SEJ_2-2017_Articol_Ngeow
ENDODONTICS
A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE”
Original Articles
AGAINST ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
Wei Cheong Ngeow1a*, Dionetta Delitta Dionyssius1b, Hayati Ishak1b
1
Department of Oro-Maxillofacial Surgical and Medical Sciences, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia
BDS (Mal), FFDRCS (Ire), FDSRCS (Eng), MDSc (Mal), PhD (Sheffield), FAMM
a
BDS (Mal)
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 mental paraesthesia related to root canal treatment
The mental foramen is located close to the of mandibular premolar teeth. However, all these
mandibular premolars, especially the second incidents were related to periapical infection or
premolar.1 A morphometric study by Philips et al.2 pathology, instead of being a complication of the
reported the mental foramen to be located on root canal treatment itself as the authors excluded 2
average at a distance of 2.18 mm mesially and 2.4 (0.24%) cases of severe overfill and iatrogenic root
mm inferiorly from the plain radiographic apex of perforation with mechanical instrumentation into the
the second premolar. More precisely, the mental mental nerve.3
foramina could be located anywhere 3.8 mm mesially Eliminating infection in the pulp and dentin,
2.7 mm distally, 3.4 mm above or 3.5 mm below the followed by adequate intra-canal preparation
apex of the second premolar. Various cadaveric and proper sealing constitute the basic principles
studies reported the apices of the second premolars of root canal treatment. Ideally, mechanical
to be between 0 and 4.7 mm away from the mental preparation and filling should be limited within the
foramen.3,4 Using a newer technology of cone beam root canal as overinstrumentation or the extrusion
computed tomography (CBCT), BÜrklein et al.5 also of chemical fillings beyond the apical foramen to
reported similar findings, with an average distance of the adjacent nerve can give rise to NSD such as
4.2 mm. However, 3.2% of the mental foramen was paraesthesia or anaesthesia.7,8 Paresthesia related
directly in contact with the second premolar. to overinstrumentation usually resolves within
Because of this close proximity, various events several days.9 In addition, minor material extrusions
affecting the second premolar, such as odontogenic are generally well tolerated by the periradicular
infection and orthodontic, endodontic, periodontal tissues as long as they do not spread to the adjacent
or surgical misadventure, may result in the nerve.10 However, long-term NSD has been reported
neurosensory disturbance to the area innervated by in cases where the nerve fibre is lacerated due to
the mental nerve that exits the mental foramen.1,6 A overinstrumentation or in contact with toxic overfilled
retrospective study found an incidence of 0.96% of 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: ngeowy@um.edu.my
108 Stoma Edu J. 2017;4(2): 108-113 http://www.stomaeduj.com
A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE” AGAINST
ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
As the close proximity of the apices of the a radiograph view-box. A transparent tracing paper
Original Articles
mandibular premolar to the mental foramen acts was placed over the radiograph and fixed properly
as an important contributory factor for NSD when to ensure it remain static in relation to the film. An
overinstrumentation or overfilling of endodontic imaginary line was drawn to outline the second
materials happen, it is the aim of this study to premolar. A line was drawn to join the mesial and
determine the distance of the mental foramen to distal points of the cement-enamel junction (CEJ).
the second mandibular premolar tooth. We chose Another line was drawn at the tip of the crown, parallel
to concentrate on the second premolar only as an to the line joining the CEJs. A line vertical to both
earlier study has shown that most of the terminal end these lines was then drawn. It represents the crown
of the inferior alveolar nerve is located in line with height of the second premolar. A pair of caliper was
the apex of the second premolar.12 In this pilot study, used to transfer this distance to a metal ruler to obtain
also conducted on a selected Malay population, an exact measurement. This measurement was then
we seek to determine the average distance of divided by 4 (calculated to the nearest millimeter) to
the mental foramen from the apex of the second give the height of a quarter-crown. The distance from
premolar by using the crown height of the second the mental foramen to the apex was measured using
premolar as a ruler. The identification of this distance, the second premolar crown height as a ruler (Fig. 1)
will hopefully enable us to come up with a so called and was categorised as below:
“safe zone” to ensure that root canal treatment in
the lower premolar region can be performed with I. located at apex
minimum complications in case files or endodontic II. within ¼-crown-distance
filling materials are accidentally extruded beyond III. within ½-crown-distance
the apices of these premolars. IV. within ¾-crown-distance
V. within 1-crown-distance
2. Methodology VI. within 1½ -crown-distance
2.1. Materials VII. within 2- crowns-distance
One hundred twenty panoramic radiographs of VIII. Could not be identified
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
Figure 1. An illustration showing the method used to
radiolucency. determine the distance of the mental foramen to the apex of
3. Radiographs must be free from any radiolucent or the second premolar using the crown height as a ruler
radiopaque lesion in the lower arch. There should (Note: In this dental panoramic radiograph, the mental
be no evidence of jaw fracture around the mental foramen is located at the apex of the second premolar).
foramen region.
