Midterm Flashcards
What is imbibition?
Uptake of water by hydrocolloid when immersed in water
When are anti-sialogogues contraindicated?
• Prescribe with caution in older adults Many medications have a more profound affect on older patients Glaucoma incidence is higher • Should not be used in patients with heart disease • Contraindicated in patients with Glaucoma Incidence of undiagnosed glaucoma in general population in high Consider Ophthalmological evaluation prior to use of anticholinergics
What two impression materials exhibit long-term stability?
Poly- ethers and addition silicones are preferable because they exhibit sufficient long-term dimensional stability; the other materials, particularly the reversible hydrocolloids, must be poured immediately.
What are the advantages and disadvantages of displacement paste?
Advantages of the system include good hemostasis with less discomfort than traditional cord. However, less tissue displacement is achieved than with cord, which may make die trimming more problematic. Improved displacement may be achieved if the paste is directed into the sulcus by applying pressure with a hollow cotton roll.
What is the difference between drying a tooth and desiccating a tooth?
Desiccation is losing water via evaporation, drying (not losing water)
Does alginate reproduce fine detail?
No
Why don’t you want to completely remove the smear layer when prepping a tooth for a crown? And how do hemostatic agents affect the smear layer?
Can cause pulpal irritation, and they are very acidic and remove more smear layer than we would like usually.
What is the composition of alginate (irreversible hydrocolloid)?
! Sodium and Potassium and other salts 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 its concentration adjusted to control set time. ! Alginic acid is a naturally occurring hydrophilic colloidal polysaccharide obtained from brown seaweed
What are the factors influencing resistance?
! Magnitude & Direction of Dislodging Forces ! Geometry of the Tooth Preparation ! Physical Properties of the Luting Agent
What does Decreased Axial Wall Taper do to resistance?
Increases it
What is the indirect-direct procedure for interim restorations? Advantages?
In this technique the indirect component produces a “custom-made preformed ESF” similar to a pre- formed polycarbonate crown. In most cases, the practitioner uses a custom ESF with an underprepared diagnostic cast as the TSF. The resulting mold forms a shell that, after tooth preparation, is lined with additional resin (the patient serving as the TSF). This last step is the direct component of the procedure. Another method of creating the shell eliminates the need for an indirect TSF. It is accomplished by painting monomer liquid into the ESF and care- fully sprinkling or blowing resin powder on it. The thickness of the resin shell is difficult to control with this technique, however, and may result in the need for time-consuming corrective grinding. The indirect-direct approach has these ad- vantages: 1. Chairside time is reduced. Most of the procedures have been completed before the patient’s visit. 2. Less heat is generated in the mouth. The volume of resin used during lining is comparatively small. 3. Contact between the resin monomer and soft tissues is minimized in comparison with the direct procedure. Because pontic ridge areas do not normally require lining, there is reduced risk of allergic reaction. However, even with the diagnostic cast method, adjustments are frequently needed to seat the shell completely on the prepared tooth. This is the chief disadvantage of the indirect-direct procedure.
What is the best luting agent for cementation of an interim restoration?
Zinc oxide eugenol, doesn’t bond that strong to make it easier to get it off in the end.
An undercut is?
The axial reduction near the gingival is greater than the occlusal. Answer is B.
What is the relationship between the size of the monomer molecule and exothermic heat and physical strength? And what do fillers do?
In general, the greater the size of the monomer molecule, the less is the exothermic heat of reaction on setting and the lower the physical strength of the set mass. An increase in filler content reduces the relative amounts of exothermic heat and contraction while increasing the strength of the set material.
What are the disadvantages to PFM’s?
Significanttoothreductionisnecessarytoprovide
sufficientspacefortherestorative materials
-Asub-gingivalmarginisoftenrequiredonthefacialaspectwhichhasthepotentialto increase the risk of periodontal disease Increasedriskforcontactdermatitis(gingivitis)withsomemetals(Thesemetalsmust have a melting point higher than the fusing point of the porcelain. Many are not high noble and some are base metal.) -Moredifficulttoachievepremiumestheticsthanwithallporcelainrestorations -Porcelainfracturerisk -Feldspathicporcelaincanbeabrasivetoopposingtoothstructure -Laborintensivenatureoftherestorationcanleadtohigherlaboratoryexpenses
Nerve impulses from the periodontal ligament form part of the mechanism that regulates saliva flow. What can help stop saliva production and flow?
Profound anesthesia
Why is the lingual concavity important in an anterior PFM preparation, following the anatomy of the tooth?
