Evaluation of the sealing ability of resin cement used as a root canal sealer: An in vitro study.

AIM: This study was designed to evaluate the apical seal of root canals obturated with resin cement as a root canal sealer and compare with that of the glass ionomer and zinc oxide eugenol sealers using a cold lateral condensation gutta-percha technique.
BACKGROUND: Successful root canal treatment requires three-dimensional obturation of the root canal system with nonirritating biomaterials. None of the available materials are capable of providing a fluid tight seal.
MATERIALS AND METHODS: The prepared teeth were randomly divided into three groups of 15 each to be obturated using three different sealers. Group I: zinc oxide eugenol (Tubliseal), Group II: Glass ionomer (Ketac Endo), and Group III: resin cement (C & B Superbond). All the specimens were stored in 100% relative humidity at 37° for 24 h. The specimens were placed in 2% methylene blue dye for 48 h and sectioned. The dye penetration was evaluated under a stereomicroscope.
RESULTS: The "Kruskal" Wallis test was carried out to test the equality of mean. All the specimens showed dye leakage, and there was a statistically significant difference (P < 0.0001) among the groups. The specimens in Group III showed a minimal leakage and the specimens in Group I showed a maximum leakage.
CONCLUSION: Resin cement sealed the root canals significantly better when compared with zinc oxide eugenol and glass ionomer sealers.

INTRODUCTION

The final stage of endodontic treatment is the three-dimensional obturation of the root canal system. To achieve this, root canal filling must seal the canal walls both apically and laterally in order to prevent ingress of microorganisms or tissue fluids into the root canal space. Many filling materials have been used in root canal treatment in an attempt to achieve this objective.

The methods most frequently used to obturate root canals employ either a semisolid, solid, or rigid core material. The most commonly used core material is gutta-percha, but this material does not seal the canal when used alone. Therefore, a root canal sealer or cement is required to adhere to the dentin and fill the irregularities and minor discrepancies between the core filling material and canal walls. The sealer also acts as a lubricant during the obturation procedure and fills any patent accessory canals.

Many sealers have been developed for the use in root canal treatment. They can be classified according to their chemical composition as calcium hydroxide based, zinc oxide eugenol based, glass ionomer based, and resin-based sealers. Most commonly used root canal sealers, however, are zinc oxide based and have been used for several decades because of their satisfactory physicochemical properties.[1]

Until recently, none of the root canal sealers were capable of bonding chemically to the root canal walls.[2] A root canal sealer based on the glass ionomer was introduced because of its chemical adhesion to dental hard tissue. Preliminary in vitro studies suggest that the material is superior to the Grossman's sealer[3] and possesses many ideal characteristics expected of the root canal sealer.[4]

However, none of the available sealers prevent leakage consistently. Actually, it is impossible to prevent the leakage unless sealer bonds both to the tooth structure and to the core material.[5]

Currently, the latest generation of dentin bonding agents are purported to achieve a micromechanical and chemical bond to dentin forming hybrid layer thereby, producing high bond strength[6] thus reducing microleakage.[78] The use of resin cements may have a potential to enhance the root canal seal by reducing microleakage, thereby contributing to the success of the root canal treatment.

Therefore, a study was conducted to evaluate the sealing ability of the resin cement, glass ionomer, and zinc oxide eugenol sealers with gutta-percha using a cold lateral condensation obturation technique.

MATERIALS AND METHODS

Forty-five freshly extracted human central incisors were selected and decoronated at the cemento-enamel junction using a water-cooled fissure bur. The working length was determined using No. 15 K file and the biomechanical preparation was done using K3 NiTi rotary files. Sodium hypochlorite (5.25%) was used as an irrigant throughout the preparation followed by 17% EDTA solution as a final irrigant to remove the smear layer.

The prepared teeth were randomly divided into three groups of 15 each to be obturated using three different sealers.

Group I: Zinc oxide eugenol (Tubliseal, SybronEndo)

Group II: Glass ionomer (Ketac Endo Aplicap, 3M ESPE)

Group III: Resin cement (C & B Super Bond, Sun Medical Co., Japan).

The teeth in Group III were pretreated with 10:3 citric acid–ferric chloride solution (dentin activator) by placing 1.0–2.0 ml of solution for 10 s followed by rinsing with distilled water and drying with paper points. The samples from all the three groups were obturated with gutta-percha as core material with respective sealers using a cold lateral condensation technique.

All the specimens were stored in 100% relative humidity at 37° for 24 h. The teeth were dried, and the root surfaces coated with two layers of nail polish with the exception of 1.0–2.0 mm of the apical surface. The specimens were placed in 2% methylene blue dye and were stored at room temperature for 48 h, after which they were thoroughly washed with distilled water, dried, and nail polish was removed using a periodontal curette. The roots were split longitudinally using diamond discs, and the dye penetration was measured from the apical end of the specimens using a stereomicroscope. The results were tabulated and subjected to statistical analysis.

