An Ex Vivo Evaluation of Antimicrobial Efficacy of Root Canal Preparation With Hand K-Files, Hand Pro Taper, and Pro Taper Rotary Files.

BACKGROUND: Microorganisms are considered to be the primary cause behind persistent pulpoperiapical pathologies as well as endodontic failures. It has been found that Enterococcus faecalis is one of the most commonly isolated organisms in failed endodontic treatment. Proper and appropriate mechanical instrumentation is necessary to eradicate these microorganisms. AIMS AND
OBJECTIVES: The aim of this study was to compare antimicrobial efficacy of various root canal instrumentation techniques. This study was designed to compare antimicrobial efficacy of root canal preparation using hand K-files, hand Pro Taper files, and Pro Taper rotary files.
MATERIALS AND METHODS: Forty intact maxillary premolars extracted for orthodontic reasons were used. After extirpation of pulp, teeth are decoronated and autoclaved. Then the root canals were infected with E. faecalis suspension and the teeth were incubated at 37°C for 24 h. Thereafter the teeth were divided into five groups and were prepared using the following instruments: group 1 (hand K-files), group 2 (hand Pro Taper files), group 3 (Pro Taper rotary files), group 4 (Control I; treatment consists of irrigation with 1 mL of sterile physiological saline with no instrumentation), and group 5 (Control II; teeth received no treatment at all). Before and after treatments, samples were taken from the root canals for culture and were transferred to physiological saline. Results were evaluated after 24-h incubation in selective culture medium.
RESULTS: The results showed that the teeth prepared with Pro Taper rotary files showed significant reduction in number of bacteria from the root canals.

INTRODUCTION

One of the goals of endodontic therapy is the reduction or elimination of bacteria and their by-products from the root canal system. Proper cleaning, shaping, and irrigation have been shown to significantly reduce and sometimes eliminate bacteria from canals.[1] Several studies show that two major causes of endodontic failures were imperfect instrumentation and incomplete obturation. Incomplete obturation may be the result of inadequate instrumentation also.[2] Once the canal is prepared, it should have a uniformly tapered funnel shape increasing in diameter from the end point to the orifice; this shape provides enough space for the irrigants that are important to complete the canal cleaning and allows the placement of effective root filling.

Canal shaping is relatively easy in straight root but has always been challenging, demanding a high skill, when performed in curved roots.[3] This difference is a result of the stiffness of stainless-steel files, which are able to follow canal curvatures without developing high lateral forces responsible for canal straightening and aberrations.[4] With the creation of superelastic nickel–titanium (NiTi) instruments, achieving a correct canal shape appears to be more predictable and safe. Several studies demonstrate that compared with instrumentation by stainless-steel files, NiTi mechanical preparations are faster, more centered in canal lumen, rounder, and better maintained in their original anatomy.[5]

Pro Taper files introduce a new design with progressively increasing taper, a convex triangular section, and a modified guiding tip. Working time required by Pro Taper files was significantly shorter. Pro Taper files cut in less time as a result of more aggressive triangular flute section.

Regarding working safety and better instrumentation, canal alteration did not occur confirming again the ability of NiTi instruments to respect canal anatomy.[6] Hence, this study was designed to compare the eventual differences in the cleaning efficacy using traditional K-files, hand Pro Taper files, and Pro Taper rotary files using standardized technique.

For this purpose, the root canals of extracted human teeth were infected with Enterococcus faecalis, and after standardized canal preparation technique, the canals were evaluated for the number of colonies of the remaining microorganisms.[7]

MATERIALS AND METHODS

Source of data

40 intact human maxillary upper premolars

Hand K-files (Mani files, Japan)

Pro Taper hand files (Dentsply Switzerland)

Pro Taper rotary files (Dentsply files)

Stock culture of E. faecalis (Department of Microbiology, Yenepoya Dental College, Mangalore)

Method of collection of data

Inclusion criteria

Freshly extracted maxillary premolar for orthodontic reasons

Non-carious tooth

Exclusion criteria

Carious tooth

Hypoplastic tooth

Forty intact maxillary premolars extracted for orthodontic reasons were used in our study. After pulpectomy, teeth were decoronated and autoclaved. A 24-h broth culture of E. faecalis was prepared in peptone water and used as the inoculum. Each root canal was flushed (inoculated) with 10 µL of broth culture under standardized conditions. These teeth with infected canals were then dropped in sterile test tubes and incubated at 37°C for 24 h. At the end of 24 h, the teeth were allocated into five groups by random sampling.

