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Influence of Ultrasonic Irrigation and Chloroform on cleaniness of Dentinal Tubules during endodontic retreatment- an invitro SEM study |Dr. Vineet Vinayak

ABSTRACT
Background:
Ultrasonic irrigation has been proved for its remarkable cleaning efficiency in the field of endodontics. But its role in endodontic re-treatment has been understated. There is not much data available to understand the effect of ultrasonic irrigation for the evaluation of cleanliness of dentinal tubules when it is used with or without chloroform, a gutta percha solvent during endodontic retreatment.

Aim:
To compare the influence of ultrasonic irrigation with syringe irrigation on cleanliness of dentinal tubules after gutta perch removal for endodontic retreatment with or without the use of chloroform a gutta percha solvent using scanning electron microscope (SEM).

Materials and Methods:
Freshly extracted 45 human mandibular premolar teeth for periodontal and orthodontic reasons were taken and were occlusally adjusted to a working length of 19 mm. The root canals of all teeth were prepared chemo mechanically to a master apical file size 40 and were divided in various groups. In Group 1 (n = 5; control group), the canals remained unfilled. In Groups 2 and 3 (n = 20 each), the canals were filled using lateral compaction with gutta-percha and AH plus sealer, removal of root fillings was undertaken after 2 weeks using Gates Glidden drills and H files without chloroform in Group 2 and with chloroform in group 3. The specimen of Group 2 and 3 were further divided into two subgroups I and II (n=10). In subgroup I, irrigation was done using side vented needles and sodium hypochlorite. In subgroup II irrigation was done using passive ultrasonic irrigation with sodium hypochlorite. Thereafter, the roots were split and the sections were observed under SEM. The number of occluded dentinal tubules /total number of dentinal tubules were calculated for the coronal, middle and apical third of each root half. Statistical analysis was performed using one-way ANOVA followed by Tukey’s test using standardized technique.

Result:
Results indicated that the cleanest dentinal tubules were found in the control group (Group 1 where the canals were unfilled) followed by the non chloroform group with ultrasonic irrigation (Group 3 subdivision II) followed by chloroform group with ultrasonic irrigation (Group 2 subdivision II), the non chloroform group with syringe irrigation (Group 3 subdivision I) and least cleanliness was found in the chloroform group with syringe irrigation (Group 2 subdivision I).

Conclusion:
Under the limitations of this study it could be concluded that both ultrasonic and syringe irrigation showed cleaner canals when chloroform was not used. Irrigation when done with ultrasonics leads to cleaner tubules than syringe irrigation. Hence, mechanical methods of retrieval in conjunction with use of passive ultrasonic irrigation should be a part of retreatment protocol.

Scanning Electron Microscope (SEM) analysis of specimen
Estimated mean, standard deviation (SD), standard error (SE), of the ratio evaluated in SEM (number of occluded dentinal tubules/total dentinal tubules) analysis and number of evaluated images (N)CCl3=chloroform US=ultrasonic
canals and canal curvature angles varying between 0–10° as given by Schneider [5] were selected, after radiographic evaluation. All teeth were stored in 10% ethyl alcohol solution. Access cavity preparations were done and the incisal edges were adjusted, so that the final working length of each tooth was 19.5 mm. The working length was confirmed by radiographs. Radiographs were taken to confirm that the distance of file from the apical foramen remained between 0.5-1mm in all the specimens.

Canal preparation-
All the roots were instrumented using K- type file (Dentsply, Maillefer, Ballaigues, Switzerland). The apical enlargement was done up to size 40 using K file at the working length by using the files in sequence according to increasing order of their tip diameter size (size 15-40 K file). Frequent recapitulation was done by using number 15 K file. A step back technique was followed for cleaning and shaping of the canal. K files of sizes 45,50,55 were used in progressing order at file lengths 1 mm short of the preceeding file. (i.e. at 18.5mm,17.5mm and 16.5mm for K file 45,50 and 55 respectively). K file size 40 was used for recapitulation to prevent iatrogenic ledge formation. Using side vented needles (canal clean), 3% sodium hypochlorite was delivered in the root canals each time before using instrument of larger diameter. Finally, the root canals were rinsed for 1 minute using EDTA, followed by 3% NaOCl (10 ml) for final rinse. A 28-gauge side vented irrigation needle, inserted 1–2 mm short of the working length was used for irrigation. All root canals were dried with paper points.

Obturation-
All samples were randomly divided into three groups. Group 1: (Control Group, n = 5) The roots remained unobturated and it served as a baseline parameter for comparison. The root canal of each tooth in experimental Groups 2 and 3 were obturated using lateral compaction. The roots were radiographed in buccolingual and mesio-distal directions in order to confirm the adequacy of the obturation. The access cavities were filled temporarily by Cavit (3M ESPE). All teeth were stored in a humid or for two weeks in 100% humidity to allow complete setting of the sealer.

