4. Metals in the mouth Flashcards
LOs
- each LO is like an exam Q - if can answer each LO with a paragraph or so, should be okay in exams
- important to understand concepts for clinical applications
What are the 3 main types of biomaterials?
What are the types of bonding in different biomaterials?
METALS
CERAMICS
POLYMERS
what is metallic bonding?
- metal atoms sit in a sea of e-
- e- can move in any direction around atoms (unlike covalent bond = e- move in fixed orbitals)
- least understood bonding mechanism
- ordered crystalline structure
what is cast and wrought?
- metals may be processed by various methods
- can heat metal up in furnace (to about 1000 degrees) and can CAST liquid metal into a given shape, once cooled = CAST structure
- can take CAST structure and mechanically deform it (eg hit with hammer) = changes structure and you end up with WROUGHT structure
EXTRA
- a CAST structure is hot work in process
- WROUGHT structure is a cold work in process
1
EG of where alloys are used
2
why are alloys used in dent?
1
- restorations
- instruments/ equipment
2
- so they have a range of mechanical properties so more suited to our clinical needs
- offer strength and ductility (can still be shaped)
EG of alloys used in restorations
SLIDE 6
What are metals and alloys used for in dentistry?
key properties alloys used in restorations need to have?
Restorations
Instruments / equipment
restorations need to have:
* high corrosion resistance (pH range, chemical composition)
* high mechanical strength
* Biologically inert
why are titanium alloys used for implants?
Metals can be used to produce for eg titanium alloys for implants
Titanium alloys have correct modulus to match that of surrounding bone
1
what is Lost Wax Casting Technique?
2
what is the objective and what needs to be allowed for?
1
- technique to shape metals into a clinically useful shape
- can make tooth shape, part of zygomatic arch etc
2
how does Lost Wax Casting Technique work?
- take wax shape
- put on a sprue (little piece of wax)
- this sprue sits on sprue base
- pack around base with sand or investment material
- let investment material dry and set
- can take base away
- heat up investment material and melt wax out
- create burnout region (void)
- have hole = shape of tooth + sprue runner that connects it to outside of chamber
- can turn it upside down and fill with molten metal
- allow it to cool
- and chip away investment
- what we had in wax we now have in metal
- can remove it from the sprue system
- clean + polish and have a finished crown
Simple video:
https://www.youtube.com/watc
h?v=yFbmtJyBthg
why may we overlay enamels and polymers after Lost Wax Casting Technique
- by using this technique can we can develop elaborate prosthesis EG full bridges, denture plates, etc
- can overlay enamels and polymers to make more aesthetically pleasing + clinically relevant
1
what is CAD/CAM Production of Prostheses?
2
what is subtractive process
3
advantages?
1
- more modern way of producing crowns, bridges, etc
2
- This is a subtractive process: cutting or grinding from a blank shape
- rotating dental drill is used to burr out and produce shapes you want
- can produce complex shapes
3
- relatively low cost and low time
1
what is Additive manufacturing
2
advantages
3
disadvantages
1
- Emerging CAD/CAM Process
- start with bowl of powder
- use laser system to melt layer upon layer of powder together
2
- allows us to build more texture
- easier to add undercuts + other shapes
- fast production
3
- as produced layer upon layer, each interface = potential zone of weakness
- in compression it works well but moving it in sheer (side to side, forces rub against each other) the interfaces can break easily
- in sheer would only have 2/3 of the mechanical strength compared to if produced by subtractive manufacturing
- https://www.youtube.com/watch?v=zTutyVxbOXk
COOLING CURVE OF PURE METALS
What does the graph look like ?
Feature of cooling curve of pure metals?
COOLING CURVE OF PURE METALS:
COOLING CURVE OF PURE METALS
what is a phase?
structurally homogeneous part of a system with clear physical boundaries
COOLING CURVE OF PURE METALS
1
what is latent heat of fusion?
2
when does it happen?
1
energy released while it goes from complete liquid to solid
2
during thermal arrest
COOLING CURVE OF PURE METALS
why does the temp not change during thermal arrest
add photo
Microstructure of metals?
