Let us clear up the confusion between overbite and overjet

There is a lot of confusion as to the difference between overbite vs overjet. Truthfully, there are even a number of orthodontic office websites that also are confused as to the difference between the two. In this article, we discuss the differences between overbite and overjet, how they develop, the relationship between the two, and how they can be treated.

When patients first come into the office, they frequently mention that they have an "overbite" they would like corrected. The first question Dr. Skarin will ask at the initial appointment is for them to define "overbite" so that everyone is on the same page. Nine times out of ten, patients say overbite but what they are really describing is "overjet"! Let's look at the definitions of the two terms and how they relate:

• "Overbite is defined as the vertical overlap of the incisors"
• "Overjet is defined as the horizontal overlap of the incisors"

To be clear, normal overbite would have the upper incisors vertically overlapping the lower incisors by 1-2 millimeters when the individual is biting with their posterior teeth completely together. Most of the height of the lower incisors should be easily seen from the front!

Normal overjet would find the upper and lower incisors in contact, with the upper incisors ahead of the lower incisors by the thickness of the edge of the upper incisors, by about 2-3 millimeters.

Most of the time, prospective patients are concerned about overjet, where the upper teeth are well in front of the lower teeth. There are problems associated with this excessive protrusion of the teeth, but potentially far more serious problems can occur when overbite is allowed to continue developing. Before we proceed to discuss overbite and the multiple problems associated with it, let's look at overjet/protrusion of the teeth.

Every normal bite needs overjet. The upper anterior teeth should rest their incisal third on the incisal edges of the lower anterior teeth when biting down. If the upper anterior teeth are further forward than that, then overjet becomes excessive.

What problems are associated with overjet?

The two most common problems are :

1. The aesthetics of very procumbent upper front teeth is generally unacceptable to most everyone. "Buck teeth" do not help one's confidence.
2. Procumbent upper front teeth are quite susceptible to being injured through falling in their early years and chipping the front teeth.

How can excessive overjet develop?

1. A skeletal prognathic relationship - This genetic relationship occurs when the upper jaw, or maxilla, develops well forward of the lower jaw, or mandible and the positions of the teeth will follow the skeletal pattern.
2. A dental Class II relationship - This dental relationship makes up nearly 45% of the population's bites. This is where the teeth erupt in a relationship where the upper teeth come in well in front of their normal position. Again, most of these bites have the upper anterior teeth well in front of the lower anterior teeth.
3. Thumb, finger or lower lip-sucking habits - If an individual has an active and prolonged thumb or finger sucking habit, then not only will the upper anterior teeth be pulled forward excessively, the anterior maxilla or front of the jaw will be re-shaped in a prow-like fashion. In addition, the lower anterior teeth will sometimes end up leaning backward or lingually as a result of the pressures being placed between the upper and lower anterior teeth.
4. Tongue habits - Tongue thrusting habits or a reverse swallowing habit can, over months and years, will force the anterior teeth forward ahead of the lower anterior teeth, usually developing an open bite in the anterior as well.
5. Loss of posterior teeth and resulting loss of vertical dimension - As a bite deepens with the loss of posterior teeth, the lower incisors will bump harder into the lingual of the upper anterior teeth, forcing the upper anterior teeth to begin tipping forward, creating more overjet.
6. Lower anterior tooth crowding - This happens frequently as we age and mesial drift of teeth occurs. What is mesial drift? It is the gradual physiologic movement of all teeth towards the front of the mouth as a result of the way our jaws come together in a biting fashion. As this drifting of the teeth occurs, the lower incisors will tend to rotate and crowd, creating earlier contact with the upper incisors and forcing them forward into a greater lean or "buck teeth".

Correcting overjet problems is relatively easy unless a deep overbite is present. As long as there is excessive horizontal space between the upper anterior teeth and the lower anterior teeth and there is excess arch length/spaces in the upper posterior teeth, the upper anterior teeth can be retracted or pulled back to a normal overbite/overjet relationship.

How can overbite develop?

