Journal of Conservative Dentistry

: 2006  |  Volume : 9  |  Issue : 4  |  Page : 134--139

Histological evaluation of the effectiveness of four instrumentation techniques for cleaning the apical third of root canals - An invitro study

Lalit Chandra Boruah, AC Bhuyan, R Kataki 
 Department of Conservative Dentistry & Endodontics, Regional Dental College, Guwahati, Assam, India

Correspondence Address:
Lalit Chandra Boruah
Department of Conservative Dentistry & Endodontics, Regional Dental College, Guwahati, Assam


The main objective of root canal preparation is to remove vital pulp tissue, residual necrotic materials , debris and infected dentin and thus eliminate most of the micro-organism from the root canal system. The present in vitro study was designed to compare the cleaning efficacy of K-Files (stainless steel), NiTi K- Files, ProTaper(Manual) & ProFile Rotary Systems in cleaning apical third of root canals.

How to cite this article:
Boruah LC, Bhuyan A C, Kataki R. Histological evaluation of the effectiveness of four instrumentation techniques for cleaning the apical third of root canals - An invitro study.J Conserv Dent 2006;9:134-139

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Boruah LC, Bhuyan A C, Kataki R. Histological evaluation of the effectiveness of four instrumentation techniques for cleaning the apical third of root canals - An invitro study. J Conserv Dent [serial online] 2006 [cited 2020 Jul 7 ];9:134-139
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" ...One of the important factor, which forms the foundation of successful root-treatment, is the manner in which the mechanical cleansing of the canal is carried out."

From Hofheinz RH: Dent Cosmos 34:182-186,1892 Bio-mechanical preparation of the root canal is a basic requirement of root canal treatment. Its aim consist of cleaning of root canal and its ramifications, removing most of debris to create ideal conditions, which lead to healing and tissue regeneration. The main objective of root canal preparation is to remove vital pulp tissue, residual necrotic materials debris and infected dentin and thus eliminate most of the micro-organism from the root canal system. (European society of endodontology 1994; American Association of Endodontics 1998).

Over the years a variety of instruments and techniques have been proposed to reach the goal of proper cleaning and shaping. Since optimal shaping and cleaning of root canals with manual files is one of the most difficult aspects, in recent years a greater awareness of the complexities of the root canal system has lead to the development of newer techniques, instruments and materials. These new developments have greatly enhanced the clinicians ability to achieve the mechanical and biological objectives of root canal treatment.

 Aims and Objectives

The present study was designed to compare the cleaning efficacy of K-Files (stainless steel), NiTi K-Files, ProTaper (Manual) & ProFile Rotary Systems in cleaning apical third of root canals.

 Materials and Methods

125 nos freshly extracted non-carious anterior teeth with complete roots and fully formed apices were collected for this study. After removal of stain, calculus & organic debris by ultrasonic scaling , sample teeth were stored in physiologic saline solution.

Conventional endodontic access cavity were prepared as applicable to particular tooth & patency of the canal was checked by a # 10 K-File.

Working length was determined by radiograph with a small K-File, inserted into the canal upto 0.5mm short of the anatomical length of tooth.

Experimental groups:

The sample teeth are divided into following 5 groups consisting of 25 samples each.

Stainless Steel hand K- files group (Step-back technique)

Nickel-Titanium hand K- tiles group(Step-back technique)

ProFile Rotary system files group (Crown-Down Technique)

ProTaper hand files group (Crown-Down technique)

Non-instrumentation group (Control Group)

Stainless steel K-file group

The root canals were prepared by STEP BACK­TECHNIQUE using K-Flexofile (Dentsply) with circumferential filing motion. Apical preparation was done at the WL with #15 through #25 tiles. Preparation was completed using step-back of 0.5mm increment. Recapitulation with a #25 file at WL was done after each larger file size.

NiTi K-File Group

Canals were prepared by step-back technique using NiTi files (Diadent).Apical preparation was done to # 35file. Preparation was completed using step-back of 0.5mm increment. Recapitulation with a#35 file at W L was done after each larger file size

ProFile rotary system group

Canals were prepared with ProFile rotary instruments (Dentsply)using crown-down technique. A gear reduction handpiece (Anthogyr NiTi control)was used Canal patency was established with a #15 S.S K-file. Orifice shapers #3 were used for coronal shaping (3-6mm from WL) followed by0.06/#25 & 0.06/#20 files until resistance was encountered(within 1-2 mm from WL). Apical shaping was done with 0.04/#20, 0.04#25 & 0.04/ #30 files to the WL.

