The main objective of endodontic treatment is to clean, shape and obturate all the portals of root canal system, three- dimensionally to prevent reinfections1. Root canal therapy despite having a high degree of success, may not lead to desired response and failure may occur.2 Although success rates are varying between 86% and 98%,3 endodontic therapy may result in failures by a number of biological and technical factors such as untreated canals,4 perforations,5 inadequately filled canals,6 coronal leakage.7 These factors cause persistency of bacteria within the root canal system and as a result the microorganisms or their byproducts may induce an inflammatory response within the peri-apical tissue causing peri-radicular lesions. When peri-apical disease is formed,the options for treatment are non-surgical re-treatment, surgical procedures or surgical extraction of the tooth.3 Among those non-surgical root canal re-treatment, which is an attempt to re-establish peri-apical tissues after inadequate treatment or reinfection of an obturated root canal system has become a routine practice in dentistry because of the etiological factors.8
The main goal of orthograde re-treatment is regaining access to the apical foramen by complete removal of root canal filling material, thus facilitating sufficient cleaning and shaping of complete root canal system and final obturation.8 Only if the filling material can be removed completely and root canal negotiated to the apical foramen, allowing thorough debridement, can the pre-requisites for a successful re-treatment be fulfilled.9
Removal of obturation material can be effected with hand files, heat carriers or ultrasonic instruments or engine driven rotary files with or without the aid of solvent. In many cases the combined use of different techniques may be the most efficient and time saving method.9,11
Conventionally, H Files with or without solvent have been used in routine practice for the removal of filling materials from the root canals. Rotary Ni-Ti instruments have also been proposed for the same. Review of literature revealed that only few studies12,13 investigated the effectiveness of rotary files in the removal of gutta percha during endodontic re-treatment.
Hence, the aim of this in-vitro study is to compare the efficiency of H files, ProTaper Universal Retreatment files, Mtwo re-treatment files and SybronEndo K3 re-treatment system; during root canal re-treatment for the removal of Gutta Percha in straight canals.
MATERIALS AND METHOD
One hundred twenty single, straight rooted freshly extracted mandibular premolar teeth, each with one single root canal, were used.Following extraction, soft tissue and calculus were mechanically removed from the root surfaces. The teeth were stored for two days at room temperature in 3% NaOCl to remove organic debris. Subsequently they were stored in normal saline solution which was changed every two weeks until the procedure was initiated.
The length of specimens was standardized. All samples were marked at 16 mm from the apex with the help of verneer caliper. The specimens were then sectioned at this mark using diamond disc. A size 10 K file was inserted into the canal until it was visible at the apical foramen and the working length was determined to be 1mm short of this position. Apical patencies were determined with a size 10 K-file. A glide path was then made upto size of 20 K-file till working length.
Root canal preparation and obturation
All the canals were instrumented with NiTi twisted rotary files with size 25 and 35 of 0.08 and 0.06 taper respectively in a crown down manner using a 16:1 reduction handpiece powered by a torque controlled electric motor operated at 500 rpm. Final apical preparation was done with 40/0.04 NiTi twisted file.
The canals were irrigated copiously using 2ml of 3% sodium hypochlorite solution after each instrument was used and before proceeding to the next one. The solution was carried to the canal using 30 gauge MAX-I-Probe. It was inserted passively upto 1mm short from the working length. When instrumentation was complete, 17% EDTA was applied for three minute to remove the smear layer followed by a final rinse with 3 ml of normal saline to remove the previously used solutions to allow better contact of the sealer with the root canals walls. The root canals were then dried with absorbent paper points.
For obturation a master Gutta Percha cone ISO size 40 was selected and tug-back was checked. The root canals were filled with cold lateral condensation of Gutta Percha and AH plus sealer. Thereafter, accessory Gutta-Percha cones ISO sizes 20 and 25 were laterally compacted using finger spreaders. A heated plugger was used to remove the coronal 1mm of Gutta Percha. This 1mm of space was filled by temporary restoration (Cavit Temp).
Subsequently, the quality and apical extent of the root canal filling was accessed with digital radiograph in buccolingual direction using a radiographic grid. The distance between the X-ray source and radiographic film and the direction of the beam were same throughout the study. The exposure time was 0.4 s and the films were automatically processed. All teeth were stored in 100% humidity at 37 degrees celsius for 1 week to allow complete setting of sealer. After 1 week temporary restorations were removed and the root canals were reopened.
