Author: Dr Shaun Goh
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Treatment Indications & Timings
Clinical Assessment & Presentations
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Description
Class I
“The position of the dental arches is normal, with first molars in normal occlusion.”
– Angle 1900
Class I malocclusion
“There is normal relationship of the molars, but the line of occlusion is incorrect because of malposed teeth, rotations, or other causes.”
– Angle 1900
Class I occlusion
The red line is Angle’s line of occlusion, and any Class I occlusions with deviations to this line are defined as a Class I malocclusion. The green line is the Esthetic line or smile line of the upper arch. (Adapted from Proffit et al. 2018)
Treatment Indications
When to treat or refer:
➤ Transverse issues (i.e. posterior crossbites)
➤ Vertical issues (i.e. open bites or deep bites)
➤ Underlying skeletal malocclusion
➤ Tooth arch size discrepancies (i.e. crowding or spacing)
Clinical Assessment & Presentations
Extra-oral Features
Mild convex facial profile
Class I skeletal patterns usually have a mild convex facial profile. The maxilla and mandible are in harmony to the soft tissue glabella.
Intra-oral Features
Class I incisors
The lower incisors occlude or lie below the cingulum plateau of the upper incisors (British Standards Institute 1983)
Class I canines
The upper canine’s cusp tip occludes directly in the embrasure between the mandibular canine and first premolar.
Class I molars
The upper first molar mesiobuccal cusp occludes directly in the lower first molar buccal groove.
Diagnosis & Considerations
Dental Class I (incisors, canine, molars – see features)
Skeletal Class I (maxilla and mandible are in the correct sagittal relationship – see features)
Clinical Considerations
Dental vs Skeletal Class I
A dental Class I may not necessarily occur on a skeletal Class I base. For example a patient may present with a Class II retrognathic mandible skeletal base but has molars, canines and incisors in a Class I dental occlusion. The reverse may also occur where a skeletal Class I base may present with a dental Class II malocclusion with increased overjet.
When to treat?
Dental Class I malocclusions often present with crowding, spacing or bimaxillary dentoalveolar protrusive issues. See associated problems below for more information on these problems.
Treatment Options
No specific treatment options are listed for Class I as indications for treatment are usually due to their associated problems. Find treatment options specific to each associated problem below.
Associated Problems
Crowding | Spacing | Bimaxillary dentoalveolar protrusion | Posterior crossbites
