Occlusion• In Latin: Oc= up clusion= closing • Occlusion means (closing up)

• When the jaws are closed and teeth are in contact, this is termed as (static occlusion).

• However, occlusion mainly occurs as momentary contacts during mandibular movements and is termed as(dynamic occlusion)

•It is the contact relation ship of upper & lower teeth during different mandibular movements.

*Simplistic definition of occlusion:The way teeth meet and function.

*Tooth positioning is not a random process but a number of controlling factors are involved

*Occlusion is not only refer to contact between the teeth but also to all those factors concerned with the development and stability of the masticatory system and with the use of teeth in oral motor behavior

The components of human dental occlusion:

1- The teeth and their investing tissue.2- The jaws. 3- The temporo-mandibular joint. 4- The muscles of mastication.

* To study occlusion the following items must be understood:1- Dental arch formation.2- Compensating curvatures of the dental arch ( curved occlusal

planes).3- Compensatory curvatures of individual teeth (curved tooth axes). 4- Angulation of teeth in relation to different planes.5- Functional form of the teeth at their incisal and occlusal third.6- Facial and lingual relation of each tooth in one arch to its

antagonist in the opposing arch during centric occlusion.7- Occlusal contact and inter-cusp relation of all teeth of one arch with those of the opposing arch in centric occlusion. 8- Occlusal contact and inter-cusp relation of all teeth during

various mandibular movement.

• Parabolic curve.• Phases of development of permanent dental arch.• Bonwill triangle.

Parabolic curve

The maxillary arch is larger than the mandibular arch giving a horizontal space between upper and lower teeth during occlusion called overjet.

Also the upper teeth overlap the lower teeth, the vertical distance between them is named overbite.

Two Types of Overlap Horizontal Overlap= OverjetVertical Overlap= Overbite

parabolic curve.

The upper &lower dental arches have a horse- shoe shape

From an occlusal view the facial and lingual outlines of the dental arch conform to a Parabolic curve.

1-Anterior segment.

2- Middle segment.3- Posterior segment.

Anterior segment

straight

Posterior segment

semicircular

Middle segment

1-Anterior segment:

Semicircular and equally bisected by the midline.

Facial surfaces of anterior teeth and the first premolar of both sides.

2- Middle segment: Straight line and continuous

with the anterior segment in buccal direction. Included the first and second premolars and the mesial half of the first molar.

3- Posterior segment: Straight line parallel to the

midline of the jaw& slightly directed to the midline in the maxillary dental arch.

Middle segment

Posterior segment

Middle segment

Anterior segment

Anterior segment

Posterior segment: Straight line parallel to the midline of the jaw but slightly directed to the midline in the maxillary dental arch. * The buccal outline of the upper molars curves toward the midline more than the lower due to 1- Second and third maxillary molars located lingual to the first molar.2- Distal convergence of the first maxillary molar.

First phase: Second phase: At 6 years eruption of

the first permanent molars lead to increase the masticatory efficiency and jaw growth.

Eruption of the permanent incisors.

Third phase: Fourth phase: Premolars replace the

deciduous molars and spacing of teeth occur due to smaller size of premolars than deciduous molars.

The canines and the second permanent molar erupted nearly at the same time. The arch is considered to be physiologically complete.

Fifth phase:

• Eruption of the third molar.

Fifth phase