Mandibular Movements PDF

MANDIBULAR MOVEMENTS MANDIBULAR MOVEMENTS AND THEIR RELATIONTO COMPLETE DENTURE CONSTRUCTION Centric relation The maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the antero-superior position against...

MANDIBULAR MOVEMENTS MANDIBULAR MOVEMENTS AND THEIR RELATIONTO COMPLETE DENTURE CONSTRUCTION Centric relation The maxillomandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective disks with the complex in the antero-superior position against the slopes of articular eminences. This position is independent of tooth contact. This position is clinically discernible when the mandible is directed superiorly and anteriorly. The centric relation is a jaw to jaw relation determined by the condyles in the fossae. Centric relation is used to transfer position of mandible in relation to maxilla, to an articulator. Maximum intercuspation: The complete intercuspation of teeth independent of condylar position, sometimes referred to as the best fit of the teeth regardless of condylar position Centric occlusion: It is said when centric relation and maximum intercuspation are at same position. mandibular movements Many different mandibular movements occur during Mastication Speech Swallowing Respiration Facial expressionParafunctional movements (bruxism, clenching) Factors that regulate mandibular movements: Anatomy and physiology of TMJ’s The action of muscles. The action of ligaments. Influence of opposing tooth contacts. Neuromuscular regulation.  MANDIBULAR MOVEMENTS Anatomy of the temporomandibular joint: (Fig.1) The temporomandibular joint is the articulation between the mandibleand the cranium. The temporomandibular joint consists of: 1. Articular fossa and articular eminence in the temporal bone. 2. Condylar head of the mandible. 3. The articular disc which is called the meniscus. It is present betweenthe temporal bone and the condyle, dividing the joint into maxillary and mandibular compartments. 4. The temporomandibular ligament. 5. The synovial membrane. Fig1: Temporomandibular joint anatomy 1. The articular fossa of the temporal bone: It is concave in both directions. The anterior border of the fossa isconvex forming the articular eminence. 2. The Condylar Head: It is the other bony part of the T.M.J. and is convex in bothdirections. 3. The Articular Disc: It is a thin oval fibrous plate of great firmness, placed between thecondylar head of the mandible and the articular fossa. Its maxillary surface is concavoconvex to fit the articular fossa and articular eminence. Its under surface is concave to fit the condyle. The disc separates the joint into two compartments an upper compartment and lower compartment.  MANDIBULAR MOVEMENTS 4. Articular Capsule (Capsular Ligament): It is a loose fibrous envelop attached from above to the zygomatic archand articular eminence and from below to the neck of the condyle. 5. The Temporomandibular Ligament: It is considered as a lateral thickening of the capsular ligament. It is attached from above to the articular eminence and zygomaticarch and from below to the lateral side of the neck of the condyle. It is wider at the zygomatic origin than at its condylar insertion. 6. Synovial Membrane: Each compartment of the joint is lined with asynovial membrane which is in the form of a loose sac containing synovial fluid. One sac is above and the other is below the articulardisc. The synovial fluid is lubricant and also nutrient to the non- vascular surface of bone and disc. The action of muscles. They are responsible for mandibular movements. https://www.youtube.com/watch?v=QY_IL7y49Ds MASSETER Functions:- Elevation Superficial portion: protrusion Deep portion : stabilization against articular eminence TEMPORALIS:- It is a significant positioning muscle of the mandible It has 3 types of fibers Function Anterior fibers – or vertical elevation. Middle fibers –run obliquely. Elevation and retrusion Posterior fibers – consists of fibers that are aligned almost horizontally. retrusion  MANDIBULAR MOVEMENTS MEDIAL PTERYGOID: Function : Along with masseter it forms a muscular sling that supports the mandible at mandibular angle. When fibers contract the mandible is elevated. Muscle is active in protruding the mandible. Unilateral contraction will bring about mediotrusive movement of the mandible. LATERAL PTERYGOID: Two bellies: Inferior lateral pterygoid- outer surface of lateral pterygoidplate & extends