4. Radiographs with supernumeraries and unerupted 3. Results
teeth were excluded because the impacted/ There were a total of 97 radiographs with bilateral
unerupted teeth might obscure the appearance of sites that fulfilled the criteria and were examined.
mental foramen. Thirty-one of the subjects fell into those aged
5. Films should be devoid of any radiographic between 20-29 years, 24 subjects were between
exposure or processing artefacts. 30-39 years old, 22 between 40-49 years old and
6. Radiographs where the lower canine was missing the final 20 were aged 50 years and above. The
were excluded because of the possibility of mesial number of subjects (hence radiographs) that fulfilled
premolar drift. the criteria set became less with the age increase as
7. Radiographs in which the upper premolars were there was a high number of subjects who become
missing were excluded because of the possibility of fully edentulous or partially edentulous beginning
overeruption of the lower premolars. from the first premolar.
2.2. Methods The mental foramen was visible in 77.8% (151) of the
The dental panoramic radiographs were placed on sites reviewed. It was slightly more pronounced on
Stomatology Edu Journal 109
A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE” AGAINST
ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
Original Articles Table 1. Distribution for location of mental foramina according to age-groups.
Location 20-29 years 30-39 years 40-49 years ≥ 50 years
[site/percentage] [site/percentage] [site/percentage] [site/percentage]
Apex 23 (37.1%) 17 (35.4%) 9 (20.4%) 7 (17.5%)
¼-crown 14 (22.6%) 11 (22.9%) 11 (25%) 4 (10%)
½-crown 4 (6.4%) 5 (10.4%) 3 (6.8%) 0 (0%)
¾-crown 4 (6.4%) 2 (4.2%) 11 (25%) 2 (5%)
1-crown 6 (9.7%) 7 (14.6%) 2 (4.5%) 3 (7.5%)
1½-crown 0 (0%) 2 (4.2%) 1 (2.3%) 3 (7.5%)
2-crown 0 (0%) 0 (0%) 0 (0%) 0 (0%)
Not visible 11 (17.8%) 4(8.3%) 7 (16.0%) 21 (52.5%)
the left (80.5%; 78 sites) than the right side (75.3%; Age-wise, all mental foramina were noted to be
73 sites) of the mandible. Out of the mental foramina located within a one-crown distance from the apex
that were visible, 96% were found to be located in panoramic radiographs of subjects aged 20-29
within a one-crown distance from the apex. More years. However, between 84.2% and 95.4% of them
mental foramina (37.1%; 56 sites) were located at the were located within a one-crown distance for the
apex than at any other locations. This is followed by remaining 3 age groups.
finding the mental foramina located within a ¼-crown Figure 2 shows the distribution of the mental
distance from the apex (26.5%; 40 sites). foramina according to the gender of the subjects.
Table 1 shows the overall distribution of mental The majority of the foramina were located within a
foramen according to various age groups. The one-crown distance from the apex, irrespective of
mental foramina were visible in the majority of gender (female 95.4%; male 96.5%). The apex of the
panoramic radiographs of subjects under the age second premolar was the most common location
of 50 years (20-29 years: 82.3%; 30-39 years: 91.7%; for finding mental foramen in both genders (female
40-49 years: 84.1%). However, they did not become 40.9%; male 34.1%). However, there were gender
visible in more than half (52.5%) of panoramic differences for other locations, with the ¼-crown
radiographs of subjects aged 50 and above. This distance being the second most common for female
finding is statistically significant (Pearson Chi-square; but ¼- and ¾-crown distance for the male. When
p<0.001) the mental foramina were not observed, more of
Figure 2. Distribution of the mental foramina according to the gender of the subjects.
