introduction · introduction andrews who is the first one studied normal occlusion in 120 cases...

introduction

Normal occlusion

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introduction

Andrews who is the first one studied normal

occlusion in 120 cases with the following

criteria:

1. Correct bite

2. Did not have orthodontic treatment

3. Straight teeth and pleasing appearance

Andrews described six keys to normal occlusion:

1. Molar relationship.

2. Crown angulation (tipping).

3. Crown inclination (torque).

4. Absence of rotation.

5. Tight contact.

6. A flat occlusal plane or slight curve of Spee.

Key I. molar relationship

Key I. molar relationship

The mesiobuccal cusp of the upper first molar

should occlude within the mesiobuccal groove of

the lower first molar.

The mesiolingual cusp of the upper first molar

should occlude in the central fossa of the lower

first molar.

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The crown of the upper first molar must be

angulated so that its distal marginal ridge

occludes with the mesial marginal ridge of the

lower second molar.

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• Molars and premolars

cusp embrasure buccally

cusp fossa lingually

• The tip of ,maxillay canine occlude slightly

mesially to the embrasure between lower canine and premolar ( canine rise concept)

Key II. Crown angulation (tipping)

It’s the mesiodistal tip of the long axis of the

crown

Angle formed between the long axis of the

crown and perpendicular line erected from the

occlusal plane (mesiodistal view)

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The gingival part of the long axis of the crown

must be distal to the occlusal part of the axis.

(Positive angulation)

The gingival part of the long axis of the crown

must be distal to the occlusal part of the axis

(positive) and vice versa

In normal occlusion, the crown angulation was

positive for all teeth

Key III. Crown inclination (torque)

It’s the faciolingual inclination of the long axis

of the crown

Its angle formed between the facial long axis of

the crown and a perpendicular to the occlusal

plane. (viewed from proximal surface)

When the gingival portion of the long axis of the crown

is lingual to the incisal portion , the crown inclination

is positive.

(and vice versa)

In normal occlusion, the crown inclination for all teeth

was negative except maxillary central and lateral

incisors

•Lingual crown inclination was similar in maxillary

canines and premolars, and more pronounced in the

maxillary molar

•Lingual crown inclination progressively increased from

mandibular canine through the mandibular second

molars.

Key IV. rotations

In normal occlusion, the dentition should be

free from undesirable rotations.

If the molar rotated, it would occupy more

space than normal within the arch.

The reverse is true for the anterior teeth.

Key V. tight contact

In normal occlusion, contact area should be

tight.

Key VI. Occlusal plane

Occlusal plane: is the imaginary plane on which

the teeth meet in occlusion.

In normal occlusion, the occlusal plane should

be flat or nearly flat.

Deep curve of Spee, result in a more confined

area for the maxillary teeth

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Goals of functional occlusion (ROTH)

• Coincident centric relation and occlusion

• Cusp embrasure relationship buccally

• Cusp fossa relationship palatally

• Equal posterior forces along teeth long axis

• There should be 0.005 inch (0.13mm) space between

the anterior teeth when posterior teeth in occlusion

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Goals of functional occlusion

• In protrusive movement, anterior guidance

produces posterior disocclusion.

• In lateral movement, canine serve as the main

guiding inclined surface ( canine guidance).

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