Root Canal Preparation

After approval by the Research Ethics Committee of the Mashhad University of Medical Sciences (protocol number #88160), 34 teeth were selected from a large series of single-rooted anterior teeth which had recently been extracted. The teeth had mature apices, no caries or internal or external resorption, no cracks on root surfaces and no curves (curves less than 20° were included). After sample collection the root surfaces were cleaned with a periodontal curette to remove all calculi and soft-tissue. Then, the samples were disinfected by 5.25% sodium hypochlorite (Naocl) for an hour and were kept in distill water.[18 (link)] The coronal part of the samples was cut in order to standardize 15 mm of each root. Apical foramen diameter of all samples were checked by inserting a #15 K-file (Dentsply, Maillefer, Ballaigues, Switzerland) into the canal. Using this method, the apical foramen of all teeth was standardized. Canal preparation was carried out using K-file #40 (Dentsply, Maillefer, Ballaigues, Switzerland) with step-back technique. Coronal portion of canals were flared by Gates-Glidden drills #2, 3 and 4 (Dentsply, Maillefer, Switzerland). After using each instrument, canals were rinsed by 1 ml of 5.25% Naocl.[16 (link)] Then, samples were randomly divided into two experimental groups, each group containing 15 samples; positive and negative control groups had four samples.
In experimental groups, the apical 3 mm of each root was resected at 90° to its long axis and root end preparation was done with ultrasonic tips (piezo-electric [Spartan, Fenton, MO, USA]) to a depth of 3 mm. In order to provide an intracanal matrix to support the condensation of retrograde filling material, high convergence gutta-percha was adapted into the coronal part of the apical cavity [Figure 1a]. Then, the 3 mm apical cavity was filled with MTA (Dentsply, Tulsa Dental, Tulsa, OK, USA) or CEM (BioniqueDent, Tehran, Iran) using an MTA carrier and filling density was verified by radiographs [Figure 1b]. Samples were kept in 100% humidity and 37°C for retrograde material setting.
External surfaces of the experimental samples, except the apical region, were sealed with two layers of nail polish and sticky wax. Two samples of positive control group were prepared, but not filled and external surfaces were sealed similar to experimental samples. The outer surface and apical region of 2 samples of negative control group, which were prepared and filled according to the experimental groups, were sealed with two layers of nail polish and sticky wax.