Impression for fixed restorations - Semmelweis Egyetem · Crowns and other extra-coronal restorations: Impression materials and technique R W Wassell, D Barker & A W G Walls British

Semmelweis University

Faculty of Dentistry

Department of Prosthodontics

Peter Hermann

Impression for fixed restorations

WHAT IS AN IMPRESSION?

WHAT IS AN IMPRESSION?

DEFINITION!

• IMPRESSION:

A NEGATIVE LIKENESS OR

COPY IN REVERSE OF THE

SURFACE OF AN OBJECT; AN

IMPRINT OF THE TEETH AND

ADJACENT STRUCTURES FOR

USE IN DENTISTRY.

The Glossary of Prosthodontic Terms. Journal of Prosthetic Dentistry, July 2005.

AIM

1.

accurate models of the oral tissues made from high

quality impressions

exact duplication of the prepared tooth, including:all of the preparation andenough uncut tooth surface beyond the preparation to be certain of the location and configuration of the finish line.

teeth and tissue adjacent to the prepared tooth:articulation of the castcontouring of the restoration

METHODsoft, semifluid material placed in the mouth and allowing that material to set

CLASSIFICATION OF

IMPRESSION MATERIALS

CROWNS AND OTHER EXTRA-CORONAL RESTORATIONS: IMPRESSION MATERIALS AND TECHNIQUE

R W WASSELL, D BARKER & A W G WALLS

BRITISH DENTAL JOURNAL 192, 679 - 690 (2002) PUBLISHED ONLINE: 29 JUNE 2002

DOI:10.1038/SJ.BDJ.4801456

Non-elastic impression materials are generally not used for obtaining impressions of crown preparations because of their inability to accurately record undercuts.

Elastic impression materials!

http://www.nature.com/bdj/journal/v192/n12/full/4801456a.html

CROWNS AND OTHER EXTRA-CORONAL RESTORATIONS: IMPRESSION MATERIALS AND TECHNIQUE

R W WASSELL, D BARKER & A W G WALLS

BRITISH DENTAL JOURNAL 192, 679 - 690 (2002) PUBLISHED ONLINE: 29 JUNE 2002

DOI:10.1038/SJ.BDJ.4801456

6

Opposing arch impression


Stock TrayThe size of tray is selected so that the

teeth sit centrally within the trough of the

tray.

Special TraySpecial trays are made from either acrylic (light or

cold cured) or shellac

They are constructed on the primary cast which

helps with adaptation of the impression material and

reduces the amount required.

Impression Trays

GINGIVAL RETRACTION

To insure adequate reproduction of the preparation, the gingival finish line must be temporarily exposed by enlarging the gingival sulcus.

GINGIVAL RETRACTION

• RETRACTION CORD

DISPLACES GINGIVAL TISSUE MECHANICALLY;

THEY ALSO CAN HAVE A CHEMICAL ACTION WHEN IMPREGNATED WITH ASTRINGENTS AND

VASOCONSTRICTORS THAT CAUSE TISSUE CONTRACTION AND HEMOSTASIS

• CHEMICAL ACTION

ASTRINGENTS IMPREGNATED IN RETRACTION CORDS INCLUDE ALUMINUM CHLORIDE, FERRIC

SULFATE, ALUM (POTASSIUM ALUMINUM SULFATE) AND ZINC CHLORIDE.

• ELECTROSURGERY

CREATES A TROUGH AROUND THE TOOTH BY REMOVING SUPERFICIAL CELL LAYERS FROM

THE GINGIVAL SULCUS’ INNER LINING THROUGH APPLICATION OF AN ELECTRIC CURRENT

• ROTARY GINGIVAL CURETTAGE

REMOVES THE SULCULAR EPITHELIUM WITH A HIGH-SPEED DIAMOND BUR

Crowns and other extra-coronal restorations: Impression materials and techniqueR W Wassell, D Barker & A W G WallsBritish Dental Journal 192, 679 - 690 (2002) Published online: 29 June 2002


Single cord technique

Double cord technique

A piece of fine retraction cord is placed in the gingival sulcusA thicker cord is placed over the first leaving a tag for removalThe thicker cord is removed after washing (note clearly defined sulcus)and impressionThe buccal tissues are relatively thin and great care is needed to avoid recession. Sufficient haemostasis can usually be achieved with ferric sulphate solution to allow the impression to be recorded

Two cord technique:


good

access

poor

access


IMPRESSION TERMS

• PUTTY-WASH TECHNIQUE

• MOST COMMONLY USED

• PUTTIES WERE DEVELOPED INITIALLY TO REDUCE THE SHRINKAGE OF

CONDENSATION SILICONES, BUT THE HEAVY FILLER LOADING IS NOT NEEDED

FOR ADDITION SILICONES SINCE THEIR POLYMERISATION CONTRACTION AND

DIMENSIONAL STABILITY ARE IN ANY CASE EXCELLENT.