Allows you to mimic the anatomy that was there and recreate marginal ridges, contributes to anti-deformation strength of the crown as well.
The recommended convergence angle for something is……
6 degrees
What does shortening proximal projections of the impression material do?
Shortening proximal projections of the impression material facilitates complete reseating of the ESF
What is the only thing that changes between a gold crown or zirconia crown prep for a maxillary bicuspid?
The non-functional cusp bevel
When are PFM’s contraindicated?
Largely whenever maximum esthetics is indicated and feasible, with young patients with large pulp chambers, when a more conservative approach would suffice, with patient with caries.
When doing an anterior PFM in two planes, what are the gingival and incisal 1/3rd’s parallel to?
! Gingival 1/3 is parallel to the path of insertion or line of draw ! Incisal 2/3 is parallel to the facial surface of the tooth
What is the ideal margin adaptation with Gold, PFM’s, and PCC?
10, 50, and 50-200 microns
Which impression material is affected by latex gloves?
Addition silicones (PVS)
What are some disadvantages to polyether?
The stiffness of the set material is one such disad- vantage, which causes problems when a stone cast is separated from the impression. Thin and single teeth, in particular, are liable to break unless the practitioner uses great care. Polyether is stable only if stored dry, because it absorbs moisture and under- goes significant dimensional change.
What is a colloid?
A colloid is composed of two substances, one dispersed within another, and can exist in two distinct phases.
Which two components are elastomeres supplied in?
Catalyst paste and Base paste
What is a solution?
A solution, on the other hand, exists only in a single phase.
Which provisional material is the most deficient in contours and marginal fit and cannot be used for bridges?
Aluminum and tin-silver
Which of the following can be indications for a full coverage restoration?
F, all of the above
What is polycarbonate mainly used for?
It is lined with light cured PMMA to be helpful when no matrix is available.
The preparation for a tooth for a zirconia crown can be the same as for…….
All of the above, although the ideal would be like the full metal preparation.
What are the main indications for PFM’s?
-Teeth that require complete coverage, and that… -Require considerable attention to esthetics -Teeth requiring more durability than all ceramic restorations -Excellent choice for bridge retainers -The incorporation of occlusal or cingulum rests and proximal and reciprocal guide planes in metal make it an excellent choice for removable partial denture abutments in the esthetic zone -The indications for Porcelain Fused to Metal (PFM) Crowns are similar to those for the FGC, when esthetics are also important
What is the ideal clearance of the area of the lingual cavity where you’re putting porcelain over the metal?
1.5 mm
Electrosurgery facts:
- The electrode should be passed rapidly through the tissue with a single light stroke and kept moving at all times. 8. If the tip drags, the instrument is at too low a setting, and the current should be increased. 9. If sparking is visible in the tissue, the instrument is at too high a setting, and the current should be decreased. 10. A cutting stroke should not be repeated within 5 seconds. 11. The electrode must remain free of tissue fragments. 12. The electrode must not touch any metallic restoration. Contact lasting just 0.4 second has been shown to lead to irreversible pulpal damage in dogs.23 13. The sulcus should be irrigated with hydrogen peroxide before the displacement cord is placed.
Where on teeth do you not build?
Posterior excursive interferences
What are the names of the two surface forms involved in making interim restorations?
External surface form and Tissue surface form
What is the main drawback to reversible hydrocolloid materials?
Not stable, doesn’t last long, subject to imbibition and syneresis.
What is one of the biggest drawbacks of porcelain fused to zirconia?
You don’t have a real good bond, better with PFM’s
When should polysulfide impressions be poured up?
Immediately
What are the main consequences of an inadequate axial reduction?
Overer-contoured Crown ! Ledging at Margin ! Poor Esthetics ! Plaque Retention ! Gingival Margin Inflammation ! Periodontal Disease ! Furcation Involvement ! Recurrent Caries
What does a surfactant do when pouring up silicone in stone?
Helps prevent bubbles
Is alginate accurate?
Yes
What is the preferred design of an anterior PFM?
Wingless is the preferred design • Better esthetics • Slightly less retentive • Easier
Which of the following numbers best describes the clinically acceptable range for fixed prosthodontics overall taper?
5-22 degrees
In taking an impression with polysulfide or silicone materials, if the heavy bodied tray material begins to set before seating, the resulting dye will be…….. Or if you are using the technique of a silicone putty in a tray with a spacer, you will get………
Overall smaller. Distortion, and it will also be smaller.
