Copyright © 2008 LSTR
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Journal of LSTR Therapy (International WEB version) VOL 7: 6-10, 2008

Evaluation of Obturation by Image Analyses and Macrogol and Propylene Glycol
Penetration
Nunéz P. Phides D.D.S., Ph.D. and Etsuro Hoshino, D.D.S., Ph.D.
Oral Ecology in Health and Infection, Niigata University Graduate School of Medical and Dental Sciences, Niigata,Japan
Abstract
Objectives: This study aimed to evaluate obturations using radiographs and micro-computed tomography (MCT) andto determine if macrogol and propylene glycol could penetrate obturations until the apex.
Method: 30 extracted single-canal incisors were obturated with gutta-percha plus root canal sealer. Obturation was
evaluated with radiographs and MCT using a scoring system (1-4) where a lower score means a better obturation. Dye
mixed with macrogol and propylene glycol was applied to see whether it could penetrate through the obturation to the
apex.
Results: MCT images often demonstrated voids not shown in the radiographs. 26 out of 30 samples had higher MCT
scores (mean= 3.1; SD= ± 0.8) than radiographic scores (mean= 1.8; SD= ± 0.8). The dye-macrogol-propylene glycol
mixture penetrated the obturation and exited through the apical foramen in all samples.
Conclusion: Obturation defects that were not shown by radiographs were often revealed by MCT. The dye-macrogolpropylene glycol mixture may have passed through those defects to the apex.
Key words:
Image analysis, micro-computed tomography (MCT), root canal obturation

Introduction
It is important to evaluate root canal obturation because
inadequate obturation may not only produce areas wherebacteria may remain and survive (1), but also provides routes
through which bacteria may migrate to the periradicular
tissues. Radiographs have often been used to examine root
canal systems and evaluate obturations of the root canal,
partly because of its non-destructive nature (2). However,radiographs often cannot detect voids and other minor
obturation defects (3). They only show a two-dimensional
picture, and may be quite inadequate considering current
knowledge of root canal complexities (4-5). Aside fromradiographs, another non-destructive method to study root
canals is micro-computed tomography (MCT), which iscapable of producing three-dimensional images (6). In thisstudy, we used MCT to show obturation defects that may beundetected by radiographs.
As mentioned earlier, voids within an obturation may
become areas for bacteria to thrive which may then becomea source of re-infection of the canal. Such endodontic failures
would then routinely undergo re-treatment based on theattending clinician’s best judgement. A possible alternative
treatment for such cases is Lesion Sterilization and Tissue
Repair (LSTR) therapy. The basic concept of this therapy is
the elimination of the cause of infection, in this case bacteria,
by introducing the appropriate antibacterials into the tooth
thereby resulting in disinfection of the lesion and resolution of
inflammation. The main component of LSTR therapy is amacrogol-propylene glycol-antibiotic mixture (3Mix-MP)
which has been used as an endodontic treatment for bothprimary and permanent teeth successfully (7-8). The abilityof propylene glycol to penetrate an unfilled tooth has beenshown by Cruz et al (9). However, it has not been
demonstrated whether those vehicles could penetrate an
obturated canal. In this study, we used a mixture of dye withmacrogol and propylene glycol (MP). We substituted the dye
Accepted: February 1 2009
Published: March 1 2009

for the antibiotics to see whether such mixture would be able
to penetrate an obturated canal thus testing the efficiency of
MP as a vehicle to carry antibiotics within a filled canal.
This study aimed to evaluate root canal obturation by
detection of defects with the use of radiograph and MCT. A
second aim was to determine whether MP could penetrate
the obturation to the apex.