110 Stoma Edu J. 2017;4(2): 108-113 http://www.stomaeduj.com
A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE” AGAINST
ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
this happened in panoramic radiographs of female magnification from 10% to 30%, image distortion and
Original Articles
subjects (28 sites) than male (15 sites). This difference invisibility in the facio-lingual dimension. Therefore,
was statistically significant (Pearson Chi-square; measuring directly on different radiographs taken
p=0.01) using different machines with different distortion
would result in a compromised finding. However, by
4. Discussion calculating a ratio based on the crown height as a tool
Neurosensory disturbance (NSD) after root canal of measurement, it is hoped that this will ensure that
treatment is an outcome of a rare accident at the we are always consistent in relating distance between
apical region of the mandibular posterior teeth. the mental foramen and the apex of the second
Numerous reports have been published describing premolar. This ratio can be used to provide a mental
the occurrence of NSD during and after endodontic picture of the distance available based on the average
treatment of the mandibular premolars7,8,13,14 with crown height of a mandibular second premolar of 8.2
the possible mechanisms attributed to 3 factors, mm, with a crown to root ratio of 1:1.8.17
namely mechanical, chemical, and thermal damage. Translating the finding that 96% of mental foramina
Mechanical damage results from compression that were found to be located within one-crown distance
occurs during overinstrumentation or by the filling from the apex, this can easily suggest that a majority
material forced into the mandibular canal.15 Chemical of the mental foramina were located within a 8.2 mm
damage, on the other hand, happens where there perimeter from the apices of the second premolar.
is an extrusion of cytotoxic products used during Worse, almost two-thirds (63.6%) of the mental
root canal preparation (irrigation and/or root canal foramina were located either at the apex or within
medication) or obturation while thermal damage a quarter crown-height distance from the apex,
is related to a lack of control in thermocompaction translating to a ‘safe zone’ between 0 to 2 mm only!
filling techniques.9,16 Nevertheless, the distance recorded in this study is
The close proximity of the apices of the mandibular still larger than that reported by Phillips et al.2 where
premolar and molar teeth to the mental foramen and the centre of the mental foramen was located on an
mandibular canal fascilitate NSD to happen when average distance of 2.18 mm mesially and 2.4 mm
overinstrumentation or overfilling of endodontic inferiorly from the radiographic apex of the second
materials happened.1,15 In the molar/premolar premolar. Our finding, together with that reported by
region, the inferior alveolar nerve describes a curve Phillips et al.2 earlier, suggests that there is no really
that brings the second premolar as well as the “safe zone” against accidental extrusion of endodontic
second molar root apices in closest proximity to the files and materials in the second premolar region.
nerve.4 Not many researchers have looked into the Two secondary findings that are statistically significant
distance of the premolar teeth to the terminal end of are the fact that more mental foramina were not
the inferior alveolar nerve, namely the mental nerve noticeable in female patients and in patients aged
and its foramen.2,3,4,5 Worse all of these studies were more than 50 years old. The latter finding has been
undertaken on Caucasian subjects. We, therefore, feel reported in an earlier publication.18 The effect of
it is timely to study this relationship in Asia due to the gender on non-visibility of mental foramen has not
fact that endodontic extrusions with complication are been reported, and could be related to the difficulty
still being reported every now and then. We hoped to to distinguish it from trabeculae pattern in these
define a “safe zone” apical to the mandibular second patients, in addition to poor radiograph quality (over
premolar, if one indeed exists. dark radiographs).19 As osteoporosis affects female
Bürklein et al.5 recently undertook such a study subjects more than males, it is possible that is a
using data generated from cone beam computed potential contributing factor although this suggestion
tomography. However, CBCT is not as widely used remains a hypothesis due to the fact that we did not
in our centre, and we instead have a huge archive actively seek to determine if these subjects were
of data stored in panoramic radiographs. Hence indeed having bone metabolism disorder.
we decided to study the premolar-mental foramen
relationship in panoramic radiographs as this is still 5. Conclusion
relevant clinically. However, as measurement done More mental foramina were significantly not visible
on panoramic radiographs is generally considered in panoramic radiographs of female subjects than
distorted, it was decided that the crown height was male. Of mental foramina that were visible, 96% were
used as a comparative ruler because of two reasons: found to be located within one-crown distance from
a) the inability to accurately measure the length/ the apex. Almost two-thirds (63.6%) of the mental
distance as these images were in hard copies, as foramina were located either at the apex or within
opposed to the newer machine with a measuring a quarter crown-height distance from the apex. The
software, and visibility of the mental foramen was found to be
b) for clinical application sake, whereby it was felt that significantly limited in patients aged 50 and above.
dentists/endodontists may want to have a mental These findings suggest that there is no “safe zone” for
map of the “safe zone” around the premolar region, accidental extrusion of endodontic files and materials
which can easily be related to the crown-height of the in the second premolar region.
tooth concerned. This may become important when
only a periapical radiograph is taken for endodontic Acknowledgments
purpose. The authors report no conflict of interest and there
It is well accepted that dental panoramic radiographs was no external source of funding for the present
have some disadvantages, namely, variable study.
