occlusion and restorative dentistry 1 Flashcards
define occlusion
how the teeth meet
what is the TMJ
The TMJ is the joint between the condylar head of the mandible and the mandibular fossa of the temporal bone
TMJ is a synovial, condylar and hinge-type joint
what are the different parts of the TMJ
- Cranial base
- Mandible
- Muscles of mastication
- Innervation
- Vascular supply
- Articular disc
what are the superior and inferior articular cavities lined by
The superior and inferior articular cavities are lined by separate superior and inferior synovial membranes
what is the capsule
The capsule is a fibrous membrane that surrounds the joint and attaches to the articular eminence, the articular disc and the neck of the mandibular condyle
what is the articular disc
The articular disc is a fibrous extension of the capsule that runs between the two articular surfaces of the TMJ
what does the articular disc articulate with
The disc articulates with the mandibular fossa of the temporal bone above and the condyle of the mandible below
how is the disc attached to the condyle
The disc is also attached to the condyle medially and laterally by the collateral ligaments
what does the anterior disc attach to
The anterior disc attaches to the joint capsule and the superior head of the lateral pterygoid muscle
what does the posterior disc attach to
The posterior portion attaches to the mandibular fossa and is referred to as retro-discal tissue
what is the retro-discal tissue like
Unlike the disc itself the retro-discal tissue is vascular and highly innervated and is a major contributor in the pain of TMD
what muscle groups are involved in the mandibular movement
• Muscles of Mastication
• Suprahyoid Muscles ○ Elevate the hyoid bone or depress the mandible ○ Suprahyoids are the: § Digastric § Geniohyoid □ These 2 depress the mandible and elevates the hyoid § Stylohyoid □ Initiates swallowing by pulling the hyoid bone posterior superior § Mylohyoid muscles Elevates the hyoid bone and the floor of the mouth
what mandibular movement does the muscles of mastication cause
Involved in depression, elevation and lateral movements of the mandible
what are the suprahyoid muscles
§ Digastric § Geniohyoid □ These 2 depress the mandible and elevates the hyoid § Stylohyoid § Mylohyoid muscles
how does the stylohyoid muscle iniates swallowing
Initiates swallowing by pulling the hyoid bone posterior superior
what does the mylohyoid muscle do
Elevates the hyoid bone and the floor of the mouth
what mandibular movement does the suprahyoid muscles cause
Elevate the hyoid bone or depress the mandible
what is the function of the temporalis
Elevates and retracts the mandible
Assists in rotation
Elevates the mandible closing the mouth and also retracts the mandible pulling the jaw posteriorly
where is the temporalis muscle found
Originates from the temporal fossa and condenses into a tendon which inserts onto the coronoid process of the mandible
what are the functions of the lateral pterygoid muscle
Positions disc in closing (superior - SLP)
Protrudes and depresses mandible and causes lateral movement (inferior - ILP)
Unilateral action produces a side to side or lateral movement of the jaw
where does the superior head originate from
Superior head originates from the greater wing of the sphenoid
where does the inferior head originate from
Inferior head originates from the lateral pterygoid plate of the sphenoid
where do the 2 heads of the lateral pterygoid muscle converge
The 2 heads converge into a tendon which attaches at the neck of the mandible
what are the functions of the medial pterygoid muscle
Elevates the mandible
Lateral movement and protrusion
where does the superficial head of the medial pterygoid muscle originate from
The superficial head originates from the maxillary tuberosity and the pyramidal process of the palatine bone
where does the deep head of the medial pterygoid muscle originate from
The deep head originates from the medial aspect of the lateral pterygoid plate of the sphenoid bone
where do the heads of the medial pterygoid muscle attach to
Both heads attach to the ramus of the mandible near the angle of the mandible
what are the functions of the masseter muscle
Elevates and protracts the mandible
Assists in lateral movement
where do the superficial and deep parts of the masseter muscle originate from
Superficial part originates from the maxillary process of the zygomatic bone
The deep part originates from the zygomatic arch of the temporal bone
what does the masseter muscle attach to
Both parts attach to the ramus of the mandible
