Anatomy of mandible and its importance in implant placement

1. ANATOMY OF MANDIBLE AND ITS
IMPORTANCE IN IMPLANT
PLACEMENT

2. INTRODUCTION
 The word mandible derived from Latin word mandibula-
"jawbone" or inferior maxillary bone.
 Only movable bone in the skull
 It consists of an anterior Horseshoe-shaped body, and of two
rami that project upwards from the posterior part of the body.
 It provides structural and protective support for the oral
cavity.
 The mandible is articulated in ball and socket fashion at the
condylar process.
 Strength resides in its dense cortical plates

3. ANATOMY
OF
MANDIBLE

4. embryology
 Mandible is the second bone after clavicle to
ossify in the body.
 Parts that ossify in cartilage includes: incisive
part below the incisor teeth, coronoid and
condyloid processes
 Upper half of ramus above the level of the
mandibular foramen
 A single ossification centre for each half of the
mandible arises in the 6th week of I.U. life in
the region of bifurcation of inferior alveolar
nerve into mental and incisive branches. As the
ossification continues, the meckel’s cartilage
become surrounded and invaded by bone.

5.  It is partly membranous & partly cartilaginous in ossification.
• Incisive part below symphysis
menti
• Coronoid
• Condyloid process
• Upper half of ramus
Cartilage
• Whole of body except lower incisive
part
• Lower half of ramus upto mandibular
foramen
Membrane

6. OSTEOLOGY
BODY OF THE MANDIBLE
 Horseshoe-shaped BODY
 Has two surfaces EXTERNAL and INTERNAL surfaces ,
 Two borders UPPER and LOWER borders

7. FEATURES SEEN ON OUTER SURFACE OF THE BODY
 Symphysis Menti
 Mental Protuberance
 Mental Tubercles
 Mental foramen
 External Oblique line
 Incisive fossa

8. FEATURES ON THE INNER SURFACE OF THE BODY
 Genial tubercles
 Mylohyoid line
 Submandibular fossae
 Sublingual fossae
 Mylohyoid groove
 Upper alveolar border
 Lower border base
 Digastric fossae

9. BORDERS OF THE MANDIBLE

10. SUPERIOR BORDER (ALVEOLAR BORDER)
It is hollowed into cavities for the reception of the teeth, these cavities are
sixteen in number, and vary in depth and size according to the teeth which
they contain.

11. INFERIOR BORDER (base of mandible)
Is rounded, longer than the superior,
and thicker in front than behind.

12. RAMUS OF MANDIBLE
Is quadrilateral
2 surfaces
Lateral
Medial
4 borders
Superior
Inferior
Anterior
Posterior
2 processes
Coronoid
Condylar

13. PROCESSES
CORONOID PROCESS
 Flat ,triangular
 Upward and forward projection
from anterolateral part of ramus
 Anterior border continuous with
anterior border of ramus
 Posterior border bounds the
mandibular notch

14. CONDYLAR PROCESS
 Upward projection from postero
superior part of ramus
 Apically enlarged as head of
condyle.
 Articulates with temporal bone’s
mandibular fossa to form
temperomandibular joint
 Lateral aspect palpable in front
of tragus
 Pterygoid fovea anterior to neck

15. ATTACHMENTS AND RELATIONS

16. ON THE LATERAL
SURFACE:
1. From The Oblique line :
Buccinator, and depressor anguli
oris below the mental foramen
2. Incisive fossa:
gives origin to MENTALIS mental
slips of ORBICULARIS ORIS.
3. Whole of lateral surface of
ramus except posterosuperior part
provides insertion to MASSETER.
4.Posterosuperior part : covered
by PAROTID GLAND

17. 5. Lateral surface of the neck
provides insertion to the
LATERAL LIGAMENT OF
TMJ.
6. Parts of both the inner and
outer surfaces just below the
alveolar margins are covered by
mucous membrane of the
mouth.
7. PLATYSMA is inserted into
the lower border.
8. The deep cervical fascia (
investing layer) is attached to
the whole length of the lower
border.

