Evaluation And Comparison Of Amount Of Dentin Removed After Retreatment Using Three Different Retreatment Methods: An In-vitro Study

INTRODUCTION

Endodontic therapy is one of the most progressive aspects of modern dentistry. Significant advancements in debridement and obturation techniques have occurred in recent years¹ . Over the years studies have shown a wide range of success rates for endodontic treatment reflecting the complex nature of Endodontics. Outcomes vary based on the clinician's expertise and experience, the type of tooth involved and a myriad of other clinical and biological factors. Consequently success rates approaching 90% have been reported. However, endodontic procedures are among the most technically challenging faced by many dentists.²

With all the potential for endodontic success the fact remains that clinicians are confronted with post treatment disease. In 1986, late Dr Herbert Schilder quoted the term “RETREATODONTICS” and said that the future of Endodontics lies in the retreatment of endodontic failures³. Given the large number of treatments performed, the very low rate of unsuccessful outcomes translates into relatively large number of patients requiring further treatment. Dental clinicians should be able to diagnose persistent or reintroduced apical periodontitis and be aware of the options for treatment. If they wish to approach treating these teeth, they should have proper armamentarium and be capable of performing these very specialized techniques at the highest level. Clinicians must always have a scientifically sound, evidence based rationale for every treatment decision.²

Many techniques and materials have been used to obturate the root canal system, but gutta-percha combined with a sealer is still the most commonly used combination of materials.⁶ Several techniques are being to remove the gutta-percha, which induces endodontic hand instruments, ultrasonics, lasers, heat carrying instruments as well as NiTi rotary systems.⁵ Various rotary NiTi systems have been used for retreatment like Rendo, Profile, K3, Protaper.

Stainless steel hand H files and K files have been regularly used for removal of root canal fillings. Previous studies have shown that manual instrumentation using Stainless Steel Hand Files remove root fillings more effectively than NiTi rotary instruments. This could be attributed to the t that stainless steel hand files helps in removal of obturation material in chunks and pieces, while rotary instruments thermo softens the gutta-percha.²

The aim of this study was to evaluate and compare the amount of dentin removed after retreatment using 3 different methods namely Protaper Universal Retreatment system, Profile 0.4 taper instrument and hand instruments.

MATERIALS AND METHODS

Forty eight Maxillary Anterior teeth and Mandibular Premolars with single canal were collected from the Department of Oral and Maxillofacial surgery, D. A. Pandu Memorial R .V. Dental College, Bangalore, which were indicated for extraction due to poor periodontal prognosis and orthodontic reasons.

The surfaces of all the 48 selected teeth were debrided of all adhering tissues. They were then disinfected by overnight immersion in 2.5% sodium hypochlorite. The teeth were then rinsed and stored in a moist atmosphere during the study period at room temperature. The samples were decoronated using diamond disc with a slow speed micromotor handpiece to obtain a uniform length of 15mm. each. The working length was determined by reducing 1 mm from 15mm of the root length. The cleaning and shaping of canals were performed using K-files with a crown down technique upto an apical enlargement of size 35 K-file and was flared upto a size of 50 K file cervically. Copious irrigation with 1 ml of 3% sodium hypochlorite and saline were done at each change of instrument. Root canals were then dried with paper points.

The specimens were then mounted on clear acrylic blocks and digital radiographs of the specimens were made in the mesio-distal and labio-lingual plane. Root canals were then obturated using 2 % taper G.P points and AH plus sealer with cold lateral condensation technique. All the teeth were then stored for 15 days at room temperature .The teeth were then randomly divided into 3 groups, with sixteen teeth in each group. (n=16).

Group 1: Stainless Steel Hand K Files Group

From the 16 obturated teeth, gutta-percha was removed from the coronal 2 mm with sizes 2 and 3 Gates Glidden drills. 0.1ml of eucalyptol solution was added into the canal space .Asize 40 K file was introduced into the root canal by crown down technique until working length was reached with size 20 K file.

Group 2: Protaper Universal Retreatment Instrument Group

From the 16 obturated teeth, gutta-percha was removed from the coronal 2 mm with sizes 2 and 3 Gates Glidden drills.1ml of eucalyptol solution was added into the canal space . D1, D2, D3 instruments were introduced sequentially using a crown down technique until working length was reached .

Group 3: Profile 0.04 Taper Instrument Group

From the 16 obturated teeth, Gutta-percha was removed from the coronal 2 mm with sizes 2 and 3 Gates Glidden drills. .1ml of eucalyptol solution was added into the canal space. A PROFILE 0.04 size 40 file was introduced into the root canal by using a crown down technique until working length was reached with size 20 0.04 taper.