Materials and Methods
Sample preparation
A total of 30 single-canal incisors with fully-formed roots
was selected from a pool of extracted teeth; the histories ofwhich could not be determined. Each tooth was cut with adiamond disk about 1 mm coronal to the cemento-enamel
junction. An initial apical file with stopper was inserted into
the root canal until its tip could be seen at the apical foramenthen withdrawn 1 mm. The distance from the stopper to thetip of the file was measured with an endodontic ruler and thiswas considered as the working length. After the root canal
was enlarged with hand instruments (K-files) up to file size
40, the canal was then irrigated alternately with NaClO andwater, and then obturated with gutta-percha using cold lateral
condensation technique with Canalis® (Showa Shizai Kako
Co., Ltd., Tokyo, Japan) containing zinc-oxide and eugenol
as sealer. The samples were then kept for two weeks in
100% humidity to keep from dehydration while allowing forcomplete setting of the sealer.
Radiographic and MCT examination
Radiographs and MCT images of the root canal fillings were
evaluated by two scoring methods. The first method (10), as
modified, is shown in Table 1. Minimal detection level was
set at 0.25mm as the least dimension of radiolucency thatcan be seen by the naked eye on an x-ray film. For thesecond scoring method (11), the root canal was divided into
four sections from the apex to the orifice, with the apical area
6

Nunez and Hoshinoas the first section. Each section was scored either with 0(no voids, indicated with a negative sign) or with 1 (with voids,
indicated with a positive sign), regardless of the size or
number of voids. The score for each sample was the sum of
the scores of each root section. For both scoring systems, a
low score, such as 1 or 2 (+ or ++ for the second scoring
method), meant a well-obturated canal with minimal defects.
MCT (Nittetsu Elex, Osaka, Japan) was operated as follows:
pixel matrix: 256 x 256 x 256; slice thickness: 21 µm;
projection number: 600 x 32; magnification: x 3.88; voltage:
60 - 70 kV; electrical current: 0.1 mA. Individual images
were reconstructed by using a software program (NDTView,
Sony, Tokyo, Japan; 3D bone for WinNT, Ratoc System
Engineering, Tokyo, Japan).
Root canal fillings were
evaluated three-dimensionally from the labial, lingual, mesial,and distal aspects, so that for each radiographic score (RS)there were four corresponding MCT scores (MCTS). The
average of the four scores was considered as the MCTS.
Table 1. First scoring method for evaluation of root canalobturation.
Score
1
2
3
4

Description
Well condensed - no or few minute voids (0.25mm in diameter or length) with good adaptation to
canal walls
Imperfectly condensed- with voids or defects
found between obturation materials and canalwalls more than 0.25 mm but less than 1 mm
Insufficiently condensed- with voids or defects
found between obturation materials and canalwalls 1 mm to 2 mm.
Poorly condensed- with voids or defects foundbetween obturation materials and canal walls
more than 2 mm.

Evaluation of obturation
prepared at the orifice of the filled root canals. A dye mixture
consisting of MP, mixed at a 1:1 ratio was added to red fooddye (Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan) and placed
into the cavity which was then sealed with Caviton (GC Asahi
Corp., Aichi, Japan), as shown in Figure 1. For the controls,
dye mixed with water was used. Each tooth was placed on
separate tubes which had white paper packed at the bottom.
Care was taken to ensure contact between the root tip andthe paper so that any dye exiting from the apical foramen
would be absorbed into the white paper. The time thatelapsed from dye application until dye penetration throughthe apex was recorded. A pink color observed at the apicalforamen was considered as positive dye penetration.
Statistical Analysis
To determine if the differences between the RS and MCTS
were significant, the Student’s t-test was used. To determine
whether there was a correlation between number of voids
and speed of dye penetration, we used the Spearman Rank
analysis.

Results
Radiographic and MCT examination
Figure 2 (left) shows defects or voids as detected onradiographs. MCT produced a more porous image when thesame obturation was examined (Fig. 2, right).
Figure 2. Radiographicand MCT images ofdefects within an obturation.
(Left) Radiograph showed
obturation defects.
(Right)MCT
showedlarger defects on thesame obturation.

Dye + MP penetration test
To show whether macrogol and propylene glycol (MP) could
penetrate the obturated canals, a 2-3 mm deep cavity was
Figure 3.
Radiographic and MCT
images of an obturated
tooth.
(Left)
Radiographshowed no obturation
defects.
(Right) Same obturation
had
defects
when
evaluated by MCT.

Figure 1. Schematic illustration of specimen for dye
penetration test. (a) Dye + MP; (b) Gutta-percha + sealer;
Arrows indicate passage of dye + MP.

