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Lower supporting cusps on the laterotrusion side mostly track out ______ from their ICP holding contacts:
- straight laterally
- due to geometry of rotation of the working side condyle about its vertical and sagittal axes, AND the arcs of movement of each mandibular cusp about these axes
- usually not a Problem to space the upper guiding cusps to allow the easy tracking of the lower supporting cusps, without introducing ocllusal interferences
Laterotrusion exit pathways are aligned in _____ to exit laterally.
embrasures and molar buccal groves
laterotrusion contacts are common between the _____ occlusal aspects of the upper guiding cusps against the functional outer aspects of lower supporting cusps.
lingual cusps of working side (functional outer aspect of upper supporting cusps against inner occlusal aspects of lower guiding cusps
how are molar laterotrusion contacts or interferences adjusted?
- reshaping the upper guiding cusps
- no effect on ICP
- contact stability provided that ICP contacts are marked first and only guiding inclines are reshaped.
What is essential in reducing liklihood of laterotrusion interferenes in indirect restorations?
establish better molar cusp alignment even if distorted from normal anatomy.
canine guidence vs group function
- canine: all disclusion provded by canines w absent posterior tooth contacts in laterotrusion when cusps leave their ICP occlusal holding contacts
- group: canines & premolars shared guidance, disclusion in molars, no contralateral side contacts in mediotrusion
What must be done for group function guidence?
modify lower supporting cusps and upper guiding cusps positions & lengths to come into shared guidance contact at the upper bucal cusp to lower buccal cusp position when the casts are held in laterotrusion vs. the standad cone placement to avoid all posterior excursion contact,leaving the canines to provide all the disclusion by canine guidance
in left lateral movement what is the movement of right condyle?
- non-working side condyle rotates about the vertical and sagittal axes of the working-side condyle in this left lateral jaw movement, AND the arcs of movement of each right side mandibular cusp also rotates about these axes.
- Lower supporting cusps on the right side are tracking out foruard and downwards (which is OK) However they are also tracking MEDIALLY and this places them close to being in opposing contact with the lingual part of the upper right molars: and potential occlusal interference
What opposing occlusal surfaces are most likely to come into occlusal contact or occlusal interference in mediotrusion?
- inner occlusal aspects of supporting cusp ridges
- ex: opposing triangular ridges
- risk increases with increased curve of Wilson
Method for drawing picket fence
- 1. 18 Line W for upper (C to M3)
- 2. add line to create lower canine
- 3. divert ICP contacts of upper premolar supporting (lingual cusp to make DISTAL FOSSA CONTACTS) on lower premolars
exit pathway arrow points at a right angle to the line of the dental arch
- laterotrusion side movement
- working side
exit pathway arrow is oblique,
- non-working side
What cusps do the arrows represent on upper occlusion illustration?
- mandibular cusp that is moving, which is therefore moving in the actual (real) direction that the jaw is moving in.
- The cusp pathway & jaw are moving in the same direction, ls this a ? right or ? left, or ?protrusive, ? or retrusive, jaw movement
What cusps do the arrows represent on lower occlusion illustration?
- maxillarycusp that is moving, which is therefore in fact stationary and left behind to track out in the opposite direction to the real direction the Jaw is moving in.
- Therefore the cusp pathway & jaw are moving in the exact opposite directions. Is this a ? right or ? left, or ? protrusive or retrusive
In developing occlusion what are the problems focused on?
- 40% placement of cusps (to optimize axial loading)
- 60% how the cusps ate going to "get out of there l exit from ICP) without running into or creating eccentric contacts and occlusal intetferences (non-axial forces)
- Think "grooves" rather than just cusps!
The requirement is to stabilize each tooth (and crown restoration) overall(rather than every cusp) requires ___
- 1. coupled contacts involving opposing supporting cusps
- 2. >3 points of ICP contact involving different planes -not necessarily around a single cusp
- 3. intact dental arch with contacts at right angles to the line of the arch.
- 4. provide single stable end point of jaw closure (aka ICP)
Central Fossa Lines are a _____ of all the central fossa grooves
How do you keep the predominant loading on posterior teeth axial?
- COUPLED CONTACT
- supporting cusps of lower molars and premolars(buccal cusps) occlude along the central fossa line of the upper teeth
- supporting cusps of upper molars and premolars(lingual cusps) occlude along the central fossa line ofthe lower posterior teeth
relative facial location of the upper lingual cusps and the relative lingual location of the lower buccal cusps(due to the rounding over ofthese cusps) maintains the loading on the teeth axially
Do cusp tips make ICP contact?
no, parabolic form, shouldn't be involved in excursion guidance either
advantages of small ICP contacts against parabolic ridges using the drop wax technique
- Easier separation and immediate disclusion from ICP in excursion movements
- Less chance of occlusal interferences
- Less wear due to absence of contact during jaw movement:::
- Axially directed forces
- (hard to get in porcelain)
Broad flat ICP contacts lead to:
- zone of ICP contact
- Lack of immediate disclusion* from ICP in excursion movements
- more chance of occlusal interferences
- More wear due to more movement in contact More non axial forces
What increases likelihood of creating broad contacts?
- 1. carving with blade shaped instruments
- ghost over cut surfaces with a hot PKT probe instrument to re-melt the wax cusp incline back into a natural parabolic surface and contact again,:.
