NBDE II Prothodontics: General Considerations (impression materials, occlusion, lab)
When comparing high-noble alloys to base-metal alloys, base-metal alloys have a lower modulus of elasticity. higher specific gravity. lower yield strength. higher melting point.
higher melting point.
Tolerates moisture the most - hydrocolloid, polyether, addition silicone, polysulfide
hydrocolloid
The thinnest/weakest portion of a wax pattern should be placed in the deepest part of the ring. against the ring. the same direction as the casting arm. opposite the direction of the casting arm.
in the deepest part of the ring.
Impressions, what's wrong with polyether?
it's hard and engage undercuts
Which of the following will occur if you increase the proportion of water to class IV gypsum die stone when pouring a master cast? More expansion and less strength Less expansion and less strength More expansion and more strength Less expansion and more strength
less expansion and less strength
Pt bites down after cementing down and deviates to the right #30:
lingual incline of the buccal cusp
centric occlusal interference
mandible deflects forward and laterally when condyle is in it's superior position
non-working interference
max- buccal incline of lingual cusp mand- lingual incline of buccal cup
13)patient allergic to? Nickel Cobalt Chromium Berrylium
nickel
which interference is most destructive non-working interference
non-working interference
byproduct of polyether
none
centric occlusion
occlusion during centric relation
Most rigid impression material
polyether
Which is hardest one to remove from the oral cavity (STIFFEST)?
polyether
Which of the following impression materials is most prone to fracture when forcibly removed from the mouth due to its stiffness? Addition silicone (poly-vinyl siloxane) Reversible hydrocolloid Polysulfide Polyether Condensation silicones
polyether hydrophilic and stiff but can fracture when forcefully removed
elastic impression materials
polysulfide, polyether, condensation silicone, addition silicone
What material would you not use for a single crown: a) polyether b) polysulfide c) PVS
polysulfide= water evaporation= worst detail production
specific gravity
ratio between the density of one material against the density of different material's standard in air ratio of a mineral's weight compared with the weight of an equal volume of water
polyether makes a polymer by which reaction
ring opening
shallow angle of eminence will cause ____ cusps
shallow cusps and vice versa
Bennet shift
shift of the mandible towards the working side during lateral excursions
Which of the following materials provides the most accurate means of evaluating centric occlusion and/or occlusal interferences on fixed prostheses? Shim stock Occlusal indicator spray (Occlude®) Patient feedback Articulating paper
shim stock very thin foil used to asses unusual occlusal interferences
The only property of a base metal alloy which is numerically lower than gold is tensile strength. specific gravity. modulus of elasticity. hardness. fusion temperature.
specific gravity.
Polyvinyl siloxanes (PVS) gets affected by
sulfur in latex gloves retard the setting of PVS
Alginate impression in 100% humidity, why will shrinkage occur? Imbibemnt, syneresis, historgysm
syneresis= extraction of liquid from gell--> shrinkage
Bennet movement
the left and right condylar motions caused by lateral movements
Wax patterns for cast restorations should be invested as soon as possible after they are completed to minimize distortion caused by microfractures caused by vibrations from laboratory instruments in the area. evaporation of water from the wax. continued expansion of the wax. the relaxation of the internal stress of the wax pattern.
the relaxation of the internal stress of the wax pattern.
tensile strength
the resistance of a material to breaking under tension/stress
what is the purpose of occlusal stop
to prevent overseating of the impression on insertion and removal
byproducts of polysulfide
water
Zinc-oxide eugenol setting times can be accelerated by adding acrylic monomer. petroleum jelly. water. glycerin.
water think about using IRM
For a gold casting alloy, which of the following is added primarily to act as a scavenger for oxygen during the casting process? A. Copper B. Palladium C. Silver D. Zinc
zinc copper and silver discolors the PFM in to green
Which is the purpose of using a liner when casting gold with a casting ring? It allows for uniform setting of the casting. It helps prevent porosity. It allows for the casting to be removed from the investment. It allows for quicker cooling of the casting and less shrinkage.
It allows for uniform setting of the casting.
Modulus of elasticity is directly proportional to which property? Ductility or malleability Stiffness or rigidity Tensile strength Ultimate strength Yield strength
Stiffness or rigidity
When casting chrome-cobalt (CrCo), how much shrinkage should you expect? 2.2% 2.6% 1.8% 1.2% 1.6%
2.2
Which percentage is required for an alloy to be considered a "noble" metal? 60% platinum, palladium, or silver 80% gold 25% silver 40% gold 25% platinum, palladium, or gold
25% platinum, palladium, or gold
high noble alloys contain
60% Pt, Pd, 40% Au
What happens when you take an impression & lip immediately swells?
angioedema (allergic rxn)
condensation silicone reaction and byproduct
condensation ethanol
polysulfide makes a polymer by which reaction
condensation reaction, releases water (impression will shrink), exothermic reaction
Porcelain fused to metal (PFM) crowns with a high-noble base typically have the highest percentage of platinum. palladium. silver. gold. chrome-cobalt.
gold
high noble metals used in dentistry
gold, palladium, platinum
protrusive interference
DUML prevents the posterior teeth from being dis-occluded by incisors, the mesial aspect of the mandibular and the distal aspect of maxillary have a premature contact
Which of the following is the principal physical property that makes polyether elastomeric impression materials less desirable than polyvinyl siloxanes? Bad taste Adherence to teeth Decreased accuracy High stiffness Long working time
High stiffness also adheres to teeth bad taste=polysulfide
Upper molar crown has a wear facet in porcelain on the MB inclination of MB cusp. Most likely associated with?
