An underbite is a common orthodontic concern that often becomes noticeable in childhood. This condition occurs when the lower jaw protrudes forward, causing the bottom teeth to extend past the upper front teeth when the mouth is closed. While a properly aligned bite has the upper teeth slightly overlapping the lower teeth, an underbite creates a reverse relationship. Addressing this misalignment early is crucial, as timely intervention can significantly simplify treatment and improve long-term oral health and function. This guide explores how this condition is identified in children and the growth-modifying appliances used to fix it.
Identifying an Underbite and Its Causes
Parents can often observe the visual sign of an underbite, which may include a prominent chin or a lower jaw that appears to jut out from the face. Inside the mouth, the lower row of teeth sits in front of the upper teeth, a configuration that interferes with proper biting and chewing. If left uncorrected, this misalignment can lead to abnormal wear on the teeth, speech difficulties, and chronic jaw discomfort.
Understanding the cause requires differentiating between the two main types of malocclusion. A dental underbite involves only the positioning of the teeth, such as when the upper incisors are tipped inward or the lower incisors are tipped outward. A skeletal underbite, however, is a structural issue where the jawbones themselves are mismatched, either because the upper jaw (maxilla) is underdeveloped or the lower jaw (mandible) is overgrown.
Skeletal underbites are largely driven by genetics, as the size and shape of a child’s jaw structure are inherited. Environmental factors and habits can contribute to the severity or development of a dental underbite. Prolonged thumb-sucking, chronic tongue thrusting, or extended pacifier use can place pressure on developing teeth and jaw structures, influencing misalignment.
Why Timing Matters for Treatment
The decision to treat an underbite while a child is still growing is based on interceptive orthodontics, often referred to as Phase 1 treatment. The ideal window for this intervention is typically between the ages of seven and ten, when the child still has substantial facial growth potential. During this period, the sutures connecting the bones of the face and upper jaw are still relatively pliable and have not yet fully fused.
Orthodontists leverage this period of active development to guide jaw growth in a favorable direction. Attempting to fix a skeletal discrepancy allows the clinician to harness the body’s natural growth mechanisms to reposition the maxilla. This early intervention aims to maximize the forward growth of the deficient upper jaw, simultaneously limiting the forward expression of the lower jaw.
Delaying treatment until after the pubertal growth spurt is complete significantly limits the available non-surgical options. Once the skeletal structure matures, usually by the mid-to-late teens, the jaws become fixed, and growth modification is no longer possible. Correcting a severe skeletal underbite may then require orthognathic surgery to realign the upper and lower jaws into a balanced position. Early treatment offers the best chance of achieving a stable, non-surgical correction and reducing the overall complexity of future orthodontic care.
Appliance-Based Correction Methods
Correcting a skeletal underbite in a child focuses on using specialized appliances to stimulate the upper jaw’s growth and restrict the lower jaw’s position. Treatment often begins with an assessment to determine if the upper jaw is also too narrow. If a width deficiency exists, a palatal expander is usually fitted first, which works by gradually widening the upper dental arch over a few weeks or months.
Once the upper arch is widened, the main orthopedic appliance, the reverse-pull headgear or face mask, is introduced. This device consists of a framework that rests on the forehead and chin, connected by elastic bands to an anchor point inside the mouth, usually a palatal expander or specialized dental braces. The elastics apply a consistent, forward-and-downward pulling force directly onto the upper jaw.
The goal of the face mask is to “protract” the maxilla, pulling it forward to catch up to the lower jaw and establish a positive overjet. For this orthopedic movement to be successful, the child must wear the appliance consistently, often for 12 to 14 hours per day, including while sleeping, over a period of 6 to 18 months.
Another method, the chin cup, is occasionally used, but its primary function is to directly restrict the forward growth of the mandible by applying pressure to the chin. However, the chin cup is generally considered less effective than the reverse-pull headgear because focusing on advancing the upper jaw is often a more reliable strategy for correction.