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Pediatric Dental Journal

journal homepage: www.elsevier .com/locate /pdj

Original Article

Determination of H-file sizes being more suitablefor measuring of working length in immature teethusing an EAL

Michiyo Miyashin

Pediatric Dentistry, Department of Oral Health Sciences, Division of Medical and Dental Sciences, Graduate School,

Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan

a r t i c l e i n f o

Article history:

Received 15 October 2013

Received in revised form

24 December 2013

Accepted 29 January 2014

Keywords:

H-file size

Working length

Root canal treatment

Immature permanent teeth

Electronic apex locator

E-mail address: [email protected]

Please cite this article in press as: Miyaslength in immature teeth using an EAL, P

http://dx.doi.org/10.1016/j.pdj.2014.01.0040917-2394/Copyright ª 2014 The Japanese So

a b s t r a c t

Successful root canal treatments of immature permanent teeth require data on the exact

working length (W.L.) for the preparation of root canal in the clinic. The author and col-

leagues have previously reported that root canal length of an immature tooth can be

measured using an electronic apex locator (EAL; Apit 11�, Osada Electric Co., Ltd., Tokyo,

Japan) in in vitro experiments. This study aimed to find the sizes of H-files that are more

suitable for root canal length measurements of immature teeth using Apit 11�. Extracted

human immature permanent teeth were prepared to have accesses to their pulp cavities,

and the root canal length of each tooth was measured physically and electronically using

H-files, rular and Apit 11� in the in vitro experimental system. Six types of file diameters

that are generally utilised in the clinic were used to take measurements in order to observe

the relationship between the position of the file tip and the meter-indicated area. The

results suggest that, of the H-files of sizes No. 10 to No. 70, No. 15 is probably the most

reliable to locate the apical foramen when it is used with Apit 11�.

Copyright ª 2014 The Japanese Society of Pediatric Dentistry. Published by Elsevier Ltd. All

rights reserved.

1. Introduction

Removal of the pulp tissue and necrotic dentine in a root canal

is essential for the success of endodontic therapy [1]. This is

achievable first and foremost if the root canal length has been

accurately determined in the clinic. Electronic apex locators

(EALs), which are electric root canal length measurement

apparatuses, offer the possibility of ready, comfortable, ac-

curate, safe and painless use, and they are able to reduce the

number of X-ray photographs of the patient that need to be

.

hin M, Determination oediatric Dental Journal

ciety of Pediatric Dentist

taken with a dose of ionising radiation [2]. However, it has

been reported that some EALs have failed to obtain accurate

results with immature permanent teeth with broad apical

foramens [3,4]. In a previous report, the author and my col-

leagues have suggested that the Apit 11� (Osada Electric Co.,

Ltd., Tokyo, Japan), which is an EAL, could be useful for root

canal length measurements of immature teeth with apical

foramen diameters of 1e3 mm. However, files of different

sizes gave different meter-indicated areas when the file tip

reached the apical foramen in the in vitro experimental system

f H-file sizes being more suitable for measuring of working(2014), http://dx.doi.org/10.1016/j.pdj.2014.01.004

ry. Published by Elsevier Ltd. All rights reserved.

mailto:[email protected]

www.sciencedirect.com/science/journal/09172394

www.elsevier.com/locate/pdj

http://dx.doi.org/10.1016/j.pdj.2014.01.004



p e d i a t r i c d e n t a l j o u r n a l x x x ( 2 0 1 4 ) 1e52

[5]. This study, therefore, aimed to find the sizes in diameters

of H-files that are more suitable for root canal length mea-

surements of immature permanent teeth using an EAL;

Apit 11�.

2. Materials and methods

The sample included 20 human immature permanent teeth

with single root, free of caries and fractures and with di-

ameters of the apical foramen of 1e3 mm. Their stages of root

development were from three-fourths of root completed to

root almost completed with open apex. The teeth were

extracted for the orthodontic treatment after obtaining

informed consent from the patients or the patient’s parents.

Pulp cavities of the sample teeth were accessed from the

coronal side in order to prepare the root canal and they were

stored in saline and kept in a refrigerator at 4 �C.H-files (28-mm long, stainless steel; by Zipperer) of sizes

No. 10, No. 15, No. 20, No. 30, No. 50 and No. 70 were used for

the root length measurements. The actual root canal length

was recorded by inserting the No. 10 H-file to the apical fora-

men from the incisal reference point. Thereafter, the length

from the tip to the incisal reference point was measured with

calipers. A rubber stopper was fitted to a position that corre-

sponded to a certain distance from the file tip so that the tip of

the measuring file would reach fixed positions in 1-mm in-

crements from 3 mm inside (�3 mm) to 1 mm outside

(þ1 mm) the apex of each tooth.

