Group 5 assignment 7

GROUP 5 ASSIGNMENT

OBASANYA Adedotun Augustine-DEN/2007/051 (CHAIRMAN)

OGUNLOLA Omowumi Abosede-DEN/2007/057 (SECRETARY)

DADA Babatunde- DEN/2007/036

OKUNOLA Ibukunoluwa Esther- DEN/2007/063

IWEGBU Samuel Enere -DEN/2007/046

JAW MOVEMENTS AND POSITIONS

MANDIBLE It is the largest and strongest bone of the face. It develops from the first pharyngeal arch. It has a horse - shoe body which lodges the teeth, and a pair of rami which projects upwards from the posterior ends of the body and provide attachments to musclesTo study mandibular movement one should have knowledge about anatomy of temporomandibular joint, function and neurophysiology of masticatory system and mechanism of mandibular movement.

Introduction

Temporomandibular joint

The temporomandibular joint, or TMJ, connects the lower jaw called the mandible, to the temporal bone at the side of the head. There are two temporomandibular joints, one on each side of the jaw.

Since TMJ are flexible, the jaw can move smoothly up and down and side to side, allowing us to talk, chew and yawn.

Muscles attached to, and surrounding the joint, control its position and movement


When opening the mouth, the rounded ends of the lower jaw joint, called condyle, glide along the joint socket of the temporal bone The condyle slide back to their original position when we close our mouth

Articular disc divides the joint cavity into upper and lower cavities

Mandibular notch

MovementsProtrusion or protraction, Retraction, Depression, Elevation


Muscles involved are known as muscles of mastication. Muscles of mastication are –temporalis, masseter, lateral pterygoid (L Pt), Medial pterygoid( M Pt)

Protraction is brought about by lateral pterygoid assisted by medial pterygoid


Retraction by posterior fibers of temporalis

•Elevation-temporalis , masseter and medial pterygoid

Lateral chewing movements-alternately protruding and retracting the mandible on each side with a certain amount of rotation

Determination of mandibular movements

Factors that determine mandibular movements are:1. Condylar guidance2. Incisal guidance3. Neuromuscular factors

Condylar guidance(posterior determinant) It can be defined as the mandibular

guidance generated by the condyle and articular disc traversing the contour of the glenoid fossa.

The condyle moves along the glenoid fossa during mandibular movements . Hence, the surface of the glenoid fossa determines the path of movement of the condyle.

The slope of the glenoid fossa is a S-bend, hence the condyle moves along a S-shaped path.

Incisal Guidance(anterior determinant) It is defined as the influence of the contacting

surfaces of the mandibular and the maxillary teeth during mandibular movements.

During protrusion, the incisal edge of the lower anteriors slide along the slope of the lingual surface of the upper anterior teeth before reaching edge-to-edge contact.

The incisal guidance is absent in a completely edentulous patient. It is reproduced in the complete denture by arbitrarily setting the anteriors using a standard incisal guide value and modifying to suit the patient during aesthetic anterior try-in.

Neuromuscular factors

The muscles of mastication are the most important determinants of mandibular movements.

Many neurological disorder like parkinsonism produce muscle dysfunction

Each muscle has a specific action on the mandible

The movement of the mandible in any direction is predominantly controlled by one particular muscle and is coordinated by the remaining.

When there is hypertrophy or dysfunction of one group of muscles, the movement of the mandible is un-coordinated and asymmetrical.

MECHANISM OF MANDIBULAR MOVEMENT

Mandibular movement occurs as a complex series of interrelated three dimensional rotation and transitional activities. It is determined by combined and simultaneous activities of both temporomandibular joints. Although the TMJ is cannot function entirely independent of each other, they also rarely function with identical concurrent movement.

Types of mandibular movement

A. Based on the dimension involve in the movement.1. Rotation2. Translation

B. Based on the type of movement3. Hinge 4. Protrusion5. Retrusion6. Lateral movement

C. Based on the extent of movement7. Border movement8. Intra-border movement

CLASSIFICATION

Mandibular movement occur as a complex series of interrelated 3-D ROTATIONAL and TRANSLATION

activities.

Movements of the

mandible :

RotationalUpper

compartment

Translational

Lower compartme

nt

1) ROTATIONAL MOVEMENT• This is the movement of a body about its

axis”. • In the masticatory system, rotation occurs

when the mouth opens and closes around a fixed point or axis within the condyles.

• In TMJ, rotation occurs as the movement within the superior surface of the condyle and the inferior surface of articular disc.

