(2) Anatomy of Edentouls Maxilla and Mandible

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    Anatomy of edentulous maxilla and

    mandible

    - First of all I want to tell you that this lecture is veryinteresting lecture and as DR said it is very important to

    understand this lecture very well . only study it well .

    - Denture- bearing Area ( DBA) :

    We will discuss the anatomy of supporting areas of completedenture

    - In the maxilla we call denture bearing area Denture

    foundation but in the mandible we call it Denture Basal

    Seat .

    - In any denture we have two types of area :

    1. Stress bearing areas or supporting areas

    (provide support to denture )

    2. Peripheral or limiting areas (determine the

    periphery of the denture )

    - Maxillary denture foundation :

    1. It is made up of bone of hard palate and RAR

    (residual alveolar ridge) covered by mucus

    membrane .

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    - may contain glands , fat , mucle fibers.

    - It transmit blood and nerve supply to the

    mucosa.

    - It attached to bone by periosteum

    - Very important notes :

    1.The support of complete denture relies on two things

    :

    - type of bone of denture-bearing area.

    - the thikness and consistency of submucosa :

    1. if submucosa is firmly attached to bone so itcan withstand the pressure of denture --------

    good for support

    2. if submucosa is thin and loosely attached to

    bone so soft tissue will non-resilent , and

    mucus membrane will be easily traumazied

    ----- poor support.

    2. soft tissue is very important for support of complete

    denture .

    so the arragment finally is :

    mucosa----- lamina propria ----- submucosa----

    periosteum ----- bone

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    - Hard palate :

    1. It is formed by the palatine processes of the two

    maxillae and palatine bone .

    2. It covers with soft tissues varying in thickness.

    - Median sagittal suture :

    1. It is the junction between two maxillae.

    2. We consider it relief area because soft tissue

    that cover it is thin although madian sagittal

    suture is on the palate but we consider it as

    Relief area .

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    3. Relief area : it means that fitting surface of

    denture or the base of the denture doesnt have

    intimate contact with this area so we provide a

    little space for relief .

    - Posterior palate :

    We cosider it primary stress-bearing area ( it

    means it provides the main support to complete

    denture during function )for two reasons:

    1. The submucosa of soft tissue is firmly attached

    to bone .

    2. Posteriotr palate is perpendicular to vertical

    forces and it is resistant to resorption.

    The submucosa of posterior palate is mainly

    contain minor salivary glands.

    - Anterior palate (rauge ) :

    It is mainly composed of fat tissues so this

    increase the displace ability .

    We consider it as secondry stress bearing area fortwo reasons 1. Soft tissue is more displaceable

    3. Rugae is inclined so inclinations of this rugae are

    not perpendicular to vertical forces.

    - Residual alveolar ridge (RAR) :

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    1. Shape and size change after tooth extraction

    due to resorption if the patient wear denture or

    not .

    2. The resorption is a physiological not

    pathological process .

    3. The rate of resorption : it continues forever

    from time of extraction until patients death(allah yrhamo )

    4. The rate of resorption in the mandible is 3-4

    times higher than in the maxilla and this is the

    reason why in most cases we suffer from

    supporting problems in maxillary arch .

    5. Most of resorption happen in the first three

    months of extraction after that the rate of

    resorption declined but it continues of

    significant amount until first year after that

    resorption happens with lesser rate .

    6. Direction of resorption in maxilla it happens

    upward ,backward , inward because there is

    a palate which is resistant to resorption so most

    of resorption happened facially so

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    - the labial wall of the ridge goes backward

    - the lateral wall of the ridge goes inward

    -the vertical height shorten

    the net result of that resorption is :

    1. smaller maxilla

    2. lack of cortical bone so we will have spaces in

    the bone we call this type of bone cancellousbone (trabecular, spongy )

    7. soft tissue is firmly attached to bone and it is

    perpendicular to vertical forces but we consider

    crest of RAR secondary stress- bearing area

    because the lack of cortical bones .

    8. slopes of RAR provide little support because

    they arent perpendicular to vertical forces

    (inclination ) and we have what we call it muco-

    gingival folds ( junction between keratinized and

    non-keratinized mucosa )

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    - Note:

    sometimes in tuberosity area we can find cortical

    bones this is why in some textbooks they consider

    tuberosity as primary stress- bearing area.

    -Types of RAR and palate :

    Please refer to the pic on the slides from left to

    right i will explain the pictures.

    1. The first picture on the left :

    This is the most favourable types of

    palate(horizontal palate) because it provides

    good support, stability , retention.

