MARGINAL MICROLEAKAGE PROPERTIES OF ACTIVA BIOACTIVE RESTORATIVE AND NANOHYBRID COMPOSITE RESIN USING TWO DIFFERENT ADHESIVES IN NON CARIOUS CERVICAL LESIONS - AN IN VITRO STUDY

Abstract

Background

In clinical practice, the restoration of non-carious cervical lesions is a challenge, because most of the time the cervical margin is located in cementum or dentin. This characteristic makes the cervical margin more susceptible to microleakage, causing cavosurface stains, postoperative sensitivity and also favours the incidence of carious lesions.

Aim

To compare and evaluate the microleakage in class V lesions restored with Activa Bioactive restorative and nanohybrid composite resin using two different bonding agents.

Methodology

In this study, 50 class V cavities were prepared in freshly extracted teeth. The samples were randomly divided into 5 groups (n=10), depending on the type of restorative material and bonding agent:

Group 1 - Activa Bioactive (Pulpdent, USA) + No bonding,

Group 2 - Activa Bioactive + Tetric N Bond (Ivoclar Vivadent, Colombia),

Group 3 - Activa Bioactive + G Bond (GC Corp., Tokyo, Japan),

Group 4 - Nanohybrid Composite (Ivoclar Vivadent, Colombia) + Tetric N Bond,

Group 5 - Nanohybrid Composite + G Bond.

The samples were restored with their respective material based on the group. After curing all the specimens were subjected to thermocycling and cyclic loading. Specimens were stained with 2% rhodamin b dye and evaluated for dye penetration.

Results

Results were obtained based on Kruskal Wallis and Mann Whitney U- test.

Conclusion

Within the limitations of this study, none of the materials were free from microleakage. All the materials showed more microleakage at gingival margins compared to occlusal margins. Among all the groups Activa Bioactive restorative when used in combination with Tetric N Bond showed the least microleakage.

Introduction

Non carious cervical lesions (NCCLs) are the cynosure in clinical dentistry, especially among clinical practitioners because of their increasing prevalence1. Restoring such lesions is technique sensitive and may lead to failure of cervical adhesive restorations due to a variety of factors like, poor isolation, cusp movement during occlusion or adhesion to different substrates (enamel and dentin/ cementum).

A variety of materials are available for restoring class V lesions, like Glass ionomer cement, resin modified GIC and composite resin. Out of these, the most popular restorative material is composite resin due to its esthetics and strength. However it has a drawback in the form of polymerization shrinkage, which is the main reason for marginal gap formations and subsequent marginal leakage2.

Bioactive restorative materials are a relatively new concept in dentistry. They are reported to release more fluoride than glass ionomers. Additionally, they react to pH changes in the mouth by uptaking calcium, phosphate, and fluoride ions to maintain the chemical integrity of the tooth structure. Activa Bioactive restorative (Pulpdent, USA) is one such restorative material which comprises of a patented bioactive shock-absorbing rubberized ionic-resin (Embrace resin) matrix that contains a small amount of water. It contains no Bisphenol A, Bis-GMA or BPA derivatives3. This class of composites is delivered via a dual-barrel automix syringe and can be placed with or without a bonding agent. However, as per the manufacturer, it is advisable to use a bonding agent in cases of additional retention, like in class V lesions.

There is a constant ongoing research towards the development of an ideal restorative material as well as new adhesives to reduce the microleakage & enhance the bond strength. However, despite the advances in these materials, the marginal integrity, which is the most important feature of adhesive restorative materials, still remains a challenge. A substandard marginal integrity can lead to formation of gaps at the tooth- restorative interface resulting in microleakage, which poses serious clinical problems such as, secondary caries, marginal discoloration and hypersensitivity, all of which may result in failure of restorations4.

Thus the purpose of this in vitro study was to compare the Activa bioactive restorative (Pulpdent, USA) with the commonly used nanohybrid composite (Ivoclar Vivadent, Colombia) by varying the bonding agents in NCCLs. The null hypothesis states that there is no difference in the performance of the two materials.

MATERIALS AND METHODS

Fifty freshly extracted human premolar (both maxillary and mandibular) teeth free of caries, cracks, abrasions, attrition, and restorations were collected from the Department of Oral and Maxillofacial Surgery, Army College of Dental Sciences. Any extrinsic stains or calculus deposits on the teeth were cleaned and specimens were stored in isotonic saline until use

Preparation of sample

Box-type Class V cavities of dimension, 2mm x3mm x2mm (2mm inciso- gingivally, 3mm mesio-distally & 2mm in depth), were prepared on the buccal surface of the premolars as shown Fig 2, A. The dimensions of the prepared cavities were standardized using Vernier caliper. The prepared cavities were rinsed thoroughly with air/water spray.

