Introduction to Material Categories Flashcards
_____________ share valence electrons between all the atoms in the solid.
Metals!
____________ are a mixture of two metals in a single phase.
Metal Alloys
Metallic structures are almost exclusively ___________ in nature
Crystalline
The crystals in metals are called ___________.
The edges of these _____ can be seen clearly by treating them with _______ which remove electrons at the edges which are of _______ energy.
The crystals in metals are called _GRAINS_.
The edges of these _GRAINS_ can be seen clearly by treating them with _ACID_ which remove electrons at the edges which are of __HIGHER__ energy.
grain boundaries are shown as _________ between the individual grains because atoms here are at a ______ energy.
grain boundaries are shown as Discontinuities between the individual grains because atoms here are at a Higher energy.
Metals are prone to what two types of corrosion.
Chemical and Electrochemical
What is Chemical Corrosion?
Chemical corrosion occurs by direct chemical reation on the surface of a metal with OXYGEN and other chemicals.
remember: stainless steels are resistant to corrosion because the chromium in them reacts with oxygen at the surface producing a film which prevents the metal underneath from corroding.
What is Electrochemical Corrosion?
occurs when two metals act as electrods of differing structure which being connected by a circuit and an electrolyte. One acts as the Cathode the other as the Anode. The anode is broken down as electrons flow from anode to cathode.
What is a common electrochemical reaction that takes place in the mouth?
Amalgam and Gold restorations interact with each other through saliva (the electrolyte) forming a circuit, which can result in a current being sensed by the pulp (ie: it hurts)
What are Ceramics made of?
Ceramics are substances consisting of metallic and non-metallic elements ionically or covalently bonded to one another.
Ceramics are very ________ to heat
RESISTANT
The three most common ceramics in dentistry are:
1
2
3
SiO2
Al2O2
K2O
What are 3 ceramics that are commonly made from corrosion of metals?
Fe2O3
SnO
Ag2S (from corrosion of amalgams)
When Active metals corrode they form _______products
Active metals corrode to form SOLID CERAMIC products
ie: iron with oxygen froms rust
When Passive metals corrode they ____________
Form Thin Films which prevent further corrosion
ie: In stainless steel chromium reacts with oxygen to form thin layer to protect underlying metal.
What is an “Immune metal”??
IMMUNE METALS are NOT REACTIVE under normal conditions.
Ceramics in dentistry are often _________
Silicate oxides.
Polymers are _____ molecules, made primarily of _______ elements that are chemically bonded via _______ bonds.
Polymers are LONG molecules, made primarily of nonmetallic elements that are chemically bonded via Covalent bonds.
Polymers are made from a process called ______ where multiple subunits called _______ link together.
Polymers are made from a process called Polymerization where multiple subunits called Monomers are linked together.
______ ________ is a polymer that is very commonly used for dentuers and temporary restorations.
methyl methacrylate.
Under normal conditions are polymers crystalline or noncrystalline?
ALMOST ALL POLYMERS ARE NONCRYSTALLINE UNDER NORMAL CONDITIONS
what are the two types of polymerization reactions?
Chain Reaction Polymerization
Stepwise Reaction Polymerization
What is CHAIN REACTION POLYMERIZATION?
it is where monomers are rapidly added to growing chains of polymers
what is STEPWISE REACTION POLYMERIZATION?
monomers are slowly added by random addition to any growing chain ends.
Acrylic monomers undergo what type of polymerization?
chain reaction polymerization
What are the 4 stages of Chain Reaction Polymerization?
Activation (production of free radicals)
Initiation (free radical combination w/ monomer)
Propagation (addition of monomers)
Termination (cancellation of the growing chain)
__________ increase the rate of activation.
Accelerators
3 common accelorators in polymerization are:
1
2
3
1 chemical
2 light
3 heat
_________ are added to polymers to prevent or postpone initiation.
retarders or inhibitors.
Dental Composites consist of ______ particles within a _____ matrix.
Dental composites consist of CERAMIC particles mixed within a POLYMER matrix.
Properties of composites depend on their ____/_____ ratio.
Composite properties depend on their filler/matrix ratio.