On withdrawal, the files were cleansed of any obturating material before being reintroduced into the root canal .Each file was discarded after being used in five teeth. Irrigation with 3 % NaOCl was performed during the procedure at each change of instrument .All the teeth were retreated by a single operator.

Retreatment was considered complete for all groups when no filling material was observed on the instruments and no filling material was detected in the canal for each tooth. Digital radiographs of the retreated specimens in the mesio-distal and labio- lingual plane were taken.

Digital Image Analysing Software

To evaluate amount of dentin removed, the radiographic images were transferred to a image analyzing software (Image Pro Express version 6.0) in the Department Of Oral and Maxillofacial Pathology, DAPMRV Dental college. The images were magnified to a 4x magnification. The outlines of the dentin on either side of the root canal space were traced using the digital marker and they were reviewed by two examiners. A consensus was reached on the tracings after both the examiners had agreed upon. The area of the dentin after bio mechanical preparation and area of the dentin after re-treatment were recorded for both labio-lingual and mesio-distal planes. The amount of dentin removed was calculated by subtracting the above values.

RESULTS

NULL HYPOTHESIS: There is no significant difference in the mean dentin removed using the three groups i.e. µ₁ = µ₂= µ₃

STATISTICAL TECHNIQUE USED: Analysis of Variance (ANOVA).

DECISION CRITERION: The decision criterion is to reject the null hypothesis if the p-value is less than 0.05. Otherwise we accept the null hypothesis. If there is a significant difference between the groups, we carry out multiple comparisons (post-hoc test) using Bonferroni test.

COMPUTATIONS: The following tables give us the results from ANOVAand the P-Value

Higher mean dentin removal was recorded in Protaper Retreatment file followed by Profile .04 and K-File respectively. The difference in mean dentin removal between them was found to be statistically significant (P<0.001). In order to find out among which pair of groups there exists a significant difference, multiple comparisons were carried out using Bonferroni test and the results are given below:

The difference in mean dentin removed was found to be statistically significant between Protaper Retreatment file & Profile.04 (P<0.01), Protaper Retreatment file & K-File (P<0.001) as well as Profile & K-File (P<0.001).

Higher mean dentin removal was recorded in Protaper Retreatment file followed by Profile and K-File respectively. The difference in mean dentin removal between them was found to be statistically significant (P<0.001). In order to find out among which pair of groups there exists a significant difference, multiple comparisons were carried out using Bonferroni test and the results are given below:

The difference in mean dentin removed was found to be statistically significant between Protaper Retreatment file & Profile (P<0.01), Protaper Retreatment file & K-File (P<0.001) as well as Profile & K-File (P<0.001).

DISCUSSION

There has been a massive growth in the endodontic treatment in recent years .This increase in clinical activity can be attributed to better trained dentists and specialists and also due to the general public's growing selection for endodontic treatment as an alternative to the extraction.² Although initial endodontic therapy has been shown to be a predictable procedure with a high degree of success, failures can occur after treatment.⁵

In the present study, removal of the root filling material followed current retreatment strategies. Gates Glidden drills, recommended for gutta-percha removal at the canal orifice level, were used in the coronal 2mm of the canal. This step facilitates access to the more apical portions of the canal. The remaining root filling was removed by engine driven instruments, Protaper Universal Retreatment System and Profile 0.04 taper files, as they have shown to efficiently remove gutta-percha and sealer from root canals(Bramante and Betty 2000, Sae lim et al 2000, Ferriera et al 2001, Masiero and Barletta 2005, Schirrmeister et al 2006).²⁸

The Protaper Universal Retreatment files used in our study consists of three instruments, D1, with tip size 30 and taper 0.09, D2 with tip size 25 and taper 0.08, D3 with tip 20 and taper 0.07.³⁶ In addition, D1 working tip facilitates initial penetration into the root filling material .We have used Protaper Retreatment System in the present study since it had been earlier proved that NiTi rotary files were faster than hand files in reaching the working length during retreatment. This is probably due to the gutta-percha plasticization resulting from rotation of the instrument. The rotary instrument were used in electric motor at a constant speed of 500 rpm D1 and 400 rpm for D2 and D3 and the torque was set at 3 Ncm.³

Previous studies have shown that even though Protaper Retreatment System does not remove the root canal filling material completely, it decreases the working time as well as reaches the working length faster than hand files. The incomplete removal might be due to the fact that rotary instruments thermosoftens the gutta-percha and its fine remnants get smeared on the root canal walls. Since rotary instrumentation plasticizes the gutta-percha through frictional heat, it enables reaching the apical third easily and quickly.³