RESULTS

A test for normality was carried out for the data using a Q–Q plot. From the plot, it was concluded that the normal distribution does not fit well to the obtained data. Therefore, a nonparametric test namely, “Kruskal–Wallis” test was carried out to test the equality of mean [Table 1]. The obtained P-value was less than 0.0001 hence, it was concluded that there is statistically significant difference among the groups. To find out which pair of mean(s) differed, a multiple comparison test given by Dunn was carried out [Table 2]. The critical value of the test is 5.543 and if the mean ranks of the groups exceed the critical value, it can be concluded that there is statistically significant difference among the groups.

Table 1

Kruskal–Wallis Test

Table 2

Dunn multiple-comparison test

All the specimens showed dye leakage, and there was statistically significant difference among the groups. The specimens in Group III showed a minimal leakage and specimens in Group I showed a maximum leakage.

DISCUSSION

The successful root canal treatment requires three-dimensional obturation of the root canal system with nonirritating biomaterials. The majority of endodontic failures are attributed to the incomplete sealing of the root canals.[9] Thus, it is necessary to use materials, which will be able to create fluid tight seal[10] between the root canal system and the periapical tissues.

Several studies have indicated that whenever endodontic treatment has failed clinically, persistent microbial infection caused by either inadequate root canal debridement or an inadequate seal has maintained periradicular inflammation. Presently, there are no available materials that possess ideal properties or techniques that provide a complete seal of the root canal system.

Leakage into the root canal system could occur via the following four possible routes:[11]

Through the apical foramen, between the root filling material, and the root canal wall.

Through the apical foramen by infusion into the core material.

From the outside of the tooth through exposed cementum, accessory canals or secondary canals.

Through the coronal access cavity.

In this study, all the specimens showed evidence of dye penetration although, the resin cement (C & B Super Bond) sealed the root canals more completely than the glass ionomer and zinc oxide eugenol sealers.

Methylene blue dye was used as the leakage marker in this study for several reasons: It is readily detectable under visible light, highly soluble in water, and is able to diffuse easily.[12] Moreover, methylene blue dye is not absorbed by the dentinal matrix apatite crystals. The methylene blue dye has leakage comparable to butyric acid, which is a metabolic product of microorganisms.[13]

More leakage with the zinc oxide eugenol sealer as compared to the glass ionomer sealer and resin cement may be due to its nonadherence to the root canal dentinal walls.

The leakage with the glass ionomer sealer was less as compared with the zinc oxide eugenol sealer in this study. The newly developed glass ionomer sealer Ketac Endo has many ideal characteristics:[4] increased working time, ease of manipulation, radio opacity, and adaptation to root canal walls. Glass ionomer sealer bonds chemically to the dentin of the root canals conferring a distinct advantage in endodontic therapy by preventing percolation and bacterial penetration at the sealer-dentin interface.

In this study, there was less leakage and better seal of the root canals obturated using resin cement when compared with zinc oxide eugenol and glass ionomer sealers. A successful concept of dentin bonding in restorative dentistry has been introduced to endodontic treatment and promising results have been reported in (4-META) MMA-TBB based resins in the literature.[1415] The fourth generation dentin bonding agents adhere micromechanically and chemically to the root canal dentin to achieve good bond strength. In addition gentle dentinal etching was provided by 10:3 solution of ferric chloride and citric acid and the hydrophilic propensity of 4-META provided more thorough seal.

The quality of adherence of dentin bonding agents to dentin is a function of smear layer removal[16] and 17% EDTA liquid proved to be effective.[17] The removal of the smear layer exposes the peritubular and intertubular substrates thus allowing penetration of resin and formation of hybrid layer.[7] The resin cement resisted the dye penetration better than the other two sealers because of formation of the hybrid layer.[18]

As the resin is not originally intended for endodontic use, working properties have to be altered to make the material clinically predictable.[19] The material, however, is radioopaque and sets chemically lending it useful in root canal therapy. Potential benefits are obvious in the management of fractured roots as well as in immature pulpless teeth where the additional strength afforded by the resin may allow an otherwise hopeless tooth to be retained.

In vitro leakage studies comprise a major portion of contemporary endodontic research though it is difficult to draw in vivo correlation. No evidence exists that demonstrates the amount of leakage a root canal system must exhibit before being detrimental in a clinical situation. This study used a semiquantitative data of dye penetration to evaluate a nontraditional material in an attempt to use a material that may totally seal the root canal system. Preliminary results are promising while bearing in mind that more stringent evaluation methods are indicated.

CONCLUSION

The resin cement sealed the root canals significantly better when compared with zinc oxide eugenol and glass ionomer sealers. This study evaluated only one aspect of root canal sealers that is adhesion to the root canal dentin. Further investigation of various aspects of the resin cement to be used as a root canal sealer is recommended.