• Rotational movement of mandible can occur In 3 ways(plane): horizontal , vertical/ frontal and saggital.

A) HORIZONTAL

1. Mandibular movement in horizontal axis is an opening and closing motion.

2. Know as hinge movement (example of mandibular activity In which a pure rotational movement occurs )

b) Frontal mandibular movement around the frontal axis occurs when one condyle moves anteriorly out of the terminal hinge position while the other vertical axis of the opposite condyle remains In the terminal hinge position.

because of the inclination of the articular eminece, which dictates the frontal axis tilt as the moving condyle travels anteriorly.

c) Saggital Occurs when one condyle

moves inferiorly while the other remains In the terminal hinge position.

because the ligaments and musculature of TMJ prevent an inferior displacement of the opposite condyle movements.

All these movements do not occur naturally, they occur in

conjunction with other movements.

2) TRANSLATION MOVEMENT

Define as: movement in “which each point of moving object has simultaneously the same direction and velocity”

In the masticatory system it occurs when the mandible moves forward as in protrusion.

Teeth, condyles and rami all move In the same direction and same degree.

occurs within the: superior cavity of the joint

between the superior surface of articular disc & inferior surface of articular fossa.

Based on the type of movement

1. Hinge movement This is a purely rotational movement

that takes place around a horizontal axis till the mouth is opened to about 20-25mm.

This kind of movement usually occurs while crushing food or taking in food. The hinge movement is produced by the action of the lateral pterygoid, suprahyoid muscle and is aided by gravity.

2. Protrusive movement It occurs while incising and grasping

food. This movement occurs after the condyle rotates for more than 13⁰ in the temporomandibular joint.

When the mandible slides forward and the mandibular and maxillary anterior teeth are in edge to edge relation, the protrusive movement is said to be complete.

3. Retrusive movement It occurs when the mandible is forcefully moved behind its centric relation. It is usually not a common movement and the patient cannot voluntarily produce it.

4. Lateral movements They are of two typesa) Lateral rotation or laterotrusionb) Bennett movement

Lateral rotation:-This is said to occur when the mandible moves away from the mid-sagittal plane either on the left or the right. It should be noted that when the mandible moves laterally, the condyles on both sides do not share the same path of movement.

Simply put Lateral movement of mandible occurs when one condyle rotates within TM fossa and the other condyle translates forward and inward. The translating condyle is called the non-working condyle and the rotating condyle is called the working condyle.

The direction of lateral movements is determined by external – pterygoid muscle on the non-working side and by deep capsular ligaments of the condyle on working side.

The right condyle is allowed only a small rotatory movement because its lateral pole is limit by TM ligament and cannot move backwards for more than 1mm.

Bennett in 1908 studied the working condylar path and called it ‘Bennett movement’ now referred to as laterotrusion. Bennett movement is a bodily side shift of mandible that occurs during lateral movement.

During lateral movement working condyle rotates and moves slightly outward. This movement is between 2-4 mm.

If the TM ligament of rotating condyle is very tight, there is no bodily side ship of the mandible and there fore no Bennett movement occurs.

Bennett movement

BENNETT ANGLE It is defined as the saggital plane and

the path of the advancing condyle during lateral mandibular movements as viewed in the horizontal plane.

This is the angle formed between the path of the non-working condyle and the saggital plane

It therefore moves forwards and medially in an arc around the opposite condyle while moving over the temporal bone

OVERBITE AND OVERJET

The majority of patients with natural dentitions have upper anterior teeth which overlap their opposite number in the lower jaw both

horizontally (‘overjet’) normal is 2mm

and vertically (‘overbite’), normal is 2mm

Base on the extent of movementBorder movement The maximum amount of movement in any

plane or direction is termed the border movement.

Within the confines of the border movements there is an extremely wide range of movement called intra-border movement. Most mandibular movement occurs as intra-border movements.

Function at the border limits is usually demonstrated during Para-functional activities such as bruxism or wide opening yawning.

Base on the extent of movement The border positions are limited by nerves

muscles and ligaments. Border movement demonstrates the

movement from centric occlusion backward to centric relation and forward to protrusive border movement. The lowermost point in the point of maximum opening from where the mandible can be taken to all border movements.

Border movements are recorded and measured because they are repeatedly reproducible.

Single Plane Border Movement

Sagittal plane border and functional movement

Horizontal plane border and functional movement

Frontal (vertical) border and functional movement

Sagittal Plane Border Movement


Posterior open border

Anterior open border Superior contact

border Functional

movements


Posterior open border movement


Anterior open border movement


Superior contact border movement


Superior contact border movement (cont.)


