The simplest way to keep these straight: overjet is horizontal and overbite is vertical. That one rule sorts out most of the confusion in the overbite vs overjet question. Overjet is how far the upper front teeth sit forwards of the lower ones, measured out towards the lip. Overbite is how much the upper front teeth cover the lower ones, measured downwards. They are different measurements, taken in different directions, and a person can have too much of one and a perfectly normal amount of the other.
Key takeaways
- Overjet is horizontal, measured forwards. A normal overjet is roughly 1.5 to 2.5 mm.
- Overbite is vertical, measured downwards. A normal overbite is roughly 2 to 3 mm, or about 20 to 30 per cent of the lower incisor height.
- In everyday speech, overbite is usually used to mean what dentists call overjet.
- An increased overjet raises the risk of trauma to the upper front teeth, especially in children playing sport.
- A deep overbite can cause palate trauma, wear on the back of the upper front teeth and gum damage.
- An orthodontic assessment around age 7 to 8 is useful, once the first adult molars and incisors are through.
Overjet: the horizontal one
Overjet is measured from the front surface of the lower incisor to the front edge of the upper incisor, horizontally. In a typical bite, the upper front teeth sit just ahead of the lower ones, roughly 1.5 to 2.5 mm.
When that distance increases, the upper front teeth become more exposed and less protected by the lip. This is the pattern people usually mean when they say a child has buck teeth or an overbite, and it is the measurement that actually carries the injury risk.
Why increased overjet matters
An increased overjet is one of the clearest predictors of trauma to the upper front teeth. The teeth stick out further, the lip covers them less, and a fall on the playground or a stray elbow at sport lands directly on them. This is why a mouthguard recommendation often follows an overjet finding, particularly for children in contact sports, and why treatment timing sometimes gets brought forward for kids with a large overjet rather than waiting for all the adult teeth.
Reverse overjet, where the lower front teeth sit ahead of the upper ones, is the opposite pattern and is commonly called an underbite. It usually reflects the relative size or position of the jaws rather than the teeth alone.
Overbite: the vertical one
Overbite describes vertical overlap: how much of the lower incisors disappear behind the uppers when you bite together. Normal is roughly 2 to 3 mm, or about 20 to 30 per cent of the height of the lower incisor crown.
A deep overbite means the uppers cover much more of the lowers, sometimes all of them. When that happens, the lower incisor edges can bite into the palate behind the upper front teeth, causing sore, inflamed tissue and sometimes gum damage. The back surfaces of the upper front teeth can also wear, and heavy contact on those teeth can cause chipping and sensitivity over time. Grinding on top of a deep bite accelerates all of it, and abfraction and toothbrush abrasion covers the related wear patterns people often notice at the same time.
At the other extreme, an open bite means there is no vertical overlap at all, with a gap between the upper and lower front teeth when the back teeth are together. People with an open bite often cannot bite cleanly through a sandwich or a slice of pizza and end up tearing food with their back teeth. Open bites are frequently linked to habits such as prolonged thumb sucking or dummy use, or to tongue posture and mouth breathing.
The four patterns side by side
| Pattern | Direction | What normal looks like | Common concerns | Typical approach |
|---|---|---|---|---|
| Overjet | Horizontal, forwards | Roughly 1.5 to 2.5 mm | Trauma risk to upper front teeth, lip not covering teeth, appearance | Growth modification in children, braces or aligners with elastics in teens and adults, mouthguard for sport |
| Overbite | Vertical, downwards | Roughly 2 to 3 mm, about 20 to 30 per cent overlap | Palate trauma, wear on back of upper front teeth, gum damage | Braces or aligners to intrude front teeth or open the bite, occasionally surgery in adults |
| Open bite | Vertical, no overlap | Front teeth should meet or overlap slightly | Difficulty biting into food, speech effects, habit related | Habit management, appliances, aligners or braces, surgery for skeletal cases |
| Underbite (reverse overjet) | Horizontal, lowers ahead | Uppers should sit slightly ahead of lowers | Wear on front teeth, chewing efficiency, jaw joint loading, appearance | Early growth appliances in children, braces or aligners, jaw surgery for large discrepancies |
What causes them
Most of it is inherited. The relative size and position of the upper and lower jaws is largely genetic, and a lot of what looks like a tooth problem is really a jaw relationship problem showing up at the front of the mouth. That distinction matters because moving teeth can camouflage a jaw difference up to a point, and beyond that point surgery becomes part of the conversation.
