Evaluation of the Quality of Margins in Class ІІ Bulk Fill Composite Restorations when Restored in Bulk and in the Incremental Filling Technique Using the Total Etch and Self Etch Technique

Introduction

With the rising demand for esthetic restorations, there has been a lot of improvement in the properties and techniques of application of composite restorations.^1,2 Even with their far superior esthetic characteristics, they may still be ineffective clinically due to drawbacks like insufficient polymerization, especially in the gingival areas of Class II restorations.³

Various measures have been recommended to prevent microleakage in Class II composite restorations by reducing the polymerization shrinkage. These include: 1) altering the curing techniques - soft curing, dual curing, ramp and delayed curing; minimizing the C-factor by following incremental build up techniques; 2) Using glass ionomer, self-curing composites and flowable composites under conventional composites; 3) Altering the resin composition, e.g., increasing the filler load in the resin; 4) Modifying the filler particle size and shape; 5) Adding pre-polymerized fillers; 6) Incorporating matrix expanding monomers; 7) Reinforcing composite with fiber inserts.⁴

Studies show that these incremental techniques reduce premature gap formation at the resin– dentin interface, cuspal deflection, formation of enamel cracks or fractures, and postoperative sensitivity.^5,6,7

To overcome the problems involved with the layered techniques, like increased time consumption and placement of more than recommended thickness of increments, bulk-fill material was introduced.^8,9,10 

However, even after the advancements in the formulation of new bonding agents with superior bond strengths and marginal adaptation, along with techniques aimed at reducing the shrinkage, a perfect marginal seal is still not achievable and long term microleakage occurs with all restorations.¹¹

The aim of the study was to evaluate the marginal quality of class II composite restorations using a newly introduced bulk fill composite when placed in bulk compared to an incremental technique, following two different strategies, total etch and self-etch using a recently introduced universal adhesive. Materials and

Methods

The materials used for the study are listed out in Table 1. 

Sample processing

Each specimen was mounted in a stainless-steel ring of 1-inch diameter and filled with modeling wax. Fortyeight standardized class II box-shaped cavities were prepared on both the proximal surfaces of twenty-four human mandibular molar teeth. Cavities were prepared with no-245 carbide bur on proximal surfaces using an airotor with water coolant. The bur was replaced after five preparations. The dimensions of the prepared cavity are proximal depth of 6 mm, occlusal depth of 5 mm and bucco-lingual width was kept at 4 mm. The teeth were divided into two groups:

Group 1 followed the self-etch strategy (n=12)

Group 2 followed a total etch strategy (n=12) (Table 2)

Each group was further divided into two subgroups based on the restorative technique followed

Sub group A – cavities on the mesial side which were bulk filled and

Sub group B – cavities on the distal side which were incrementally filled

All surfaces of the teeth, except for a 1-mm zone surrounding the restorations’ margins were covered with nail polish (two coats) to provide an impermeable barrier to the test fluid (dye). Specimens were placed in 2% methylene blue dye for a period of 24 hours and were then sectioned mesiodistally in a vertical plane using a diamond disc. They were evaluated under stereomicroscope for microleakage and were then scored (Table 3).

Statistical analysis

Data obtained was statistically analyzed using Kruskal Wallis test and Dunn’s multiple comparison test.

Results

Summary of microleakage scores for all the groups are represented in the bar graph (Figure 1).

From the above illustrated graph (Figure 1), it can be clearly noted that best result was given by group IB, followed by IA, IIB and IIA. Microleakage score of 3 was observed only in the samples belonging to group IIA. Among all the observed groups, higher number of IB group teeth samples had microleakage score of 1. A higher number of teeth samples in the group IIA had microleakage score of 2.

Mean microleakage values for all the groups are shown in Table 4 and represented in bar graph (Figure 2). The statistical analysis of microleakage values was done by Kruskal Wallis test to determine whether there was significant difference between the study groups. Higher mean microleakage score of 2.16 was observed in group IIA and 1.52 in group IIB i.e. total etch group. In the selfetch groups, group IA had a mean microleakage score of 1.19 and group IB had least microleakage score of 0.62. It was also found that there was statistical significant difference among all the groups.

The intragroup comparisons of Group I and Group II are shown in Table 5. The intragroup comparisons for Group I and Group II were done using Dunn’s Multiple Comparison test which showed a mean microleakage difference of 10.19 between groups IA and IB, which was statistically non-significant at p>0.05. In contrast, group IIA and IIB had a lower mean difference of 12.58 which was statistically significant at p<0.05.

Intergroup comparison between group IA and IIA showed a mean difference in microleakage score of 11.61 and between IA and IIB, microleakage difference of 10.54 was seen, both of which were non-significant at p>0.05. Whereas, intergroup comparison of mean microleakage scores between group IB Vs. IIA showed a mean difference in microleakage score of 25.71 which was statistically significant at p<0.001 (Table 6). Again, mean difference in microleakage score between group.

Discussion Incremental technique involves multiple steps making it technique sensitive and is more time consuming. Recently manufacturers have introduced bulk fill material which they claim can be filled in a single increment to a depth of 6 mm and is completely polymerized at this depth.¹² 

These bulk fill materials have reduced percentage of inorganic filler particles (45-55% in volume) and higher amount of resinous component, which makes the material more translucent and allows for deeper penetration of light.1 The advantages of using dual-cured bulk fill composites as restorative material is that apart from bulk insertion which saves clinical time, polymerization occurs in deep areas due to chemical curing and low contraction stresses are developed.¹³