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Page 1: Impression compound

IMPRESSION COMPOUND

Dr. Anjana Maharjan

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CONTENT Introduction

Composition

Type

Properties

Dimensional Stability

Precaution

Advantage/Disadvantage

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INTRODUCTION

Impression compounds are thermoplastic

materials softened to their working

consistency by immersion in hot water or by

warming over the flame.

Rigid after setting and has poor elastic

properties

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COMPOSITION

Ingredients Parts

Rosin 30

Copal resin 30

Carnauba wax 10

Stearic acid 5

Talc 25 (75)

Coloring agent Appropriate Amount

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TYPE

1. Lower Fusing - Impression Compound

2. Higher Fusing – Tray Compound

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TYPE I

Available as sheets, sticks, cylinders and cones

Should flow readily at just above mouthtemperature

Should be capable of recording sharp grooves0.2-4 mm wide into the surface of metal testblock

Most viscous of impression material i.e 4000(pas) thus characterized as mucocompressive

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TYPE I – SHEETS

Recording Impression of edentulous ridge

Manipulation:

Compound softened in water bath kneaded

with finger to improve qualities

Temperature of water bath 55-60◦C is ideal

for 4-5 mins to ensure complete softening

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Conti..

Gauze is placed at bottom of water bath to

prevent adherence

Soften by heat, inserted in an impression tray

and placed against tissue before it cools to a

rigid mass

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TYPE I - STICKS

Soften with flame

Skill and experience is required

Material is tempered in a water bath before placing in the patient’s mouth

Used to refine /modify peripheral extent of special tray for CD or edentulous region of RPD

Used for securing rubberdam retainer and occlusal registration plate

Recording single crown preparation

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STICKS - COPPER RING

TECHNIQUE

Recording a single

tooth preparation

using stick

Hollow open ended

copper tube used as

a tray

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Conti…

A separate locating impression is also

recorded of the prepared tooth

The die is inserted into this impression and a

stone working model is made by pouring a

stone

This technique is superseded by the use of

rubber base

Still used where moisture control is a problem

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STICKS - MANIPULATION

For adequate border seal for retention of CD

Trimming special tray until it is short of lines

of movement of mucosa

Tray periphery is coated with soften

greenstick and tray replaced in mouth

Cheeks are manipulated to stimulate

functional movement to produce dynamically

generated shape

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Conti..

Care should be taken not to burn patient

Used in distal extent of palatal coverage of

upper denture for border seal

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TYPE II

Also k/a tray compound

Making impression tray

Not distorted at mouth temperature

Used for corrective wash impression by

adapting soften compound on study model and

border of denture area trimmed

Tray compound lacks dimensional stability and

strength

Thus replaced by acrylics and plastics

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PROPERTIES

Glass transition temperature

Temperature at which material losses its

hardness i.e. 39◦C or brittleness

At this stage it is not plastic or soft enough for

making impression

Forms a rigid mass upon cooling

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PROPERTIES

Fusion Temperature:

Indicates definite reduction in plasticity of

materials during cooling

Heating at approximately 43.5◦C material

soften to plastic mass that can be manipulated

Above this temperature soften material

remains plastic while impression being made

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PROPERTIES

Fusion Temperature:

Once the impression tray is seated, it should

be held gently(passively) in position until the

impression cools below the fusion temperature

Impression should not be removed until it

reaches oral temperature

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THERMAL PROPERTIES

Coefficient of thermal expansion 0.3% is

acceptable

conductivity is very low thus need extended

time to achieve thorough heating and cooling

The materials should be uniformly soft at the

time it is placed on the tray and thoroughly

cooled in the tray before the impression is

withdrawn from the mouth

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THERMAL PROPERTIES

Cold water can be sprayed on the tray while it

is in the mouth until the compound is

thoroughly hardened prior to removal of

impression tray from mouth

Low thermal conductivity influences cooling

Outerside cools rapidly and innerside remains

soft thus adequate time is required for cooling

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SOFTENING AND FLOW

Soften at point just above mouth temperature

and exhibit adequate flow to adapt closely to

tissue and register details

Hardens at mouth temperature and exhibit

minimum flow to reduce danger of distortion

on removal

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SOFTENING AND FLOW

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VISCOSITY

Most viscous of impression material i.e.

4000(pas)

70 times greater than impression plaster

100 times greater than light body elastomers

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VISCOSITY

Significance

1. Limits degree of fine detail which can be

recorded in impression

2. Characterizes compound as a mucocompressive

impression material

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VISCOSITY

Advantage

1. Recording impression of some edentulous

patient for recording full depth of sulcus so

that a denture with adequate retention can be

designed

2. Able to displace the lingual and buccal soft

tissue sufficiently

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DIMENSIONAL STABILITY

Relaxation can occur in short time period with

increased temperature

Relaxation causes warpage or distortion of

impression

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DIMENSIONAL STABILITY

To reduce distortion one has to allow the

thorough cooling of impression before

removal from mouth

Construct cast or die as soon as possible

(within 1 hr)

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PRECAUTIONS

Prolong heating /immersion in water bath

cause compound to be brittle and grainy due

to leaching out of low molecular weight

ingredients e.g. stearic acid

Compound should not be allowed to boil or

inginite so that the constituents are volatized

while using flame

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PRECAUTIONS

Incorporation of water acts as plasticizer

Wet kneading causes incorporation of water in

compound causes increased flow at mouth

temperature causing distortion on removal

Reheating also causes increased flow

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ADVANTAGES

Cheap and reusable

Does not produce irritation to patient

Can be remodify and resoften again till the

accurate impression is obtain

Compatible with die and model materials

Easily electroplated to form accurate and

abrasion resistant dies

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DISADVANTAGES

Difficult to record details because of high

viscosity

Mucocompressive

Distortion due to poor dimensional stability

Difficult to remove from severe undercuts

Does not have pleasant taste

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DISINFECTION

In 2% alkaline glutaraldehyde solution

impression is immersed for 10 minutes ,

rinsed and poured

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ADA specification 3 for impression compound

1. Requires to be homogenous

2. Should be smooth and glossy in appearance afterpassed through flame

3. Must be firm and smooth while trimming withsharp knife at room temperature

4. Manufactures must indicate:

Method of softening

Working temperature

Data/curve showing shrinkage from 40-20◦C

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REFERENCES

Applied Dental Materials - 9th edition-Jhon

F.McCabe and Angus W.G.Walls

Restorative Dental Material – Craige

Phillips’ Science of Dental Materials 11th

edition - Knneth J Anusavice

Dental Material Science, Mannippalli

Dental Materials and Their Selection, 3rd

edition, William J O’Brein

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Thank you


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