Manual Definitions Flashcards
The maximum stress a material can endure before failure (fracture). It is an important property of any dental restorative material which is subject to significant stress.
Ultimate Tensile Strength (UTS)
The stress that is required to permanently deform a material a specific amount (usually 0.1-0.2%). It is particularly important to consider in the selection of an alloy for FPDs. Not important in the discussion of ceramics because they are brittle.
Yield Strength
The slope of the elastic region of the stress-strain curve. The measure of the material’s stiffness or resistance to deformation.
Modulus of Elasticity
The amount of permanent strain or deformation which occurs in a material at the point of fracture. A measure of the alloy’s ductility.
Elongation
The resistance of a material to withstand penetration or permanent indentation. This can influence potential wear characteristics.
Hardness
The ratio of mass to volume of a material. It is of particular importance in the consideration of casting alloys during the casting procedure.
Density
Characteristics that are of particular importance for biocompatibility.
Tarnish and Corrosion
The change in length per unit of material for 1 degree change in temperature.
Thermal Expansion
Color and translucency characteristics are the most important of this category.
Optical Properties
Inlay Golds are Type ____ or Type ____ alloys.
Type I (soft) or Type II (medium)
Crown and Bridge alloys are Type ____ or Type ____.
Type III (hard) or Type IV (extra hard)
Metal Ceramic Alloys are either _____ or ______.
Hard or Extra-Hard
Casting alloys are classified based on the noble metal (Au, Pd, Pt) content in what percentages?
> 80% Au = very high noble metal
60% noble metal (>40% Au) = high noble metal
25% noble metal (no Au requir.) = noble metal
below 25% noble (no Au requir.) = predom. base metal
The noble metal alloy “Gold-Platinum-Palladium” would be considered a _________.
Very High Noble Metal
Which properties would be ideal for an alloy in metal ceramic restorations?
- High corrosion/tarnish resistance
- High Strength
- High Elastic Modulus
- Closely matched thermal expansion
- Bonding and wetability
- Good Optical properties
- Decent tensile strength
How does a porcelain “wet the surface” of a metal?
By forming an oxide layer on the metal to facilitate the setting process. Chemical and mechanical mechanisms are involved.
Are noble metals able to form an oxide layer for bonding?
No, pure noble metals must have other elements adding in small amounts in order to obtain an oxide layer and achieve good bonding.
What are the two alloy systems used in the clinics for ceramo-metal single unit and FPD?
- Freedom Plus (noble- 78%Pd)
- Olympia (high noble- 51.5% Au)
* these are not yellow*
Do Freedom Plus and Olympia alloy systems have elements added in order to help form an oxide layer?
Yes: Copper (Cu), Indium (In), and Gallium (Ga)
Which material in the clinic is classified as Very High Noble Metal, containing 90% gold?
Jelenko O
Which alloy is used in the clinic for fabrication of CVCs and is classified as Noble (46%Au)? What does this product lack?
Midas
Lacks oxide-forming capabilities (cant bond porcelain)
What is the primary reason for choosing porcelain?
esthetics
True or False: Porcelain is the most biocompatible dental material in use due to its high corrosion resistance and low solubility in the oral cavity.
True
Which property of porcelain can be related to “abrasion resistance”?
Hardness
True or False: Natural tooth enamel is softer than porcelain and wear of opposing teeth must be considered.
True
Ceramics have generally _____ thermal expansions compared to metals.
Lower
The process of mixing feldspar, quartz, and kaolin at high temperatures and then rapidly cooled by quenching.
Fritting
Porcelain is primarily _____ matrix with dispersed crystalline structures.
glass
By controlling the percentage of ______ present in the final composition of porcelain, the thermal expansion can be made to approximately match the alloy.
Leucite
The process by which the porcelain powders are drawn together and condensed under high temperatures as a result of viscous flow; leading to volumetric shrinkage.
Sintering
There are generally at least ____ different porcelain layers which are veneered over the metal to produce a tooth-like appearance.
Three
What are the three layers of porcelain that are layered to create a tooth-like appearance?
Opaque- aids bonding, highly reflective
Body (Dentin)- medium translucency, color
Incisal (Enamel)- high translucency
