ISTR Test 2 Flashcards
What are the incompatibility issues for PFM?
Metal has a lower fusing temp, a higher coefficient of thermal expansion, and is flexible compared to brittle porcelain.
If the coefficients of thermal expansion are not very close, what will happen?
The metal and porcelain will fail through porcelain fracture upon cooling.
How does a PFM compensate for the ceramic’s weakness?
When the two are cooled while bonded, the metal shrinks and it puts the porcelain under compression, increasing it’s properties and making less likely to crack and propagate a crack. The coefficient of thermal expansion is slightly greater for alloy than porcelain.
What do the layers of porcelain attempt to stimulate?
Optics of a natural tooth.
What is the optical limitation of PFM systems?
Light doesn’t pass through. You have to make the opaque appear not opaque.
What is the dimension for unveneered metal?
1 mm.
What is the dimension necessary for ceramic?
1-1.2
What is the ideal dimension of ceramic at the incisal edge?
1.5
What is the ideal dimension of veneered metal?
0.3
What are the steps in PFM fabrication?
- Waxing to full contour.
- Cutback.
- Casting.
- Degassing or conditioning bake.
- Opaque application.
- Body and incisal application.
- Glazing.
What are the three types of porcelain and what are they used for?
Opaque: Responsible for the bond to metal, masks out the metal and begins color development. Body: Dentin shade, color and effects. Incisal: Enamel shade, color and effects.
What areas of a PFM require the most tooth reduction?
Areas veneered with ceramic.
Where should porcelain-metal junction lines not be placed?
On occlusal contacts.
What type of alloys exhibit wear patterns more similar to natural tooth?
Noble and high noble.
What areas should ideally be in metal?
Occlusal contacts, proximal contacts, guide planes and RPD occlusal rests. Esthetics often indicate porcelain.
Why is metal better suited to occlusal contact?
It is less brittle. It is more precise in fabrication and easier to adjust and polish.
What does the gingival finish line design depend upon?
The desired termination of the restoration. It is important to talk to the patient.
What are the metal collar options for a gingival termination?
Shamfer, shoulder, shoulder with a bevel.
What are the possible gingival terminations?
Metal collar, no collar or M-P junction, porcelain butt, modified porcelain butt.
What are the possible esthetic gingival terminations?
All are shoulders. MP Junction. Porcelain Butt. Modified Butt.
What are the even optimum thickness for porcelain in the framework design?
1 mm for strength.
1.5-2 mm for esthetics.
Never greater than 2 mm.
What are the requirements of the fusing temperatures of metals and alloys in PFMS?
High fusing alloys–above that of ceramics.
Lower fusing ceramics–lower than the metal.
What are some good things about dental porcelain? Challenges?
Esthetic, biocompatible, hard, high compressive strength, low solubility.
Brittle, low tensile and fracture strength meaning it needs to be supported.
What are some good things about metal ceramic alloys? Challenges?
Provide a stiff substrate and reinforcement for the ceramic. Good physical properties of tensile and compressive strengths. Easier to fabricate and adjust.
Unesthetic. Low tensile and fracture strength???
In veneers, how do you make up for the weakness of the materials?
Bonding it to the tooth.
Feldspathic Ceramics
Not strong. Prettiest, but the weakest.
Silica SiO
Type of feldspathic?
Acidulated Phosphate Fluoride
Fluoride gel. Effective F- penetration. Etch glass. Etch dental porcelain. Roughens porcelain within 4 min.
What is the ADA Alloy Classification?
High noble
Noble
Base metal
High Noble
60% or more noble metals. At least 40% gold. Ease of manipulation.
Noble
Noble metals are 25% or more. No gold requirements.
Base metal
Less than 25% noble metals. Have a high modulus of elasticity, hardness and etchability.
What are the big 3 noble metals?
Gold, platinum, palladium
What creates the oxide layer and chemical bond in Porcelain metal bond?
Add 1% iron, indium and or tin.
Noble vs. Base Metal Alloys
Clinical performaces are equal. The cost of noble is WAAAAY higher. Metal is a small percentage of restoration cost and scrap of noble alloys has value. Base metal is more difficult to fabricate, adjust and polish, especially in a clinic situation. Base metals also carry some health risks,
Beryllium and Nickel
Both can be hazardous as dust. Be can be bad as a vapor too, causing acute and chronic lung disease. Ni has a high incidence of allergic reactions (especially in women) and has potential cancerous effects.
