Clinical Assessment & Presentations
Extra-oral Features
Start your assessment by looking at the patient’s extra-oral features.
Narrow and long face appearance
Posterior crossbites with skeletal discrepancies are often present in patients with narrow or long face appearance. These patients can present with typical characteristics of Adenoid facies and are obligatory mouth breathers.
A patient who has a narrower facial profile, transversely deficient maxilla and narrower alar base. Skeletally narrow palates and posterior crossbites are often present in these patients. They also have higher incidences of anterior open bites.
In obligatory mouth breathers, the tongue adapts a lowered position and the cheek muscles become more active. A net inward force results on the upper teeth causing palatal tipping and a higher incidence of posterior crossbites.
Class III deficient maxilla
Skeletally deficient maxillas that present with a Class III malocclusion often also present with a transverse constriction as the maxilla is usually hypoplastic in all dimensions. These patients have a higher incidence of posterior crossbites with skeletal discrepancies.
A deficient maxilla in skeletal Class III patients are often hypoplastic in all 3 dimensions. The reduced transverse dimension of the maxilla means a higher incidence of posterior crossbites.
Thumb or digit sucking
Thumb and digit sucking has the secondary effect of contributing to a posterior crossbite by changing the soft tissue equilibrium. As the thumb is sucked, the tongue adapts to a lowered position and the cheek (buccal) muscles become more active. These changes have a net palatal pressure on the upper teeth causing a transverse constriction of the dental arch and hence increasing the likelihood of posterior crossbites. The other dental effects of thumb or digit sucking is an anterior open bite. If the habit is stopped early enough, the occlusion can reestablish itself.
Thumb or digit sucking can contribute to a posterior crossbite and anterior open bite.
A thumb sucking malocclusion can often be seen with an anterior open bite and posterior crossbite. The tongue adapts to a lowered position leading to a net inward pressure on the upper teeth and a posterior crossbite – see diagram.
Intra-oral Features
Bilateral posterior crossbite
Bilateral crossbites can occur when the dental or skeletal discrepancies between maxilla and mandible widths are large (Cobourne and Dibiase 2010).
Bilateral posterior crossbites can be due to dental or skeletal causes.
Unilateral posterior crossbite with or without a functional shift
A unilateral posterior crossbite can occur when the dental or skeletal discrepancy between the maxilla and mandible widths are small. A displacement of the mandible often occurs from the initial contact to the maximal intercuspal position. A midline deviation is usually present as well. (Cobourne and Dibiase 2010)
On initial contact the mandible shifts to one side causing a unilateral posterior crossbite.
A unilateral crossbite with no skeletal discrepancy but an associated functional shift.
Narrow palate
Typical characteristics are a narrow and high palatal vault, narrow inter-molar distance, posterior crossbites and crowding and/or proclined incisors.
A narrow palate associated with soft-tissue changes due to mouth-breathing.
Single tooth crossbite and displaced teeth
A localised posterior crossbite is often caused by a single tooth or localised group of teeth which have been displaced due to crowding. Correction of the crowding should resolve the posterior crossbite.
The upper right second premolar is in complete crossbite due to dental crowding.
The same upper right second premolar was displaced palatally because of dental crowding.