Habits contribute too. Prolonged thumb sucking or dummy use past the age of about three can push upper front teeth forwards and stop the front teeth meeting, producing both an increased overjet and an open bite. Mouth breathing, often related to blocked nasal airways or enlarged tonsils and adenoids, changes tongue posture and how the face grows, and is worth investigating with a GP or ENT alongside dental care.
Grinding is a separate but overlapping issue. It does not cause overbite or overjet, but it changes how much wear a deep bite produces. In young children grinding is usually a passing phase, as teeth grinding in toddlers explains.
Treatment options in outline
Growing children
While the jaws are still growing, appliances can influence how they develop. Functional appliances that encourage the lower jaw forward are commonly used for large overjets, and habit appliances can help stop thumb sucking where a child wants to give up but is struggling. Timing is the whole advantage here, which is why an assessment around age 7 to 8 is worthwhile. By then the first adult molars and incisors are usually through, which is enough to see how the bite is developing, and there is still growth left to work with.
Teenagers and adults
Fixed braces or clear aligners are the usual tools. Elastics are commonly added to shift the bite relationship rather than just straighten individual teeth. Deep overbites are typically addressed by intruding the front teeth or opening the bite slightly at the back. Large skeletal discrepancies in adults, where growth has finished, may need jaw surgery combined with orthodontics to get a stable result.
If treatment involves aligners, trays that stop tracking properly are a common hiccup, and what it means when an aligner tray does not fit explains what to do. Root resorption is another thing worth understanding before starting, covered in root resorption after braces.
Afterwards
Retention is not optional. Deep bites and large overjets both have a tendency to drift back towards their original pattern, and the retainer is what holds the correction. Hawley retainers compared with clear retainers sets out the trade offs between the two main types.
Frequently asked questions
What is the difference between overbite and overjet in one sentence?
Overjet measures how far the upper front teeth sit forwards of the lower ones, and overbite measures how far they cover them downwards.
Is a small overbite normal?
Yes. Around 2 to 3 mm of vertical overlap, or roughly 20 to 30 per cent of the lower incisor, is typical. Having no overlap at all is an open bite, which brings its own issues.
Does an overjet need treating for health reasons or just appearance?
Both can apply. A larger overjet increases the risk of injury to the upper front teeth, which is a genuine health reason, particularly for children playing sport. Appearance is a valid consideration too, and the two often overlap.
At what age should a child be assessed?
Around age 7 to 8 is the common recommendation, once the first adult molars and incisors have come through. That does not mean treatment starts then, only that the pattern can be seen while growth is still available.
Can adults still have this corrected?
Yes. Braces and aligners work at any age with healthy gums and bone. What changes is that growth cannot be used, so very large skeletal differences may need surgery to correct fully rather than camouflage.
Will a deep overbite damage my teeth over time?
It can. Heavy contact on the front teeth may cause wear on the back of the upper incisors, chipping, and trauma to the palate or the gums behind the lower teeth. Whether it needs treating depends on what is actually being damaged, which an examination can establish.
The takeaway
Overjet is horizontal, overbite is vertical, and knowing which one you are dealing with changes the whole conversation. An increased overjet mostly raises the risk of injury to the upper front teeth. A deep overbite mostly causes wear and gum trauma. An open bite makes biting into food awkward. All four patterns have well established approaches, and in children the timing of an assessment can widen the options available.
If you are unsure what you are looking at in your own bite or your child's, an examination with photos and measurements will answer it clearly. Take a look at our current deals page, or book an assessment with the team at Lumi Dental in Melrose Park. We are open Monday to Saturday, with Sunday by appointment.