Teeth were taken out from test tubes and the canal sampling was performed using No. 15 paper points. These paper point samples were immediately transferred to 5 mL of sterile physiological saline. Group 1 canals were subjected to instrumentation with hand K-files using step-back technique; group 2 canals were subjected to instrumentation with Pro Taper hand files; group 3 canals were subjected to instrumentation with Pro Taper rotary files and were irrigated with 1 mL of sterile saline; in group4, no instrumentation was performed, only irrigation was performed with saline; and group 5 canals were not prepared at all. After treatment, sampling of canals was carried out using paper points and immediately these were transferred to 5 mL of sterile physiological saline. The paper points collected before and after treatment of canals were cultured into solid medium. Physiological saline (5µL; with paper points) was pipetted and streaked onto blood agar plates. These plates were incubated for 48 or 24 h at 37°C under aerobic conditions. The number of colonies was counted using a colony counter.

Statistical analysis

The reduction in colony counts before and after the treatment were compared among the five groups. Results were statistically evaluated using the Kruskal–Wallis test. All the five groups were compared for bacterial reduction by using Kruskal–Wallis test and there was significant difference in bacterial reduction between five groups. To show the difference between two groups, a Mann–Whitney U test was used.

RESULTS

Using Kruskal–Wallis test, the mean bacterial reduction was least in no treatment group (group 5), and it was maximum in Pro Taper rotary files (group 3), followed by Pro Taper hand files (group 2), K-files (group 1), and only irrigation group [Table 1].

Table 1

Bacterial reduction in different groups

	N		Mean	Standard deviation
Hand K-files	8		2.75	0.462
Pro Taper hand files	8		3.75	0.463
Pro Taper rotary files	8		4.75	0.463
Saline irrigation	8		1.75	0.886
No treatment	8		1.00	0.000
Total	40
Kruskal–Wallis test = 35.142		P = 0.001 sig

To show the difference between two groups, we used Mann–Whitney U test. The tables are summarized as follows.

Hand K-files show significant difference with Pro Taper hand files (0.003), Pro Taper rotary files (0.0005), saline (0.003), and no treatment group (0.027) [Table 2].

Table 2

Mann–Whitney U test for hand K-files (group 1)

	Mann–Whitney U test	P value
Hand K-files vs. Pro Taper hand files	−3	0.003 (s)
Hand K-files vs. Pro Taper rotary files	−3.486	0.0005 (vhs)
Hand K-files vs. saline	−2.928	0.003 (hs)
Hand K-files vs. no treatment	−2.213	0.027 (s)

hs = highly significant, s = significant, vhs = very highly significant

Pro Taper hand files show significant difference when compared with Pro Taper rotary files (0.003), saline (0.001), and no treatment (0.0005) group in bacterial reduction [Table 3].

Table 3

Mann–Whitney U test for Pro Taper hand files (group 2)

	Mann–Whitney U test	P value
Pro Taper hand files vs. Pro Taper rotary	−3.009	0.003 (hs)
Pro Taper hand files vs. saline	−3.289	0.001 (hs)
Pro Taper hand files vs. no treatment	−3.703	0.0005 (vhs)

hs = highly significant, vhs = very highly significant

Pro Taper rotary files show difference when comparing with saline (0.0005) and no treatment (0.0005) group in bacterial reduction [Table 4].

Table 4

Mann−Whitney U test for Pro Taper rotary files (group 3)

	Mann–Whitney U test	P value
Pro Taper rotary files vs. saline	−3.703	0.0005 (vhs)
Pro Taper rotary files vs. no treatment	−3.703	0.0005 (vhs)
Saline irrigation vs. no treatment	−2.213	0.027 (s)

s = significant, vhs = very highly significant

Saline irrigation when compared with no treatment group shows significant difference in bacterial reduction [Table 5].