ProTAPER (Hand) File group:

Canals were prepared with ProTaper (Hand) files (Dentsply) using crown-down technique. Canal patency was established with a #15 S.S. K-file. SI shaping file was used first& moved apicaly to 2mm short of WL. SX files were then used sequentially until resistance was encountered (4-5mm from WL) followed by S 1 &S2 for shaping of coronal 2/3rd. The apical 3 rd was finished by using F1,F2,F3 sequentially to the WL.

During all procedures the teeth remained wrapped by wet gauze. Irrigation was done with 5% NaOC1. The apical 5mm of sectioned root was stored in 10% Neutral Formalin. Decalcification was done with 5% Nitric acid. Serial cross sections of 6p at 1,2,3 mm were examined & evaluated under 100 X magnification.

Evaluation criteria:

The cross-sections are evaluated using a scale ranging from 0-3, adopted by Langeland et al. [9]

0 = the canal was cleaned in all around the section examined without pulptissue, predentin or debris.

1 = the canal was relatively cleaned with minor areas of predentin, pulptissue,or debris present in some part of the section.

2 = the canal contained some pulp tissue, predentin or debris in most or all part of the section.

3 = the canal contained major amount of pulp tissue, predentin debris in all around the section.

All the sections from Control group was established at scale 3.

 Results and Observations

[Table 1]


Over the years many instruments with varying designs made of different materials & with system oriented techniques were applied to achieve the mechanical &biological objective of root canal treatment. Though the instruments in conjugation with irrigation plays the major role in debridement still it will not sufficiently clean the complex root canal system. In the present study neither of the instrumentation techniques achieved total cleansing of root canal with pulp tissue remnants and debris on the dentinal walls. This finding is supported by study carried out (Heards & Walton [6] ; Siqueira Jr. et al [15] , Langeland K et a1 [9] ). Comparative studies between manual and rotary instruments in terms of cleaning efficacy have found that hand instrumentation leave more debris in all levels which is highest in the apical third (Amin N and De Bri E [3] 2001,Ahlquist et al [1] 2001).

From the observation in the present study, it was seen that the scores in different levels taken into account i.e. 1mm, 2mm, 3mm from apex were not always same in every sample. This was due to the fact that the original canal diameter and curvature and internal contour were not identical in all the levels. So contact between the instrument and canal wall was different in different areas each sample producing different scores. In our study Stainless steel K-flex file (Group I) and Nickel-Titanium K-­file (Group II) was found to be significantly different from ProTaper (Group Ill) and ProFile rotary system (Group IV). Group II was found to be least efficient in cleansing of apical third.

The cross-section of K-flex file (Group I) is rhombus shaped and with alternate sharp cutting edges and obtuse non-cutting edges which is considered to be beneficial (Weine [16] ). The step­-back technique using stainless steel K-Flex files (Group I) has been demonstrated to effectively clean and shape root canals, and better than NiTi K­-files (Group 11) in cleaning the apical third of root canals (Walton [17] ; Cimis Et at [4] ; Siqueira, Jr. et al [15] ). These findings are in agreement with the results in the present study. This may be correlated to the geometry of K-flex file with its increased ability to remove debris due to its alternating obtuse flute angle which provide a reservoir to collect canal debris (Miserenino [12] ; Newman et al [13] ). A possible cause of poor cleansing ability of Ni-Ti K-Files may be the lack of force applied to dentin laterally due to its increased flexibility. This may have less effect in canal wall cleaning and on the amount of debris left. It is thus justified to compare the root canal cleanliness achieved after instrumentation with conventional stainless steel instruments with nickel-titanium instruments of various design feature as well as different techniques.

ProTaper files have a continuously changing helical angle and pitch this balancing of pith and helical angles optimizes its debris removing capacity. ProTaper manual files (Group III) were found to be more efficient than those with a constant helical angle i.e. ProFile rotary system (Group TV), stainless steel K-Flex file (Group I) and Nickel Titanium K-Files (Group II) with reference to their debris removal ability justifies the finding of this study.