• ADDITION SILICONE PUTTY-WASH IMPRESSIONS ARE PREFERRED PRINCIPALLY

FOR THEIR HANDLING CHARACTERISTICS

ViscositiesPutty- kneadableHeavy bodied-high viscosityRegular-medium viscositylight bodied- (extra) low viscosity

Amount of fillers determine viscosity

The high filler loading of the putty was initially devised to reduce the effects of polymerisation shrinkage.

The putty is commonly combined with a low viscosity silicone a procedure known as the 'putty-wash technique'

IMPRESSION TECHNIQUES

• II. DOUBLE MIX

• LOW VISCOSITY-CORRECTION MATERIAL OR WASH

• HIGH VISCOSITY-HEAVY-BODIED OR PUTTY OR TRAY MATERIAL OR

PREIMPRESSION MATERIAL

• ONE STAGE OR ONE STEP

• TWO STAGE OR TWO STEP

• I. SINGLE MIX• Regular viscosity -intermediate flow

• Monophase pastes /monophase technique

• Custom/special tray



I. SINGLE MIX

ONE STEP/ ONE PHASE -MONOPHASE

• THE SAME MEDIUM VISCOSITY MATERIAL FILLED INTO THE

TRAY AND SYRINGED AROUND THE PREPARATION

Nauman M.: More than high quality impression

II. DOUBLE MIXTHREE WAYS OF RECORDING A PUTTY-WASH

IMPRESSION:

1. ONE STAGE IMPRESSION - PUTTY AND WASH ARE RECORDED

SIMULTANEOUSLY (ALSO CALLED TWIN MIX OR LAMINATE TECHNIQUE)

2. TWO STAGE UNSPACED PUTTY IS RECORDED FIRST AND AFTER

SETTING RELINED WITH A THIN LAYER OF WASH

3. TWO STAGE SPACED AS FOR TWO STAGE UNSPACED EXCEPT A SPACE

IS CREATED FOR THE WASH. THIS SPACE MAY BE MADE BY:

• POLYTHENE SPACER OVER THE TEETH PRIOR TO MAKING THE PUTTY

IMPRESSION

• RECORDING THE PUTTY IMPRESSION BEFORE TOOTH PREPARATION

• GOUGING AWAY THE PUTTY AND PROVIDING ESCAPE CHANNELS FOR

THE WASH.



ONE STEP TECHNIQUE/TWO PHASE

(DOUBLEMIX)

ONE STAGE IMPRESSION TECHNIQUE

TWIN MIX

• LIGHT BODIED IMPRESSION MATERIAL IS PLACED IN A SYRINGE, AND PLACED OVER

THE AREAS WHERE HIGH DETAIL IS REQUIRED (E.G. OVER A CROWN PREPARATION).

• SOME IS THEN SQUIRTED OVER THE HEAVY-BODIED IMPRESSION MATERIAL WHICH

HAS BEEN LOADED INTO AN IMPRESSION TRAY.

• THE IMPRESSION IS THEN TAKEN AS NORMAL.

• THIS TECHNIQUE SAVES TIME, BUT IT CAN BE VERY LABOUR INTENSIVE BECAUSE

THE TWO NEED TO MIXED AT THE SAME TIME.

TWO STEP/ TWO PHASE

TWO STAGE UNSPACED

IMPRESSION TECHNIQUE• AN IMPRESSION IS TAKEN WITH THE HEAVY-BODIED MATERIAL. THIS IS

THEN REMOVED FROM THE MOUTH AND INSPECTED.

• THE LIGHT BODIED MATERIAL IS THEN PREPARED AND SQUIRTED OVER

HEAVY-BODIED MATERIAL AND THEN IMPRESSION RELOCATED.

• HEAVY- BODIED PUTTY SERVE AS A CUSTOM TRAY FOR A THIN „WASH” OF A

LESS HIGHLY FILLED, LOW-VISCOSITY SILICONE.



TWO STEP/TWO PHASE

TWO STAGE SPACED - ESCAPE

CHANNELS• PRIMARY IMPRESSION WITH A PUTTY MATERIAL

• REMOVING UNDERCUTS AND CUT IN „RELAXATION” GROOVES (BY PRINCIPLE

THIS WILL BE JUST A VERY VERY ACCURATE CUSTOM TRAY)

• CORRECTION WITH A LOW VISCOSITY MATERIAL-OPTIMIZED PRESSURE

BUILD-UP TO REACH ESPECIALLY SUBGINGIVAL MARGINS



TWO STEP/TWO PHASE

TWO STAGE SPACED - ESCAPE

CHANNELS• KEEP IN MIND!