Table 5

Mann−Whitney U test for saline irrigation only (group 4)

	Mann–Whitney U test	P value
Saline irrigation vs. no treatment	−2.213	0.027 (s)

s = significant

DISCUSSION

Successful endodontic therapy is dependent on the practitioner’s ability to safely and effectively debride and shape the root canal system and thus eliminate infection. Many new instrument systems and instrumentation techniques have been introduced to the profession that has not been thoroughly evaluated.

E. faecalis is a facultative gram-positive organism often present in persistent endodontic infections.[8] This bacterium was chosen because of the following reasons: it is heat resistant and can survive at 600°C for 30 min; it has ability to multiply after standard chemo-mechanical procedures; it survives under unusual environmental stresses; it is resistant to medications used during root canal therapy; and it is easy to culture and multiply.

K-file was chosen as a comparative technique because it is frequently taught in dental schools and is commonly used by many practitioners. Walton et al.[9] using stainless-steel K-type files showed that step back filing was the most effective method in removing debris and a layer of dentine from the pulp walls compared with other hand instrumentation techniques. Luiten et al. reported that most instrumentation techniques with stainless-steel instruments in curved canals result in apical transportation.[10] It can be hypothesized that the hand instrumentation left the possibility of the canal space being inadequately debrided of vital or necrotic pulp tissue, which might result in inadequate obturation of root canal space. In this study, it was found that hand K-files showed less effectiveness against bacterial reduction when compared to Pro Taper hand and Pro Taper rotary files.

Pro Taper hand files provide a relatively cheap and efficient system for clinicians venturing into the world of NiTi and variable tapered instrumentation. Hence in this study, Pro Taper hand files are used. The “Archimedes Screw” action may also pull debris and bacteria out of canals during instrumentation, resulting in cleaner canals.[6] Zualo et al. in their study on endodontic complications of root canal therapy when using stainless-steel K-files and NiTi hand files concluded that deviation of apical third of canals and bacterial reduction were significantly reduced by the use of NiTi hand files.[11] Results of this study suggest Pro Taper hand (NiTi) files are effective against E. faecalis when compared to stainless-steel K-files,[11] but less effective in comparison to Pro Taper rotary files.

Pro Taper rotary files introduce a new design with progressively increasing taper, a convex triangular section, and a modified guiding tip.[6] Hence in this comparative study, Pro Taper rotary files are introduced against hand K-files and Pro Taper hand files. Glossen et al. also suggested that it produces significantly less transportation when compared with stainless-steel instruments used in a balanced force technique.[5] Jeffry et al.[12] in their study of comparison of NiTi instrument systems with hand files on their effect of canal transportation and bacterial reduction concluded that NiTi systems remained to be better centered in the canal than in stainless-steel hand files. The NiTi systems were all faster and effective in bacterial reduction than hand filing.[12]

In this study, Pro Taper rotary files showed significantly higher efficiency against E. faecalis when compared to stainless-steel K-files and Pro Taper hand files. The primary difference between Pro Taper rotary and hand files concerns on their degree of taper. The transportation caused by these rotary instruments is extremely low in relation to standard filing techniques. This investigation go in accordance with the results of several other authors that instrumentation times or other performance outcomes with Pro Taper rotary files are substantially better than H- and K-files and Pro Taper hand files.

In contrast to this study, Dalton et al.[13] in their study suggested that on comparing intracanal bacterial reduction of teeth instrumented with NiTi and stainless-steel K-files using sterile saline irrigation both types of instrumentation were not significantly different in their ability to reduce intracanal bacteria.[13] A similar contrast study by Ahalguist et al.[14] concluded that manual technique used produced cleaner root canals than rotary technique.[14]

Although instrumentation is indispensable for a significant reduction in bacterium content, in this study the physiological saline irrigation per se yielded a slight reduction in bacterial population; it obviously cannot be accounted for by chemical action but it likely occurred owing to the rinsing effect. The instrumentation proved to be definitely effective.[15] In this manner, not only the canal surface is cleaned from bacteria, but the number of bacteria penetrated into the dentinal tubules can also be diminished.

CONCLUSION

Although all of the instrumentation yielded marked reductions in bacterial content, a total absence of bacteria could not be achieved by mechanical preparation. These results underline the necessity for the use of other chemical irrigants (sodium hypochlorite) and the strongly alkaline calcium hydroxide as an intracanal medicament.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.