Overbite and overjet

The distinction

Overbite is vertical: how far the upper front teeth overlap the lower ones when you bite together, viewed from the side. A small overlap of two to four millimetres is normal and desirable.

Overjet is horizontal: how far the upper front teeth sit forward of the lower ones. Again, a couple of millimetres is normal. What people usually mean when they say "overbite" in ordinary conversation is overjet — front teeth that stick out.

They occur independently. A deep overbite with no overjet is common, as is a large overjet with an open bite where the teeth barely overlap vertically at all.

Deep overbite

When the overlap is excessive, the lower incisors can bite into the gum behind the upper front teeth. Over years that causes recession, tooth wear and occasionally loose upper incisors. Correction means intruding the front teeth, erupting the back teeth, or both — work that fixed appliances do well and that takes time to hold, which is why deep bite cases often run longer than they look like they should.

Increased overjet

Protruding upper front teeth are usually a jaw relationship rather than a tooth position: the lower jaw sits behind where it should. In a growing child, a functional appliance can improve that relationship while growth is available. In an adult, options are camouflage with extractions and elastics, anchorage devices, or jaw surgery in severe cases.

There is also a practical reason to treat it: teeth standing well forward are markedly more likely to be broken in a fall or a collision. That risk is one of the clearer arguments for early treatment in children, alongside the appearance.

Getting a straight answer

Ask which measurement your case involves and what the number is. Both are recorded at every orthodontic examination, and knowing which one is being corrected tells you a great deal about what the treatment will involve.