Functional movements

Horizontal Plane Border Movement

Left lateral border Continued left lateral border

with protrusion Right lateral border Continued right lateral border

with protrusion Functional movements


Left lateral border


Continued left lateral border with protrusion


Right lateral border


Continued right lateral border with protrusion

Envelope of motion

The “Full Envelope” of Hinge and Translatory Movements as viewed in the mid-saggital reference plane appears as a special “envelope-like figure” known as: POSSELTS ENVELOPE

Intra-border movement


- chewing cycle- Swallowing- Yawning- speech

Para-functional movement

- Clenching- Bruxism- Others

Functional movements Functional mandibular movement included

all natural and characteristic movement occurring during mastication, swallowing, speech and respiration.

Much of the functional movements of the mandible take place inside the physiologic limits established by teeth, TMJ, muscles and ligaments.

Among the functions of masticatory system swallowing and respiration are innate where as chewing and speech are learned.

Mastication Mastication is defined as the act of chewing. This act is

made up of rhythmic and well controlled separation and closure of maxillary and mandibular teeth. Each opening and closing of mandible represents a chewing stroke. The chewing movement in the frontal view has tear shaped pattern.

It can be divided into opening phase and closing phase. Closing phase is further divided into crushing phase and

grinding phase. While chewing, adults open their mouth to a comfortable distance and move the mandible in a forward direction until the edges of maxillary and mandibular teeth meet. The food bolus is then transported to the centre and mandible goes to its original position.

Children below 10 years begin their chewing stroke with lateral movement but after 10 years of age the chewing pattern varies and the stroke is more vertical.

Deglutition Deglutition or swallowing is an innate function. It

is starting point of peristaltic transport of food to stomach. This activity may be divided into-oral, pharyngeal and esophageal phases of which first is voluntary and other two one reflex.

In order that deglutition may be initiated, the air passage through mouth must be closed. The anterior seal is normally accomplished by the lips, but the edge and apex of the tongue may substitute in some cases.

During deglutition mandible is generally stabilized against maxilla by contraction of masseter and temporalis muscle. This results in contact of the upper and lower teeth.

Respiration The role of mouth in respiration is secondary to that of nasal cavity. If there is nasal obstruction, mouth becomes a primary respiratory passage. The mouth remains open, mandible depresses and the air passes through the mouth instead of the nose.

Speech The teeth, tongue, lips, floor of mouth

and soft palate form the resonance chamber that effects pronunciation.

During speech the teeth are generally not in contact although the anterior teeth may come very close together. During speech the various mandibular movements take place.

Para-functional Movements

Para-functional movements of the mandible are activities that serve no useful function and are potentially harmful to the dentition and its contagious structures. They can result in tooth mobility, migration, excessive wear or fracture, PDL widening. TMJ pain, muscle pain, restricted mandibular movements.

Bruxism Normal person masticate with chewing strokes that are well rounded, within definite borders, and less repeated.In bruxism the strokes are much shorter and slower and have an irregular but repeatable pathway appear to relate to the altered functional movement of the condyle which the disorder is centered.Bruxism may be due to habit, general stress, pain, exertion, anger, occlusal interference.

Clenching In vertical affort (clenching in centric

occlusion), most of the elevator muscles are activated maximally. In some subjects the medial pterygoid

muscle activity is low. The variation between subjects related

to occlusal contacts and musculoskeletal morphology.

The inferior head of the lateral pterygoid produces little activity or only 25 percent of maximum activity compared to the superior head.

Clenching Muscle activity decreases when

less posterior teeth only the incisors in contact

The digastric muscle slightly active during vertical effort

with intercuspal clenching more active during vertical incisive

clenching.

Jaw positions

Physiologic rest position The position assumed by mandible when the head is

in an upright position, the muscles are in equilibrium in tonic contraction and condyles are in a unstrained neutral position is the physiologic rest position of mandible.

The mandibular resting position is one of the earliest postural positions to be developed. The jaws are not clamped together but, they are separated by rather constant distance, even before there are any teeth in the mouth. Even though the muscles are not in active function, a limited number of fibers are apparently still contracting to maintain the relaxed position of the mandible and posture of the head.

Jaw positions The postural position can be altered by

conditions in the masticatory system as well as by systemic factors. Factors influencing the postural rest position are 1) Body and head posture.2) Sleep 3) Psychic factors influencing muscle tonus.4) Age 5) Proprioception from dentition and muscles6) Occlusal changes, such as attrition.7) Pain8) Muscle disease and muscle spasms.9) Temporomandibular joint disease.

