KNOWLEDGE OF THE SIZE OF MANDIBULAR
CORONOID PROCESS IN DETERMINATION OF SEX

 

Abstract

Background-
The coronoid process  derived from a
Greek word ‘korone’ is a flat piece of triangular bone projecting upwards from
the anterior margin of the mandible ramus. The coronoid process of the mandible
is being used as a graft material in reconstructive craniomaxillofacial
surgeries and as a non metric skull variant in assessment of age, sex, race and
species.  Hence the present study was
undertaken to assess the size of the coronoid process existing in south Indian
adult population on both sides and to assess the feasibility of using this
knowledge in identification of sex. Material
and methods- The study includes 30 male and 30 female mandibles which were
collected from various medical colleges. The size of the process was assessed
by measuring the height and widths of the coronoid process at its base. Total
length of the ramus at the coronoid process was also measured. Results were
tabulated and statistically analysed using student paired T test with p?0.05. Results-The height of coronoid process
and the length of the ramus at the coronoid process have significant differences
on right and left sides in males and female mandibles and can thus be used as
metric variants in determination of sex.

Key words  –
coronoid process ; mandible ; size ; sex determination

Introduction

The mandible is the largest, strongest and the only
movable bone of the skull with slow resorption rate. As such it is a frequent
entity found in long standing skeletal remains and forms an important marker in
identification. It has an arched body with two ascending rami ending in two
processes namely the condylar  and coronoid
processes. The coronoid process derived from a Greek word ‘korone’ (meaning
crow’s beak/crown) is a triangular flat piece of bone projecting upwards from
the anterior margin of the mandibular ramus. It receives the insertion of the
temporalis on its medial surface, anterior margin, apex and massetter on its
lateral surface. These two are important muscles of mastication which show functional
as well as morhpological dependence 1.
The shape of ramus is species specific amongst primates.  Human ramus resembles that of a chimp with
relatively slender coronoid process (particularly at its tip), shorter in
height, separated from the condylar process by a deep notch.  Several other primates resemble gorillas
having a broad coronoid process and separated by a shallow mandibular notch2.  Recently many authors like  Isaac, Narayana and M subbaramaiah have
described  various forms of coronoid
process that are evident in human mandibles like triangular, rounded, hook
shaped, rectangular, flattened etc3,4,5.

The various forms of coronoid process help in determination
age and sex to a large extent4,5. The coronoid
process is large and projects above the level of condyle at birth. Gradually
with the growth of the neck of the mandible, condyles almost reach the same
height as coronoid process at adulthood. Further age increase is associated
with resorption of the alveolar processes and coronoid process once again
becomes taller1. Bilateral elongation of the coronoids of the
mandible made of histologically normal bone goes more in favour of it being
hyperplasic. Elongated coronoid process leads to a progressive, painless
difficulty in opening the mouth; due to contact of coronoid process with the
temporal surface of the zygomatic bone or medial surface of the zygomatic arch.
Coronoid
process enlargement may be also seen in some pathological conditions like
osteochondroma, exostosis, osteoma and other developmental anomalies6.
Hernandez-Alfaro noticed a new joint inbetween the enlarged coronoid process
and the zygomatic bone (Jacob’s disease) which causes restriction during mouth
opening7.

The coronoid process of the mandible is gaining
vital importance as a graft material in all aspects of reconstructive
craniomaxillofacial surgeries like orbital floor reconstruction, paranasal
augmentation and  temperomandibular joint
ankylosis due to its close proximity , slow resorption rate and easy
accessibility8,9,10.  Coronoid process is also being used as a non
metric skull variant in assessment of age, sex, race and species2. The clinical applications
of coronoid morphology in the field of craniofacial reconstructive surgery has
already been well documented in literature5.  The present study was under taken to assess
the size of the coronoid process existing in Indian adult population on both
sides and to assess the feasibility of using this knowledge of coronoid
morphology in identification of sex.

Material and methods

The mandibles were collected from departments of anatomy
in and around Bangalore. 30 male and 30 female mandibles were retrieved during
routine cadaver dissection for undergraduate M.B.B.S students, and assessed
regarding the size of the coronoid process on right and left sides.  Mandibles of adult age group were included in
the study. The mandibles in which the coronoid  process was damaged or deformed were excluded
from the study.

