ANATOMY AND CLINICAL SIGNIFICANCE OF DENTURE BEARING AREAS

GROUP 3

DEN/2012/004……….. Chairman DEN/2012/001……….. Secretary DEN/2012/003DEN/2012/024DEN/2011/015DEN/2012/019

OUTLINE

INTRODUCTIONANATOMY OF DENTURE BEARING AREAS

CLINICAL SIGNIFICANCE OF DENTURE BEARING AREAS

CONCLUSIONREFERENCES

INTRODUCTIONM.M Devan Dictum “Aim of a prosthodontist is not only the

meticulous replacement of what is missing, but also perpetual preservation of what is present”

A prosthesis must function in harmony with the tissues that support them and those that surround them.

Hence the dentist must understand the macroscopic as well as microscopic anatomy of the supporting and limiting structures of the denture.

ANATOMY OF DENTURE BEARING AREASThe anatomy of edentulous ridges in the maxilla and mandible

is very important for the design of the complete denture.

The total area of support from the mandible is significantly less than from the maxilla.

The average available denture bearing area for an edentulous mandible is 14cm2,whereas for edentulous maxilla it is 24cm2. Therefore the mandible is less capable of resisting occlusal forces than the maxilla.

THE ORAL MUCOUS MEMBRANEServes as a cushion between the denture base and the

supporting bone.

Mucous membrane is composed of mucosa and sub mucosa.

Sub-mucosa is formed by connective tissue that varies from dense to loose areolar tissue.

Mucosa covering the hard palate and the crest of the ridge is classified as MASTICATORY MUCOSA.

The mucosa is characterized by its well defined KERATINIZED EPITHELIUM.

ORAL MUCOUS MEMBRANE

ANATOMY OF DENTURE BEARING AREA - MAXILLAThe ultimate support for the maxillary denture are the bones

of the two maxilla and the palatine bone.

The anatomical land marks in the maxilla are

LIMITING STRUCTURESSUPPORTING STRUCTURESRELIEF AREAS

LIMITING STRUCTURES OF THE MAXILLA Limiting structures are sites that will guide us in having an

optimum extension of denture so as to engage maximum surface area without encroaching upon the muscle action.

These are structures that limit the extent of the denture:1. Labial frenum2. Labial vestibule3. Buccal frenum4. Buccal vestibule5. Hamular notch6. Posterior palatal seal7. Fovea palatinae

LABIAL FRENUM Single or double fibrous band covered by

mucous membrane which extends from labial aspect of residual alveolar ridge to the lip.

Absence of muscle fibers.

CLINICAL SIGNIFICANCE Limits labial flange of denture.

It has to be relieved while making impression in other to prevent dislodgement of the denture and to prevent ulceration. It is seen as a V-shaped notch in the impression.

LABIAL VESTIBULE It extends from buccal frenum on one side to

the other, being divided into right and left by labial frenum.

Anteriorly: orbicularis oris muscle Posteriorly: labial aspect of alveolar ridge.

It has a thin mucosa and thick submucosa with large amount of loose areolar tissue and elastic fibers.

CLINICAL SIGNIFICANCE The labial flange of the denture will be in

complete contact with labial vestibule to provide a peripheral seal in the denture.

BUCCAL FRENUM Band of fibrous tissue overlying the levator anguli oris,

that divides labial vestibule from buccal vestibule.

The orbicularis oris pulls frenum forward and the buccinator pulls it backward.

CLINICAL SIGNIFICANCE Since it has muscular attachments, adequate relief

must be provided to prevent the dislodgment of denture.(that is, it can move posteriorly as a result of the buccinator muscle and anteriorly as a result of the orbicularis oris.)

It requires more clearance for its action than labial frenum because it moves mesially, buccally and vertically by orbicularis oris, buccinator and levator anguli oris respectively.

BUCCAL VESTIBULE Buccal vestibule extends from the buccal frenum to

the hamular notch.

Bounded externally by cheeks and internally by residual alveolar ridge.

The size of the vestibule varies with the contraction of the buccinator muscle.

CLINICAL SIGNIFICANCE The patient’s mouth must be half open during

impression taking, because opening of mouth during final impression causes the coronoid process to move anteriorly narrowing the buccal vestibule.

