The pilot study was approved by the Ethics Committee (PROT. PG/2017/16759, Ca, November 2017) and was conducted in the Department of Conservative Dentistry and Endodontics of the University Hospital in accordance with the Declaration of Helsinki of 1975 (as revised in 2000) between 1 May 2016 and 31 December 2017.
Fifty-five Caucasian subjects aged between 18 and 80 years who were referred for endodontic treatment at the university clinic were included in the study. The selected subjects had at least one permanent single or multi-rooted mature tooth with signs and/or symptoms indicating the need for endodontic treatment (primary or secondary) according to ESE guidelines , and teeth requiring retreatment with a poor prognosis (root canal morphology altered) were excluded. Clinical and medical data were recorded before treatment. During the visit, each tooth was clinically examined to determine whether it needed endodontic treatment; the history of pain was assessed, and responses to sensitivity tests, palpation, and percussion were performed . One or more periapical radiographs of the involved teeth were obtained at baseline and evaluated to assess the crown, root, and periapical status.
Patients with any medical condition, immune-compromised status, or with an overall poor prognosis for their treatment were not included.
Informed consent to undergo the treatment and follow-up and a second consent to participate in the study were obtained from all patients before treatment commenced.
The 55 selected patients required root canal treatment of 84 single or multi-rooted teeth.
Endodontic therapy was performed using a standardized protocol that varied only in terms of the technique and sealer used for the obturation of the root canal. Four endodontic residents performed the primary and secondary RCTs, who were divided into two groups of two (depending on the day of the week they worked in the hospital). The clinical supervisor of the day assigned each resident either Bioactive cement or ZOE sealer respectively. This was randomly done by a flip of the coin. Every day, each patient was randomly assigned to one technique or another: the first patient who arrived on the same day of treatment was randomly assigned (by a flip of the coin) to one of the two obturation groups, while the second was assigned to the other group; the third patient was assigned to the initial group, and so on until the end of the day.
Dental treatment and follow-up
Local anaesthesia was administered, the teeth were isolated under a rubber dam, and the root canals were subjected to preflaring using K-files 08/10/15 (Kerr© Corporation, Orange, California) and NiTi Protaper NextTM X1, X2, and X3 rotary files (Dentsply Sirona, Ballaigues, Switzerland) when necessary. For the secondary RCTs, the GP and sealer were removed by hand and with rotary instrumentation by using Gates-Glidden drills #4, #3, and #2 (in this sequence) and 0.1 mL of solvent (Endosolv® E, Septodont, Saint-Maur-des-Fossés, France); the canals were then renegotiated by hand with K-files. In all cases, the working length was assessed with the apex locator (DentalPort ZX, J. Morita MFG. CORP©, Kyoto, Japan) and confirmed with one or more periapical radiographs Kodak ultra-speed dental film, size 31 × 41 mm (Carestream Health©, Stuttgart, Germany) and X-safe 70 70 KV/8 mA (Cefla Medical Equipment, Imola, Italy). The root canals were continuously irrigated with 5% sodium hypochlorite (Niclor 5-Dentale, Ogna lab, Muggiò, Italy) throughout the instrumentation.
Following instrumentation, the canals were dried with sterile paper points and obturated as follows:
BIO group: A standardized GP master cone that fit snugly at the working length was selected; BioRootTM RCS (Septodont) was prepared according to the manufacturer’s instructions. A coating of the sealer was applied onto the canal walls using the GP point. Obturation was completed by inserting the GP master cone that had been previously coated with the sealer into the canal; a hot instrument was used to remove the excess GP.
PCS group: Warm vertical compaction with GP and Pulp Canal SealerTM EWT (Kerr© Corporation, Orange, CA) was performed .
A periapical radiograph was obtained to assess the quality of the root canal fillings, and subsequently, all teeth were restored with direct composite.
Clinical and radiographic follow-up were performed at 1, 3, 6, and 12 months for each tooth, and data were recorded in a dedicated chart and updated at every follow-up.
All radiographs were digitally scanned, saved in JPEG format and imported into ImageJ software version 1.41 (National Institute of Health, Bethesda, MD). The application Turbo Reg (Biomedical Imaging Group, Lausanne, Switzerland) was used to reduce the distortion factors of the radiographs .
Two trained and calibrated examiners (weighted kappa values, k = 0.8 for inter-examiner agreement and k = 0.9 for intra-examiner agreement)  assigned a PAI score to each radiograph ; in the case of a disagreement, the highest of the two scores was retained. In multi-rooted teeth, the root with the highest score was used as the reference. Following the assignment of a PAI score, the radiographs of each tooth were divided into two groups: absence of AP (score 1) or presence of AP (score 2–5).
The same examiners then assessed the quality of the coronal restorations according to the criteria described by Ng et al [3, 6].
Treatment success was assessed using two outcome measures.
The primary outcome measure was “periapical healing”, including clinical and radiographic evidence of the healing of each tooth or the absence of apical periodontitis . Treatment success was defined according to strict criteria as the absence of pain or clinical evidence of inflammation or swelling and by conventional radiographic measures of complete healing/continuous presence of a normal periodontal ligament space (PAI score < 2).
The secondary outcome measure was “tooth survival”. Success was achieved if the tooth was asymptomatic and considered to be functional regardless of its PAI score .
If a tooth had been extracted because of endodontic problems (persistent pain, swelling, or sinus or periapical radiolucent lesion), treatment was considered to have failed. Tooth extraction without any exit data regarding the postoperative periapical status excluded the tooth from further analysis for “periapical healing”. The whole tooth was considered the assessment unit.
Continuous variables were reported as the mean ± SD, while dichotomous variables were reported as the number of cases and the percentage; qualitative ordinal variables were reported as the number of cases and the median value. Different tests were used to verify the presence of a statistically significant difference between the BIO and PCS groups; the test for the equality of proportions, t tests for the equality of means, and non-parametric k-sample tests for the equality of medians were applied when appropriate. The level of significance was set at 5% (p < 0.05); STATA version 14 (STATA Corp., TX, USA) was used to perform all statistical analyses.