Biological Consideration of Mandibula Denture I (1)

7/29/2019 Biological Consideration of Mandibula Denture I (1)

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INTRODUCTION:

Dentures and their supporting structures are tocoexist for a length of time

It is important that the practitioner understandthe anatomy of the supporting and limitingstructures which form the foundation of thedenture bearing area

The foundation area mainly comprises of boneof the hard palate and the residual ridge whichis covered by a mucous membrane



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Mucous membrane: It is the tissue that supports the denture base

It is composed of 2 parts: Mucosa

Submucosa

Mucosa: It is formed of stratified squamous epithelium which is often

keratinized

Lamina propria is the subjacent layer of connective tissue

In an edentulous person the mucosa covering the hard palateand the crest of the residual ridge is called masticatorymucosa



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Normal epithelium

Stratum basale

Stratum spinosum

Stratum granulosum

Stratum corneum



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CLASSIFICATION OF ORAL MUCOSA

Depending upon its location in

mouth the oral mucosa can be

divided into :-

The Masticatory Mucosa

The Lining Mucosa

The Specialized Mucosa



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MASTICATORY MUCOSA:-

It covers the crestof the residual alveolar ridge,including the residual attached gingiva that is

firmly attached to the supporting bone & thehard palate

Masticatory mucosa is characterized by a well

defined keratinized layer on its outermostsurface that is subject to changes in thicknessdepending on whether the dentures are worn &on clinical acceptability of the dentures



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LINING MUCOSA:-

The lining mucosa is generally foundcovering the mucous membrane in theoral cavity that is not firmly attached to theperiosteum

The lining mucosa forms the covering ofthe lips & cheeks, the vestibular spaces,the alveololingual sulcus, the ventralsurface of the tongue, & the unattachedgingiva found on the slopes of the

residual ridgesSunday, September 08, 2013 8


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It is devoid of the

keratinized layer&

is freely movable

with the tissues towhich it is attached

because of elastic

nature of thelamina propria

AREAS COVERED BY LINING

& MASTICATORY MUCOSA


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SPECIALIZEDMUCOSA:-

The specializedmucosa covers thedorsal surface of the

tongue The mucosal

covering iskeratinized&

includes the specialpapillae on the uppersurface of the tongue

AREAS COVERED WITH

SPECIALIZED MUCOSA


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Submucosa: The attachment of the mucosa to bone occurs due to

the attachment between the submucosa and theperiosteum

It contains glandular, fat or muscle cells and transmitsblood and nerve supply to the mucosa

The thickness and consistency of submucosa isresponsible for the support that the mucous membranegives the denture base. When it is thin, it easily getstraumatized& when it is loosely attached, inflamedoredematous, it gets displaced

Bone: The underlying bone may consist of compact or

cancellous bone



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In denture wearers, the keratinization is

reduced& stratum corneum of epithelium

is thinner, which reduces the resistance ofthe epithelium to trauma

Removing the dentures for6 8 hours

everyday can provide rest to the softtissues, toothbrush physiotherapyover

the soft tissues can stimulate

keratinisation of the epitheliumSunday, September 08, 2013 12

HISTOPATHOLOGIC


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HISTOPATHOLOGIC

CHANGES IN DENTURE

SORE MOUTH Brinch (1932) first to study the histologicdetails of denture sore mouth

Thinning of Stratum Corneum is the firstobservable sign of tissue injury associated

with wearing of denture. No other epithelialchange is seen .

As long as conventional stratum granulosumexists, the horny layer persists. But as soon asthe granular layer disappears or degenerates,

stratum corneum loses it character and nucleiappear over the entire surface. Hence, withincreasing thinning of stratum corneum, adecrease in the number of cells in stratumgranulosum can be seen.



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The histologic picture after a conventionalstratum granulosum has disappeared isthat of PARAKERATOSIS.

The next phase of the parakeratotic stageis characterized by domination of thesurface layer by flattened pycnotic nuclei. Adefinitive stratum corneum is no longerpresent.

Even at this histologic stage, the mucosa isclinically normal.



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When there is complete disappearance

of the keratin, the mucosa gives the

clinical diagnosis of diffuse reddening.

This absence of keratin may be local.This will give the clinical picture of local

inflammation.



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ACANTHOSIS : the most striking

change in the stratum spinosum is an

increase of the epithelial mass.

SWELLING OF CELL CYTOPLASM

Increase in the VOLUME OF NUCLEI.

Increase in TISSUE VOLUME &

MITOSIS.



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In connective tissue edema is seen

The connective tissue papillae press

towards the epithelial surface.