Why use base metals?
Stiffness is significantly higher, it is etchable and lower cost.
Indicated in resin bonded bridges and long span FPD’s.
What is the standard occlusal reduction? Why?
2 mm. .5 for metal, 1 mm porcelain for strength, an additional .5 porcelain for translucency.
What is the absolute minimum for a finish line?
1 mm. Reasonable esthetics are 1.2.
What drives the decision of the gingival finish line design?
Esthetics! Gotta check with the patient.
What’s the worst esthetic gingival termination?
MP Junction. It is a bad compromise.
When do you use a modified butt?
For gummy smile, thin biotype, light shade.
What are the problems encountered with an inadequate two plane reduction?
Thin porcelain, (not enough) over-contour (not enought), pulpal trauma (too much) or loss of retention/resistance. (Too much)
What is the most common error with an anterior tooth PFM preparation?
Not following the gingival contour, resulting in encroachment into the biologic width.
What are the things you check for making sure the crown is fully seated. Which do you check first?
Proximal contacts (check first), intaglio, soft tissue interference.
What are some things you watch out for chairside with PFMs?
Porcelain fragility on seating. Porcelain adjustment (brittle, contamination from metal), esthetic concerns (shade, contour, texture). You’ve got to make sure you rotate parallel so you don’t take the metal into the porcelain and they don’t cut unevenly. If significant adjustment is required you may eliminate the porcelain esthetic effects.
What do you use to adjust porcelain?
Stones, fine diamonds, disks (not carbides)
What can you use to disclose proximal contacts?
Disclosing media such as occlude, accufilm IV, Hi-Site. Check with articulation paper ad shim stock.
Can you polish porcelain?
Yes! May be better than glazing for smooth surface and reduction in abrasion to opposing dentition. May obliterate surface texture. Generally used for minimal adjustments. There are specific kits that you don’t want to mix with those used for metal.
Does Chairside Surface Staining work?
Yes….but will eventually wear off. Not for significant hue or value changes. Will decrease the value and increase opacity.
Prior to glazing what do you need to check for?
Stray porcelain in the metal area and in the intaglio.
What are the two types of glazing?
Auto glaze and overglaze.
What is metal polishing’s main goal?
Remove the oxide layer. Use white stone, then polish to high luster using rubber wheels and polishing compounds.
What do you base your choice of cement off of?
Available retention, anticipated load, available dentin if bonded system is chosen.
What are the choices of cement?
ZOP, Glass ionomer, resin ionomers, resins.
What is the most frequently used cement?
Resin-ionomers.
What is the cement that is very soluble and it is important to manage moisture?
Glass ionomer
What cement has solubility and sensitivity issues?
ZOP.
What are the three ways you can cure resins?
Chemically, dual, light.
What cements do you clean up only after firmly set?
ZOP and Glass Ionomer. They are quite soluble until set.
What cements do you clean up with cotton pellets immediately upon verification of proper seating?
Resin-Ionomers and resins that are chemical cure or dual cure. Anything with resins, CLEAN UP. Otherwise removal is extremely difficult because they are much less soluble.
What are the post-op instructions for a crown?
Nothing to chew for one hour, nothing hard or sticky for 25 hours. Nothing exceptionally hard, ever.
What is color?
A phenomenon of light or visual perception that enables one to differentiate otherwise identical objects.
What are the main influences of color?
Physical properties of the object. Nature of incident light. Assessment of the observer. Relationship of other colored objects.
Define Metamerism
The appearance of a certain color varies depending on the light source.
The same thing looks very different under different light.
What is the best light source? The worst?
Best: Natural diffuse light (North light)
Worst: Harsh/direct dental chair light.
Hue
Name of the color. Specific wavelength. Basic color of the shade.
Value
Lightness-white/black. Brightness. The quality by which we distinguish lighter shades from darker ones. Most obvious to the human eye.
Chroma
Saturation. Distance from grey. Shade of the same color.
In a tooth, what determines the hue?
Primarily dentin.
What are some limitations of shade systems?
