Comparison between the rotary (Hyflex EDM®) and manual (k-file) technique for instrumentation of primary molars: a 12-month randomized clinical follow-up study

Abstract Rotational instrumentation is an alternative for the clinical practice of pediatric dentists. However, there are few records in the literature on the clinical and radiographic aspects of treated teeth over time. Objectives: Compare instrumentation time and filling quality between manual (k-file) and rotary (Hyflex EDM®) files, and clinically and radiographically follow-up the treated teeth for 12 months. Moreover, the characteristics of glass ionomer restorations and their interference in the treatment prognosis over time were evaluated. Methodology: In total, 40 children with pulp involvement in primary molars received treatment with Hyflex EDM® or manual rotary files, performed by an operator. Clinical and radiographic aspects were observed at different times to determine the effectiveness of each technique. Results: The rotary system reduced instrumentation time when compared to the use of manual files (p≤0.05), but there was no difference in filling quality between the groups (p≥0.05). Moreover, both types of instrumentation were effective for 12 months (p≥0.05), and restoration retention influenced the emergence of periapical lesions (p≤0.05). Conclusion: Although rotary files reduce clinical time, the clinical and radiographic aspects of both techniques were similar over 12 months. Moreover, restoration retention has been shown to be related to treatment prognosis.


Introduction
Despite advances in caries prevention measures and the reduction of its incidence rates worldwide, deep caries lesions that compromise pulp vitality remain a common occurrence in clinical practice. 1 In these cases, pulp treatment (for example, pulpectomy) is essential to maintain the integrity of oral tissues, preserving deciduous teeth until their physiological exfoliation. 2 However, the success of the pulpectomy procedure depends on an effective biomechanical preparation of the root canal system. 3 This biomechanical preparation can be performed with rotary or manual files, and automated systems have been shown to significantly reduce instrumentation time, and more effectively clean and shape the root canal. 4,5,6 However, other aspects contribute to the success of treatment. Some factors associated with clinical failure, such as the quality of root canal filling and coronal restoration, still need to be investigated. 7 A recent systematic review of the clinical success of pulpectomy procedures in pediatric patients showed that there is no substantial evidence to determine whether instrumentation affects long-term clinical and radiographic success. 8 Therefore, in this study, we compared instrumentation time and quality of root canal filling between manual and rotary techniques for the biomechanical preparation of primary molars, considering a follow-up period of 12 months. The characteristics of glass ionomer restorations and their interference with treatment prognosis were further examined. The null hypothesis of this study was that instrumentation with rotary files (Hyflex EDM ® ) would not be more effective than manual instrumentation (k-files) for treating pulpectomy in primary molars.

Methodology
This study was previously approved by the and a statistical power of 80%, a total sample size of 34 participants (n=17/group) was needed to detect any clinically significant difference of 5% between the groups. Thus, the final sample size consisted of 40 participants (n=20/group) to compensate for any sample loss during the follow-up period. The randomization method is further described in this section.

Study design
This was a randomized clinical study whose experimental units were the primary teeth of children in need of endodontic treatment. The primary outcome was the instrumentation time required for root canal preparation (technique: one-way analysis). Secondary outcomes consisted of the quality of filling (technique: one-way analysis) and treatment success (technique and follow-up time: two-way analysis). The quality of coronal restorations was also determined over time.
Of note, only the examiner was blind to the analysis, because there were remarkable differences in each technique which were impossible to mask to the operator or to study participants.

Inclusion and exclusion criteria
Mandibular primary molars were selected based on the following inclusion criteria: presence of a deep carious lesion and pulp vitality, with pulp involvement on radiographic examination; provoked or spontaneous pain which was unresponsive to the use of analgesic drugs; provoked pain or absence of pain, with no hemostasis in a period of up to 5 min after pulpotomy and macroscopic signs of reversibility; absence of fistula or abscess and absence of bone rarefaction on radiographic examination, as well as absence of internal or external resorption of more than 2/3 of the root; and dental remnants which could be feasibly restored. Participants meeting the following criteria were excluded from the analysis: systemic diseases; teeth with less than 2/3 of the root remnant; teeth with mobility or rupture of the pericoronal follicle of the permanent successor; and cases in which restoration of the dental remnant was unfeasible. Only one tooth was eligible for each child.
Randomization and allocation of study participants J Appl Oral Sci. 2022;30:e20210527 3/10 files, and the control group (n=20), instrumented with manual files. Patients were assigned sequential numbers during recruitment, and were allocated based on a previously set computer-generated randomized sequence. Treatment was completed in a single session and all procedures were performed by the same operator. Intra-examiner consistency and reliability were analyzed independently using the unweighted kappa test, with a score of 0.90 (excellent). All data were collected at the pediatric dentistry clinic of the Universidade Federal de Alfenas, between February 2019 and March 2020. Participants were enrolled by a member of the research team who also assigned the interventions. The random allocation sequence was generated by a second researcher, with the aid of a computer.

