Introduction

Malocclusion of the teeth is found in all races and even occasionally among the lower animals. Malocclusion is a developmental condition where there is a deflection from the normal relation or alignment of the teeth to other teeth in the same arch and/or to the teeth in the opposing arch. 

Line of occlusion

When teeth are in normal occlusion, there are many points at which contacts are made. These points are said to lie on an imaginary line.

According to Angle, An imaginary line ( smooth catenary curve) passing over the points of the buccal cusps of the molars and bicuspids, and the cutting-edges of the cuspids and incisors of the lower arch, and along the sulcus between the buccal and lingual cusps of the upper molars and bicuspids, crossing the lingual ridge of the cuspids and the marginal ridges of the incisors at a point about one-third the length of their crowns from their cutting-edges is called line of occlusion.

Angle’s Occlusion

According to Angle, the occlusion of the first molar pair was the center of the morphogenesis of the face. 

Angle (1899) emphasized the relationship of the mesiobuccal cusp of the maxillary first molar to the buccal groove of the mandibular first molar as the “key factor” in the establishment of a class I molar “normal” relationship. He considered the maxillary first molar to be a stable tooth. 

Angle’s malocclusion

Class I:

Arches in normal mesio-distal relations. Normal relationship of molars but the line of occlusion is incorrect because of malposed teeth, rotations or other causes.

Class II:

Lower arch distal to normal in its relation to upper arch. Line of occlusion not specified. 

DIVISION 1 - Bilaterally distal, protruding upper incisors. Usually mouth-breathers. 

Subdivision - Unilaterally distal, protruding upper incisors. Usually mouth-breathers. 

DIVISION 2 - Bilaterally distal, retruding upper incisors. Normal breathers. 

Subdivision - Unilaterally distal, retruding upper incisors. Normal breathers. 

Class III: 

Lower arch mesial to normal in its relation to upper arch. Line of occlusion not specified.

DIVISION - Bilaterally mesial. 

Subdivision - Unilaterally mesial.

Drawbacks 

• Angle considered malocclusion on the anteroposterior plane. He did not consider malocclusions in the transverse and vertical planes. 

• Angle considered the first permanent molars as fixed points in the skull. But is not found to be so

• The classification cannot be applied if the first permanent molars are extracted or missing. 

• The classification cannot be applied to the deciduous dentition. 

• The classification does not differentiate between skeletal and dental malocclusions. 

• The classification does not highlight the etiology of the malocclusion.

• Individual tooth malpositions have not been considered by Angle.

Dewey’s modifications

Class I modifications:

Type 1: Class I malocclusion with crowded anterior teeth. 

Type 2 : Class I with protrusive maxillary incisors. 

Type 3: Class I malocclusion with anterior crossbite. 

Type 4: Class I molar relation with posterior crossbite. 

Type 5: The permanent molar has drifted mesially due to early extraction of second deciduous molar or second premolar.

Class II modifications:

No modifications in class II.

Class III modifications:

Type 1: The upper and lower dental arches when viewed separately are in normal alignment. But when the arches are made to occlude the patient shows an edge to edge incisor alignment, suggestive of a forwardly moved mandibular dental arch. 

Type 2: The mandibular incisors are crowded and are in lingual relation to the maxillary incisors. 

Type 3: The maxillary incisors are crowded and are in cross bite in relation to the mandibular anterior.

Lischer’s Modifications 

He added a few more terms which designated certain other malocclusion.

Neutrocclusion: Synonymous with Angle’s Class I malocclusion. 

Distocclusion: Synonymous with Angle’s Class II malocclusion. 

Mesiocclusion: Synonymous with Angle’s Class III malocclusion.

Buccocclusion: Buccal placement of a tooth or a group of teeth.

Linguocclusion: Lingual placement of a tooth or a group of teeth.

Supraocclusion: When a tooth or group of teeth have erupted beyond normal level. 

Infraocclusion: When a tooth or group of teeth have not erupted to normal level. 

Mesioversion: Mesial to the normal position. 

Distoversion: Distal to the normal position. 

Transversion:Transposition of two teeth. 

Axiversion: Abnormal axial inclination of a tooth. 

Torsiversion: Rotation of a tooth around its long axis.