Potentializing the Effect of Calcium Hydroxide on Chemomechanical Preparation in Teeth with Post-treatment Apical Periodontitis: a Randomized Clinical Study

Eligibility criteria The study population consisted of 16 patients (6 women and 10 men, aged 19-63 years, mean age 34.43) presenting to the endodontic clinic at Istanbul Medipol University Dental School, for nonsurgical endodontic retreatment of teeth with apical periodontitis lesions. Sixteen previously root canal-treated teeth exhibiting clinical and radiographic evidence of chronic apical periodontitis lesions were included in this study. Radiographically, the diameter of the periapical radiolucency ranged from 2 to 7 mm. Teeth with post-treatment apical periodontitis had endodontic therapy completed more than 2 years earlier and required retreatment. Termini of the root canal fillings ranged from 0-4 mm short of the radiographic apex, with no overfilling. The teeth had intact coronal restorations, with no obvious exposure of the root-filling material to the oral cavity. Selected teeth had enough crown structure for adequate isolation with a rubber dam and showed an absence of periodontal pockets or attachment level deeper than 4 mm. Exclusion criteria were also applied, as follows: teeth from patients who had received antibiotics within the previous 3 months or who had any general disease, teeth that could not be properly isolated with rubber dam, teeth with absence of coronary sealing, teeth with periodontal pocket depth >4 mm; and teeth with crown/root fracture. Only one tooth was included from each patient.

Root canal treatment procedures and sampling Rubber dam and an aseptic technique were used throughout the endodontic retreatment. After plaque removal and rubber dam isolation, the operative field was cleaned with 3% hydrogen peroxide and disinfected with 2.5% NaOCl solution. Then, all coronal restorations, posts and carious defects were removed and access preparation was completed when the root canal filling was properly exposed. Afterwards, the tooth (including the pulp chamber), clamp, and adjacent rubber dam were once again disinfected with 2.5% NaOCl, followed by inactivation with 10% sodium thiosulfate in order to avoid interference with bacteriological sampling. Sterility control samples (SR1) were taken from the tooth surface with a sterile Omni Swab (Whatman FTA, Sigma-Aldrich) with an ejectable head. Paper points were transferred to cryotubes containing phosphate buffered saline (PBS) solution stored at -20°C. In each case, a single root canal was sampled in order to confine the microbial evaluation to a single ecological environment. In multirooted teeth, the root with the periapical lesion was selected. If there were periapical lesions in all roots, the wider canal was selected. Two of the canals included in this study were from single-rooted teeth, 3 were buccal canals in maxillary premolars, 1 palatal canal in maxillary molar, and 10 distal canals in mandibular molars.

Old root fillings were removed using Gates-Glidden drills (Dentsply Maillefer, Ballaigues, Switzerland) and endodontic files without the use of chemical solvents. The working length (WL) was established 1 mm short of the apical foramen with an apex locator (Raypex6; VDW GmbH, Munich, Germany) and then periapical radiographs were taken to ensure that all filling material was removed. Irrigation with sterile saline solution was performed in order to remove any remaining materials and to moisten the canal prior to sample collection. Next, the canal was left filled with saline, and a small hand instrument was placed at the WL and used to gently file the canal walls. An initial microbiologic sample (S1) was taken from the root canal with sterile paper points consecutively placed at the WL. Three sterile paper points were inserted into the root canal for sampling. Each paper point was left in the canal for about 1 minute. Both the paper points and the endodontic hand instument, without the handle, were transferred to cryotubes containing 300 μL of PBS solution stored at -20°C. The samples were transferred to genetic analysis laboratory for further analysis in cold chain.

Root canals were prepared by using the Revo S files and copious irrigation with 2.5% NaOCl. The canals were apically enlarged to size 35 (AS35) at the working length. Between each instrument change, the root canal was irrigated with 5 mL of 2.5% NaOCl solution. Hence, a total of 30 mL of the irrigating solution was used. After instrumentation was completed, the smear layer was removed with 17% EDTA, which was left in the canal for 3 minutes, followed by 2.5% NaOCl. The root canal was dried with sterile paper points and flushed with 2 mL of 10% sodium thiosulfate for 1 min to inactivate the NaOCl solution. Next, a sample (S2) was taken from the canals as described for S1. After preparation, the canal was medicated with either the Ca(OH)2 or 2% chlorhexidine gel based on the study group. In the CH group, calcium hydroxide powder (Calxyl; OCO Products, Dirnstein, Germany) was mixed with saline in a ratio 1:1 and the paste was inserted into the canal by using lentulo spirals (Malleifer-Dentsply). In CHX group, chlorhexidine gel 2% (Gluco-Chex 2% gel, Cerkamed, Stalowa Wola, Polland) was placed into the root canals of this group with an Ultradent Capillary Tip (Ultradent products). All root canals of the 2 above groups were sealed with a 1-mm cotton pellet and at least 3 mm layer of temporary filling material (Cavit G; 3M ESPE AG, Seefeld, Germany).

After 7 days, the tooth was isolated, the temporary restoration removed, and disinfection procedures of the operative field were performed following the same protocol used in the first visit. A new control sample of the dental crown and dentin surrounding the pulp chamber was obtained (SR2). The medication was removed with 5 mL of saline solution and by carefully filing the canal with a master apical file. For the groups using Ca(OH)2, the calcium hydroxide antimicrobial activity was neutralized with 0.5% citric acid for a period of 1 minute, which was then removed with 5 mL of saline solution. Thus, for the groups with CHX gel, the medicament was neutralized with a mixture of 0.3% L-α-lecithin and 3% Tween 80 (Zamany A, Spangberg LS (2002) An effective method of inactivating chlorhexidine. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics). Next, the root canals were irrigated with 2 mL of saline solution. The post medicament sample (S3) was obtained in the same way as the pre-medicament sample was collected and sent for the PCR analysis.