Introduction

The dental pulp is a sterile environment. A number of confounding factors such as caries can cause infection in the pulp and its spread to periapical tissues (1). Elimination of infectious microbial agents in the root canal and prevention of re-infection are the main goals of endodontic therapies (2). Because cleaning and shaping the root canal cannot eliminate all the microorganisms in the canal even with widespread use of cleaning agents, creation of a complete apical seal for an unlimited period as a barrier to prevent the passage of microorganisms and their products is another objective of endodontic therapy, which prevents the development or continuation of inflammation in this area and leads to success of treatment in the long run (1, 3-5). The quality of root canal filling, type of the filling material, method of removal, and quantity of filling material are the factors affecting the quality of apical seal (6-10).

Gutta-percha is a standard material with minimal toxicity among the currently available filling materials, has a tendency for self-sterilization, is easy to work with, and can be conveniently removed from the canal. Inability to bind to dentin walls, which is the main disadvantage of this material, is the reason for simultaneous use of a root canal sealer material (1). Resilon is a synthetic thermoplastic polymer, which has been introduced to create a more effective seal due to the formation of resin tags within the dentinal tubules. The tissue biocompatibility of this material, which is used similar to gutta-percha, has been indicated, and it is capable of binding with resin sealers such as Epiphany. This sealer material is resistant to bacterial leakage by creating a bond between dentin walls and the central core (1, 5, 11, 12).

Several studies have compared the apical seal created by Resilon/Epiphany with that created by gutta-percha/sealer, which have reported different results (13, 14). Today, a post space is used in the teeth subject to endodontic treatment to cause retention for core structure, reinforce the remaining crown tissue, and distribute forces along the root (15, 16).

Preparation of a post space can be done immediately or with delay. The immediate method of post space preparation decreases the number of patient visits, which will result in increased patient’s satisfaction
(4, 17).

Various methods are used to prepare the post space, including the application of solvents, heating instruments such as heat carrier, and rotary instruments like Peeso Reamers. The aim of this study was to evaluate the effect of post space preparation with rotary devices, as well as using heated instruments on microbial leakage of canals obturated with gutta-percha and Resilon-Epiphany.

Materials and methods

To conduct this experimental study, 64 extracted human premolars meeting the following criteria were used: single-root and single-canal, straight canals, initial apical foramen diameter equal to file ≠20 or 25. Teeth with internal or external resorption, root caries, canal calcification, extra canals and cracks were excluded from the study.

The teeth were randomly divided into four experimental groups of 15 premolars as well as positive and negative control groups (two premolars each).

The crowns were cut from CEJ region using diamond saw at approximately 300 rpm, with water coolant, so that 11-12 mm of each root remained. In all groups, the preparation of root canals was done using manual K-file (Dentsply Maillefer, Switzerland) by Step back technique. The working length was determined through passing the file through apical foramen and subtracting 1 mm from its length, and the last applied apical file (MAF) was considered 35 in all the samples. The coronal part of root canal was prepared using Gates Glidden drills #1-3, (Dentsply Maillefer, Switzerland), the canal was irrigated using 2.5% sodium hypochlorite followed by distilled water and dried using paper points.

Gutta-percha (Ariadent, Iran) and AH-26 root canal sealer (Dentsply, De Trey, Konstanz, Germany) were used for canal filling in GP and GH groups, The master gutta-percha cone having the same number with the master apical file (MAF) was selected. The AH 26 sealer with a creamy consistency was prepared and the gutta-percha cone was smeared with it and placed in the canal, so that it went through the working length and had a slight tug back. A size B finger spreader (Dentsply Maillefer, Switzerland) reaching 1 mm of working length and a secondary gutta-percha #20 (Ariadent, Iran) were used for lateral compaction. Secondary gutta-percha cones were used until the spreader was not able to penetrate over 2 mm beyond the canal orifice. After completing the filling, a hot heat carrier was used to cut the extra gutta-percha.

Resilon and Epiphany root canal sealer were used to fill the canals in RP and RH groups, and the Resilon cone with the same number of the master apical file (MAF) was selected. Resilon cone was smeared with Epiphany sealer and placed in the canal, so that it went through the working length with a slight tug back. Size B finger spreader reaching 1 mm of the working length and a secondary Resilon can #20 were used for lateral compaction. Secondary Resilon cones were used until the spreader was not able to penetrate over 2 mm beyond the canal orifice. After cutting excess material from the Resilon cone, the obturated coronal surface was light cured for 40 s.

Then, in GP and RP groups, Peeso Reamer #3 (Dentsply Maillefer, Switzerland) was used to leave behind 4 mm of gutta-percha for post space preparation but a heat carrier was used for this purpose in GH and RH groups (18).

The teeth in the positive and negative control groups were prepared similar to the experimental groups; but the root canals in the positive control group were not filled. All root canals in negative control group were obturated in the same way as experimental groups but no post space preparation was done.

The samples were prepared to investigate the bacterial leakage. (Fig. 1) The external surfaces of specimens were covered with two layers of nail varnish from the coronal edge to 2mm short of the apex. All teeth in negative group completely covered with nail varnish including root apex. Coronal third of each root was inserted individually in the latex surgical tube and the connection was sealed with cyanoacrylate glue. The system was sterilized using ethylene oxide gas and placed in the 5 ml sterile glass vial, containing 3 ml sterile Brain Heart Infusion (BHI) (Merck, Germany) to insure that the root apex was placed in the liquid. The coronal chamber inoculated with 0.5 ml BHI containing approximately 10 ⁸ bacteria ml ^-1E. faecalis (ATCC 29212, obtained from Iranian Center for Scientific Research) using a sterile syringe.. The medium with microorganisms was changed every 5 days. The samples were incubated at 37°C and were daily checked for turbidity in the broth in the apical chamber for 90 days. The time taken for the turbidity of broth in the apical chamber was recorded for each sample.

Statistical analysis

The data were analyzed using statistical tests. The distribution numerical data were examined using Kolmogorov-Smirnov test. The average duration of bacterial leakage was compared between groups using independent samples t-test.  Statistical significance was inferred if the P value was less than .05.

Figure 1. Evaluation of bacterial leakage in specimens: The right sample shows evidence
for turbidity of culture medium

Results

  One specimen in GH group and two in RP group were lost during preparation. Statistics tests confirmed normal distribution of data in groups.

The average leakage results in different groups are shown in Table 1. Data analysis showed no significant difference between the canals of GP and GH groups (P=0.549), nor between RH and RP groups (P=0.097).

Comparison of leakage time between GP and RP groups showed a significant difference, which was also observed between GH and RH groups (P=0.018 and P=0.001, respectively). The average duration of leakage was significantly higher in GP and GH groups than RP and RH groups, respectively.

Table 1. Descriptive statistics of the study groups