The basal point of mandibular notch was marked as a
reference point. The height and width of coronoid process were measured from
the reference point using vernier callipers. Total length of the ramus at the
coronoid process was also measured (Photographs A and B). Results were
tabulated. The data was statistically analysed for the purpose of comparison
and correlation by calculating the mean, range and standard deviation of width
,height of coronoid process and length of ramus at coronoid process. Student’s
paired t-test with two-tailed distribution was applied for comparison of the different
parameters on both sides in male and female mandibles. P-value ?0.05 was
considered as statistically significant.

 

Results

From the present study it was noted that the length
of the ramus at the coronoid process and the height of coronoid process have
significant differences on right and left sides in males and female mandibles.(Table
and Graph)

Coronoid height – Average height of coronoid process
in Indian population -1.39±0.34cm (0.6-2.2cm). 
Average height of coronoid process was greater on right side by 0.21cm.
Difference is statistically significant(p-value 0.046). No significant
variation in height of coronoid process between male and female mandibles.  However when side was taken into
consideration female mandibles showed higher variation.

Coronoid width – Average width of coronoid process
in Indian population -1.67±0.23cm (1.1-2.2cm). No significant variation in
width of coronoid process between male and female mandibles on right and left
sides. However when sex was taken into consideration male mandibles showed
higher variation between right and left sides.

Ramus length at coronoid process-Average length of
ramus at coronoid process in Indian population -5.89±0.51cm (4.4-7.1cm). Average
length of ramus at coronoid process was greater on left side. Significant
variation was seen in length of ramus at coronoid process between male and
female mandibles (p-value 0.038).  When
side was taken into consideration male mandibles showed greater length on left
side.

Thus from the present study it was noted that the
length of the ramus at the coronoid process and the height of coronoid process
have significant differences with respect to laterality and sex of the mandible
.

 

Discussion

The mandibular coronoid process derived from a Greek
word ‘korone’ meaning crow’s beak or crown is a flat piece of triangular bone
projecting upwards from the anterior margin of the mandibular ramus 1.   Initially development of coronoid process
begins on the 55th day of intrauterine life (24mm stage) in membranous
form. At about the 70th day of intrauterine life (43mm stage) two bony
processes are mapped out. At 13th
week of intrauterine life, a strip of cartilage appears along the anterior
border of coronoid process which is later displaced by the membrane bone. This
cartilage usually disappears before birth but can persist as subcoronoid sutures. Further
development of coronoid process is associated with much variation in morphology
and morphometry of the coronoid process. This can be attributed to various
factors like-

 a) socio
demographic profile of the individuals (eating habits ,occupation) which has a
direct or indirect affect on the size of the temporalis muscle altering the
size ansd shape of the coronoid process .

b) Diet as we know has a vital role in affecting the
muscular pull on the bony process thereby altering the final  shape and size of the process 11,12.

c) Masseter-Temporalis (M-T) component is active in
the robust vertical thrust during mastication. The functional factors
necessitate the right coronoid process to be longer than the left as most
people tend to chew on the right side. This is vindicated by the data of
previous studies in the dentulous mandibles. Lateralization of the M-T-lever
effect largely depends upon the individual masticatory behavior. . This is also
reflected in the shape of the coronoid process as larger stress helps it to get
remodeled as triangular with pointed tip, less stress for rounded and further
less being the hooked coronoid process.

d) Male hormonal impact on muscle growth, bone
remodelling and psychology probably lead to enhanced functional stress on the
mandible due to mastication as compared to that of females13.Hook
shaped coronoid process goes in favour of female mandibles5.

e) Genetic impact also play a role in remodelling of
the coronoid process13.As such samples taken from different
population may lead to variation in size and form of the process.

The final form and size of coronoid process depends
on all the above factors. According to S. Nayak et al.  the size of coronoid process was found to be
approximately 1.5 mm longer on the right side than on the left side. Triangular
coronoid process was found to be the longest followed by round and then hook
shaped14. The findings of the
present study are consistent with most other previous studies done, the size of
the right coronoid process being greater than the left. This difference was
even more marked when sex was taken into consideration. However the actual
height, width of the coronoid process and length of ramus at coronoid showed
variation which could be due to any of the above factors or due to sample
variation. Thus larger population needs to be included in order to generalise
the data14, 15, 16.

