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The
complex morphology of human teeth has never failed to amaze the clinician.
Presence of main pulpal canal along with many lateral and accessory canals in
tooth results in complex pulpal morphology.1
It is imperative to adequately clean and shape these canals to achieve sterile
enviornment.2

One
of the major cause of failure in endodontic therapy is inability to locate and
obturate root canal.3,4 As these unfilled and unlocated canals may
harbor number of bacteria and can lead to post-treatment infection.5 According to Hoen and Pink, incidence of 42% missed
roots or canals have been reported which resulted in the root canal failure and
needed retreatment.6

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Slowey
reported that mandibular premolars are the difficul teeth to treat during
endodontic treatment.6 Mandibular first premolar exhibits
greatest challenge due to highly variable root canal morphology.7

It
is important to study the human teeth anatomy so that one can presume the
possible variations in the root canal system. Although many different methods have been
employed to study the root canal morphology such as direct observation under
microscope, macroscopic sectioning, polyester resin cast replica of pulp space,
placing instrument in the canal, clearing technique and dye injection, in vitro
radiopaque gel infusion, conventional radiography, digital and contrast medium
enhanced radiography, spiral computed tomography and cone beam computed
tomography (CBCT).8 ,9  But tooth
clearing technique remains the gold standard method. Therefore current study
was planned to evaluate the root canal morphology of mandibular first premolars
using tooth clearing teeth.

MATERIALS AND METHOD

A total of two hundred mandibular first premolar teeth
with mature apices were collected which were indicated for extraction. The
extracted teeth collected were stored in 10% formalin until used. Samples were
then immersed in 5.25% concentration of sodium hypochlorite for 30 minutes to
remove organic debris and adherent soft tissues before proceeding for the
decalcification procedures. After washing, samples were again stored in 10%
formalin until clearing.

For clearing, samples were first placed in 10% hydrochloric
acid at room temperature for 2 days for decalcification. The hydrochloric acid
solution was stirred frequently and changed after 24 hours to fasten the
process of demineralization. Once delcalification of desired level was achieved,
teeth were removed from the acid. In the next step, samples were washed under
running tap water for 2 hours. Excess water was removed and teeth were left to
dry on the tissue papers. After drying, samples were subjected to process of
dehydration. This was accomplished using ascending concentrations of ethanol.
Teeth were dehydrated at 50%, 60%, 70%, 80%, 90%, & 96% of ethanol for 5
hours in each concentration. Following this, teeth were immersed in 2% methyl
salicylate to make them clear and transparent. Samples were then stored in
clearing agent indefinitely in order to maintain the translucency until
examination. The transparent specimens were then examined by the naked eye and
under Dental Operating Microscope at magnification of 12.8x for the whole tooth
and 19.2x for the apical area. Morphological features which were studied
include number of root canals, type of root canal configuration according to
Vertucci’s classification and location of apical foramen. Collected data was
evaluated and analyzed.

RESULTS

Root canal morphology of
mandibular first premolar teeth was studied by categorizing the root canal pattern
according to Vertucci’s classification as shown in (Table 1). It was found that
76% of the teeth exhibited
Vertucci’s Type I root canal pattern which states that single canal extends
from the pulp chamber to the apex. Majority of mandibular first premolar had
Type I root canal configuration. Type V pattern was found to be the second most
common root canal configuration as seen in 13.5% of the specimens. Type II
pattern was prevalent in 5.5% of the cases followed by Type III configuration
found in 2% of teeth, Type VI pattern in 1.5% and Type IV pattern was seen in
1% of the specimens. Only 0.5% of the specimens showed Type VII configuration
and none of the specimen had three canals showing Type VIII root canal pattern. In context to
position of apical foramen, only 13.5% of the specimen showed foramen emergence
with the apical root tip while 86.5% of the teeth had lateral position of the
apical foramen (Graph 1).

 

Type
of configuration

Number
of Teeth

Percentage

Type I (1)

152

76%

Type II (2-1)

11

5.5%

Type III (1-2-1)

4

2%

Type IV (2)

2

1%

Type V (1-2)

27

13.5%

Type VI (2-1-2)

3

1.5%

Type VII (1-2-1-2)

1

0.5%

Type VIII (3)

0

0%

Total

200

 

Table
1 – Type of root canal configuration according to Vertucci’s
classification showing number and percentage of teeth

Graph 1 – Representing the location of apical foramen

Figure: 1
– Dental operating Microscope images of mandibular first premolar showing root
canal configuration according to Vertucci’s classification.

A.
Type I, B. Type II, C. Type
III, D. Type IV, E. Type V, F. Type VI, G. Type
VII

Discussion

Root canal morphology appears in
myraid types of configurations, forms and patterns. As we know that mandibular premolars are the most difficult
teeth to treat for the clinician.10 The most
apparent reason could be the inability to acknowledge the variations in canal morphology.
If all the canals are not located and thoroughly cleaned, it might lead to root
canal failure.

