Apex Locator Simulation: A comparison of the accuracy of various

techniques used to simulate in-vivo use of apex locators

Ryan Walker
University of Missouri-Kansas City School of Dentistry

ABSTRACT
Accurate working length determination is a very important aspect of root canal therapy. There have been
many methods developed to estimate the length of a canal. One of the most accurate methods of
determining the length of a canal is the use of an electronic apex locating device. The purpose of this study
was to compare the accuracy of saline, alginate, Endo Q, and Endo Dent as in-vitro apex locator training
devices. 60 maxillary anterior teeth were used in this study. Teeth were randomly assigned to 4 groups.
Group 1 was evaluated using the saline model for apex locator use. Group 2 was evaluated with the teeth
embedded in alginate. Group 3 teeth were placed in the Endo Q system, and Group 4 teeth were placed in
the Endo Dent system. Root lengths and canal lengths were recorded for all teeth. The Root ZX and
A.F.A. apex locators were used to measure the canals in each group. The results showed that both apex
locators were extremely accurate in determining the canal length when used in the various models. The
results also showed that there was no statistical difference in apex locator readings when using saline,
alginate, Endo Q, and Endo Dent models. The Endo Dent offers the ability to mount teeth onto a typodont
which allows the user a very realistic simulation of patient treatment.

