Operative2 Flashcards
UV light curing systems are no longer used and that is because dual-cure systems fixed the problem of “incomplete curing.”
• both the statement and the reason are correct and related
• both the statement and the reason are correct but not related
• 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 but not related (visible light-cured composites had many advantages over UV light-cured composites)
what is the initiator in light cure composites which absorbs energy from a visible (474 nm-blue light) light source?
The alpha-diketone
The minimum acceptable level for visible curing light outputs is ?
300 mW/cm2
All of the following statements are true concerning posterior composite restorations EXCEPT one. Which one is the EXCEPTION?
• posterior composite restorations are frequently indicated in the treatment of occlusal lesions that allow conservative preparations
• posterior composite restorations are contraindicated in a patient with heavy occlusion (bruxism)
• posterior composites are contraindicated in patients with high caries risk
• posterior composite restorations may be indicated for the restoration of Class II cavities in premolar teeth where the appearance is very important, the cavity margins are in the enamel, and the occlusal contacts are on the enamel
• posterior composites are contraindicated for cusp replacements unless a dry operating field is maintained
posterior composites are contraindicated for cusp replacements unless a dry operating field is maintained
The most serious limitation of the visible light-cured posterior composite restoration is ?, which can cause internal stresses and gap formations at butt-joint interfaces, which are seen at the gingival floor of Class II and V restorations
the polymerization shrinkage
? is the ratio between bonded and unbonded surfaces; an increase in this ratio results in increased polymerization stress. Three-dimensional cavity preparations (Class I) have the highest (most unfavorable) C-factor because only outer unbonded surfaces absorb stress
The C-factor (Incremental curing reduces the C-factor and, therefore, reduces the residual stress of the resulting composite restoration)
posterior composite restorations are contraindicated in a patient with ?.
a caries active mouth
For Class III composite preparations, the retentive grooves are placed along ? line angles (entirely in dentin).
the gingivoaxial and incisoaxial
Which property of filled resins is primarily to blame for the failure of Class II composite restorations? • low flexural strength • low compressive strength • low tensile strength • low wear resistance
low wear resistance
The difficulty in finishing composite resin restorations is due primarily to ?. The most desirable finished surface for composites is obtained with ?
- the softness of the resin matrix and hardness of the filler particles
- aluminum oxide disks
Which composite type is 70% to 77% percent filled by volume and has an average particle size ranging from 1 to 3 µm. • microfills • hybrids • microhybrids • packables • flowables
hybrids
Microfills: are 35% to 50% filled by volume and have an average particle size ranging from 0.04 to 0.1 µm
Composite filler particles function to do which of the following? Select all that apply.
• reduce the coefficient of thermal expansion
• increase the tensile strength and compressive strength
• reduce the polymerization shrinkage
• increase the hardness
• improve wear resistance
- reduce the coefficient of thermal expansion
- increase the tensile strength and compressive strength
- reduce the polymerization shrinkage
- increase the hardness
The normal wear mechanism of the composite resins is best explained by the following events: abrasion of ?, followed by exposure of filler particles and subsequent dislodgement of these filler particles.
the matrix
When comparing the physical properties of filled resins to unfilled resins, all of the following are true EXCEPT one. Which one is the EXCEPTION?
• filled resins are harder
• unfilled resins have a higher coefficient of thermal expansion
• filled resins have a higher compressive strength
• unfilled resins have a lower modulus of elasticity
• filled resins have a lower tensile strength
filled resins have a lower tensile strength (they have a higher tensile strength)
When restoring a darker shade of composite, keep in mind the following:
• UV light is better than visible light
• you must keep the light 2 mm away or more
• you should cure for longer than normal
• darker shades have less chemical bonding
you should cure for longer than normal
Of the following, which ones are current monomers for composite resins? Select all that apply. • bis-GMA • PMMA • UEDMA • TEGDMA
- bis-GMA
- UEDMA
- TEGDMA
The main ingredient in traditional acrylic resin temporary materials for intraoral fabrication is: • ethyl methacrylate • isobutyl methacrylate • bis-GMA • ethylene imine • methyl methacrylate
methyl methacrylate
Which restorative material has the lowest thermal conductivity and diffusivity? • amalgam • gold • unfilled resin • filled resin
unfilled resin (undesirable effects of the relatively high coefficient of thermal expansion, which is 7 to 8 times that of the tooth)
Acid etching enamel prior to placement of a composite restoration is required for all of the following reasons EXCEPT one. Which one is the EXCEPTION? • conserves tooth structure • reduces microleakage • provides rnicromechanical retention • increases esthetics
increases esthetics (the bevel is for both retention and esthetics)
Studies indicate that acid-etched composite resin restorations have the best initial seal (microleakage), however, over time, this weakens. (? has the best seal over time)
amalgam
Enamel etching is typically completed with: • 37% phosphoric acid • 13% phosphoric acid • 37% hydrochloric acid • 13% hydrochloric acid
37% phosphoric acid (for 15 seconds and with a 15-second rinse and a 15-second drying)
Little correlation exists between resin tag length and ? strength.
