An occlusal cant refers to an asymmetry in the bite plane, specifically a tilt or rotation of the chewing surfaces of the teeth in the vertical plane. This deviation means the plane of the upper or lower teeth is not parallel to the true horizontal plane, often referenced by the line connecting the pupils of the eyes. The occlusal plane is an imaginary surface that theoretically touches the incisal edges of the front teeth and the tips of the cusps on the back teeth. An occlusal cant represents a noticeable inclination of this plane relative to the rest of the face. This asymmetry affects both the appearance of the smile and the overall function of the jaw and bite.
Identifying the Slanted Occlusal Plane
The presence of an occlusal cant is often first perceived as an uneven smile, where one side of the dental arch appears higher than the other. Clinically, initial assessment involves comparing the occlusal plane to horizontal facial landmarks, such as the interpupillary line. A dentist may place a wooden tongue depressor across the back teeth and visually check its alignment against the patient’s pupils.
More precise diagnosis relies on specialized imaging, including posteroanterior cephalograms and three-dimensional (3D) cone beam computed tomography (CBCT) scans. These methods allow clinicians to measure the angle of the cant in degrees relative to the true horizontal plane. Research suggests that a cant of four degrees or more is typically noticeable to the average person.
Patients may also notice visual indicators of a cant, such as an uneven display of the gums, where more gingiva is visible on one side during a full smile. Identifying the exact degree and location of the slant is the first step toward creating an effective treatment plan, as the severity determines the complexity of intervention.
Primary Causes of Occlusal Cant
The origin of an occlusal cant is generally classified into two main categories: skeletal and dentoalveolar, which may occur separately or in combination. Skeletal causes involve an underlying asymmetry in the jaw bones themselves, making them more difficult to correct without surgical intervention. This type of cant often results from uneven growth of the maxilla (upper jaw) or the mandible (lower jaw), sometimes linked to developmental asymmetry like condylar hyperplasia.
An uneven growth pattern causes the basal bone structure to tilt, forcing the dental arches to follow the same asymmetrical line. These skeletal discrepancies are associated with significant facial asymmetry, reflecting an overall imbalance in the craniofacial structures. Traumatic injuries to the jaw during growth or certain hereditary factors can also contribute to this bony asymmetry.
Dentoalveolar causes, in contrast, refer to problems localized to the teeth and the supporting bone, even when the underlying jaw structure is symmetrical. Uneven tooth eruption, missing teeth that allow opposing teeth to over-erupt, or a functional shift of the mandible can all cause the occlusal plane to tip. These dental-based cants are often more amenable to purely orthodontic correction because they involve repositioning teeth within the existing bone.
Functional and Aesthetic Consequences
The presence of an occlusal cant impacts both the patient’s ability to use their mouth properly and the harmony of their facial appearance. Functionally, the misalignment can compromise chewing efficiency (mastication) because the uneven plane prevents the upper and lower teeth from meeting correctly. This leads to an unbalanced distribution of bite forces across the dental arches.
An occlusal cant can also contribute to the development of temporomandibular joint (TMJ) disorders. The jaw is forced to deviate to one side to achieve a functional bite, and this uneven strain on the muscles and joint structures can result in pain, clicking, or limited jaw movement. The asymmetry may even affect speech patterns due to the altered relationship between the jaws and the tongue.
Aesthetically, the cant is a primary factor affecting the smile, as the slanted line of the teeth draws attention to the facial imbalance. The tilt can make one side of the face appear vertically shorter or longer than the other, disrupting the visual midline and overall facial symmetry.
Treatment Strategies for Correction
The approach to correcting an occlusal cant is entirely dependent on its origin and severity, with the goal being to level the occlusal plane relative to the facial midline. For cants caused by dentoalveolar discrepancies, non-surgical orthodontic correction is often the first line of treatment. Traditional fixed braces or clear aligners are used to reposition teeth, incorporating methods to intrude (push back into the bone) or extrude (pull out of the bone) specific teeth to level the plane.
A major advancement in non-surgical treatment is the use of Temporary Anchorage Devices (TADs), which are small screws placed temporarily into the jawbone. TADs provide a stable point of anchorage, allowing orthodontists to apply precise forces to intrude over-erupted teeth on the higher side of the cant. This localized intrusion of molars can effectively level a dental-based cant, often avoiding the need for more invasive surgery.
When the cant is severe and caused by a skeletal asymmetry, orthognathic surgery (jaw surgery) is typically required to physically reposition the maxilla or mandible. A common procedure for correcting a maxillary cant is a Le Fort I osteotomy with asymmetric impaction, which involves cutting the upper jawbone and fixing it in a level position. This major surgical correction is combined with pre- and post-surgical orthodontics to align the teeth properly before and after the skeletal movement. The choice between non-surgical and surgical correction is guided by the degree of the cant and whether the underlying problem lies in the teeth or the jawbone.