Comparative Evaluation Of The Effect Of Curing Lights On The Microleakage Of Posterior Resin Composite Restoration – An Invitro Study

Introduction: The primary goal of successful restorative treatment is the effective replacement of lost tooth structure and maintenance of the integrity of the restoration. The success of Resin composite restorations depends on many factors, including the degree of moisture control, the effects of shrinkage during polymerization and how well the resin is cured. The purpose of this study was to evaluate the effect of two LED curing units on microleakage of posterior composite resins. Methods: For determination of microleakage, standardized MO or DO box cavities were prepared on 50 human extracted premolar teeth which was divided into 5 groups. Control group were only acid etched but adhesive was not applied. All other groups were etched with 37% phosphoric acid for 15 seconds, rinsed for 30 seconds with water and blot dried, adhesive was applied and light cured. Results: FiltekTM Bulk ll composite cured with Valo curing light exhibited least microleakage when compared to all other groups. Conclusion: The study showed that control group as well as other groups exhibited microleakage but FiltekTM Bulk ll composite resin showed lesser microleakage than Tetric N-Ceram.


Introduction
Resin composite is the most commonly used direct tooth coloured restorative material. Composite resins have gained popularity because of 1 the increasing demand for esthetic restorations .
For success and longevity of esthetic restorations 2,3 it is important that the restoration has perfect seal . Despite improvements in materials and techniques for light-cured composites polymerization 4,5 shrinkage has remained a problem .
There are many parameters that inuence the degree of polymerization of composite resins such as their composition, shade and translucency, characteristics of the light -curing unit used, rate of 6,7 curing and duration of photopolymerizaion .
One of the reasons for failure of a composite resin is their insufcient polymerization. The compromised mechanical characteristics such as reduced hardness, microleakage and secondary caries are the consequences of poor curing which 7 leads to failure of composite restorations .
The standard equipment used for polymerizing composite resins is conventional quartz tungsten halogen (QTH) light curing units (LCU's). The limitations of these lights are degradation of the bulb, reduction of light intensity and the lter all of which may lead to incomplete polymerization. Light-emitting diode (LED) LCU's that produce blue light have been advocated for curing dental materials. LEDs produce less heat hence cooling fan is not required. The other advantages of LED are they are small in size and cordless and they can operate for thousands of hours with a constant light 8 output in power and spectrum .
The study was done to evaluate the effect of two different LED curing units on microleakage of posterior composite resins. On selected teeth, standardized Class II (MO or DO) box cavities were prepared with the following dimensions: Gingival seat width 1.5mm (Mesio-Distal) and 2.5mm (Bucco-lingual), depth of 1.5mm. The preparations were made with a No. 245 carbide bur under copious water coolant with the help of a high speed airotor handpiece. The control group comprising of 10 teeth were only acid etched, with 37% phosphoric acid for 15 seconds, rinsed with water for 15 seconds and excess water was removed with blotting paper, leaving a glistening hydrated surface. The other 40 teeth were acid etched, followed by application of Adper single bond adhesive to etched enamel and dentin and light cured. The restoration were then nished and polished, and the specimens were washed under running tap water for 2 minutes and stored in distilled water at 37 degree Celsius for 2 weeks and then thermocyled at 1500 cycles between 5to 55 degree Celsius at a dwell time of 30 seconds, prior to testing for microleakage.

GROUPS FOR MICROLEAKAGE STUDY
Apices of the samples were sealed with sticky wax, then teeth were painted with 2 coats of varnish, except for the restoration and 1 mm around the gingival margins and air dried. It was then immersed in 0.5% methylene blue for 24 hours. After removal from the dye, the samples were cleaned under running tap water for 2 minutes and were sectioned mesio-distally through the centre of the restoration with a water cooled diamond disk to obtain two sections from each tooth. Dye penetration was examined (both-halves) at the gingival margins using Stereomicroscope under 10X magnication.
Dye penetration was evaluated at the toothrestoration interphase based on the scoring criteria given below 1. Dye penetration less than half the length of gingival oor 2. Dye penetration greater than half, up to the whole length of gingival oor.
3. Dye penetration the whole length of gingival oor plus up to half of the axial wall. 4. Dye penetration the whole length of gingival oor plus greater than half the axial wall and existence of lateral microleakage at dentinal tubules. responsible for the formation of internal stresses in the material and leakage between the lling and the walls of the cavity and formation of post treatment 9 sensitivity .

RESULTS
Microleakage studies are the most common method of detecting the causes that result in bond failure along the tooth restoration interface. There are many methods for detecting marginal leakage and the organic dye method was chosen for this study because of its simplicity & extensive use in the literature. 0.5% basic fuchsin, 2% methylene blue and 50% silver nitrate are the routinely used dyes. The advantages of dye penetration assay are rst, no reactive chemicals are used along with no radiation. Second, different dye solutions are available; therefore, the technique is highly feasible and easily 10 reproducible .
In the present study, the groups were restored with two different bulk ll composite resins such as  Table 1 shows comparison of stereomicroscopic results between different groups and sub-group IA exhibited microleakage with mean value of 6.4 followed by sub-group IB with a mean value of 11.10.
Sub-groups IIA and IIB exhibited values of 12.70 and 11.80 but after comparison with all other groups it was found to be non-signicant with a p value of 0.294.

DISCUSSION
In early 1960s Resin based composites were rst developed and provided materials with higher mechanical properties than acrylics and silicates.
Polymerization shrinkage is the biggest disadvantage of composite material which is TM 3M ESPE Filtek Bulk Fill posterior restorative material is a visible, light-activated restorative Ceram cured using Valo (sub-group IB) then FiltekTM cured using Blue phase LED curing unit (sub-group IIA) and last Tetric N-Ceram cured using Blue Phase (sub-group IIB). TM In the present study Filtek showed superior properties to Tetric N Ceram and this could be attributed to Valo LED light curing system which has shown to have better penetration depth.

Conclusion
Within the limitations of the methodology followed and procedures performed; following conclusions were drawn from this study: TM Both Bulk ll resin composite materials Filtek and Tetric N-Ceram Bulk Fill exhibited microleakage.
There was signicantly less microleakage for TM Filtek followed by Tetric N-Ceram.