FP Flashcards by Glen Ho

What are the five blueprints for excellent impressions? 5x

Adequate Moisture Control * Maintain Visibility & Accessibility * 3Good Soft Tissue Management * 4Proper Use of Appropriate Impression Material * 5Proper Care of the Impression

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What is the advantage of polyether over polysulfide base?

Polyether is very accurate and stable while polysulfide is only accurate

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Does alginate reproduce fine detail? YES/no

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What is the composition of alginate (irreversible hydrocolloid)?

Sodium& Potassium of alginic acid react with calcium to form calcium alginate !
Calcium sulfate dihydrate is added to provide a source of Ca+2 ions to cross-link the alginic acid !
Sodium phosphate is added as a retarder and to control set time. ! Alginic acid is a naturally occurring hydrophilic colloidal polysaccharide obtained from brown seaweed

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What does Decreased Axial Wall Taper do to resistance?

Increases it

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What is the indirect-direct procedure for interim restorations? Disadv? Advantages?3x

Custom shell made in advance of tooth preparation using an unprepared diagnostic cast. Disadv: relining and careful marginal trimming are necessary prior to cementing [patient serving as the TSF-direct component].

Adv: 1. Chairside time is reduced. 2. Less heat is generated in the mouth as resin used during lining is less. 3. Contact between residual monomer and soft tissues is minimized compared to the direct technique. Ridge areas usually don’t need relining, further reducing allergic reaction risk.

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An undercut is?

axial reduction near the gingival is greater than the occlusal.

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What is the relationship between the size of the monomer molecule and exothermic heat and physical strength? And what do fillers do?

↑ size of the monomer molecule, ↓ exothermic heat on setting and ↓ physical strength of the set mass.

↑ filler content ↓ exothermic heat and contraction while ↑ strength of the set material.

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disadvantages to PFM’s?6x

Significant tooth reduction needed to create space for materials.

Subgingival margin (especially facial) ➔ higher periodontal disease risk.

Increased risk of contact dermatitis/gingivitis from some metals (not high noble; often base metals).

Harder to achieve excellent esthetics VS all-ceramic restorations.

Risk of porcelain fracture.

Feldspathic porcelain can abrade opposing teeth.

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When are PFM’s contraindicated?3x

Whenever maximum esthetics is indicated and feasible.
Young patients with large pulp chambers, and when a more conservative approach would suffice

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disadvantages to polyether?

Stiffness of the set material —> Thin and single tooth on stone cast are liable to break when separated from the impression.

Polyether is stable only if stored dry, because it absorbs moisture and under- goes significant dimensional change

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What is polycarbonate mainly used for?

lined with light cured PMMA to be helpful when no matrix is available.

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What are the main indications for PFM’s?

req > durability than all-ceramic restorations; Excellent choice for bridge retainers

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What are the names of the two surface forms involved in making interim restorations?

External surface form and Tissue surface form

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Drawback to reversible hydrocolloid materials?4x

Not stable, doesn’t last long, single pour (immediately), subject to imbibition and syneresis.

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When should polysulfide impressions be poured up?

Immediately

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What are the main consequences of an inadequate axial reduction? 8x

Overer-contoured Crown ! Poor Esthetics ! 3 Ledging at Margin ! 4Plaque Retention ! 5Gingival Margin Inflammation ! 6Periodontal Disease ! 7Furcation Involvement ! 8Recurrent Caries

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What does a surfactant do when pouring up silicone in stone?

Helps prevent bubbles

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What is syneresis?

Exuding liquid if left standing

What are the Perfect Provisional material requirements? 8x

1Biocompatible 2No mal odor/ taste 3No exotherm on polymerization 4No polymerization shrinkage 5 Wide range of shades, including translucent 6 Color stable over time 7 Good compressive and tensile strength 8 Easy to manipulate and repair

Which acrylic material is the easiest to add to? what happen when they cure?2x

PMMA. Poly-methylmethacrylate. They shrink a lot when they cure, and they give off heat.

gingival margin for a preparation for a full coverage crown should be placed at least

1 mm supra-gingivally, ideally

disadvantages to PVS?
x (add ….to be less x) - …..contamination from …. can inhibit set by interfering with ….. catalyst - esp with ….PVS -resulting in …. or …. …. gloves do not have this effect

Hydrophobic (add surfactant to be less hydrophobic) - Sulfur contamination from latex gloves can inhibit set by interfering with platinum catalyst - esp with putty PVS - Sulfur compounds , resulting in retarded or no polymerization -Nitrile gloves do not have this effect

Which acrylic exhibits the greatest polymerization shrinkage?