    We can see well-developed ridges .

    The arrow

    indicate to

    Muco-buccal fold

    or

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    2.The one on the right :

    v-shaped palate it is good for stability (can resist

    displacement during function ) but adhesion and

    cohesion are reduced so (good stability ,

    reduced retention)

    3. The second one in the left corner :

    We can see resorped ridges and more

    displacable soft tissue

    Poor retention because reduced surface area

    Poor stability because no resistant to

    retentional forces

    Poor support because most of the bones are

    lost

    4. The last one :

    We can see developed ridges but we have

    undercuts , if we have undercuts we have the

    following :

    If undercuts are mild ---- good for retention

    If undercuts are moderate to severe specially if

    bilateral ----not good for retention either we

    need to do relief of the denture or surgical

    reduction of the ridges to avoid trauma and loss

    of peripheral retention.

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    - Incisive papilla :

    1. It covers incisive foramen or canal .

    2. Indicator of amount of resorption

    If incisive papilla is closed to the crest of the

    ridge this indicate that significant amount of

    resorption happened

    If incisive papilla is still higher than crest of RAR

    this indicate that the ridges are still good (little

    resorption)

    3. It is considered as relief area

    4. It is helpful in setting of teeth

    - Maxillary tuberosity (area posterior to third

    molar) :

    1.Supportive area

    The arrow indicate to :

    Incisive papilla Not incisive

    foramen why???

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    2. May hang down and need surgical removal

    3. Could be fibrous or bony enlargement

    - Other relief areas:

    1. Sharp spiny processes (it happens because of

    the resorption of the bone and we should relief

    the denture beneath it )

    2. Torus palatinus : it just bony enlargement , and

    the soft tissue that cover it is thin so we

    consider it as relief area.

    - Anatomy of peripheral structures :

    1.Labial sulcus or vestibule :

    From one buccal frenum to the other .

    This is picture of torus palatinus be

    careful this is not osteosarcoma thisis just benign bony growth or

    enlargement

    It is not uncommon thats mean it is

    common ( less than common)

    If it is too big like this picture we

    prefer surgical reduction not

    necessarily completetly removal .

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    The labial vestibule divided to right and left

    labial vestibule by the labial frenum .

    2. Labial frenum : fold of mucous membrane with

    no muscular attachment , because of this we

    need relief in the denture flange we call it labila

    notch and this notch shouldnt be wide from

    latral side to the other because we dont have

    muscular attachment in this region and for our

    luck as dentists (hahah) orbicularis oris muscle

    its fibers are run horizontal so whe this muscle

    contracts it doesnt dislodge the denture.

    As we know from anatomy we know what

    modiouls means

    Modiouls : it is the junction between the fibers

    of orbicularis oris muscle and buccinator muscle

    .

    3.Buccal frenum :

    - Divides labial and buccal vistibues

    - It could be single or double folds ( note that labial

    frenum is always single fold)

    - Buccal frenum should have wide notch than on

    denture than labial frenum because of more

    movements

    - Buccal frenum moves :

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    1. Up and down by levator anguli muscle

    2. Posteriorly by buccinators muscle

    3. Anteriorly by orbicularis oris muscle

    - If we dont provide sufficient room or space for this

    range of movement in the buccal frenum we will

    end up with frenum ulceration .

    4.Buccal sulcus or vestibule :

    - From buccal frenum to hamular notch

    - Its size varies depend on :

    1.Amount of resorption

    2.Buccinator contraction3.Masseter contraction

    4. Coronoid process of mandible

    - Usually this vestibule has the longest and highest

    space in the upper complete denture.- Distal to it there is root of zygoma (soft tissue that

    cover it is thin so we need relief the denture )

    how???

    During border molding we ask the patient to open

    widely and move from side to side because if

    buccal flange of denture was thick , opening willbe limited , trauma could happen , dislodgment of

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    denture could also happen because of the

    thickness of the flange .

    5.Hamular notch :

    1. It is the area between tuberosity and hamulus of

    medial pterygoid plate .

    2. It composed of thick submucosa so it is

    compressible and this help in achieve posterior

    palatal seal (peripheral seal of upper completedenture)

    3. The posterior extension of upper complete

    denture is hamular notch.

