Crooked teeth are teeth that grow in misaligned, whether overlapping, twisted, tilted, or spaced unevenly. The clinical term is malocclusion, which refers to any deviation from a properly aligned bite. It’s remarkably common: studies across different populations report rates ranging from 10% to as high as 97%, depending on the criteria used and the group studied. A large meta-analysis of Chinese schoolchildren found a pooled prevalence of nearly 48%.
Crooked teeth aren’t just a cosmetic concern. They affect how you chew, how easily you can keep your mouth clean, and in some cases, how your jaw functions day to day.
Types of Crooked Teeth and Bite Problems
Not all misalignment looks the same. Crowding happens when teeth are too large for the available jaw space, causing them to overlap or rotate. Spacing is the opposite: gaps form between teeth that don’t fill out the arch. Beyond individual tooth position, the way your upper and lower jaws meet also matters. The most common types of bite misalignment include:
- Overbite: Your upper teeth overlap your lower teeth more than they should when you close your mouth.
- Underbite: Your lower front teeth extend beyond your upper front teeth.
- Crossbite: Some upper teeth sit inside (rather than outside) your lower teeth when your jaw is closed.
- Open bite: Your upper and lower front teeth don’t make contact at all when your mouth is closed.
- Overjet: Your upper front teeth protrude outward significantly, sometimes called “buck teeth.”
Orthodontists also classify misalignment by severity. Class I is the mildest, where the jaw itself is properly aligned but individual teeth are slightly off. Class II involves an underdeveloped lower jaw, meaning the upper teeth sit well ahead of the lower ones. Class III is the reverse, with the lower jaw jutting forward. More severe classes involve increasingly significant discrepancies between the upper and lower jaw positions.
Why Teeth Grow In Crooked
Genetics plays the largest role. The size and shape of your jaw, the size of your teeth, and how those two relate to each other are all inherited. If your teeth are too large for your jawbone, crowding is almost inevitable. Some populations are more genetically predisposed to specific types of misalignment, and extreme overbites or underbites in particular tend to run in families regardless of other factors.
There’s also an evolutionary dimension. Research suggests that as human diets shifted from tough, unprocessed foods to softer, cooked ones over thousands of years, jaw size shrank. But tooth size didn’t shrink at the same rate. This mismatch between a smaller jaw and teeth that haven’t caught up is thought to be a major reason crooked teeth are so widespread in modern populations.
Childhood habits matter too, especially thumb sucking and pacifier use. Evidence shows that sucking habits become increasingly harmful after about 24 months of age, with clear risk of permanent bite changes if the habit continues past 36 to 48 months. Children who sucked their thumbs beyond age three showed significantly higher rates of open bites (where front teeth don’t touch) and crossbites. Other contributors include early loss of baby teeth, which can cause neighboring teeth to drift into the gap and block adult teeth from coming in straight, as well as mouth breathing, tongue thrusting, and injuries to the jaw.
How Crooked Teeth Affect Your Health
The most direct health consequence is an increased risk of gum disease and cavities. Crowded or overlapping teeth create tight spaces where plaque and food particles get trapped. Even diligent brushing and flossing can’t always reach these areas, which become breeding grounds for bacteria. Over time, plaque hardens into tartar, which irritates the gums and leads to inflammation. This early stage, gingivitis, is marked by red, swollen, bleeding gums. Left untreated, it can progress to full periodontal disease, which destroys the bone supporting your teeth and can eventually lead to tooth loss.
Misalignment also causes uneven pressure when you bite and chew. Certain teeth absorb more force than they’re designed for, which can wear down enamel faster, cause gum recession, and make the tissue more vulnerable to infection.
Jaw Pain and Joint Problems
Crooked teeth can contribute to problems with your temporomandibular joint (the hinge connecting your jaw to your skull). When teeth don’t fit together properly, the muscles that control chewing have to compensate. This can lead to muscle hyperactivity and uneven loading on the joint itself, which over time may result in jaw pain, clicking, headaches, and difficulty opening your mouth fully.
Specific bite problems carry specific risks. Overbites and increased overjet have been linked to excessive joint loading. Open bites and crossbites compromise joint stability because the teeth don’t provide adequate support when the jaw closes. Class II misalignment (where the lower jaw is set back) is associated with joint hypermobility, while Class III (lower jaw forward) tends toward restricted movement. Both patterns, sustained over years, can contribute to long-term joint deterioration.
How Orthodontists Assess Alignment
An orthodontic evaluation typically starts with a visual examination, dental impressions or digital scans, and X-rays. The most informative imaging tool is a lateral cephalogram, a side-view X-ray of your skull. From this single image, an orthodontist can measure dozens of relationships: how far forward or back your upper jaw sits relative to your skull, the effective length of your lower jaw, the angle of your jaw relative to the rest of your face, and the exact position of your front teeth.
By comparing the lengths of the upper and lower jaw, orthodontists calculate the “maxillomandibular differential,” which reveals whether a bite problem stems from the teeth themselves or from the underlying bone structure. This distinction is critical because it determines whether braces alone will work or whether jaw repositioning is needed.
Treatment Options
The two main approaches for straightening teeth are traditional braces and clear aligners, and both work by applying sustained pressure that gradually moves teeth through bone. Braces use metal brackets bonded to each tooth, connected by an archwire that’s periodically tightened with thicker wires as treatment progresses. They apply continuous force and can handle virtually any type or severity of misalignment.
Clear aligners are removable plastic trays, swapped out every one to two weeks, that apply intermittent force. Small composite buttons are sometimes bonded to certain teeth to help guide more complex movements. For mild to moderate crowding, aligners perform as well as or better than braces at straightening teeth and aligning the arches. Standardized scoring systems show nearly identical outcomes between the two for these cases.
Where the two approaches diverge is in complexity. Clear aligners handle straightforward crowding, minor bite corrections, and premolar crossbites well. They’re less reliable for rotations, open bites, and severe cases that require significant vertical tooth movement. For those situations, traditional braces remain the more effective option.
Beyond braces and aligners, some cases require additional intervention. Palatal expanders can widen a narrow upper jaw in children and adolescents whose bones are still growing. In adults with severe skeletal discrepancies, where the problem is the jaw itself rather than just tooth position, orthognathic surgery may be needed to reposition the upper jaw, lower jaw, or both. Retainers are used after any orthodontic treatment to prevent teeth from gradually shifting back toward their original positions.
When Treatment Timing Matters
Orthodontic treatment can happen at any age, but certain problems are easier to address during childhood. The American Association of Orthodontists recommends a first evaluation by age seven, when enough adult teeth have come in to spot developing problems. At this stage, the jaw is still growing, so interventions like palatal expansion or guided growth appliances can take advantage of natural development rather than fighting against it.
For most children, active treatment with braces begins between ages 10 and 14, when the majority of permanent teeth are in place. Adults can achieve the same tooth movement results, though treatment may take somewhat longer because bone remodeling happens more slowly in mature skeletons. The key factor isn’t age but the health of your teeth and gums: as long as the supporting bone and tissue are in good condition, orthodontic treatment works.