7

For some well-obturated samples where no defects wereobserved on radiographs, such as the one shown on Figure
3 (left), defects were revealed when the same obturation was
visualized with MCT (Fig. 3, right).
As shown in Table 2, radiographic scores (RS) for the firstscoring method (n = 30; mean 1.83 ± 0.75 SD) weresignificantly lower (P < 0.0001) than MCT scores (MCTS)(mean 3.10 ± 0.80 SD). This means that MCT could detectobturation defects more efficiently than radiographs. Similar
results were obtained with the second scoring method where
RS (mean 1.87 ± 1.28 SD), were significantly lower than
MCTS (mean 3.47 ± 0.73 SD). This was also demonstrated
with the tally of the number of teeth with the same score
evaluated by radiographs and MCT (Table 3). Twenty-four
out of 30 samples (for the first scoring method) and 20 out of
30 samples (for the second scoring method) had RS nohigher than “2”. In six samples, the defects were detected
only with MCT, and not by radiographic evaluation (Table 3).

Sample

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30

Scoring
Scoring
Method 1
Method 2
RS
MCTS RS
MCTS
2
1
2
2
3
2
1
1
1
2
2
2
3
1
2
2
2
2
2
1
1
1
1
1
1
3
3
3
2
3

3
1
4
4
4
4
3
3
2
3
3
4
3
3
4
3
3
4
3
2
3
2
2
3
3
4
3
4
2
4

++
+
+++
++++
+++
+++
++
+
+
++
+++
++
++++
+++
++
++
+++
+
+
+++
++
++++
++
++

+++
C+
++++
++++
++++
++++
++++
++++
++
++++
++++
++++
++
+++
++++
+++
++++
++++
++++
++++
++++
+++
++
+++
++++
++++
+++
++++
+++
+++

It should be noted that not all samples had a higher MCTS
than RS, indicating that radiographs could show defects
depending on the size and orientation of the said defects.
Dye + MP Penetration
Dye + MP mixture penetrated through obturation and exited
to the root apex in each of all 30 samples tested. The meantime of dye exit was 48 hours ranging from 0.5 hour to 120
hours. However, dye exit time was not correlated to the
obturation scores (Table 1; Spearman rank; P = 0.758857 : rs
= 0.0585). For the controls, where dye was mixed with water,dye did not exit to the apex in almost all cases (Table 2).

Dye Penetration
MP
+ Dye
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+

water
+Dye
+
+
+
-

Discussion
It has been demonstrated that radiographs may not always
present an accurate picture of the actual condition of a root
canal (12) partly because radiographs show only a twodimensional image, so that some areas in the root canal are
not visualized. By the same analysis, it can be assumed thatradiographic images of a filled root canal do not give an
accurate image of the true condition of the fillings. Defects or

Journal of LSTR Therapy (International WEB version) VOL 7: 6-10, 2008

Table 2. Radiographic (RS) and Micro-CT scores(MCTS) and dye penetration

Scoring details are explained in the text, Materials andMethods section.
Low score: good obturation; High score: poor
obturation.
-: No visible dye penetration through the apex.

voids located in areas not accessible to the x-rays are thus
obscured from the naked eye of the clinician evaluating an
obturation. MCT, on the other hand, is a method that has
been used by many researchers to evaluate the anatomy of
the root canal system both before and after instrumentation(13), and has been shown to give a high accuracy in terms ofreproducing images of the outer surfaces of teeth as well as
the interior parts including the root canal space (14). It has
been demonstrated that MCT could produce images of root8

