ORIGINAL RESEARCH

https://doi.org/10.5005/jp-journals-10005-2957
International Journal of Clinical Pediatric Dentistry
Volume 17 | Issue 10 | Year 2024

Comparative Evaluation of Microleakage in Class II Composite Restorations Using Three Bulk-fill Composites with or without Resin-modified Glass Ionomer Cement Liner: A Stereomicroscopic Study

Vijay Amarnath C Mundaragi¹, Nandini T Niranjan², Kusuma S Chandrashekhar³, Dhanu G Rao⁴, Thimmanagowda N Patil⁵, Suvarna C Chavan⁶

^1,4Department of Pedodontics and Preventive Dentistry, Subbaiah Institute of Dental Sciences, Shivamogga, Karnataka, India

²Department of Conservative Dentistry and Endodontics, Bapuji Dental College and Hospital, Davanagere, Karnataka, India

^3,5,6Department of Conservative Dentistry and Endodontics, Subbaiah Institute of Dental Sciences, Shivamogga, Karnataka, India

Corresponding Author: Suvarna C Chavan, Department of Conservative Dentistry and Endodontics, Subbaiah Institute of Dental Sciences, Shivamogga, Karnataka, India, Phone: +91 9980906209, e-mail: dr.sona628@gmail.com

ABSTRACT

Aim: To compare the microleakage of three bulk-fill composite resins with or without resin-modified glass ionomer cement (RMGIC) liner.

Materials and methods: A total of 30 maxillary human 1st premolar teeth were selected. Two box preparations were made on the mesial and distal sides. Teeth were randomly divided into three groups of 10 teeth each. RMGIC liner with 1 mm thick were applied to the mesial box. The specimens were divided into three groups according to the type of bulk-fill composites used and restoration of the cavities were done according to manufacturer instructions and light cured. Finishing and polishing were done and stored for 1 week in distilled water at 37°C. Thermocycling was then performed in a thermocycling unit. The specimens were then immersed in 0.5% methylene blue for 8 hours at 37°C. All the specimens were sectioned longitudinally in a mesiodistal direction and analyzed under 20× magnification in a stereomicroscope. The degree of dye penetration was scored.

Results: Subgroup M showed comparatively less microleakage compared to subgroup D in all the groups which was statistically significant. When microleakage between the study group on mesial and distal sides was compared, group smart dentin replacement (SDR)-M showed less microleakage compared to group F-M and this difference was statistically significant.

Conclusion: RMGIC is the recommended liner beneath the bulk-fill composites in class II cavities and SureFil SDR bulk-fill flowable can be the recommended composite resin for class II restorations.

Clinical significance: Bulk-fill composite is a time-saving material as it eliminates the incremental placement. RMGIC is always recommended beneath bulk-fill composites. SDR bulk-fill is the recommended composite restoration.

How to cite this article: Mundaragi VAC, Niranjan NT, Chandrashekhar KS, et al. Comparative Evaluation of Microleakage in Class II Composite Restorations Using Three Bulk-fill Composites with or without Resin-modified Glass Ionomer Cement Liner: A Stereomicroscopic Study. Int J Clin Pediatr Dent 2024;17(10):1146-1152.

Source of support: Nil

Conflict of interest: None

Keywords: Bulk-fill composites, Class II composite restorations, Flowable composites, Microleakage, Resin-modified glass ionomer cement.

INTRODUCTION

Indeed, composites have become favored in esthetic dentistry due to advancements in their properties and application techniques, addressing previous limitations such as strength, dimensional stability, and wear resistance. This evolution has significantly reduced issues like the loss of anatomical form and secondary caries occurrence, enhancing the longevity and effectiveness of restorations.¹^,²

Yes, polymerization shrinkage is a major challenge in modern posterior resin composites despite advancements in wear resistance and strength. The shrinkage that occurs while polymerization can create stress at the interface between the composite and the tooth which might result in gap formation or microleakage. These issues can compromise the durability of the restoration leading to secondary caries and other complications.³