- can see grain boundaries under a microscope
Crystal structure
what is a unit cell?
inside grains - metal atoms pack in a recognised position
- these atoms form a unit cell
1
- the smallest atomic unit in crystal which are repeated in three directions
Atomic arrangement in solid materials
what is a crystalline phase?
- have regular array of atoms in a 3-D space
- have long range order
What are the Seven 3D Crystal Lattice Systems?
What does each look like?
Ways atoms can be arranged:
- cubic
- tetragonal
- orthorhombic
- rhombohedral
- hexagonal
- monoclinic
- triclinic
3 Dimensional Unit Cell
What is a structural cell?
What are the 3 most common 3D unit cells?
can pack diff amount of atoms in diff shapes
Body centred cubic
Face centred cubic
Hexagonal close packing
What is the packing factor formula ?
2
what does it mean
3
what properties does packing factor affect?
2
EG 52% of that given cube is packed with atoms
Packing factor of 0.74 means 74% filled with atoms
3
affect the mechanical properties
Purpose of etch on metals?
why do metal structures stained with acid etch show diff colours of black white and grey?
Visualization of metal grain structure with etching
due to being packed in diff orientations
EXTRA
- grains may be orientated in diff directions
- so when apply acid etch to surfaces roughnesses will be diff and reflect light in diff ways
- if all atoms packed the same way then colour wil be same
Metal alloys
What are alloys?
Examples of alloys in dentistry and what they’re made of?
Metal alloy - blend of one or more alloys
Can have binary system (made of 2 metals) eg brass
Or ternary system (made of 3 )
Brass - zinc + copper
Dental gold alloy - gold, copper, silver
Implant alloy - Titanium, vanadium, aluminum
(binary and ternary systems)
1
Difference between cooling curve of pure metal and alloy?
2
Why are the cooling curves different?
2
due alloys having diff metals hence which have diff MPs
what are phase diagrams?
Phase/phase diagram relevant in ALLOYS
Cooling curves help establish alloy composition behavior = phase diagram
- can join these dots together to find out phase where we have liquid and solid
Phase diagrams
What is phase?
What can we use phase diagrams for?
Phase diagrams can be used to measure different chemistries within melt of that phase
How do we construct phase diagrams?
Explain part of phase diagram?
What are the three different phases that can form in alloys?
as we cool metal alloy back down, there are 3 diff alloy states that they solidify into. what are they?
slide 28
what are the 2 types of solid solutions?
- Substitutional Solid Solution
- Interstitial Solid Solution
Substitutional Solid Solution - what are they?
2 only possible if?
3 EG?
Interstitial Solid Solution - what are they?
2 only possible if
3 EG
4
typical solute elements?
IF 60 PERCENT DIFFERENT in atomic sizes INTERSTITIAL SOLID SOLUTION
1
what are inter-metallic compounds?
2
EG?
3
properties?
In this diagram - Light grey - solid substituion
Dark grey - inter metallic compounds
Go through to find Q
In solid substitution can’t predict exact structure
Diffusion in metals
add phot 34
Eutectic alloys
Eutectic alloys
Wrought structures and deformation in metals
What does deformation of grains result from?
What happens to crystals under elastic loading?
Creating a wrought structure
Creating a wrought structure – exceed the elastic limit and deform the crystal structure
Wrought structure grain deformation
Lattice structures have ?
Influence of impurities and imperfections
Schematics of slip causing plastic deformation within the metal lattice
Grain deformation and elongation
What are slips exhibited as in metal alloys?
Slip is exhibited as plastic deformation in metals/alloys (fine grained structures)
What is annealing?
Changes when annealing wrought structures
Example of dental relevance of wrought and cast structures
(WHEN YOU PLACE Endodontics file into root canal, turn it three times and then remove
Endodontics file has soft core so flexible and cast like structure but external structure has wrought like structure so hard and cut through canal
As you keep turning file, applying more dislocations through wrought surface making it more brittle
If you turn more than three times may split and break in the canal)
Metals offer?
Metals can also be used for
