Sumitted by:Calibo, Jansen

DMD2AA

Submitted to:Dr. Nunag

Mechanisms of Tooth Eruption & Mammalian Teeth 3 Categories on

the Basis of Eruptive Charateristics

ERUPTION1. Mechanism of Tooth Eruption

2. Mammalian Teeth 3 Categories on the Basis of Eruptive Characteristics

Eruption is the movement of the developing teeth through the bone and the overlying mucosa of the jaws to appear in the oral cavity and reach the occlusal plane.

Eruption

A Close Look at Tooth EruptionBaby teeth are lost naturally due to the pressure of the permanent teeth

erupting from below. This process is called root resorption. Note the continued development of the permanent crown and root as it erupts.

MECHANISM OF TOOTH ERUPTION

Phases:1. Pre-eruptive phase

2. Eruptive or Pre-functional phase3. Post-eruptive or Functional phase

Preparatory to the eruptive phases.

It consists of the movements to the developing and growing tooth germs within the alveolar process before root formation.

1. Pre-eruptive phase

During this phase, the growing teeth move in various directions to maintain their position in the expanding jaws. This is accomplished by both bodily movement eccentric growth. Bodily movement is a shift of the entire tooth germ, which causes bone resorption in the direction of tooth movement and bone apposition from behind. These movement occur as the jaws grow.

Early in the pre-eruptive phase, the successional permanent teeth develop lingual to, and near the

incisal or occlusal level of, their primary predecessors.

At the end of this phase, the developing anterior permanent teeth are positioned lingually and near the apical third of the

primary anterior teeth.

The premolars are located under the roots of the primary molars.

The upper molars develop in the tuberosities of the maxilla, with their occlusal surfaces slanting distally. The lower molars develop in the base of the mandibular rami, and their occlusal surfaces slant messially.

Two types of tooth movement in pre-eruptive phase:

1. Total bodily movement2. Movement where one part remains

fixed while the rest◦ continues to grow leading to

change in the center of the◦ tooth germ

Begins with the initiation of root formation and ends when the teeth reach occlusal contact.

Five major events take place during this phase:1. The secretory phase of amelogenesis is completed just before the onset of root formation and perfunctional eruption. There is realtion between the cessation of mineralization and activation of the epithelial cells beyaond the enamel-forming area.

2. Eruptive or Pre-functional phase

2. The intraosseous stage occurs when the root formation begins as a result of the proliferation of both the epithelial root sheath and the mesenchymal tissue of the dental papilla and dental follicle.

3. The supraosseous stage begins when the erupting tooth moves occlusally through the boneof the crypt and the connective tissue of the oral mucosa, so that the reduced enamel epithelium covering the crown comes into contact with the oral epithelium.

As this occurs, the reduced enamel epithelium of the crown proliferates and forms a firm attachment with the oral epithelium. A fused, double epithelial layer over the erupting crown is then formed.

4. The tip of the crown enters the oral cavity by breaking through the center of the double -layered epithelial cells. This breakthrough is accomplished by the cusp tip causing degeneration of the membrane and is the beginning stage of clinical eruption.

The crown erupts further, and the lateral borders of the oral mucosa become the dentogingival junction.

The reduced enamel epithelium, now surrounding the crown like a cuff, becomes known as the junctional or attchment epithelium. When the tip of the crown appears in the oral cavity, about one-half to two-thirds of the roots are formed.

5. The erupting tooth continues to move occlusally at a maximum rate, and there is gradual exposure of more of the clinical crown.

3. Post-eruptive or Functional phase Begins when the teeth reach occlusion, and continues

for as long as each tooth remains in the oral cavity. Alveolar processes increase in height and the roots

continue to grow. Teeth continue to move occlusally, which accomodates

jaw growth and allows for root elongation. The most marked changes occur as occlusion is established.

Alveolar bone density increases, and the principle fibers of the periodontal ligaments establish themselves into separate groups oriented about the gingiva, the alveolar crest, and the alveolar surface around the root.

The diameter of the fiber bundles increase from delicate, fine groups of fibers to heavy, scurely stabilized bundles.

When root canal narrows, as a result of root tip maturation, apical fibers develop to help cushion the forces of occlusal impact.

Later in life, attrition may wear down the occlusal surfaces of the teeth.

The teeth erupt slightly to compensate for loss of tooth structure and to prevent occlusal overclosure.

If the occlusal wear is excessive, cementum deposited on the apical third of the root; it is deposited in the furcation region of molars to compensate for hypereruption of these teeth.

3 CATEGORIES ON THE BASIS OF ERUPTIVE CHARACTERISTICS

1. Continuously Growing Tooth2. Continuously Extruding Tooth

3. Continuously Erupting Tooth

no gross separation between the anatomical crown & anatomical root.

continuous growth of the tooth at the apex & continuous eruption occur throughout the life of the animal.

clinical crown is constantly replaced by root covered with enamel in the progressive stages of development.

with the loss of tooth substance due to occlusal attrition, more tooth substance is extruded from the socket to maintain the clinical crown

1. Continuously Growing Tooth

this form of tooth is characteristic of animals with rapid occlusal wear & eruption.

(ex. Rodent incisor teeth)

has a defined crown & anatomical root. as the tooth is worn, more of the

anatomical crown extrudes & epithelial attachment migrates apically.

2. Continuously Extruding Tooth

since no new tooth structure is being formed, it results to gradual loosening & final exfoliation of the tooth.

this tooth form is characteristic of the lower incisors of sheep & cattle.

eruption does not occur by enlargement of the clinical crown but rather by addition to the alveolar process.

this is characteristic of human teeth.

3. Continuously Erupting Tooth

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