Compared to labial flange, buccal flange has less interference and so provides maximum retention.

HAMULAR NOTCH Hamular notch forms the distal limit of the buccal

vestibule, located between the tuberosity and the hamulus of the medial pterygoid plate.

Pterygomandibular raphe is attached to the hamular notch.

It has thick submucosa made up of loose areolar tissue.

CLINICAL SIGNIFICANCE If denture border is short of the hamular notch The

denture will not have a posterior seal resulting in loss of retention of the denture.

If denture extend beyond hamular notch The pterygomandibular raphe is pulled forward when patient opens mouth causing dislodgement of denture.

POSTERIOR PALATAL SEAL AREA Also known as post dam.

“The soft tissues at or along the junction of the hard and soft palate on which pressure along the physiological limits of the tissues can be applied by the the denture to aid in the retention of the denture.”-GPT (GLOSSARY OF PROSTHODONTICS TERM)

POSTERIOR PALATAL SEAL AREAPARTS postpalatal seal pterygomaxillary seal

EXTENSIONS anteriorly- anterior vibrating line posteriorly- posterior vibrating line laterally- 3-4mm anterior-lateral to hamular notch

Pterygomaxillary seal Postpalatal seal

DIFFERENCES

It is the part of the posterior palatal seal that extends across the hamular notch and extends 3 to 4 mm anterolaterally to end in the mucogingival junction on the posterior part of the maxillary ridge.

It is the part of the posterior palatal seal area that extends between the two maxillary tuberosities.

Pterygomaxillary seal Postpalatal seal

POSTERIOR PALATAL SEAL AREA

VIBRATING LINE “The imaginary line across the posterior part of the palate marking

the division between the movable and immovable tissues of the soft palate which can be identified when the movable tissue is moving’’-GPT

Denture should extend 1-2mm posterior to this vibrating lines.

Types:

Anterior vibrating line Posterior vibrating line

ANTERIOR VIBRATING LINE It is an imaginary line lying at the

junction between the immovable tissue over the hard palate and the slightly movable tissues of the soft palate.

It is cupid bow shaped(because of the shape of the underlying bone).

Valsalva maneuver: The patient is asked to close his nostrils firmly and gently blow through his nose, to locate the anterior vibrating line.

Arrow showing the bone that gives bow shape to anterior vibrating line in edentulous patients.

POSTERIOR VIBRATING LINE It is an imaginary line located at the junction of the soft palate that

shows limited movement and the soft palate that shows marked movement.

This line is usually straight.

POSTERIOR PALATAL SEAL CONTDCLINICAL SIGNIFICANCE: It maintains contact with the anterior portion of the soft palate during

functional movements of the stomatognatic system (i.e mastication, deglutition and phonation). Therefore, the primary purpose of the posterior palatal seal is the retention of maxillary denture.

Reduces the tendency for gag reflex as it prevents the formation of the gap between the denture base and the soft palate during functional movements.

Prevents food accumulation between the posterior border of the denture and the soft palate.

FOVEA PALATINAE These are the depresssions or indentations situated on

the soft palate on the either side of the midline.

It is formed by coalescence of the duct of several mucous glands.

The position of the fovea palatinae also influences the posterior border of the denture.

The secretion of the fovea spreads as a thin film on the denture therefore aiding in retention.

CLINICAL SIGNIFICANCE In patients with thick ropy saliva, the fovea palatinae

should be left uncovered or else the thick saliva flowing between the tissue and the denture can increase the hydrostatic pressure and displace the denture.

SUPPORTING STRUCTURES OF MAXILLA

PRIMARY STRESS BEARING HARD PALATE POSTERO-LATERAL SLOPES OF THE RESIDUAL

ALVEOLAR RIDGE

SECONDARY STRESS BEARING AREA RUGAE MAXILLARY TUBEROSITY ALVEOLAR TUBERCLE

HARD PALATE It is formed by palatine shelves of the

maxillary bone and the premaxilla.

Lined by keratinised epithelium.

The horizontal of the hard palate provides the PRIMARY STRESS-BEARING AREA.

CLINICAL SIGNIFICANCE The trabecular pattern in the bone is

perpendicular to the direction of force, making it capable of withstanding any amount of force without marked resorption.

