1. Laboratory Materials and Procedures
Chapter 47
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2. Chapter 47
Lesson 47.1
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3. Learning Objectives Pronounce, define, and spell the Key Terms.
Discuss the safety precautions that should be taken in the dental laboratory.
List the types of equipment found in a dental laboratory and their uses.
(Cont’d)
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4. Learning Objectives
(Cont’d)
Describe dental models and how they are used in dentistry.
Discuss gypsum products and their role in making dental models.
Mix dental stone.
Pour a set of dental models using the inverted-pour method.
Trim and finish a set of dental models.
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5. Introduction
Procedures that take place away from the patient take place in the dental laboratory.
Where is the in-house dental laboratory located?
Discuss the distinctions between in-house and outsourced dental laboratories.
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6. Uses of the Dental Laboratory
Making models from preliminary impressions
Trimming and finishing diagnostic models
Preparing custom trays
Polishing
Provisional coverage
Partial or full dentures
Indirect restorations
What are preliminary impressions used for?
What are diagnostic models used for?
What are custom trays used for?
What is provisional coverage?
What is an indirect restoration?
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7. Laboratory Rules Eating, drinking, and smoking are prohibited.
Keep all cosmetics out of this area.
Wear personal protective equipment when working in the laboratory.
Keep hair back.
Report all accidents to the dentist immediately.
Follow the manufacturer’s instructions for the operation of equipment.
Clean the work area before and after every procedure.
These rules should be followed in the laboratory on campus as well.
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8. Safety in the Lab Physical safety Chemical safety Biohazards
Know the location of the fire extinguisher and fire-escape routes.
Chemical safety
Take care in the handling of corrosive, toxic, and carcinogenic substances.
Biohazards
Items brought into the laboratory can harbor blood and saliva that may be infective.
Do you know the correct procedure for a fire?
What is an MSDS sheet?
How is biohazardous material labeled?
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9. Dental Laboratory Equipment
Wall-mounted bins
Work pans
Heat source
Model trimmer
Vacuum former
Vibrator
Laboratory handpiece
Sandblaster
Articulator
Dental lathe
Lab instruments
What is the purpose of each piece of equipment in the dental laboratory?
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10. Dental Models
Dental models are three-dimensional reproductions of the teeth and the surrounding soft tissue of a patient’s maxillary and mandibular arches. They are also referred to as study casts.
Dental models are also known as study models or diagnostic casts.
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11. Fig Dental models.
What type of impression material is used to obtain these study models?
Models should be free of voids and errors before presentation.
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12. Use of Dental Models Diagnosis for a fixed or removable prosthetic
Diagnosis for orthodontic treatment
Visual presentation of dental treatment
In the making of custom trays
In the making of orthodontic appliances
In the making of provisional coverage
In the making of mouth guards
How many students have had study models made?
For what reasons?
What is one example of a fixed or removable prosthetic?
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13. Gypsum Products Used extensively in dentistry to make dental models
Chemical properties of gypsum
A mineral that is mined from the earth
In its unrefined state, the dihydrate form of calcium sulfate
Converted into a powdered hemihydrate
The differences in hemihydrate crystals determine the water-to-powder ratios for all three types of gypsum.
What are the three types of gypsum?
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14. Physical Forms of Gypsum
Model plaster
Commonly called plaster of Paris.
Used primarily for pouring preliminary impressions and the making of diagnostic models
Dental stone
For use as a working model when a more durable diagnostic cast is required.
Examples include the making of custom trays and orthodontic appliances.
(Cont’d)
Model plaster is white in color.
What are diagnostic models used for?
What is the correct water-to-powder ratio?
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15. Physical Forms of Gypsum
(Cont’d)
High-strength stone
Also known as densite or improved dental stone
Ideal, because of its strength, hardness, and dimensional accuracy, for the creation of the dies used in the production of crowns, bridges, and indirect restorations
Densite is blue.
Mostly used by dental laboratory technicians.
What is the appropriate water-to-powder ratio?
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16. Recommended Powder/Water Ratios for Gypsum Products
Model plaster (100 g) to 45 to 50 mL of water
Dental stone (100 g) to 30 to 32 mL of water
High-strength stone (100 g) to 19 to 24 mL of water
Dental stone is yellow/gold.
What are working models used for?
What is the appropriate water-to-powder ratio?
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17. Pouring Dental Models Two parts Anatomic portion Art portion
Created from the alginate impression
Art portion
Forms the base of the model
Strict measurements must be followed.
The mix should be smooth and creamy.
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18. Fig. 47-8 Anatomic and art portions of a dental model.
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19. Different Pouring Methods
Double-pour method
The anatomic portion of the model is poured first; then a second mix of plaster or stone is used to prepare the art portion.
Box-and-pour method
The impression is surrounded with a “box” made of wax and poured as one unit.
