Effect of Two Disinfecting Agents on the Microleakage of Resin-Based Composite Restorations in Primary Teeth

Introduction

Today, dental caries is among the most common problems in dentistry. Moreover, it has been reported that recurrent carries are the major problems after dental restorations (1). In recent years, there has been an increase in the utilization of tooth-colored restorative materials, such as resin-based composites, glass ionomers, and the combination of both in primary teeth. Indirect pulp therapy is a method of treatment for deep carious lesions without causing degeneration of the pulp.  The caries lesion is completely removed; however, the affected dentin above the pulp is retained in this treatment (2).

Research has shown that bacteria may proliferate in the smear layer and release toxins that can cause inflammation of the pulp. The topic being discussed currently is to integrate antibacterial agents into restorative material or water to eliminate the bacteria that exist in the cavity wall. Therefore, the use of antimicrobial solutions may reduce the incidence of post restorative sensitization (3). However, the effect of antibacterial agents on restorative material still raises some concern for dentists (4). Chlorhexidine gluconate is a chlorine containing bisphenol which has been used as a safe and wide spectrum disinfectant for years (3). Chlorhexidine has a broad spectrum effect on both gram-positive and gram-negative bacteria. Research has shown that chlorhexidine reduces the bacterial load in saliva and plaque as well as Streptococcus mutans levels in occlusal grooves and root surfaces (5).

Recently, it has been shown that chlorhexidine has an inhibitory effect on the endogen collagen degradation process in the dentin. Considering recent and limited in vivo and in vitro studies in this field, chlorhexidine can be used with the etching and rinse procedure as a disinfectant to enhance bond endurance. However, long term clinical studies are required to verify this (5). Sodium hypochlorite is an effective organic solution that is used vastly in clinical dentistry as a detergent. Sodium hypochlorite was first employed in the 1920s as an antimicrobial antiseptic for endodontic treatment.  Sodium hypochlorite breaks down to form sodium chloride and oxygen as soon as it comes into contact with dentin which starts the oxidation process in the dentin matrix. Studies have been proven sodium hypochlorite’s antibacterial and tissue degrading effects on remnant microbes (4).

Microleakage is a dynamic process which allows the exchange of liquid, ions, molecule, debris, and microbial products across the tooth-restoration interface. Microleakage leads to post-operative sensitization of the tooth, discoloration of restoration margins, recurrent caries, and pulp damage (6). Different studies have expressed different opinions and results regarding the effect of antibacterial substances on the bonding of restorative material to dentin.

 In a study conducted by Memarpour et al. (2), it was found that adding chlorhexidine to resin-based composite restorations increased microleakage.

This study was carried out to analyze the effects of antibacterial material on the microleakage resin-based composite restorations in deciduous teeth.

Materials and Methods

In this experimental study, 40 primary canines without caries were collected from patients underwent orthodontic treatment. The teeth were cleaned using non-fluoride pumice and immersed in 0.1 % Chloramine T solution for 2 weeks for disinfection. Then, the teeth were kept in distilled water during the study.

Standard class V preparations (2.5mm width, 3mm height, and 1mm depth) were performed on the buccal surface adjacent on the cementoenamel junction (CEJ) using a fissure diamond bur (008, Tizkavan Co., Iran) and high-speed handpiece with water coolant. No bevel was made in the cavity preparation. The incisal margin was placed on enamel and the gingival margin on cementum.

The teeth were then randomly allocated into four groups of 10 teeth, and each group was specified with a certain antibacterial agent. Group 1 (control group) was etched with 37% phosphoric acid (Diadent, Korea) for 15 seconds and then rinsed for 15 seconds and dried with a low-pressure air syringe. Two layers of the etch and rinse Adper single bond 2 (3M, ESPE, USA) as well as adhesive were applied and thinned with low-pressure air syringe cured for 20 sec with a LED light cure system (Woodpecker, China) with an intensity of 600 mW/cm². The teeth were restored using resin-based composite (Z250, 3M, ESPE, USA) and cured for 40 seconds.
The light intensity was measured using a light intensity meter.