PMMA

What does resistance mean?

Prevents dislodgement of restoration along a path other than path of insertion.

What are the three most common deficiencies of provisionals?

1. Exothermic 2. Polymerization shrinkage 3. Color degradation over time

The accuracy of a reversible hydrocolloid impression is improved if the material has ...... VS elastomeric impression materials, whose accuracy is improved by .... bulk (e.g., polysulfide and condensation silicone), because stresses produced during removal are reduced. Therefore, an additional advantage of reversible hydrocolloid is that a .... tray is ... required.

The accuracy of a reversible hydrocolloid impression is improved if the material has as much bulk as possible VS elastomeric impression materials, whose accuracy is improved by minimizing bulk (e.g., polysulfide and condensation silicone), because stresses produced during removal are reduced. Therefore, an additional advantage of reversible hydrocolloid is that a custom impression tray is not required.

What is the most hydrophillic elastomeric impression material?

Polyethers

What is cellulose acetate?

For interim restorations and it is a clear preformed shell used.

Resin thicknesses of ...to ... mm are needed for adequate rigidity of ... trays. Clearance between the tray and the teeth should also be ... to ... mm with stops; however, greater clearance is necessary for the .... materials. Should be shaped to allow ...... ; ......, with no .... edges. Finally, the handle should be sturdy and shaped to fit between the patient’s....

Resin thicknesses of 2 to 3 mm are needed for adequate rigidity of custom trays. Clearance between the tray and the teeth should also be 2 to 3 mm by using stops; however, greater clearance is necessary for the more rigid polyether materials. Should be shaped to allow muscle attachments, smooth, and with no sharp edges. Finally, the handle should be sturdy and shaped to fit between the patient’s lips.

What is working time?

Working time begins when mixing is started, and ends immediately before elastic properties develop

Which provisional material exhibits the least polymerization shrinkage?

Microfilled Bis-GMA and Urethane DMA

When is a sub-gingival margin placement necessary?

Occluso-gingival height of preparation (less than 3 mm) Caries/existing restoration extending sub-gingivally. Necessary for esthetics (only if anterior porcelain, not gold)

What does silicone and polysulfide give off from their polymerization reactions?

Both are condensation polymers, which, as a byproduct of their polymerization reactions, give off alcohol and water, respectively.

An impression material with a higher elastic limit should exhibit more permanent deformation. True or False?

False. An impression material with a higher elastic limit should exhibit less permanent deformation.

How much space is there between the tray and teeth during alginate impression?

4 – 5 mm

What is the double-cord technique for gingival displacement?

Cord#000(thinnest) is placed at the bottom of the gingival crevice. A second cord #0 /#00 (thicker) is placed on top to achieve lateral tissue displacement. The latter is removed immediately before impression making, whereas the initial cord is left in place to help minimize seepage.

What does retention form mean?

Prevents dislodgement of restoration parallel to path of insertion.

What is the cheapest elastomer? disadv

Polysulfide, but it stinks, takes 10 min to set in mouth, can stain because of a metal.

Which material has the most natural look out of all of them for interim restorations?

Polycarbonate

What is the difference between dimensional accuracy and dimensional stability?

DIMENSIONAL ACCURACY: Lack of dimensional change during setting, and shortly after removal from the mouth DIMENSIONAL STABILITY: Lack of dimensional change over time

Irreversible hydrocolloid is not sufficiently accurate for cast restorations. True or False?

True. But can be used for diagnostic casts, just not definitive.

Which provisional material is the most brittle and difficult to repair?

Microfilled Bis-GMA

What is set time?

time from the beginning of mixing until the impression can be removed from the mouth with no distortion

What is the name for addition silicones and what are they made up of?

Polyvinylsiloxane. - The base paste consists of polymethylhydrosiloxane, divinylpolysiloxane and a filler - The accelerator paste contains divinylpolysiloxane and a platinum salt catalyst - a scavenger such as palladium which absorbs H2 gas - H2 gas can create bubbles in stone if impression is poured too soon - Best to simply avoid addition silicones that realease H2 gas -