Intervention protocol
Pulpectomy procedures were performed under local anesthesia of the mandibular alveolar nerve and rubber dam isolation. The carious tissue was removed with a dentin spoon, followed by cavity opening with 1014-1015 spherical diamond tip drills (Kg Sorensen, Barueri, São Paulo, Brazil) in high rotation under irrigation. The root canal was explored using a K-file #10 (Maillefer Instruments, Ballaigues, Switzerland) and working length was determined by passively inserting the file in each root canal with a rubber stopper. When the tip of the file was at the apical foramen height, the rubber stopper was leveled with the respective cusp tip and the length of each root canal was recorded. Working length was obtained by subtracting two millimeters from the total length of the root canal. Thus, the primary outcome of this study was the time used to instrument root canals, and its secondary outcomes were the analysis of the quality of filling and restoration, as well as their clinical and radiographic aspects during follow-ups. To assess the primary outcome, a stopwatch was used, and clinical and radiographic examinations were performed to analyze secondary outcomes. Only the evaluator was susceptible to blinding, since he was the only one who had no contact with the patients or participated in the procedures.

Root canal preparation
In the control group, biomechanical preparation of the root canal was performed by the conventional method (manual technique) with stainless steel K-files #15 to #30 (Dentsply Maillefer, OK, USA), using the quarter-turn-and-pull technique. In the experimental group, Hyflex EDM ® files (Coltene / Whaledent, Allstätten, Switzerland) were used for rotary instrumentation using 25/.12, 10/.05, and 25/~ taper files. Instrumentation started with the 25/.12 file to shape the cervical third; then, the 10/.05 file (Glidepath) was used for an initial exploration of the apical third; lastly, the 25/~ file variable taper was used to complete the preparation of the apical third. Rotary files were used on an X-Smart engine (Dentsply-Maillefer, OK, USA) operating at 500 rpm with a torque of up to 2.5 Ncm (25 mnm), except for the Glidepath files, which were used at 300 rpm with a torque of up to 1.8 Ncm (18 mnm). In both groups, canals were cleaned and shaped by the "crowndown" technique using progressively larger conical files. In between each instrument change, canals were irrigated with 1 ml of 1% NaOCl. Therefore, at each instrument change, 3 ml of NaCL solution were used. Irrigations were performed with a 30-G needle placed 2 mm before the working length. Thus, at the end, 12 ml of 1% NaOCl were used in each tooth in both groups. All irrigation procedures were performed with a 30-G needle placed 2 mm before the working length. Each instrument was replaced according to the manufacturer's recommendations. The time spent during biomechanical preparation was recorded on a clinical chart.

Root canal filling
After final irrigation with a saline solution, root canals were dried with paper tips and filled with a mixed paste composed of calcium hydroxide and polyethylene glycol (Calen ® -SS White, São Paulo, SP, Brazil) thickened with zinc oxide (slow curing -Biodinâmica Quím. e Farm. Ltda, Ibiporã, PR, Brazil).
A pressure syringe and a manual file were used to push the paste into the apex. The quality of the root canal filling was classified as satisfactory, underfilled or overfilled. Roots in which the filling paste reached either the instrumentation limit or the root apex were considered "acceptable"; roots in which the material was placed before the instrumentation limit were considered "insufficiently filled"; and cases with material leakage to the periapex were considered "overfilled" (Figure 1). Analysis of the quality of root canal filling was performed separately for mesial and distal roots. Participant follow-up Patients were followed up after three, six, and 12 months after the pulpectomy procedure to assess the presence of pain, fistula or abscess, pathological mobility, and sensitivity to percussion. A periapical radiograph was obtained to assess the presence of a radiolucent inter-radicular area, the periodontal ligament condition, and the presence of periapical lesion(s). Radiographic assessment was considered successful when teeth showed no radiolucency in the inter-radicular area, no periapical lesion, an intact periodontal ligament, and satisfactory root canal filling. Assessment of coronal restorations followed the USPHS criteria.

