Lecture 6 Posselt's Envelope Of Movement 2009 1w3a1k

Posselt’s Envelope of Movement

Reference Positions Centric Relation

Maximum Intercuspal Position Postural Position – resting position

Centric Relation according to Okeson

The position of the mandible in which the condyles are in the most superior and anterior position in the articular fossae, resting against the posterior slopes of the articular eminences with the articular discs interposed.

Centric Relation (CR) Condyle determined position Repeatable, Reproducible, Recordable

When the mandible is in centric relation the condyles can rotate around a horizontal axis up to an opening of 20-25 mm measured at the central incisors. If opening of the mandible continues beyond 20-25 mm then translation of the mandible occurs. This pure rotational movement is also referred to as hinge movement and the axis is referred to as terminal hinge axis.

Maximal Intercuspal Position or Maximum Intercuspation This is a position in which the maxillary and mandibular teeth make maximum surface with each other. The mandible is elevated as superiorly as possible in the sagittal plane.

Maximum Intercuspation (MIP) Tooth determined position Does not provide any information about the TMJ In most people, MIP does not coincide with CR

Maximum Intercuspation In MIP the condyle-disc assembly is anterior and inferior and/or medial or lateral or a combination of the above compared to their position in CR.

Usually the condyle-disc assemblies are ANTERIOR and INFERIOR.

Maximum Intercuspation Clinically if the patient needs minimal restorations (e.g. amalgam alloy or composite resin restorations, single crowns, a short span fixed partial denture) this is the position that the restorations are made.

Maximum Intercuspation Centric Occlusion

Postural Position (PP) Is the habitual position of the mandible when the patient is resting comfortably in the upright position and the condyles are in a neutral unstrained position in the glenoid fossae. In this position there is an equilibrium between the forces acting on the mandible.

Postural Position In the PP the muscles are not totally relaxed. There is a degree of electromyographic activity. This position is determined by the muscles and the forces of gravity. IT DOES NOT GIVE US ANY INFORMATION ABOUT THE CONDYLES OR THE TEETH

Postural Position The condyles are usually anteriorly and inferiorly compared to their CR position. This position can be sustained and it is comfortable for the patient.

Postural Position In this position, the teeth are apart and there is a wedge space between the teeth. The wedge shaped space is called the INTEROCCLUSAL SPACE and is usually 2-3mm between the incisors, 2mm between the premolars, and 3/4-1mm between the molars.

(There is 1:3 ratio from anterior to posterior)

Physiologic Rest Position

2-3mm

Postural Position also called the Physiological Rest Position

Clinically is used to determined the Occlusal Vertical Dimension (OVD) in edentulous patients or in patients with severely worn dentition. The Occlusal Vertical Dimension is the distance measured between two points when the occluding are in .

Postural Position also called the Physiological Rest Position

The Vertical Dimension at Rest (in the physiological rest position) is usually 2-3 mm greater than the Occlusal Vertical Dimension.

Type of Movement Rotation- pure Translation Combination of rotation and translation

Border Movements The mandibular movements are limited by ligaments, the articular surfaces of the TMJ, and the morphology and alignment of the teeth. The outer range of movement is reproducible and called border movements.

Functional Movements (occur within border movements) Occur during functional activity of the mandible Are confined within the Border Movements Begin and end in the maximum intercuspation position.

Border and Functional Movements in the Sagittal Plane Posselt’s Envelope of movement Movement Components  Posterior Opening Border  Anterior Opening Border  Superior Border  Functional movements

Posterior Opening Border Movement During opening of the mouth the condyles will move forward and down the articular eminence. Maximum opening is reached when capsular ligaments prevent further movement.

Anterior Opening Border Movement This represents the movement from maximum opening to maximum protrusion. Maximum protrusion is determined partly by the stylomandibular ligaments. The condyles are in the most anterior position.

Superior Border Movement The initial tooth occurs between the mesial inclines of the maxillary teeth and the distal inclines of the mandibular teeth. The mandible will then move superioanteriorly (shift) until maximum intercuspation occurs. There may also be a lateral component to the shift. The average distance between CR-MIP in 90% of the population is 1.25  1 mm.

Superior Border Movement The mandible moves forward from MIP to edge to edge. This is determined by the lingual surfaces of the maxillary anterior teeth. The pathway inclines inferiorly. From edge to edge the mandible can move forward horizontally for the width of the incisal edges.

Superior Border Movement Continued forward movement of the mandible, with the anterior teeth in , results in superior movement guided by the lingual surfaces of mandibular anterior teeth. Continued forward movement of the mandible is guided by the posterior teeth until the mandible reaches maximum protrusion.

Postural Position

Functional movements The chewing stroke starts at the MIP and drops downwards and forwards to the position of desire opening. It returns in a straighter pathway slightly posterior.

h: represents the movement from maximum opening to MIP r: represents the rest position

Border and Functional Movements in the Horizontal Plane Rhomboid-shaped pattern. Four movement components 1. Left lateral border 2. Continued left lateral border with protrusion 3. Right lateral border 4. Continued right lateral border with protrusion and Functional movements

Left Lateral Border movement Contraction of the right inferior lateral pterygoid causes the right condyle to move anteriorly and medially. The left inferior lateral pterygoid relaxes. Left condyle: rotating or working condyle Right condyle: orbiting or non-working

Left Lateral Border with Protrusion From the left lateral the left inferior lateral pterygoid starts to (the right stays contracted) and causes the left condyle to move anteriorly and to the right to maximum protrusion.

Right Lateral Border movement The exact opposite to the Left Lateral Border movement occurs.

Right Lateral Border with Protrusion The exact opposite to the Left Lateral Border with Protrusion occurs.

Functional movements Occurs near MIP. The outer range of movement is greater in the early stages of mastication. The outer range of movement is smaller in the late stages of mastication.

Border and Functional Movements in the Frontal Plane Shield-shaped pattern Four distinct movement components: 1. Left Lateral Superior Border 2. Left Lateral Opening Border 3. Right Lateral Superior Border 4. Right Lateral Opening Border and Functional movements

Left Lateral Superior Border From MIP the mandible moves to the Left. The path is determined primarily by the morphology and interarch relationship of the teeth. The maximum lateral border position is determined by the ligaments of the rotating condyle.

Left Lateral Opening Border Lateral convex path As maximum opening approaches, ligaments tighten and produce a medial shift

Right Lateral Superior Border similar to the Left Lateral Superior Border

Right Lateral Opening Border similar to Left Lateral Opening Border

Functional movements Occurs near MIP Occur within the outer range of the border movements.

Envelope of Motion 3D Combination of border movements in all 3 planes: a.sagittal, b.horizontal, c.frontal The envelope differs from person to person but it has the same characteristic shape

CR MIP

Envelope of Motion The superior surface of the envelope is determined by the tooth s

The other borders are primarily determined by the TMJ anatomy and the ligaments

Sample Question(s)

What is the name of this envelope Define the position of all the numbers and letters What does it represent