User:Rebeccaridout/sandbox

= Occlusion (Dentistry) =

Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary (upper) and mandibular (lower) teeth when they approach each other, as occurs during chewing or at rest.

Static occlusion refers to contact between teeth when the jaw is closed and stationary, while dynamic occlusion refers to occlusal contacts made when the jaw is moving. The masticatory system also involves the periodontium, the TMJ (and other skeletal components) and the neuromusculature, therefore the tooth contacts should not be looked at in isolation.

Development of Occlusion
As the primary (baby) teeth begin to erupt at 6 months of ago, the maxillary and mandibular teeth aim to occlude with two teeth of the opposing jaw. This is not the case for the lower central incisors and the upper second molars. The teeth should be correctly occluding and aligned after 2 years whilst they are continuing to develop, with full root development complete at 3 years of age. Around a year after development of the teeth is complete, the jaws continue to grow which results in spacing between some of the teeth (diastema). This effect is greatest in the anterior (front) teeth and can be seen from around age 4 - 5 years. This spacing is important as it allows space the permanent (adult) teeth to erupt into the correct occlusion, and without this spacing there is likely to be crowding of the permanent dentition.

The development of tooth contact is influenced by a number of factors including whether there is permanent teeth or not, condyle development, the position of the tooth germ during development of the tooth and the angle of incline on the cusps of the teeth.

Concepts of Occlusion
Intercuspal Position (ICP), also known as Habitual Bite, Habitual Position or Bite of Convenience, is defined at the position where the maxillary and mandibular teeth fit together in maximum intercuspation. This position is usually the most easily recorded and is almost always is the occlusion the patient closes into when they are asked to 'bite together'. This is the occlusion that the patient is accustomed to, hence sometimes termed the Habitual Bite.

ICP is also called 'Centric Occlusion ' (CO) by some, but ICP does not always occur in CO so these terms should not be used synonymously. Posselt (1952) determined that only in 10% of natural tooth and jaw relationships does ICP = CO. CO is the occlusion of the maxillary and mandibular teeth when the mandible is positioned in Centric Relation (CR).

CR describes a reproducible jaw relationship (between the mandible and maxilla) and is independent of tooth contact. This is the position in which the mandibular condyles are located in the fossae in an anteror-superior position in contact with the central bearing surface (thin avascular part) of the interarticular disk, against the posterior slope of the articular eminence. When the mandible is in this retruded position, it opens and closes on an arc of curvature around an imaginary axis drawn through the centre of the head of both condyles. This imaginary axis is termed the terminal hinge axis. The first tooth contact that occurs when the mandible closes in the terminal hinge axis position, this is termed Retruded Contact Position (RCP).

Intercuspal Position vs Centric Relation
It is common practice to mount mandibular and maxillary casts on an articulator in ICP when constructing restorations that conform to the patient's existing occlusion. Casts mounted in ICP are useful for diagnostic purposes or simple restorations, but where more extensive treatment is planned it is necessary to consider occlusal contacts relative to CR e.g. RCP -> ICP slide. Other situations a CR registration may be more appropriate than ICP include where there is plans to reorganise or adjust the existing occlusion (including changes to the occluso-vertical dimension). In these circumstances, in order to accurately stimulate mandibular movement around CR (particularly opening and closing of the mouth), using a facebow the maxillary cast should be mounted onto a semi-adjustable articulator and then the mandibular cast should be mounted using a CR registration. The patients new occlusion is then arranged so that the new ICP occurs when patient is in CR.