To
avoid such circumstances one should be aware regarding the different pattern
and configuration that could be present inside the tooth. In this perspective, tooth
clearing technique is the most valuable tool for revealing internal root canal
anatomy so that one can see it to believe it!!11 This procedure not only helps in
three-dimensional understanding of pulp cavity but also provides a reliable
medium to assess the entire root canal system without entering the cleared
teeth with instruments.12 One of the
main advantage of this technique is that the original shape and form of the
canals can be maintained and preserved throughout the procedure.

In
the current study, clearing
technique was simplified to clear the samples without damaging or altering the
original anatomy. Teeth were not subjected to any kind of
preparation prior to clearing. No access cavity preparation and instrumentation
was which helped in preserving the original root canal anatomy.

For decalcification, 10%
Hydrochloric acid was used at room temperature to demineralize the samples.
Dehydrating the samples in six different concentrations of ethanol in ascending
order helped in slow and maximum removal
of water from the tooth. This also
facilitated the penetration of clearing agent into the samples. Methyl
salicylate was used as clearing agent due to its good penetration ability and suitable
refractive index required for clearing the teeth.13
Moreover, it infuse into the dehydrated sample without providing any colour or stain
to the tooth.

 In most of the clearing techniques, dyes or
contrast media are inserted to expose the internal root canal anatomy.13, 14, 15, 16 However, dye or ink penetration in the canal through
injections may damage the internal structure and create artefacts altering the
root canal anatomy. Adding to this, dye –penetration can be time-consuming and
technique- sensitive. Main concern with using dyes is that the amount of
internal structure revealed depends on the pressure at which dye is injected by
the operator. Inadequate dye penetration may not reveal the complete anatomy of
the root canal system and can lead to false results. Therefore, in the present
in-vitro study no dye or ink was penetrated into the canals. Root canal anatomy
was shown without any tooth structure being changed and compromised during the
clearing procedure.

Results showed that out of 200
samples of mandibular first premolar, 154 teeth (76%) predominantly had single
canal (Type I pattern). These findings were in agreement with
study done by Vertucci in 1984 who also reported 70% incidence of
type I configuration. Cleghorn et al
also reviewed the literature and found the average incidence of 75.8% regarding
presence of single canal in mandibular first premolars. 11,17

Type II canal pattern
was seen in 5.5% of the teeth where two canal join together to form one and
Type III canal configuration was evident in 2% of the teeth. This root canal
configuration is difficult to clean and shape. Vertucci reported Type III pattern in 4% of mandibular first
premolars.11

In this study, Type IV
canal system was found in only 1% mandibular first premolars. Whereas Vertucci reported 1.5% incident and Sandhya, Velmurugan & Kandaswami and Jain & Bahuguna found the
configuration in 2% and 2.89% of mandibular first premolar teeth. 11,18,19 It can inferred  from
these findings that mandibular first premolar can have more than one canal.                

Next was Type V canal
pattern which was observed in 13.5% of the specimens which is similar to the
study done by Parekh et al who
reported an incidence of 12.5% in mandibular first premolars.20 Vertucci also reported Type V
configuration to be the second most common root canal pattern in mandibular
first premolars.11 In this pattern, one canal bifurcate into two
during its course through the apex. During root canal treatment of teeth with
such configurations coronal flaring is very important as it provide better
access for bifurcated canals.

 In the present study, 1.5% of the cleared
samples showed Type VI canal pattern. Vertucci
did not report any Type VI canal pattern in his study.11 Very few
teeth had Type VII canal pattern and 0% incidence of Type VIII canal pattern in
the samples was reported in the present study.

Studying the exit of
canal in the apical foramen is also crucial as it holds a clinical significance while performing root canal
therapy. 21 If the foramen opens laterally, the working
length may appear short on the radiograph. Therefore it is important for the clinician
to be aware of the apical anatomy as well. As all these landmarks helps in
determining the apical stop during root canal treatment. It has been reported
that lateral emergence of apical foramen is more common than the central exit.21,22
In this study also,
only 13.5% of the specimen showed apical foramen emergence coinciding with the
apical root tip while 86.5% of the specimens had lateral exit.

Conclusion

Within the limitations of this study, it can be
concluded that mandibular first premolar possess variable root
canal anatomy. Variation in the root canal anatomy has become a rule rather
than an exception. Therefore, awareness of the complex pulpal anatomy is an
essential prerequisite for the success of root canal treatment. It would be
wise to presume that root canals in mandibular first premolar may show highly
variable morphology during root canal procedure.

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