Retreatment technique-
In Groups 2 and 3, from the coronal 5 mm of the root canal of each specimen the obturating material was removed using Gates Glidden drills of sizes 2, 3 and 4 in sequential increasing order of their size. In the middle and apical part of the canal, Hedstrom files sizes 15-40 (Dentsply, Maillefer, Ballaigues, Switzerland) were used in order to remove gutta-percha and sealer from the canal. In Group 2, chloroform (Rankem, Ranbaxy), a gutta percha solvent was used along with H files to ease the removal of gutta percha. In Group 3 also gutta-percha removal was done by using H files without using chloroform. In Group-2 chloroform was deposited for 15 sec into the reservoir created by Gates Glidden drill. The gutta-percha was removed with Hedstrom files sizes 40–15 (in descending order) to the working length using a push and pull action. Once the working length had been reached with a size 15 file, sizes 20, 25, 30, 35, 40 were instrumented to the working length. When no gutta-percha could be seen on the flutes of the file, radiographic confirmation was done and the gutta-percha removal was ceased. After gutta-percha removal, specimens from both the groups were divided in two sub groups. In subgroup I (n=10), the canals were irrigated with 3% NaOCl (10ml) for one minute using side vented needles 1-2mm short of working length. In subgroup II (n=10), canals were subjected to passive ultra sonic irrigation by ultrasonic file along with 3% sodium hypochlorite for one minute. Finally, all canals were dried with paper points (Dentsply, Maillefer, Ballaigues, Switzerland).

Evaluation-
The teeth were grooved with a diamond saw and split longitudinally using chisel and mallet. For the SEM analysis, the specimens were dehydrated with ascending concentrations of ethyl alcohol (30-100%) and then sputtered with gold. The root halves were examined using a SEM at 10–15 kV and at a standard magnification of 2000 X. Each root half was evaluated by an observer who was blinded to which technique was used for the removal of the gutta-percha. Evaluation was done for three different locations i.e. coronal, middle and apical third. For statistical analysis, the total number of dentinal tubules and the number of dentinal tubules either completely or partially occluded with obturating material were recorded.

STATISTICAL ANALYSIS
A one-way ANOVA test was performed to calculate the mean value and standard error in each group for each third of canal for occluded tubules over total tubules. Normality of error terms can be assumed. In the analysis, all observations were included distinguishing between the coronal, middle and apical third. The group effect was calculated and the p-values for the pair wise comparisons were adjusted using Tukey’s test. Significance was established at 1% (p< 0.01).

RESULTS
After combining the mean values of occluded tubules/total number of dentinal tubules of all thirds of the canal, the cleanest dentinal tubules was found in following order: Group 1> Group 3 subdivision II> Group 2 subdivision II> Group 3 subdivision I> Group 2 subdivsion I [Table/Fig-1,2]. [Table/Fig-3a-e] shows representative SEM images from all groups.

DISCUSSION
The most important factor associated with endodontic failure is the persistence of microbial infection in the root canal system and/or the periradicular area. Bacteria located in areas such as isthmuses, ramifications, delta’s, irregularities and dentinal tubules may be seldom not affected by endodontic disinfection procedures . In such anatomical regions, bacteria entombed by the root filling usually die or are prevented from gaining access to the periradicular tissues. If the root canal filling fails to provide a complete seal, seepage of tissue fluids can provide substrate for bacterial growth. In such cases the endodontic treatment often fails and requires retreatment. To prevent failure, it is necessary that disinfectant and delivery system is chosen wisely to ensure its availability and wettability in the uninstrumented areas. To improve the wettability of irrigant, various agitation techniques have been developed, like manual brushes, rotary brushes, ultrasonic and sonic devices and pressure alternating devices . However, using hand held syringe needle (both open ended and side vented) irrigation may show more cases of unsuccessful root canal treatment due to weak mechanical flushing of debris . According to a survey by Ravanshad S. despite of introduction of various newer techniques the most commonly used protocol by majority of dentists in endodontic therapy is use of hand files for instrumentation, use of sodium hypochlorite as chief irrigant, use of syringe for delivery of irrigant and use of cold lateral condensation technique for obturation . Dunter reported that passive ultrasonic irrigation is used as second most commonly used irrigation system after syringe irrigation in USA as per a survey done in the year 2011 . Due to the above reasons, the study incorporated cold lateral condensation as an obturation technique and compared passive ultrasonic irrigation against syringe irrigation for their efficacy in retreatment.Previous data suggests that further studies should be conducted to evaluate the effect of ultrasonic irrigation on the cleanliness of dentinal tubules during endodontic retreatment . Therefore,Depicting ratio of occluded/total number of dentinal tubules of all specimens.

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