Comparative Evaluation of Apical Extrusion of Bacteria Using Two Rotary Systems -an in -vitro study

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Comparative Evaluation of Apical Extrusion of Bacteria Using Two Rotary Systems –An in -vitro study”.

Authors: Dr. Sheetal Ghivari, Dr.Girish Kubasad.


Aim: To evaluate and measure the bacteria extruded apically during root canal preparation using two rotary instrumentation techniques.

Material method: Forty freshly extracted mandibular premolars were mounted in bacterial collection apparatus after standard access cavity preparation. Root canals were contaminated with the pure culture of E. fecalis (ATCC 29212) and dried at 370 C for 24 hours. After root canal instrumentation bacteria extruded were collected, incubated in brain heart infusion agar for 24 hours at 36 degrees and the colony forming units (CFU) of bacteria counted.

Statistical Analysis: The data analyzed statistically to determine the mean difference between the groups. The mean number of bacteria extruded was within the group and between the group calculated by Students t test.

Results: The K-3 system extruded higher number of bacteria compared to M-two system.

Conclusion: All instrumentation techniques are associated with the extrusion of debris, irrigant and bacteria in periapical area. It is prudent on part of clinician to select the instrumentation techniques which extrude least number of bacteria to prevent flare –up phenomena.

Key words: Bacteria, Apical extrusion, rotary systems.


The goals of endodontic instrumentation include thorough debridement and disinfection of root canal system. In an effort to achieve these goals debris such as dentinal filings, necrotic pulp tissue, bacteria and their products may be extruded from apical foramen into the periradicular region which has been referred to as ‘worm of necrotic debris’. This has been related to periapical inflammation and postoperative flare-ups. (1)

Bacteria extruded from the root canal are mainly gram positive, gram negative and obligate anaerobes.(2) Enterococcus fecalis, Propionibacterium Alactolyticus, Propionibacterium Propionicum were found in root canal failure cases.(3) Recently Enterococcus fecalis has been identified as a species most commonly recovered from post treatment disease.

Seltzer S and Naidrof 1(1985), Tanlap J et al 4(2006) studied the immunological aspects of post operative flare-ups and concluded that antigens originating from root canal result in the formation of antigen-antibody complex when forced beyond the apical foramen, which may lead to severe inflammatory response. The intensity of inflammatory response will depend on the number (quantitative factor) and virulence (qualitative factor) of bacteria.5

Er et al 6 and Kustarci A et al 7 reported that the intracanal bacteria can be extruded apically along with debris, during instrumentation utilizing a new experimental model.

Engine driven Nickel titanium instruments are shown to prepare the root canal rapidly and maintain the canal shape and working length with few aberrations during root canal preparation. K-3 instruments have positive rake angle in combination with radial land relief and asymmetrical cross section. Recently M-two a new instrumentation system has been introduced which has cross section design resembles that of S-files, no radial lands, progressive blade pitch and non cutting tip.

Various studies have been used in the past in evaluating the apical extrusion of debris and irrigant and but very few studies are reported in the literature about bacteria extrusion using an experimental model.

Material and method:

A total of forty freshly extracted human mandibular premolars were used for the study.

Teeth with complete root formation , having single canal and mature apical foramen, length of roots approx 21mm,canal curvature between 0-10 degrees ,apical diameter confirming to #15 K- file were selected. Teeth were observed under stereomicroscope and digital radiographs in buccal and proximal directions to determine the presence of single canal.

Test apparatus to determine apical extrusion of intracanal bacteria was shown in figure .1. The tooth was forced through the rubber stopper of a vial after endodontic access cavity preparation. The rubber stopper with the tooth was then fitted into the mouth of a vial. Two coats of nail varnish applied to the external surface of the root and than fitted into mouth of the vial. 23 gauge needle was placed into the mouth of the vial to equalize the air pressure. Entire apparatus was then sterilized in an autoclave.

Before experiment the vial was filled with normal saline solution. The hole was created in nail varnish that covered the apical foramen using #10 K-file. In this way, standard size foramen and apical patency was achieved. The tooth with rubber stopper needle unit was placed into the mouth of the vial. The same procedure was repeated to all experimental teeth.

A pure culture of E.fecalis (ATCC 29212) was used to contaminate the root canal. Suspension was prepared by adding 1ml of pure culture of E-fecalis grown in brain-heart infusion broth for 24 hour to fresh brain heart infusion broth. The McFarland standard number 0.5 was used to evaluate the broth to ensure that number of bacteria was 1.5 x 108 colony forming units (CFU) m1-1. Root canal was completely filled with the E-faecalis suspension. During incubation, canals were hand instrumented with 10 K-file to carry the bacteria down the length of the canal. The contaminated root canal was dried at 370 C for 24 hours.