Stomatology Edu Journal 111
A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE” AGAINST
ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
References
Original Articles
1. Ngeow WC. Is there a “safety zone” in the mandibular 11. Morse DR. Endodontic-related inferior alveolar nerve and
premolar region where damage to the mental nerve can mental foramen paresthesia. Compend Contin Educ Dent
be avoided if periapical extrusion occurs? J Can Dent 1997;18(10):963-968, 970-973, 976-978 passim; quiz 998.
Assoc. 2010;76:a61. Review.
[Full text links] [Free Article] [PubMed] Google Scholar(11) [PubMed] Google Scholar(60) Scopus(33)
Scopus(6) 12. Ngeow WC, Yuzawati Y. The location of the mental
2. Phillips JL, Weller RN, Kulild JC. The mental foramen: foramen in a selected Malay population. J Oral Sci.
2. Radiographic position in relation to the mandibular 2003;45(3):171-175.
second premolar. J Endod. 1992;18(6):271-274. [PubMed] Google Scholar(151) Scopus(73)
[PubMed] Google Scholar(85) 13. Scarano A, Di Carlo F, Quaranta A, et al. Injury of the
3. Knowles KI, Jergenson MA, Howard JH. Paresthesia inferior alveolar nerve after overfilling of the root canal
associated with endodontic treatment of mandibular with endodontic cement: a case report. Oral Surg Oral
premolars. J Endod. 2003;29(11):768-770. Med Oral Pathol Oral Radiol Endod. 2007;104(1):e56-59.
doi:10.1097/00004770-200311000-00019 doi: 10.1016/j.tripleo.2007.01.036
[Full text links] [PubMed] Google Scholar(55) Scopus(30) [Full text links] [PubMed] Google Scholar(42) Scopus(14)
4. Denio D, Torabinejad M, Bakland LK. Anatomical 14. Grötz KA, Al-Nawas B, de Aguiar EG, et al. Treatment of
relationship of the mandibular canal to its surrounding injuries to the inferior alveolar nerve after endodontic
structures in mature mandibles. J Endod. 1992;18(4):161- procedures. Clin Oral Investig. 1998;2(2):73-76.
165. doi: 10.1016/S0099-2399(06)81411-1 [PubMed] Google Scholar(62) Scopus(38)
[Full text links] [PubMed] Google Scholar(117) Scopus(52) 15. Scolozzi P, Lombardi T, Jaques B. Successful inferior
5. Bürklein S, Grund C, Schäfer E. Relationship between root alveolar nerve decompression for dysesthesia following
apices and the mandibular canal: a cone-beam computed endodontic treatment: report of 4 cases treated by
tomographic analysis in a German population. J Endod. mandibular sagittal osteotomy. Oral Surg Oral Med Oral
2015;41(10):1696-1700. doi: 10.1016/j.joen.2015.06.016 Pathol Oral Radiol Endod. 2004;97(5):625-631. doi:
[Full text links] [PubMed] Google Scholar(12) Scopus(7) 10.1016/S1079210404000502
6. Ngeow WC. Lower lip numbness due to peri-radicular [Full text links] [PubMed] Google Scholar (93) Scopus(49)
dental infection. Med J Malaysia. 1998; 53(4): 446-448. 16. Tilotta-Yasukawa F, Millot S, El Haddioui A, et al.
[Full text links] [Free article] [PubMed] Google Scholar(9) Labiomandibular paresthesia caused by endodontic
Scopus(4) treatment: an anatomic and clinical study. Oral Surg Oral
7. Poveda R, Bagan JV, Fernandez JM, et al. Mental nerve Med Oral Pathol Oral Radiol Endod. 2006;102(4):e47-59.
paresthesia associated with endodontic paste within the doi: 10.1016/j.tripleo.2006.02.017
mandibular canal: report of a case. Oral Surg Oral Med [Full text links] [PubMed] Google Scholar(67) Scopus(30)
Oral Pathol Oral Radiol Endod. 2006;102(5):e46-49. doi: 17. Scheid RC, Weiss G. Woelfel's Dental anatomy:
10.1016/j.tripleo.2006.03.022 Its relevance to Dentistry. 8th ed. Chapter 3: Basis
[Full text links] [PubMed] Google Scholar(75) Scopus(31) terminology for understanding tooth morphology.