INTRODUCTION
The goal of endodontic therapy is to foramen. However this can only be used
debride, disinfect, and seal the canal to verify the length of the canal and
system of the tooth from its most coronal should not be used as a trial length
aspect to its most apical aspect in determination technique. Measurements
preparation for its definitive restoration. derived from radiographs have been
The apical extent of the preparation is advocated for estimating the trial length
most commonly considered to be the of a tooth3-6. However, many in-vitro
minor diameter (cementodentinal studies have shown that radiographic
junction) of the foramen. Accurately determined lengths vary from actual
measuring the length of a canal as it canal lengths a considerable amount.
relates to the apical foramen has shown This is due to the fact that that the apical
to be a key factor in the success of foramen is not usually located at the
endodontic therapy1. Therefore it is radiographic apex of the tooth7,8.
critical that an accurate technique for Magnification occurring with a
measuring canal length be devised and radiographic image can also account for
implemented. measurement errors4,9. One of the most
Many techniques for determining root revolutionary inventions in endodontics
canal length are now available. Some is the invention of the electronic apex
experienced clinicians are able to use locating device. Sunada first introduced
tactile sense to locate the apical this method for measuring the length of
foramen2. Measurements taken using a root canal in 1962. From the
paper point verification have also proven introduction of this device to present day
to be useful when locating the apical
apex locators have undergone many media such as saline or alginate. The
modifications. purpose of this study was to compare the
Results of many studies have shown accuracy of Endo Q, EndoDent, saline,
electronic apex locators to be an accurate and alginate when used as an in-vitro
method for determining root canal model for apex locator use. The models
length10-14. The newest generation of will also be evaluated on how easy they
electronic apex locators prove to be are to set up and operate.
much more reliable with a greater
accuracy than those in the past. With
these improvements it is of no surprise MATERIALS AND METHODS
that apex locators are becoming almost 60 maxillary anterior teeth were
standard issue in most dental practices. selected for the experiment. All teeth
It therefore seems reasonable to assume were stored at 37°C in a 0.9% NaCl
that the preclinical curriculum in the solution. The criteria for tooth selection
dental school should train students in the were: straight, single-rooted teeth;
use of apex locators as an adjunct in root complete root formation; no root caries,
canal therapy. There have been several and no evidence of fracture. Teeth were
in-vitro studies performed using saline cleaned using ultrasonic scalers. The
as the conductive media for electronic crowns were sectioned at the C.E.J.
apex locators15,16while others have perpendicular to the long axis of the
suggested the use of agar or tooth with a fissured carbide bur #557 at
alginate10,17,18. There has never been a high speed with water spray. The teeth
model designed to incorporate the use of were then randomly assigned to four
electronic apex locators to simulate in- groups. The teeth were numbered 1-60
vivo root canal therapy for training and kept in labeled test tubes. The
purposes. Recently an apex locator measurement of the root length was
simulation device called the Endo Q was recorded to the nearest tenth of a
developed. This device allowed students millimeter using a micrometer caliper
to mount their extracted teeth into a (Fisher Scientific, Pittsburgh,
small box with materials developed to Pennsylvania). The distance from the
simulate the PDL of a tooth for use with coronal portion of the tooth to the minor
an electronic apex locator. The box also diameter of the canal was then measured
contained a material that gives the for each tooth. This measurement was
radiographic appearance of bone obtained by passing a #15 K-File (Kerr,
allowing students to take radiographs of Romulus, MI, USA) down the canal
the tooth as the root canal therapy is until visible passing into the major
being performed. The newest generation diameter of the apex when viewed under
of this product Endo Dent is now 5x magnification. The stopper on the
allowing students to mount their file was set and the file length recorded.
extracted teeth in a manikin allowing the The minor diameter of the canal was
most realistic simulation of patient then guaged by recording the size of the
treatment in endodontics to date. first ISO K-File that bound at the length
However there have been very few measured above.
studies performed to evaluate the
accuracy of these new products In group 1 the teeth were placed in a ¼"
compared to the use of other conductive x 3" x 8" piece of baseplate wax with 15
premade holes. The wax was then placed into the container so that the
heated around the teeth to form a apical third of the teeth were submersed
watertight seal. The plate of wax was in alginate. The grounding clips for the
then positioned over a container filled apex locating devices were then placed
with 0.9% NaCl so that the apical third as above. The alginate was allowed to
of the roots were submersed. The set for 10 minutes and then the canals
grounding clips for the Root ZX (J. were measured and recorded using 0.9%
Morita, Irvine, California) and A.F.A. NaCl and 5.25% NaOCl in the canal as
(Sybron Endo, Glendora, CA) devices above.
were then secured with wax in the saline
solution. 1ml of 0.9% NaCl was then In group 3 the teeth were embedded in
placed into each canal. The Root ZX the Endo Q system. The teeth were
apex locator was then attached to a wiped clean and allowed to lie on a
#15K-File which was placed in the canal paper cloth until completely dry. A ½”
and turned clockwise until the display long piece of 3/8” tubing was then
indicated that the file was at the apex. placed over the apical portion of each
The stopper was set on the file and the root until snug with hand pressure. The
length was measured as above. The open portion of the tubing was then
previous steps were repeated using the filled with the periodontal ligament
A.F.A. device with the length being simulating paste included in the Endo Q
recorded at 0.0. After recording the data kit. The Endo Q holders were then
for all 15 teeth the wax plate was prepared to accept the teeth. The holders
removed from the container. All canals were placed in a preheated oven at
were rinsed with 5ml triple-distilled 150°F for 8 minutes. The holders were
water and dried with air and paper then removed and the grounding plate
points. The wax plate was then placed was inserted into the slot at the base of
back in the container of NaCl. 1ml of the holder. A hole was then made in the
5.25% NaOCl (Clorox, Oakland, CA),) material contained in the holder with a
was then placed in each canal. The apex mirror handle. The teeth were brought
locating devices were then used in the to place into the premade holes and the
same process as above and the material was packed around the tooth.
determined lengths were recorded. The material provided to secure the teeth
was then mixed and adapted around the
In group 2 the teeth were placed into the teeth so that the level of material was
baseplate wax as above in group 1. The flush with the top of the holder. The
same container was used to hold alginate containers were allowed to cool for
for this group. The alginate (Dentsply, 30minutes before measurements were
York, Pennsylvania) was weighed and recorded. The measurements were
combined with the recommended determined using both NaCl and NaOCl
volume of room temperature, distilled as in group 1 & 2.
water. After brief hand spatulation the
alginate was mixed using a vacuum In group 4 the teeth were embedded in
mixing device for 20 seconds to the Endo Dent system. The teeth were
eliminate any air entrapment. The prepared as in group 3. The teeth were
alginate was then quickly vibrated into placed on top of the material located in
the container and the baseplate wax was the simulated tooth socket. The entire
area around the tooth was then filled slightly longer than the mean canal
with the provided bone material to length (13.3mm). This is to be expected
secure the teeth in the socket. The keeping in mind that the apical foramen
grounding device for the apex locator is rarely coincident with the actual apex
was hooked up to the preinserted clip on of the root7,8. The average deviation
the Endo Dent device. The from actual canal length was slightly less
measurements were recorded using the than 0.3mm for this group. Furthermore
same solutions in the canals as in groups the greatest deviation from the actual
1,2, &3. canal length in this group was .86mm
found using the Root ZX with 5.25%
After recording all of the data the mean NaOCl. This deviation was lower
values calculated in each group were compared to other groups which had as
evaluated using multivariate tests for much as a 1.5mm deviation from the
statistical significance (p<0.05). canal length.

RESULTS DISCUSSION
There was no statistical significance The results of this study show that
(P>0.05) between each series in all four saline, alginate, Endo Q and Endo Dent
groups. Results showed that there was are all extremely accurate for use as an
no difference in the accuracy of the apex in-vitro model for apex locator use. This
locating devices with either NaCl or study supports the use of 0.09% NaCl
NaOCl placed in the canal. Fig. 1 shows and alginate as conductive media in apex
the average measurements acquired with locator studies. If the accuracy of the 4
teeth placed in 0.09% NaCl. The models is equal then it must be
average root measurement for this group determined which model is more
was approximately .75mm longer than suitable for simulation of root canal
the actual length of the canal as treatment. Saline has been the most
determined by the file placed to the common model used for apex locator
apical foramen though not statistically research and proves to be very accurate
significant (P>0.05). Fig. 2 shows the in this study as well. However, saline
average measurements acquired with has limited application for use as a
teeth placed in alginate. The average simulation model because it is
root measurement in this group was impossible to keep it in the reservoir
approximately .6mm longer than the with the manikin in a reclined position.
average length of the canal. Fig. 3 In comparison, alginate is just as
shows the average measurements accurate with it’s own unique
acquired with the teeth embedded in the drawbacks. Alginate must be mixed and
Endo Q system. The A.F.A. w/NaOCl once set it would provide some
average was close to the mean of the stabilization of the tooth. However
root length though not statistically alginate quickly dries making it
significant (P>0.05). Fig. 4 shows the impossible to use after a few hours. The
average measurements acquired with the Endo Q device addresses many of the
teeth embedded in the Endo Dent shortcomings of the previous models. It
system. There was only slight variation is extremely accurate offering stability
in the mean values of this group as well. and relatively long term storage. The
The mean root length (13.6mm) was PDL paste included in the kit is able to
 17