Single operator, using aseptic techniques, carried out the preparation and sampling procedures on each specimen under a classI laminar airflow cabinet to prevent airborne bacterial contamination. The crown down technique was used during instrumentation process , 1ml of distilled water was used after each instrument change. Apical preparation was done till #30 file in all instrumentation techniques.

Group I- Instrumentation with M-two Ni-Ti rotary instruments were used at 300 rpm. The standard set for this system includes four instruments with variable tip sizes ranging from #10 to #25, and tapers ranging from .04 to .06 (size 10/.04 taper, size15/.05 taper, size 20/.06 taper, size 25/.06 taper).

A glide path has been established with a #10 stainless steel K-type file/ All instruments were taken to the working length (WL) with light apical pressure. M-two instruments are used in a simultaneous technique without any early coronal enlargement.

Group II- Canals were prepared with 0.12 taper K-3 instrument to the resistance followed by 0.10 taper and 0.08 taper instruments. Canals were further prepared with 0.06 taper #45 K-3 instruments to the resistance from largest instrument to smallest reaching the working length. After middle third scouting with #10 K-files #40,#35,#30 K-3 instruments are used in crown down fashion till the working length. Apical patency was established with #10 K-file after each rotary instrument and irrigated with 1ml of distilled water after each instrument change.

Subsequently after root canal preparation 0.1ml of saline was taken from experimental vial in order to count the bacteria and incubated in Brain-heart infusion agar at 370 C for 24 hours. Colonies of bacteria were counted using a colony counter ((Yarco colony counter) by a classical bacterial counting technique given by Collins et al 8 (1995) and results were given as number of CFU ml-1.

Table 1. Mean number of apically extruded intracanal bacteria




Std. Deviation

Std. Error Mean

Group A





Group B





Table 2




Mean Difference

Std. Error Difference

95% Confidence Interval of the Difference











Table 2: Comparison of number of bacteria extruded within the groups.
Results: Data regarding the number of bacteria extruded are presented in table 1. The results indicated that both the instruments tested caused a measurable apical extrusion of bacteria.

The K-3 system extruded significantly more amounts of bacteria (fig 2) as compared to M-two system (0.000S, p<0.05) (Fig 3).There is a statistically significant difference found in number of bacteria extruded between both the groups.


The major reason for Endodontic flare-up is extrusion of debris present within and created during the instrumentation of root canal system. Endodontic flare up is characterized by swelling, pain and discomfort which commences within few hours or a days after root canal procedures and require an emergency treatment. (9,10)

Shovelton DS11, Seltzer and Naidorf 1, Sequiria 12 have reported that along with debris, the bacteria are also extruded through the apical foramen. The number of bacteria extruded apically has a direct correlation with weight of debris (quantitative factor), type and virulence of bacteria (qualitative factor).

Naidorf (1985)13 Studied the immunological aspects of flare-ups and stated that an antigen-antibody complex forms when canal contents containing antigens are pushed through apical foramen and react with the immunoglobulin (antibodies) present in the periapical area. This causes damage to cell membrane resulting in series of immunological reactions that ultimately cause pain.14

The aim of present study was to access extrusion of intracanal bacteria as a result of canal shaping by two rotary instrumentation techniques. Methodology employed in this study was described by Er et al (2005).The amount, type of irrigant and operator is common to all techniques. Enterococcus fecalis was chosen as the bacteriological marker because it can survive alone without symbiotic support from other bacteria.

In this study K-3 system (Group II) extruded more bacteria because of it’s instrument design. The presence of variable helix angle and pitch, slightly positive rake angle, asymmetrical cross-sectional design, and presence of three radial lands with relief behind two radial lands produce more amount of debris during root canal preparation. In M-two (Group I) system instrument design has some variation, the distance between the cutting blades increases from the instrument tip to the shaft and the pitch is progressive. The space for dentin removal is deeper at the back of the blade. This reduces the risk of apical extrusion. 15

The results of present study were in accordance with Adl et al in which M-two extruded less debris as compared to Flex-master instrument. The variation in apical extrusion of bacteria among two groups is related to their instrument design and technique of use. K-3 is used in crown down method where as M-two system used in single length technique thus it extruded less debris. 16

Every effort should be made to limit the periapical extrusion of intracanal material during treatment which has the potential to bring about serious systemic disease such as endocarditis, brain abscess and septicemia, particularly in compromised patients. Further in-vivo research in this direction could provide more insight into the biologic factors associated with correlations and consequences of apically extruded debris and may focus on bacterial species that essentially play a major role in post instrumentation flare-ups.

Conclusion: Among the engine driven techniques (M two & K-3 system),

K-3 technique extruded highest number of bacteria and M-two system extruded the least. Further more in vivo research should be focused on type microorganism associated with flare–up and associated biological consequences.


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