Conclusions

The coronoid process is a membranous bone showing
less resorption and remains unaltered for a long time and can serve as a very
useful anthropological marker.  From the
present study it can be said that coronoid process exists in many sizes.
Numerous factors either directly or indirectly affect the final appearance of
the coronoid process. The data of size of the mandibular coronoid process as
seen from the study can be utilised for comparison  of anthropometric results from different
population. The height of coronoid process and the length of the ramus at the
coronoid process have significant differences on right and left sides in males
and female mandibles and can thus be used as metric variants in determination
of sex. The data will also help the dental and maxillo-facial surgeons in
planning graft implants and reconstructive surgeries.

Conflict of interest – Nil

References

1. Susan Stranding ed. Gray’s Anatomy:  The Anatomical basis of clinical practice
40th Ed. Churchill Livingstone, Elsevier; 2008, 530-533.

2. Rak Y., Ginsbing A., Geffen E. Gorilla like
anatomy of Australapithicus aferensis mandible. 
Proc. Nat. Acad. Sci. U. S. A., April 2007; 104(16):  6568-6572.

3. Isaac B. and Holla S. J. Variations in the shape
of coronoid process in the adult human mandible. Journal of Anatomical Society
of India 2001; 50(2): 137-139.

4. Prashanthi N., Narayana K., and Nayak S. R. ;
Morphology of lingula, coronoid process and the mandibular notch in Indian dry
mandibles. Folia Anatomica, Belgrade 2004; 31(1): 13-16.

5. Subbaramaiah M, Bajpe R, Jagannatha SR .Jayanthi
KS. A Study of Various Forms of Mandibular Coronoid Process in Determination of
Sex. Indian Journal of Clinical Anatomy and Physiology. 2015;2(4):199-203.

6. Fernandez FM, Fernandez SJ, Sandoval GJ, Costas
LA, Lopez de SA, Etayo PA. Treatment of Bilateral Hyperplasia of the Coronoid
Process. Med Oral Patol Oral Cir Bucal. 2008;13:595–598.

 7.
Herna´ndez-Alfaro F, Escuder O, Marco V. Joint formation between an
osteochondroma of the coronoid process and the zygomatic arch (Jacob disease):
report of case and review of literature. J Oral Maxillofac Surg.
2000;58(February (2)):227– 232.

8. Mintz S. M., Ettinger A Schmakel T and Gleason M.
J. ;  Contralateral coronoid process bone
grafts for orbital floor reconstruction- an anatomic study and clinical study.
Journal of Oral and Maxillofacial Surgery, 1998; 56(10): 1140-1144.

9. Choung P., Kim S. ;  The coronoid process for paranasal
augmentation in the correction of midfacial concavity. Oral Medicine, Oral
Pathology, Oral Radiology, Endod. 2001; 91: 28-33.

10. Egito
Vasconcel B.C., Gabriel Granja Porto, Ricardo Viana, Bessa Nogvelira ; Tempero
mandibular joint ankylosis.  Revista
Brasilaria Otorrinolaringologia, Feb. 2008; 74(1): 34-38.

11.  Avis. V ; 
The relation of the temporal muscle to the form of coronoid process.
American Journal of Physical Anthropology, 1959; 17: 99-104.

12. Meopi N Syropoulos ; The morphogenetic
relationship of the temporalis muscle to the coronoid process in human embryos
and fetuses. American Journal of Anatomy, April 1977; 150: 395-410.

13. Coronoid-condylar index in assessing of
mandibular coronoid hyperplasia : Advances in Medical Sciences ; Vol. 58(2) ;
2013 : 429-433 . DOI: 10.2478/ams-2013-0005 © Medical University of Bialystok,
Poland .

14. Study of the Size of the Coronoid Process of
Mandible S. Nayak1 , S. Patra2 , G. Singh3 , C. M IOSR Journal of Dental and
Medical Sciences (IOSR-JDMS) e-ISSN: 2279-0853, p-ISSN: 2279-0861.Volume 14,
Issue 6 Ver. I (Jun. 2015), PP 66-69.

15. Kasat PA, Bhuiyan PS. A study on coronoid
process of the dry adult human mandibles. Journal of the Anatomical Society of
India. 2016 Jun 30;65(1):9-14.

16. Bakirci S, Ari I, Kafa IM. Morphometric
characteristics and typology of the coronoid process of the mandible. Acta Med
Mediter. 2013;29:683–686