While the incremental filling or layering technique has benefits, including improved curing and reduced shrinkage stress, it also has some drawbacks. Layering can be time-consuming, technique sensitive, and there may be air entrapment between the layers.⁴

To address the challenges associated with layering techniques in posterior cavity restorations, there has been a focus on simplifying clinical procedures. The development of bulk-fill flowable restorative composite represents a significant advancement in composite technology. These materials allow for bulk placement of up to 4 mm thickness, simplifying the restoration procedure and potentially reducing the risk of void entrapment and operative field contamination.⁵^,⁶

Flowable resin-based composites represent a modification of conventional composites, with reduced filler loading to enhance resistance to functional wear and improve physical properties. This reduction in filler content, typically ranging from 37 to 53% by volume compared to 50–70% in conventional composites, results in a less viscous material. Introduced in the late 1990s, flowable composite resins offer better adaptability to cavity walls and improved wettability. Additionally, they serve as a resilient layer between restoration and the tooth thus helping to distribute the stresses evenly during polymerization. These characteristics make flowable composite resins valuable in simplifying restoration procedures and improving clinical outcomes.⁷^,⁸

Bulk-fill flowable resin-based composites are a recent addition to the dental market, designed to be used underneath conventional resin-based composite materials. Bulk-fill composites are formulated to achieve effective curing even in thicker layers often up to 4–5 mm which thereby reduces the stress caused due to polymerization shrinkage. Clinically, this eliminates the need for incremental placement and curing, reducing the need for material manipulation during insertion. Overall, bulk-fill flowable composites streamline the restoration process and offer improved clinical outcomes.⁹^,¹⁰

Smart dentin replacement (SDR Dentsply) is supplied as a single paste, contains fluoride, and is cured using visible light which was initially marketed as a flowable composite resin. It reduces stress during polymerization, makes it safer to apply in bulk, thus simplifying the restorative procedure, saves time, and reduces the chance of air entrapment between layers.⁹^,¹¹

Another specialized composite designed to streamline the restorative process, particularly for posterior teeth is Filtek bulk-fill flowable (3M ESPE). It is a visible light cure with reduced viscosity and can be filled to a depth of 4 mm. It is flowable in nature and bulk-fill capability allows it to adapt to the cavity wall, and hence reduces the shrinkage and stress caused due to polymerization.¹¹

Tetric EvoCeram Bulk-fill (Ivoclar Vivadent) is a combination of nano-sized and micro-sized inorganic fillers with a mean particle size of 550 nm and contains dimethacrylate monomer matrix (20–21% weight). In addition, the manufacturer claims the material to have a key feature of the inclusion of shrinkage stress relievers which reduces the polymerization shrinkage and shrinkage stress.¹²

Evaluating the performance of contemporary flowable composites in posterior restorations, especially in challenging situations like deep and narrow cavities with a high configuration factor (C-factor) is critical for ensuring the longevity and success of the restoration. In high C-factor cavities, the flow of the composites during polymerization is restricted due to the geometry, which limits the material’s ability to relieve stress. So, these challenging scenarios require strategies like the application of a liner underneath the bulk-fill composite. Liners act as a stress absorbing layer, helping to dissipate the stress and protect the bond interface. This approach helps to optimize the clinical outcomes and longevity of posterior restorations by minimizing the impact of polymerization shrinkage and stress on the restoration.¹³

Resin-modified glass ionomer cements (RMGICs) are often preferred as liners due to their numerous advantageous properties. These include higher mechanical strength, ability to set on command, reduced technique sensitivity, and decreased polymerization shrinkage compared to other materials. In addition, RMGICs have excellent adhesion to tooth structure which helps in creating a tight seal around the restoration, thus reducing the risk of microleakage. One of the standout features of RMGIC is their ability to chemically bond to both enamel and dentin which in turn helps to enhance the strength and durability of the restoration. They also inhibit the growth of bacteria, further reducing the risk of secondary caries. The thermal expansion closely matches that of enamel and dentin. It undergoes slow setting reaction which is accompanied by low polymerization shrinkage, minimizing the risk of stress being introduced into the tooth, hence reducing the likelihood of marginal gaps. Additionally, RMGICs provide protective properties for the pulp, making them a favorable choice for liner materials in dental restorations.¹⁴^,¹⁵

