Understanding Class 1 and Class 2 Malocclusions

Class 1 Malocclusion: Issues and Variations

Crossbite Complications

Crossbite (failure of dental arches to occlude correctly in the lateral dimension) can manifest in several ways within Class 1 malocclusion (normocclusion, often with a good relationship between the osseous bases):

• Unilateral Crossbite: Affects one side, from the canine to the last molar.
• Bilateral Crossbite: Affects both sides, from canine to molar. Often associated with maxillary micrognathia (narrow upper jaw) relative to the mandible. May be linked to habits like mouth breathing and finger sucking.
• Dental Crossbite: Normocclusion with a good skeletal base relationship, but involves incorrect inclination of a specific molar or canine due to lack of space, resulting in palatal or buccal eruption.
• Midline Deviation: Normocclusion with a good skeletal base relationship, but the upper and lower dental midlines do not align. This can be caused by premature loss of temporary teeth, absence of permanent teeth, or lack of space for the eruption of permanent incisors or canines, causing the midline to deviate towards the side of tooth loss.

Anterior-Posterior Problems

In Class 1 malocclusion, maxillary incisors may be positioned too far forward (protrusion) or too far back (retrusion).

• Superior Dento-alveolar Protrusion: Superior central incisors show anterior vestibuloversion (tipped forward). May include diastemata (spaces between teeth), lack of anterior coupling, and increased overjet. Associated habits can include a protruding upper lip (procheilia) resting on the superior incisors.
• Dentoalveolar Biprotrusion: Both upper and lower incisors and alveolar processes are proclined (tipped forward). This alters the facial profile and can be associated with habits like tongue thrust, which may worsen the malocclusion.

Malocclusion with Crowding

The appearance of crowding depends on the timing during tooth development and the etiological factors involved.

• Primary Crowding: A discrepancy between the available dental arch length and the length required to accommodate all teeth. Contributing factors include genetics, diet, tooth size versus jaw length, skeletal base relationships, dental arch width, incisor inclination, and the presence of supernumerary teeth.
• Secondary Crowding: Caused by environmental factors. Contributing factors include dental decay leading to premature tooth loss (resulting in lost arch length) and soft tissue abnormalities or habits (e.g., sucking leading to protrusion or retrusion).
• Tertiary Crowding: Occurs during adolescence and post-adolescence. Often linked to late compensatory tooth eruption (especially third molars) and facial growth patterns, such as residual anterior mandibular rotation, which can influence the inclination of mandibular incisors and contribute to crowding.

Class 2 Malocclusion: Distoclusion

Class 2 Malocclusion, also known as distoclusion, is characterized by the following occlusal relationship:

• The mesiobuccal cusp of the maxillary first molar does not occlude in the mesiobuccal groove of the mandibular first molar; it is positioned anterior to it.
• The cusp tip of the maxillary canine occludes anterior to the interproximal space between the mandibular canine and the mandibular first premolar.

This often results from a skeletal discrepancy, specifically an anteroposterior alteration where the mandibular arch is positioned distally (further back) relative to the maxillary arch. This skeletal issue can be due to basic bone dysplasia, such as:

• Mandibular retrognathia (recessed lower jaw)
• Maxillary prognathism (protruding upper jaw)
• A combination of both