Journal of Conservative Dentistry

ORIGINAL ARTICLE
Year
: 2012  |  Volume : 15  |  Issue : 3  |  Page : 218--222

Detection of residual obturation material after root canal retreatment with three different techniques using a dental operating microscope and a stereomicroscope: An in vitro comparative evaluation


Raju Chauhan1, AP Tikku2, Anil Chandra2,  
1 Department of Conservative Dentistry and Endodontics, Institute of Dental Sciences, Pilibhit Bypass Road, Bareilly, India
2 Faculty of Dental Sciences, CSM Medical University, Lucknow, Uttar Pradesh, India

Correspondence Address:
Raju Chauhan
Department of Conservative Dentistry and Endodontics, Institute of Dental Sciences, Pilibhit Bypass Road, Bareilly 243 006, Uttar Pradesh
India

Abstract

Aim: The study was designed to compare the efficiency of three different methods used for retreatment using a dental operating microscope (DOM) and a stereomicroscope and to evaluate and compare the two methods for detection of residual obturation material after retreatment. Background: The DOM can play an important role in the successful retreatment by detecting the remaining obturation material. Materials and Methods: Thirty extracted maxillary central incisors were collected and obturated after biomechanical preparation. The samples were divided into three groups depending on the method of retreatment: Group I, H-files; Group II, ProTaper Universal retreatment files; and Group III: H-files + Gates-Glidden drills, with 10 samples in each group. After retreatment, the samples were observed under a DOM for detection of residual obturation material. Later, the teeth were cleared and observed under a stereomicroscope for detecting the remaining filling material. The results were subjected to the Spearman«SQ»s rank order test and other statistical analysis. Results: The maximum cleanliness of the root canal walls was seen in Group I while Group II showed the least. The difference between the mean scores obtained with a DOM and a stereomicroscope was statistically significant (P = 0.05). Conclusion: None of the techniques could completely remove the obturation material. The root canal cleanliness is best achieved when retreatment is performed under a DOM.



How to cite this article:
Chauhan R, Tikku A P, Chandra A. Detection of residual obturation material after root canal retreatment with three different techniques using a dental operating microscope and a stereomicroscope: An in vitro comparative evaluation.J Conserv Dent 2012;15:218-222


How to cite this URL:
Chauhan R, Tikku A P, Chandra A. Detection of residual obturation material after root canal retreatment with three different techniques using a dental operating microscope and a stereomicroscope: An in vitro comparative evaluation. J Conserv Dent [serial online] 2012 [cited 2019 Jul 21 ];15:218-222
Available from: http://www.jcd.org.in/text.asp?2012/15/3/218/97940


Full Text

 Introduction



The extremely high predictability of endodontic success has made it possible to retain the pulpally involved teeth, the main reason behind this is the much advancements in endodontics. The main causes of endodontic failure, making retreatment necessary, are thought to be insufficient cleaning and inadequate obturation. [1] The endodontic failure cases can be treated in three ways: nonsurgical retreatment, surgical retreatment, or extraction. Among all these treatment alternatives nonsurgical retreatment should be considered as the first choice of treatment. Success rates for orthograde retreatment are 65% [2] to more than 80%. [3] The main goals of orthograde retreatment are gaining access to the apical foramen by complete removal of the root canal filling material thus facilitating sufficient cleaning and shaping of the complete root canal system and final obturation. [4]

Gutta-percha can be removed using rotary instruments, heat carrying instruments, and solvents. [5] However, previous studies have revealed that canal walls completely free of debris are not usually obtained. [6] It remains unclear what method of evaluation indicates complete removal of filling material during orthograde retreatment. In some retreatment studies, the criteria for completion of retreatment was no evidence of gutta-percha or sealer on the files or paper points. [7] In other studies, radiographs were exposed and evaluated. [8] But none are conclusive methods for arriving at a decision that the retreatment is completed. Clearly, more convincing methods are required for detecting the remaining root canal filling material. The dental operating microscope (DOM) is used increasingly in vivo for routine endodontic procedures because of enhanced visibility and lighting. [9] The reported advantages of using an operating microscope for conventional endodontics include improved the visualization of root canal anatomy that enables the operator to investigate the root canal system and to clean and shape it more efficiently. [9],[10]

