BIOLOGICAL CONSIDERATIONS OF MAXILLARY DENTURE FOUNDATION AREA

INTRODUCTION:

Dentures and their supporting structures are to coexist for a length of time

It is important that the practitioner understand the anatomy of the supporting and limiting structures which form the foundation of the denture bearing area

The foundation area mainly comprises of bone of the hard palate and the residual ridge which is covered by a mucous membrane

ANATOMY OF THE SUPPORTING STRUCTURES:

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 palate and the crest of the residual ridge is called masticatory mucosa

Submucosa: The attachment of the mucosa to bone occurs

due to the attachment between the submucosa and the periosteum

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

The thickness and consistency of submucosa is responsible for the support that the mucous membrane gives the denture base

Bone: The underlying bone may consist of compact or

cancellous bone

ANATOMICAL LANDMARKS IN MAXILLA:

They are divided into: Supporting structures Limiting structures Relief structures

SUPPORTING STRUCTURES: Primary stress bearing areas:

Hard Palate:▪ The ultimate support for the maxillary

denture is derived from the bone of the 2 maxillae and the palatine bone

▪ Palatine processes are joined by the median palatine suture

▪ A cross-section of the hard palate reveals it to be covered by soft tissue of varying thickness

Microscopically: ▪ The mucosa is stratified squamous epithelium and

contains dense collagen fibers that vary in thickness▪ Anterolaterally – submucosa contains adipose tissue▪ Posterolaterally- submucosa contains glandular

tissue

The tissue contributes to the support of the denture but the primary support is derived from the horizontal portion of the hard palate

The trabecular pattern of the bone is perpendicular to the direction of force making it capable of withstanding the forces it is subjected to

Residual Alveolar Ridge: “The portion of the alveolar ridge and its soft

tissue covering which remains following the removal of teeth” (G.P.T)

It is a primary stress bearing area

The resorption following the extraction of teeth is rapid at first but continues at a reduced rate throughout life

Over a prolonged period the ridge may become small and lack a smooth bony surface

Microscopically:

▪ Thick mucous membrane is made up of stratified sqamous epithelium which is keratinized

▪ Submucosa is devoid of fat and glandular cells but is sufficiently thick enough to provide adequate resiliency to support the denture

▪ The crest of the ridge may act as more of a secondary stress bearing area and the posterolateral portion is the primary stress bearing area

Secondary stress bearing areas: Rugae:▪ Rugae are raised areas of dense connective

tissue radiating from the median suture in the anterior one third of the palate.

▪ It is a secondary stress bearing area, set at an angle to the residual ridge and thinly covered by soft tissue

▪ They help in stabilization of the maxillary denture during function.

▪ Microscopically:▪ Amount of keratinization is similar to the hard

palate▪ Submucosa is thick and contains a lot of

adipose tissue

Maxillary Tuberosity: It is the bulbous extension of the residual ridge in the

second and third molar region terminating in the hamular notch

It is one of the most important areas from which the denture derives support as it is least likely to resorb

When the maxillary posteriors are retained after the mandibular posterior teeth have been extracted and not replaced, maxillary teeth over erupt and the tuberosity region hangs down abnormally low

The enlargements are often fiberous but may be bony

If they interfere with the proper location of the occlusal plane then surgical removal is indicated

The undercuts lateral to tuberosity can be used for the retention of the denture.

Relief Areas: These area areas under constant load

and contain fragile structures within

Incisive Papilla:

▪ Located on a line immediately behind and beneath the central incisors

▪ It is a structure which relates to incisive foramen which is the exit point of the nasopalatine nerves and vessels

▪ The papilla comes to lie near the crest of the ridge as resorption pregresses

Microscopy: Nasopalatine nerves and vessels are

contained in the sunmucosa

Mid Palatine suture: It is the area extending from the incisive

papilla to the distal end of the hard palate

The submucosa in this region is extremely thin and the soft tissue covering is non resilient in this area

This area needs to be relived for 2 reasons▪ As pressure on this area can lead to soreness

& severe pain.

▪ if not adequately relived, it can act as a fulcrum point led to rotation of the dentures.

Fovea Palatinae:

It is formed by the coalescence of the ducts of several minor mucous glands the secretions from which aid in retention

Usually 2 in number, found on either side of the midline & slightly posterior to the junction of hard & soft palate.

They indicate the vicinity of the posterior palatal seal area.

The position of fovea palatine influences the position of the posterior border of the denture.

The denture can extend 1-2 mm beyond fovea palatinae.