POSTERO-LATERAL SLOPES OF THE RESIDUAL ALVEOLAR RIDGE “The portion of the alveolar ridge and its soft tissue covering which remains following removal of the teeth.”-GPT

Lined by thick stratified squamous epithelium.

Even though the sub-mucosa is thin it sufficiently provide adequate resiliency to support the denture.

It resorbs rapidly following extractions and continues throughout life at a reduced rate.

CLINICAL SIGNIFICANCE The vertical forces during physiological activities

like mastication falls on denture and is transmitted posteriorly. The postero-lateral slopes of the ridge bears the force and hence is the primary supporting structure.

RUGAE These are the mucosal folds located in the anterior region

of the palatal mucosa.

In the area of rugae, the palate is set at an angle to the residual alveolar ridge and is thinly covered by soft tissue which contributes to the secondary stress bearing area.

CLINICAL SIGNIFICANCE It is associated with the sensation of taste and the function

of speech. They assist the tongue to absorb via its papillae. They also enable the tongue to form a perfect seal when it

is pressed against the palate in making linguo-palatal constant stops of speech.

Rugae should not be displaced, otherwise the rebounding may dislodge the denture.

They provide antero-posterior resistance to movement of the denture and increased surface surface area helps in retention.

MAXILLARY TUBEROSITY It is the bulbous extension of the

residual alveolar ridge in the 2nd and 3rd molar region, terminating in the hamular notch.

CLINICAL SIGNIFICANCE The area is less likely to resorb.

Artficial teeth are not set on tuberosity region.

The tuberosities sometimes exhibit buccal undercuts, if it is unilateral it can be utilized for the retention.

NOTE Residual ridge was first considered to be a primary stress bearing

area but it is now considered a secondary stress bearing area because of the fact that bone is subjected to continuous resorption though it decreases as the span of edentulism increases.

RELIEF AREASThese are areas in the denture bearing areas which should be relived during construction of dentures. Incisive papillaeMid-palatine rapheFovea palatinePalatine torusRugae

INCISIVE PAPPILAE It is the midline structure situated behind the

central incisors.

Incisive foramen lies immediately beneath the papillae.

As resorption progresses, it comes to lie nearer to the crest of the ridge.

The naso-palatine nerves and vessels pass through it.

CLINICAL SIGNIFICANCE While making final impression pressure

should not be applied on this region.

MID-PALATINE RAPHE This is the median suture area covered

by a thin sub-mucosa, so the mucosa layer is in close contact with the underlying bone

For this region, the soft tissue covering the median palatal tissue is non-resilient in nature and may need to be relieved.

CLINICAL SIGNIFICANCE If pressure is applied during

impression making,the denture base will cause soreness over the midpalatine raphe area.

FOVEA PALATINE Bilateral indentations near the midline of

palate. Posterior to junction of hard and soft palate

These are a pair of mucous gland duct orifice near the midline at the junction of the hard and the soft palate

Formed by coalescence of several mucous gland duct

CLINICAL SIGNIFICANCE Aids in determining vibrating line These landmarks provide a guide to the

position of the posterior palatal border of a denture

PALATINE TORUS A developmental bony prominence

sometimes seen in the centre of the palate. This structure is often covered by relatively incompressible mucoperiosteum

CLINICAL SIGNIFICANCE If it is small, the denture is relieved A mucosally supported denture may

need to be relieved over the torus to prevent the denture rocking and flexing about the mid line.

RUGAE Irregular shaped ridges of the

connective tissue covered by mucous membrane in the anterior third of the hard palate

CLINICAL SIGNIFICANCE Should not be disturbed by

impression for maximum comfort

ANATOMY OF DENTURE BEARING AREAS- MANDIBLE These are areas in mandible that are closely related to the base of

the mandibular complete denture. They are covered with mucosa and sub mucosa of varying degree of thickness and compressiblity.

The anatomical landmarks in the mandible are ;

LIMITING STRUCTURESSUPPORTING STRUCTURESRELIEF AREAS

ANATOMICAL LANDMARKS OF EDENTULOUS MANDIBLE

LIMITING STRUCTURES OF THE MANDIBLE

LABIAL FRENUMLABIAL VESTIBULEBUCCAL FRENUMBUCCAL VESTIBULELINGUAL FRENUMALVEOLOLINGUAL SULCUSRETROMOLAR PADPTERYGOMANDIBULAR RAPHE

LABIAL FRENUM It is a fold of mucous membrane at the median

line. It divides the labial vestibule into left and right labial vestibule.

