity and wettability, low surface tension, and hence will better fill irregular internal surfaces and proximal boxes, thereby improving the final marginal integrity and thus cause less leakage and post operative sensitivity.[21516]

The use of low modulus flowable composite may also increase the flexibility of the bonded assembly and might act as a shock absorber and relieve stress induced by the polymerization shrinkage of the resin composite.[17] Though there is reduction in microleakage at the gingival margin after placing flowable composite as a liner, this reduction in microleakage is not very much significant. Although the low stiffness of composite may compensate the polymerization contraction of the low modulus restorative composites, they also shrink more because of their reduced filler content.[18] In another study, when flowable resin was used without fiber reinforcement, microtensile bond strength to dentin decreased in cavities with a high c-factor. On the other hand when fibers were inserted into the bed of flowable resin, microtensile bond strength to cavity dentin surface was increased compared to the flowable resin lined group.[9] The results of our study showed that the placement of fibers in both packable and flowable resin compositessignificantly decreases the microleakage along the gingival margin in deep Class II cavities. Though, in recent years, indirect composite restorations have been developed to counteract the inferior properties of direct composites like, wear rate and marginal seal;[19] this also has disadvantages. As it is very technique sensitive, it requires a high level of operator skill during preparation, impression, seating and finishing the restoration. Also, there are multiple appointments required with the need for temporary restorations which require dental laboratory steps, thus increasing the cost as compared to the direct composites.[2021]

CONCLUSION

The use of fiber inserts’ significantly reduces microleakage in Class II resin composite restorations with gingival margins on the root surface, as compared to the restorations without fiber inserts.

Use of flowable composite as a liner also helps in reducing the microleakage.

No significant difference is seen in the microleakage between the different fiber inserts groups; however, further studies are required to find newer methods and materials to reduce/eliminate the problem of microleakage along the tooth-restoration- interface.