A Comparative Evaluation of Microleakage between Resin-Modified Glass Ionomer, Flowable Composite, and Cention-N in Class V Restorations: A Confocal Laser Scanning Microscope Study.

BACKGROUND: Microleakage is a concern while restoring cervical lesions. Many products have attempted to minimize the interfacial gap between the tooth and restoration, the main pathway of microleakage. AIMS AND
OBJECTIVE: To compare and evaluate the microleakage in Class V cavity restored with nanohybrid flowable composite, Resin modified Glass Ionomer and Cention N.
METHOD: Class V cavities were prepared on mandibular premolars on buccal surface with their occlusal margin placed in enamel and the gingival margin in dentin. The teeth were randomly assigned to three groups of 20 teeth each and restored with Flowable composite , Resin Modified GIC and Cention N. Samples were immersed in 0.5% Rhodamine dye, sectioned and microleakage measured using Confocal Laser Scanning Microscopy. Statistical analysis was done using Oneway ANOVA Bonferroni's test and Kruskal Waliis test.
RESULTS: The average depth of penetration of dye and scoring of depth were noted. On comparing dye penetration values between groups, RMGIC is compared with Flowable composite and Cention N, statistically significant result was obtained suggesting lesser dye penetration in RMGIC group (P < 0.001) where other comparison did not.
CONCLUSION: RMGIC showed significantly less microleakage compared to the other two restorative materials used in the study and enamel margin of all restorations showed lesser microleakage than dentin margin. Copyright:

INTRODUCTION

Achieving a biocompatible restoration which maintains a proper marginal seal without compromising the pulp is one of the goals in restorative dentistry.[12] Hypersensitivity, secondary caries, pulpal pathosis, and failure of restorations occurs as a result of microleakage. Hence, microleakage is an important property which evaluates the success of any restorative material.[3] Tensile and shear stresses generated in cervical region of the teeth causes cuspal flexure, disrupts the bonds among hydroxyapatite crystals of tooth, leading to crack formation and together with difficulty to obtain a moisture-free environment, the cervical lesions are associated with increased incidence of microleakage. Currently, materials of choice for restoring cervical lesions include glass ionomer cements, resin modified glass ionomer cement (RMGIC), compomers, and resin composites.[45]

RMGIC are hybrid restorative material which combines fluoro-aluminosilicate glass particles, polyacrylic acid, water, water-soluble methacrylate monomer with photoinitiator.[6] Restoring with conventional composite resin, low success rates were observed in cervical lesions resulting from the stiffness of the material. To overcome this, flowable composite resins which have filler loading reduced to 37%–53% (volume) when compared to conventional composites were introduced.[7] Cention-N (Ivoclar, Vivadent) is a new “alkasite” restorative material, and manufacturers claim they have minimal shrinkage stress and volumetric shrinkage due to a patended filler technology (partially functionalized by silanes) and their monomer composition. They also claim that the material has improved flexural strength, and flexural fatigue resistance.[8]

Confocal Laser Scanning Microscopy (CLSM) has advantages over other conventional techniques such as scanning electron microscopy or transmission electron microscopy in studying microleakage. There is high correlation between the results of the fluorescence and radioisotope studies, indicating that these two microleakage methods can be directly compared.[9]

The aim of the study was to evaluate and compare the microleakage in Class V cavity restored with nanohybrid flowable composite (Filtek Z350 XT 3M ESPE), with RMGIC (Fuji II LC, GC America), Cention-N (Ivoclar Vivadent AG, Schaan/Liechtenstein).

MATERIALS AND METHODS

Sixty intact permanent mandibular premolars with fully formed apices, extracted for orthodontic purpose were selected. Teeth with caries, restoration, visible cracks, root canal treatment, fracture, abrasion, malformations, structural deformities, and developmental defects were excluded from the study.

Sample preparation and restoration procedures

On buccal surfaces, class V cavities were prepared using No. 169 L bur with occlusal margins in enamel and the gingival margins in dentin, placed 1 mm above the cementoenamel junction. The cavity dimensions-3 mm in length, 2 mm in width and 2 mm in depth was standardized using an graduated probe. The cavities were cleaned, rinsed, and dried. The teeth were then randomly assigned to three groups of 20 each.