Interference in protrusion & working interference
Which problem can occur when a custom tray without occlusal stops is used to make a polysulfide final impression? An inaccurate final impression occurs due to permanent distortion incurred during the setting reaction. An inaccurate final impression is created due to distortion incurred during the removal of the impression tray from the patient's mouth. The setting time in the mouth increases before the tray can be removed. The clinician will have to hold the tray during the entirety of the polymerization procedu
An inaccurate final impression occurs due to permanent distortion incurred during the setting reaction.
Which of the following describes how far an impression tray should extend posteriorly when making a maxillary impression for diagnostic casts? To the uvula To the pterygomaxillary notches To the fovea palatine Slightly beyond the tuberosity Beyond the vibrating line
Beyond the vibrating line
Light sources have an effect on the perception of color because light sources must contain the wavelength of the color to be matched if the color is to be seen by the eye. Both the statement and the reason are correct. The statement is correct but the reason is NOT. The statement is NOT correct but the reason is correct. NEITHER the statement NOR the reason is correct.
Both the statement and the reason are correct.
Which of the following contributes to the dimensional instability of condensation silicones? Condensation polymers begin reacting with the impression tray, which may cause distortion over time. Evaporation of volatile by-products results in shrinkage of the impression. Condensation impression materials expand as they absorb water from the air if left unpoured. The amount of polymerization is initially high before decreasing with time, making the impression less accurate.
Evaporation of volatile by-products results in shrinkage of the impression= alcohol (evaporates faster than water)
Which of the following best describes a property of a material to resist fracture under bending? Strain Force/Load Fracture toughness Flexural strength Stress
Flexural strength
Which of the following is the best description of a Bennett angle? It is the angle that is formed by the condyle and the horizontal plane during protrusive movements. It is the angle that is formed by the non-working condyle and the sagittal plane during lateral movements. It is the difference in condylar inclination between protrusive and lateral movements. It is the difference between the condylar and incisal inclinations.
It is the angle that is formed by the non-working condyle and the sagittal plane during lateral movements.
Non-working interferences typically present on which of the following aspects of teeth? Buccal inclines of the lingual cusps of mandibular molars Lingual inclines of the buccal cusps of mandibular molars Buccal inclines of the buccal cusps of mandibular molars Lingual inclines of the lingual cusps of maxillary molars
Lingual inclines of the buccal cusps of mandibular molars non-working interference= interferences on the balancing side during lateral excusion
working side interference
Maxillary lingual incline of the lingual cusp mandibular buccal incline of the lingual cusp
Which of the following describes the physical property which gives cast gold the ability to be burnished? Modulus of elasticity Percentage elongation Compressive strength Modulus of thermoplasticity
Percentage elongation describes increase in the length of a material when subjected to tensile forces
Which of the following mechanical properties are INCORRECTLY paired? Flexural strength-measures the ability of a material to resist fracture under bending loads Elastic modulus- ability to sustain deformation without permanent change in size or shape Fracture toughness- ability to resist the propagation of a crack Tensile strength- volume loss due to abrasion and opposing contact area
Tensile strength- volume loss due to abrasion and opposing contact area
elasticity
The ability of a material to bounce back after being disturbed
ductility
The ability to be pulled into thin wires
maximum intercuspation
The complete intercuspation of the opposing teeth independent of condylar position used to be called centric occlusion
Each of the following are characteristics of addition silicone (polyvinyl siloxane) impressions EXCEPT one. Which of the following is the EXCEPTION? They produce ethyl alcohol during their setting reaction. They can be poured after 24 hours of being made and still remain accurate. They remain accurate after the first pour. They can rebound from undercuts without permanent deformation.
They produce ethyl alcohol during their setting reaction (this is condensation silicone)
A denture that is set in group function occlusion will exhibit which of the following contacts during excursive movements? Long centric contacts Protrusive contacts Non-working contacts Working contacts
Working contacts but no contact on the balancing side
addition silicone (PVS) reaction and byproduct
addition H2 but not consider byproduct
dimensional stability best to worst
addition silicone> polyether> polysulfide> condensation silicone ethanol evaporates faster than water
order of detail reproduction best to worst
addition silicone>polyether>condensation silicone> polysulfide
adv and disadv of polysulfide
adv: tear strength high, hydophylic disadv: shrinkage, dimensional stability, bad odor and taste, not good detail production
The most stable elastic impression in moisture environment? a. polyether b. additional silicone c. condensation silicone d. polysulfide
b. additional silicone (hydrophobic)
Anterior occlusion is determined by both horizontal and vertical overlap of anterior teeth. the vertical overlap of anterior teeth only. the horizontal overlap of anterior teeth only. cusp inclination. cusp height.
both horizontal and vertical overlap of anterior teeth (overjet, overbite)
A material that fractures easily without substantial dimensional changes is best described by which of the following terms? Brittle Ductile Malleable Resilient Tough
brittle
Which term describes a material that possesses a high compressive strength and low tensile strength? Resilient Brittle Malleable Ductile
brittle
Back-pressure porosity is caused by excessive burnout. can be diagnosed by rounded edges of the casting when they should be sharp. describes the same phenomena as occluded gas porosity. is caused by too large of sprue size.
can be diagnosed by rounded edges of the casting when they should be sharp.
What kind of occlusion if in right lateral movement all posterior teeth are not in occlusion
canine guidance
malleable
capable of being shaped or bent
which metal prevents corrosion on noble metal
chromium
If you decrease water temp (colder), you have ______ working time for an irreversible hydrocolloid
colder water=more working time
In restoring a canine protected occlusion, with anterior overbite of about 2mm. The buccal cusps of posterior teeth should be flat, BECAUSE they will guide the protrusion. a. both are true b. only the second statement is true c. both are false d. only the first statement is true
d. only the first statement is true
Ductility - gold's ability to be worked into _________
different shapes