- 2. Direct restorations
- 3. New castings made against an existing worn occlusion(that has not been therapeutlcally reshaped [to be determined in the diagnostic wax-up stagel
- 4. Relieve occlusal contact (fossa or developmental groove area on cusp tips
Consequence of uncoupled contact
- could expose crown margin
what is phony coupled contact?
- only occluding contactts are on opposing inclines facing same direction
- -> drift
what is the problem with cusp to open-fossa contacts?
- faster functional and parafunctional wear or holding tips
- receive most eccentric contact
- (common in direct restorations)
What is the acid test?
cut the canines off the dental casts and examine whether you can put the casts into a single Intercuspal Occlusion, or whether there isc onfusion multiple positions
What are some problems with flattened posterior anatomy
- cant find ICP
- wide envelope of proprioception feed back
Lower supporting cusps occlude along ____ in ICP and are also in alignment _____.
- opposing central fossa line
- alignment facially
- lower molars wider than premolars therefore the lingual cusp tip cones MUST BE PLACED MORE LINGUAL THAN THE PREMOLAR LINGUAL CUSP CONES
overwidening lower crowns periodontally leads to:
non-axial forces (especially with over contoured PFM from insufficient reduction.
Why do you keep lingusal cusp tip wax cones of lower molars wide?
form open lingual groove exit-pathway for upper molar ML cusp in laterotrusion
Which upper cusps of molars are aligned along lingual occlusal line?
- ML (almost as if mesial molar is premolar)
- occlude along lower central fossa line
- lingual cusp ridge at rt angle with buccal cusp ridge of ML cusp
oblique ridge made from:
- distal cusp ridge (wrap around) of ML
- triangualr ridge of DB cusp
What creates the central fossa of a max molar?
- ML cusp triangular ridge
- MB cusp triangular ridge
- oblique ridge
What is formed from 2 ridges meeting?
What is the purpose of normal inter occlusal spaces or fossa w/o occluding cusps?
pestle & mortar for mastication displacement up out and away from interproximal ebrasures.
goals of occlusion
- 1. stabilize each tooth (tripoding)
- 2. stable/single most closed end point of jaw closure (ICP)
- 3. ICP loading forces axially
- 4. cusps placed to optimize movement/exit pathways reduce non-axial loading in excursion
Which teeth don't oppose 2 teeth in ICP?
- most distal upper molar
- lower central incisionrs
in Class I ICP all lower supporting cusps make ____ ICP contacts except for ____
- marginal ridge
- except lower DB which make central fossa and lower 1st D which make distal fossa contact
Class I ICP, upper supporting cusps make ____ ICP contacts?
- premolars make D fossa
- molars make central
- excep molar D cusps with make marginal ridge contacts
In class I, how are the L cusps of upper premolars positioned?
slightly mesial to make lower D fossa contact
Class II adjustment
- move mandible distal
How are molar laterotrusion contacts or interferences adjested?
reshaping upper guiding cusp inclines
- any tooth contact that inhibits the
- remaining occluding surfaces from achieving stable and harmonious contacts. (In an excursion contact position, anterior guidance would be interrupted by the interference and.transferred to the interfering posterior cusp for disclusion guidance; or be an occlusal contact that interferes with full closure into ICP, or interferes with the closure pathway into ICP'Posterior occlusal interference may encourage recruitment of full closing power of the jaw elevator muscles leading to primary occlusal trauma on the hard and supporting dental tissues' but inonlv a few susceDtible cases to myalgia. Most patients.adapt byalt"ri", th"*f"* position on closure or in the masticatory cycleto avoii an interference in function (e.9. on a new crown)'Avoidance of ICP occlusal interferences may be more difficult than avoiding excursion interferences. Contact patterns during sleep bruxism-may be different. However the notion that occlusal interferences are the etiotogy of bruxism and of TMD, and that TMD should be treated by coronoplasty or other occlusal changes is incorrect,and these are much more complex multifactor disease entities
eccentric occlusal contacts
- shared or mutual occlusal contacts (not at ICP) in a contact jaw movement, that do not disclude the anterior guidance or act as apivoting interference or fulcrum. However, more contacts may mean more occlusal attrition. Eccentric occlusal contacts "every way which way" is a goal oF denture
- Balannd Occluion
condition in centric and^eccentric jaw relation in which there are no interceptive or deflective contacts of occluding surfaces (and there is a progressive gradual disclusion rather than overly steep or abrupt anterior guidance)
occlusal interference posterior eeth
- supra-contact interferes with other teeth coming into ICP
- high contacdt in eccentric that interferes with anterior guidance
The resistance permits maximum recruitment of muscle force, which likely produces (non-axial) occlusal trauma to the tooth involved,eld may act as a fulcrum that increases loadon the contralateral TM ,oint + CA!! recruit perticular jaw muscle pain.
difference between providing disclusion vs. balanced occlusion orocclusal interferences
- Disclusion is direcdy impaired by an absence of orworn out anterior guidance (loss of disclusion occlusion)
- Careless setting of an articulator
- Creating monoplane occlusions
- Careless placement of supporting cusps, and leaving cusps out of contact (teeth witl rip md rotate over time to re-establish ICP contact but beingh interference in excursion jawmovements