1Anatomy and histology of the denture bearing area

Dr. Aylin BAYSANThe University of Birmingham

School of Dentistry

Anatomy of the edentulous area

In the mouth, complete or partial dentures are surrounded by muscles.

Muscles tend to distabilise the denture if they are encroached upon during contraction.

Anatomy of the edentulous area

Other structures should also be identified to establish their precise relation to denture base. These are as follows:

Ligaments Frenulum Glandular tissues

Upper and Lower jaw

Lower jaw Labial frenulum

It is a fold of fibrous tissue in the midline between lip and alveolus.

Mentalis muscleThis muscle arises from the symphysis menti and is inserted downward into skin of the chin.

It elevates the lower lip and may lift up the lower denture.

Orbicularis orisOrbicularis oris forms a muscular circle within the lips. It is inserted near the midline into labial aspect of the maxilla and mandible.

ModiolusThis muscular knot is at the angles of the mouth where the dilator muscles:- Levator anguli oris- Zygomaticus major and minor- Depressor anguli oris

Modiolus is lateral to the lower premolars so it will displace a lower denture if those teeth are set too far BUCCALLY.

2Muscles of facial expression which form modiolus Mental nerve

This nerve emerges from the mental foramen near the apices of the lower premolars.

In patients with extreme alveolar resorption, the nerve may lie on or near the crest of the alveolar ridge.

Pain or paraesthesia may be experienced if the nerve is trapped by a denture base, usually by the fitting surface.

Buccinator muscleIt arises from both jaws opposite the molar alveolar area and posteriorly from the pterygomandibular raph.

As the buccinator fibres run almost parallel to the denture border, they can slightly be displaced for additional retention.

In this respect, it is the UNIQUE and ONLY muscle that can be used this way.

Massater muscleThis muscle is the MOST powerful of the muscles which close the MANDIBLE.

The lower denture periphery related to it should be shaped according to its structure so that displacement of the denture can be avoided when the muscle contracts.

Denture bearing area Anterior fibres of temporalis

These fibres are sometimes attached low down on the anterior border of the ramusas far as the attachment of the buccinatorin the retromolar fossa.

The contraction of these fibres may sometimes displace a lower denture.

3 Retromolar padRetromolar pad lies distal to the lower third molar and is composed of fibrous tissue and mucous glands.

Superior constrictor muscle This muscle originates from the pterygomandibularraph with a small extension continuing on the lingual surface of the mandible to the posterior end of the mylohyoid line.

Mylohyoid muscleIt is a thin sheet of muscle and forms the floor of the mouth. Its linear origin from the mylohyoid line of the mandible continues posteriorly to the level of the third molar.

Sublingual salivary gland This gland rests on the mylohyoid muscle medial to the mandible. It is usually adjacent to the lower canine region.

Its indentation is often seen on lower impressions

Genioglossus muscle and genial tubercle The genioglossus arises from the superior genial tubercles on the lingual surface of the mandible.

When the tongue is protruded, this muscle may lift the lower denture.

When the edentulous mandible is severely resorbed, the superior genial tubercle may project above the level of the alveolar ridge and the mucosa may become traumatised by a lower denture.

Muscles limiting the extension of a lower denture

Anterior labial flangeOrbicularis oris as far as the first premolar region.

BuccallyBuccinator muscle

Retromolar padBuccinator and its insertion into the pterygomandibular raph.

Muscles limiting the extension of a lower denture

LinguallyThe posterior extension is limited by fibersfrom the superior constrictor muscle.

Fibres from the palatoglossus also form a posterior limit.

The depth of the lingual flange is governed by the mylohyoid.

Upper jaw Coronoid process

Coronoid process lies lateral to the maxillary tuberosity.

It may sometimes impinge on the buccal flange of a denture and cause pain or instability.

Hamular notchThis notch is the junction of the maxillary tuberosity and hamular process.

The periphery of a correctly extended denture should extend through these notches via the area of the fovea palatinae.

4 Fovea palatinaeThese are a pair of mucous gland duct orifices near the midline at the junction of the hard and soft palate.

These landmarks provide a guide to the position of the posterior palatal border of a denture.

Incisive papillaIncisive papilla is a mass of fibrous tissue about 1 cm behind the upper incisors.

Its position in the edentulous mouth indicates where the incisors and canines should be set.

Muscles limiting the extension of a upper denture

Anterior labial flangeAnterior labial flange is limited by the orbicularis oris as far as the first premolar region.

BuccallyFrom the second premolar region posteriorly, the buccal flange is limited by the buccinator.

Facial curtain

The orbicularis oris and buccinator muscles are draped around the mouth to form a curtain, which is supported by teeth and alveoli.

In edentulous patients, this curtain collapses to give the characteristic toothless look.

Collapse of elevator and depressor muscles and modiolus following loss of teeth

Maxilla and mandible

There is difference in resorption pattern for maxilla and mandible.

This leads to the appearance of prognatismand gross positional discrepancies between opposing residual ridges.

Edentulous face

5Muscles attachment changes with progressive bone loss

Oral mucous membrane Oral cavityStratified squamous type and shows differences in degree of development, which correlates with the functions of a particular area.

Apart from systemic that affect the integrity of the oral mucous membrane, it should be noted that there are age changes that are frequently seen in the elderly edentulous patient including tendency to dryness and general atrophy of the mucous membrane.

The varying thickness of the mucosa covering the oral cavity

Oral mucosa

Tongue

The tongue is highly mobile muscular organ that needs careful attention during the construction of complete dentures.

In coordination with lips, cheek, palate and pharynx, the tongue functions in speech, mastication and swallowing.

Tongue

The tongue is in intimate contact with a complete lower denture and its position in relation to an edentulous ridge varies widely.

This relationship must be considered very carefully in each particular patient.

6Salivary glands

Saliva is derived from the major and minor salivary glands. The major salivary glands consist of three pairs of glands:

Parotid Gland Submandibular Gland Sublingual Gland

Submandibular GlandExtension of the lingual flange of a denture in this region can lead to obstruction of the submandibular gland.

Patients may complain of developing swellings under the jaws when eating.

The outline of the lingual flange of the lower denture in relation to submandibular gland