The study of dental occlusionis important aspect of dentistry. The study and practice of most branches of dentistry should be based on a strong foundation of the knowledge of occlusion.
Orthodontics is no exception to this as great many changes occur in the occlusion during orthodontic therapy. The orthodontist should know what constitutes normal occlusion in order to be able to recognize abnormal dental occlusion.
Angle defined occlusion as the normal relation of the occlusal inclined planes of the teeth when the jaws are closed. This definition is an over-simplification of what it actually constitutes.
Occlusion is a complex phenomenon involving the teeth, periodontal ligament, the jaws, the temperomandibular joint, the muscles and the nervous system. The aim of this article is to throw light on normal occlusion and to highlight the orthodontic aspects of dental occlusion.
Ideal occlusion: It is a pre-conceived theoretical concept of occlusal structural & functional relationships that includes idealized principles & characteristics that an dental occlusion should have.
Physiological occlusion: This refers to an occlusion that deviates in one or more ways from ideal yet it is well adapted to that particular environment, and is aesthetic and shows no pathological manifestations or dysfunction.
Balanced occlusion: An dental occlusion in which balanced and equal contacts are maintained throughout the entire arch during excursions of the mandible.
Functional occlusion: It is defined as an arrangement of teeth which will provide the least efficiency during all the excursive movements of the mandible which are necessary during function.
Therapeutic occlusion: An dental occlusion that has been modified by appropriate therapeutic modalities in order to change a non-physiological occlusion to one that is at least physiological if not ideal.
Traumatic occlusion: Traumatic dental occlusion is an abnormal occlusal stress which is capable of producing or has produced an injury to the periodontium.
Trauma from occlusal: It is defined as periodontal tissue injury caused by occlusal forces through abnormal occlusal contacts.
Types of Cusps
The human posterior teeth constitute two types of cusps. They are the centric holding cusps and the non- supporting cusps.
Centric holding cusps
The facial cusps of mandibular and palatal cusps of maxillary posterior teeth are called the centric holding cusps. They occlude into the central fossae and marginal ridges of opposing teeth. They are also called the stamp cusps.
Non supporting cusps
The maxillary buccal and mandibular lingual cusps are called non-supporting cusps. They contact and guide the mandible during lateral excursions & shear food during mastication. Hence they are also called hearing or guiding cusps.
Arrangement of Teeth in Humans
Human dentition exhibits two types of tooth arrangement when the upper and lower teeth occlude with one another. They are:
a. Cusp fossa occlusion
b. Cusp embrasure occlusion
Cusp- fossa occlusion
In this type of dental occlusion, the stamp cusp of one tooth occludes in a single fossa of a single opponent. The upper stamp Cusps fit into all except the mesial fossae of the lower teeth while the lower stamp cusps fit into all the upper fossae except the distal ones of bicuspids.
This kind of arrangement where contacts occur between single opposing teeth is called a cusp-fossa dental occlusion or a tooth to tooth arrangement
Another type of dental occlusion between the upper and lower teeth is called the cusp-embrasure or tooth to two teeth occlusion. In this type of arrangement each tooth occludes with two opposing teeth.