impression for fixed restorations - semmelweis egyetem · crowns and other extra-coronal...
TRANSCRIPT
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!
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:
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
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
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
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.
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
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.
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
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
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
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
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
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
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
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.
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
• 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
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