 Materials and Methods



Thirty freshly extracted human maxillary central incisors were collected from the Department of Oral and Maxillofacial Surgery, Faculty of Dental Sciences, CSMMU, Lucknow. In all the samples, the clinical crowns were resected before cleaning and shaping of the root canal in order to keep similar length of all the samples which was 16 mm. The access opening was made using #2 round diamond instrument in a high speed hand-piece. The working length was determined using a radiograph which was kept 1 mm short of the radiographic tip. The apical preparation was then enlarged up to # 50 k-file (DENTSPLY Maillefer, Switzerland) size in all samples while irrigating frequently with 5% NaOCl and EDTA and the rest of the canal was prepared using the step-back technique using successively larger number files. After biomechanical preparation, the root canals were dried and obturated with gutta-percha and AH-Plus sealer (DENTSPLY DeTrey, Germany) by the cold lateral condensation method. The samples were then radiographed to confirm the adequacy of obturation. Access cavities in all samples were sealed with composite Synergy D6 (Coltene Whaledent, Switzerland) restorative material. The samples were then stored in normal saline for 1 week.

The 30 samples were randomly distributed into three groups (n = 10).

Group I: Hedstroem files.

Group II: Protaper Universal retreatment files.

Group III: Hedstroem files + Gates-Glidden Drills.

Retreatment procedure

Group I

The samples were retreated using H-files (DENTSPLY Maillefer, Switzerland). Gutta-percha was removed from the root canals using H-files with sizes 25, 30, 35, 40, 45, and 50 in a circumferential quarter-turn push-pull motion. The retreatment was deemed completed when no gutta-percha and sealer material could be seen on the instrument and also when the canal appeared clean when inspected with naked eyes.

Group II

The samples in these groups were retreated with ProTaper Universal retreatment files (DENTSPLY Maillefer, Switzerland). Without engaging dentin, D 1 was gently pressed into the obturation material. D 1 was used to remove the obturation material from the coronal one-third of the root canal. After using D 1 , D 2 was used to progressively remove material from the middle one-third. The remaining obturation material from the apical one-third of the root canal was removed with D 3 . In between the files were removed frequently for inspecting the flutes. Continued as long as the obturation material was visualized between the cutting blades.

Group III

The samples were retreated with H-files and Gates-Glidden drills. The filling material was removed using Gates-Glidden drills from the coronal and middle third of the root canal and the apical third was cleaned using H-files.

After retreatment was completed, the samples were observed under a DOM at 5.1× magnification (OPMI PROergo Carl Zeiss Germany) to detect residual obturation material. The photographs of all the samples were stored on a computer and later on evaluated for the remaining filling material using Image Analysis Software (Image Tool 3.00 UTHSC San Antonio). Linear measurement of the remaining filling material was done in millimeters and scores were given to each sample for cleanliness of canal walls as follows. [8],[11]

[INLINE:1]

The teeth in all the groups were made transparent by Robertson's method: After observing the samples under a DOM, the specimens were decalcified in 5% nitric acid for 72 h, then washed for 4 h and dehydrated in increasing concentrations of alcohol, i.e. 80% alcohol for 12 h, 90% alcohol for 1 h, and 99% alcohol for 3 h. The samples were then subsequently cleared by storing them in methyl salicylate.

After clearing, the samples were observed under a stereomicroscope at 6.5× (SZX7 Olympus America Inc.) and the images were subjected to Image Analysis Software (Image Tool 3.00 UTHSC San Antonio), for detection of residual obturation material [Figure 1]. The samples were scored for residual obturation material, and the criteria adopted for scoring was the same as the one followed when observed under a DOM. Apart from measuring the residual filling material linearly, the area of residual obturation material was also measured in mm 2 . {Figure 1}

Analysis

The upper and lower confidence limit for the mean was calculated to show the significant difference between the scores obtained with a DOM and a stereomicroscope. Furthermore, the mean was calculated to show the significant difference among the three groups in scores given by a DOM and a stereomicroscope and the areas measured in mm 2 by a stereomicroscope. The degree of correlation between measurements was determined using Spearman's correlation coefficient. In addition, statistically significant differences were evaluated using the paired t-test. The confidence limits and paired t-tests were used to show statistically significant differences between the scores given by a DOM and a stereomicroscope.

Spearman's correlation coefficient was used to determine the correlation between the area of remaining obturation material measured in transparent roots and the scores obtained by the DOM and the stereomicroscope. The level of significance was set at 0.05.