Group 1 - Flowable Composite (Filtek Z350 XT 3M ESPE)

37% phosphoric acid etching done for 15 s rinsed and then air dried till white frosty appearance. Adaper single bond 2 adhesive applied and cured for 20 s. Followed by restoration with Filtek Z350 XT and cured for 40 s.

Group 2 - Fuji II LC - Resin modified GIC (Fuji II LC, GC America)

Cavity was conditioned with GC cavity conditioner for 10 s, RMGIC was mixed according to powder liquid ratio of 3.2:1 and placed in cavity and light cured for 20 s.

Group 3 - Cention-N-. (Ivoclar, Vivadent AG, Schaan/Liechtenstein)

37% phosphoric acid etching done for 15 s and air dried till white frosty appearance. Tetric N Bond Universal adhesive applied and cured for 20 s. One scoop of powder used per 1 drop of liquid (powder/liquid ratio of 4.6:1) mixed for 30 s and cavity was restored.

Microleakage testing

Two layers of nail varnish were then coated over the specimens, except for the tooth- restoration interphase and 1 mm around it, following which the specimens were immersed in 0.5% aqueous rhodamine dye for 48 h. Specimens were then rinsed and sectioned buccolingually through the center of restorations with a slow speed diamond disk. Confocal microscopy at ×10 magnification (LSM 510 Meta Confocal Microscope, Zeiss, Germany) was used to measure the microleakage and images were recorded. The depth of penetration of dye was measured in millimeters with Image J for Windows, v 3.0 software (National Institutes of Health, University of Wisconsin) and microleakage scoring was done according to the criteria given by Wahab et al. [Figure 1].

Figure 1

Scoring of dye penetration using CLSM. (a) No penetration. (b) Penetration limited to enamel wall of preparation. (c) Penetration into dentin walls without involving pulpal floor. (d) Penetration involving pulpal floor of preparation

Grade 0 - No dye penetration

Grade 1 - Penetration to enamel aspect of preparation wall

Grade 2 - Penetration into dentin aspect of preparation wall, but not including pulpal floor

Grade 3 - Penetration including pulpal floor.

RESULTS AND STATISTICS

The results were statistically evaluated using with one-way analysis of variance (Post hoc tests) - Bonferroni's test and Kruskal–Wallis test for comparison between groups.

The mean depth of penetration of dye Flowable composite, RMGIC, and Cention-N were 1.052 mm, 0.494 and 0.949 respectively in enamel margin and 1.72, 1.38 and 1.68 respectively in dentin margins [Table 1]. On comparing dye penetration values between groups, RMGIC when compared with other groups, they showed significantly lesser dye penetration. When flowable composite and cention were compared with other groups, no significant results were obtained [Table 2].

Table 1

Mean values of dye penetration (mm) in enamel and dentin margin

	n	Mean	SD	Significance
Dye penetration in enamel margin
FC	20	1.052	0.4743	<0.01
RMGIC	20	0.494	0.4436
Cention N	20	0.949	0.4507
Total	60	0.831	0.5109
Dye penetration in dentin margin
FC	20	1.7135	0.26027	<0.01
RMGIC	20	1.3830	0.19828
Cention N	20	1.6850	0.24172
Total	60	1.5938	0.27944

RMGIC: Resin-modified glass-ionomer, SD: Standard deviation, FC: Flowable composite

Table 2

Comparison between groups for dye penetration in enamel and dentin margin

	Group (I)	Group (J)	Mean difference (I-J)	SE	Significance
Dye penetration in enamel margin	FC	RMGIC	0.559*	0.1443	<0.01
		Cention	0.103	0.1443	>0.05
	RMGIC	FC	−0.559*	0.1443	<0.01
		Cention	−0.455*	0.1443	<0.01
	Cention	FC	−0.103	0.1443	>0.05
		RMGIC	0.455*	0.1443	<0.01
Dye penetration in dentin margin	FC	RMGIC	0.3305*	0.07427	<0.001
		Cention	−0.0015	0.07427	>0.05
	RMGIC	FC	−0.3305*	0.07427	<0.001
		Cention	−0.3320*	0.07427	<0.001
	Cention	FC	0.0015	0.07427	>0.05
		RMGIC	0.3320*	0.07427	<0.001

