By appearance, patients with Underbites have a strong jaw with a chin that juts straight out. The lower front teeth are positioned before the upper front teeth. This condition is caused by the horizontal underdevelopment of the upper jaw, the horizontal overdevelopment of the lower jaw, or most frequently a combination of both.
Nonsurgical orthodontic attempts at treating skeletal underbites can result in the chin's already prominent appearance being further accentuated by the orthodontic retraction of the lower front teeth. This occurs because the lower lip (which is supported in its normal position by the lower front teeth) falls backward when the lower front teeth are orthodontically retracted. Finaly, nonsurgical orthodontic attempts to treat skeletal underbites can result in lower front teeth which are periontally compromised.
Examples of Underbites caused by an underdeveloped upper jaw can be found by clicking on: AF, SO, JB.
Examples of Underbites caused by an overdeveloped upper jaw can be found by clicking on: JJ, KP, AR
Examples of Underbites caused by a combination of underdeveloped upper jaw and an overdeveloped lower jaw can be found by clicking on: SD, SH, CM, RM, TM, ED, GG.
By appearance, patients with Overbites are "bucktoothed" and have a receding chin. The lower front teeth are positioned; too far behind the upper front teeth. This condition can result from a horizontal overdevelopment of the upper jaw or an underdevelopment of the lower jaw or a combination of both. Some Overbites can be treated by tooth extraction only when the upper and lower jaw are normally sized and positioned: and extraction therapy will not produce flattening of the face or apparent elongation of the nose which occurs when the upper lip (which is supported by the upper front teeth) moves backward when the upper teeth are orthodonticly retracted.
This occurs when the upper teeth are biting inside the lower teeth. This is frequently the result of a narrow upper jaw. Crossbites also occur because of a mismatch in jaw size and position between the upper and lower jaw. Some crossbites also lead to asymmetry of the lower jaw by causing the jaw to be abnormally deflected to one side when closing the teeth together. Proper diagnosis determines how and when a crossbite needs correction.
This occurs when the upper front teeth can not meet or overlap the lower front teeth even though the back teeth have closed together. Clearly this makes eating difficult. It's hard to eat a slice of pizza when your front teeth don't meet! Open bites are caused by the overdevelopment of the back portion of the upper jaw in a vertical direction. As the back portion of the upper jaw grows vertically downward, the lower jaw will open in a clockwise direction. This explains why open bite patients have a long facial appearance. (Put a pen between your back molars and look in the mirror and see how your face has grown vertically longer in appearance. )
Lip Incompetence and Lip Strain
When the upper jaw has become overdeveloped in a vertical direction, the upper and lower lip may not meet together at rest. This condition is know as lip incompetence. People do not like to walk around with their lips wide open. Consequently they must constantly contract their chin muscles to forcibly (hence the term lip strain bring their lips together).
When the upper jaw has become overdeveloped in a vertical direction this may lead to a very gummy smile and "horsey appearance." Not only is the situation cosmetically undesirable, it can also result in sore, red, bleeding gums from chronic exposure to air (a phenomenon call air gingivitis).
When the upper jaw is horizontally underdeveloped (backward positioned), there is a flattening or shallowness on either side of the nose. This "dished-in" appearance will actually make the nose look larger than it really is. Advancement of the upper jaw has the effect of decreasing the apparent size of the nose.
An asymmetry will occur when there is a difference of growth between the right and left sides of either the upper jaw, lower jaw, or both. The lower jaw asymmetry can be identified because the chin point will be deviated off to one side. The upper jaw asymmetry can be identified by looking at the position of the two front teeth. If the upper jaw is symmetrical, the line dividing the two upper middle teeth should be the same as the line dividing the face into two equal halves (the facial midline).
This is also a form of asymmetry. In this particular form of asymmetry the upper jaw is being rotated-about a frontal midpoint. This occurs when one sides of the upper jaw becomes much more vertically overdeveloped than the opposite side.
This is the groove between the chin and the lower lip. A vertically long chin can have an underdeveloped mental-labial fold. Occasionally, severe Overbites cause a deepening of this mental-labial fold by causing the lower lip to turn outward.
This is a surgical procedure which is performed to recreate the normal shape of the chin. A large chin may require both a vertical and horizontal reduction, while a small chin may require vertical and/or horizontal augmentation to create an esthetic chin appearance. In addition to the obvious cosmetic benefits, a genioplasty procedure will help reduce lip strain and lip incompetence.
This is mother nature's way of camouflaging a skeletal bite deformity. Let's say a lower jaw grows out in an excessive horizontal forward fashion to create an Underbite. In an effort to minimize the size of the Underbite, the lower front teeth will "compensate" by tipping backwards (opposite the direction of the excessive horizontal forward growth). The upper front teeth will also "compensate" by tipping forwards in effort to meet the lower front teeth. Unfortunately this "compensation" is not good for the health and longevity of the front teeth. In preparation for surgery the orthodontist will remove this dental compensation and put their teeth in their ideal position. Continuing our example, this means the orthodontic "decompensation" will make the Underbite appear more severe presurgically. (If an Overbite existed, the Overbite would appear to get worse presurgically. Fortunately, this is only a temporary condition as the repositioning of one or both jaws will completely correct the more dramatic Underbite (or Overbite).