The study was approved by the local university clinical research ethics committee with vide letter no. PKUSSIRB-201735063. Using the PASS software, the required sample size in this study was determined by comparing the mean preparation time for HyFlex EDM GPF and PathFile. In this study, a bilateral test was used, with a test level of 0.05 and a power of 90%. Informed consent was obtained from the patients before enrollment in the study.
The sample consisted of 80 patients aged 23-73 years old who were treated at the Second Dental Center of Peking University School of Stomatology between June 2018 and February 2019. All participants were informed about the study and had provided written informed consent prior to treatment. The following inclusion criteria had to be fulfilled by the patients to be enrolled in the study: 1) No previous history of systemic diseases. 2) Selected for root canal treatment for asymptomatic or symptomatic irreversible pulpitis in the maxillary or mandibular molars with at least one severely curved canal (>25°). The exclusion criteria were 1) pulp necrosis, with or without apical periodontitis. 2) Acute or chronic apical abscess. 3) Signs of systemic infection. 4) Allergic to local anesthetic agents. 5) Progressive periodontal disease at any stage (clinical attachment loss ≧5 mm, probing depth ≧6 mm, or furcation involvement class II or III).
Before the procedure, pulpal and periradicular status was evaluated by means of vitality tests such as a cold test, an electric pulp tester (Diagnostic, SybronEndo, USA), palpation, and percussion. Periodontal probing was performed and patients with deep periodontal pockets were excluded. After the administration of local anesthesia with 4% mepivacaine with adrenaline 1:100,000 and isolation of the tooth with a rubber dam, a standard access cavity was prepared using diamond burs. At this stage, a sealed envelope containing the randomization code was opened and the patient was assigned to receive glide path enlargement with either the HyFlex EDM GPF or PathFile, with 40 patients in each group. Patients were blinded regarding the file system utilized. All the patients were treated by an endodontic dentist.
HyFlex EDM GPF group
The working length (WL) was determined using the Root ZX apex locator (SM-DP-ZX, Morita, China) by inserting a size 10 K-file into the root canal up to the apical foramen. The WL was confirmed radio-graphically and was also repeatedly checked during the treatment procedure. The HyFlex EDM GPF (size 10/0.05) was operated with an endomotor (X-SMART; Dentsply Maillefer, Switzerland) in continuous rotation at a speed of 300 rpm and 1.8 Ncm of torque, according to the manufacturer’s instructions. Irrigation with 5.25% NaOCl and 17% EDTA was carried out during the glide path enlargement and the preparation time was recorded from the insertion of the GPF till the completion of the enlargement, including irrigation time during the enlargement. After the instrumentation was completed, the root canal was irrigated with 5 mL of 5.25% NaOCl and 5 mL of 17% EDTA.
The WL was determined as described above in the HyFlex EDM GPF group. The PathFile (size 13/0.02 and 16/0.02) instruments were operated using the same endomotor (X-SMART) at a speed of 300 rpm and 5 Ncm of torque. Irrigation with 5.25% NaOCl and 17% EDTA was carried out during the glide path enlargement and the preparation time was recorded from the insertion of the PathFile 13/0.02 till the completion of the PathFile 16/0.02 enlargement, including the irrigation time during the enlargement and the time required to change files. After enlargement, the root canal was irrigated with 5 mL of 5.25% NaOCl and 5 mL of 17% EDTA.
After glide path creation, subsequent endodontic procedures were standardized as per the protocol. The root canals were then prepared with X1 and X2 instruments by using the ProTaper Next (Dentsply Maillefer, Switzerland) rotary instrumentation system and then irrigated with 5.25% NaOCl and 17% EDTA.
The preparation time of the severely curved canal for the GPFs and ProTaper Next were recorded. Only the times used for active instrumentation such as checking the WL, cleaning the flutes of the instruments, and irrigation were included. The time taken to change files was not considered. The preparation times were recorded by a nurse and other canals for the same molar were prepared using only the ProTaper Next.
Finally, the prepared root canals were irrigated again with 10 mL of 5.25% NaOCl with a 30-gauge needle syringe and then dried with sterile paper points. Calcium hydroxide [Ca(OH)2] was placed in the canals, temporary filling was performed, and an appointment was scheduled to complete the subsequent root canal procedure.
All patients were instructed to record postoperative pain intensity twice daily (morning and evening) for 1 week using a visual analog scale (VAS) on paper. The pain score was recorded on a scale of 0 to 10. Pain intensity was categorized as no pain (0), mild pain (1–3), moderate pain (4–6), and severe pain (7–10). All patients returned the original copies of the VAS form on the next visit.
SPSS version 20.0 (IBM Corp., Armonk, NY, USA) was used for statistical analysis. The distributions of age, sex, the tooth treated, and the angle of root canal curvature in the two treatment groups were compared by using the chi-square test. The preparation time and the postoperative pain scores were compared using one-way analysis of variance (ANOVA). Statistical significance was recognized at P ≤ 0.05 (two-sided). Considering that multiple pain measurements were performed for the same individual within 7 days after the preparation of the curved root canal, the repeated measurement ANOVA model was used to analyze the differences between groups and the trend of pain changes over time in different groups.