Occlusion is defined as the way the teeth meet when the lower jaw (mandible) and upper jaw (maxilla) come together. It is how the teeth contact in any type of functional relationship. Normal occlusion is desirable as it allows oral functions to operate properly, provides the best esthetics and is helpful in the prevention of disease. Anytime normal occlusion does not occur in the mouth, it is termed malocclusion. Malocclusion can have an effect on dental diseases, chewing, speech and esthetics (especially facial profile) and other functions of the oral cavity. Malocclusion can occur for a variety of reasons. These include, but are not limited to, heredity, trauma, diseases, and habits (such as thumb sucking).
Occlusion is designated according to certain classifications. Figure 9 shows the relationship of the teeth and the variations of the malocclusion classifications. It is based on how the maxillary and mandibular first molars come into contact with one another when closing the teeth. The common system used to classify occlusion is termed Angle’s classification system. Class I is considered normal occlusion. Class II and III are considered malocclusion and have different divisions.