You may have noticed a reference was made that overbite can continue to develop or worsen with time. Overbite develops when the upper anterior teeth are not in contact with the mandibular teeth during normal function. When teeth are not in contact with one another, teeth will continue to erupt. For example, if a person loses a posterior tooth for whatever reason, the tooth opposing the lost tooth will, over time, erupt vertically into that space, changing the level of the arch it is part of. This vertical change can often be significant, sometimes half the vertical height of the crown of the tooth that is erupting. This is a slow, insidious, painless process that usually goes unnoticed until significant problems develop. This very same movement will occur when the upper anterior teeth are well forward of the lower front teeth and do not touch one another. Unless there is some tongue habit, such as a tongue thrust, reverse swallow or digital habit, the lower front teeth will erupt upward toward the upper arch of teeth and palate and the upper front teeth will erupt downward toward the lower lip.

What problems can an increase in overbite cause?

1. Increase in overbite can cause greater procumbency of the upper anterior teeth. As the anterior teeth continue to erupt, they can force the upper anterior teet to tip further forward.
2. Increase in overbite can force the lower teeth to tip lingually toward the tongue and contribute to crowding of the lower anterior teeth which, in turn, will make it easier for mesial drift to increase crowding, and subsequent periodontal problems due to the crowding.
3. A deep overbite that finds the lower incisors bumping into the palatal tissue behind the upper anterior teeth will apply pressure to the soft tissue it is hitting, causing recession of the soft tissue and subsequent bone loss. This periodontal involvement is also visible from the front view and can leave unsightly large gaps between the teeth at the gingival margin at the "necks" of the teeth. If this condition continues, tooth loss could occur.
4. A deepening overbite can be a direct or contributing cause of temporo-mandibular joint (TMJ) problems. If and when an overbite worsens as we age, the upper anterior teeth will continue to overlap the lower anterior teeth so that the incisal edge of the lower anterior teeth will make contact with the upper anterior teeth at an ever-thickening segment of the lingual contour of the upper anterior teeth. This very gradual change in the vertical position of contact with the anterior teeth will begin to very slowly cause the lower jaw to be forced back into the joints when a person tries to bring their teeth together. At some point, the movement will eventually elicit sharp, stabbing pains as the ligaments are stretched in the joint capsule or a dull ache as the jaw is forced to rest in a different location from its resting position. The term excessive incisal guidance is frequently the cause of such joint problems and can only be corrected by changing the overbite-overjet relationship to avoid forcing the lower jaw backward into the joints.

How is overbite corrected?

As mentioned and explained earlier, correction of overjet by itself is pretty straight forward and can be done in some cases with a removable appliance, certainly with braces and probably aligners as well. But adding to the deep overbite problem, depending on its severity and skeletal growth vector, can take from months to years and could require a large number of appliances applied at different stages of treatment with significant attention to long-term (life-time) maintenance to keep relapse from occurring. Certain procedures and appliances can be employed, if appropriate and needed, to open up a deep bite or impinging overbite.

Palatal expansion, if a skeletal crossbite is present, will help open a deep bite. Headgear set up in certain ways to help correct a skeletal prognathia, as explained earlier, can also help open the bite. Removable appliances started early to utilize passive eruption of the posterior teeth can help significantly. Some of the European functional appliances developed in the last century have been shown to help in the mixed dentition. Placing acrylic on the top/occlusal surfaces of molars or bonded turbo blocks placed on the inside surfaces of the upper anterior teeth to artificially open the bite in order to place braces on the lower arch are additional techniques. And fixed appliances/braces are essential to apply needed intrusive/ extrusive forces on certain teeth.

However, the most important variable in knowing how difficult and how long the treatment will go is based on a patient's growth pattern. Your orthodontist will be able to show you through a cephalometric evaluation and multiple analyses based upon over a century of growth data whether the treatment will be slightly difficult but manageable in a normal treatment time, or exceedingly difficult taking far longer than normal with the possibility of some damage to the teeth through the needed forces that must work against the periodontal structure that is in place to naturally prevent against the movements needed to correct the problem. If you think this type of bite can be difficult to treat to an acceptble result, then you are correct.

It is highly recommended that you visit an A.A.O. accredited orthodontist in your area to get a thorough evaluation of your overbite problem as it is not a treatment that just aligning the teeth will fix. You can visit the American Association of Orthodontists to find an accredited orthodontist near you or give us a call to schedule a complimentary consultation.