Thus, the aim of this in vitro study is to compare the microleakage of three bulk-fill composite resins with or without RMGIC liner, that is, SDR bulk-fill flowable, Filtek bulk-fill flowable, and Tetric EvoCeram bulk-fill composite resins. Hence, the null hypothesis states that there is no difference in the microleakage of SDR bulk-fill flowable, Filtek bulk-fill flowable and Tetric EvoCeram bulk-fill composite resins in class II restorations with or without RMGIC liner.

MATERIALS AND METHODS

Thirty freshly extracted maxillary 1st premolar teeth were collected and stored in distilled water until the study was undertaken. The study included maxillary human 1st premolar teeth with completely developed roots which were extracted for orthodontic and periodontal reasons. Any teeth with caries or cracks, external or internal resorption, developmental anomalies, and restored teeth were excluded from the study.

The teeth were mounted in putty impression material (Aquasil, Dentsply) to simulate clinical conditions and supporting structures as closely as possible.¹⁶ Two box preparations were made, one on the mesial side and the other on the distal side of each tooth using #245 bur held parallel to long axis of the tooth (Fig. 1). The cavity dimensions are: mesiodistally 2 mm, buccolingually 2 mm, and occlusogingivally 4 mm. Tofflemire matrix band and retainer was applied and stabilized with a wooden wedge.¹⁶ Teeth were randomly divided into three groups of 10 teeth each (20 cavities). RMGIC liner with 1 mm thick⁵ was applied to the mesial box according to manufacturer instructions and light cured for 40 seconds. Then etching was done with 37% phosphoric acid (Ivoclar Vivadent) for 15 seconds on enamel and dentin and rinsed with water spray for 1 minute and gently air-dried. The bonding agent (Adper Single Bond 2) was applied, air thinned and light cured for 10 seconds. The teeth were randomly divided into three groups.

Fig. 1: Mesial and distal box preparation

Experimental Groups

Groups: Three groups.

Group SDR: SureFil SDR bulk-fill flowable.
Group F: Filtek bulk-fill flowable.
Group TEC: Tetric EvoCeram Bulk-fill.

Subgroups

Each group were subdivided into two subgroups.

Subgroup M: With RMGIC liner (mesial box).
Subgroup D: Without RMGIC liner (distal box).

Group SDR (10 specimens) were restored with SureFil SDR bulk-fill flowable according to manufacturer instructions and light cured for 20 seconds with the LED curing device (Bluedent, Smart Xpress) and a 2 mm of conventional composite (Filtek Z350XT) was placed upon it and light cured for 40 seconds. Group F (10 specimens) was restored with Filtek bulk-fill flowable and light cured for 40 seconds and a 2 mm of conventional composite (Filtek Z350XT) was placed upon it and light cured for 40 seconds. Group TEC (10 specimens) was restored with Tetric EvoCeram bulk-fill and light cured for 10 seconds. All the materials were restored according to manufacturer instructions (Fig. 2). Then the restorations were finished and polished using polishing kit (Shofu). After polishing, specimens were removed from the impression material and stored for 1 week in distilled water at 37°C. The apex of each tooth was sealed with a self-curing acrylic resin and two coats of fingernail varnish were used to coat all tooth structures except the restorations and 2 mm around them. Thermocycling was then performed in a thermocycling unit. All specimens were subjected to 500 thermocycles between 5 and 55°C, with 30 seconds dwell time at each temperature with an exchange time of 13 seconds between baths (ISO TR 11450 STANDARD 1994).¹⁷ Specimens were immersed in 0.5% methylene blue for 8 hours at 37ºC. After that, specimens were left in running tap water for 12 hours. All the specimens were sectioned longitudinally in a mesiodistal direction toward the center of the restorations using a hard tissue microtome. A total of 60 sections were obtained. The specimens were analyzed under 20× magnification in a stereomicroscope. The degree of dye penetration was scored according to criteria described by Demarco et al.¹⁸

Fig. 2: Composite restoration of mesial and distal cavities

0—No leakage.
1—Leakage at the gingival wall.
2—Leakage at the axial wall.