8. Pogrel MA. Damage to the inferior alveolar nerve as Philadelphia, PA: Lippincott Williams & Wilkins; 2012.
the result of root canal therapy. J Am Dent Assoc. Google Scholar(90)
2007;138(1):65-69. 18. Ngeow WC, Dionysius DD, Ishak H, et al. Effect of ageing
[Full text links] [PubMed] Google Scholar(134) Scopus(73) towards location and visibility of mental foramen on
9. Di Lenarda R, Cadenaro M, Stacchi C. Paresthesia of the panoramic radiographs. Singapore Dent J. 2010;31(1):15-
mental nerve induced by periapical infection: a case 19. doi: 10.1016/S0377-5291(12)70004-4
report. Oral Surg Oral Med Oral Pathol Oral Radiol [Full text links] [Free article] [PubMed] Google Scholar(8)
Endod. 2000;90(6):746-749. Scopus(7)
[Full text links] [PubMed] Google Scholar(50) Scopus(29) 19. Yosue T, Brooks SL. The appearance of mental
10. Pertot WJ, Camps J, Remusat M, Proust JP. In vivo foramina on panoramic and periapical radiographs. II.
comparison of the biocompatibility of two root canal Experimental evaluation. Oral Surg Oral Med Oral Pathol.
sealers implanted into the mandibular bone of rabbits. 1989;68(4):488-492.
Oral Surg Oral Med Oral Pathol. 1992;73(5):613-620. [PubMed] Google Scholar(76) Scopus(33)
[PubMed] Google Scholar(52) Scopus(17)
Wei Cheong NGEOW
BDS (Mal), FFDRCS (Ire), FDSRCS (Eng), MDSc (Mal)
PhD (Sheffield), FAMM, Professor Dr
Department of Oral & Maxillofacial Clinical Sciences
Faculty of Dentistry, University of Malaya
Kuala Lumpur, Malaya
CV
Professor Dr Wei Cheong Ngeow graduated from the Faculty of Dentistry of the University of Malaya
in 1992 and went into private practice before being offered a tutorship at his alma matter. In 1996, he
obtained his Fellowship in Dental Surgery from the Royal Colleges of Surgeons in Ireland and England,
respectively. Back in Malaysia he was a pioneer lecturer at the newly established Universiti Kebangsaan
Malaysia. He returned to private practice in 1999 but in 2000 returned to the University of Malaya He
obtained an MDSc (2008) and a PhD from the University of Sheffield (2010). He has published over
160 articles, letters, comments and reports in local and international journals, and was the Editor of the
Malaysian Dental Journal (2005-2007) and Editor of the MDA Newsletter (2015). His research interests
are craniofacial anthropometry, variations of the mandibular nerve, recovery of peripheral nerves after
microsurgical repair.
112 Stoma Edu J. 2017;4(2): 108-113 http://www.stomaeduj.com
A RADIOGRAPHIC STUDY TO DETERMINE THE POSSIBLE EXISTENCE OF A “SAFE ZONE” AGAINST
ENDODONTIC PERIAPICAL EXTRUSION IN THE LOWER PREMOLAR
Questions
Original Articles
1. Which tooth is usually closely related to the mental foramen?
qa. First premolar;
qb. Second premolar;
qc. First molar;
qd. Second molar.
2. Which of the following statements is not the main principle of endodontic treatment?
qa. Eliminating pain;
qb. Eliminating infection in pulp and dentine;
qc. Achieving adequate intracanal preparation;
qd. Achieving proper seal.
3. The following is not a factor that contributes to the occurrence of neurosensory disturbance
during endodontic treatment of the mandibular premolars:
qa. Mechanical;
qb. Chemical;
qc. Thermal;
qd. Psychological.
4. When translating the finding that 96% of mental foramina were found to be located within
one-crown distance from the apex, how far are the majority of the mental foramina located
within from the apices of the second premolar?
qa. 6 mm;
qb. 7 mm;
qc. 8 mm;
qd. 9 mm.
Stomatology Edu Journal 113