Transcript Chapter 7 Body Systems

Laboratory Materials and
Procedures
Chapter 47
Copyright © 2009, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.
Chapter 47
Lesson 47.1
Copyright © 2009, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.
Learning Objectives
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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)
Copyright © 2009, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.
Learning Objectives
(Cont’d)
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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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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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Making models from preliminary impressions
Trimming and finishing diagnostic models
Preparing custom trays
Polishing
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Provisional coverage
Partial or full dentures
Indirect restorations
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Laboratory Rules
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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.
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Safety in the Lab
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Physical safety
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Chemical safety
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Know the location of the fire extinguisher and fireescape routes.
Take care in the handling of corrosive, toxic, and
carcinogenic substances.
Biohazards
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Items brought into the laboratory can harbor blood
and saliva that may be infective.
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Dental Laboratory Equipment
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Wall-mounted bins
Work pans
Heat source
Model trimmer
Vacuum former
Vibrator
Laboratory handpiece
Sandblaster
Articulator
Dental lathe
Lab instruments
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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.
Copyright © 2009, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.
Fig. 47-7 Dental models.
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Use of Dental Models
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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
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Gypsum Products
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Used extensively in dentistry to make dental
models
Chemical properties of gypsum
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A mineral that is mined from the earth
In its unrefined state, the dihydrate form of calcium
sulfate
Converted into a powdered hemihydrate
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Physical Forms of Gypsum
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Model plaster
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Commonly called plaster of Paris.
Used primarily for pouring preliminary impressions
and the making of diagnostic models
Dental stone
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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)
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Physical Forms of Gypsum
(Cont’d)
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High-strength stone
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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
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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
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Pouring Dental Models
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Two parts
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Anatomic portion
• Created from the alginate impression
Art portion
• Forms the base of the model
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Fig. 47-8 Anatomic and art portions of a dental model.
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Different Pouring Methods
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Double-pour method
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Box-and-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.
The impression is surrounded with a “box” made
of wax and poured as one unit.
Inverted-pour method
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One large batch of plaster or stone is mixed and
both portions of the model are poured in a single
step.
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Fig. 47-9 Examples of pouring methods.
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Trimming and Finishing
of Dental Models
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Prepare the model
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Soak it in water for 5 minutes.
Trimming the maxillary model
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Trim the base.
Trim the posterior area.
Trim the sides.
Trim the heel cuts.
Trim the angled portion from canine to canine.
(Cont’d)
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Trimming and Finishing of
Dental Models
(Cont’d)
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Trimming the mandibular model
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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.
(Cont’d)
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Trimming and Finishing of
Dental Models
(Cont’d)
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Finishing the model
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Mix a slurry of gypsum and fill in any voids.
Polishing a plaster model
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Soak the model in a soapy solution for 24 hours.
Dry the model and then polish it with a soft cloth.
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Chapter 47
Lesson 47.2
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Learning Objectives
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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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Custom Impression Trays
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Criteria
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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.
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Guidelines and Terminology for
Creating a Custom Impression Tray
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Undercuts
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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
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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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Guidelines and Terminology for
Creating a Custom Impression Tray
(Cont’d)
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Spacer
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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.
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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.
(Cont’d)
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Guidelines and Terminology for
Creating a Custom Impression Tray
(Cont’d)
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Spacer stops
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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.)
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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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Guidelines and Terminology for
Creating a Custom Impression Tray
(Cont’d)
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Separating medium
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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
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(Cont’d)
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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Guidelines and Terminology for
Creating a Custom Impression Tray
(Cont’d)
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Spacer removal
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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.
(Cont’d)
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Guidelines and Terminology for
Creating a Custom Impression Tray
(Cont’d)
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Finishing
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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.
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Give the tray a final rinse and disinfect it in accordance with
the manufacturer’s instructions.
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Custom Tray Materials
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Self-curing acrylic resin
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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)
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Custom Tray Materials
(Cont’d)
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Material for light-cured resin trays
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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.
(Cont’d)
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Custom Tray Materials
(Cont’d)
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Vacuum-formed thermoplastic resin
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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
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Dental Waxes
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Boxing wax
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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)
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Dental Waxes
(Cont’d)
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Utility wax
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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
(Cont’d)
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Dental Waxes
(Cont’d)
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Sticky wax
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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
(Cont’d)
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Dental Waxes
(Cont’d)
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Inlay casting wax
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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
(Cont’d)
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Dental Waxes
(Cont’d)
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Casting wax
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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
(Cont’d)
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Dental Waxes
(Cont’d)
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Baseplate wax
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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
(Cont’d)
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Dental Waxes
(Cont’d)
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Bite-registration waxes
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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.
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