Cleaning capacity promoted by motor-driven or manual instrumentation using ProTaper Universal system: Histological analysis.

AIM: The aim of this study was to assess the cleaning capacity of the Protaper system using motor-driven or manual instrumentation.
MATERIALS AND METHODS: Ten mandibular molars were randomly separated into 2 groups (n = 5) according to the type of instrumentation performed, as follows: Group 1 - instrumentation with rotary nickel-titanium (Ni-Ti) files using ProTaper Universal System (Dentsply/Maillefer); and, Group 2 - instrumentation with Ni-Ti hand files using ProTaper Universal (Dentsply-Maillefer). Afterwards, the teeth were sectioned transversely and submitted to histotechnical processing to obtain histological sections for microscopic evaluation. The images were analyzed by the Corel Photo-Paint X5 program (Corel Corporation) using an integration grid superimposed on the image.
RESULTS: Statistical analysis (U-Mann-Whitney - P < 0.05) demonstrated that G1 presented higher cleaning capacity when compared to G2.
CONCLUSIONS: The rotary technique presented better cleaning results in the apical third of the root canal system when compared to the manual technique.

INTRODUCTION

Biomechanical preparation of the root canals plays an important role in endodontic treatment, as the main objectives of the latter are to clean, disinfect and shape the root canals to enable easy and appropriate filling.[1] Given that well performed mechanical instrumentation of root canals provides a great probability of success, it is also true that inadequate instrumentation is almost always responsible for treatment failure.[23] Due to the difficulty in treating curved root canals, nickel-titanium (Ni- Ti) instruments have been developed, which may be used as hand files or motor-driven files for the debridement of root canals.[4] As they have great flexibility and cutting efficiency, they are indicated for the debridement of curved root canals. Thus, they help to reduce the instrumentation time, causing less stress to the professional dentist, and providing greater comfort for the patient.[4]

With the release of ProTaper instruments (Dentsply/Maillefer), the authors of this study have reported their experiences with this system. They can be differentiated from the other commercially available instruments by the variations in their taper. The rotary file kit is comprising of three ProTaper instruments called the “Shaping” instruments (SX, S1 and S2), and three “Finishing” instruments (F1, F2 and F3). The handle is golden and the length of the files is shorter than the other systems, except for the K3 files.[5] They have colored rings on their handles, standardized by the International Organization for Standardization (ISO) system, which identify the instrument and direct the operator to use them in the sequence proposed by the manufacturer.[45]

ProTaper Manual instruments appeared as an alternative for rotary ProTaper. They have the same philosophy for use, indications and sequence; hwoever, are available at a lower cost as no electric motor is needed.[5] The aim of this study was to compare the two endodontic instrumentation techniques, manual and rotary, with regard to their cleaning capacity of the apical third in mesial canals of human mandibular molars.

MATERIALS AND METHODS

Ten human mandibular molars were used in this experiment. The necessary approvals were obtained from the Research Ethics Committee of our institute before starting the study. Radiographs were taken of the teeth, and teeth with endodontically treated root canals, incomplete rhizogenesis, internal or external resorption or root fractures, were excluded from the study. Teeth with root canal angulations of 0° to 5°, and 10 mm in root length were used. The crowns of the teeth were sectioned close to the amelocemental junction with a double-faced diamond disk (KG Sorensen; São Paulo, SP, Brazil) mounted on a high-speed handpiece (Silent - MRS 400; Dabi Atlante, Ribeirão Preto, SP, Brazil). As soon as the mesial roots were separated, debridement of the root canals was performed. Afterwards, the teeth were randomly separated into two groups with five specimens each. Considering that each mesial root has two canals, ten samples for each group were used.

Initial root canal exploration was performed by introducing a K-type file #10 (Dentsply/Maillefer; Tulsa, OK, United States of America) into the canal until it was seen in the apical foramen of each tooth, and then the file was withdrawn 1 mm, thus determining the real working length. The working length was respected during the entire instrumentation procedure. During debridement of both groups, 1 ml of 1% Sodium Hypochlorite (NaOCl) solution was used for irrigation at each change of instrument. Irrigation and aspiration were performed using the Ultradent irrigation - aspiration kit (Dentsply/Maillefer).

In the roots of Group 1, initial debridement was performed with K file # 10 (21 mm - Dentsply/Maillefer, Tulsa, OK, United States of America), at the working length, previously obtained, with movements of catheterism, and followed by instrumentation with Ni-Ti rotary files of the ProTaper Universal system (Dentsply/Maillefer) using the endodontic motor X-Smart, according to the technique recommended by the manufacturer. These special files were used following the order: SX, S1, S2, F1 and F2. The root canals were debrided until each file reached the real working length, being immediately withdrawn. This procedure was performed twice.