backward, upward& outward…inserted on to the neck of the condyle. Superior lateral pterygoid- infratemporal surface of the greater wing of sphenoid…..inserted on the articular capsule, the disc & the neck of the condyle. Funtions : Inferior lateral pterygoid: Opening ,protracting ,Lateral movement in contralateral direction Superior lateral pterygoid: During opening… inferior pterygoid active superior pterygoid remains inactive Become active only in conjunction with the elevator muscles Active during power stroke & when teeth hold together. Summary Protrusion by Lateral ptreygoid with medial pterygoid Retrusion by Posterior fibers of temporalis deep part of temporalis and geniohyoid Elevations (mandibular closure) by temporalis, masseter, medial ptreygoid muscle. Depression (mandibular opening) by digastric muscle, geniohyoid, Inferior head of lateral ptreygoid muscle  MANDIBULAR MOVEMENTS Basic mandibular movements: Two basic movements are recognized in the joint (Fig.2,3). A- Rotation (Hinge) movement: This movement takes place in the lower compartment of T.M.J between the head of the condyle and the under surface of the disc. The condylar head of the mandible rotates on the under surface of the disc. Such rotational movement can occur in several axes. And is called Simple Hinge or Pure terminal hinge movement (Fig. 3) B- Translation movement: This movement takes place in the in upper compartment “maxillary” compartment between condylar head and the disc as one unit, and the glenoid fossa. (Fig.2b). These two types of movements (rotation and translation) take place either solely or in combination. Axes of mandibular rotation 1. Terminal (Transverse) hinge axis Terminal hinge axis: It is an imaginary line between the mandibular condyles around which the mandible rotates during the early opening and late closing (Fig.3). The hinge axis can be located clinically by the kinematic face bow (exact method) or through the canthus-tragus line (arbitrary method).  MANDIBULAR MOVEMENTS 2. Vertical axis:- Mandible moves in lateral excursion. Centre of this rotation is vertical axis extending through rotating or working side condyle. 3. Sagittal axis:- Mandible moves forward. Possible Mandibular Movements 1. Opening and closing movements. 2. Forward movement, (protrusion). 3. Backward gliding movement, (retrusion). 4. Lateral gliding movement. Limiting factors of mandibular movements 1- C N S and Muscles. 2- Teeth. 3- TMJ.  MANDIBULAR MOVEMENTS a b Fig. 2 a, b : condylar translation during wide mouth opening. Axes of rotation: A-Horizontal axis. B- Sagittal axis. C- Vertical axis. Fig. 3: Mandibular centers of rotation. A, Horizontal-sagittal (transverse or retruded condyle axis). B, Horizontal-coronal axis (sagittal axis).Permits descent of balancing condyle C, Vertical axis with horizontal rotation. Frontal (coronal) Fig.4: The three planes of the skull (from Posslet).: Physiology of occlusion and rehabilitation)  MANDIBULAR MOVEMENTS Border and intra-border movements Border movements: These are movements occurring following the boundaries ofmovement space. They are repeatable positions. Intra-border movements: These are movements occurring within the boundaries of movement space. They are non-repeatable positions (Fig.5). Fig.5: A: Border movements. B: Intra- border movements. Possible mandibular movements: 1) Opening and closing: Such movement can only be described when looking at thepatient from a profile view (Sagittal view) a) Terminal hinge opening: In the first 4-8mm of opening movements, pure rotation occurs inthe mandibular compartment, the rotation occurs around the transverse hinge axis with no apparent condylar translation. b) Opening with forward translation: On further opening, rotation and translation occur in themaxillary compartment. 2) Habitual intra-border Opening: This movement is carried out inside the envelope of motion. It is the movement path of theincisal point from the intercuspal position till the maximal opening position. It consists of a combination of rotation and translation.  CHAPTER VI MANDIBULAR MOVEMENTS TRACING AND RECORDING OF MANDIBULAR MOVEMENTS 1. Tracing in sagittal plane (Envelop of motion) Posselt described a curve drawn by the mandible during such movement, and named it “Posselt’s envelope of motion”.