labaratory materials in dentistry

8/2/2019 Labaratory Materials in Dentistry

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Copyright 2003, Elsevier Science (USA). All rights reserved.

Laboratory Materials and

Procedures


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Introduction

Procedures that take place away from thepatient, 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 whenworking in the laboratory.

Keep hair back. Report all accidents to the dentist immediately.

Follow the manufacturers instructions forequipment operation.

Clean the work area before and after everyprocedure.


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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 alsoharbor blood and saliva that could bepotentially 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 identificationlabels used to hold laboratory work inprogress.


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Dental Laboratory Equipment-contd Heat source

A propane or butane torch or Bunsenburner is used for this purpose.

Model trimmer

A machine used to trim stone or plastermodels.

Vacuum former

Used to construct custom trays for

bleaching, mouth guards, and positionersfor orthodontics.



Dental Laboratory Equipment-contd

Vibrator Used to remove air bubbles and to aid inthe flow of the plaster or stone whenpouring diagnostic models.

Laboratory Handpiece Low-speed handpiece used for trimming

custom impression trays, adjustingdentures, and polishing provisional and

indirect restorations.



Dental Laboratory Equipment-contd

Sandblaster

Hand-held unit that sprays sand at a highspeed, creating an etching, or pitting, on asurface area of metal, porcelain, or acrylic.

Articulator

A machine that works as close as practicalto the way the mouth works.



Dental Laboratory Equipment-contd Dental lathe

Used to polish or trim custom trays,provisional coverage, dentures, andindirect restorations.

Instruments Wax spatulas

Mixing spatulas

Rubber bowls



Dental Models

Three-dimensional reproductions of theteeth and the surrounding soft tissue of apatients maxillary and mandibular arches.

Also referred to as study casts.



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.



Gypsum Products

Used extensively in dentistry to make dentalmodels.

Chemical properties

A mineral that is mined from the earth.

In its unrefined state, gypsum is thedihydrate form of calcium sulfate.

Converted into a powdered hemihydrate.



Physical Forms of Gypsum

Model plaster Commonly called plaster of Paris, is used

primarily for pouring preliminaryimpressions and the making of diagnostic

models.


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Physical Forms of Gypsum-contd

Dental stone

For use as a working model when a moredurable diagnostic cast is required.Examples are in the making of custom

trays and orthodontic appliances.


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Physical Forms of Gypsum-contd

High-strength stone

Also known as densiteor improved dentalstone. Its strength, hardness, anddimensional accuracy make it ideal to

create the dies used in the production ofcrowns, 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 ispoured first. Then a second mix of plasteror 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 ofplaster or stone and pouring both portionsof 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 tocanine.


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Trimming and Finishing of DentalModels-contd

Trimming the mandibular model

Trim the posterior portion of themandibular model until it is even with themaxillary model.

Trim the base. Trim the lateral cuts to match the maxillarylateral cuts.

Trim the back and heel cuts.

Trim from canine to canine in a roundedform.


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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 24hours.

Dry, and then polish with a soft cloth.

Trimming and Finishing of DentalModels-contd


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Custom Impression Trays Criteria

Be sufficiently rigid to hold and support the materialduring tray placement and removal.

Fit and adapt well to the arch and maintain patientcomfort.

Provide accurate adaptation to an edentulous or apartially edentulous arch.

Maintain an even distribution of 3 to 4 mm of theimpression material between the tray and the teeth.

Maxillary tray must cover the teeth and hard palateand extend slightly beyond the gingival margin.

Mandibular tray must cover the teeth and extendbeyond 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. Themajor disadvantage of this material is the

hazards of working with the liquidmonomer, which is very volatile.


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Custom Tray Materials-contd Light-cured resin tray materials

A premixed, prefabricated light-cured traymaterial that does not containmethylmethacrylate monomer. The

properties of this material provide excellentadaptation of the model, and may be usedfor any impression situation: dentulous,edentulous, or partially edentulous.


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Custom Tray Materials-contd Vacuum-formed thermoplastic resin

A vacuum former uses heat and vacuum toshape a sheet of thermoplastic resin to adiagnostic model.


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Dental Waxes

Boxing wax Soft pliable wax with a smooth and shiny

appearance.

Supplied in long narrow strips measuring 1to 1 inches wide and 12 to 18 incheslong.

Used to form a wall or box around a

preliminary impression when pouring it up.


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Dental Waxes - contd

Utility wax 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 - contd 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 orjoining acrylic resin together.


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Dental Waxes - contd

Inlay casting wax Hard brittle wax made from paraffin wax,

carnauba wax, resin, and beeswax.

Used to create a pattern of the indirectrestoration 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 - contd Casting wax

Makeup is paraffin, ceresin, beeswax, andresins.

Supplied in sheets of various thicknesses.

Used for single-tooth indirect restorations,fixed bridges, and casting metal portions ofa partial denture.


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Dental Waxes - contd Baseplate wax

Made from paraffin or ceresin with beeswax andcarnauba wax.

Hard and brittle at room temperature.

Supplied in sheets.

Three types:

1. Type I, which is a softer wax used for dentureconstruction.

2. Type II, a medium-hardness wax used inmoderate climates.

3. Type III, a harder wax for use in tropicalclimates.


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Dental Waxes - contd 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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