Posselt's envelope of motion

Anatomical concept in dentistry

Posselt's envelope of motion is a concept in dentistry that describes the range of motion of the mandible (lower jaw) in three dimensions. This concept is crucial for understanding the functional dynamics of the temporomandibular joint (TMJ) and is used in prosthodontics, orthodontics, and other dental specialties to assess and plan treatments that involve jaw movement.

Overview

Posselt's envelope of motion is named after Ulf Posselt, who first described it in 1952. It represents the maximum range of mandibular movement in the sagittal, frontal, and horizontal planes. The envelope is a three-dimensional space that encompasses all possible positions of the mandible relative to the maxilla (upper jaw).

Sagittal Plane

Posselt's Envelope of Motion (Sagittal View)

In the sagittal plane, the envelope of motion is often depicted as a diagram showing the path of the incisal edge of the lower central incisors. The sagittal view includes several key positions:

• Centric Occlusion (CO): The position where the teeth are in maximum intercuspation.
• Centric Relation (CR): The position of the mandible when the condyles are in their most anterior-superior position in the glenoid fossae, independent of tooth contact.
• Maximum Protrusion: The furthest forward position of the mandible.
• Maximum Retrusion: The furthest backward position of the mandible.
• Maximum Opening: The widest opening of the mouth.

Frontal Plane

In the frontal plane, the envelope of motion is less commonly depicted but is important for understanding lateral movements. The mandible can move laterally to the left and right, and these movements are limited by the ligaments and the muscles of mastication.

Horizontal Plane

In the horizontal plane, the envelope of motion is often illustrated as a diamond-shaped diagram. This view shows the lateral and protrusive movements of the mandible. The key positions include:

• Centric Occlusion (CO): The starting point of the diagram.
• Lateral Excursions: The movement of the mandible to the left and right.
• Protrusive Movement: The forward movement of the mandible.

Clinical Significance

Understanding Posselt's envelope of motion is essential for diagnosing and treating disorders of the TMJ, planning dental prostheses, and designing orthodontic treatments. It helps clinicians visualize the functional limits of mandibular movement and assess any deviations from normal motion patterns.

Related Pages

• Temporomandibular joint
• Occlusion (dentistry)
• Prosthodontics
• Orthodontics