44332591 anatomical landmarks mandible

7/29/2019 44332591 Anatomical Landmarks Mandible

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ANATOMICAL

LANDMARKS MANDIBLE


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Mandible is the movable member of thestomatognathic system. The total area ofsupport from the mandible is less than from themaxilla.

Available denture bearing area is 14sqmm. Thebony foundation for the mandibular denturebecome shorter vertically and narrowerbuccolingualy

Less bony support

Bony crest narrower and sharper


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Supporting structures

Crest of the residual ridge

Buccal flange area

External oblique ridgeMylohyoid line

Mental foramen area

Torus mandibularis


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Crest of the residual ridge

Is covered by fibrous connective tissue

But underlying bone is thin and cancellous

containing nutrient canals so is a releif

area

It has spongy bone in the molar region


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Buccal flange and buccal shelf

Is a primary stressbearing area

Is an area between thebuccal frenum and edge

of masseterBoundaries

Medially- crest of theridge

Ant-buccal frenumLat- external oblique line

Distal retro molar pad


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It is a wide area and at right angles to vertical

forces and is covered with smooth cortical bone.

Inferior part of the buccinator is attached in the

buccal shelf thus contraction does not lift thelower denture.

Muscle fibers run antero posteriorly paralleling

the bone. The tray come to direct contact with

mucosa of buccal shelf and soft tissue is slightly

displaced as the final impression is made


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The external oblique line-

is a ridge of dense bone extending from

the mental foramen and become

continuous with the anterior border of the

ramus of the mandible. In most individualsit is the anatomic guide for the lateral

termination of the buccal flange of the

lower denture


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The mental foramen

Is located on the lateral surface of the

body of the mandible between the first and

second premolars, about half way from the

alveolar crest and the lower border. If theresorption is greater it occupies a superior

position and the denture base must be

relived over the foramen


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The mylohyoid line

Is an irregular rough bonycrest extending from thethird molar region to thelower border of the

mandible in the region ofthe chin. It is moreprominent in the thirdmolar region to the 2ndpremolar region. The

lingual flange mustextend inferior to and notlateral to the mylohyoidline


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The lingual tuberosity

Is an irregular bony prominence on the

distal end of the mylohyoid line

The mental spine is situated on the lingual

aspect of the mandibular body


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Torus mandibularis

Is a bony prominence found near the I &II

premolar between the soft tissue and the

floor of the mouth

Covered by extremely thin mucous

membrane may be irritated with slight

movement.

It may be removed surgically without

breaking the border seal


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Limiting structures

Labial frenum

Labial vestibule

Buccal frenum

Buccal vestibule

Masseter muscle region

Distal extension of mandibular impression

Retromolar region

Mylohyoid muscles and ridge

sublingual gland region

Lingual frenum and lingual notch

Lingual vestibule


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Labial frenum

Contains a band of fibrous connective

tissue that is attached to the orbicularis

oris

Sensitive and active

It is accommodated by a groove on the

mandibular denture


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Labial vestibule

Is the area extending from the labialfrenum to the buccal frenum.

The denture should not be extended

beyond the mucolabial fold as it is limitedby the fibers of the orbicularis oris and theincivious labi inferioris which is fairly closeto the ridge

Tone of the lip depends on the thicknessof the flange and position of teeth


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Recording labial and buccal flanges

The labial frenum is molded by moving the

lip outward, upward and inward.


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Buccal frenum

Overlies the depressor anguli oris

Connected to the buccal frenum in maxilla as a

continuous band through the modiolus at the

corner of the mouthClearance must be achieved in the denture base

to avoid displacement of the denture

The fibrous and muscular tissues pull activelyacross the denture borders

Denture must be extended less in this region


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Buccal vestibule

Extends from the buccal frenum posteriorly to

the outside back corner of the retromolar pad

and from the crest of the ridge

Overlies buccal shelf and ex oblique lineBuccinator attached to oblique ridge

Buccinators action occurs in horizontal direction

so it cannot lift the dentureBuccinator extends from modiolus to the

pterygomandibular raphae


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Recording the buccal frenum

The buccal frenum is recorded by moving

cheek outward, upward backward and

forward.

To record the disto buccal sulcus the

cheek should be well retracted and moved

upward and inward.


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Masseter muscle region

The distobuccal border of the mandibulardenture must converge rapidly to avoiddisplacement by the contracting pressure of themasseter muscle.