What is syneresis?
Exuding liquid if left standing
What are the Perfect Provisional material requirements?
Biocompatible No mal odor or taste No exotherm on polymerization No polymerization shrinkage Good compressive and tensile strength Easy to manipulate Easy to add to and or repair Wide range of shades, including translucent Color stable over time
What is the strain in compression a measurement of?
The rigidity of a material. In general, polyethers are the stiffest impression material, followed by the addition silicones. Excellent for implant impressions.
What are the advantages and disadvantages of reversible hydrocolloid?
! Advantages: Few ! Hydrophilic – “Likes water” ! Injected material stays on tooth, in sulcus, etc… ! Easily poured up ! Once equipment is purchased, cost per impression is low ! Disadvantages: Many ! Expensive start-up costs ! Difficult to read accuracy of impression ! Can’t double-pour impression ! Impression must be poured immediately ! Impression material distorts when it cools to room temperature ! If left in water, the impression will imbibe (absorb) water, thereby distorting and losing accuracy ! If left standing, the impression will undergo syneresis (exuding liquid) thereby contracting and dimensionally distorting ! Temperamental at higher altitudes
What are the four types of elastomeric impression materials?
! Addition silicone ! Polyether ! Polysulfide Rubber Base ! Condensation silicone
Refrigerating addition silicone material can add up to two minutes of working time, if needed. True or False?
True
Should the non-functional cusp bevel be smooth or sharp and why?
Making the non-functional cusp bevel smooth instead of sharp so you don’t catch as many air bubbles when taking impressions.
What does PMMA in a light cured formulation help overcome?
Both polymerization shrinkage and exothermic deficiencies
What do you do with cementing if the provisional is overly retentive?
Only place cement around marginal area.
What does decreased crown height do to resistance?
Decreases it
Which acrylic material is the easiest to add to?
PMMA. Poly-methylmethacrylate. They shrink a lot when they cure, and they give off heat. (Bite splints). It is easy to add to, that is a test question, if you break it or need to repair it you can add some, the liquid is called monomer.
The gingival margin for a preparation for a full coverage crown should be placed……
At least 1 mm supra-gingivally, ideally with a gold crown keep your margins as high as you can.
Noble metals do not form chemical bond. True or False?
True
What are the disadvantages to PVS?
Hydrophobic (Relative to Hydrocolloid) - Sulfur contamination from latex gloves can inhibit set - Typically only a problem when working with a putty PVS - Sulfur compounds interfere with platinum catalyst, resulting in retarded or no polymerization at the site of contamination - Vinyl and nitrile gloves do not have this effect
When is electrosurgery for tissue preparation for impressions contraindicated?
- It is contraindicated on or near patients with any electronic medical device (e.g., a cardiac pace- maker, transcutaneous electrical nerve stimula- tion [TENS] unit, insulin pump)22 or patients with delayed healing as a result of debilitating disease or radiation therapy. 2. It is not suitable on thin attached gingivae (e.g., the labial tissue of maxillary canines). 3. It should not be used with metal instruments, because contact could cause electric shock. (Plastic mirrors and evacuation tubes are available.)
What are the two best impression materials for implants?
-The two best impression materials for implants are addition silicones and polyethers, and polyethers might have the edge.
Which acrylic exhibits the greatest polymerization shrinkage?
PMMA
What are the effect of luting agents on resistance?
Complete Seating of Restoration (Decreased Cement thickness) = Increased Resistance ! Luting Agents with Increased Compressive Strength = Increased Resistance ! Luting Agents with Increased Modulus of Elasticity = Increased Resistance ! Chemically Bonded Restoration = Increased Resistance ! Micro-Mechanically Bonded Restoration = Increased Resistance 
For a PFM crown on tooth 8, the ideal facial reduction is?
1.2-1.7 mm
What is syneresis?
! With time, relaxation of internal stresses within the hydrocolloid expresses fluid onto the surface of the impression, resulting in dimensional change and distortion ! This expression of fluid from the hydrocolloid impression material is called syneresis
How do you measure wettability?
Assessed by measuring the advancing contact angle of water on the surface of the set impression material. Only the hydrocolloids are considered truly hydrophilic. Surfactants reduce the contact angle, improve wettability and simplify the pouring of elastomeric impressions. Also, simply using caution and pouring slowly can yield bubble-free casts with any impression material.
What is urethane dimethacrylate DMA?
Putty, light cure
What does decreased taper of axial walls to to retention?
It increases it