principles of occlusion Flashcards
Occlusion
- act or process of closure or of being closed of shut off (without inclusion of teeth)
- static relation between the incising or masticating surfaces of the maxillary or mandibular or tooth analogues (with inclusion of teeth)
- i.e. closure of the mouth until teeth come into contact
ICP intercuspal position
- complete intercuspation of the opposing teeth independent of condylar position, sometimes referred as the best fit of the teeth regardless of condylar position
- i.e. habitual bite
Physiologic rest position
- the postural position. of the mandible when an individual is resting comfortably in an upright position and the associated muscles are in a state of minimal contractual activity
- position of jaw when we are comfortable, teeth are not together during the day, mandible is resting in a position
vertical dimension
- distance between two seated anatomic or marked points (usually one on the tip of the nose and other on the chin)
resting vertical dimension
- same points, whilst jaw is in physiological rest position
occlusal vertical dimension
- same points, ask patient to close together into ICP
what is the free way space on average
2-4mm
what is freeway spac
space between two positoons
VD-OVD = FWS
types of excursions
protrusion
latterotrusion
recursion (posterior movement of jaw_
Laterial excursion sub types
mediotrusion
laterotrusion
mediotrusion
side moving towards the midline
laterotrsusion
side moving away from the midline
what happens in the Codyls during lateral excursion
mediotrusion
- condyle moves out from the glenoid bossa onto articular eminane
laterotrusion
- condyle remains on fossa purely rotates
centric relation
- Maxillomandibular relationship, independent of tooth contact, in which the condyles articulate in the anterior superior position against the posterior slopes of the articular eminences, in this position the mandible restricted to a purely rotary movement
- i.e. a maxillomandibular relationship not a tooth based position, relationship when the condyles are in the glenoid fossa in the anterior and superior position, against the posterior surface of the articular eminence
RCP
- contact of a tooth or teeth along the retruded path of closure, initial contact of a tooth or teeth during closure around the transverse horizontal axis
- tooth contact whilst mandible is in CR, condyle is in the glenoid fossa, unstrained and comfortable, as the jaw closes RCP is the first tooth contact that occurs
RCP vs iCP
RCP is tooth contact whist mandible is in centric relation
ICP is habitual bite, tooth contact when we close toegher
mandibular rest postions
Physiologic rest position CR mandibular protrusion Mandibular laterotrusion LVD
tooth contact relationships
ICP
Tooth contacts during protrusive excursions
RCP
OVD
anterior guidance and poster guidance
Pathway taken by the mandible is guided anteriorly by the teeth (anterior guidance) and also by the condyles (posterior guidance)
why is anterior guidance with incisors better
incisors further from the hinge therefore load is reduced
morhoplogy - longer roots help in distributing lateral loads rather than facial or compressive loads on posterior teeth in ICP
anterior guidance in anterior open bites
reverse and large overset involves posterior teeth
Ideal protrusion steps
- anterior teeth come into contact and guide the mandible anteriorly
- condyle comes out of the glenoid fossa and onto the articular eminence
- typically causes posterior teeth to disclude (christensens phenonmenon)
- This is ideal as posterior teeth are not ideal to revive lateral loads in mandibular movements and are closer to the hinge, therefore would receive higher loads
lateral excursion teeth used
canines
- when this occurs the canines (in contact) guide on the working side only (side which the jaw is moving to), all other teeth are discluded
- Most optimum anterior guidance relationship in lateral excursions
why is canine guidance for lateral ideal
1) Morphology
- very strong tooth with long roots
2) Favourable crown to root ratio
3) distant from the hinge of the mandible
4) distance from the powerful muscles of mastication
group function
canine guidance not always present
guidance provided by a number of teeth on the working side
no contacts on balancing side
significance of RCP
often only involved 2 opposing teeth
- these teeth carry all load of occlusion when patientslides from RCP to ICP (vice versa)
if these are unrestored tsound teeth no problem, restored failure of restoration is liekly
classifications of occlusion
skeletal
incisor
angle
skeletal classification of occlusion
relationship between md and mx
no association to teeth
incisor classification of occlusion
class 1/2/3 nbeween incisors
Angle classification of occlusion
molar relationship between upper 1st molar and lower 1st molar
ideal occlusion (e.g. one to make dentures)
1) Multiple simultaneous contact
2) no cuspal incline contact
3) occlusal contacts that are in line with long axis of the tooth
4) ICP=CR
5) Anterior guidance on anterior teeth (canine during lateral excursions, anterior during protrusion) and posterior disclusion
6) Mutually protected occlusion
mutually protected occlusion
posterior teeth protect anterior in ICP
anterior protect poster teeth during excursions
why are the anterior teeth capable of taking load whilst in protrusive excursion
- ther are the furtherest away from the hinge of the mandible and therefore the force exerted is limited
- they are distant from the massester and therefore the force exerted is limited
High restorations can lead to
- Patient discomfort/pain (muscle soreness, pain on biting, headache)
- tooth fracture
- tooth mobility
- additional time and money
- professional pride?
what happens if a restoration is not in occlusion
- tooth drifting
- overeruption (teeth continue to erupt until they reach a contact
- further occlusal issues may stem from this (interferences or suboptimal contacts)
restoration aims
- Contact in ICP
- Maintaining contacts on all other teeth (not changing the occlusal schemes)
- fitting our restoration within the existing scheme
- contact in protrusion or laterotrusion, in most cases no unless the tooth previously had these contacts
how to measure occlusion
- mark up occlusion with articulating paper
- use of shimstock foil to feel contacts between the teeth
May also measure - skeletal/incisor/angle classifications
- signs of occlusion issues (wear facets, craze or fracture lines, fremintus)
- OVD (occlusal vertical dimension) – can often be decreased due to tooth wear
Additional record taking
- photographs
- impression and mounting of study models on an articulator
- facebow record (generally used if we are restoring num. of teeth that are involved in the occlusal movements)