Free-way space

This is referred to the space between the at rest.free -way space exist only at rest.

During occlusion,the teeth come in contact with one another and the space is lost.

Denture js fabricated in vertical dimension at occlusion so that the free-way space js formed

Rest Vertical Dimension(RVD)

It is defined as the length of the face when the mandibule is at rest

This is the position of the mandibule in relation to the maxilla when the maxillofacial musculature are in a state of tonic equilibrum.

This position is influenced by the muscles of mastication,muscles involved in speech, deglutition and breathing.

Rest vertical dimension acts as reference point during recording the occlusal vertical dimension(ovd)

Vd at rest=VD at occlusion+free-way space

Moving the head backwards tends to increase RVD, while tilting it forward has the opposite effect

Factors to consider when recording RVD

1. The position of the mandible is influenced by gravity and the posture of the head. Hence while recording the patient should be asked to sit upright with his/her head upright and eyes looking front.2. when recording all muscles affecting this record should be relaxed.3. presence of any neuromuscular disease in the patient can influence at rest position.

Method used to measure RVD

1. Facial measurements after swallowing and relaxing

2. tactile sense 3. measurement of anatomical

landmarks4. speech5. facial expression

Occlusal vertical dimension(OVD)

OVD is the length of the face when the teeth are in contact and the mandible is in centric relation

When the teeth are fully intercuspidated, the position is known as intercuspal position(IP)

The free-way space is at zero and the RVD is equal to the OVD.

Method of recording OVD

Mechanical

- Ridge relation- Pre-extraction record- Measurement from former

dentures

Physiological

- Using wax occlusal ring- Physiological rest

position- Phonetics- Aesthetics- Swallowing threshold- Tactile sense or

neuromuscular perception

- Patient perception of comfort

Centric relation Centric relation is the most posterior position of the mandible

relative to the maxilla at the established vertical dimension. The mandible is deviating neither to the right nor to the left and is

neither protruded nor retruded. The condyle and disc movement is negligible as the mandible closes the 3 to 4 mm inter-incisal clearance from postural rest position to centric occlusion. The centric relation does not require-occlusal contact.

Centric relation is not a resting or postural position of the mandible. Contraction of muscles is necessary to move and fix the mandible in it.The temporal, masseter and medial pterygoid muscles elevate mandible to a particular vertical relation with the maxilla.

The lateral pterygoid shows little activity when the mandible is in centric relation.

Goldman described centric relation as the intermaxillary relationship dictated by neuromuscular mechanism during functional act of swallowing.

Centric Occlusion Centric occlusion is relation of opposing

occlusal surfaces that provides maximum intercuspation or planned contact.

Centric relation is bone to bone relationship where as centric occlusion is a relationship of upper and lower teeth to each other. Once CR is established centric occlusion can be built to coincide with it or to provide a broad area of tooth contact in this position.

CHRISTENSEN PHENOMENON

When an edentulous patient protrudes the mandible with record rims in place, a space opens between them at the back of the mouth (Christensen phenomenon).

This gap is proportional to the condylar angle, and a wax wafer recording it may subsequently be used to set the condylar angle on an adjusted articulator.

When making this record the mandible should not be protruded so far as to bring the condyles over the articular eminences.

IMPORTANCE OF THE JAW POSITIONS IN EDENTULOUS PATIENTS

Edentulous patients have lost the proprioceptive feedback from the oral cavity.

Hence the dentist’s only landmarks are an estimate of the patient’ RVD and a determinant of the position of the RCP/RCA.

To build the occlusion for complete dentures these two landmarks are considered, any other observation being pure conjecture.

It is conventional to provide the patient with an IP on the RCP/RCA at vertical dimension slightly less than the RVD.

While in the natural dentition IP is often slightly in front of the RCP/RCA, it has been found that this system works well clinically.

Some dentists prefer to adjust the artificial dentition so that the patient may glide the mandible slightly forwards from the RCP with the teeth still evenly in contact.

CONCLUSION The mandibular movement is considered as the

chewing apparatus of masticatory system. It should be borne in mind that mandibular movements occurs besides mastication like biting, chewing swallowing, vomiting, breathing, speaking, singing, yawning, facial expressions.

In other words, it plays life promoting roles and other important roles in the digestive and respiratory acts, vocal performances and more or less every day human activities and behaviors.

Group 5 assignment 7

Spiritual

Transcript of Group 5 assignment 7