Occlusion

Occlusion:

It is the relation between the upper and lower teeth during the

various activities of the mandible as mastication and

swallowing.

Items of occlusion: 1 - Dental arch formation.

2 - Compansatory curves of the dental arch.

3 - Compansatory curves of individual tooth..

4 - Angulations of individual tooth to various plans.

5 - Functional form of the teeth at their incisal and occlusal surface

6 – centric occlusion

Facial and lingual relation of each tooth to its antagonists in centric occlusion.

7 - Occlusal contact and intercuspation of each tooth to its antagonist in centric occlusion

8- Occlusal contact and intercuspation of the teeth during the various functional activities.

1 - Dental arch formation.

The dental arches conform to a parabolic curves.

The maxillary dental arch is somewhat larger than that of the mandibular arch facially and buccally (overjet) so the mandibular arch appear to fall inside the maxillary arch (overbite).

[overjet) this overjet gaurds the lips and cheeks from being clipped during jaw movement.

The dental arches have three segments.

1) The anterior semicircular segment.

2) Middle straight segment premolars till mesiobuccal.cusp of 6

with the anterior semicircular segment and it includes the first, second premolars and the mesial half of the First molar.

3) The posterior segment is a straight line which is parallel to the median plane. It includes the distobuccal half of the first molar, the buccal surface of the second and third molars.

Phases of dental arch formation

FIRST PHASE

*The first permanent molars erupts at 6 years of age (keystones).

*They serve to back up the deciduous teeth.

*They add considerably to chewing efficiency and jaw development.

Second phase

*The permanent central and then lateral

incisors emerge at first lingual to the

deciduous predecessors.

*The permanent location of the incisors

cannot established until development of

the dental arch form is complete

Third phase

The 1st and 2nd premolars take

the places of the deciduous

molars.

Fourth phase

The canines (corner stones) force

themselves between the lateral incisors

and first premolars in both jaws.

Also the second molars emerge distally to

the first molars backing them up during

the wedging.

Fifth phase

Eruption of the wisdom

tooth.

Bonwill triangle

,,

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4 inches

Bonwill triangle

*The mandibular dental arch adapts itself to an

equilateral triangle of 4 inches length.

*The apex of the triangle is located at the mesial contact area of the lower central incisors

*The angles of the base are found at the centers of

each condyle.

Compensating

curvatures of

the dental

arches

2- Compensatory curves of dental arches

- These curves refer to the curved plane to

which the occlusal surfaces of the teeth

conform.

- The important of these compensatory curves is

to provide balance in all mandibular

movements.

- This occlusal balance occurs when one

segment of the arch is supported by one or more

other segments.

Curve of Spee-1

* It is seen within the sagittal plane, when the teeth are observed from a point opposite to the 1st molar.

* The mandibular curve of Spee is concave whereas the maxillary curve is convex.

*This curve ends at the anterior border of the condyle.

* This curve helps to achieve occlusal balance during mastication.

The occlusal table is not flat, it has a linear

curve in the antero-posterior direction.

2-Curve of Wilson It is seen in the coronal ( transverse) plane.

The occlusal surfaces of the posterior teeth conform to a curved

plane.

The crowns of mandibular posterior teeth must incline to the

lingual.

The crowns of maxillary posterior teeth must incline toward the buccal.

This curve becomes deeper posteriorly so that the molars inclination is greater than that of the premolars.

of buccal cusps*The

mandibular molars and the

of maxillary lingual cusps

molars appear to be longer.

*The purpose of this curve

the paths complementis to

of the condyles of the

mandible in its movements

Curve of Monson or sphere of Monson-3

It is the combination of the curve of Spee and the curve of Wilson.

This curve is within coronal and sagittal planes.

This curvature is concave for the mandibular arch and convex for the maxillary arch.

These two curved planes become identical in centric occlusion.

They form a segment of a sphere of 4 inches radius with the center of the sphere at the glabella.

With age and as a result of attrition, the cusps of

the teeth are worn away, so that the curvatures

of the occlusal plane are lost and the plane

becomes flat.

4- Bonwill Triangle

Bonwill was the first to describe the

mandible and found that the

mandibular dental arch adapts itself

to an equilateral triangle of L4 inches

length. The apex of the triangle is

located at the mesial contact area of

the lower central incisors while the

angles of the base are round at the

centers of each condyle.