Profile rotary instruments in crown-down technique have been found to ProFile, a U file with three radial lands The U-shaped groove provides the space to accommodate dentin shavings while planning of the canal wall The 20° helical angle present in ProFile geometry was designed to remove the shaving debris coronally while the instrument rotates clockwise.

Research evaluating canal cleanliness has shown that preparation need to taper at least 0.08 mm/mm to ideally 0.10 mm/mm to ensure that a sufficient volume of irrigant can efficaciously circulate into canal anatomy (Allison et al [2] , Machtou et al [10] , McGreevey [11] ), so instruments with larger taper (ProFile Orifice Shapers, 0.06 and 0.04 tapers; ProTaper F 1 , F 2 , F 3 , with 0.07,0.08 & 0.09 tapers and S 1 , & S X , (1.2 tapers) and S 2 , (1.1 tapers) can be expected to result in a cleaner canal than stainless steel K-Flex and NiTi K-Files with aISO0.02 taper.

The cleaning efficacy of canal instrumentation has been evaluated either by a bacteriologic method or by observing remaining tissue debris In the present study, cleansing of the root canals were evaluated for tissue remnants, pre-dentin, or debris using a numerical scale ranging from 0-3, adopted by Langeland et al [9] . This criterion also was used in other studies (Reynolds et al [13] ; Siqueria J F et al [14] 1997).Debris is defined as dentin chips, and residual vital or necrotic pulp tissue attached to root canal wall (Hulsmann et al [8] ). Particles or chips of any structure on the surface of the root canal were judged as debris (Wu & Wesselink [18] ).

The presence or absence of the predentin layer may not be a good monitor of instrument effectiveness (Hill RL et al [7] ) In our study also some of the teeth were obviously from older individuals and had no predentin layer to evaluate. In such cases scoring was done comparing the remaining pulp tissue and debris. In studies considering degrees of cleanliness and instrumentation techniques, there are several options available to the examiner. A cross sectional view would permit an evaluation of lateral canals and isthmuses and other accessory anatomy that may be present which is of greater clinical importance.

All histological sections used for analysis were free of artifacts and had an intact, undistorted root canal outline. Cross sections at 1,2 and 3 mm from the apex of each root were examined in a microscope attached to an imaging software (M Otic imaging system) under 100 X magnifications.

The use of light microscope at magnification up to 200X allows the detection of fragments of pulpal or dentinal debris and a large surface area of the canal wall (Goldman et al [5] , Wu & Wesselink [18] ). The residual pulp tissue was observed as non descript heterogeneous mass. Photographs captured with this software were with high resolution and contrast, which gives highly predictable results. Interpretations of the sections were performed by two examiners to avoid the bias in numerical scale for each of the examined sections.

Although in our study we did not account for smear layer; in cross sectional studies like the present one it is not generally possible to get an overview of dentinal tubules for smear layer in histological sections of 6m width. The variation and complexity of canal anatomy makes it hard to achieve complete canal instrumentation. Probably, neither by using mechanical instrumentation nor by chemical agents, we can ensure that complete instrumentation has been achieved. Root canals are irregular complicated systems that are difficult to clean and shape. These problems have resulted in a wide search for innovative materials, instruments, and techniques to obtain a clean, disinfected, debris free canal for obturation. With new instruments shaping procedure can be completed more easily, quickly, and predictably; but effective cleaning of the entire root canal is still challenging.


None of the instrumentation technique can clean the apical third completely. Average remaining debris score was lowest in ProTaper (Crown-down technique) followed by Profile (Crown-down technique), Stainless steel K-flex files & NiTi K-file (Step back technique). Stainless Steel K-Flex files & Nickel-Titanium K-files with step-back technique resulted higher remaining debris than ProTaper &Profiles with crown-down technique which is statistically significant (p<0.05).There was no statistically significant difference in between ProTaper and Profile intrumentations and in between Stainless Steel K-Flex files & Nickel­-Titanium K-files.

Further studies are required to make a final judgment about the effect of various instrumentation techniques on root canal cleaning achieved in the apical third.[Figure 1]


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