A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE” AGAINST
ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE”
AGAINST ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
Wei Cheong Ngeow 1a* , Dionetta Delitta Dionyssius 1b , Hayati Ishak 1b
Department of Oro-Maxillofacial Surgical and Medical Sciences, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia
1
BDS (Mal), FFDRCS (Ire), FDSRCS (Eng), MDSc (Mal), PhD (Sheffield), FAMM
BDS (Mal)
a
b
Received: March 09, 2016
Revised: May 30, 2016
Accepted: June 29, 2016
Published: July 01, 2016
Academic Editor: Paula Perlea, DMD, PhD, Associate Professor, Dean, “Carol Davila” University of Medicine and Pharmacy Bucharest, Bucharest, Romania
Cite this article:
Ngeow WC, Dionyssius DD, Ishak H. A radiographic study to determine the possible existence of a “safe zone” against endodontic periapical extrusion
in the lower premolar. Stoma Edu J. 2017;4(2):108-113.
ABSTRACT
DOI: 10.25241/stomaeduj.2017.4(2).art.3
Introduction: Studies have shown that the most common position of the mental foramen in several
Asian populations was in line with the apex of the second premolar. Therefore, we seek to determine
the average distance of the mental foramen to the apex of the second premolar by using the crown
length of the second premolar as a ruler. We hope to define a “safe zone” in this region.
Methodology: Measurements were made from the apex of the second premolar to the mental
foramen of ninety seven dental radiographs fulfilling the criteria set.
Results: Non-detection of mental foramina happened significantly more often in female subjects
than male (Pearson Chi-square; p=0.01). Of the mental foramina that were visible, 96% were found
to be located within one-crown distance from the apex. More mental foramina (37.1%; 56 sites)
were located at the apex than any other locations. This is followed by finding the mental foramina
located at ¼-crown distance from the apex (26.5%; 40 sites). The visibility of the mental foramen was
found to be significantly limited in females and in patients aged 50 and above (Pearson Chi-square;
p<0.05).
Conclusion: These findings suggest that there is no safe zone against accidental extrusion of
endodontic files and materials in the second premolar region.
Keywords: endodontology, complication, inferior alveolar nerve, mental nerve, mental foramen.
1. Introduction
The mental foramen is located close to the
mandibular premolars, especially the second
premolar. 1 A morphometric study by Philips et al. 2
reported the mental foramen to be located on
average at a distance of 2.18 mm mesially and 2.4
mm inferiorly from the plain radiographic apex of
the second premolar. More precisely, the mental
foramina could be located anywhere 3.8 mm mesially
2.7 mm distally, 3.4 mm above or 3.5 mm below the
apex of the second premolar. Various cadaveric
studies reported the apices of the second premolars
to be between 0 and 4.7 mm away from the mental
foramen. 3,4 Using a newer technology of cone beam
computed tomography (CBCT), BÜrklein et al. 5 also
reported similar findings, with an average distance of
4.2 mm. However, 3.2% of the mental foramen was
directly in contact with the second premolar.
Because of this close proximity, various events
affecting the second premolar, such as odontogenic
infection and orthodontic, endodontic, periodontal
or surgical misadventure, may result in the
neurosensory disturbance to the area innervated by
the mental nerve that exits the mental foramen. 1,6 A
retrospective study found an incidence of 0.96% of
mental paraesthesia related to root canal treatment
of mandibular premolar teeth. However, all these
incidents were related to periapical infection or
pathology, instead of being a complication of the
root canal treatment itself as the authors excluded 2
(0.24%) cases of severe overfill and iatrogenic root
perforation with mechanical instrumentation into the
mental nerve. 3
Eliminating infection in the pulp and dentin,
followed by adequate intra-canal preparation
and proper sealing constitute the basic principles
of root canal treatment. Ideally, mechanical
preparation and filling should be limited within the
root canal as overinstrumentation or the extrusion
of chemical fillings beyond the apical foramen to
the adjacent nerve can give rise to NSD such as
paraesthesia or anaesthesia. 7,8 Paresthesia related
to overinstrumentation usually resolves within
several days. 9 In addition, minor material extrusions
are generally well tolerated by the periradicular
tissues as long as they do not spread to the adjacent
nerve. 10 However, long-term NSD has been reported
in cases where the nerve fibre is lacerated due to
overinstrumentation or in contact with toxic overfilled
endodontic materials. 8,11
*Corresponding author:
Professor Dr Wei Cheong Ngeow, Department of Oral & Maxillofacial Clinical Sciences, Faculty of Dentistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
Tel: 603-79674862, Fax: 603-79674534, e-mail: [email protected]
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Stoma Edu J. 2017;4(2): 108-113
http://www.stomaeduj.com
As the close proximity of the apices of the
mandibular premolar to the mental foramen acts
as an important contributory factor for NSD when
overinstrumentation or overfilling of endodontic
materials happen, it is the aim of this study to
determine the distance of the mental foramen to
the second mandibular premolar tooth. We chose
to concentrate on the second premolar only as an
earlier study has shown that most of the terminal end
of the inferior alveolar nerve is located in line with
the apex of the second premolar. 12 In this pilot study,
also conducted on a selected Malay population,
we seek to determine the average distance of
the mental foramen from the apex of the second
premolar by using the crown height of the second
premolar as a ruler. The identification of this distance,
will hopefully enable us to come up with a so called
“safe zone” to ensure that root canal treatment in
the lower premolar region can be performed with
minimum complications in case files or endodontic
filling materials are accidentally extruded beyond
the apices of these premolars.