It consist of band of fibrous connective tissue and helps to attach orbicularis oris muscle.

It is shorter and wider than the maxillary labial frenum.

CLINICAL SIGNIFICANCE During final impression, making sufficient relief

must be given without compromising the peripheral seal.

The frenum is quite sensitive and active, and the denture must be fitted carefully around it to maintain a seal without causing soreness.

LABIAL VESTIBULE It runs from the buccal frenum to buccal

frenum. It is divided into left and right by labial frenum.

Fibers of orbicularis oris,incisivus and mentalis are inserted near the crest of the ridge. Mentalis muscle is an active muscle.

CLINICAL SIGNIFICANCE Extent of the denture flange in this region is

often limited because of muscle that are inserted close to the crest of the ridge.

Thick denture flanges may cause dislodgement of dentures when patient opens the mouth wide open.

BUCCAL FRENUM The buccal frenum forms the dividing

line between the labial and buccal vestibule.

May be single or double, broad U shaped or sharp V shaped.

It overlies depressor anguli oris muscle.

Fibres of the buccinator muscle attach to the frenum.

CLINICAL SIGNIFICANCE Relief for buccal frenum is given in

denture to avoid displacement of the denture.

BUCCAL VESTIBULE Extends from buccal frenum to retromolar pad.

It is nearly at right angles to biting forces.

Extent of the buccal vestibule is influenced by buccinators muscle,which extends from modiolous anteriorly to pterygomandibular raphe.

The masseter muscle contracts under heavy closing force and pushes inward against the buccinators muscle to produce a massetric notch in the distobuccal border of the lower denture.

CLINICAL SIGNIFICANCE The distobuccal border of the lower denture should

accommodate the contracting masseter muscle so that the denture does not dislodge during heavy closing force.

LINGUAL FRENUM It is a fold of mucous membrane existing when

the tip of the tongue is elevated. It overlies the genioglossus muscle which takes

origin from the superior genial tubercle. The anterior region of the lingual flange is

called sub-lingual crescent area.

CLINICAL SIGNIFICANCE The relief for the lingual frenum should be

registered during function. A short frenum is called tongue tie. It should be

corrected if it affects the stability of the denture.

ALVEOLOLINGUAL SULCUS It is the space between residual ridge and tongue. Extends from lingual frenum to rectomylohyoid curtain It has 3 regions (anterior, middle and posterior) The anterior region extends from the lingual frenum back to where mylohyoid

muscle curves above the level of the sulcus (premylohyoid fossa) The middle region extends from premylohyoid fossa to the distal end of the

mylohyoid ridge, curving medially from the body of mandible. The curvature is caused by the prominence of mylohyoid ridge and the action mylohyoid muscle

The posterior region: here, the flange passes into the rectomylohyoid fossa and completes the TYPICAL S FORM of the correctly shaped lingual flange

CLINICAL SIGNIFICANCEThe lingual flange of the lower denture will be short anteriorly than posteriorlyThe lingual flange in the middle region slopes medially towards the tongue

ALVEOLOLINGUAL SULCUS- RETROMYLOHYOID SPACE The retromylohyoid space lies at

distal end of the alveololingual sulcus

It is bounded by anterior tonsillar pillar, posteriorly by the retromylohyoid curtain

ALVEOLOLINGUAL SULCUS- RETROMYLOHYOID CURTAIN

Formed posteriorly by the superior constrictor muscle, laterally by the mandible and pterygo-mandibular raphe, anteriorly by lingual tuberosity, and inferioirly by the mylohyoid muscle

NOTE: RMC IS RETROMYLOHYOID CURTAIN

RETROMOLAR PAD It is a non-keratinised triangular pear-shaped pad

of tissue at the distal end of the lower ridge. Submucosa contains glandular tissue, fibers of

buccinators and superior constrictor muscle, pterygomandibular raphe and terminal part of the tendon of the temporalis.

