The need for orthodontic treatment, commonly known as braces, arises from malocclusion—a poor alignment of the teeth or an improper bite. This misalignment involves complex relationships between the size of the jawbones, the number and shape of the teeth, and how the upper and lower arches meet. Understanding why these issues develop requires looking at the underlying causes, which are broadly categorized as structural, developmental, and environmental.
Genetic and Skeletal Factors
The foundational structure of the mouth and face is largely determined by inherited genetic traits, making skeletal factors a primary cause of misalignment present from birth. Jaw size and the relative positions of the upper jaw (maxilla) and lower jaw (mandible) dictate the basic framework for the dental arches. When the size of the jaw does not match the size of the teeth, a tooth-size/arch-size discrepancy occurs, often leading to crowding or spacing.
Crowding happens when the jaw is too small to accommodate the full set of teeth, forcing them to overlap and rotate. Conversely, if the jaw is proportionally larger than the teeth, excessive spacing (diastema) can result. Beyond size mismatches, the positioning of the jaws relative to each other creates the major classifications of bite problems, referred to as Angle’s classifications.
A skeletal Class II malocclusion (overbite) typically involves an undergrown lower jaw (mandibular retrognathism) or an overgrown upper jaw, causing the upper teeth to protrude over the lower teeth. A skeletal Class III malocclusion (underbite) occurs when the lower jaw is positioned too far forward (mandibular prognathism) relative to the upper jaw. This leads to the lower front teeth biting in front of the upper teeth and often results in a prominent chin. These major jaw discrepancies are strongly influenced by genetic inheritance and often require comprehensive orthodontic or surgical interventions.
Disruptions in Tooth Eruption and Spacing
Even with a favorable genetic blueprint, the process of permanent teeth replacing primary (baby) teeth can face developmental disruptions resulting in misalignment. Primary teeth act as “space holders,” reserving the correct position and path for the permanent teeth developing beneath them. The premature loss of a primary tooth, often due to decay or trauma, can cause adjacent teeth to drift into the vacant area, closing the space.
This loss of space leaves insufficient room for the permanent tooth, forcing it to erupt out of alignment, sometimes causing impaction or severe crowding. Conversely, the delayed shedding of primary teeth can block the eruption path, causing permanent teeth to deviate from their trajectory and emerge in an abnormal position. The eruption path can also be problematic with impacted teeth, which are fully formed but physically blocked from breaking through the gum line by bone, adjacent teeth, or dense tissue.
The timing and sequence of the eruption process determine whether the dental arches maintain the necessary space for all permanent teeth. Disturbances in this sequence, such as the early emergence or late development of teeth, can cascade into a misaligned bite pattern. Anomalies in tooth development, such as extra teeth (supernumeraries) or the absence of teeth (hypodontia), further complicate eruption and necessitate orthodontic correction to manage spacing issues.
Environmental Habits and Physical Injury
While genetics sets the stage, external forces and learned muscular patterns can significantly alter jaw development and tooth position, especially during childhood growth. Prolonged oral habits, such as thumb-sucking or pacifier use, exert sustained pressure on the teeth and the malleable palate. If these habits persist past the age of four or five, they can lead to an anterior open bite (where the front teeth do not meet) and a flaring or protrusion of the upper front teeth.
The chronic pressure from the thumb or pacifier can also narrow the upper dental arch and cause a posterior crossbite, where the upper back teeth bite inside the lower back teeth. Another influential muscular pattern is tongue thrusting, where the tongue pushes forward against the teeth during swallowing or speech instead of resting against the roof of the mouth. This repeated pressure contributes to the development or persistence of an open bite.
Chronic mouth breathing, often associated with nasal airway obstructions like enlarged tonsils, changes the resting posture of the jaw and tongue. This potentially leads to a longer, narrower facial structure and a higher risk of malocclusion. Finally, physical trauma to the face or mouth can directly displace erupted teeth or damage developing tooth buds and jaw joints in younger individuals. Such injuries can disrupt the normal growth trajectory of the jaw or lead to the early loss of permanent teeth, requiring subsequent orthodontic treatment to restore alignment and function.