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Chapter 47 Laboratory Materials and Procedures. Copyright 2003, Elsevier Science (USA).

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Chapter 47 Laboratory Materials and Procedures

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Chapter 47 laboratory materials and procedures l.jpg

Chapter 47Laboratory Materials and Procedures

Copyright 2003, Elsevier Science (USA).

All rights reserved. No part of this product may be reproduced or transmitted in any form or by any means, electronic or mechanical, including input into or storage in any information system, without permission in writing from the publisher.

PowerPoint® presentation slides may be displayed and may be reproduced in print form for instructional purposes only, provided a proper copyright notice appears on the last page of each print-out.

Produced in the United States of America

ISBN 0-7216-9770-4


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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

  • 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 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

    • 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

    • 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.


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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

  • 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

    • 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

    • 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

    • Supplied in different forms depending on its use.

    • Its makeup is beeswax, petrolatum, and other soft waxes.

    • Uses:

      • Extend the borders of an impression tray.

      • 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:

      • Type A: Hard-inlay wax.

      • Type B: Medium-inlay wax.

      • 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

    • Made from paraffin or ceresin with beeswax and carnauba wax.

    • Hard and brittle at room temperature.

    • Supplied in sheets.

    • Three types:

      • Type I, which is a softer wax used for denture construction.

      • Type II, a medium-hardness wax used in moderate climates.

      • 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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