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SALIVA

The primary exocrine gland that secrete salivaare: Parotid, Submaxillary and Sublingualglands. Numerous small glands distributedthroughout the oral cavity in the lips, tongue andpalate.

Saliva contains two type of secretions:

1. Serous secretion (thin, watery) containing

enzyme ptyalin for digestion of starchy foods.2. Mucous secretion (viscid, sticky, or adhesive) for

lubricating purpose.

The quantity of daily secretion normally ranges

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Under Physiologic conditions, salivation

can be divided into three phases:

1. Cephalic:- when one thinks about,

smells, or sees food.

2. Buccal :- Response to tactile or tastestimuli.

3. Gastrointestinal :- Reflexes originating

in stomach or GIT, thought to beassociated with foods which are

irritating.



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Physiologic factors that affects salivation :-

1. Agreeable taste stimuli results in profusesalivation, distasteful stimuli results in

temporary cessation of salivation.

2. Smooth surface salivation

Rougher object salivation

3. Dehydration salivation

4. With age saliva becomes more ropy in

consistency.


PATHOLOGICAL CONDITIONS


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PATHOLOGICAL CONDITIONS

DECREASING THE

SALIVATION Senile atrophy of salivary glandAfter radiotherapies

Diseases of brainstem that depress

salivary nuclei and block salivation

Some types of encephalitis including

poliomyelitis

Diabetes mellitus/insipidus

Vit. Deficiencies particularly of vit. A .


PATHOLOGIC CONDITIONS


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PATHOLOGIC CONDITIONS

THAT MAY INCREASE

SALIVATION Digestive tract irritants Painful afflictions of oral cavity. These

may be due to vit. deficiency or trauma,

an ill-fitting denture.



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Saliva is a major factor contributingtowards retention of denture. The physicalforces in which saliva is involved are:

ADHESION is the binding force exerted by

molecules of unlike substances in contact. COHESION is that force by which

molecules of same kind or the same bodyare held together.

CAPILLARITY is a form of surface tensionbetween the molecules of a liquid andthose of a solid.



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Patients who have ropy saliva do have problems

with denture retention as do those have profuse

watery saliva.

Craig, Berry and Peyton concluded thatcapillary forces are the principal forces

involved in denture retention. They found that

increasing or decreasing surrounding pressure

and temperature influences the retention ofdenture because capillary force is affected.

Discontinuity of saliva film will reduce retention.



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TONGUE

Muscular organ, base and central part is

attached to floor of the mouth.

Function in coordination with muscle of lips,

cheeks, throat, and palate in association withmastication, deglutition and speech.

Tongue not only detect particle size of food but

also defects on teeth or denture base.



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Intimately contact with the lingual

flanges of mandibular denture.

Denture flanges must be contoured to

allow the tongue its normal range offunctional movement.

Takes food from floor of the mouth and

labial and buccal vestibules and placesit to the occlusal surface of the teeth.



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Muscular activity of tongue is controlled

by two groups of muscles- intrinsic and

extrinsic.

Intrinsic muscles, being wholly inside thetongue, produce changes of shape in

the tongue.

Extrinsic muscles takes origin fromoutside of tongue and can move and

alter its shape.



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MUSCLE ARISES INSERTION FUNCTION

Genioglossus Genial tuburcles Anterior fibers intotip of tongue.

Posterior in base

of tongue

Protractor anddepressor of

tongue.

Styloglossus Anterior surface of

styloid process

Enters tongue

near the base

Pull tongue

backward and

upward.

Hyoglossus Hyoid bone Insert in side of

tongue

Depress the tongue

palatoglossus Draws the tongue and soft palate

together



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MUSCLE AND DENTURE

RETENTION

As pointed out by Fish(1952) and

others, the position and shape of

polished surface of dentures regard to

retention, function, comfort, andesthetics.

The general cross-sectional shape of

the polished surface of a denturethrough the residual ridge area should

be triangular.



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The buccal surface of lower denture shouldbe concave, to face up and out, permitting thecheek to cradle in against the flange and give

the desired inferior component of forces. The lingual flange of the lower denture should

be concave and face in and up.

Because of shape of mandible and functional

movements in alveolingual sulcus, this flangecannot closely approximate the body ofmandible below the attachment of themylohyoid



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Greatest extension can be achieved by

turning it lingually under the lateral

surface of the tongue.

This permits the tongue to direct forcesinferiorly against the flange.

The bundle of tissue just lateral to

corner of mouth called the modiolus.