Statistical analysis
Quantitative data were analyzed by the Mann-Whitney test and qualitative data were analyzed by the chi-squared test. Generalized estimation equations (GEE) were used to check for differences in the longitudinal data. A 5% significance level was considered (α≤0.05) in two-tailed tests. All statistical tests were carried out in SPSS version 20.0 (Armonk, NY, United States). Table 1 describes the demographic characteristics of the sample. CONSORT guidelines were followed for planning and reporting study outcomes, as shown in Figure 2. There were no differences between groups regarding age and sex. As shown in Table 2, the mean instrumentation time in the control group   Table 3).

Results
Both groups were treated successfully and no postoperative pain, sensitivity to percussion, abscess/ fistula, secondary caries or pathological mobility were observed during the 12-month follow-up in any of the groups. As shown in Table 4, there was no significant difference in radiographic success and failure rates between teeth treated with manual and rotary files (GEE analysis, p≥0.05). The variables indicating radiographic failure can be found in Table   5. Overall, there was no significant difference between radiographic failure rates in both groups over 12 months (GEE analysis, p≥0.05, Table 5).
The data shown in Table 6 revealed no significant differences between the groups concerning the integrity, retention, discoloration, anatomical shape, and roughness of the coronal restorations over time (GEE analysis,p≥0.05 for all variables). However,     Although several studies agree that automated instrumentation reduces the instrumentation time for root canal preparation, 13,15,16,17,18 not all evidence is from randomized clinical trials and some results were obtained only in permanent teeth. Thus, even though principles and approaches are similar for both primary and permanent dentitions, some aspects, such as tooth anatomy, and patient acceptance and cooperation, among others, must be considered before generalizing the results. Therefore canal treatment in primary teeth 27,31,32 . Regrettably, one of these studies 9 failed to report the success of different techniques and only showed the results for instrumentation times. Therefore, this study was assigned a high risk of bias due to the selection of reported results. Despite the limited number of trials, rotary and manual techniques showed similar success rates in the endodontic treatment of primary teeth, with a moderate level of evidence due to imprecision 33 . In our study, the higher -albeit nonsignificant -frequency of periapical lesions in the experimental group must be interpreted considering Monitoring final restorations is of great importance for the prognosis of endodontic treatment. In our study, there was a statistically significant relation between restoration retention and the onset of periapical lesions over time. The hermetic sealing of the cavity prevents microleakage and bacterial contamination inside the root canals. Therefore, a good alternative for these specific cases, which was previously proposed by Garg, et al. 35 (2016), is the use of precast metal crowns, which (i) protect the residual tooth, possibly damaged after excessive caries removal; (ii) are cost-effective in the long term; and (iii) have a low failure rate due to their hermetic sealing. In this study, the difference in the number of cases with radiographic success was insignificant between the groups at three, six, and 12 months, thus showing that both instrumentation techniques were effective. Moreover, there was no harm or unwanted effect during this study.
The main limitation of this study lies in its small sample size, which failed to allow the detection of small differences in qualitative variables. This study was designed with a focus on its primary outcome, so the results of secondary outcomes should be interpreted with caution, although they are of great clinical relevance. The analysis of secondary results is prone to type II errors due to lack of statistical power. 36 A major difficulty of our study consisted of recruiting eligible children, which resulted in a small sample size and a relatively wide age group. Importantly, there was a considerable sample loss during the last followup due to the Covid-19 pandemic, which interrupted this study. Another limitation to be considered was the impossibility of blinding the operator and participating children due to the remarkable differences in instrumentation techniques.

Conclusion
Within the limitations of this study, it is concluded that both techniques showed good clinical and radiographic results during the 12-month follow-up, but rotary files allowed a faster instrumentation of the root canal system in primary molars. Furthermore, our findings indicated that failures in coronal restorations were related to the emergence of periapical lesions during the follow-up period.