In Group 2, debridement was performed with K file #10 (21 mm - Dentsply/Maillefer, Tulsa, OK, USA) at the working length, followed by instrumentation with Ni-Ti ProTaper hand files (Dentsply/Maillefer) according to the technique recommended by the manufacturer in the following order: SX, S1, S2, F1 and F2. The root canals were debrided using the same method as the one for the root canals in Group 1. The rotary and hand files were replaced by new files after every five canals were debrided. After debridement, the roots were placed into distilled water at room temperature for 24 hours. Next, the teeth were submitted to routine histotechnical processing. First, the specimens were dehydrated by alcohol in the ascendant scale (70%, 90%, 95% and 100%). Then, they were immersed into xylol and paraffinization was performed to obtain the blocks and sections of the tissues that would be analyzed. The paraffin blocks were placed in a microtome and the cross sections were made of the apical third at 2 mm from the apical foramen. Three semi-serial sections measuring 5 μm each were placed on the same lamina and the process was repeated three times for each tooth, totaling 90 sections on 30 laminae, which were then stained with hematoxylin and eosin.

Histological analysis was carried out blindly by a single examiner under an optical light microscope (Axio Star Plus; Carl Zeiss, Oberkachen, Germany) at 120X magnification. The images referring to these sections were analyzed using the Corel Photo-Paint X5 program (Corel Corporation; São Paulo, SP, Brazil). An integration grid with 300 (20 x 15) points, generated by the program, was superimposed onto each image obtained. The total area and percentage area occupied by the debris was then calculated. The total area of squares present in the canal lumen as well as the squares that coincided with the canal wall and lumen were considered.

The results of all measurements were submitted to the U-Mann-Whitney statistical test, at a 5% level of significance, using the software Graphpad Prism 4.0 (GraphPad Software, La Jolla, CA, EUA).

RESULTS

The mean values in percentage for the cleaning capacity using different techniques may be seen in Figure 1. The analysis of the results demonstrated that Group 1 presented higher cleaning capacity of root canals in the apical third [Figure 2] with a statistically significant difference, when compared to Group 2 (P < 0.05).

Figure 1

Graphic representation of the mean values (%) of debris after debridement in the different groups in the study

Figure 2

(a and b) Photomicrographs of serial sections from Group 1 (rotary instrumentation) (H and E, ×120). (db) debris in the canal lumen; (c) canal lumen; (de) dentin. (c and d) Photomicrographs of serial sections from Group 2 (manual instrumentation) (H.E. -×120). Debris in the isthimus region (arrow)

DISCUSSION

Correct biomechanical preparation is the key for a successful endodontic treatment. The purpose is to clean the root canal and its ramifications, creating ideal conditions for the regeneration of the periapical tissues. Internal anatomical variations may interfere in the success of endodontic therapy. Also, tissue remains may persist in the ramifications and the isthmus area, making the debridement difficult, as was found in the histological sections in both groups.[2]

Successful endodontic treatment depends the meticulous cleaning, shaping, disinfection and sealing of the root canals. Cleaning occurs simultaneously with biomechanical preparation, causing elimination of the bacteria and degenerated pulp tissue, and creating a space that allows proper sealing. This process occurs by the action of instruments on the root canal walls, the chemical properties of irrigation solutions and by irrigation-aspiration.[4] A widely used methodology to assess the cleaning capacity of endodontic instrumentation is the use of the optic microscope to analyze serial histological sections by the superimposition on an integration grid,[46] as the one used in the present study. This methodology quantifies the remaining debris after debridement of the root canals by calculating the percentage area occupied by debris in relation to the total area of the root canal lumen.[6]

Instrumentation techniques have become widely studied particularly after the development of Ni-Ti alloy files, which allow faster and safer debridement of curved and flattened root canals. Some studies have shown that the canal shape obatined after debridement with motor-driven nickel-titanium files was not significant.[47] With regard to the percentage of remaining debris in the total area of the root canal, the results shown in the present study are similar to the results presented by Gonηalves et al.[6] and Barbizam et al.[8] regarding rotary instrumentation technique. On the other hand, the access of these instruments in some areas is critical, because the roots are flattened and additional biomechanical preparation with hand files is recommended.[9] In the present study, the presence of debris in areas in the flattened canals as well as in the region of isthmus was found, which confirms that debris remain even after biomechanical preparation is finalized, as it has been found in other studies.[610-13]

To reduce the amount of the remaining debris, Baratto-Filho et al.[10] conducted a study with rotary instrumentation using Ni-Ti files; however, used different irrigation solutions. Thus, the study showed that 2.5% NaOCl solution is more effective to clean root canals than at other concentrations (1% and 0.5% NaOCl). Whereas Passarinho-Neto et al.,[11] also used a rotary instrumentation system with 1% sodium hypochlorite as the irrigation solution, but in combination with ultrasound in the apical third of flattened canals, and showed that it was more effective to remove debris when compared with irrigation without using the ultrasound. The present study used 0.8% physiological solution as the irrigation solution without modifying the solution components or concentrations of the irrigation solution used.

Therefore, due to internal anatomical variations of mesial canals of mandibular molars, this study confirms that debris remain in the root canal even after biomechanical preparation, irrespective of the instrumentation technique used.[9] It was found that the instrumentation technique recommended by the manufacturer using rotary files of the ProTaper Universal system was more effective than the manual technique, which was also recommended by the manufacturer of the ProTaper Universal system. Furthermore, it may be suggested that this difference occurred because of the constant and uniform instrumentation provided by the electric motor X-Smart, since hand instruments of the ProTaper Universal system have the same conformation as the rotary instruments.[1213]

Therefore, it may be concluded that the rotary technique showed better cleaning results in the apical third of the root canal systems; however, further studies using other irrigation solutions and instrumentation techniques are needed to standardize the results.