dental disorders
Malocclusion
Introduction
Malocclusion is abnormal contact between the maxillary and mandibular teeth. (See also Evaluation of the Dental Patient .) Normally, each dental arch consists of teeth in side-by-side contact, forming a smooth curve, with the maxillary anterior teeth overlying the upper third of the mandibular anterior teeth (see figure). The buccal (outer) cusps of the maxillary posterior teeth are external to the corresponding cusps of the mandibular posterior teeth. In most cases, the anterior buccal cusp of the maxillary first permanent molar fits into the anterior buccal groove of the mandibular first molar. Because the outer parts of all maxillary teeth are normally external to the mandibular teeth, the lips and cheeks are displaced from between the teeth so that they are not bitten. The lingual (inner) surfaces of the lower teeth form a smaller arch than those of the upper teeth, confining the tongue and minimizing the likelihood of its being bitten. All the maxillary teeth should contact the corresponding mandibular teeth, so that the masticatory forces (which may be>150 pounds [>1000 kilopascals] in the molar region and 250 pounds [>1700 kilopascals] when clenching during sleep) are widely distributed. If these forces are applied to only a few teeth, those teeth may eventually become mobile or show abnormal wear. The numbering system shown is the one most commonly used in the United States. 