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mineral gypsum
Dihydrate Calcium Sulfate CaSO4*2H2O
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Gypsum Products
- Made through calcination
- Calcium Sulfate Hemihydrate CaSO4*1/2H2O
- CaSO4 • 2H2O + heat--> CaSO4 • 1/2 H2O
- General reaction:
- CaSO4 • 1/2 H2O + 11/2 H2O --> CaSO4 • 2 H2O + 3900 cal/gm mole
- EXOTHERMIC
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Expansion
- crystals->fibril network->expansion->decreased accuracy
- plaster .2-.3%
- stone .08-.1%
- improved (die) stone .05-.07%
- More water->less expansion
- More spatulation->increases expansion
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Water temperature
higher->faster
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Calcination
- water of crystallization or hydration is driven off
- 1. Heating open kettle 110-120C=Beta form CaSO4 * 1/2 H2O, porous irregular, impression plaster (some model)
- 2. Autoclave 130C=alpha form=dense regular, needle-like- model plaster & regular stone
- 3. Boiling in 30% CaCl2=alpha form, stubby, regular dense crystals= high-strength(improved, die) stones
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W/P ratios
- plaster .5
- stone .3
- improved die stone .2
- (less water, stronger)
- more water
- Longer setting
- Smaller expansion
- WEAKER
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Increasing spatulation
- decrease setting time
- increase expansion
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Optimum Occlusion (Okeson's)
- CR = ICP
- Axial loading of teeth
- Canine guidance laterally
- Anterior guidance protrusively
- Posterior contacts are heavier than anterior
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Condylar guidance
steep condylar path, taller posterior cusps may be
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anterior guidance
- mandibular incisor edge contact lingual of maxillary
- protrusive incisal inclination = 50-70 degrees
- steeper protrusive path, taller posterior cusps may be
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Horizontal overlap
- maxillary anteriormost to incisal edge of mandibular
- Greater HO, less steep the protrusive angle
- Greater VO, (mandibular incisal to maxillary incisal), the more steep protrusive angle
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Influence of posterior teeth disclusion (function)
- 1. anterior guidane
- 2. Condylar inclination angle (TMJ)
- closer to each the greater the effect
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Superior border movement
when CR=ICP
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Gypsum product strengths
- COMPRESSION (8X) Tensile
- DRY (2X) wet
- improved>stone>plaster
- Compression strenght similar to abrasion resistance
- Spatulation and temp have no strength effect
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Impression interference
- K2SO4, blood, saliva may interfere w setting
- sprinkle dry stone on impression then rinse
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thixotropy
- softening, or reducing of viscosity, by application of rapid shear stresses
- vibrate to make flow
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Restorative Dentistry goal
maintain or obtain stable occlusion
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Centric Relation
- CONDYLAR
- anterior, superior braced along emininence of glenoid fossa with articular disc interposed between condyle and eminence
- SAM = superior, anterior, mid
- restorative reference for diagnosis and treatment
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Retruded Contact Position
In CR, 1st point of contact
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Optimal occlusion
ICP while CR (40-60%)
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TMJ anatomy
articular eminence comprised of thick cortical bone
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Where is nerves and vessels of disc?
posterior, not for stress bearing
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Where is anterior disc attached?
- superior head of lateral pterygoid via muscle fibers
- medial lateral heads of condyle via liagaments
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Bennett Angle
- During Right lateral
- Left condyle moves in a line downward and to the left as viewed from the horizontal plane
- ANGLE with sagittal Plane is bennett angle about 7.5 degrees is normal
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Immediate side shift (bennett shift)
- immediate straight medial movement of non-working condyle
- 0.4-3.0mm
- occurs prior to condyle translating forward
- As ISS increases the Buccal-Lingual dimension of marginal ridge, fossa and Central groove increses
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Progressive Side Shift (bennett shift)
- continued medial movement of non-working (orbiting) condyle
- proportional to forward movement
- ass progressive side shift increases, balancing angles become flatter
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Bennett movement
- In a lateral movement
- working condyle ROTATES
- non-working condyle ORBITS
- lateral shift of mandible to working side
- working side teeth=>working inclines
- non-working side teeth=> balancing inclines
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What are the determinates of mandibular movement?