18. 1. Digastric fossa: arises
ANTERIOR BELLY OF
DIGASTRIC
2. Genial tubercles: arises
GENIOGLOSSUS and
GENIOHYOID.
3. Mylohyoid line : arises
MYLOHYOID MUSCLE.
4. From an area above the
posterior end of mylohyoid line:
arises SUPERIOR
CONSTRICTOR OF PHARYNX.
5. Pterygomandibular raphe:
Attached immediately behind the
third molar tooth in continuation
with the origin of superior
constrictor
ON THE MEDIAL SURFACE

19. 7.Below and behind the mylohyoid
groove: insertion of MEDIAL
PTERYGOID muscle .
8.At the apex of coronoid process :
TEMPORALIS is inserted ;extend
downwards on ant. Border of ramus.
9.Into the pterygoid fovea: insertion
of LATERAL PTERYGOID.
10.Sphenomandibular ligament : is
attached to the lingula.

20. BLOOD SUPPLY OF THE MANDIBLE
ARTERIAL SUPPLY
Mainly by Maxillary artery,
Branch of external carotid
artery
By its branches, mainly
through inferior alveolar
artery

21. Venous supply of mandible
 Drains into
Internal jugular vein and external
jugular vein through maxillary vein,
facial vein and pterygoid plexus

22. Nerve supply of mandible
Mainly through the trigeminal nerve -
V cranial nerve
MANDIBULAR NERVE
 Main trunk
 Anterior trunk
 Posterior trunk

23. FORAMINA AND OTHER RELATIONS
 Mental foramina - mental nerve and
vessels
 Mandibular notch - massetric nerve
and vessels
 Medial side of neck - auriculo
temporal nerve
 Mylohyoid groove - mylohyoid nerve
and vessels
 Mylohyoid groove in front of ramus -
lingual nerve
 Mandibular canal and foramina -
inferior alveolar nerve and vessels

24. POSTNATAL GROWTH OF
THE MANDIBLE

25.  According to the data from the vital staining experiments, the
posterior surface the ramus, the condyle and coronoid process are
principal sites of growth.
 Growth is quite general during the first year of life with all
surfaces showing bone apposition.
 Mandibular growth becomes more selective.
Postnatal Growth Of Mandible

26. The mandible can be divided into several sub-units like
 Chin
 Alveolar process
 Body
 Lingual tuberosity
 Ramus
 Angular process
 Coronoid process
 Condylar process

27.  Chin:
 1-2 years→ chin prominence is seen
 The mental protuberance forms by bone
deposition
 The change in the contour occurs by
following two mechanism.
1) The area just above the chin and
the base of the alveolar process,
is a resorptive area.
2) There is forward translation of
chin as mandible grows forward.

28.  Alveolar process:
 This develops in response to the developing tooth buds.

29.  Body: (corpus)
 The length of the body increases as the ramus
moves posteriorly

30.  Lingual tuberosity:
 It forms the boundary between
the ramus & body
 A combination of the resorption
and deposition accentuates its
prominence.

31.  Ramus:
 The ramus is seen to move posteriorly due to
deposition at its posterior border and resorption on
its anterior border

32.  Angle:
 The combined deposition and resorption causes flaring
of the angle of the mandible

33.  Coronoid process :
 Enlow’s enlarging “V” principle.
 Birth: Coronoid process is at
higher level than condylar
process.
 Childhood: Coronoid & condylar
processes are at same level.
 Adult: Condylar process is at
higher level.

34.  Condyle:
 Condylar growth rate increases at
puberty and reaches its peak by
12-14 years.
 The growth ceases at around 20
years
 Role of condyle:
o Primary displacement

36. APPLIED ANATOMY OF MANDIBLE
 Parasymphysis region lateral to the mental prominence is a
naturally weak area susceptible for parasymphyseal fracture.
This is because of the presence of incisive fossa and mental
foramen
 The body of the mandible is considerably thicker than the
ramus and the junction between these two portions
constitutes a line of structural weakness.
 Strength of the lower jaw varies with the presence or absence
of teeth. The presence of impacted lower third molars or
excessive long roots of canines make the area more
vulnerable for fracture.

