3.2 metal alloys and metal framework fabrication part 2

which investment consists of:

• 80% refractory fillers (silica in form of cristobalite or quartz)

• binder (magnesium oxide and phosphate)

• carbon is added to produce clean castings and facilitate easy removal of castings

phosphate bonded

which investment advantages:

• high strength 

• easily withstand temp that reach 1650℉

• used w high-fusing ceramometal alloys 

phosphate bonded

which is the preferred investment material for rpd?

ethyl silicate

which investment consists of:

• the binder is silica gel which reverts to silica

• can be heated from 2000-2150℉

ethyl silicate bonded

which investment advantages:

• ability to cast high temp alloys (base metal alloys)

• good finish

• low distortion

• high thermal expansion 

ethyl silicate bonded

what lab manipulation affects the microstructure and mechanical properties of Cr-Co alloys?

casting temp

what lab manipulation is used to adjust the alloy due to hardness and strength?

high speed lab equipment

cast clasps can break in service even in short period of time, due to ?

fatigue

it is (easy/difficult) to adjust hardness, strength and low elongation

difficult

T or F: high hardness can cause excessive wear of restorations or natural teeth that contact the cast framework 

true

which metal:

• most allergic metal known w 10-20% incidence

• most common in women/chronic exposure through jewelry 

• can be quite severe 

nickel

T or F: all nickel allergic indivs will react to intra oral nickel

false, immunological tolerance, possible genetic component

T or F: nickel ions (Ni²⁺) are mutagens but not carcinogens

true

various Ni compounds may contribute to development of which cancers

nasal and lung

which material:

• increase risk of lung CA and tumors

• paired with Ni reveal high leakage

• acidic environment enhances its release from Ni-Cr alloys

beryllium

what is berylliosis?

chronic allergy-type lung response and chronic lung disease caused by exposure to Be and its compounds 

occupational lung disease occur only in indiv

w hypersensitivity to beryllium

T or F: berylliosis is curable

false incurable, symptoms can be treated tho

six initial steps of fabrication of metal framework

• survey by retripoding master cast and outline the partial design on the cast 

• beading (score for better adaptation) 0,5mm deep and wide

• block out and relief (four types)

• duplication w reversible hydrocolloid

• refractory cast trimmed and treated w model spray or beeswax

• waxing

what are the four types of block out and reliefs?

• parallel block out

• shaped

• arbitrary 

• relief 

A: parallel block out

B: shaped block out

C: arbitrary aka soft tissue block out 

D: relief, tissue stopper

what is a refractory cast?

refractory cast is a heat-resistant material, often a dry mixture of refractory aggregates, powders, and binders, that becomes a pourable, cement-like mass when mixed with water

why would you duplicate during fabrication of metal framework?

To create a precise, high-heat resistant model on which the framework can be waxed and cast without damaging the original master model. The duplication process produces a special model called a refractory cast. 

• agar storage unit, duplicating flask

what is then added to metal framework?

• major connector and denture base minor connectors 

• clasps

• spruing

• investing

what is a spruing?

the process of attaching wax patterns of sprues to a wax-up of the RPD framework. These sprues form channels that will allow molten metal to flow into the mold to cast the final metal framework after the wax is removed. Proper spruing is critical to prevent casting defects and ensure the RPD framework fits correctly

paint-on investment A first or second?

paint on investment B first or second?

what are the final steps of fabrication of metal framework?

• burn out and casting

• recovering the casting

• finishing and polishing 

what alloys are used for the retentive clasp?

cast alloy clasps or WW clasps 

which alloy for retentive clasp: cast as part of framework?

cast alloy clasp

which alloy for retentive clasp: should be soldered to the framework?

WW clasp

why should excessive heating of the ww clasp be avoided during casting or soldering?

bc it will cause recrystallization compromising the wire’s mechanical properties

ww have (reduced/increased) flexibility when overheated

reduced

ww clasps should be soldered (near/at a distance from) retentive terminal reducing the likelihood of overheating during soldering procedure

at a distance

what gauge thickness are ww clasps available in?

18-20

advantages of which retentive clasp?

• flexible in any direction

• greater undercut 0.02”

• more esthetic 

• minimum tooth contact

• less fatigue failure

ww

disadvantages of which retentive clasp?

• extra step in fabrication

• distorted by pt careless handling 

• distortion with function 

ww

what to look for w extraoral exam?

• presence of defects (positive bubbles or nodules, voids or porosities)

• continuity (reproduction of anatomy)

• thickness of components

• finish lines (staggered and less than 90°)

• polish tissue surface of major connector not too much tho for good adaptation 

• fit

• any occlusal contacts on metal components?

• retention

• interference

• relief and block outs correct?

• esthetics

• damage on master cast?

describe thickness of major connector, rest, and clasp

• major connector: rigid and strong 

• rest: minimum 1.5 mm at junction

• clasp: uniformly tapered 

internal vs external finish lines

Internal and external finish lines are the junctions where the acrylic resin denture base meets the metal framework

The external finish line is on the visible, polished surface of the RPD, while the internal finish line is on the tissue-facing side.

They are staggered, or offset, to prevent a thin, weak area at the junction, which improves the strength and durability of the denture. 

which portion of major connector is highly polished?

• tissue surfaces crossing the gingival margin

• mandibular major connector 

T or F: technician can change design w/o doctor permission

false!

what to note for extraoral examination fit?

• guide plate, rest confined in rest seat & tissue stop

• intimate adaptation of rests, linguoplates, clasp arms

• any spaces will promote plaque accumulation, decay & tissue inflammation

• rocking

common areas to check for complete and stable seating: locating interferences: contacts btwn framework and abutment teeth

• areas: above the survey line

  • shoulder region of circumferential clasps A

  • under rests B

  • on minor connectors and interproximal extension of lingual plates C

extraoral or intraoral exam: disclosing medium, show-through metal, carbide but or abrasive stone in high speed handpiece

intraoral

which part of intraoral exam:

• confirm intimate contact w disclosing medium (no psaces)

• abutment teeth and mucosal surfaces

adaptation 

5 things to consider for occlusal eval (articulating paper and carbide bur in high speed handpiece)

1. check pt occlusion w nothing in the mouth

2. check centric contacts w on framework at a time

   1. adjust contacts until original contacts established

   2. repeat w other framework

3. check eccentric contacts and repeat w other framework 

4. check occlusal contacts w both frameworks 

5. final correction 

what are some considerations for intraoral exam?

• overcutting leading to mechanical failure

  • lost rest = lost support for denture

  • weakend clasp will fracture

• reduction of opposing teeth 

  • avoid if possible

  • adequate design and sufficient prep

what should be used for finishing and polishing?

mounted stone, rubber point