Assessment of Extruded Debris in Primary Molars Comparing Manual and Reciprocating Instrumentation

Objective: To compare the amount of extruded debris in primary molars after manual instrumentation or WaveOne system. Material and Methods: Twenty-five primary molar roots with mild and moderate root angulation (between 10 to 20o), having at least two thirds of root length, no pathological reabsorption (internal or external) or furcation perforation, were selected for this study. Roots were standardized at 6 mm in length, inserted and stabilized in individual acrylic resin blocks with random distribution into two groups: G1 (n=12): Instrumentation with crown-down manual technique; and G2 (n=13): instrumentation with WaveOne system. Blocks with roots were weighed before and after instrumentation, allowing the calculation of extruded debris using both mechanical preparations. Data analysis was performed by Bioestat 4.0 statistical software using Mann Whitney test. Results: The mean weight of extruded debris in manual instrumentation and WaveOne system have no significant difference (p=0.8704). Conclusion: Manual crown-down instrumentation or WaveOne system does not influence the amount of extruded debris after mechanical preparation, suggesting that both techniques were effective in canals clean causing similar extrused debris, however more studies with largest sample should be done to better validate this evidence.


Introduction
Endodontic therapy in deciduous teeth requires special attention during chemical-mechanical preparation, which includes good instrumentation and elimination of debris from root canals.At this stage of eruptive development, morphology results in more friable teeth as rhizolysis evolves [1], implying a greater risk of ejecting debris into the periapical area [2].
Extrusion can generate pain, edema, discomfort, persistent inflammation and also damage the permanent germ, therefore, instrumentation techniques have been developed with the aim to minimizing the presence of extruded material in the apical region and decrease the postoperative symptomatology, overcoming the efficacy of the crown-down manual instrumentation technique most used in conventional endodontic therapy [2][3][4].
Given the above, the use of reciprocating instrumentation was recently proposed as an alternative to manual instrumentation and rotational instrumentation [5].The WaveOne system allows greater flow of irrigating solution by removing smaller amounts of dentin from the channel walls [6], thus reducing the extrusion of debris and reducing the risk of damaging or frustrating the instrument in irregular channels as presented the primary teeth [5][6][7].This method has also been shown to be more effective in disinfecting the radial channels of deciduous molars [8][9][10].
The WaveOne system stands out also because it requires less work time compared to other techniques [9,10].In pediatric dentistry, the use of techniques that reduce office work time by improving the quality of care and patient well-being are extremely important.There are few reports in literature of studies that have used reciprocating systems in the preparation of root canals in deciduous teeth.The objective of the present study was to compare the amount of extruded debris in deciduous molars after instrumentation using the crown -apex manual technique and reciprocating instrumentation with WaveOne ® , aiming to aid with scientific evidence on endodontic techniques used in deciduous teeth.

Design and Ethical Aspects
The present study, an in vitro model with human teeth, was approved by the local ethics committee of the, Sao Leopoldo Mandic Dentistry Faculty, under Protocol no.811.721.

Data Collection
A convenience sample of sixty primary molars roots was selected.Specimens were collected from the human teeth bank of the "Sao Leopoldo Mandic" Dentistry Faculty according to the following inclusion criteria: having at least 2/3 of root length; no pathological root reabsorption (external and/or internal); no external and/or internal furcation perforation; mild and moderate root angulation (between 10 to 20º) [11], according to the Schneider method, confirmed after radiographic examination.
Radiographs were standardized using E-Speed film (Kodak Brazil, São José dos Campos, SP, Brazil) with exposition time of 0.8 sec and manually processed in portable camera at 25°C (1 min), rinsed with water (30 sec) and finally fixed (2 min).
Teeth were sectionated individualizing roots that met the inclusion criteria, totaling twenty five roots.Therefore, root length was visually standardized by 6 mm through cervical wear with Carborundum discs (Labordental Ltda., São Paulo, SP, Brazil).It was used a # 15 endodontic K file to stablished the root length from the cervical region up to the extremity is noticed in the apex.The working length was determined by subtracting 1 mm from the apex [12].
Then, roots were individually included in acrylic resin (Vipi Produtos Odontológicos, Pirassununga, SP, Brazil) to the cement enamel junction (CEJ).The obtained blocks were weighed three times on analytical scale (Marte, Ohaus, USA) and their mean initial weight (Pi) was calculated.
Subsequently, specimens were randomly divided through a random sequence generated by a computer software into two groups: G1 (n =12): Manual technique and G2 (n =13): WaveOne system.

Crown-down Manual Instrumentation
Root canals were manually instrumented by one operator, specialist in endodontics previously trained with practical and theoretic classes lasting 8 hours.The crown-down technique using three K-files was used (Dentsply Maillefer, Ballaigues, Switzerland).The first file was the best adapted in the cervical third.Subsequent files were used for the middle and apical thirds up to their working length [13].After each file, root canals were irrigated with 1 ml 1% sodium hypochlorite.
Limes were changed at the end of instrumentation of each root, preventing the dentin scrapes removed from one sample interfering with the next sample.

