Malocclusion (misaligned teeth)
Malocclusion is the dental term for an improper bite relationship between the upper and lower teeth (Figure 1). In some cases, the misalignment is due to a size or positional mismatch between the jaw bones (the maxilla and mandible), and in some, it is the size or position of the teeth within the jawbones. Combinations are also possible. When the jawbones are mismatched, the condition is called a “skeletal malocclusion” (Figure 2). When the malocclusion is due to tooth size and position issues, the condition is called a “dentoalveolar malocclusion”.
Dentists use a system called “Angle Classification” to describe the relative closed-bite positions of the upper and lower first permanent molars and canines (measured forward-backward along the dental arches). The first permanent molars appear in the mouth around age six, and are an important determinant of how the patient’s overall bite relationship will develop.
Angle Class I is considered to be normal position (with the forward, outermost “mesiobuccal” cusp of the upper six-year molar resting in the “Buccal” groove of the lower six-year molar, between its cusps); Angle Class II is where the lower molars are positioned distal (toward the back of the mouth) of Class I position; Angle Class III is where the lower molars are positioned mesial (toward the front of the mouth) of Class I position.
Malocclusion ranges in severity from slightly tipped or rotated individual teeth, to poorly matched jaw bones, with undersized dental arches and oversized, crowded teeth. Depending on the severity of the patient’s malocclusion, significant problems can occur. These include abnormal wear (attrition), chipping /cracking, and premature loss of teeth; reduced chewing efficiency; improper nutrition; jaw joint pain, popping, clicking and/or locking (TMJ Disorders); reduced ability to perform effective oral hygiene; development of tooth decay (caries); development of periodontal disease; and what some may view as an unattractive smile.
Terms used to describe positional features include “prognathic”, “retrognathic”, “overjet”, and “overbite”. Prognathic means one (or both) of the jaw bones is positioned too far forward (Figure 2). Maxillary prognathism means the upper jaw is positioned too far forward for the teeth to align properly. This condition also gives the face too much convexity when the patient is viewed in profile.
Retrognathic means one (or both) of the jaw bones is positioned too far backward. Mandibular retrognathism means the lower jaw is positioned too far back for the teeth to align properly. This has the some of the same effects on tooth alignment as maxillary prognathism.
Overjet is the term used to describe the horizontal distance between the outer biting edges of the upper and lower teeth when the patient has their teeth fully closed. Normally this distance is about one to three millimeters, with the upper teeth sitting outside of the lowers.
“Reverse overjet” or “underjet” is where the lower teeth sit outside the uppers when the patient closes fully together (Figure 2). Other terms used when the lower teeth close on the outside of the upper teeth include “crossbite”, and “reverse occlusion”.
“Overbite” is the vertical distance between the upper incisor biting edges and lower incisor biting edges when the patient has their teeth fully closed. Normally, the upper incisors overlap (on the outside of) the lower incisors by about 50% of the height of the lower incisor crowns.
“Underbite” is where the lowers incisors are positioned outside of the uppers when the patient is fully closed together. An “open bite” is where the upper and lower teeth do not make it as far as the closed bite plane, leaving the affected opposing teeth separated when the patient is biting together fully.
Ideal position and size of the jaws for proper alignment of the dental arches can be influenced while growth and development of the patient is still occurring. The specialty of dentistry known as orthodontics involves diagnosing and treating various types of malocclusion, so that the patient’s teeth close together with even force distribution when the jaw muscles are relaxed and the jaw joints are in a stable position. Orthodontists try to accomplish these goals while achieving esthetic facial proportions and an attractive smile.