Comparative Evaluation of Novel Bulk Fill Resin Composites with Conventional Composites for Microleakage Formation - A Steromicroscopic Study.

Aim: The purpose of this study was to assess and compare microleakage of two novel bulk-fill resin composites with traditional incremental composites. Materials and
Methods: Standardized conservative Class II cavities were made on 120 sound maxillary premolars having approximately 4 mm of width with 2 mm gingival extension below CEJ keeping all line angles round and cavosurface margins beveled. Samples were categorized into the group of three (n = 40), based on composites used; Smart Dentine Replacement (SDR), X Tra Fill, and Z350 XT. The prepared cavities were filled with respective composites to a depth of 4 mm. Post thermocycling, Specimens were absorbed in 0.5% methylene blue for 8 h and soaked in tap water for 12 h samples were later split in mesiodistal direction at the center of the composite restorations with diamond disc. A total of 240 samples were obtained. The samples were viewed with ×20. One-way ANOVA and post-hoc Bonferroni test were used to derive statistical data.
Results: SDR demonstrated considerably less micro leakage in comparison with X-Tra fill composites. Significantly high microleakage was observed in the traditional composites (Z350 XT).
Conclusion: Novel Bulk-fill resin composites exhibited better adaptability and less microleakage compared to traditional multilayer composites. Copyright:

INTRODUCTION

Resin composites are undoubtedly recognized as materials of preference in contemporary restorative dental practice due to the mounting quest for superior esthetics. Composite resins have been subjected to extensive improvement including esthetics, wear resistance, and handling properties.[1] The major problem with composites is their polymerization shrinkage and stresses concentration. They principally depend on multiple determinants like c-factor, constituent of resin composites, and their properties also on various placement techniques.[2] The conventional incremental technique has many disadvantages: It is difficult to place the multiple increments with uniform consistency leading to an increase in the time consumed. Any error in placing manifold layers can result in shrinkage and lead to microleakage.[3] In light of this new composites were developed known as “bulk-fill composites.” These novel composites are recommended to be used in bulk to a thickness of 4 mm because of high reactivity to light curing.[4]

Microleakage is an occurrence where in oral microbes, saliva and various inorganic components scatter throughout the junction of tooth and restoration. This seepage later leads to dentinal hypersensitivity, pulpitis, and dislodgement of previous fillings.[5] Studies have reaffirmed the fact that polymerization shrinkage leads to bond failure and loss of resin material. Microleakage is a hurdle in any restoration as it leads to marginal discoloration of resin composites, frequent decay, sensitivity, and pulpal changes.[26]

Hence, this in vitro experiment was done to assess and contrast the microleakge among two novel composites (SureFil Smart Dentine Replacement [SDR], x-Tra Fil) with conventional composite resins (Z350 XT).

MATERIALS AND METHODS

The present study was undertaken to assess the microleakage from different restoration techniques of composites.

Inclusion criteria

Extracted Maxillary human premolar teeth.

Exclusion criteria

Any teeth with hypoplastic defects, caries or cracks

External or internal resorption

Developmental anomalies.

120 extracted maxillary premolar teeth [Figure 1] were selected and kept in distilled water.

Figure 1

Specimens used in the study

Experimental groups

Three groups (n = 40)

GROUP I: SureFil SDR (Dentsply)

GROUP II: X-Tra fill (Voco, U.S.A.)

GROUP III: Z350 XT (3M, Latin America).

Cavity preparation

Conservative Class II slot cavities (on mesialsurface) were made with no. 245 carbide bur (DENTSPLY/Caulk, Milford, DE, USA) using airoter [Figure 2]. The width of the cavities were standardized to be 4 mm wide. The gingival extension was designed to be located just 2 mm surpassing the contact point of the tooth; All the line angles were made round and margins were beveled.[7]

Figure 2

Class II cavity prepared on maxillary premolar

Placement of resin composites

The samples were stabilized in putty material (3M ESPE) to recreate as closely as possible the clinical condition of a tooth with its supporting structures. To replicate contact points, adjacent teeth were also placed. Tofflemire retainer along with band and wedges were placed to establish contacts and contours.[8]

Samples later split into three groups of forty each.[6] The prepared samples were bonded using a three-step adhesive (All-Bond 2® Dual-Cured Universal Adhesive System)

Slot cavity preparations were made dry for 30s, before applying etchant (Ivoclar Vivadent) for 15s. Later excess etchant was removed using water spray. The successive layer of the primer was applied five times (All-Bond 2® Universal Dental Adhesive System) with a applicator tip till the surface became shiny. Later primed surface slightly dried for 2–3 s and a coat of adhesive was smeared to the prepared surface.[7]

Group I: Samples with depth of 4 mm were restored using Shade “A” of surefil SDR (dentsply) and light cured for 40s using light emitting diode (LED)

Group II: Samples with the depth of 4 mm were restored using Shade “A” of x-Tra fill composite resin and light cured for 40s using LED

Group III: Z350 XT (3M, Latin America) composite wasplaced in multiple layers. A slanting increment of 2 mm was laid. Each increment was light cured for 40s using LED.

Special Teflon lined instruments (DENTSPLY) were used to handle conventional resin composites.