Torus Palatinus: It is a hard bony enlargement that

occurs in the midline of the roof of the mouth

Found in 20% of the population

It is covered by a thin layer of mucous membrane that is easily traumatized by the denture base unless relief is provided

ANATOMY OF PERIPHERAL OR LIMITING STRUCTURES:

These structures determine and confine the extent of the denture The mucosa covering this region is given the term ‘lining mucosa’

Labial Frenum:

It is a fiberous band covered by mucous membrane that extends from the labial aspect of the residual ridge to the lip right in the midline

It has no muscle fibres so it is a passive frenum

It divides the labial vestibule into 2 equal parts

Starts as a fan shape and converges towards the residual ridge

It is loosely attached to underlying bone and is flexible

A V-shaped notch is recorded during impression making to accommodate the frenum

Microscopically: Consists of stratified squamous non-

keratinized epithelium with loose areolar tissue and elastic fibres

Buccal Fenum: It separates the labial and buccal vestibule and

is usually multiple

It is an active frenum because of the muscle attachments from the following:▪ Levator anguli oris – attaches beneath the frenum▪ Orbicularis oris – pulls frenum in a forward direction▪ Buccinator- pulls frenum in a backward direction

Sufficient allowance should be created for the movement of frenum because overriding the function of the frenum will cause pain & dislodgement of the denture

If frenum is attached close to the crest of the ridge frenectomy should be done.

Labial vestibule: It is that portion of the oral cavity that is

bounded on one side by the teeth, gingiva and alveolar ridge and on the other side by the lips and cheeks

It extends bilaterally from labial frenum to buccal frenum

The reflection of the mucous membrane superiorly determines the height of the denture

Buccal Vestibule: Bounded by ▪ Anteriorly - buccal frenum▪ Laterally – buccal mucosa▪ Medially - residual alveolar ridge▪ Posteriorly - hamular notch.

During the impression procedure the vestibule should be suitably filled with impression material for proper border contact between denture & the tissue.

When the denture flange properly occupies the vestibular space that is distal & lateral to the alveolar tubercles, the stability & retention is greatly enhanced.

The buccal flange borders depends upon movement of the ramus of the mandible at the distal end of the buccal vestibule & hence the patient should move the mandible in a lateral & protrusive relation to make sure that the coronoid process does not interfere with these functions.

The effectively record the maxillary buccal sulcus ,the mouth should be half away closed b’coz wide opening of the mouth narrows the space & does not allow proper contouring of the sulcus.

Hamular notch:

This structure is bounded by the maxillary tuberosity anteriorly & the pterygoid hamulus posteriorly& marks the posterio-lateral limit of the upper denture.

The pterygomandibular ligament attaches to the hamulus.

The narrow cleft of loose connective tissue is approximately 2mm in extent anterioposteriorly.

A seal can be obtained by utilizing this area as it can be displaced to a certain extend without trauma.

The denture should not extend beyond the hamular notch, failure of which will result in

restricted pterygomandibular raphe movement.

when mouth is wide open ,the denture dislodges

Posterior Pakatal Seal Area:

“The soft tissue along the junction of the hard & soft palate on which pressure within the physiological limits of the tissues can be applied by a denture to aid in the retention of the denture” (G.P.T)

It is a 3 dimensional seal area.

It provides retention to the maxillary denture.

The seal prevents passage of air between the denture & the tissues.

It is found distal to the junction of the hard and soft palate

Functions of Posterior Palatal Seal:

Aids in retention by maintaining constant contact with the soft palate during functional movement like speech ,mastication and deglutition.

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

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

Compensates for polymerization shrinkage that occur during the polymerization

The posterior palatal seal area can be divided into 2 regions based upon anatomical landmarks:

Pterygomaxillary seal Postpalatal seal

Pterygomaxillary seal-

this is the part of the P.P.S that extends across the hamular notch & it extends 3-4mm anterolaterally to end in the mucogingival junction on the posterior part of maxillary ridge.

The posterior extent of the denture in this region should end in the hamular notch & not extent over the hamular process as it can lead to severe pain during denture wear.

Postpalatal seal- this is a part of the posterior palatal seal that extends

between the 2 maxillary tuberosities.

Vibrating line: This is the area in the anterior junction of

the soft palate where movement is seen in the mucosa when the patient says ‘ahhh’ in a moderate manner

It extends from one hamular notch to another

The distal end of the denture is 1-2mm posterior to this line

Classified as 2: Anterior vibrating line Posterior vibrating line

Anterior vibrating line: The line between the immovable

tissues over the hard palate and the slightly movable tissue of the soft palate

Cupid’s bow shaped

Posterior vibrating line: Located at the junction of the soft

palate which shows limited movement and soft palate that shows marked movement

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