Class II (Overbite)
Class II problems represent abnormal bite relationships in which the upper jaw and teeth project ahead of the lower jaw called “overjet” (sometimes called an overbite). Class II patients usually exhibit a convex facial profile with a deficient chin prominence. Typically, a Class II problem is inherited and results in a shorter than normal lower jaw. Other factors, such as persistent thumb sucking can aggravate these problems. Correction of this disorder generally requires influencing facial growth to bring the upper and lower jaws and teeth into proper position.
Class III (Underbite)
Class III problems are also primarily genetic in origin. In this instance, the lower jaw and teeth are displaced to the front of the upper jaw structures. Facially, the appearance may give the impression that the lower jaw is excessively large, but in many cases the lack of upper jaw development is at fault.
Crowding of the teeth is the most common problem associated with the need for orthodontic care. Although many factors contribute to the dental crowding, this problem usually stems from a discrepancy between space available in each jaw and the size of the teeth. Aside from aesthetic considerations, poor alignment of teeth may be associated with abnormal wear of tooth surfaces, periodontal problems, and an increased risk of dental decay due to difficulty in maintaining proper oral hygiene.
Spaces between teeth are another common problem associated with the need for orthodontic care. Like crowding, spacing may be related to a tooth-to-jaw size disharmony. Gum tissue attachment called “frenae” are also a common cause of spacing between the front teeth. Excessive vertical overlap of the front teeth as well as incisor protrusion may lead to spacing. Other contributing factors include atypical or unusually narrow teeth, and missing or impacted teeth.
A lack of vertical overlap of the incisor teeth can usually be traced to jaw disharmony or persistent habits (i.e. digit sucking habits and posturing of the tongue between the front teeth) or excessive vertical growth of one or both jaws. Early assessment and intervention with this disorder is critical to the overall success of treatment.
Excessive vertical overlapping of incisor teeth called “deepbite” is generally found in association with a discrepancy between the length of the upper and lower jaws. It usually results in excessive eruption of either the upper of lower incisors or both. Associated problems include: 1) lip protrusion or entrapment, 2) biting the roof of the mouth and 3) incisor wear.
Excessive Gingival Display
Also known as a gummy smile, this orthodontic problem gives the appearance of excessive exposed gums on the upper arch. There are several treatment options for this problem. In severe cases surgery may be necessary to actually remove a section of the upper jaw shifting the jaw upward vertically reducing the amount of exposure of the upper gum tissue.
Posterior crossbites usually result from a narrow upper jaw or unusually wide lower jaw. A narrow upper jaw will often force a patient to move their lower jaw forward or to the side when closing into a stable bite. When closed into this accommodated position, the lower teeth are located outside the upper teeth. This posturing may result in abnormal growth of the lower jaw with accompanying facial asymmetry.
In a perfect bite, the upper jaw should be slightly wider than the lower jaw, and all of the upper teeth should slightly overlap the lower teeth. The center between the upper incisors should align with the upper incisors, and with the midline of the face.