what are the 2 major types of mandibular movement in terms of occlusion
- rotation
- translocation (lateral translation)
what is rotation movement
- Small amount of mouth opening (up to 20mm)
- Condyle and disc remains within the articular fossa
- No downwards or forwards movement
- Also known as “hinge movement”
what is the rest position of the TMJ
The resting position of the TMJ is with the mouth slightly open, lips together and the teeth not in contact
○ Resting vertical dimension
○ The space between the teeth is the free-way space
what can be measured when the patients clench their teeth in a closed-pack position ie teeth are closely clenched
Occlusal vertical dimension
what happens when the mouth is opened just a small amount (20mm)
When the mouth is opened just a small amount (20mm) the condyle hinges within the articular fossa
There is no downwards or forwards movement ~ no protrusion
what are hinge movements
Rotation of the condylar heads around an imaginary horizontal line through the rotational centres of the condyles
The imaginary line is termed the terminal hinge axis
what does a facebow record
Terminal hinge axis
Distance between the condyles
what is a facebow
It allows a maxillary cast to be placed in an equivalent relationship on the articulator
what does using a facebow allow for
a facebow is a caliper like instrument that records the relationship of the maxilla to the terminal hinge axis of rotation of the mandible
what is translation
- Lateral pterygoid contracts
- Articular disc and condyle begin to move
- Travels downwards and forwards along the incline of the articular eminence
- May also travel laterally (laterotrusive movement)
what does posselts envelope show
Extremes of mandibular movement
Border movements of the mandible in the Sagittal Plane
what are the different points on posselts envelope
ICP = Intercuspal Position E = Edge to Edge Pr = Protrusion T = maximum opening R = Retruded Axis Position RCP = Retruded Contact Position
what is ICP
Intercuspal Postion (ICP)
• Tooth position regardless of the condylar position
• The comfortable bite
• Best fit of teeth
= maximum interdigitation of the teeth
what else can ICP be called
• Can be called centric occlusion (CO)
what is edge to edge
- Tooth position
- Teeth slide forward from ICP guiding on palatal surfaces of anterior teeth
- Incisal edges of upper and lower incisors touch
what is protrusion
- Condylar moves forwards and downwards on articular eminence
- Only incisors + / - canines touch
- No posterior tooth contacts
- Eventually no tooth contacts
what is maximum opening
- No tooth contacts
- Mouth wide open
- Full translation of the condyle over the articular eminence
what is the retruded axis position
- No tooth contacts
- Most superior anterior position of the condylar head in the fossa
- Terminal hinge axis
what is the retruded contact position
- First tooth contact when the mandible is in retruded axis position
- ICP is approximately 1mm anterior to RCP in 90% of the population
what is the relation of the ICP to the RCP
ICP is approximately 1mm anterior to RCP in 90% of the population
RCP and ICP not coincident so the mandible slides forward to achieve ICP
what is lateral translation
When the lateral pterygoid muscle on one side contracts the mandible moves to the opposite side
The bony wall of the glenoid fossa stops the working side condyle moving any further to the right
the side the mandible moves towards is the working side
the side the mandible is moving away from is the non-working side
eg When the mandible is moving to the right, the left condyle moves forward and inward
Whilst the condyle on the right will shift slightly in a lateroposterior direction (or rotate on a vertical axis)
what is lateral translation of the mandible known as
This slight lateral translation of the mandible is known as the Bennet movement (bodily shift of the mandible at the working side)
what is the bennet angle
The path of the non-working condyle in the horizontal plane during lateral excursion
The Bennet angle is the angle formed by the Sagittal plane and the path of the mandibular condyle during lateral movement when viewed in a horizontal plane
what is the frontal plane
• ICP is maximum intercuspation
• PP is the physiological rest position with no tooth contacts
• Divets are a result of canine guidance
○ When the mandible is moving laterally the long strong canines of the upper and lower jaw ensure that the posterior teeth do not touch when the mandible is sliding to the side
○ This protects them from lateral forces and gives rise to the term a mutually protected occlusion