An EAL; Apit 11� was used for themeasurement of the root

canal length in accordance with the manufacturer’s in-

structions and set to the auto-adjustment mode.

For the experimental device, the tooth was securely fixed

in an acrylic box filled with saline solution so as to have the

full length of the root soaked in saline solution. Consequently,

the full length of the root canal was automatically filled with

saline. In addition, the Lip Clip (neutral electrode) of the Apit

11� was also securely fixed in the saline solution of the acrylic

box (Fig. 1). The file fitted with the metal clip (Apit 7� File

Holder) of the Apit 11� was inserted into the root canal from

the access opening and advanced in the apical direction in

order to confirm first on the meter display that the zero-point

Fig. 1 e Experimental model for electronic apical location.

Please cite this article in press as: Miyashin M, Determination olength in immature teeth using an EAL, Pediatric Dental Journal

adjustment was being performed automatically. Then, the

meter-indicated area of the Apit 11�was recorded at the point

where the rubber stopper reached an incisal reference point.

Fig. 2 represents themeter-indicated areas and these included

three areas: an area to the left of the working length (W.L.;

LW), an area of W.L. to APEX (WL) and an area to the right of

APEX (RA).

3. Results

Fig. 3e8 show the results of Apit 11� measurements using H-

files of six types. The horizontal axis in each graph is the

meter-indicated area of the Apit 11� and the vertical axis

represents the number of teeth. For the position of the file tip

in relation to the apical foramen, 0 indicates the file tip being

just on the position of the apical foramen.

When comparing these graphs, the greater-sized files

tended to have decreased numbers of teeth in which the in-

dicator moved into the LW area, and increased numbers of

teeth in which the indicator moved into the WL area. When

the file tip comes outside from the root canal to 1 mm beyond

the apical foramen, the indicator of Apit 11� moved into the

RA area in every case. However, when the file tip comes just on

the apical foramen, the indicator of Apit 11� remains in the

WL area in some cases except when using files No. 15 and No.

30.When the file tip remained inside the root canal at 1 mm

from the apical foramen, it was theoretically expected that the

indicator would move into the WL area in every case. How-

ever, the indicator moved into the RA area in some cases of

every file size utilised in this experiment. However, the

number of such cases was minimumwhen the No. 15 file was

used: the indicator moved into the RA area in two out of 20

cases. When the file tip remained inside the root canal at 3

mm from the apical foramen, the indicator of Apit 11�

remained in the WL area in every case with No. 10 and No. 15

files.

The usability of the Apit 11� during measurements was

characterised by the auto-adjust being sharply attained by the

No. 15 and No. 20 files. However, in five teeth, the auto-adjust

reacted poorly with the No. 50 and No. 70 files, which had two

teeth and three teeth, respectively. In these cases, the

adjustment button was pressed to run for zero-point

adjustment.

Fig. 2 e Division of area on digital display of APIT11�. LW

area: an area to the left of W.L.; WL area: an area W.L. to

APEX; and RA area: an area to the right of APEX.




Fig. 3 e The measurement results using the No. 10 H-file.

The horizontal axis of the graphs is the meter-indicated

area of the Apit11� and the vertical axis represents the

number of teeth. For the position of the file tip in relation to

the apical foramen, L3 indicates that the file tip remains

inside the root canal at 3 mm from the apical foramen, D1

indicates that the file tip comes outside from the root canal

to 1 mm beyond the apical foramen and 0 indicates that

the file tip being just on the position of the apical foramen.


p e d i a t r i c d e n t a l j o u rn a l x x x ( 2 0 1 4 ) 1e5 3

4. Discussion

For more than 50 years, EALs have been used for locating the

root canal terminus in the clinic [6,7]. For root canal treat-

ment, the use of an EAL is recommended followed by the

confirmation of canal length with undistorted X-ray photo-

graphs and files [3,4]. For immature permanent teeth with

open apices, the preparation of the root canal has been carried

out through to the X-ray photographic apex [8]. However,

some studies have pointed out that an EAL does not give ac-

curate results in immature permanent teeth with wide open

apices above size No. 90 (diameter 0.9 mm) [3,4,9]. Therefore,

in this study, the samples that were selected were teeth with

an apical foramen diameter of 1 mm or more. The maximal

diameter of the sample teeth was 3 mm.