RESULTS

Kruskal–Wallis ANOVA was employed to compare the microleakage. Scheffe’s post hoc test was employed if there exists any statistically significant difference between the groups. Wilcoxon signed-rank test was employed to assess the microleakage with and without RMGIC liner. Statistical analysis showed that subgroup M showed comparatively less microleakage compared to subgroup D in all the groups which was statistically significant (Table 1). Group SDR (Fig. 3) showed less microleakage followed by group TEC (Fig. 4) and group F (Fig. 5), but there was no statistically significant difference in microleakage between all the three groups (Table 2). When microleakage between the study group on mesial and distal side was compared, group SDR-M showed less microleakage compared to group F-M and this difference was statistically significant (Table 3). Figure 6 shows comparison of microleakage values between the three study groups.

**Table 1:** Comparison of microleakage between the study group on mesial and distal side
Group		N	Median (Q1–3)	Range	Kruskal–Wallis test		Mann–Whitney U test (p-value)
Group		N	Median (Q1–3)	Range	Chi-square value	p-value	Group I vs II	Group I vs III	Group II vs III
Mesial	SDR	10	0 (0–1)	0–1	6.07 (2)	0.048*	0.02*	0.38 (NS)	0.09 (NS)
	F	10	1 (1–1)	0–2
	TEC	10	1 (0–1)	0–1
Distal	SDR	10	1 (1–2)	0–2	3.16 (2)	0.21 (NS)	–	–	–
	F	10	2 (1–2)	1–2
	TEC	10	1 (0.75–2)	0–2

*p < 0.05 statistically significant; p > 0.05 nonsignificant (NS)

**Table 2:** Comparison of microleakage between mesial and distal side in each study group
Group		N	Median (Q1–3)	Range	Kruskal–Wallis test		Mann–Whitney U test (p-value)
Group		N	Median (Q1–3)	Range	Chi-square value	p-value	Group I vs II	Group I vs III	Group II vs III
Mesial	SDR	10	0 (0–1)	0–1	6.07 (2)	0.048*	0.02*	0.38 (NS)	0.09 (NS)
	F	10	1 (1–1)	0–2
	TEC	10	1 (0–1)	0–1
Distal	SDR	10	1 (1–2)	0–2	3.16 (2)	0.21 (NS)	–	–	–
	F	10	2 (1–2)	1–2
	TEC	10	1 (0.75–2)	0–2

*p < 0.05 statistically significant; p > 0.05 nonsignificant (NS)

**Table 3:** Comparison of microleakage between the study group on mesial and distal side
Group		N	Median (Q1–3)	Range	Wilcoxon signed-rank test
Group		N	Median (Q1–3)	Range	Z	p-value
SDR	Mesial	10	0 (0–1)	0–1	–2.27	0.02*
SDR	Distal	10	1 (1–2)	0–2	–2.27	0.02*
F	Mesial	10	1 (1–1)	0–2	–2.45	0.01*
F	Distal	10	2 (1–2)	1–2	–2.45	0.01*
TEC	Mesial	10	1 (0–1)	0–1	–2.24	0.03*
TEC	Distal	10	1 (0.75–2)	0–2	–2.24	0.03*

*p < 0.05 statistically significant; p > 0.05 nonsignificant (NS)

Fig. 3: Stereomicroscopic image of dye penetration of group SDR

Fig. 4: Stereomicroscopic image of dye penetration of group F

Fig. 5: Stereomicroscopic image of dye penetration of group TEC

Fig. 6: Comparison of microleakage values between three study groups

DISCUSSION

To ensure the longevity of a composite restoration, the material used must meet satisfactory physical, chemical, and biological properties beyond just esthetics. Among these properties, the mechanism of polymerization shrinkage is an important factor to consider for composite resins. Polymerization shrinkage is a critical factor that can significantly impact the marginal integrity of composite restoration, leading to issues such as marginal staining, postoperative sensitivity, and secondary caries. Therefore, understanding and managing polymerization shrinkage are essential aspects of achieving successful composite restorations.¹⁹^,²⁰

