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 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
- can mechanically deform cast structure to change structure and get wrought structure
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
what are metals and alloys used for in dent?
- restorations
- instruments/ equipment
why are alloys used a lot in dent?
as they have properties more suited to clinical needs
key properties alloys used in restorations need to have
- restorations need to have:
- high corrosion resistance (pH range, chemical composition)
- high mechanical strength
- Biologically inert
why are titanium alloys used for implants?
- as has 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 happens?
add photo
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
Microstructure of metals
- can see grain boundaries under a microscope
CRYSTAL STRUCTURE
1
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?
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
1
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 as it’s packing factor = 0.52
3
affect the mechanical properties
1
- purpose of etch on metals?
2
why do metal structures stained with acid etch show diff colours of black white and grey?
1
to visualise the metal grain structure
2
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
1
diff between cooling curve of pure metal and alloy
2
why’re the cooling curves different
2
due alloys having diff metals hence which have diff MPs
what are phase diagrams?
- 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
1
what is a phase?
2
what can we use phase diagrams for?
2
- to measure diff diff chemistries within melt of that phase
how do we construct phase diagrams?
explain part of phase diagram
as we cool metal alloy back down, there are 3 diff alloy states that they solidify into. what are they?
what are the 2 types of solid solutions?
- Substitutional Solid Solution
- Interstitial Solid Solution
1
what are Substitutional Solid Solution?
2
only possible if?
3
EG?
1
what is Interstitial Solid Solution
2
only possible if
3
EG
4
typical solute elements?
1
what are inter-metallic compounds?
2
EG?
3
properties?
MAKE Q
- in solid sub CANNOT predict exact structure
DIFFUSION IN METALS
EUTECTIC ALLOYS
WROUGHT STRUCTURES + DEFORAMATION IN METALS
- what does deformation of grains result from?
what happens to crystals under elastic loading?
creating a wrought structure
wrought structure grain deformation
lattice structures have?
influence of impurities + imperfections?
chematics of slip causing plastic deformation within the metal lattice
grain deformation + 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?
Eg of dental relevance of wrought and cast structures
metals offer?