Stainless steel hand K files were used in this study because K files and H files are the most commonly used instruments for non surgical retreatment. Previous studies have shown that manual instrumentation using Stainless Steel Hand Files remove root fillings more effectively than NiTi rotary instruments (Bramante and Betti 2001). This could be attributed to the fact that stainless steel hand files helps in removal of obturation material in chunks and pieces, while rotary instruments thermosoftens the gutta-percha¹⁶ . Zmner et al observed that the more effective removal of debris in the coronal middle thirds of the oval shaped canals by the manual instrumentation may be explained in that the stainless steel hand instruments are stiffer than NiTi rotary instruments and can be safely directed towards the root canal walls allowing a better performance in the oval shaped areas of the canal walls.²⁵

Gates Glidden drill was used in the present study in the coronal 2 mm of the canals. This step facilitates access to the more apical portions of canals and it provides a receptacle for the placement of the solvent .In previous studies Gates Glidden drills were taken as deep as 5-6 mm into the canals, compared to 2mm used in this study. The deep penetration with Gates Glidden drill would have removed the entire root filling material and even an extensive amount of surrounding root dentine .This would have hindered and provided inaccurate results in our study. Eucalyptol (the main constituent of eucalyptus oil) exhibits antibacterial effects and anti-inflammatory properties, and its potential of dissolution of guttapercha increases significantly when heated. If not heated, it dissolves the material more slowly.⁴⁰

Digital radiographs were taken of the specimens in the bucco-lingual and mesio-distal plane. To maintain uniformity, exposure time was kept at 4sec and the distance between the X-ray source and the CCD was 5cm. The specimens were mounted in rectangular acrylic blocks prior to instrumentation, so that the radiographic images can be taken in the same plane.

The root canal walls were identified by the operator through the difference of radioopacity and were outlined. The Pro image Express 6.0 was used in the present study to trace and evaluate the area of dentine removed after retreatment. The images were traced using a digital marker and the images were re-evaluated by two specialists, blinded to the group to which imaged belonged. If they did not agree with the outline areas the measurement was repeated until a final consensus was reached. However, the radiographic analysis has its own limitations as radiographic images provide only 2- dimensional information of a 3-dimensional structure. In order to counter this disadvantage, the images from both mesio-distal and bucco-lingual views.

The amount of dentine removed by three groups was measured in micro meter square. The statistical analysis used to compare the amount of dentin removed after retreatment was ANOVA. The mean amount of dentin removed of Protaper retreatment file group was 316.49µm² (Bucco-lingual view) and 523.10µm² (Proximal view). Profile group showed 262.78 µm² (Bucco-lingual view) and 433.01 µm² (Mesio-distal view). K-file showed 150.22 µm² (Bucco-lingual view) and 266.35 µm² (Mesio-distal view).

The highest amount of dentin removed after retreatment was shown by the Protaper retreatment file group, followed by Profile. 04 taper file group and the least was shown by the Hand K-file group. Statistical analysis of mean dentin removal between the three groups was found to be statistically significant in both bucco-lingual and mesio-distal views. The difference in mean dentin removed was found to be statistically significant between Protaper and Profile, Protaper and K-file, and Profile and K-file in both mesio-distal and bucco-lingual views.

The reason for Hand K-files showing least amount of dentin removed following retreatment may be due to the fact that manual instrumentation tend to remove gutta-percha in chunks and pieces and also due to the lesser taper of instruments.

Among all groups, Protaper retreatment system files showed maximum amount of dentin removal after retreatment. This is due to the fact that Protaper Retreatment instruments have progressive tapers and lengths which enable them to cut not only gutta-percha but also superficial layers of dentin during root filling removal.

In the present study, radiographic evaluation was the method used to evaluate the amount of dentin removal after retreatment. The main limitation of radiographic evaluation is that it provides a two dimensional information of a three dimensional object and the accuracy of a radiograph depends on many parameters. Further studies using three dimensional imaging like CBCT, CTscan will have to be done for accurate analysis of amount of dentin removal after retreatment.

Thus it can be concluded considering the limitations of the present study that hand k files removes less dentin compared to rotary Protaper Universal Retreatment System and Profile .04 files during retreatment.

CONCLUSION

Within the limitations of this in vitro study, it can be concluded that stainless steel hand K files removed significantly less dentin compared to rotary Protaper Universal Retreatment System and Profile .04 files during retreatment. Further, long term in-vivo studies and in vitro studies using advanced imaging technologies like CT scan and CBCT will also be necessary to evaluate the effect of various retreatment techniques on the root dentin