    6.The vibrating line (ah line ):

    - It is an imaginary line from one hamular notch to

    the other

    - It is 2mm away from fovea palatinae

    - Fovea palatinae : small identations in the

    anterior part of the soft palate formed by

    coalescence of gland ducts( arrow in pic)

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    - Denture extends to vibrating line or 1-2 mm

    posterior to it and extends into hamular notch

    7. Perygomandibular raphe:

    - It extends from hamulus to the top of disto-medial

    corner of retromolar pad area in the mandible

    ( buccinator musle when it turns medially behind

    retro-molar pad area it will merge with superior

    constrictor muscle of the pharynx in this raphe .

    - It is very important in ID block.

    - If denture manily lower is over-extended

    posteriorly trauma to the raphe could happen .

    - Please look at these pictures they are useful

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    - This picture sammarizes every things:

    Oh 25eeeran 5alsna anatomy of maxilla we will move to

    anatomy of mandible (eshrabo fnjan 2hweh w rja3o 3la

    tafree3) .

    - Anatomy of supporting structures :

    - Mandibular DBA ( denture-bearing area) =

    14 cmsquare

    - Maxillary DBA =24 cm square

    1- Labial frenum

    2- Labial vestibule

    3- Buccal frenum

    4- Buccal vestibule

    5- Coronoid bulge

    6- Residual alveolar ridge

    7- Maxillary tuberosity

    8- Hamular notch

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    - We notice that mandibular DBA is about half

    surface area of maxillary arch so this is why

    maxillary dentures are more successful than

    more mandibular dentures ( increase surface

    area ------ better retention ).

    - Crest of RAR : keratinized mucosa and

    variable submucosa attachment it could be firm

    or loose , it contains cancellous bone so we

    consider it secondary stress bearing area .

    - RAR:

    1. Shape and size change after teeth extraction

    due to resorption

    2. Rate of resorption : it is 4 times faster than

    maxilla and as we know most of resorption

    happened after 3 months of extraction so we ask

    the patient to visit us after 3 months to be sure

    that we dont need to do relining to the denture .

    3. Direction :

    - In the mandible the alveolar ridge and the

    base are not on the same level so after extraction

    the resorption takes place in the alveolar bone

    not the base .

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    - In anterior area : there is no palate to

    resist resorption as maxilla so ---- labial wall of

    ridge resorption happened backward

    Lingual wall of ridge it goes forward

    Net result is RAR becomes more forward

    - In premolar area : labial wall ---- goes

    lingually

    Lingual wall --- goes labially

    But the crest of RAR stays static (in the same

    place )

    - In the molar region :

    you dont have resorption from labial wall

    resorption from lingual wall ----- labially

    the net result : larger mandible ,smaller maxilla

    ( class III ) prognathic .

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    - In this picture we can see the progressive

    resorption of maxillary and mandibular ridges

    makes the maxilla narrower and mandible wider.

    A and B represent the centers of the ridges notice

    that distance become greater as maxilla and

    mandible resorb.

    - We know that after resorption we will end

    with sharp spines .

    - Sometimes when the resorption is of

    significant amount the lingual fold ( soft tissue of

    In this pic we can

    see resorption that

    take place

    In this picture we

    see resorption that

    take place

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    floor of the mouth and submandibular gland duct

    underneath it ) , so when it becomes higher than

    the ridges it self it complicate the construction of

    lower complete denture .

    - Retro-molar fossa : it is the space between

    the external and internal oblique ridges.

    -The anatom of supporting structures :

    1. Buccal shelf (buccal flange area ):

    - Boundaries :

    Medially ----- crest of RAR

    Laterally ----- external oblique ridge

    Anteriorly ---- buccal frenum

    Posteriorly---- retromolar pad

    - The mucus membrane is loosely attached and less

    keratinized but because there are high amount of

    cortical bone and perpendicular to vertical forces

    we consider it primary stress bearing area

    - Buccinators muscle fibers are horizontal so it

    doesnt dislodge the denture.

    Note very important :

    - In lower complete denture :

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    The primary stress bearing area is buccal shelf

    area but

    The secondary stress- bearing area is crest of RAR

    2.Mylohyoid ridge :

    - Obligue

    - It is close to inferior border of the mandible

    anteriorly

    Left picture : the arrow indicate buccal shelf area

    Right picture : the dotted area is the buccal shelf area that extend

    from buccal frenum (A) to retromolar pad area (B) and from external

    oblique ridge to the crest of the residual alveolar ridge (C)

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    - It is close to superior border of mandible

    posteriorly

    - The mucus membrane over a sharp mylohyoid

    ridge will be easily traumatized by denture base

    .so we need to do relief to the denture base.

