Malocclusion is the technical term for crooked teeth, referring to any improper alignment between the upper and lower teeth when they come together. This common condition involves teeth that may be crowded, rotated, or spaced too far apart, resulting in an uneven bite. Misalignment often begins during the developmental years as the jaw grows and teeth erupt. Understanding these root causes, which range from inherited structure to childhood habits and timing issues, is essential.
Inherited Differences in Jaw Structure
The foundation for tooth alignment is largely set by genetic factors that determine the size and shape of the jaws and teeth. Misalignment often occurs when these two features are inherited independently. For example, inheriting a small jaw size but large tooth size leads to dental crowding because the teeth lack sufficient space.
The skeletal relationship between the upper jaw (maxilla) and the lower jaw (mandible) is also heavily influenced by genetics. This structural mismatch results in distinct types of malocclusion classified by their bite pattern. Class I malocclusion, the most frequent type, involves a normal jaw relationship but still features misaligned or crowded teeth.
More significant skeletal discrepancies result in Class II and Class III malocclusions. Class II malocclusion, often called an overbite, occurs when the upper jaw is positioned significantly forward compared to the lower jaw. Conversely, Class III malocclusion, or an underbite, is characterized by the lower jaw protruding, causing the lower teeth to overlap the upper teeth. Studies indicate that identical twins often share similar malocclusion types, underscoring the strong role of heredity.
How Childhood Habits Influence Tooth Alignment
External pressures from certain childhood behaviors can physically push developing teeth out of alignment. One common acquired factor is the prolonged habit of non-nutritive sucking, such as thumb sucking or pacifier use past the age of three or four. This constant pressure on the front teeth can push the upper teeth outward and the lower teeth inward.
Persistent sucking habits can alter the shape of the jawbones and the palate (roof of the mouth). This often results in an open bite, where the upper and lower front teeth do not meet when the mouth is closed. Pacifier use can also lead to narrow dental arches, restricting the space available for permanent teeth to erupt straight.
Another force is tongue thrusting, a pattern where the tongue pushes forward against the front teeth during swallowing or rest. Since a person swallows frequently, this repeated force gradually moves the teeth, creating gaps or causing them to flare outward. Chronic mouth breathing, often due to allergies, also disrupts the natural balance. This causes the tongue to rest low instead of against the palate, which can lead to a high and narrow palate and subsequent crowding.
Timing and Space Issues During Tooth Eruption
Mechanical factors during the transition from primary to permanent teeth are frequent causes of crookedness. The premature loss of a primary tooth can severely disrupt the process by causing a loss of arch length. When a primary tooth is lost too early, adjacent teeth tend to drift and tilt into the newly created space.
This shifting means that when the permanent tooth erupts later, the path is blocked, or the space is no longer wide enough, leading to crowding. Conversely, a primary tooth that is retained too long physically blocks the permanent tooth. This forces the permanent tooth to erupt out of its correct position, sometimes resulting in a “double row” of teeth.
Later in life, the eruption of wisdom teeth, or third molars, can contribute to crowding. There is often insufficient space for these last teeth to emerge, which typically happens between ages 17 and 25. As the wisdom teeth attempt to erupt, they can exert pressure on adjacent molars, causing the misalignment or shifting of the front teeth.