With the Apit 11�, measurements can be obtained under

the relative value method using two different measuring fre-

quencies (1 kHz and 5 kHz) to detect the apical constriction

[10]. Fig. 2 shows the coloured-liquid crystal display of the

device. The W.L. is a marker indicating a position of 0.7 mm

from the apical foramen in the root canal for mature perma-

nent teeth according to the instruction manual. This position

is an indicator of the W.L. for the preparation of root canal in

adults. The APEX is a marker indicating the position of the

apical foramen for mature permanent teeth. Other scale

marks are the points in between W.L. and APEX and have not

been quantified.

In a previous report, we used a similar experimental model

in which a No. 15 H-file was connected to the Apit 11� to take

measurements of the W.L. of root canals of immature per-

manent teeth. The H-file is recommended for endodontics for

immature teeth [11,12]. When the file tip was set to be just on

the position of the apical foramen, the indicator of the Apit

11� pointed the APEX marker on the meter panel [5].

These results will support the following report in which

Apit 11� and H-files were used for the W.L. measurements of

immature permanent teeth in the clinic [4]. When the indi-

cator of Apit 11� pointed the APEX marker during






p e d i a t r i c d e n t a l j o u r n a l x x x ( 2 0 1 4 ) 1e54

instrumentation of the No. 15 H-file in the root canal, the W.L.

was measured according to the ordinary procedure. Then, a

gutta-percha point cut to the W.L. was inserted into the root

canal and X-ray photographs were taken. The X-ray photo-

graphs suggested that the W.L. measurements with this sys-

tem could be proper and useful in the clinic.

It has been reported that, in some instances, the mea-

surement value of the EAL is affected by the size of the mea-

surement file used, the diameters of the apical foramina and

so forth [9,10]. The H-file is recommended for the endodontic

treatment of immature permanent teeth [11,12]. Therefore, in

the present study, H-files of multiple sizes were used for the

root canal length measurements in order to determine the

accuracy in each size of file. As a result, files of different sizes

showed different meter-indicated areas even though the file

tips were on the same position. However, among the files of

different sizes, the No. 15 H-file showed minimum number of

cases in which the indicator of Apit 11� moved into a wrong

meter-indicated area. It is, therefore, suggested that the No. 15

H-file is the most suitable measuring file for detecting the

apical foramen with Apit 11� at the meter-indicated APEX.

Other sizes of files offered less of a relationship between the

position of the file tip and a specific meter-indicated area, and

they were thus assessed as being of less significance as

measuring files.



The present report would confirm the opinion by Angwar-

avong and Panitvisai that EALs offer the possibility of ready,

comfortable, accurate, safe and painless use, and they are able

to reduce the number of X-ray photographs of the patient that

need to be taken with a dose of ionising radiation [2].

Further clinical researches are needed to provide higher

accuracy in the W.L. determination by the Apit 11� in imma-

ture permanent teeth with the apical foramen of diameter

larger than 3 mm, and to evaluate the use of other apex lo-

cators and instruments.

5. Conclusions

With the aim to find the sizes of H-files that are more suitable

for root canal length measurements of immature teeth using

Apit 11�, the root canal lengths of extracted human immature

permanent teeth weremeasured physically and electronically

using H-files, rular and Apit 11� in the in vitro experimental

system. Six types of file diameters that are generally utilised in

the clinic were used to takemeasurements in order to observe

the relationship between the position of the file tip and the

meter-indicated area. The results suggest that, of the H-files in

the size No. 10 to No. 70, the No. 15 H-file is probably the most

reliable to locate the apical foramen.

Acknowledgements

I express my sincere gratitude to Emeritus Professor Yuzo

Takagi of TokyoMedical andDental University for his valuable

instructions and proofreading.

Appendix A. Supplementary data

Supplementary data associated with this article can be found

in the online version at doi:10.1016/j.pdj.2014.01.004.

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[3] Dummer PM, McGinn JH, Rees DG. The position andtopography of the apical canal constriction and apicalforamen. Int Endod J 1984;17:192e8.

[4] Moore A, Howley MF, O’Connell AC. Treatment of open apexteeth using two types of white mineral trioxide aggregateafter initial dressing with calcium hydroxide in children.Dent Traumatol 2011;27:166e73.

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