16.5

16

15.5

15
Root Measurement
14.5
File Measurement
Length (mm)

14
Root ZX 0.9% NaCl
13.5
A.F.A. 0.9% NaCl
13
Root ZX 5.25% NaOCl
12.5

A.F.A. 5.25% NaOCl

12

11.5

11

10.5

10

Fig. 1 Measurements With Teeth Placed In 0.9% NaCl

18

17.5

17

16.5

16

15.5 Root Measurement

15
File Measurement
Length (mm)

14.5
Root ZX 0.9% NaCl
14
A.F.A. 0.9% NaCl
13.5

13 Root ZX 5.25% NaOCl

12.5 A.F.A. 5.25% NaOCl

12

11.5

11

10.5

10

Fig. 2 Measurements With Teeth Embedded In Alginate

 18
17.5
17

16.5 Root Measurement

16

15.5
File Measurement

15
Root ZX 0.9% NaCl
Length (mm)

14.5
14
A.F.A. 0.9% NaCl
13.5
13
Root ZX 5.25% NaOCl
12.5
12 A.F.A. 5.25% NaOCl
11.5
11

10.5
10

Fig. 3 Measurements Using Endo Q

17

16.5

16

15.5

15

14.5 Root Measurement

File Measurement
14
Length (mm)

Root ZX 0.9% NaCl

13.5
A.F.A. 0.9% NaCl

13 Root ZX 5.25% NaOCl

12.5 A.F.A. 5.25% NaOCl

12

11.5

11

10.5

10

Fig. 4 Measurements Using EndoDent

be used for weeks once it is placed apical foramen of a tooth. There are
around the root of the tooth. It also benefits to each system that one must
gives the radiographic appearance of take into consideration before purchase.
trabeculation which makes radiographic The A.F.A. automatically turns on when
evaluation more realistic. Endo Q the circuit is completed. The readout in
however does not allow mounting of the millimeters is easy to interpret though it
system on to a typodont for patient should not be considered an actual
simulation. Finally the Endo Dent millimeter reading of the file distance
model must be evaluated. This from the foramen. The Root ZX has a
particular model maintains all of the colored display, volume controls, and
features of its predecessor and the arch the ability to calibrate the point of
mount can easily be placed onto a greatest sensitivity within the canal.
typondont. This makes simulating Both of these devices are excellent
patient treatment very realistic when adjunct for root canal therapy. This
performing root canal therapy. research showed no difference in the
In this study the direct root accuracy of apex locators when used
measurements averaged out to be .5mm with either NaCl or NaOCl in the canal
longer than the average measurement of system.
the actual canal. The root measurement
would be similar to the measurement CONCLUSION
taken from a radiograph without the Saline, alginate, Endo Q and Endo
magnification factor. This finding also Dent are all acceptable models for use
attests to the fact that the apical foramen with apex locators. The advantages of
is not always located at the actual apex these different models are found in their
of the tooth. It would appear that any ability to more accurately reproduce the
measurement taken from a film would experience of patient treatment with root
then be at least .5mm long if not more canal therapy. It is evident that the Endo
due to this magnification. This supports Dent is the best model available for in-
the idea of subtracting .5 to 1.5mm from vivo simulation of root canal treatment.
the radiographic measurement to acquire The use of this product will give the
a working length. Furthermore this dentist the most realistic experience that
study proves that the new electronic can be achieved without having a real
apex locators are extremely accurate in patient in the chair. This research proves
locating the minor diameter of the apical that there are in-vitro models for apex
foramen. Though many discussions are locator use that can be considered
focused around which particular type of extremely accurate and reliable. If a
electronic apex locator is better or more universal method of root canal
accurate, the Root ZX and A.F.A. were simulation can be adopted throughout
both found to be equally efficacious. dental institutions and for continuing
Therefore it is a matter of preference education classes there will be a greater
from the standpoint of cost, appearance, level of understanding apex locator
and display that is the issue and not the usage throughout the profession. This
devices ability to accurately locate the greater understanding is certainly a
benefit for everyone involved in root 13. Trope, M., Rabie, G., Tronstad, L.
canal therapy, both the patient and the Accuracy of an electronic apex locator under
controlled clinical conditions. Endod Dent
practitioner. Traumatol 1985;1:142-145.
14. Kaufman, A.Y., Szajkis, S., Niv, N. The
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