4. Metals in the mouth Flashcards by Madeeha Umair

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

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what are the 3 main types of biomaterials?

what are the types of bonding in biomaterials?

metals
ceramics
polymers

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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

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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

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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)

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EG of alloys used in restorations

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what are metals and alloys used for in dent?

restorations
instruments/ equipment

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why are alloys used a lot in dent?

as they have properties more suited to clinical needs

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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

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why are titanium alloys used for implants?

as has correct modulus to match that of surrounding bone

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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

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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

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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

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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

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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

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COOLING CURVE OF PURE METALS

what happens?

add photo

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COOLING CURVE OF PURE METALS

what is a phase?

structurally homogeneous part of a system with clear physical boundaries

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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

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COOLING CURVE OF PURE METALS

why does the temp not change during thermal arrest

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Microstructure of metals

can see grain boundaries under a microscope

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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

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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 what metals is brass made of? 2 what metals may be used in dental gold alloy? 3 what metals may be used in implant alloy?

1 zinc + copper 2 gold, copper, silver 3 Titanium, vanadium, aluminum (binary and tertiary systems)

1 how do we investigate if metals will work well together in alloys 2 why is it important to study how metals work together?

1 - study of phase diagrams - physical properties - microstructure - study cooling curves 2 - the metals in alloys will react together in diff ways at diff temp - hence need to investigate what we need to have the right chemical properties for certain clinical applications

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