Nunez and Hoshino
canals filled with gutta percha that have a high correlation tohistological sections (15).
In the present study, obturations were evaluated withradiographs and MCT. Root canals of most samples seemed
to be better-obturated based on radiographic evaluation.
Some defects that were undetected in the radiographic
images were revealed in the MCT scans. In this study
obturation was done in our hands, in vitro,
Table 3. Root canal obturation condition.
Number of Teeth
Scoring Method 1
Scoring Method 2
Score
RS
MCTS
RS
MCTS
0
----6
0
1
11
1
5
0
2
13
5
9
4
3
6
14
7
8
4
0
10
3
18
30
30
30
30
Scoring details are explained in the text, Materials andMethods section. Low score: good obturation; High score:poor obturation.
RS- Radiographic score;
MCTS- Micro-CT score;
Score 0 is applicable only to Scoring Method 1.
so that it was reasonable that radiographs showed rather
good root canal obturation. Despite that, however, MCT
images revealed quite a number of obturation defects hidden
in radiographic evaluation. The results of this study suggestthat the inherent limitations of radiographic images must not
be overlooked.
The detection of voids is important as it has been
established that adequate filling of the canal space after
instrumentation is one of the essentials for the success ofroot canal therapies.
However, successful root canaltreatments in general suggest that the presence of defects
may not always lead to endodontic failures. Still, it is possiblethat obturation defects may serve as niches where viablemicroorganisms may lodge. In addition, when those defects
form continuous structures to the apex, they may provide aroute for the migration of microorganisms to the periradicular
tissues thus causing re-infection of the canal or theperiradicular areas. Some studies have concluded that somebacteria may persist in the root canal even after obturation asa result of inadequate canal preparation and debridement,
and apical or coronal leakage through defective restorations(1, 16). Such persistent bacteria have often been cited as thecause of most endodontic failures, rather than whether theroot canal was satisfactorily obturated or not (17), warranting
the need for a re-treatment of the tooth.
Conventional re-treatment often means removal of the oldfilling, re-cleansing and sometimes re-preparing the root
canal (18).
Depending on various factors, success ofendodontic re-treatments range from moderate to high levels
although there has been no general agreement as todecision-making when it comes to the clinical management ofendodontic retreatment cases (19). One possible approach,a non-invasive pulpal treatment, also known as Lesion
Sterilization and Tissue Repair (LSTR), involves the use ofantibacterials combined with a mixture of macrogol andpropylene glycol (MP) as the efficient vehicle to carry the
antibacterials within the tooth (20). This antibacterial mixture(3Mix-MP) has been used successfully as an alternative form

9

Evaluation of obturationof treating teeth with deep-seated carious lesions or evenwith periapical lesions (21).
In this study, we tested whether MP would be a good carrierof the antibacterial mixture within an obturated canal. We
hypothesized that defects within an obturation may form
continuous channels to the apex that may allow passage ofMP. To determine this, we let MP penetrate the obturation by
performing a dye penetration test. We substituted a dye thatwas completely soluble in MP for the antibacterials tovisualize the MP clearly. Since the dye mixture exited
through the apex in all the samples, we have shown that it
was possible for MP to penetrate even the minute voids
present in obturation. There was, however, no correlation
between the speed of dye penetration and obturation scores.
This may mean that much finer-sized gaps and spaces within
the obturation that cannot be detected by radiographs or
MCT contributed to constitute tunnel structures together withthe larger-sized defects. This may indicate that someobturation defects were connected to each other and may
have formed labyrinthine structures to the root apex. An
obturation with labyrinthine structures is actually beneficial
and contributes to the success of the treatment because they
may trap any remaining microorganisms within the filling andprevent them from moving to the periradicular areas.
However, trapped bacteria may, after some time, eventuallyfind their way to the periapical areas. These rare cases may
ultimately lead to endodontic treatment failure and would beindicated for re-treatment.
For the controls in this experiment, dye mixed with water did
not exit through the apex in almost all samples. This may be
due to the water’s surface tension or hydrophobic
components of the obturation materials, making it difficult forwater to pass through. Cruz et al. have shown that water
could not penetrate an unobturated canal as efficiently as
propylene glycol, one of the components of MP (9).
Although inconclusive, it must be noted that the mixture of
MP may have been essential to the consistent penetration of
the dye mixture to the apex. This may suggest that MP could
be a good vehicle to carry the prescribed antibacterials within
a filled root canal. Being such, the antibacterials + MP
mixture (3Mix-MP) need only be placed at the orifice of thecanal and allowed to penetrate the obturation. By following
the prescribed protocol of LSTR therapy, it may be possible
to perform an endodontic re-treatment without having to
remove the existing obturation. Researches have been andare still presently being conducted to investigate thepossibility for such form of treatment to be considered as apossible alternative endodontic re-treatment procedure forcertain endodontic failures especially those which are
deemed to be caused by viable bacteria remaining within afilled canal (22-23).

Acknowledgments
This research has been supported by Grants-in-Aids for
Scientific Research 1440628 and 17390500 and JSPS Joint
Research Projects 151075 and 151076.
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