 Results



The mean score of residual filling material after observing the samples under a DOM and then under a stereomicroscope is given in [Table 1]. The statistically significant difference was found between the mean scores of Groups I and II for a DOM and a stereomicroscope (P = 0.014 and P = 0.0045, respectively). The difference between the mean scores of Groups II and III for a DOM and a stereomicroscope was also significant (P = 0.016 and P = 0.0022, respectively).{Table 1}

The mean area of residual obturation material after observing the three groups under a stereomicroscope was the highest in Group II (3.5820 mm 2 ) and the lowest in Group I (2.9520 mm 2 ) [Table 2]. There was a low and nonsignificant correlation between the scores obtained by the DOM and areas of residual filling material measured in transparent roots [Table 3]. In addition, there was a low and nonsignificant correlation between the scores obtained with the stereomicroscope and areas of residual filling material measured in the transparent root [Table 3]. The difference in the mean scores obtained with the DOM and the stereomicroscope taking all the samples together was statistically significant (P = 0.05). Therefore, the scores given by a stereomicroscope were significantly higher than the scores given by a operating microscope. No method of retreatment could completely clean the root canal walls, but the H-file was found to be more efficient than the other two methods for the root canal retreatment. The DOM detected the residual obturating material left in the canal after completion of retreatment, but stereomicroscopic evaluation of the samples showed that DOM underestimated the amount of residual material left inside the canal though the difference was found to be small.{Table 2}{Table 3}

 Discussion



The retreatment can be accomplished by various instruments and techniques, i.e., stainless steel hand files, heat, ultrasonic, laser, and rotary instruments with and without the aid of solvents. [11] In many cases, the combined use of different techniques may be the most efficient and time saving method. [6],[12] Several automated instrumentation techniques can also be used for retreatment. [11],[13] The criteria for completion of retreatment may be no evidence of gutta-percha or sealer on the files or paper points [14] and evaluation of post-treatment radiographs. [8],[11] However, a previous ex vivo study showed that radiographic examination provided an over optimistic impression of cleanliness compared with examination of vertically split roots. [14] The DOM can be indispensible during retreatment because of its several advantages. [9],[10]

Tooth clearing has been employed to obtain information on various aspects of endodontic treatment including morphology, [15] canal instrumentation techniques, [16] the influence of post-design and its influence on the root fracture, [17] sealer placement techniques in curved canals, [18] and quality of canal fillings. [19]

A similar method for detection of residual obturation material by the operating microscope was utilized in previous studies. [20],[21] It has been previously demonstrated that it is almost impossible to remove all traces of gutta-percha/sealer from the canal walls. [6],[22] This was also evident in the present study. Here H-files were found to be more effective in removing gutta-percha/sealer. [8] H-files are better in adapting themselves to the root canal walls during hand instrumentation by a circumferential filling technique, thereby digging into the softened gutta-percha adhering to the root canal walls. The Gates-Glidden drills are effective removers of gutta-percha within coronal one-third and middle part of the root canal. [23] There was statistical difference found in the cleanliness of canal walls as observed under DOM in Groups I and II [P = 0.014]. [11] This was due to the fact that it proved to be difficult if not impossible to direct the NiTi instruments to a certain aspect of the root canal wall at least in the apical region. The use of rotary devices in endodontic retreatment should be followed by hand instrumentation to achieve optimal cleanliness. [8] The stainless steel hand files remove filling material more effectively than NiTi rotary instruments. [14]

In this study, the roots were cleared to allow the measurement of the area of residual obturation material because remaining gutta-percha or sealer might get lost by splitting the roots longitudinally. [20],[24] Comparing the scores obtained in each group by examining the samples under a DOM and stereomicroscope, there was statistically significant difference between the scores obtained by the two methods of evaluating the re-treated roots (P = 0.05). Even though the co-relation between the scores given after microscopic examination of the roots and the area measured in the transparent roots was low, the microscope with its increased illumination and magnification seemed to facilitate detection of remaining filling material that may harbor necrotic tissue or bacteria. [20] Therefore, it can be argued that DOM is indispensable in the root canal retreatment especially in teeth with straight roots.

 Conclusion





From this study, it can be concluded that:It is not possible to remove gutta-percha/sealer from the root canal completely during retreatment.No single instrument is capable of removing gutta-percha completely from the root canals during retreatment. Hand instruments produce better root canal cleanliness.Visualization of the root canal under a DOM during retreatment increases the ability of the operator to remove remaining obturation material.

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