The marginal gap resulting from polymerization shrinkage is a critical issue that can lead to a cascade of problems including pain, failure of the restoration, esthetic concerns, and secondary caries. In addition, the gap at the margins allows oral fluids and food particles to penetrate between the restoration and tooth causing problems like marginal staining, postoperative sensitivity, and eventually secondary caries. Since the coefficient of thermal expansion is different for composite and tooth, the problem of marginal leakage is further exacerbated. Addressing these factors is crucial in achieving successful composite restorations with minimal complications.¹^,¹⁹^,²¹

Flowable bulk-fill composites are an innovation in restorative dentistry that allow clinicians to efficiently replace dentin in a single increment of up to 4 mm, reducing chair side time and minimizing the risk of errors during placement. They are a versatile material particularly valued for their unique properties like less viscosity, which allows them to flow easily and adapt well to the tooth surface because of which they can create more intimate contact with the tooth surface, thereby reducing microleakage. Studies, such as one by Leevailoj et al. showed that the microleakage at the gingival margins of class II restorations are reduced due to the use of flowable composites.¹^,⁷^,²²

The bulk-fill flowable used in the present study are SureFil SDR bulk-fill flowable (Dentsply) and Filtek bulk-fill flowable (3M ESPE). The SDR Posterior Bulk-Fill Flowable Base by Dentsply was introduced as a flowable composite designed for posterior bulk-filling. The flowable composite is typically used for the initial layer, often as a base because it adapts well to the contours of the cavity preparation. Thus, after placing a 4 mm thick base of flowable composite, a more durable paste-like composite is often layered on top to provide the necessary strength and wear resistance. Several studies have indeed shown that a specific type of flowable composite base can result in significantly lower stress following polymerization compared to conventional flowable composites. In fact, the flowable composites have the ability to achieve similar results to other low shrinkage composites in terms of polymerization stress. In addition, it has been reported that the flowable composites performed extraordinarily well in terms of marginal integrity of the restorations compared to conventional composites. These findings suggest that the SDR Posterior Bulk-Fill Flowable Base offers promising results in terms of reduced polymerization stress and improved marginal integrity compared to conventional flowable composites.⁸^,²³

The second bulk-fill flowable composite used is Filtek bulk-fill flowable (3M ESPE). The shade used for this material in the present study was shade A2 as it is the most commonly used shade.

The nonflowable bulk-fill composite used in the present study is Tetric EvoCeram bulk-fill (Ivoclar Vivadent). It is available in three shades IVA, IVB, and IVW. IVA is used for restorations in “A” range.¹² In the present study, IVA shade was used as it is the most commonly used shade. Tetric EvoCeram bulk-fill is designed with several advanced features like light sensitivity inhibitor which allows for extended working time, shrinkage stress inhibitor to help minimize polymerization shrinkage, and Ivocerin photoinitiator that allows the composite to cure in thicker layers of up to 4 mm.¹¹

Establishing a predictable marginal seal is crucial in cavity restorations, and microleakage serves as a vital indicator for the restoration to be successful. It is the most common method which can be used to assess the sealing efficiency of a restorative material and is often associated with polymerization shrinkage, which is a significant disadvantage of composite restorative materials. Microleakage refers to the penetration of fluids, bacteria, or other substances into the tooth-restoration interface. Evaluating microleakage provides valuable insights into the effectiveness of the restorative material in preventing marginal gaps and ensuring long-term restoration success.¹^,²^,²⁴

The purpose of using RMGIC liners, such as Vitrebond by 3M ESPE, under composite resin restorations is a strategy aimed at improving marginal sealing and reducing microleakage. RMGIC liners offer several advantages, including an exceptionally strong, immediate, and long-term bond to dentin, sustained fluoride release, and low viscosity and elastic modulus. These properties contribute to increased strain capacity and reduced microleakage in restoration. Additionally, RMGIC liners can help mitigate the effects of the configuration factor and lower the internal stresses within the placed restoration. Overall, incorporating RMGIC liners can enhance the longevity and effectiveness of composite resin restorations by promoting better marginal sealing and reducing the risk of microleakage.²⁰