Instrumentation with WaveOne System
According to Group 1 (G1), a specialist in endodontics previously trained with practical and theoretic classes lasting 8 hours and in use of rotating and reciprocating instruments, followed with instrumentation was performed with counter-angle X-Smart Plus 6:1 (Dentsply Maillefer, Ballaigues, Switzerland) coupled with handpiece X-Smart Plus (Dentsply Maillefer, Ballaigues, Switzerland) with predefined speed and torque.Primary file was used for in and out root movements for instrumentation at cervical, middle and apical thirds.
Root canals were irrigated with 1 ml 1% sodium hypochlorite (Fórmula & Ação, Sao Paulo, SP, Brazil), during in and out file movements using a total of 3 ml.Root canal drying was performed with aspiration syringe (Ultradent) and paper cones (Miltex, Germany).Limes were changed at the end of instrumentation of each root, preventing the dentin scrapes removed from one sample to interfere with the next sample, been also changed after loss of sharpness of the active part of the file.
After instrumentation, roots were re-weighed three times regardless of group, using the same analytical scale to obtain the final mean weight (Pf).Extruded debris calculation was obtained from the difference between weights (Pi -Pf).Data were descriptively analyzed using Bioestat 4.0 and Mann Whitney test, allowing comparisons between groups.

Results
Although roots instrumented with WaveOne system presented mean final weight lower than those instrumented by manual crown-down technique (Table 1), there was no statistical difference in the amount of extruded debris when comparing both techniques (p = 0.8704) (Table 2).No significant differences were found regarding the amount of extruded debris when comparing both techniques (p = 0.8704) (Table 2).

Discussion
Debris and irrigators apical extrusion during chemical-mechanical root canal preparation is one of the main causes of periapical inflammation and post-operative pain [4].All instrumentation techniques are associated to debris extrusion [14], varying according to the characteristics of instruments and used technique [15].A study compared post-operative pain after reciprocating and manual instrumentation on permanent teeth and verified more significant inflammatory response when crown-down technique with rotation files were compared [16].This could be explained as the reciprocity movement is formed by a wider cutting angle and a minor liberating angle, while in the liberating rotation angle, the canaliculi would not remove debris but push them to the apical region.
In a study that evaluated the prevalence of dentin defects, including partial and total cracks and fractures after molar root canal preparation, the WaveOne system was highlighted considering small structural changes in the dentin, producing incomplete or no cracks, for example, when compared to the reciprocating system.Another study showed that the extrusion of apical debris occurred regardless of preparation system [17].
The manual technique presented, significantly, more debris when compared to WaveOne ® system (p < 0.05).This difference could be explained by the technique used to prepare the root canal space, the use of reciprocating movements or by the use of the manual method that increases the cleaning efficacy depending on the cutting instrument capacity.A study performed in primary teeth showed a significant difference in endodontic treatment among three instrumentation techniques (Kfile, ProTaper and WaveOne), mainly with respect to the cleaning of root canals.However, it did not report the possibility of extruded debris around the peri-apex [8].In a similar manner, did not observe any influence in debris transportation to the periapical region after comparing three preparation techniques [18].
The WaveOne system uses an alternative action and is designed to use only one file, with 3 size options chosen according to the width of the canal to be instrumented.In a previous study [10], the authors used the small 21:06 CRT file of 21 mm in length, of the WaveOne system and it was observed that it was effective for disinfecting and modeling the root systems of primary molars [7,9].
In the present research, canal length was visually measured by observing the file at the apex, and the working length was determined 1 mm below the periapical foramen.This measure has caused a slight discussion among researchers in the hypothesis that the possible overcoming of the instrument beyond the apex causes discomfort to the patient by inducing inflammation in the periapical tissues due to the consequent injury caused by this technique [3].It was establish 1mm below the apical foramen as the working length, obtaining no significant differences in relation to debris extrusion [3].On the other hand, grater debris extrusion once the apical foramen was selected as a reference point in comparison to 1mm below it using the single-file technique [19].
Working length of 1 mm below the apical foramen significantly contributes to lower debris extrusion at instrumentation [20].Accordingly, choosing instrumentation to the canal apex significantly increased the amount of debris [21], however, these studies require more comprehensive results in view of the discomfort of the patient when instrumentation is performed beyond the apical foramen, especially in pediatric dentistry, since the risk of injuring the permanent germ is high.
WaveOne ® system is characterized by a triangular cross-section, projected to work with reciprocal movements, a wide rotation angle in the cutting direction (counterclockwise) and a smaller rotation angle in the wear direction (clockwise) [22].Thus, debris elimination could occur during file output movements.For rotary instruments, wear at the preparation crown portion may improve the instrument control when the apical third is being prepared.Rotary movement tends to direct debris to the orifice, avoiding its compaction within the root canal [23].
The reason why K-files extrude debris apically is that, when preparing the apical third, debris could be pushed towards the apical foramen, preventing elimination from occurring through coronal portion [2].
Considering the results found here, endodontic treatment in primary teeth under reciprocating instrumentation leads the professional to a clinical time optimization, but without the influence of the amount of extruded debris, and could be used as this technique does not influence the extruded debris amount.However, the present study presented a sample size limitation.Therefore, our results should encourage the conduction of further studies with grater sample size in order to understand and contribute to the knowledge of endodontic treatments in pediatric dentistry.

Conclusion
Although this study has shown safety and efficiency in using reciprocating systems and single-file for root canal instrumentation and the amount of debris was not influenced by the type of procedure, further studies with larger samples are still necessary in order to evaluate root canal instrumentation with rotary systems.

Table 1 . Weight of roots before and after manual instrumentation and WaveOne system instrumentation.
TRN = Tooth Root Number; *Average.