    3.Mental foramen :

    - Indicator of the amount of resorption if it is very

    close to the crest of RAR this indication of severe

    resorption.

    - The mental nerve and blood vessels could be

    compressed by denture base unless relief is

    provided .

    In the picture :

    A- Canine region

    B- Premolar region

    C- First molar

    D- Third molar

    In anterior area we see that

    mylohyoid muscle is close to the

    base of the mandible but in

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    - In some patients with severe resorption

    mylohyoid muscle becomes sometimes above the

    crest of the ridge

    4.Genial tubercules :

    - With resorption it become prominent so we need t

    do relief .

    5.Torus mandibularis :

    - It is bony prominence

    - It found bilaterally and lingually near the first and

    second premolars.

    - It covers with thin layer of mucus membrane so we

    need to do surgical removal of these tori becausetrauma could happen to the mucosa and

    peripheral seal affected also .

    - Anatomy of limiting strctures :

    1.Labial vestibule :

    This is a picture of

    torus mandibularis as

    we said if too largelike this we should do

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    - From labial frenum to buccal frenum

    - Length and thickness of labial flange vary

    - Labial frenum : it contains band of fibrousconnective tissue that helps attach the orbicularis

    oris muscle so labilal frenum is quiet sensitive and

    active .

    2.Buccal vestibule :

    -From buccal frenum to retromolar pad.

    - The extent of buccal vestibule is influenced by the

    buccinator muscle .

    - The buccal flange may extend to the external

    oblique ridge up onto it or over it depending on thelocation of muco-buccal fold and sharpness of

    external oblique ridge.

    - Posteriorly the buccal vestibule must converge to

    avoid displacement by the contraction of masseter

    muscle ( anterior fibers of this muscle run outsideand behind the buccinators muscle ) so we need to

    do relief .

    - Distal extension :

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    1. Retromolar fossa : it is the area between

    external and internal oblique ridges

    If the impression is overextend it can cause

    soreness and displacement of denture because

    pterygomandibular raphe during movement it

    will dislodge the denture anteriorly

    2.Retromolar pad :

    -It is pear shaped soft tissue pad located at distalend of RAR

    - It contains thin non-keratinized mucosa

    - Submucosa contain glandular tissue and muscle

    fibers (pterygomandibular raphe and tendon of

    temporalis )

    - The denture should cover to 2/3 over the

    retromolar pad .

    - Notice when buccal shelf turns to cover retromolar pad

    area (in that area we have only buccinators muscle)behind buccinators there is masseter muscle so when the

    The arrow indicate toretromolar pad area and

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    patient bites masseter muscle contracts and become

    wider , it pushes buccinators muscle . so in some patient

    we need to do relief to flange of denture and we do this

    during border molding we press on tray and ask the

    patient to bite aganist our fingers so masseter muscle

    contarcts and we call this ( masseteric notch )

    - In other patient we have tense mentalis muscle so we

    cant provide thick flange in this area it will dislodge so

    the flange of denture should extend to muco-buccal fold

    and some fibers of buccinators muscle will be under the

    denture.

    3. Lingual border :

    - The lingual tissues under the tounge are less resistance

    than labial and buccal and ar easily distorted.

    - Mylohyoid muscle :

    1. It forms the floor of the mouth

    2. It originates from mylohyoid ridge and inserted to hyoid

    bone

    3. The ridge more prominent posteriorly so denture flange

    must parallel to mylohyoid muscle to avoid sorness

    (pain) , peripheral seal and tounge rests on the flange

    4. Retromylohyoid fossa :

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    - It located posterior to mylohyoid muscle and it is

    bounded with

    Retromylohyoid curtain

    - The denture must extend to this fossa ( S-curve

    configuration )

    5.Retromylohyoid curtain boundaries:

    - Posteriolaterally : superior constrictor

    - Posteriomedially : palatoglossus muscle

    - Inferior wall : overlies submandibular gland

    - Medial pterygoid muscle can cause bulge in the

    wall of the curtain as masseter dose with

    buccinators

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    - The following picture may help you in

    understanding :

    - Finally i advice you to refer to my tafree3on my-

    toothy because there are alot of pictures

    In this picture sorry the letters

    are inverted

    B : buccinator muscle

    M: masseter muscle

    MP: medial ptyregoid

    PR: pterygomandibular raphe

    RM: ramus of the mandible

    SC: superior constrictor muscle

    RMC : posteriolateral portion of

    retromylohyoid curtain formed by

    the mucus membrane covering

    SC. If pic is not clear please refer

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