Submitted by:Calibo, Jansen

DMD2AA

TOOTH ERUPTION

DEFINITION………..2A close look at tooth eruption……….…….3

MECHANISM OF TOOTH ERUPTION

PRE-ERUPTIVE PHASE……………...3

2 Types of Tooth Movement in Preeruptive Phase...5

Eruptive or Pre-Functional Phase…..5Five Major Events take place during Pre-Eruptive Phase……..5

Post-Eruptive or Functional Phase…..6

Mammalian Teeth Three Categories on the Basis of Eruptive Characteristics

Continuously Growing Teeth……….……….8

Continuously Extruding Tooth…….9

Continuously Erupting Tooth………………..9

Eruption – Mechanism of Tooth Eruption Page 2

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. (Figure 1 & 2)

Tooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligaments play an important role in tooth eruption. The first human teeth to appear, the deciduous (primary) teeth (also known as baby or milk teeth), erupt into the mouth from around 6 months until 2 years of age, in a process known as "teething". These teeth are the only ones in the mouth until a person is about 6 years old. At that time, the first permanent tooth erupts and begins a time in which there is a combination of primary and permanent teeth. This stage, known as the mixed stage, lasts until the last primary tooth is lost. Then, the remaining permanent teeth erupt into the mouth.

Figure 1

Figure 2

Eruption – Mechanism of Tooth Eruption Page 3

A Close Look at Tooth Eruption:Baby 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. (Figure 3)

Figure 3

Mechanism of Tooth Eruption1. Pre-eruptive 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. (Figure 4) 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. (Figure 5)

Eruption – Mechanism of Tooth Eruption Page 4

Early in the pre-eruptive phase, the successional permanent teeth develop

lingual to, and near the incisal or occlusal level of, their primary predecessors. (Figure 6A & 7A)

At the end of this phase, the developing anterior permanent teeth are positioned lingually and near the apical third of the primary anterior teeth. (Figure 6B)

The premolars are located under the roots of the primary molars. (Figure 7B)

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. (Figure 8)

Eruption – Mechanism of Tooth Eruption Page 5

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

2. Eruptive or Pre-functional Phase Begins with the initiation of root formation and ends when the teeth

reach occlusal contact. Five major events take place during this phase:

Figure 8 – Human jaws during mixed dentition. Permanent maxillary molar in tuberosity.

Figure 7 – Relative position of primary molar and permanent premolar teeth in (A)pre-eruptive and

(B)eruptive phases.

Figure 6 – Relative position of primary and permanent teeth in (A)pre-eruptive and

Figure 5 – Bodily Movement of Crown during Pre-eruptive Phase

Figure 4 – Pre-eruptive Phase of Tooth

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. 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. (Figure 9)

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 (Figure 10). 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. (Figure 11)

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 (Figure 12). The crown erupts further, and the lateral borders of the oral mucosa become the dentogingival junction (Figure 12A). 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. (Figure 12B)

Eruption – Mechanism of Tooth Eruption Page 6

5. The erupting tooth continues to move occlusally at a maximum rate, and there is gradual exposure of more of the clinical crown. (Figure 13)

Figure 9 – Pre-Functional Eruptive Phase in formation of root

Figure 10 – Crown tip approaching oral epitheliumFigure 11 – Contact and fusion of reduced enamel epithelium and oral mucosa.Figure 12 – Clinical appearance of the 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.

Eruption – Mechanism of Tooth Eruption Page 7

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. (Figure 14)

Later in life, attrition may wear down the occlusal surfaces of the teeth. (Figure 15)

Figure 13 – Primary tooth at the end of the eruptive phase. Permanent successor in preeruptive phase.

Eruption – Three Categories on the Basis of Eruptive

Characteristics Page 8

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. (Figure 16)

Three Categories on the Basis of Eruptive Characteristics

1. Continuously Growing Teeth 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

this form of tooth is characteristic of animals with rapid occlusal wear & eruption. (ex. Rodent incisor teeth – Figure 17 & 18)

Figure 16 – Posteruptive changes: attrition and

compensative formation of cementum.

Figure 14 – Increased density of periodontal ligament fibers during eruption

Figure 15 – Formation of the junctional epithelium. A, B Preeruptive, C Prefunctional eruptive phase,

D-F Functional occlusion.

Eruption – Three Categories on the Basis of EruptiveCharacteristics

Page 9

2. Continuously Extruding Tooth has a defined crown & anatomical root. as the tooth is worn, more of the anatomical crown extrudes &

epithelial attachment migrates apically. (Figure 19) 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.

(Figure 20 & 21)

3. Continuously Erupting Tooth

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

this is characteristic of human teeth. (Figure 22)

Figure 18 - RatFigure 17 - Rabbit

Figure 19 Figure 20 – Teeth of a sheep. Figure 21 – Teeth of a cattle.

Figure 22 – Human teeth.