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Muscle of Mastication

Masseter

Temporal

Medial pterygoid

Lateral pterygoid



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The contracture of the masseter forcesthe buccinator muscle in a medialdirection in the area of retromolar pad.

This action can be recorded in theimpression and the denture border canbe contoured to accommodate theaction

If this is not done the action will displacethe mandibular denture and force it inanterior direction.



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Masseter

Originate from zygomatic arch.

Inserts to outer surface of mandible.

Action is to elevate the mandible



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Temporalis

Fan shaped muscle originates from

temporal fossa on the lateral aspect of

the skull.

Insertion occupies coronoid process andreaches down to the ramus of mandible.

Action is to retracts and elevates the

mandible.



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In the area of maxillary tuberosity, thetemporal muscle attachment to the medialsurface of the coronoid process andanteromedial aspect of ramus will affect the

upper denture flange. Inferior movements of mandible, especially

when lateral protrusive movements areincorporated, will cause the above

structure to force the buccinator andoverlying mucosa to encroach on thebuccal vestibule.



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Medial pterygoid muscle

Origin from medial surface of lateral

pterygoid plate, from the pterygoid

fossa, and from the tuberosity of the

maxilla. Insert on the medial surface of mandible

near the angle.

Elevates the mandible



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The attachment to the maxillary

tuberosity could effect the posterior

extension of denture border in

pterygomaxillary notch.



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Lateral pterygoid

Double origin, from infratemporalsurface of great wing of sphenoid boneand from the lateral surface of lateral

pterygoid plate. Insert into capsule and disk of TMJ and

into anterior and medial surface of neckof mandible.

Pull head of mandible forward,downward and inward along theposterior slope of articular eminence.



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SUPRAHYOID MUSCLES

The function of this group of muscles is

either to elevate the hyoid bone and the

larynx or to depress the mandible.

The digastric, stylohyoid, mylohyoid, andgeniohyoid comprise this group of

muscles.

The mylohyoid and genohyoid influencethe borders of mandibular denture.



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Mylohyoid

Thin sheet arise from whole length of

mylohyoid line.

The mylohyoid muscle constitute the

muscle floor for the anterior part of themouth.

It elevates hyoid bone, tongue, mucous

membrane floor of the mouth duringswallowing.



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If the denture flange is extended below

and under the mylohyoid line, it will

impinge upon the mylohyoid muscle and

affects its action adversely, or the actionof muscle will unseat the denture.

In case of extensive bone loss it is

surgically detached from the periostealattachment and reattached more

inferiorly on the body of mandible.



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Geniohyoid

Arise above the anterior end of themylohyoid line from the genial tubercleat or near the midline on the lowersurface of mandible.

The muscle presents no problem incomplete denture construction untilthere is extensive loss of residual ridge.

Surgically detached from periosteumand reattached more inferiorly to themandible.



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INFRAHYOID MUSCLES Sternohyoid

Omohyoid

Sternothyroid

Thyrohyoid

Have no particular significance in complete dentureprosthodontics insofar as having any influence onthe denture borders.

The action of muscle is important, for they are part

of kinetic chain of mandibular movement. They fixhyoid bone, as it were to the trunk. This is thefixed position, from where suprahyoid musclescan act upon the mandible.



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Mental foramen area resorption

The mental foramen on or near the crest

of ridge of these greatly resorbed cases

can result in impingement on the nerves

and blood vessels, if area is notrelieved.


Cl I t ill S I


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Close Intermaxillary Space In

Tuberosity Region

Angle of mandible become more obtuse

by early loss of posterior teeth.

Loss of necessary counterbalance

against the muscle pull at the angle ofmandible.

Close the intermaxillary space in

posterior region leads in difficulty inspace for teeth and denture base.



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Low Mandibular Ridges

Mandibular supporting area is frequently

depressed bcoz of difference in rate of

resorption of cortical bone and

cancellous bone. Lingually, the bone traveled down to

floor of mouth, makes lingual flange

area of denture more difficult to adapt.


Di ti Of R ti Of


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Direction Of Resorption Of

Ridges

The mandible inclines outward and

become progressively wider according

to its edentulous age.



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All types of body tissues are involved in

biologic environment of complete

dentures.

The epithelial surface of oral mucousmembrane provides the intimate contact

between the denture and the patient.

The deeper portion of the mucosa andthe submucosa complete the soft

structures upon which the denture rests.



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Bone provides the terminal support.

Muscle plays a large part in denture

retention, function and esthetics

because of its effects on the polishedsurface as well as the basal seat.



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Biological Consideration of Mandibula Denture I (1)

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