After removal of the temporary restoration the teeth were then randomly divided for retreatment into four groups of 30 specimens each (n=30).
Group 1 (ProTaper): This group received the retreatment by ProTaper universal retreatment files used in the Crown down motion using a brushing action with lateral pressing movements according to the manufacturer’s instructions. Instruments were used in following manner: D1 (30/0.09) was used for the cervical third; D2 (25/0.08) for the middle third; D3 (20/ 0.07) for the apical third until the working length was used. Instrumentation was completedwhen the D3 instrument reached working length,and no additional root canal filling material could berecovered on the instrument.
Group 2 (K3): K3XF instruments were used in a crown-down manner according to manufacturer’s instructions using gentle in-and-out motion. Instruments were withdrawn when resistance was felt and changed for the smaller number instrument. File sequences were as follows: size 25/0.06 was used at one half of the working length; size 20/0.06 was used between one half and two-thirds of working length; and instruments of sizes 20/0.04, 25/0.04 and 30/0.04 were used to the working length.
Group 3 (Mtwo): For the retreatment in this group Mtwo retreatment file 15/0.05 was advanced in the root canal in a brushing action with lateral pressing movements. Then the final apical cleaning was done by 25/0.05 instrument at a speed of 300 rpm and a torque of 1.2 Ncm-1. All the instruments were used to the full length of the canals using a gentle in and out motion.
Group 4 (H files): The canals were reinstrumented with H files in ISO sizes 70, 60, 55, 50 and 40 of 0.02 taper in a circumferential quarter-turn push-pull filing motion to remove Gutta Percha and sealer from the canal. The instruments were used in a crown down motion until an end-point at whichworking length was reached with a size 40 Hedstromfile, and no additional root canal filling material could berecovered on the file.
During retreatment, root canals were constantly irrigated with 3% NaOCl and 17% EDTA. The radiographs were taken after removal of filling material as described previously.
Time for Retreatment: The time required to achieve satisfactory Gutta Percha removal was recorded for each technique and were tabulated. The time elapsed from entering the root canal with hand files or rotary files including irrigation and completion of the re-intrumentation was measured in seconds with a stop watch. Time taken to change the instruments was not included in the retreatment time.
Radiographic Evaluation: The roots were then radiographed again in buccolingual direction using a radiographic grid (Figure 1). In the radiograph each third of the canals were evaluated for the remaining root fillings by counting the grids. The area of radio-opaque material in each thirds of the canal were measured and expressed as a percentage of the root canal area.
The statistical software SPSS PC+ Version 4.0.1 was used for statistical analysis.
Mean and standard deviation was estimated for the time taken by the different instruments for the removal of filling materials from the root canal (Table 1.1) and the values were compared with two way anova test for the estimation of level of significance (Table 1.2) (Graph 1). p ≤ 0.05 was considered as the level of significance.
Test of significance between the means show that there was a significant difference between the groups for the time taken by the different instruments for retreatment. Group 4 took the maximum time duration (mean = 515.8sec.) when compared to the other groups (mean ranging from 347-371sec.) and this difference of duration was significant when compared to other groups (p<0.05)
Graph 1: Depicting the mean time taken by different techniques for retreatment
Table 1.1: Time taken by different groups for retreatment in seconds
Table 1.2: ANOVA TEST FOR TIME ANALYSIS
Mean and standard deviation was estimated for each group for percentage of residual filling material as calculated by the radiographic analysis for each canal third (Table 2.1).
Tukeys test was done for intergroup comparison to calculate the level of significance (Table 2.2) (Graph 2). Coronal: Group one had less percentage of remaining debris when compared to all the other groups and the difference was significant when group 1 was compared to group 3(p=0.032).Middle: Test of significance between the groups showed no significant difference for the canal wall cleanliness in middle third as calculated by radiographic analysis.Apical: In the apical region Group 4 had the fewer percentages of remaining debris among all the other groups. There was a significant difference between the groups for the canal wall cleanliness in apical third for Group 4 when compared to Group 1 (p=0.026) and Group 3 (0.048).
Graph 2: Depicting the mean percentage of remaining debris in different groups as calculated by radiographic analysis
Table 2.1: Radiographic analysis for percentage of remaining debris
Table 2.2: Tukey test for radiographic analysis
Figure 1: Pre and post retreatment radiographs for group 1.