- 1. Posterior = R&L TMJ
- 2. Anterior = teeth (altered w ortho, restoration, occlusal equilibration)
- 3. Neuromuscular System
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Occlusal interferences
- teeth prevent normal jaw function
- 1. Centric
- 2. Working
- 3. Non-working
- 4. Protrusive
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Optimum Occlusion (Okeson)
- CR = ICP
- Axial loading of teeth
- Canine guidance laterally
- Anterior guidance protrusively
- Posterior contacts are heavier than anterior
-
Condylar guidance
- STEEPER path->TALLER the posterior cusps MAY be.
- SHALLOWER path->SHORTER cusps MUST be
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Anterior Guidance
- mandibular incisor => linguals of maxillary incisors
- protrusive incisal inclination = 50-70 degrees
- Steeper protrusive incisal path, taller poster cusps MAY be
- Shallower protrusive incisal path, shorter the posterior cusps MUST be
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OVERLAP
- the greater the HO (overjet), the less steep the protrusive angle (shorter posterior must)
- the greater the VO (overbite), the more steep the protrusive angle (taller posterior may)
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When is Superior Border Movement achieved?
when ICP is achieved in CR
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Alginate constituents and reaction
- K-alginate
- CaSO4 dehydrate-form insoluble Ca-alginate
- NaPO4 provide working time
- KSO4 counteract inhibiting effect on gypsum
- Diatomaceous earth-consistency strength, most compound
- Glycols-dustless
- Flavoring
- RXN
- 1. NaPO4+CaSO4
- 2. Ca2+ + K-alginate -> Ca-alginate
- Net:
- K-alginate + CaSO4 + H2O=>Ca-alginate + KSO4
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Alginate water temperature range?
- 64-75
- colder->longer setting and working times
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Alginate powder/liquid ratio
- more powder:
- 1. MORE strength, tear resistance, consistency
- 2. LESS working, setting times and flexibility
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Impression Removal
- faster removal:
- HIGHER Stiffness, tear strength
- LESS deformation
- Leaving in too long causes syneresis
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Bilateral Balanced
- occlusion where max tooth contacts in all excursive movements
- good for complete dentures to prevent tipping
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Unilateral balanced
- Group function
- all teeth contact on working side during laterotrusion
- usefull for full mouth reconstructions
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mutually protected
- occlusion that includes anterior and canine guidance
- anterior cause immediate disclusion of posterior during excursive movements
- posterior are loaded along long axis
- posterior protect anterior in ICP
- CR=ICP
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Molar Disclusion
- slight discrepancy between repeated excursive movements
- must allow enough room so they dont clash during disclusion
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. During a right laterotrusive movement:
A. The right condyle is orbiting.
B. The left condyle is rotating.
C. The steepness of the facial inclines of the
lingual cusps of #3 is critical.
D. All of the above.
E. None of the above.
E
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During protrusion which inclines interfere?
- distal inclines of maxillary
- mesial inclines of mandibular
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During a lateriotrusive movement on the right side of the
mandible with optimal occlusion:
A. The lingual surface of tooth #6 is providing
canine guidance.
B. The facial surface of tooth #27 is
contacting it’s opposing tooth.
C. The left condyle is orbiting.
D. All of the above.
E. None of the above.
D
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Which
posterior cusp inclines are most likely to me involved in protrusive
interferences?
A. Mesial
B. Desital
C. Facial
D. Lingual
A Mesial
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Which maxiallary posterior cusp
inclines are most likely to me involved in mediotrusive interferences?
A. Mesial
B. Desital
C. Facial
D. Lingual
C Facial
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During a right laterotrusive movement:
A. The right condyle is orbiting.
B. The left condyle is rotating.
C. The steepness of the facial inclines of the
lingual cusps of #3 is critical.
D. All of the above.
E. None of the above.
E. None
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