Final finishing and polishing

carried out instantly postrestoration with Sof-Lex disks (3M ESPE Dental Products). Followed by this samples were separated from the putty and kept for 7 days in distilled water at room temperature.

Thermocycling

Apices of all samples were closed using a acrylic resin and two coats of nail polish was applied to cover entire surface of sample excluding composite resin restorations with 2 mm of periphery surrounding it [Figure 3]. Samples later thermocycled for 500 cycles between 5°C and 55°C, with 30 s dwell time at each temperature with an switch time of 13 s amid the baths [Figure 4]. Samples were later absorbed in 0.5% methylene blue for 8 h [Figure 5]. Later Samples were left to remain in normal water for 12 h. Entire samples were sliced in a mesio-distal direction at exactly the midpoint of restoration with diamond disc [Figure 6]. A sum 240 sections were obtained. The Sections were later viewed using ×20 in a stereomicroscope.

Figure 3

Specimens coated with nail varnish

Figure 4

Thermocycles between 50C and 550C

Figure 5

Dye immersions

Figure 6

Longitudinally sectioned specimens

Microleakage test

The extent of dye absorption [Figure 7] was rated using Demarco et al. criterion.[910]

Figure 7

Measurement of dye penetration depth

0–Noleakage

1-Leakage at the gingival wall

2-Leakage at the axial wall.

Statistical analysis

An in-vitro study using 120 specimens was done to assess and compare microleakage among SDR Flow (Dentsply), X-Tra flow, and Z350 XT Composite Resin.

To explore the extent of variation in microleakge among the study groups. Significance was set at: α = 0.05. One-way ANOVA was used For Comparison between thre groups.

Post hoc Tukey's analysis– to study any major difference between the groups.

RESULTS

Present in vitro experiment revealed novel bulk-fill resin composites established better marginal adoptability and less microleakage compared to traditional composites.

Micro leakage results are depicted in Tables 1 and 2.

Table 1

Microleakage observed

Extent of dye penetration	SDR, n (%)	X-Tra fill, n (%)	Z 350 XT, n (%)
No dye penetration	73 (93.33)	72 (90)	69 (86.66)
Leakage at the gingival wall	2 (3.33)	5 (6.66)	5 (6.66)
Leakage at the axial wall	5 (6.66)	3 (3.22)	6 (7.23)
Sample (%)	80 (100)	80 (100)	80 (100)

SDR: Smart dentine replacement

Table 2

Comparison between different pair of groups for microleakage observed

	SDR	X-Tra fill	Z 350-XT
SDR	X	NS	P<0.04
X-Tra fill	NS	NS	NS
Z 350-XT	P<0.04	P<0.04	NS

a. SDR, b. X-tra fil, c. Z350 XT. SDR: Smart dentine replacement, NS: Not significant

DISCUSSION

Traditional resin cements always were autocured and primed in two tube systems and dispensed before use, resulting in unintended air absorption making restoration porous, and hampering the final strength of the restoration.[1112] Then came the incrementally placed composite resins. The challenges faced by them were similar to previously such as, incorporation of voids between increments, c factor, debonding of layers. The procedure was time-consuming as multiple layers to be laid and cured.[13] To overcome the disadvantages of the incremental technique, bulk-fill composites were developed. In comparison to traditional resin composites, the novel bulk-fill composites require less time and are more patient-friendly.[914] Thus, in the present study, incremental composite resins were compared with bulk-fill composites. In this study, the novel composites exhibited considerably improved outcomes compared to the traditional composites. It could be claimed that novel bulk-fill composites established improved wet ability leading to enhanced bonding, good flexibility, and less microleakage. This ensues low dentinal sensitivity and less recurrent caries. Placement of composite in the block of 4 mm eventually resulted in more uniform curing with excellent esthetics.[13]

According to Chuang et al., SDR is intended as a material of choice in areas of heavy occlusal forces since it can be placed in the bulk of up to 4 mm. These exhibit extremely low shrinkage of around 60%and consume half the time in comparison to traditional resin composites. It adopts on its own owing to its packable nature and is compatible with current adhesive systems.[15] In accordance with the results, research published by Van Ende et al.[4] noted that SDR proved acceptable bond strengths despite the method adopted to place and dimensions of the prepared tooth. However, traditional composites could not be placed in a single lump leading to bond failure.

SDR showed superior results in the present study. These results substantiate the research published by Orłowski et al. where Class II restorations with SDR composites marked less dye penetration compared to sonic fill system.[5] In accordance, Rheine suggested that when restoring a cavity, SDR which is in the form of the flowable composite can be easily placed as a bulk-fill base material in bulk layer of 4 mm, as also recommended.[1617] The basic reason for the unique characteristic of this material is due to modulator enriched into urethane dimethacrylate of SDR.[18] This causes less shrinkage by slowing the radical polymerization rate.

CONCLUSION

In the confines of the scope of the present research, it can be accomplished where in placement technique has a great influence on the property of polymerization shrinkage and SDR showed good results as compared to the other experimental groups. Layering composites in multiple layers has always been used as an important method to compensate for polymerization shrinkage. This study exhibited promising outcomes and showed that shrinkage stresses postpolymerization can be improved despite adopting the bulk filling technique to place composite resin.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.