Transcript Laboratory Materials and Procedures

Chapter 47
Laboratory Materials and
Procedures
Copyright 2003, Elsevier Science (USA).
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Produced in the United States of America
ISBN 0-7216-9770-4
Copyright 2003, Elsevier Science (USA). All rights reserved.
Introduction
Procedures that take place away from the
patient, take place in the dental laboratory.
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Uses of the Dental Laboratory
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Pour up preliminary impressions.
Trim and finish diagnostic models.
Prepare custom trays.
Polish:
• Provisional coverage
• Partial or full dentures
• Indirect restorations
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Laboratory Rules
 No eating, drinking, or smoking.
 Keep all cosmetics out of this area.
 Wear personal protective equipment when
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working in the laboratory.
Keep hair back.
Report all accidents to the dentist immediately.
Follow the manufacturer’s instructions for
equipment operation.
Clean the work area before and after every
procedure.
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Safety in the Lab
 Physical safety
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• Know the location of the fire extinguisher
and fire escape routes.
Chemical safety
• Take care in the handling of corrosive,
toxic, or carcinogenic substances.
Biohazards
• Items brought into the laboratory can also
harbor blood and saliva that could be
potentially infective.
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Dental Laboratory Equipment
 Wall-mounted bins

• Used to store bulk supplies of plaster,
stone, and investment materials.
Work pans
• Open plastic containers with identification
labels used to hold laboratory work in
progress.
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Dental Laboratory Equipment-cont’d
 Heat source
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
• A propane or butane torch or Bunsen
burner is used for this purpose.
Model trimmer
• A machine used to trim stone or plaster
models.
Vacuum former
• Used to construct custom trays for
bleaching, mouth guards, and positioners
for orthodontics.
Copyright 2003, Elsevier Science (USA). All rights reserved.
Dental Laboratory Equipment-cont’d
 Vibrator

• Used to remove air bubbles and to aid in
the flow of the plaster or stone when
pouring diagnostic models.
Laboratory Handpiece
• Low-speed handpiece used for trimming
custom impression trays, adjusting
dentures, and polishing provisional and
indirect restorations.
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Dental Laboratory Equipment-cont’d
 Sandblaster

• Hand-held unit that sprays sand at a high
speed, creating an etching, or pitting, on a
surface area of metal, porcelain, or acrylic.
Articulator
• A machine that works as close as practical
to the way the mouth works.
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Dental Laboratory Equipment-cont’d
 Dental lathe

• Used to polish or trim custom trays,
provisional coverage, dentures, and
indirect restorations.
Instruments
• Wax spatulas
• Mixing spatulas
• Rubber bowls
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Dental Models

Three-dimensional reproductions of the
teeth and the surrounding soft tissue of a
patient’s maxillary and mandibular arches.
Also referred to as study casts.
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Use of Dental Models
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Diagnosis for a fixed or removable prosthetic.
Diagnosis of orthodontic treatment.
Visual presentation of dental treatment.
Making of custom trays.
Making of orthodontic appliances.
Making of provisional coverage.
Making of mouth guards.
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Gypsum Products
 Used extensively in dentistry to make dental

models.
Chemical properties
• A mineral that is mined from the earth.
• In its unrefined state, gypsum is the
dihydrate form of calcium sulfate.
• Converted into a powdered hemihydrate.
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Physical Forms of Gypsum
 Model plaster
• Commonly called plaster of Paris, is used
primarily for pouring preliminary
impressions and the making of diagnostic
models.
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Physical Forms of Gypsum-cont’d
 Dental stone
• For use as a working model when a more
durable diagnostic cast is required.
Examples are in the making of custom
trays and orthodontic appliances.
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Physical Forms of Gypsum-cont’d
 High-strength stone
• Also known as densite or improved dental
stone. Its strength, hardness, and
dimensional accuracy make it ideal to
create the dies used in the production of
crowns, bridges, and indirect restorations.
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Table 47-1: Recommended Ratios of Water to
Powder for Gypsum Products
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Pouring Dental Models
 Model consists of two parts
•
•
Anatomic portion, which is created
from the alginate impression
Art portion, which forms the base of the
model
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Different Pouring Methods
 Double-pour method
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• 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
• Consists of mixing one large mixture of
plaster or stone and pouring both portions
of the model in a single step.
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Trimming and Finishing of Dental Models
 Prepare model
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• Soak in water for at least 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.
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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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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, and then polish with a soft cloth.
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Custom Impression Trays
 Criteria
• Be sufficiently rigid to hold and support the material
during tray placement and removal.
• Fit and adapt well to the arch and maintain patient
comfort.
• Provide accurate adaptation to an edentulous or a
partially edentulous arch.
• Maintain an even distribution of 3 to 4 mm of the
impression material between the tray and the teeth.
• Maxillary tray must cover the teeth and hard palate
and extend slightly beyond the gingival margin.
• Mandibular tray must cover the teeth and extend
beyond the gingival margin.
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Table 47-2 Elements of a Custom Impression Tray
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Custom Tray Materials
 Self-curing acrylic resin
• Provides a strong and easily adaptable
material to create a custom tray. The major
disadvantage of this material is the hazards
of working with the liquid monomer, which
is very volatile.
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Custom Tray Materials-cont’d
 Light-cured resin tray materials
• A premixed, prefabricated light-cured tray
material that does not contain
methylmethacrylate monomer. The
properties of this material provide excellent
adaptation of the model, and may be used
for any impression situation: dentulous,
edentulous, or partially edentulous.
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Custom Tray Materials-cont’d
 Vacuum-formed thermoplastic resin
• A vacuum former uses heat and vacuum to
shape a sheet of thermoplastic resin to a
diagnostic model.
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Dental Waxes
 Boxing wax
• Soft pliable wax with a smooth and 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 it up.
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Dental Waxes - cont’d
 Utility wax
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•
•
Supplied in different forms depending on its
use.
Its makeup is beeswax, petrolatum, and
other soft waxes.
Uses:
1. Extend the borders of an impression
tray.
2. Cover brackets in orthodontic treatment.
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Dental Waxes - cont’d
 Sticky wax
• Supplied in sticks or blocks.
• Main ingredients are beeswax and rosin.
• Very brittle wax, but when heated, it
becomes very tacky.
• Useful when creating a wax pattern or
joining acrylic resin together.
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Dental Waxes - 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 how they flow:
1. Type A: Hard-inlay wax.
2. Type B: Medium-inlay wax.
3. Type C: Soft-inlay wax.
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Dental Waxes - cont’d
 Casting wax
• Makeup is paraffin, ceresin, beeswax, and
resins.
• Supplied in sheets of various thicknesses.
• Used for single-tooth indirect restorations,
fixed bridges, and casting metal portions of
a partial denture.
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Dental Waxes - cont’d
 Baseplate wax
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•
•
•
Made from paraffin or ceresin with beeswax and
carnauba wax.
Hard and brittle at room temperature.
Supplied in sheets.
Three types:
1. Type I, which is a softer wax used for denture
construction.
2. Type II, a medium-hardness wax used in
moderate climates.
3. Type III, a harder wax for use in tropical
climates.
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Dental Waxes - cont’d
 Bite registration waxes
• Soft and very similar to casting waxes.
• Softened under warm water.
• Patient is instructed to bite down, and the
wax will form an imprint of the teeth.
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