Masseter muscle runs at right angles to thebuccinator

When masseter contracts it pushes thebuccinator and tissues inward against the

denture and alters the size and shape of thedistobuccal end of the lower buccal vestibulereducing the space in that region (dislodgingforce


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Masseter muscle pushes the buccinator towardsthe retromolar pad. The denture base must becontoured to accommodate this massetric notch.

One can register the masseter pull on theimpression by softening the compound with analcohol flame along the disto buccal bordertempering in warm water

After seating in the impression in patients mouthexert downward pressure by placing the indexfingers on the impression in the 2nd premolarregion and instructing the patient to exert aclosing force. these opposing forces will cause themasseter to contract and trim the compound inthat area recording the masseteric notch


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Distal extension of the mandibular

impression

Limited by the ramus of mandible

By buccinator fibers

By sharpness of bony boundaries ofretromolar fossa

If the impression is extended on to ramus

the buccinator will be compressedbetween the hard denture border and

sharp external oblique ridge


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Retromolar region and pad

Is a triangular pear

shaped soft pad of tissue

in the distal end of the

mandibular ridge

It must be covered by the

denture for the perfect

border seal. Aids in the

stability of the denture by

adding another plane toresist the movement of

the base


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Contents

Some glandular tissue

Fibers of temporalis tendon

From buccal side- buccinatorFrom lingual side- superior pharyngealconstrictor

Supero posterior inside corner-

pterygomandibular rapheThese structures prevent the placement of extrapressure during the impression procedure


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Retromolar papilla

Is a small pear shaped area anterior to the

pad

Is a dense fibrous connective tissue

Retro molar pad should be registered in a

resting position in the final impression


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Recording the retromolar pad

To record the distal end of the try the

patient is asked to open the mouth wide. If

notch is produced in the posteromedial

end of the try it indicates that the tray isover extended up to the

pterygomandibular raphe


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Sublingual gland region

Rest above the mylohyoid muscle. When

the floor of the muscle is raised the gland

come close to the crest of the ridge and

reduces the vertical space available for theflange extension in the anterior part of the

mouth


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Lingual frenum& lingual notch

Extremely resistant and active and wide

Should be registered in function

In function it come close to the ridgeAt rest it is much lower

Overlies the genioglossus muscle


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Lingual vestibule

Occupies the alveolingual sulcus

Distal end extend to the retromylohyoid curtain

Anteriorly influenced by mylohyoid

Flange extend below the mylohyoid ridge to occupy the

alveolo lingual sulcus.

Flange leaves the bony attachment at the mylohyoidridge and slopes inward under the tongue to fill thealveololingual sulcus

Thus there is a space between the flange and mucousmembrane when the muscle is relaxed and there iscontact when the tongue is raised and thrust out


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Recording the lingual frenum

The anterior lingual border is molded by

asking the patient to protrude his tongue to

touch the anterior part of palate.

Protrusion records the length of lingual

flange

Touching the anterior part of hard palate

helps to establish the width of the flange.


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Mylohyoid muscle & ridge

Mylohyoid muscle arise from the whole length of

the mylohyoid line extending from about 1 cm

back of the distal end of the mylohyoid ridge to

the lingual anterior portion of the mandible at thesymphysis

This ridge is near the inferior border in the

incisal region but become progressively higher

on the posterior border, so posterior part affectthe lingual impression in swallowing and tongue

movements


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The lingual flange should extend inferior but

not lateral to the mylohyoid line.

The movement of tongue and displacability ofthe floor of the mouth will determine the

length of the flange. If the flange is properly

shaped it will complete the lingual border sealin the retromylohyoid fossa and guide the

tongue on top of the flange


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Recording the mylohyoid

Protrusion of the tongue record the

movement of the mylohyoid muscle. This

raises the floor of the mouth. The lingual

flange recorded will be lingually sloping ndparallel to the direction of the mylohyoid

muscle. Increse in the thicknes odf the

posterior part otf the lingual flange caninterfere with the action of the mylohyoid

muscle.


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While border molding the distal end of the

lingual flange the action of the mylohyoid curtain

should be recorded. The superior constrictor and

the medial pterygoid determine the position ofhe retromylohyoid curtain

Superior constrictor- by protruding the tongue

Medial pterygoid- by asking the patient to

forcefully close against resistance

44332591 anatomical landmarks mandible

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