Inverted-pour method
One large batch of plaster or stone is mixed and both portions of the model are poured in a single step.
The double-pour method is the easiest to use in the learning stages; two mixes are used.
The box-and-pour is not commonly used in the dental office.
The inverted-pour method uses measurements of water and powder that must be exact; there must be enough mix for both the anatomic and art portions.
What happens if powder is added to a thin, runny mix?
What happens if water is added to a thicker mix?
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20. Fig. 47-9 Examples of pouring methods.
Which is the box-and-pour method?
What is used around the impression for the box-and-pour method?
Rubber bases can be used to eliminate trimming.
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21. Trimming and Finishing of Dental Models
Prepare the model
Soak it in water for 5 minutes.
Trimming the maxillary model
Trim the base.
Trim the posterior area.
Trim the sides.
Trim the heel cuts.
Trim the angled portion from canine to canine.
(Cont’d)
Why soak models before trimming them? (To make trimming easier.)
Follow the guidelines to obtain an even appearance.
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22. Trimming and Finishing of Dental Models
(Cont’d)
Trimming the mandibular model
Trim the posterior portion of the mandibular model until it is even with the maxillary model.
Trim the base.
Trim the lateral cuts to match the maxillary lateral cuts.
Trim the back and heel cuts.
Trim from canine to canine in a rounded form.
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23. Trimming and Finishing of Dental Models
(Cont’d)
Finishing the model
Mix a slurry of gypsum and fill in any voids.
Polishing a plaster model
Soak the model in a soapy solution for 24 hours.
Dry the model and then polish it with a soft cloth.
What is a slurry?
Why polish a model?
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24. Chapter 47
Lesson 47.2
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25. Learning Objectives
Describe the three types of custom impression trays and their use in dentistry.
Construct an acrylic resin custom tray.
Construct a light-cured custom tray.
Construct a vacuum-formed custom tray.
Describe the types of dental waxes and their use in dentistry.
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26. Custom Impression Trays
Criteria
The tray must be sufficiently rigid.
The tray must fit and adapt well to the arch.
The tray must provide accurate adaptation to an edentulous or a partially edentulous arch.
The tray must maintain an even distribution of impression material.
The maxillary tray must cover the teeth, hard palate and extend slightly beyond the gingival margin.
The mandibular tray must cover the teeth and extend beyond the gingival margin.
For whom are custom trays made?
For what procedures are custom trays used?
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27. Guidelines and Terminology for Creating a Custom Impression Tray
Undercuts
The first step in cast preparation is to fill all undercuts with wax or other molding material.
Air bubbles in the cast, the shape of the arch and ridge, carious lesions, fractured teeth, and deep interproximal spaces and malposed teeth may cause undercuts.
Outlining the tray
The margins of the cast where the finished tray will be seated are outlined in pencil.
The outline designates the area to be covered by the tray.
The outline extends over the attached gingiva to the mucogingival junction and 2 to 3 mm beyond the last tooth in the quadrant.
(Cont’d)
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28. Guidelines and Terminology for Creating a Custom Impression Tray
(Cont’d)
Spacer
Placed on the cast to create room in the tray for the impression material.
Baseplate wax, a folded moist paper towel, or a commercial nonstick molding material may be used for this purpose.
To create the spacer, cut a length of baseplate wax, warm it, and place it on the cast over the area of the tray.
A warmed plastic instrument is used to lute the wax to the cast.
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29. Guidelines and Terminology for Creating a Custom Impression Tray
(Cont’d)
Spacer stops
Triangular or round holes are cut out of the spacer with the use of a laboratory knife or wax spatula.
These cutouts are placed to prevent the tray from seating too deeply onto the arch or quadrant.
Allow for an adequate quantity of impression material around the preparations.
The cutouts form bumps on the tissue side of the tray. (The tissue side is the inner surface of the completed tray.)
An edentulous tray requires a minimum of four stops, one each on the crest of the alveolar ridge in the area of the first or second molar. Additional stops may be placed on the crest of the ridge in the area of each canine.
A tray used to take an impression of prepared natural teeth, as for a crown or bridge, has the stops placed near, but not on, the prepared teeth.
(Cont’d )
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30. Guidelines and Terminology for Creating a Custom Impression Tray
(Cont’d)
Separating medium
The prepared cast, spacer, and immediate surrounding area are painted with a separating medium so that the completed tray can be readily separated from the cast.
Handle
A handle adapted to the tray will allow easier placement in and removal from the patient’s mouth.
Always placed at the anterior of the tray, as near the midline as possible, facing outward and parallel to the occlusal surfaces of the teeth.
The handle is formed from a piece of scrap acrylic that has been cut away from the tray.
The end of the handle and the area where it will be attached to the tray are moistened with tray resin liquid.