Fig 2. A. Dimensions of cavity B. Sample coated with nail vanish and sealed with wax.

Division of samples

The samples were randomly divided into 5 groups (n=10), depending on the type of restorative material and bonding agent as shown in Fig 1.

>Fig 1. Division of samples.

Restoration of samples

Depending on the group, each group was bonded with different adhesives, Tetric N Bond (Ivoclar Vivadent, Colombia) and G Bond (GC Corp., Tokyo, Japan) as per manufacturer’s instructions except in group 1, where no bonding agent was applied. The cavities were restored with Activa Bioactive (Pulpdent, USA) and Nanohybrid Composite (Ivoclar Vivadent, Colombia), A2 shade, using incremental technique and light-cured for 20 sec. The restorations were finished and polished using Super- Snap Mini- Kit (Shofu Dental Corporation), after which the specimens were stored in 100% humidity for 24 hours.

Thermocycling and dye immersion

The samples were subjected to thermocycling in a water bath for 500 cycles between 5° and 55°C with a dwell time of 25 s followed by subjecting them to cyclic loading for 10,000 cycles. Following this, all the surfaces of the samples were triple coated with nail varnish, except a 1 mm cavosurface margin around the restoration and their apices were sealed with wax as shown in Fig 2, B. All specimens were immersed in 2% rhodamine B dye solution for 24 hrs after which they were rinsed with water and air-dried.

Microleakage

The samples were longitudinally sectioned in a buccolingual direction using a diamond disc. The sectioned restorations were examined under a stereomicroscope at 30 X magnification as shown in Fig 3. The depth of dye penetration was analyzed based on a scoring system suggested by Silveira de Araújo et al4.

Fig 3. Score criteria.

Score 0 - No dye penetration

Score 1 – Penetration involving half the occlusal/gingival wall

Score 2 – Penetration involving more than half the occlusal/gingival wall

Score 3 – Penetration involving the axial wall

Statistical analysis

The statistical analysis for microleakage was performed using the Kruskal Wallis test followed by the Mann Whitney U-tests with the Wilcoxon correction for pair-wise comparisons at a significance level of p < 0.05.

Results

A total of 50 teeth were restored during this study with Activa Bioactive & Nanohybrid composite resin restorative material using two different adhesive systems. The tooth- resin interface at the restorative margins was assessed for microleakage. The microleakage in Activa Bioactive restorative at the enamel and dentin margins in comparison to Nanohybrid Composite resin with their respective bonding agents is shown in Fig 4.

Fig 4. Mean scores and comparison of dye penetration in Activa Bioactive and Nanohybrid composite at the enamel and dentin margins, with their respective adhesives.

Fig 4,

Group 2 (Activa Bioactive + Tetric N Bond) depicts least microleakage as compared to group 5 (Nanohybrid Composite + G Bond), which has shown highest microleakage.

Microleakage in G Bond adhesive groups is greater than Tetric N Bond adhesive groups.

Maximum leakage was observed at dentin margins as compared to enamel margins.

The dye penetration was observed to be higher in dentin margins among all the groups as shown in Table 1. The Kruskal Wallis test compared dye leakage at enamel and dentin margins. However, statistically, for all the groups at the enamel and dentin margins p > 0.05.Thus, it can be concluded that although all the experimental groups showed dye leakage at the enamel and dentin margins, statistically, there was no significant difference in leakage at both the margins.

Table 1: Distribution of dye penetration scores at the enamel and dentin margins in all the groups.

Groups3	Total	Scoring Cavity margins	0	1	2
Activa Bioactive + No bonding
1	10	Enamel	4	3	2
3	10	Dentin	3	2	2
Activa Bioactive + Tetric N Bond
0		Enamel	5	4	1
1		Dentin	3	4	2
Activa Bioactive + G Bond
0		Enamel	4	3	3
2		Dentin	1	5	2
Nanohybrid Composite + Tetric N Bond
0		Enamel	4	4	2
2		Dentin	2	5	1
Nanohybrid Composite + G Bond
1	10	Enamel	3	4	2
2	10	Dentin	0	4	4

When pair-wise comparisons were made by the Mann Whitney U-test, Group 2 (Activa Bioactive + Tetric N Bond) showed lesser dye leakage than the rest of the groups along both the enamel and the dentin margins. However, this difference was not significant statistically. The results for dye leakage are obtained in the ascending order as:

Activa Bioactive + Tetric N Bond < Composite + Tetric N Bond < Activa Bioactive +No bonding < Activa Bioactive + G Bond < Composite + G Bond.

