Gaps between teeth form when there’s a mismatch between the size of your teeth and the size of your jaw, or when something pushes, pulls, or prevents teeth from sitting snugly together. The most common gap is the one between the two upper front teeth, called a midline diastema. About half of all children between ages 6 and 8 have this gap, and most of the time it closes on its own as permanent teeth come in. By age 14 or 15, only about 5 to 7% of people still have it.
Jaw and Tooth Size Mismatch
The most straightforward cause is a simple numbers problem: your jaw is one size, your teeth are another, and they don’t match up. This plays out in two ways. Some people have a jaw that’s slightly too large for their teeth, leaving extra space the teeth can’t fill. Others have teeth that are naturally smaller than average, a condition called microdontia, which creates the same result in a normal-sized jaw. Either scenario can produce a single gap or multiple gaps spread across the dental arch. This is largely genetic, which is why tooth gaps often run in families.
The Frenum: A Small Piece of Tissue With Big Effects
If you curl your upper lip upward, you’ll feel a small band of tissue connecting the lip to the gum above your front teeth. That’s the labial frenum. In some people, this tissue is thicker than usual or attaches lower on the gum, extending down between the two front teeth. When that happens, it acts like a physical wedge that keeps the teeth from coming together. Children often have a prominent frenum that naturally recedes as the face grows, which is one reason so many young kids have a front tooth gap that disappears later. When the frenum stays thick or low-attached into adolescence, though, the gap tends to persist.
Thumb Sucking, Pacifiers, and Tongue Thrust
Teeth respond to pressure. Steady, repeated force in one direction will gradually push them out of alignment, and several common childhood habits create exactly that kind of force.
Thumb sucking and prolonged pacifier use both press the upper front teeth forward and outward. The key factor is duration rather than intensity. Children who use a pacifier beyond 36 months have a significantly higher rate of open bite, where the upper and lower front teeth no longer overlap. The American Academy of Pediatric Dentistry recommends stopping pacifier use by 36 months, noting that bite changes from pacifier use will often correct themselves if the habit ends before age 3. After that point, the developing jaw and tooth positions become harder to reverse without intervention.
Tongue thrust is a related habit where the tongue pushes forward against the back of the front teeth during swallowing, talking, or even at rest. The most common result is a gap between the two upper front teeth. Because swallowing happens thousands of times a day, even moderate forward tongue pressure adds up over months and years, gradually nudging teeth apart.
Gum Disease and Bone Loss
Gaps don’t only form during childhood. Adults can develop new spaces between teeth that were previously straight, and gum disease is the usual culprit. Your teeth are anchored in bone, and advanced gum disease (periodontitis) breaks down that bone over time. As the supporting structure weakens, teeth lose their stability and begin to drift. This is called pathologic tooth migration. Aggressive forms of periodontitis can cause rapid bone loss that leads to visible shifting, spacing, and eventually tooth loss if untreated. The gaps that form this way tend to appear gradually and worsen without treatment, often accompanied by receding gums, loose-feeling teeth, or bleeding when you brush.
Extra Teeth Blocking Normal Development
Sometimes an extra tooth, called a supernumerary tooth, develops in the bone near the front teeth. The most common type in this area is a mesiodens, a small extra tooth that sits between or behind the upper central incisors. Even when it stays buried in the bone and never breaks through the gum, it can displace the neighboring teeth. Supernumerary teeth push adjacent teeth out of position in 22 to 63% of cases and disrupt the normal eruption pattern 30 to 60% of the time. While the idea that an extra tooth directly wedges the front teeth apart is commonly cited, it’s actually rare. The bigger problem is that the extra tooth blocks or deflects the permanent teeth as they try to erupt, leaving them tilted or spaced abnormally.
Missing Teeth and Tooth Loss
When a tooth is lost or never develops in the first place, the surrounding teeth slowly drift toward the empty space. Some people are born without one or more adult teeth, a condition called congenital absence. The most commonly missing teeth are the upper lateral incisors (the ones flanking your two front teeth) and the premolars. When these teeth never come in, the remaining teeth spread out to partially fill the space, creating gaps in unpredictable locations. The same drifting happens after an extraction or when a tooth is knocked out. Without something holding the space, neighboring teeth shift over months and years.
Why Some Gaps Close on Their Own
In children, a front tooth gap is so common it’s considered a normal stage of dental development. At age 6, nearly half of children have a visible midline gap. By age 10, that number drops to roughly 10 to 18%, and by the mid-teens it falls to single digits. The gap typically closes as the permanent canine teeth (the pointed ones) erupt and push the front teeth inward. This is why dentists generally recommend waiting until the canines have come in before deciding whether a childhood gap needs treatment. If the gap persists after all the permanent teeth are in place, it’s unlikely to close without orthodontic work, bonding, or veneers.
Genetics and Ethnicity
Your likelihood of having a tooth gap is partly inherited. Jaw shape, tooth size, frenum thickness, and the number of teeth that develop are all influenced by genetics. There are also well-documented differences across ethnic groups. Studies have found that Black children aged 10 to 12 have a midline diastema prevalence of about 19%, compared to about 8% in white children of the same age. These differences reflect variation in jaw and tooth proportions rather than any single gene, and they carry into adulthood.