This study is a parallel randomized controlled trial, with an allocation ratio of 1:1. The study followed the CONSORT guidelines (Suppl. material 1) and was approved by the ethics committee of Biruni University (2015-KAEK-43-19-04). All the patients read and signed an informed consent form containing details about the study, as well as the benefits and risks of the therapy.
Sample size calculation
The sample size was calculated based on data obtained from a pilot study using G*Power 3.1 (Heinrich Heine University, Dusseldorf, Germany) software. The main research protocol was the same as that of the pilot study. The power calculation showed that the smallest sample size for each group was 25 patients, following these input conditions: effect size of 0.82, power of 80% and significance level of 0.05. Due to the probability of dropouts during the treatment or follow-up stages, 30 patients were included in each group, resulting in 60 patients in total in the present study.
Patient selection and randomization
We examined 395 patients aged 18–65 y who were referred to the endodontics department of the faculty of dentistry of Biruni University. In total, 60 healthy patients who met the inclusion criteria were selected. Only patients who had asymptomatic, single-rooted teeth with a PAI score of 3 or 4 were included in this study. For diagnosis, both clinical and radiographic examinations were performed. To determine the periapical status, both panoramic radiographs (Sirona, Bensheim, Germany) and periapical radiographs (Dürr Dental, Bietigheim-Bissingen, Germany) obtained taken using the parallel technique were examined. Experienced radiology technicians took the radiographs. The exclusion criteria were antibiotic use within the last month, anti-inflammatory analgesic use within the last 5 d, systemic disorders, pregnancy or lactation, traumatic occlusions, the presence of other teeth requiring RCT, teeth with root canal fillings, calcified canals, root resorption, periodontal diseases or sinus tracts and severe crown destruction preventing rubber-dam application. The same operator performed all the endodontic treatment procedures over a period of 5 mos. To ensure randomized allocation before the RCT, a dental student blinded to the research process allocated the patients by asking each patient to select one of two sealed envelopes, which contained the group allocation code. In result, 60 patients were divided into two separate groups according to the root canal disinfection procedure: a control group and a laser group. A diagrammatical representation of the trial according to CONSORT is provided in Figure 1.
After local anaesthetic (4% articaine with 1:100,000 epinephrine) application and rubber-dam placement, the operator removed all former coronal restorations and caries present. Following access cavity preparation, the working lengths were determined electronically using a Propex Pixi device (Dentsply Maillefer, Ballaigues, Switzerland) and confirmed by periapical radiographs. The root canals were prepared using ProTaper Next nickel-titanium files (Dentsply Maillefer, Ballaigues, Switzerland) with an X-Smart Plus Endo Motor (Dentsply Maillefer, Ballaigues, Switzerland) at a speed of 300 rpm and 2 N/cm according to the manufacturer’s instructions up to the size of X4 (size 40, 0.06 taper). During root canal preparation, the canals were irrigated with 2 ml of 2.5% NaOCl using a 30-gauge, side-opening needle (Canal Clean; Biodent, Seoul, South Korea) positioned 3 mm short of the working length.
The final irrigation was performed using 5 ml of 2.5% NaOCI, followed by 5 ml of 17% EDTA for 3 min and 5 ml of distilled water. The canals were then dried with paper points, and calcium hydroxide (Ca(OH)2) paste (Calsin, Karabağlar, Izmir, Turkey) was applied as intra-canal medicament. Subsequently, a temporary restorative material (Cavit-G; 3M ESPE, St Paul, MN) was used to seal the access cavity. At the time of the first visit, all the patients were given a VAS (Suppl. material 2) to rate their PP. A second appointment was scheduled for 7 d later.
At the second appointment, the Ca(OH)2 was removed from the root canals with final irrigation and using an X4 file. The root canals were then obturated using the cold lateral condensation method with gutta-percha cones and AH Plus sealer (Dentsply Maillefer, Ballaigues, Switzerland). The coronal restoration was finished using a resin composite (Filtek Z250, 3M ESPE, St. Paul, MN). The operator contacted the patients at pre-arranged times and asked about PP levels and analgesic intake.
The final irrigation was performed as in the control group, and the canals were dried with paper-points. During the laser treatment, both the operator and patient wore protective eyewear. Laser irradiation was applied using a 980-nm diode laser (Medency Primo 10 W Diode Laser, Vicenza, Italy) coupled with a 200-µm optical fibre (spot size of 0.02 cm in diameter and an area of 0.000314 cm2). The settings were as follows: output power of 2.4 W and energy of 12 J (each cycle) in the pulsed mode (pulse duration: 20 µs), irradiation for 10 sec, followed by a 10-sec pause, which comprised one cycle. This cycle was applied four times to each root canal. The average power used was 1.2 W (average power density = 3822 W/cm2) with a low frequency of 50 Hz. The optical fibre tip (length of 25 mm) was inserted at the working length. The root canals were then slowly (at a speed of 2mm/s) irradiated from the apical to coronal using a continuous circling movement touching the dentinal walls in one cycle for each power. Following the irradiation procedure, Ca(OH)2 paste was applied as intra-canal medicament, and the access cavity was sealed using with a temporary restorative material, as in the control group. A VAS form (Suppl. material 2) was given to each patient to rate PP, and a second appointment was scheduled for 7 d later.
At the second appointment, the root canals were dried after Ca(OH)2 removal as in the control group. Afterwards, laser irradiation was performed as in the first appointment. Subsequently, the root canals were filled, and permanent restoration was performed as in the control group. At scheduled times, the patients were contacted to obtain information about PP and analgesic intake. This information was recorded on the VAS form (Suppl. material 3) by the operator.
The patients received training on how to complete the VAS form (Suppl. material 2) at home. The questionnaire assessed pain perception and the frequency of analgesic use after the first visit. None of the patients were prescribed medications immediately after the RCT. The patients completed the questionnaire 8 h, 24 h, 48 h and 7 d post-operatively. The pain level was categorized as none (0), mild (1–3), moderate (4–7) and severe (8–10). The patients were advised to take 600 mg of ibuprofen every 6 h for pain alleviation if they felt severe pain at any point during the follow-up period. Each patient recorded the time interval to medication intake. In addition, the age and sex of the patients were documented.
All statistical analyses were performed using SPSS version 22 software (IBM SPSS, Turkey). A value of p<0.05 was accepted as statistically significant. The Mann–Whitney U test was used for comparison of values at the different time points between the groups, and the Wilcoxon signed-rank test was used for within-group comparisons among the different time points. The Student’s t test was used to evaluate the age and sex distribution in the groups. For statistical analysis of differences in analgesic use, Fischer’s exact chi-square test was applied.