The retromolar papilla is a pear shaped area just anterior to the retromolar pad, it is a dense fibrous connective tissue.

CLINICAL SIGNIFICANCE The distal end of the denture pad should

cover 2/3rd of the retromolar pad. The retromolar pad provides the peripheral

posterior seal for the lower denture.

PTERYGOMANDIBULAR RAPHE Raphe is a tendinous insertion of two

muscles. Arises from the hamular process of the

medial pterygoid and gets attached to the mylohyoid ridge.

Muscular attachments present here are: superior constrictor: postreolaterally Buccinator: anterolaterally

CLINICAL SIGNIFICANCE Since it is very prominent in some

patients, a notch like relief must be provided on the denture.

SUPPORTING STRUCTURES OF THE MANDIBLE

These are areas responsible for bearing loads in the mandible.

Buccal shelf areaResidual alveolar ridge

BUCCAL SHELF AREA It is the area between buccal frenum and anterior

border of masseter muscle. BOUNDARIES:

Medially-the crest of the ridge. Distally-the retromolar pad Laterally-the external oblique ridge.

The mucous membrane covering the buccal shelf area is loosely attached, less keratinized and contains a thick submucosa overlying a cortical plate.

CLINICAL SIGNIFICANCE It lies at right angles to the vertical occlusal

force; this makes it suitable as primary stress bearing area for lower denture.

BUCCAL SHELF AREA

RESIDUAL ALVEOLAR RIDGE The edentulous mandible may become flat, due to resorption; which

results into outward inclination and progressively widening of mandible.

Similarly maxilla resorbs upward and inward making it smaller.

It is the reason for edentulous patients to have prognathic apperance

The slopes of residual alveolar ridge have thin plate of cortical bone. The slopes of the ridge are at an acute angle to occlusal forces.

Hence, it is considered as a SECONDARY stress bearing area.

Since crest of the ridge has cancellous bone, it is not favourable as primary stress bearing area.

CLINICAL SIGNIFICANCE. Any movable soft tissue overlying the ridge should not be

compressed while making impression.

RELIEF AREAMental foramenGenial tubercleMylohyoid ridgeMandibular tori

MENTAL FORAMEN It lies between the 1st and 2nd premolar

region.

Due to ridge resorption, it may lie close to the ridge.

CLINICAL SIGNIFICANCE It should be relieved in these areas

as pressure over the nerve passing through it can get compressed by denture base leading to paraesthesia (numbness) of lower lip.

GENIAL TUBERCLE The genial tubercle are a pair of dense

prominences at the inferior border of the mandible at the lingual midline

They represents the muscle attachment of the genioglossus and geniohyoid muscle.

CLINICAL SIGNIFICANCE They only become relevant in the denture

when there is excessive resorption of the residual ridge.

MYLOHYOID RIDGE The mylohyoid ridge is a bony prominence

along the lingual aspect of the mandible Soft tissue usually hides the sharpness of

the mylohyoid ridge Anteriorly, this ridge with mylohyoid

muscle is close to the inferior surface of the mandible

Posteriorly, after resorption, it often flushes with the residual ridge.

CLINICAL SIGNIFICANCE The mucosa membrane overlying the

sharp or irregular mylohyoid ridge needs to be relieved because denture base might easily traumatize it.

MANDIBULAR TORI These are the abnormal bony

prominence found bilaterally on the lingual side, near the premolar region but they may extend posteriorly to the molar area

It is covered by thin mucosa.

CLINICAL SIGNIFICANCE It has to be relieved or surgically removed,

according to its size and extent. Small tori may only require relief in the

denture Large tori requires removal before a

denture can be fabricated.

CONCLUSION

Thus, we see that a sound knowledge of the anatomical landmarks of the denture bearing area is a prerequisite, if one has to achieve the objective one has in mind; fabrication of a complete denture that has maximum retention, stability and support with preservation of underlying structures with minimum post insertion problems.

REFERENCES

Prosthodontic treatment for edentulous patient : Zarb Bolender

Preclinical manual of prosthodontics : S Lakshmi Impressions for complete dentures : Bernard Levin Textbook of Prosthodontic : Nallasyamy Boucher’s prosthodontics treatment for edentulous

patients. 13th Edition Heartwell’s syllabus of complete denture. 4th edition.