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31. Guidelines and Terminology for Creating a Custom Impression Tray
(Cont’d)
Spacer removal
After the tray has been formed, remove the spacer and clean the tissue side of the tray.
A small, stiff brush, such as a toothbrush, is used to remove most of the wax at this time.
Remove the remainder of the spacer and clean the interior of the tray after it reaches its final set.
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32. Guidelines and Terminology for Creating a Custom Impression Tray
(Cont’d)
Finishing
Rough areas on the tissue side of the tray do not need to be removed; this surface will be covered with impression material.
Smooth any rough outer edges of the tray so they do not injure the tissues of the patient’s mouth.
A laboratory knife can be used to smooth minor rough areas.
An acrylic bur in a straight handpiece can be used to remove major rough areas.
An alternative is to use the laboratory lathe to smooth the edges.
Give the tray a final rinse and disinfect it in accordance with the manufacturer’s instructions.
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33. Custom Tray Materials Self-curing acrylic resin
The resin provides a strong and easily adaptable material to create a custom tray.
Disadvantage: The liquid monomer is very volatile and so poses a hazard.
(Cont’d)
The work area must be well-ventilated
Personal protective equipment must be worn.
Self-curing acrylic resin may irritate the skin.
What does volatile mean?
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34. Custom Tray Materials Material for light-cured resin trays
(Cont’d)
Material for light-cured resin trays
The premixed, prefabricated light-cured tray material does not contain methylmethacrylate monomer.
The properties of this material provide excellent adaptation of the model.
The material is used for any impression situation: dentulous, edentulous, or partially edentulous.
Light-cured resin requires special light to cure the material.
This method and material provide low shrinkage.
Using these materials for models requires more time than the use of a self-curing resin material does.
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35. Custom Tray Materials Vacuum-formed thermoplastic resin
(Cont’d)
Vacuum-formed thermoplastic resin
Uses heat and vacuum to shape a sheet of thermoplastic resin to a diagnostic model
Uses
Impression trays
Making of provisional
Vital bleaching trays
Mouth guards
Different gauges of plastic are available and are chosen on the basis of their intended use.
A vacuum former is used to melt the plastic, and then the vacuum is turned on and the material is “sucked” onto the cast.
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36. Dental Waxes Boxing wax
Soft, pliable wax with a smooth, shiny appearance.
Supplied in long narrow strips measuring 1 to 1½ inches wide and 12 to 18 inches long.
Used to form a wall or box around a preliminary impression when pouring.
(Cont’d)
For which pouring method would the boxing wax be used?
Boxing wax is not often used in dental offices.
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37. Dental Waxes Utility wax
(Cont’d)
Utility wax
This wax is supplied in various forms, depending on its use.
It is composed of beeswax, petrolatum, and other soft waxes.
Uses
Extend the borders of an impression tray
Cover brackets in orthodontic treatment
Utility wax is clear/white or red.
It is most often supplied in long ropes.
It is easy to apply and remove.
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38. Dental Waxes Sticky wax Supplied in sticks or blocks
(Cont’d)
Sticky wax
Supplied in sticks or blocks
Main ingredients are beeswax and rosin
Very brittle but becomes very tacky when heated
Useful in the creation of a wax pattern or joining of acrylic resin
Sticky wax can be used in the dental laboratory to fix a broken tooth on a dental cast.
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39. Dental Waxes Inlay casting wax
(Cont’d)
Inlay casting wax
Hard, brittle wax made from paraffin wax, carnauba wax, resin, and beeswax
Used to create a pattern of the indirect restoration on a model
Classified according to flow:
Type A: hard-inlay wax
Type B: medium-inlay wax
Type C: soft-inlay wax
Inlay casting wax is mostly used by the dental laboratory technician.
For what processes are the different classifications of inlay wax used?
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40. Dental Waxes Casting wax
(Cont’d)
Casting wax
Made up of paraffin, ceresin, beeswax, and resins
Supplied in sheets of various thicknesses
Used for single-tooth indirect restorations, fixed bridges, and casting of metal portions of a partial denture
For what processes is casting wax used?
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41. Dental Waxes Baseplate wax
(Cont’d)
Baseplate wax
Made of paraffin or ceresin with beeswax and carnauba wax
Hard and brittle at room temperature
Supplied in sheets
Three types
Type I: softer wax used for denture construction
Type II: medium-hardness wax used in moderate climates
Type III: harder wax for use in tropical climates
Baseplate wax is pink.
What else can baseplate wax be used for? (Bite registration.)
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42. Dental Waxes Bite-registration waxes
(Cont’d)
Bite-registration waxes
These waxes are soft and very similar to casting waxes.
Bite-registration wax softens under warm water.
The patient is instructed to bite down, leaving an imprint of the teeth in the wax.
Bite-registration waxes are supplied in wafer form.
What is the purpose of a bite registration?
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