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The vertical jaw abnormalities relating to the mandible are in relation to excessive vertical growth and excessive horizontal growth, measured by the maxillary-mandibular plane angle (MMPA). The vertical jaw abnormalities relating to the maxilla are in relation to excessive downward displacement (EDD) and insufficient downward displacement (IDD).
Posselt's envelope of motion or Posselt's envelope of movement refers to the range of motion of the lower jaw bone, or mandible. This envelope was first described by Ulf Posselt in 1952. It is a diagrammatic representation of a sagittal view of maximum mandibular movement.
A common trick is to ask the patient to say the name "Emma," as the position of the mandible immediately after completing the word is a rough estimate of the patient's proper VDO. The position after saying "Emma" is referred to as the vertical dimension at rest, or VDR. Historically, the VDO has been estimated at 3 mm less than VDR because a ...
Centric relation 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 antero-superior position against the posterior slope of the articular eminence . [ 12 ]
The Temporomandibular Joint is not restricted to Centric Relation in function. At the most superior position, the condyle-disc assemblies are braced medially, thus centric relation is also the midmost position. A properly aligned condyle-disc assembly in centric relation can resist maximum loading by the elevator muscles with no sign of discomfort.
This is an important jaw position, as it defines both the anterior-posterior and lateral relationships of the mandible and the maxilla, as well as the superior-inferior relationship known as the vertical dimension of occlusion. These are important considerations in orthodontic treatment as well as for dental prostheses and their design and use.
Orthodontic camouflage so that jaw discrepancy no longer apparent; Orthognathic surgery – sagittal split osteotomy mandibular advancement carried out when growth is complete where skeletal discrepancy is severe in anterior-posterior relationship or in vertical direction. Fixed appliance is required before, during and after surgery.
When measuring the vertical range of motion, the measurement must be adjusted for the overbite. For example, if the measurement from the edge of the lower front teeth to the edge of the upper front teeth is 40 millimeters and the overbite is 3 millimeters, then the jaw opening is 43 millimeters. During jaw movements, only the mandible moves.