Discussion

There is a constant increase in aesthetic demand for a material that ensures near to perfect adhesion to the tooth surface in order to minimize microleakage and improve marginal integrity. Microleakage forms the basis for predicting the performance of any restorative material. Several methods are available for detecting microleakage. These include scanning electron microscopy, the use of dyes, chemical tracers, and radioactive tracers, neutron activation analysis, and fluid filtration5. A dye leakage method was used in this study as it is simple, reliable and well accepted.

Among the various dyes available, rhodamine b dye was selected for this study because it has greater diffusion on human dentin than methylene blue. It has a low molecular size of 1 nm, which is smaller than the diameter of a dentinal tubule and has the ability to penetrate through the smallest of gaps between the interface of the tooth and restoration6. The extent of dye penetration indicates the gaps between the interface of tooth and the restorative material which may lead to ingress of bacteria and their byproducts.

Class V cavities offer a good experiment for testing adaptation of material to the tooth substrate. The cervical lesions pose a restorative challenge due to the complex morphology, where the coronal margin is in enamel and cervical margin in dentin/ cementum. Thus, in the present study class V cavities were selected. The reasons for increased microleakage at the dentinal margin as compared to enamel margin may be7,8:

The organic content of dentin substrate and outward movement of dentinal tubular fluids.

Incomplete removal of the smear layer for adequate demineralization and hybrid layer formation, by acidic primers.

The solvent carriers such as, water, alcohol, and acetone, in the adhesives may react differently with varying degrees of surface moisture present in the tubules.

Orientation of dentin tubule to the cervical wall (CEJ) – Dentinal tubules are oriented parallel to the cervical wall in class V cavities which are located at approximately 1 mm from the CEJ. The hybrid layer formation is absent in the dentinal margins, and is an important cause of leakage.

Due to the intake of food and fluids at varying temperatures, when the restorative materials are placed in the oral environment, they are constantly exposed to thermal variations which may affect their long term performance. Thus, to simulate temperature changes that take place in the oral environment, all the specimens for microleakage evaluation were subjected to thermocycling procedures at temperatures of 5°-55°±10°C, with a dwell time of 25 s, for 500 cycles9. The cyclic loading was performed as the occlusal stresses produced in the cervical region of a tooth during normal function and parafunction may increase microleakage and deteriorate the margins of class V restorations10.

The results of the present study found that Activa Bioactive restorative exhibited less microleakage in comparison to nano hybrid composite. This could be attributed to the ionic resin component which contains phosphate acid groups with antimicrobial properties that improve the interaction between the resin and the reactive glass fillers and enhance the interaction with tooth structure11. The hydrogen ions break off from the phosphate groups through an ionization process that is dependent upon water & are replaced by calcium in the tooth structure. This ionic interaction binds the resin to the minerals in the tooth, forming a strong resin-hydroxyapatite complex and a positive seal against microleakage11,12. However, when used in combination with a bonding agent, Tetric N Bond exhibited least microleakage values among all the groups.

Tetric N Bond is a fifth generation bonding agent which contains HEMA (2-hydroxy-ethyl-methacrylate) in significantly high quantities. HEMA has the characteristic of wetting the tooth surface in a positive way and has high penetration capacity into the etched dentin. It mixes the hydrophilic and hydrophobic components of the bonding agent into one solution and acts as a co-solvent by dissolving the various components into water providing a stronger bond. On the other hand, G Bond (GC Corp., Tokyo, Japan) in group 3 and 5, exhibited greater microleakage as compared to Tetric N Bond (group 2 and 4). The reason for this can be attributed to the absence of HEMA. In absence of HEMA, the collagen peptides forms intermolecular hydrogen bonds with the nearest neighboring collagen peptides causing the collapse of the collagen network leading to weaker bonds and higher microleakage13,14.

The limitation of the study:

The present research work was carried out on a small sample size which could be the limitation of this study. Also this in vitro research was performed using standard method of themocycling with cyclic loading to simulate the intraoral environment for checking the microleakage at the tooth- restoration interface. However, further research by conducting in vivo studies could authenticate these results.

Conclusions

Based on the present study, Activa Bioactive restorative, in combination with a 5^th generation bonding agent, Tetric N Bond, showed lesser microleakage in comparison to other groups. However, the difference was not significant statistically. Thus, it may be considered as a good restorative option for restoring cervical lesions.