An underbite is a dental misalignment where the lower jaw extends forward beyond the upper jaw. Also known as a Class III malocclusion, this condition causes the lower teeth to overlap the upper teeth when the mouth is closed. It differs from an overbite, where the upper teeth protrude excessively. An underbite can alter facial appearance and affect the normal function of the mouth.
Understanding an Underbite
Underbites vary in degree, from mild cases where lower teeth barely protrude to severe cases involving significant forward positioning of the entire lower jaw. Orthodontists differentiate between two primary types: dental underbites and skeletal underbites.
A dental underbite primarily involves the misalignment of the teeth themselves, with jawbones remaining relatively aligned. This type often results from individual teeth tilting or shifting. A skeletal underbite, in contrast, stems from a structural discrepancy in the jawbones, where either the lower jaw has overdeveloped or the upper jaw has not developed sufficiently. This malformation can be present at birth and significantly affects facial structure.
What Leads to an Underbite
Genetic predisposition is a significant factor in the development of an underbite, particularly for skeletal underbites. If close family members have a history of underbites, there is an increased likelihood of inheriting this condition, as jaw and teeth characteristics can be passed down.
Environmental or habitual factors during childhood can also contribute. Prolonged thumb sucking, extended pacifier use beyond toddlerhood, and prolonged bottle feeding can exert pressure on developing teeth and jaws, leading to misalignment. Tongue thrusting, where the tongue presses against the teeth during speech or swallowing, is another habit that can influence jaw growth. Additionally, trauma or injury to the jaw during childhood, such as a fracture that doesn’t heal correctly, can result in an underbite.
Impact of an Underbite
An underbite can lead to various functional challenges. Chewing food effectively often becomes difficult because misaligned teeth cannot properly grind food, potentially affecting digestion. Speech can also be impacted, as the lower jaw’s protrusion interferes with tongue and lip movement, leading to issues like lisping or difficulty pronouncing sounds such as “s” or “f.”
The misalignment can cause chronic jaw pain and contribute to temporomandibular joint (TMJ) disorders. This may result in discomfort when talking, eating, or at rest, sometimes accompanied by clicking or popping sounds in the jaw. Uneven pressure distribution during biting and chewing can cause excessive wear on teeth, leading to enamel loss, increased sensitivity, and potential tooth damage like chipping. Beyond these functional issues, an underbite can also present aesthetic concerns due to the prominent chin and altered facial profile, potentially affecting self-confidence.
Correcting an Underbite
Correcting an underbite depends on the patient’s age and the severity of the misalignment. For younger patients whose jaws are still developing, orthodontic treatments can guide jaw growth. An upper jaw expander, fitted across the palate, can gradually widen the upper jaw to better align with the lower teeth. A “reverse-pull” headgear can gently pull the upper jaw forward.
For both children and adults, braces are a common treatment option, using brackets and wires to gradually shift teeth into their correct positions. Clear aligners, such as Invisalign, offer a more discreet alternative for mild to moderate cases, and their effectiveness can be enhanced with orthodontic elastics. In some mild to moderate cases, extracting specific teeth can create space for better alignment.
For severe skeletal underbites, particularly in adults whose jawbones are fully developed, surgical intervention may be necessary. Orthognathic surgery involves reshaping and repositioning the jawbones to achieve proper alignment and improve facial symmetry. This procedure is generally performed in conjunction with orthodontic treatments like braces or clear aligners, and recovery can take 10 to 12 weeks. Post-treatment care often includes wearing a retainer to maintain the corrected alignment.