Applied Anatomy and Physiology1

This is divided into;

Number of bones joined by sutures makeup the skull.

This consist of:

These are 32 in number together in the upper and lower jaw- with 16 in each jaw and 8 on each side of the jaw, starting from the midline of the oral cavity.

These teeth are represented as follows:

Tooth is made up of enamel, dentine, pulp and cementum. Root of the tooth is held in the alveolar bone of the main jawbone by means of periodontal membrane (Fig. 1.7).

These teeth erupt immediately behind the second deciduous molars usually at the age of six years, which is about one year before the first of the deciduous teeth, are shed.

Because these four 1st molars in proper occlusion.

When all the permanent teeth are erupted to full occlusion.

To support the denture, the area covered by the mucous membrane must have underlying bony support, called hard tissue area and this will firmly support the denture. The areas which take-up the main load of compression (of mastication) are the maxillary and mandibular alveolar ridges which are solid and unyielding, are known as Main stress bearing areas.

Denture coverage: Maxillary complete denture should cover the whole of the palate, labial and buccal aspects of alveolar ridge. The posterior border should be through the palatal fovea and completely cover the tuberosities.

Postdam: This is a raised lip on the posterior border of the fitting surface of the upper denture as a means of achieving perfect peripheral seal.

The tongue occupies the whole of the oral cavity when at rest with teeth occluded. It has a wonderful capacity to change its shape in so many ways during its many functional activities. It can be protruded, retracted, twisted and these are due to the combination of actions of intrinsic muscles of the tongue. Contraction of the intrinsic muscles shortens the tongue. These muscles are supplied by the hypoglossal (12th cranial) nerve.

Tongue is Divided into

These are:

These together form the anterior and lateral boundaries of the oral cavity. Their outer surface is covered by skin and inner surfaces by mucous membrane. They consist mainly of muscle tissue and collectively they are called “Muscles of Facial Expression” (Fig. 1.11).

With tongue on one side and lips and cheeks on another side keep the food on the occlusal surface of the teeth during mastication.

The area between tongue on one side, cheek and lips on other side is known as “Neutral Zone” as described by Sir William Kelsey Fry. And artificial teeth should be set-up in this neutral zone for the denture stability.

Roof of the mouth: Hard and soft palate

This is continuous with the hard palate and ends posteriorly in a free margin. In the center of the free margin there is uvula. The sides of the soft palate has two folds (pillars)- namely, anterior pillar of the fauces formed by palato-glossal fold, and posterior pillar of the fauces formed by palato pharyngeal fold. Between the two pillars lies the lymphoid tissue called Tonsil.

Levator veli palatini

Tensor veli palatini.

Uvula

Palato glossus

Palato pharyngeus.

This is the area between the two horizontal rami of mandible and is occupied by tongue. The mucous membrane covering the floor of the mouth extends over the inner aspects of mandible to form labial and lingual gingivae and covers the under surface and lateral surface of tongue. Sublingual salivary glands are situated between the mylohyoid muscle and the mucosa of the floor of the mouth on both sides.

Salivary glands: These are mainly 3 pairs

Parotid gland: This is situated below the ear and at the back of the mandible. Its duct (Stensen's duct) opens in the buccal vestibule in the region of maxillary second permanent molar tooth on each side.

To produce saliva and mucous.

This is a highly specialized joint and distinguished from most other joints by the fact the articulating surfaces are not covered by hyaline cartilage but by an avascular fibrous tissue. This is the joint on each side of the skull between the condyle of the mandible and the glenoid fossa and articular eminence of the temporal bone. This is a Ginglymo arthrodial joint. That means it has both hinge and sliding action.

One of the main functions of mastication (chewing) is carried out by the teeth and jaws. The muscles directly involved in this process are called muscles of mastication.

6. Mylohyoid

7. Geniohyoid

The position of the mandible is maintained by the mandibular joint and the surrounding ligaments.

The joint itself is peculiar because it is a double joint, like the knee joint, with a disc or meniscus between the head of the condyle and the glenoid fossa.

The movements are grouped as follows:

If the jaw is moved to the right side, the right condyle remains stationary in the glenoid fossa but the left condyle alone moves forward and inward on the eminentia articularis, due to the contraction of left side lateral pterygoid muscle.

On the working side, although the condyle remains stationary, it rotates around a vertical axis, causing a slight backward and lateral movement due to the contraction of masseter and temporalis of that side. The result of this is little lateral shift of the whole mandible and this is Bennet movement (Fig. 1.24).

Due to the downward and forward movement of condyle during protrusive and lateral movements, posterior teeth of artificial dentures or the posterior ends of the occlusal rims may not meet correctly; instead there will be a space between the two. This is due to changes that have taken place in the edentulous alveolar ridge.14

This is known as Christiansen phenomena, which has to be corrected if the dentures to have uniform contact of teeth throughout.

Opening begins with almost pure rotatory or hinge movement and the mandible is depressed to slightly beyond rest position- means 2/3rd of opening has taken place. Then, for the remaining 1/3rd opening, both sliding and roratory components combine to produce a smooth, movement of opening fully. In the reverse process of closing, the first 2/3rd is translatory movement and remaining 1/3rd is combination of both translatory and rotatory movement until fully closed.

It is a clear, colorless fluid secreted into the mouth by salivary glands.

Water 99 percent

Bacterias and its product: Food particles, epithelial cells, leucocytes. Enzymes– ptyalin. Water helps to dissolve food.

This is a complicated physiological process involving many structures like teeth, tongue, palate, muscles of mastication, nerves, saliva, TMJ etc; Teeth act as tool to cut, tear, and grind the food while it is getting mixed with saliva and made palatable before being swallowed. Powerful muscles of mastication apply force on the teeth, so that all kinds of food are properly cut and grinded. Incisors cut, canines tear and molars grind the food. Chewing begins with opening the jaw, and once the food is inside the mouth it is cut and torn into small pieces and taken back on to the molars to grind. All the while the mandible is making continuous opening and closing movements and lateral movements every now and then. Main and accessory muscles of mastication and tongue help in this process.

Significance: Patients wearing dentures has to learn the process of eating due to loss of periodontal membrane receptors.

This is sensitive to touch. Thus, harsh food is rejected by the palate.

Significance: Denture wearers loose this sensitivity.

These are sensitive to touch and temperature and so control the temperature of food.

This is a co-ordinated activity of various muscles and nerves.

This is voluntary. The masticated food is collected and made as bolus and kept on the dorsum of the tongue. Lips are closed. Teeth are brought together in occlusion. A mylohyoid muscle contracts, which pushes the tongue up against the palate and pushes the food backwards towards the pharynx. Soft palate is raised and thus allows the food to go into pharynx and at the same time prevents food going into nose.

This is involuntary. Food passes through the pharynx to the beginning of oesophagus.

This is also involuntary. The constrictor muscles of the pharynx contract from above downwards and push the bolus of food through the oesophagus into the stomach.