2. Methodology
2.1. Materials
One hundred twenty panoramic radiographs of
Malay patients of 4 different age-groups, taken
between 2003 and 2005 were obtained from the
records stored by the Dental Faculty of the University
of Malaya, Kuala Lumpur, Malaysia. The age-groups
were categorised as 20-29 years-old, 30-39 years-
old, 40-49 years-old and 50 years and above.
All panoramic radiographs were taken using
Siemen Orthophos® (Sirona, Bensheim, Germany)
or Planmeca® (Planmeca, Helsinki, Germany)
machines. The magnification factors reported by the
manufacturers were 1.2 and 1.25, respectively. The
radiographs were chosen according to the following
criteria:
1. High quality with respect to geometric accuracy
and contrast of the image.
2. Radiographs in which the lower teeth (between
36 and 46) were missing, had deep caries, root
canal treatment or various restorations were
excluded because of possible associated periapical
radiolucency.
3. Radiographs must be free from any radiolucent or
radiopaque lesion in the lower arch. There should
be no evidence of jaw fracture around the mental
foramen region.
4. Radiographs with supernumeraries and unerupted
teeth were excluded because the impacted/
unerupted teeth might obscure the appearance of
mental foramen.
5. Films should be devoid of any radiographic
exposure or processing artefacts.
6. Radiographs where the lower canine was missing
were excluded because of the possibility of mesial
premolar drift.
7. Radiographs in which the upper premolars were
missing were excluded because of the possibility of
overeruption of the lower premolars.
2.2. Methods
The dental panoramic radiographs were placed on
Stomatology Edu Journal
a radiograph view-box. A transparent tracing paper
was placed over the radiograph and fixed properly
to ensure it remain static in relation to the film. An
imaginary line was drawn to outline the second
premolar. A line was drawn to join the mesial and
distal points of the cement-enamel junction (CEJ).
Another line was drawn at the tip of the crown, parallel
to the line joining the CEJs. A line vertical to both
these lines was then drawn. It represents the crown
height of the second premolar. A pair of caliper was
used to transfer this distance to a metal ruler to obtain
an exact measurement. This measurement was then
divided by 4 (calculated to the nearest millimeter) to
give the height of a quarter-crown. The distance from
the mental foramen to the apex was measured using
the second premolar crown height as a ruler (Fig. 1)
and was categorised as below:
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
located at apex
within ¼-crown-distance
within ½-crown-distance
within ¾-crown-distance
within 1-crown-distance
within 1½ -crown-distance
within 2- crowns-distance
Could not be identified
ENDODONTICS
Figure 1. An illustration showing the method used to
determine the distance of the mental foramen to the apex of
the second premolar using the crown height as a ruler
(Note: In this dental panoramic radiograph, the mental
foramen is located at the apex of the second premolar).
3. Results
There were a total of 97 radiographs with bilateral
sites that fulfilled the criteria and were examined.
Thirty-one of the subjects fell into those aged
between 20-29 years, 24 subjects were between
30-39 years old, 22 between 40-49 years old and
the final 20 were aged 50 years and above. The
number of subjects (hence radiographs) that fulfilled
the criteria set became less with the age increase as
there was a high number of subjects who become
fully edentulous or partially edentulous beginning
from the first premolar.
The mental foramen was visible in 77.8% (151) of the
sites reviewed. It was slightly more pronounced on
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