Crooked teeth, technically known as malocclusion, affect the majority of the population to some degree. Malocclusion means the upper and lower teeth fail to align correctly when the mouth is closed. While typically not a serious health problem, misalignment is a functional and cosmetic concern that can range from slightly rotated teeth to severe jaw discrepancies affecting chewing and speech. Correcting dental misalignment is important because crooked teeth are harder to clean, potentially increasing the risk of tooth decay and gum disease. The reasons for imperfect alignment are complex, stemming from inherited physical traits, early childhood habits, and the mechanics of tooth eruption.
Inherited Differences in Jaw and Tooth Structure
The primary drivers of crooked teeth are often genetic, establishing the foundational size and shape of the jaws and teeth. A common cause is a highly heritable mismatch between the size of the teeth and the jawbone. For instance, inheriting a smaller jaw and larger teeth results in a crowded dental arch with insufficient room for all teeth to align properly.
Conversely, inheriting a larger jaw with smaller teeth can lead to noticeable gaps or spacing between the teeth. Genetic factors also determine the relationship between the upper and lower jaws, leading to skeletal issues like an overbite or underbite. An overbite (Class II malocclusion) occurs when the upper jaw protrudes significantly past the lower jaw. An underbite (Class III malocclusion) is defined by the lower jaw jutting forward.
Other congenital factors also contribute to misalignment, including being born with extra teeth (hyperdontia) or missing teeth (hypodontia). Hyperdontia directly causes crowding by taking up space in the dental arch, forcing adjacent teeth into abnormal positions. These inherited physical incompatibilities set the stage for alignment issues as permanent teeth emerge.
Acquired Habits and External Pressures
Beyond genetic inheritance, prolonged childhood behaviors can exert physical forces that reshape the developing dental arches. Habits persisting past age three or four, such as persistent thumb or finger sucking, introduce external pressure that pushes teeth out of alignment. This chronic pressure can cause the upper front teeth to protrude outward, potentially leading to an open bite where the upper and lower front teeth do not meet.
Prolonged pacifier use can have similar effects, pushing developing teeth and bone into incorrect positions. Tongue thrusting, an atypical swallowing pattern where the tongue pushes against the front teeth, also provides a constant force that contributes to misalignment. Chronic mouth breathing, often due to allergies, alters the resting position of the tongue and jaw, which can lead to a narrower upper dental arch and subsequent crowding.
A common acquired factor is the premature loss of a primary (baby) tooth, often due to trauma or decay. When a baby tooth is lost too early, adjacent permanent teeth can drift into the vacant space, stealing the room needed for the underlying permanent tooth to erupt correctly. This loss of space forces the permanent tooth to emerge in a rotated, blocked, or crooked position, significantly contributing to crowding.
Issues During Eruption and Crowding
The most frequent immediate cause of crooked teeth is a lack of sufficient space for permanent teeth to fit within the dental arch, resulting in crowding. When teeth attempt to emerge into limited space, they become rotated or displaced, often erupting toward the cheek or tongue. The eruption process can be disrupted, leading to a tooth becoming impacted, meaning it cannot fully emerge through the gumline or jawbone.
Impaction is most commonly seen with wisdom teeth (third molars), which are the last to erupt and often find no remaining room in the jaw. Other teeth, such as the upper canines, can also become impacted if their path is blocked by lack of space or another tooth. An impacted tooth can exert pressure on its neighbors, causing them to shift and contributing to overall misalignment.
The timing and sequence of tooth emergence is also a factor that can lead to crooked teeth. If a tooth erupts too early or too late compared to others, it disturbs the balance of space and pushes other teeth out of position. Ultimately, the physical limitation of the jawbone, whether genetically determined or influenced by habits, dictates the path of the emerging permanent teeth.
Options for Correction and Treatment Timing
A variety of methods are available to correct crooked teeth and jaw alignment issues, with treatment individualized to the specific malocclusion. The American Association of Orthodontists recommends that children have their first orthodontic evaluation no later than age seven. At this age, children have a mix of primary and permanent teeth, allowing the orthodontist to detect subtle problems with jaw growth and tooth emergence before they become severe.
Early intervention, called Phase One treatment, may be recommended for issues like a severe crossbite or significant jaw discrepancy while the child is still growing. This interceptive treatment uses appliances to guide jaw development or create necessary space, often simplifying later comprehensive treatment. For most patients, comprehensive treatment begins once most permanent teeth have erupted, typically during the early teenage years.
Corrective methods fall into general categories. These include fixed appliances like traditional metal or ceramic braces, which use brackets and wires to apply gentle, continuous pressure. Clear aligner systems offer a removable alternative for moving teeth into their correct positions. In all cases, a retainer is necessary after active treatment to hold the teeth in their new positions and prevent them from shifting back.