The cavities in group 2 were etched, rinsed, and dried similar to the former group. Then, a thin layer of 2% non-alcoholic chlorhexidine (Maquira, Brazil) was applied for 60 seconds. After drying with air for 10 seconds, the cavity was restored after bonding using resin-based composite, similar to group 1.

Similar cavity preparation was applied to group 3 and the cavities were etched, rinsed, and dried, subsequently, a thin layer of 2.5 % sodium hypochlorite was applied for 15 seconds and then dried with air. After bonding was applied, the cavity was restored using resin-based composite in a similar procedure to that in previous groups.

Group 4 was subjected to similar steps used in previous groups. A thin layer of 5.25% sodium hypochlorite was applied after etching, rinsing, and drying. After drying with air for 10 seconds, the teeth were restored using the same procedure applied to previous groups. All teeth were stored in distilled water at room temperature and thermocycled (Vafayi, Iran) 5°C and 55°C for 5000 cycles with a 30-second dwell timethermocycling.( After thermocycling, the samples from each group were prepared to be placed in staining solutions as follows:

The apexes of the teeth were sealed with sticky wax, and the root and crown surfaces were covered with 2 layers of nail polish at 1 mm margin of the cavity to prevent microleakage from other areas and interfering with the area under study.  All the teeth were then separately immersed in 2% methylene blue solution for staining and kept at room temperature for 24 h. The samples were rinsed and cut faciolingually from the middle of the restoration using a diamond disc and water coolant) 2). Two examiners calibrated with each other examined the linear penetration of the stain under a microscope (ZTX-3E, China) with a magnification of 20x. In order to increase the accuracy of the results, both segments of each tooth were examined, and the highest value was reported as the microleakage score.

The scoring system for microleakage is as follows:

Score 0: No penetration

Score 1: Penetration up to 1/3 of the cavity depth

Score 2: Penetration up to 2/3 of the cavity depth

Score 3: Complete penetration of the cavity depth but not the axial wall

Score 4: Penetration of stain into the axial wall.

Data were analyzed in SPSS software (version 18) through Kruskal-Wallis test for all groups and Mann-Whitney U test for paired difference test with a pre-set significance level of 0.05.

Results

This study was conducted on 40 extracted primary canines without caries which were divided into four groups.

Each sample was examined regarding incisal and gingival surfaces by two observers. Statistical analysis showed that there was no statistically significant difference between the two examiners (P>0.05).

The normality of the data was tested using Shapiro-Wilk test and the results showed the non-normal distribution of data in the test groups and both cervical and incisal surfaces (P<0.001).Therefore, non-parametric tests were used in this study.

Comparison of the mean values of composite microleakage showed a statistically significant difference among the four groups in terms of both gingival and incisal surfaces (Tables I, II). The highest and lowest levels of microleakage were observed in 2.5% sodium hypochlorite and the control group, respectively, regarding both gingival and incisal surfaces. Furthermore, there was no significant difference between the incisal and gingival levels regarding the mean of microleakage in any of the groups (Table III). The total mean values of microleakage in the gingival and incisal surfaces were 2.60±1.61 and 2.40±1.90, respectively. In addition, no statistically significant difference was observed regarding the comparison of mean values of microleakage in these surfaces (P=0.715).

Table IV summarizes the results obtained from the paired difference tests. According to the results, there was a significant difference between the control group and the other three groups regarding chlorhexidine, 2.5% sodium hypochlorite, and 5% sodium hypochlorite in both gingival and incisal surfaces. Consequently, the microleakage of all three groups was higher than that in the control group. However, there was no significant difference among the three groups in terms of the abovementioned variables.

Table I. The mean values of microleakage in four groups regarding incisal surface

Table II. The mean values of microleakage in four groups regarding gingival surface

Table III. Comparison of the mean microleakage in four groups regarding the incisal and gingival levels

Table IV. Paired difference test of groups with each other in terms of microleakage value