(Fig. 6) It should be noted that the outer borders of such envelope of motion, are known as “border movements”, and the inner area of this envelope is known as “intraborder movements” (Fig.6). Border movements are important in recording mandibular movements as they are; recordable and reproducible. Fig.6 2- Protrusive movements: During protrusion the condyle together with the articular disc as one unit move downwards and forwards along the glenoid fossa and the articular eminence (Fig.7). It should be noted that protrusion in dentulous patients is mainly dictated by the sliding of incisal edges of mandibular anterior teeth, on the palatal concavities of maxillary anterior teeth (Fig.8). While in edentulous cases such movement is dictated by the sliding of the condyle on the posterior wall of the eminence. 89  CHAPTER VI MANDIBULAR MOVEMENTS 3- Retrusive movement: The retrusive movement of the mandible takes place by similar movement as the protrusive one but in the reverse direction i.e. upward and backward along the same inclinations. Fig 7: Condyle position, A- centric and hinge position. B- protrusion and translation position. Incisal path Fig 8: The maxillary surface of movement area in the median plan 1- retruded contact position. 2- habitual intercuspal position. 3- Edge to edge occlusion. 4- Anterior biting to a vertical overlap. 5- Protruded contact position. The muscles responsible for the forward movement ofthe mandible are the lateral pterygoid muscles of both sides acting together. 4- Lateral (Right and left) movements: (Fig. 9) The side towards which the mandible moves is called the working side or the bolus side, while the opposite side is called the non-working, non-bolus or the balancing side. a. Working condyle movement (laterotrusion): The condyle rotates mainly around the vertical axis and at the end of the movement a lateral bodily shift occurs which is known asBody Side shift or Bennett’s movement. 89  CHAPTER VI MANDIBULAR MOVEMENTS b. Balancing condyle movement (mediotrusive): The balancing condyle moves forwards, downwards and inwards (medially). Lateral movement of the mandible is the result of contraction of one lateral pterygoid muscle. When the lateral pterygoid muscle of one side contracts the mandible moves to the opposite side. W B Lateral Movement (Bennett Shift) Lateral Movement(Bennett Angle) Fig 9: Lateral condylar path is the path traveled by the condyles in the temporomandibular joint when the mandible is carried laterally in lateral movement. Bennet movement It is the lateral bodily shift of the mandible resulting from movements of the condyles along the lateral inclines of the mandibular fossae in lateral jaw movement N.B: Lateral movement due to contraction of one lateral ptregoid muscle When it contract , the mandible moves to other side 89  CHAPTER VI MANDIBULAR MOVEMENTS Viewing the Sagittal plane is described as “Beak” shap or posselt diagram Viewing the Horizontal plane is described as “diamond” shape. Viewing the Frontal Plane is described as a “shield” diagram. ENVELOPE OF MOTION By combining Mandibular border movements in three planes, a 3-D envelope of motion can be produced that represents the maximum range of movement of the mandible. Why do we need to know mandibular movements? The complete denture prosthesis is constructed to function in the dynamic conditions of the oral cavity. It is relevant to understand and record such movements to accomplish harmony between the denture andmandibular movements. 1. Christensen Phenomenon: - When the mandible moves to an edge to edge position, separation occurs distally between the maxillary and mandibular teeth or occlusal rims.(Fig 10) due to down movement of the condyle. - Protrusive record is taken with pink baseplate wax (Fig.11). - The mandible is brought forward in a straight protrusive direction about 4-6 mm in distance, and the patient closes on the softened wax. - The record is then brought to the articulator, where it is used to set the condylar inclination (Fig.13). 89  CHAPTER VI MANDIBULAR MOVEMENTS - In denture need to make balancing contact (no space in posterior teeth) - And then incisal inclination can be set by the dentist according to esthetics and phonetics requirements. Balancing contact: at least 3 point contact between anterior and posterior teeth in denture Fig.10: Christensen Phenomenon: In protrusive relationship, the anterior teeth disengage the posterior teeth. b: In complete dentures, when cusp teeth are used, the anterior teeth should not disengage the posterior teeth during protrusive or lateral excursions. It is necessary to use a positive incisal guidance to obtain balance as illustrated. Fig. 11 a: The occlusion rims are reestablished and checked for 3mm. Clearance in a protrusive excursion. b: The protrusive relationship determines the angle of the horizontal condylar path. 2. Condylar path: It is the path traveled by the condyles in the temporomandibular joint during various mandibular movements. 