Color gaps (shades are not uniformly positioned throughout tooth color space), inaccurate interpolations (intervals between shades do not yield a single discernable intermediate shade), not systematic. Shades are not schematically organized to reflect all 3 color dimensions.
- They don’t follow a pattern.
- There are no intermediate shades.
- Not systematic. Don’t follow value, hue, chroma. Just random.
How do you use a Vita 3D Guide?
Pick Value first, then chroma, then hue.
VCH
What are some tips on shade selection?
Remove distractions. Wet shade tab. Use indirect lighting. Observe at short intervals. Hold shade tab in line with teeth. View from several angles. Determine VALUE first. Match gingival to gingival-incisal to incisal. Note variations in shading. Record basic shades and maverick colors. Make a shade map of the tooth. Record contours and surface textures.
What are the competing goals of dentistry?
Esthetics vs. Function, pulpal health, predictability. Reduction vs. Conservation.
Why are rounded line angles important in an all ceramic preparation?
Minimize the stress in the ceramic.
Is the finish line constant with all ceramic preparations?
No. Often specific manufacturer recommendations in terms of depth and finish lines.
Standardly: 90 degree termination with cavosurface and shoulder or deep chamfer finish lines. Same axial reduction 360 degrees.
What are the problems with PFM
Esthetics. “Depth”, Translucency. Opacity. “metal” restorations.
What are some issues with All-Ceramic systems?
CRACK propagation. Strength. Need to mask out existing restorative materials and/or discolored dentin. Specialized cementation protocol with some some systems. Lack of long-term clinical studies.
What are some tactics to address the limitations of ceramics?
Stronger ceramics, high strength ceramic cores, and/or bonding to tooth structure.
Bonded Cementation
Strength derived from bonding to tooth. Requires bondable dentin or restorative material. Luting media will participate in final shade if high in translucency. Doesn’t need as much retention and resistance because of the bonding to the tooth structure.
Conventional Cementation
Strength derived from restoration. May be used over metallic substrate or sclerotic dentin. Often less translucent. Limited esthetically. Needs the same retention and resistance form as a gold crown.
What are the conventionally cemented systems with “cores” of high strength porcelain which limit the crack propagation??
Monolithic zirconia core veneered with feldspathic porcelain similar to PFM systems. Generally more opaque. Inceram, procera, lava and others. Cad Cam core with conventionally stacked porcelain. Can be veneered with pressed ceramic. Can be used in FPD’s. Must have sufficient connector space.
What are the systems that require bonding?
Feldspathic, empress, and other pressed ceramics.
Why is Leucite reinforced ceramic so good?
Empress. Very versatile. Gives you the ability to control esthetics in a mouth with lot’s of different needs.
Empress
Created from “lost wax” process. Remaining tooth participates in the shade of the final product. Cut back for layered technique.
What do you consider when choosing what type of ceramic?
Method of fabrication, relative strength, type of cementation, opacity, translucency.
What are the factors of the remaining tooth structure that determine the tooth?
Dentin, underlying restorative material, color of tooth preparation, opacity/translucency of adjacent teeth.
If you have a metallic core or sclerotic dentin, what type of ceramic would you use?
Need opacity. Need Conventional cementation. Layered zirconia. Procera, inceram, lava, cercon
Veneers
Feldspathic, anteriors only.
Leucite
Press, must be bonded, premolars forward. Can be milled.
LIthium disillacate
Can be pressed or milled.
Are ceramic onlays bonded or cemented?
BONDED. That’s why zirconia doesn’t work. Dentin is very unreliable to bond to. Want as much enamel as possible.
Ceramic vs. Gold
Ceramic has: Better esthetics, but worse performance. Uses bonding to assist in retention, while gold uses mechanical retention. Limited long-term data compared to good long term success. And not as favorable of an occlusal surface.
Onlays vs Crowns
Crowns have: Superior retention for a given prep height, where onlays have retention internally and externally. Control of all axial contours while onlays preserve some of the original contours. Margins often terminate on dentin/cementum while onlays terminate on enamel. Crowns remove more tooth structure to obtain draw, while onlays preserve tooth structure.
What is the clearance for ceramic onlays?
Depends on the material. 1.5-2 mm on occlusal.
What are the terminations for ceramic onlays?
Butt joints. 90-110 degrees.
Typical axial reduction?
1 mm.