• TOO MUCH PRESSURE OR TAKING THE IMPRESSION WITHOUT CUTTING IN THE

GROOVES WILL LEAD TO ELASTIC DEFORMATION AND WILL RESULT IN DIES WITH

REDUCED DIAMETER = THE CROWN WILL BE TOO TIGHT AND INSERTION AT THE

PATIENT WILL BE DIFFICULT


Plastic tray impression:

Considerable forces are needed to seat putty impressions

outward flexion of the tray wall

tray wall rebounds on removing from the mouth

Rigid metal tray recommended


• CUT BACK IMPRESSION MATERIAL TO THE BORDERS OF THE TRAY

• REMOVE UNDERCUTS

• REMOVE MATERIAL BETWEEN UNPREPARED TEETH

• DIFFERENT SCHOOLS THINK DIFFERENTLY ABOUT CUTTING IN GROOVES AT THE

PREPARED TEETH: SOME SAY YES – SOME SAY NO:WITHOUT: MORE PRESSURE – BUT MORE DEFORMATION

WITH: LESS PRESSURE – LESS DEFORMATION

• GOOD COMPROMISE: CUT IN SMALL AND ACCURATE GROOVES WILL CREATE

ENOUGH PRESSURE BUT WILL NOT LEAD TO LARGER DEFORMATION

Escape channels



One step technique/two phase (doublemix)

One stage impression technique/ twin mix

Two step/ two phase

Two stage unspaced impression technique

OPEN TRAY

Closed tray

abutment level implant level

Impressions for implants

OPEN TRAY-ABUTMENT

LEVEL

Open tray-implant level

IMPRESSIONS FOR IMPLANTS

Closed tray

abutment level implant level

CLOSED TRAY-ABUTMENT

LEVELClosed tray-implant level

DISINFECTION OF IMPRESSION MATERIALS

• A POTENTIAL EXISTS FOR CROSS-INFECTION AS A RESULT OF

CONTAMINATED DENTAL

IMPRESSIONS

• IMPRESSIONS POSE A HAZARD TO

LABORATORY PERSONNEL

• IMPORTANT THAT ALL IMPRESSIONS

ARE DISINFECTED PRIOR TO BEING

TRANSFERRED TO A LABORATORY

• ALL IMPRESSIONS SHOULD AT LEAST

UNDERGO A DISINFECTING

PROCEDURE BY IMMERSION IN 1% SODIUM HYPOCHLORITE FOR A

MINIMUM OF TEN MINUTES

• VISIBLE FLAWS RELATED TO

IMPRESSION TECHNIQUE :

• FINISH LINE NOT VISIBLE

• AIR BUBBLES IN CRITICAL PLACES

• VOIDS OR DRAGS /LACK OF

MARGINAL DETAILS

• UNSET IMPRESSION MATERIAL ON

SURFACE OF IMPRESSION AND

CAST

Problems

Invisible impression flaws

resulting in an apparently good fit of the restoration on the die but a poor fit on the tooth:

Tray and impression recoil

Detachment of impression from tray

Permanent deformation

DISCUSSION

• MOST CONVENIENT AND RELIABLE WAY: ADDITION

SILICONE IN A RIGID METAL TRAY.

Plastic stock trays are convenient but

unreliable with putty-wash

lead to elastic deformation

recoil causes tight crowns

Special trays are recommended for monophase

technique, and with two phases only needed

where stock trays are a poor fit.



• SOMETIMES IMPRESSION DEFECTS ONLY COME TO LIGHT AFTER THE CAST

HAS BEEN POURED.

• THUS LABORATORY INSPECTION IS AN IMPORTANT PART OF QUALITY

CONTROL, BUT MANY TECHNICIANS FIND IT DIFFICULT TO FEED BACK TO

THEIR DENTISTS FOR FEAR OF THE MESSENGER BEING SHOT.

Communication!As none of us can achieve perfection every time there is much to be said for encouraging technicians to feed back

3D DIGITAL SCANNERSSystems are capable of capturing 3D virtual

images of tooth preparations, from which

restirations may be fabricated directly (ie.

CAD/CAM systems) or fabricated indirectly (ie.

dedicated impression scanning systems for

the creation of accurate master models).

Future (present?)

CONCLUSION

Text

Documents

Impression for fixed restorations - Semmelweis Egyetem · Crowns and other extra-coronal restorations: Impression materials and technique R W Wassell, D Barker & A W G Walls British