1. Saggital (horizontal) condylar path: The path taken by the condyle during protrusion and retrusion (Fig.12). 2. Lateral condylar path: The path taken by the condyle during lateral movement (Fig.9). The condylar path inclinations vary in different individuals and from side to side in the same individual. The condylar path inclination depends upon: 89  CHAPTER VI MANDIBULAR MOVEMENTS i. The shape of the glenoid fossa. ii. Thickness of the articular disc. iii. Relation of the condyle to the disc during movement. iv. The extent of mandibular movement. 3. Condylar path angle: It is the angle formed between the condylar path and the horizontal plane, itincludes: 1. Horizontal condylar path angles, is formed by the horizontal path andthe horizontal plane (Fig 12). 2. Lateral condylar path angles, is formed by the lateral path and thehorizontal plane (Fig 9). 4. Condylar guidance: Fig 12: 1-Condylar path. 2- Horizontal plane. 3- The condylar path angle. The simulation of the condylar path on the articulator (Fig 13, 14). 5. Incisal path: It is the path taken by the incisal edges of the mandibular incisors on the palatal surface of the maxillary incisors until the mandible exhibit maximum protrusion. Fig 13: Diagrammatic representation of the articulator, including the condylar and incisal guidance. 89  CHAPTER VI MANDIBULAR MOVEMENTS a b Fig. 14 a,b: Adjustment of the horizontal condylar path angle. 6. Incisal angle: It is the angle between a line extending through the incisal edges of maxillary and mandibular anterior teeth and the horizontal plane (Fig.15) or - The incisal angle depends upon: 1- The amount of vertical overlap (overbite) and 2- Horizontal overlap (overjet). The greater the amount of vertical overlap, the greater the incisal angle, the greater the amount of horizontal overlap, the lesser the incisal angle. a) Overjet (H) inversely proportion with Incisal angle b) Overbite (V) directly proportion with Incisal angle 89  CHAPTER VI MANDIBULAR MOVEMENTS 7. Incisal guidance: The simulation of the incisal paths on the articulator (Fig 13). (1 ) (2) (3) Fig 15: By keeping the vertical overlap constant and changing the horizontal overlapthe incisal angle changes. 1- Steep incisal angle. 2- Shallow incisal angle. 3- Very shallow incisal angle. 8. Bennett movement and angle: Bennett movement is the lateral bodily movement or lateral shift of the mandible resulting from movements of the condyles along the lateral inclines of the mandibular fossae in lateral jaw movement. Bennett angle refers to the angle at which the non-working condyle moves inward during a lateral excursion, measured in degrees against the sagittal plane. The Bennett angle is the same as the progressive side shift in degrees. On an articulator, the Bennett angle is seen in the angulation of the medial wall of the condylar guide assembly (Fig. 9). 9. Gothic arch tracing (Border Movements in the Horizontal Plane): A tracing device designed for recording horizontal plane border movements, is called a Gothic arch tracer. It consists of a horizontal recording plate attached to the maxillary arch, and a stylus attached to themandibular arch. 89  CHAPTER VI MANDIBULAR MOVEMENTS The teeth or occlusion blocks are kept out of contact by the stylus touching the plate so that they do not interfere with the movement of the mandible (Fig.16). Graphic registration of the lateral border movement on horizontal plane results in tracing called "Gothic arch" or arrow point tracing. R a b Fig. 16 a: Gothic arch. b: Gothic arch or arrow point tracing. RCP. Retrudedcentric position. R. Right lateral position. L. Left lateral position.. Protrusive position. 10. Pantographic tracings: A pantographic tracing is made by the use of the pantograph (fully adjustable articulators) to record lateral and protrusive excursions. Tracing the exact movements made by the mandible to register the exact direction and path and amount of those movements. a b c Fig. 19 a-c: Pantographic recording For fully adjustable articulator 89