*Significance (P<0.05). FC: Flowable composite, RMGIC: Resin-modified glass-ionomer, SE: Standard error

Scoring of dye penetration, flowable composite showed 45% score 1, 55% score 2; RMGIC group showed 25% score 0, 55% score 1 and 20% score 2 and Cention-N showed 50% score 1, and 50% score 2 in enamel margin and flowable composite showed 40% score 2, 60% score 3; RMGIC group showed 75% score 2 and 25% score 3 and Cention-N showed 45% score 2, and 55% score 3. Overall RMGIC showed lesser leakage in both margin.

On comparing dye penetration scores between groups, RMGIC when compared to flowable composite and Cention-N, statistically significant result is obtained suggesting lesser dye penetration in RMGIC group. When flowable composite and cention are compared, no significant results are obtained [Table 3].

Table 3

Comparison between groups for score penetration in enamel and dentin margin

	Mann- Whitney test (P)
Dye penetration in enamel margin
Group I (FC) versus Group II (RMGIC)	<0.05
Group II (RMGIC) versus Group III (Cention)	<0.05
Group I (FC) versus Group III (Cention)	>0.05
Dye penetration in dentin margin
Group I (FC) versus Group II (RMGIC)	<0.05
Group II (RMGIC) versus Group III (Cention)	<0.05
Group I (FC) versus Group III (Cention)	>0.05

FC: Flowable composite, RMGIC: Resin-modified glass-ionomer

DISCUSSION

Cervical lesions are an important factor when considering the long-term health of the dentition. The presence and rapid progression of caries in this area, along with difficulties in isolation, adhesion, insertion technique, and finishing the restoration are challenges in performing a cervical restoration.[610]

To improve mechanical and handling properties of glass ionomers, resin-modified glass-ionomers (RMGICs) were introduced which have the ion-releasing filler glass particles used in conventional GIC in smaller sizes.[1112] The reduced filler loading in flowable composite, modifies its viscosity and allows it to adapt to the microstructural and macrostructural defects in the cavity.[57] Cention-N is a novel restorative material which are grouped under “Alkasites” group of material which combines both esthetics and improved flexural strength. This patented alkaline filler in Cention-N, reduces polymerization shrinkage stresses and also releases hydroxide ions which helps in regulating the pH during acid attacks. The high flexural strength due to cross-linked polymer structure make them ideal for class V restorations.[131415]

According to the present study RMGIC had significantly less microleakage. A study by Maganur P et al. concluded that RMGIC had lesser degree of microleakage than flowable composite even after exposing them to different soft drinks and fruit juices for different immersion regimes.[10] Pontes et al. compared for microleakage and noticed that the RMGIC performed better compared to that of conventional GIC.[612] This is the results of two fold adhesion of RMGIC, bonding chemically to enamel and dentin and also by hybridization. CLSM demonstrated hybrid layer formation in dentin with RMGIC.[4]

In the current study, Centon N performed better than Flowable composite in both enamel and dentin margins but no significant differences were noticed. The less microleakage of Cention-N could be attributed to lesser degree of polymerization shrinkage due to the patented filler (Isofiller), its organic/inorganic ratio and also to the monomer composition. These shrinkage stress relievers, minimizes the shrinkage forces during polymerization and also expands slightly as forces increase during polymerization.[131415]

Confocal laser scanning microscope (CLSM) eliminates the need of sample sectioning, dehydration and polishing artifacts that may interfere with dye penetration. Mount described CLSM as a nondestructive method of studying the tooth - restorative material interface.[8] Other advantages of this technique are the absence of out of focus blur in images, gives opportunity for direct noninvasive serial optical sectioning and also the possibility of achieving three dimensional images which reveals more accurate information than two-dimensional images.[1617]

CONCLUSION

On comparing different groups, RMGIC showed significantly less microleakage compared to flowable composite and Cention-N and was statistically significant owing to chemical bond that RMGIC achieves.

On comparing flowable composite and Cention-N, Cention-N proved to have lesser leakage than flowable composite, but the results were not statistically significant.

Microleakage at dentin margin of all restorations was more compared to enamel margin.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.