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3 Classification of Malocclusion

Classification of malocclusion looks at the position of the teeth when the patient is in occlusion. These classifications look at the relationship of how the molars, incisors, and canines meet.

They are categorized into three groups:

 Angle’s classification

 British Standards Institute classification

 Canine relationship.

3.1 Angle’s Classification

Developed by Edward Angle in 1899, this type of classification looks at the antero‐posterior position of the first permanent molars, known as the molar relationship.

 Class I: the mesiobuccal cusp of the upper first molar occludes in the buccal groove of the lower first molar (Figure 3.1).

 Class II: the mesiobuccal cusp of the upper first molar occludes anterior to the buccal groove of the lower first molar (Figure 3.2).

 Class III: the mesiobuccal cusp of the upper first molar occludes posterior to the buccal groove of the lower first molar (Figure 3.3).

 Class II25: the mesiobuccal cusp of the upper first molar occludes one‐quarter anterior to the buccal groove of the lower first molar.

 Class II50: the mesiobuccal cusp of the upper first molar occludes half a unit anterior to the buccal groove of the lower first molar (cusp to cusp with the lower first molar).

 Class II75: the mesiobuccal cusp of the upper first molar occludes three‐quarters anterior to the buccal groove of the lower first molar (not a full unit class II).

 Class III25: the mesiobuccal cusp of the upper first molar occludes one‐quarter posterior to the buccal groove of the lower first molar.

 Class III50: the mesiobuccal cusp of the upper first molar occludes half a unit posterior to the buccal groove of the lower first molar (cusp to cusp with the lower second molar).

 Class III75: the mesiobuccal cusp of the upper first molar occludes three‐quarters posterior to the buccal groove of the lower first molar (not a full unit class III).

Figure 3.1 Class I molar relationship.

Figure 3.2 Class II molar relationship.

Figure 3.3 Class III molar relationship.

3.2 British Standards Institute Classification

This type of classification looks at the incisor relationship.

 Class I: the lower incisor edges occlude with or lie immediately below the cingulum plateau of the upper central incisors (Figure 3.4).

 Class II div I: the lower incisor edges occlude posterior to the cingulum plateau of the upper central incisors. The upper central incisors are proclined and there is an increase in the overjet (Figure 3.5).

 Class II div II: the lower incisors edges occlude posterior to the cingulum plateau of the upper central incisors. The upper central incisors are retroclined and there is a reduced or increased overjet (Figure 3.6). A common feature is proclined lateral incisors.

 Class III: the lower incisor edges occlude anterior to the cingulum plateau of the upper central incisors. The overjet is reduced or reversed (Figure 3.7).

Figure 3.4 Incisor relationship class I.

3.3 Canine Relationship

This classification looks at the position of the canine.

 Class I: the upper canine occludes and lies in the embrasure between the lower canine and first premolar (Figure 3.8).

 Class II: the upper canine occludes anteriorly and lies in the embrasure between the lower lateral incisors and the canine (Figure 3.9).

 Class III: the upper canine occludes posteriorly and lies in the embrasure between the lower first and second premolars (Figure 3.10).

 Class II25: the upper canine occludes one‐quarter anteriorly from being in embrasure between the lower lateral incisors and the canine.

 Class II50: the upper canine occludes half a unit anteriorly and lies directly over the lower canine (cusp to cusp with the lower canine).

 Class II75: the upper canine occludes three‐quarters anteriorly from being in embrasure between the lower lateral incisors and the canine (not a full unit class II).

 Class III25: the upper canine occludes one‐quarter posteriorly from being in embrasure between the lower first and second premolars.

 Class III50: the upper canine occludes half a unit posteriorly and lies directly between the lower first and second premolars.

 Class III75: the upper canine occludes three‐quarters posteriorly from being in embrasure between the lower first and second premolars (not a full unit class III).

Figure 3.5 Incisor relationship class II div I.

Figure 3.6 Incisor relationship class II div II.

Figure 3.7 Incisor relationship class III.

Figure 3.8 Class I canine relationship.

Figure 3.9 Class II canine relationship.

Figure 3.10 Class III canine relationship.

3.4 Andrew’s Six Keys

This classification was developed by Lawrence Andrews, the same orthodontist who developed the preadjusted edgewise appliance. Over time Andrews decided that it was not always possible to achieve a good class I occlusion, therefore the six keys were developed to identify each feature to evaluate why this was not possible. A seventh key was added subsequently because correct tooth size can have an effect on achieving good class I occlusion.

1 Correct molar relationship:The mesiobuccal cusp of the upper first molar occludes in the buccal groove of the lower first molar.The distobuccal cusp of the upper first molar occludes on the mesiobuccal cusp of the lower second molar.

2 Correct crown angulation:All tooth crowns are angulated mesially.

3 Correct crown inclination:Incisors are inclined towards the buccal or labial surface.Buccal segment teeth are inclined lingually; in the lower buccal segments this is progressive.

4 Flat curve of Spee.

5 No rotations.

6 No spaces.

7 Correct tooth size.