enamel/resin bond
comparison of liquid etchants and gel etchants?
Although liquid etchants produce a more uniform etch and a greater number of tags than do gel etchants, no difference in bond strength has been demonstrated between the two
When preparing a Class V composite preparation, you can have ? rounded internal line angles because it is ? to compress composite into them than amalgam. • more, easier • less, harder • more, harder • less, easier
more, easier
Which one of the following is the most important event for dentin bonding? • smear layer removal • smear plug removal • peritubular dentin decalcification • intertubular dentin decalcification
intertubular dentin decalcification
A gold onlay you placed last week fails. Which of the following reasons is most likely responsible for the failure? • you "capped" the functional cusp • you "shoed" the functional cusp • you "capped" the nonfunctional cusp • you "shoed" the nonfunctional cusp
you “shoed” the functional cusp (“Shoeing” is never indicated on functional cusps)
Rapid cooling (by immersion in water) of a dental casting from the high temperature at which it has been shaped is referred to as: • annealing • tempering • quenching • none of the above
quenching (it maintains its malleability and ductility, the investment becomes soft and granular, and the casting is more easily cleaned)
The set of 3 processes (annealing, hardening and tempering) is collectively known as ?
• Annealing is ? of a metal by controlled heating and cooling to make its manipulation easier.
• Tempering is ? something by heat treatment
- “heat treating”
- the softening
- hardening
Which of the following situations defines an Indication for a Class II gold inlay?
• a young patient with high caries rate
• a patient with little money to invest in dental work
• a patient very concerned about esthetics
• a patient with a large lesion, buccal-lingually
• a patient with low caries rate but a history of periodontal problems
a patient with low caries rate but a history of periodontal problems
for gold inlay, if cavity width exceeds ? the intercuspal width, the tooth should receive cuspal coverage
one-third
Gold alloys ? upon solidification in the investment. This needs to be compensated for by an equal amount of ? of the mold. • shrink, expansion • expand, shrinkage • shrink, shrinkage • expand, expansion
shrink, expansion
The dimensional compensation necessary is accomplished by two methods of expansion:
- Setting expansion
- Thermal expansion
Important: Thermal expansion is the principal cause for mold expansion
Variables that influence expansion:
- The older the investment is, the less expansion
- If the water/powder ratio is increased, the less expansion
- The shorter the spatulation time, the less expansion
- The longer the time between mixing and immersion in a water bath, the less expansion
Which of the following finishing margins is essentially a "hollow ground bevel", creating more bulk of restorative material near the margin and providing a greater cavosurface angle? • knife edge • beveled shoulder • chamfer • shoulder
chamfer
Which of the following allows for proper retention when preparing a tooth for a disto-occlusal Class II gold inlay? • undercut on mesial • undercut on buccal and lingual walls • occlusal lock (dovetail) • none of the above
occlusal lock (dovetail)
The cement’s main function is for ?
marginal seal, not retention
A patient arrives at your office with his full gold crown in hand. He explains to you that another dentist delivered it just last week. You then examine the crown and the preparation. What is the most likely reason that the crown fell off?
• there was very little cement in the crown
• the preparation was only 4 mm high
• the preparation walls were tapered at about 15°
• the margins were jagged and undefined
the preparation walls were tapered at about 15° (taper is the main retention, 4 mm is enough, 3 mm is minimal)