Module 4 Lab procedures

Who is a dental laboratory technician?

A trained professional who fabricates dental prostheses based on a written prescription; usually works in a private or in-house lab.

What tasks do dental lab technicians perform?

Fabricate custom trays, pour impressions, articulate models, prepare wax patterns, invest and cast restorations, prepare porcelain and PFM crowns, and fabricate prostheses.

What materials are used for gold cast restorations?

Gold alloys containing platinum, palladium, tin, and iron.

What are porcelain materials used for?

Inlays, bonded veneers, PFM crowns and bridges, porcelain crowns, and materials like Lava, Zirconia, and Procera.

What are composite resin cast restorations used for?

Inlays, onlays, and veneers; stronger than direct composites and may include fiber reinforcement.

What are stainless steel alloys used for?

Primary crowns, space maintainers, orthodontic bands, brackets, wires, and dental instruments.

What are nickel-chromium alloys used for?

Metal cores for PFMs and Maryland bridges.

What are the steps to fabricate a crown?

• Pour final impression,

• create wax pattern on die,

• pour opposing models,

• invest wax pattern, (eliminate wax),

• cast the die,

• cast crown,

• paint porcelain,

• finish and polish.

What does it mean to invest wax?

to encase the detailed wax replica of the crown in a special heat-resistant ceramic material (the "investment") to create a mold, which then allows the wax to be burned out (lost wax casting) and molten metal (or other restorative material) to be poured in

What is the lost-wax technique?

Make a wax pattern on a die → invest it → heat to melt wax → molten material poured into mold-space → restoration removed from investment.

What are the uses of gypsum stone?

• Models (study models),

• casts (for appliance fabrication), dies (working replicas for crowns/bridges/inlays/onlays).

What are the differences between model, cast, and die?

Model = full arch study model;

cast = replica used to make appliances;

die = single/multiple tooth working replica.

What are the types of gypsum stone?

• Type I impression plaster,

• Type II lab plaster,

• Type III lab stone,

• Type IV die stone,

• Type V high-strength die stone.

What is required when constructing a cast?

Rinse/disinfect impression, mix stone, vibrate carefully, add stone in small increments, fill fully, create base.

What are die materials made from?

Hard stones (Type IV/V gypsum); may be electroplated with a thin metal layer.

Why electroplate a die?

Strengthens margins and makes the die more durable.

What are the three types of pattern waxes?

• Inlay wax ( for inlay, onlay, pontics)

• , casting wax (for bridges, partial dentures),

• baseplate wax (for setting denture teeth

What is a sprue?

A cylinder of wax attached to a wax pattern that forms the channel through which molten metal flows into the mold.

What is investment material?

Is used to ‘Invest’ wax patterns

How long does investment material take to harden?

About 1 hour.

What is burnout?

Heating the investment to melt wax and leave the mold-space.

What happens during casting?

Molten metal is forced into the mold-space created by the wax burnout.

What is divesting?

Removing the hardened investment from the cast restoration.

What is quenching?

Cooling the cast restoration in water to crack the investment for easier removal.

What is pickling?

Using an acidic solution to clean oxidation from the surface of the cast restoration.

What is the purpose of CAD/CAM or CEREC technology?

Allows digital imaging, eliminates pre-op impressions and temporaries, and may allow same-day crowns.

What are pros of CEREC crowns?

Time-saving, less invasive, no temporary needed, little rework, good esthetics.

What are cons of CEREC crowns?

Not as strong as conventional crowns, not ideal for every tooth, risk of fracture if margin is subgingival, more expensive, not available in all offices.