Chapter 47: laboratory materials and procedures

Anatomic portion

The structural portion of a dental model created from the Alginate impression.

Articulator

Dental laboratory device that simulates mandibular and temporomandibular joint movement when models of the dental arches are attached to it.

Crystallization

Chemical process in which crystals form a structure.

Die

An accurate replica of the prepared portion of a tooth used in the laboratory during the fabrication of a cast restoration.

Dihydrate

Related to gypsum products and indicating two parts of water to one part of calcium sulfate.

Dimensionally stable

Resistant to changes in width, height, and length.

Facebow

Portion of articulator used to measure the upper teeth as compared with the temporomandibular joint.

Gypsum

Mineral used in the formation of plaster of Paris and stone.

Hemihydrate

Removal of water to become one-half part water to one part of calcium sulfate, forming the powder product of gypsum.

Homogeneous

Having a uniform quality and consistency throughout.

Lathe

Machine used for cutting or polishing dental appliances.

Model

Replica of the maxillary and mandibular arches made from an impression.

Monomer

A molecule that, when combined with other molecules, forms a polymer.

Polymer

Compound of many molecules.

Slurry

Mixture of gypsum and water used in the finishing of models.

Volatile

Substance that can evaporate easily and is very explosive.

Where would the dental laboratory be located in a dental office?

In a separate space away from patient care.

What specialty practices might have a more extensive laboratory setup?

Fixed prosthodontics
Orthodontics

What is an example of s contaminated item in the dental laboratory?

Impression

What place of equipment is used to grind away plaster or stone?

Model trimmer

What piece of equipment does the dentist use to determine centric relation on a diagnostic model?

Articulator

What is the most common wax spatula size used in the laboratory?

#7

What is another term for a dental model?

Dental cast

What dental materials are used to make dental models?

Gypsum

What are the three forms of gypsum?

Dental plaster
Dental stone
High-strength stone

What is the water-to-powder (g/ml) ratio of plaster?

(100g/50ml)

When mixing gypsum materials, do you add the "powder to the water" or the "water to the powder"?

Water to the powder

In what are gypsum materials mixed?

Mixing bowl and spatula

What are the two parts of a dental model?

Anatomic and art

When pouring an impression, where in the maxillary impression do you begin to place the gypsum material?

Palatal area

How long should you wait before you separate the model from the impression?

40-60 minutes

Which of the two models (maxillary or mandibular) do you begin measuring and trimming first?

Maxillary

What area on the maxillary and mandibular model is trimmed differently?

Buccal surfaces

What should be placed between the two models when one is trimming them together?

Wax bite

Of the three types of custom trays discussed, which technique uses a more hazardous material in the fabrication of the tray?

Acrylic resin

Which type of custom tray is made for a vital bleaching procedure?

Thermoplastic resin

In which two forms is acrylic resin supplied?

Powder and liquid, putty

Which type of material is used for a vacuum-formed custom tray?

Thermoplastic resin material

What is the purpose of a spacer?

A spacer is placed on the cast to create room in the tray for the impression material.

How are undercuts corrected on a material when a custom tray is prepared?

Fill all undercuts with wax or other molding materials.

What type of wax could be used to form a wall around a preliminary impression?

Boxing wax

To extend an impression tray, what type of wax would you use?

Rope utility wax

What type of wax would you use to obtain a patients bite impression?

Baseplate wax

What is the most common wax used to create a pattern for an indirect restoration?

Inlay casting wax

Which form of gypsum is used to fabricate a die for making an indirect restoration?

High-strength stone

When pouring an impression, where would you begin placing the gypsum material in a mandibular impression?

Most posterior teeth

What should be placed between the two models when they are trimmed together?

Wax bite

What is placed to prevent a tray from seating too deeply onto the arch or quadrant?

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