Microleakage evaluation in dental restorations is commonly conducted using various methods like air pressure testing, bacterial assessment, radioisotope studies, scanning electron microscopy (SEM), chemical identifiers, electrochemical studies, neutron activation analysis, artificial caries techniques, and dye penetration. Among these, dye penetration is the most frequently employed technique. Each method offers unique insights into the extent of microleakage and contributes to a comprehensive assessment of the sealing efficiency and integrity of dental restorations.¹⁶^,²⁴^,²⁵

Microleakage evaluation in dental restorations is commonly conducted using various in vitro methods, with dye penetration being the most frequently employed technique. However, other methods include air pressure testing, bacterial assessment, radioisotope studies, SEM, chemical identifiers, electrochemical studies, neutron activation analysis, artificial caries techniques, and measurement of dye penetration. Each method offers unique insights into the extent of microleakage and contributes to a comprehensive assessment of the sealing efficiency and integrity of dental restorations.¹⁴^,¹⁶^,²⁴

Marginal infiltration is often evaluated using a scoring system that numerically assesses the tooth-restoration interface, typically on a scale of 0, 1, and 2.²⁶ While this method has been widely used, it is influenced by the examiner’s ability to accurately assess the extent of infiltration at the interface. This introduces variability, as the process of evaluating microleakage by dye penetration is somewhat subjective.²⁷ This is one of the limitations of the present study.

From a biological perspective, the mechanisms of adhesion vary significantly among different adhesive systems depending on chemical composition and interaction with tooth structures. In etch-and-rinse adhesives, the adhesion primarily relies on micromechanical bonding, with the formation of tags on both etched enamel and dentin surfaces. The two-step etch-and-rinse adhesive system (Adper Single Bond 2) was chosen for this study due to it is proven effectiveness in providing a superior marginal seal. Previous research has shown that etch-and-rinse systems offer better performance in terms of marginal integrity compared to self-etch adhesive systems. This technique is well-documented, and several studies have found it to be effective in bonding resin to dental tissues. Consistent with these findings, Khoroushi et al. reported better marginal seal and less microleakage with etch-and-rinse adhesive compared to self-etch adhesive systems.²^,²⁸^,²⁹

In the current study, regardless of any type of composite used, subgroup M (with RMGIC liner) showed less microleakage compared to subgroup D (without RMGIC liner). The improved marginal seal and reduced microleakage observed with the use of RMGIC liners can indeed be attributed to their stress buffering capacity. These materials are able to absorb and dissipate the debonding stresses that can occur during polymerization contraction, thereby enhancing the overall performance of the restoration.¹⁴ This finding aligns with the results of a study by Arora et al.¹ which demonstrated that using of RMGIC as liners in class II composite restorations significantly reduced the microleakage.

The results of the present study showed that the group SDR-M showed least microleakage compared to group F-M and group TEC-M. This can be attributed to lower polymerization stress of the SDR bulk-fill flowable composites.² According to manufacturer information, the filler size of SureFil SDR bulk-fill flowable is 4.2 μm³⁰ and that of Filtek bulk-fill flowable is 5 μm.²³ The lower polymerization stress of bulk-fill flowable composite is mainly due to the lower filler content, resulting in lower modulus, and the lower viscosity releases the stress in the early stages of polymerization.³¹^,³² Therefore, the low polymerization shrinkage for SureFil SDR bulk-fill flowable shall result from the addition of the “polymerization modulator,” a chemical moiety in the resin backbone increasing flexibility and thus relaxing the polymerized network without harming degree of conversion (DC). These results are similar to the findings obtained by a study done by Scotti et al.,² Benetti et al.,³³ Finan et al.,⁹ and Ilie et al.³⁴ in which SDR bulk-fill flowable showed less microleakage compared to other groups.