37. IMPORTANCE IN IMPLANT PLACEMENT

38. Mandibular Foramen
 The location of the mandibular foramen may vary based on race and
ethnicity
 Among adult cadaveric mandibles, the foramen was found inferior to the
occlusal plane, at its level, or above it 75%, 22.5%, and 2.5% of the time,
respectively
 Therefore, according to these investigations, 2.5% to 23.5% of block
injections given at the level of occlusion would be ineffective.
 Advisable to inject patients 6 to10mmsuperior to the occlusal plane, which
usually accounts for anatomic variations
 Short needles can be used to attain anesthesia in the mandible

39. Inferior Alveolar Canal
 The inferior alveolar canal houses the IAN nerve , artery, vein and
lymphatics
 The canal is; 3.4mm wide, and the nerve is ;2.2mm thick
 Therefore, during implant placement it is possible to in advertently
penetrate into the mandibular canal and induce neurologic damage
without provoking hemorrhaging and vice versa.
 When developing an osteotomy over the mandibular canal, cortical
bone is penetrated first, and the preparation terminates within softer
cancellous bone
 The IAN may present in different anatomic configurations

40.  The IAN may present in different anatomic configurations
 The variation in the course of IAN is frequent
 Liu et al OPG classification of course of nerve

42. Mental Foramen and Nerve
 Commonly, three nerve branches of the mental nerve emerge from the
mental foramen (each ;1 mm in diameter).
 Location- Differs in horizontal and vertical plane
 Atypically near canine or molar.

43. The anterior loop of the mental foramen refers to the IAN when it
courses inferiorly and anteriorly to the foramen and then loops back to
emerge from the foramen
 The dimensions of anterior loops in panoramic radiographs varied
from 0.5 to 3 mm, and cadaver specimens manifested anterior
loops that ranged from 0.11to3.31mm
 Choose an implant length a safety margin of 2mm
 It is prudent to place the distal aspect of the implant 6 mm anterior
to the mental foramen to avoid damaging the loop when drilling the
osteotomy

45. Mandibular Incisive Canal
 Numerous investigations reported that there is ‘‘true’’ incisive canal
mesial to the mental foramen, which is a continuation of the mandibular
canal.
 The incisive canal is typically found in the middle third of the mandible
(in 86%of cases).It usually narrows as it approaches the midline and
only reaches the midline 18%of the time
 Terminates apical to lateral or central incisor
 OPG -15% CT-93%
 Only large sized canal posed problems

46. Lingual Foramen and Lateral Canals
 The lingual foramen was detected in 99% of the mandibles when
evaluating skull dissections, but only 45% in radiographs
 The lingual foramen harbors an artery that corresponds to an
anastomosis of the right and left sublingual arteries.
 Risk of haemorrhage if canal size > 1mm
Submental and Sublingual Arteries
 The submental artery (2-mm average diameter) is derived from the
facial artery, and the sublingual artery (2-mm average diameter) is a
branch of the lingual artery
 If resected can cause haematoma in submandibular and sublingual
space, leading to swelling and airway obstruction

47. Submandibular and Sublingual Fossae
 The submandibular and sublingual Fossae must be palpated prior to
osteotomy development; if there is a large undercut, the lingual
bony plate can be perforated in advertently, resulting in
hemorrhaging.
 If there is a large undercut, an instrument Can be placed into and
parallel to the undercut to visualize and measure the extent of the
depression
 A CT scan with radiopaque markers provides the most accurate
information.

48. The Lingual and Mylohyoid Nerves
 The lingual nerve is usually located 3 mm apical to the osseous crest and
2 mm horizontally from the lingual cortical plate in the flap.
 It is recommended that lingual, vertical releasing incisions be avoided.
 Furthermore, incisions distal to the second molar should be made on the
buccal aspect of the ridge to provide additional room for safety.
 Mylohyoid nerve- may contribute to incomplete anesthesia of mandibular
nerve

49. Mandibular zone of safety
Given by Carl E Misch
Determined radiograpically or clinically during surgery

50. CONCLUSION
 Familiarity with the anatomic structures pertaining to dental
implantology is critically important.
 Preplanning and review of anatomy before surgical procedures can
help to avoid problems.
 Also many of the shortcomings of two-dimensional radiography for
treatment planning can be eliminated with the use of three-
dimensional imaging.
 And an understanding of basic surgical principle is necessary to
insure a successful implant.

51. REFERENCES:
B.D CHAURASIA’S HUMAN ANATOMY – 6TH EDITION
TEXTBOOK OF ANATOMY BY INDERBIR SINGH- 5TH EDITION •
GRAY’S ANATOMY – 2ND EDITION
Greenstein G1, Cavallaro J, Tarnow D. J Periodontol. 2008 Oct;79(10):1833-46
J Oral Maxillofac Res 2010 (Jan-Mar) | vol. 1 | No 1 | e2 | p.1 -5