According to the results obtained in the present study, group TEC-M showed more leakage values compared to group SDR-M which was not statistically significant. This can be attributed to the filler loading of the composite resins.³⁴^,³⁵ Also flowable bulk-fill composites (SDR and Filtek) have less filler loading by volume than nonflowable bulk-fill composites (Tetric EvoCeram) that were used in the present study. In addition, the filler particle size in Tetric EvoCeram bulk-fill as mentioned by the manufacturer is 4–3000 nm which is lesser than the filler particle size of SureFil SDR bulk-fill flowable (4.2 μm) and Filtek bulk-fill flowable (0.01–4.5 μm). Similar results were obtained by a study done by Ilie et al.³⁴

The results of the present study were in contrast to the study done by Son et al.³⁶ in which high polymerization shrinkage and hence more microleakage was seen in SDR bulk-fill flowable and low polymerization shrinkage and less microleakage in Tetric EvoCeram bulk-fill. The reason given by the author is that this might be due to low and high filler content of SDR bulk-fill flowable and Tetric EvoCeram bulk-fill, respectively.

The microleakage scores of group F-M was more than that of group SDR-M in the present study. This can be due to two reasons: one is that the filler content of Filtek bulk-fill flowable is low due to which there is high polymerization shrinkage and therefore microleakage. The other reason might be attributed to the concentration of bisphenol A glycidyl methacrylate (Bis-GMA) in SDR bulk-fill flowable (63%) and Filtek bulk-fill flowable (25%). Bis-GMA monomer is a high viscosity monomer with a stiff backbone. At high concentrations of Bis-GMA (as seen I n SDR bulk-fill flowable), it decreases the mobility of the reaction medium to the point that the onset of autoacceleration occurs at low DC and therefore low polymerization shrinkage and microleakage. Similar findings were obtained in a study done by Son et al. and Zorzin et al. in which Filtek bulk-fill flowable showed high polymerization shrinkage and hence more microleakage compared to SDR bulk-fill flowable.³⁵^,³⁶

In this study, several limitations could have potentially led to either underestimation or overestimation of the microleakage scores in the study groups. They are:

This study is an in vitro study in which the oral conditions cannot be perfectly simulated.
The present values were measured under ideal laboratory conditions, that is, the light intensity used during curing was likely more controlled and consistent and the curing unit was placed directly in contact with the sample ensuring optimal light exposure which may not necessarily be expected in clinical set up.
Although thermocycling was performed in this study to simulate the thermal stresses experienced in the oral cavity, the temperature changes in the oral environment differ significantly from those in the thermocycling unit.

However, based on the results of the present study, related to microleakage values, the SureFil SDR bulk-fill flowable composite resin can be considered as a better choice of resin composite material when compared to Filtek bulk-fill flowable and Tetric EvoCeram bulk-fill composite resins. Further studies evaluating the longevity of bulk-fill composite resins conducted in vivo would be relevant. Hence, within the limitations of this study, it can be stated that there is a difference in microleakage values between the group SDR, group F, and group TEC with RMGIC liner which is found to be significant. Thus, the research hypothesis which stated that there is a difference in the microleakage of SureFil SDR bulk-fill flowable, Filtek bulk-fill flowable, and Tetric EvoCeram bulk-fill with RMGIC liner is accepted.

CONCLUSION

Resin-modified glass ionomer cement is the recommended liner beneath the bulk-fill composite restorations in class II cavities. SureFil SDR bulk-fill flowable can be the recommended composite resin for the success of class II restorations which can have good marginal seal and least microleakage.

Clinical Significance

Bulk-fill composite is a time-saving material as it eliminates incremental placement. RMGIC is always recommended beneath bulk-fill composites. SDR bulk-fill is the recommended composite restoration.

MANUFACTURER NAME

SureFil SDR: Dentsply

Filtek bulk-fill flowable: 3MESPE

Tetric Evoceram bulk-fill: Ivoclar Vivadent

ACKNOWLEDGMENT

We thank Bapuji Dental College and Hospital, Davanagere for the help in conducting this study.

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