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DEPARTMENT OF PROSTHODONTICS SRI RAMACHANDRA DENTAL COLLEGE & HOSPITAL,
SRMC & RI (DU) CHENNAI.
Dr. Jafar Abdulla M.D.S.,
Impressions for fixed partial dentures
Requirements of impression
• Exact duplication of the prepared tooth including finish lines• Other teeth and adjacent structures reproduced accurately• Free of bubbles or voids especially in finish lines
Requirements of impression materials 1. Wettability
Hydrophilic- Hydrocolloids, polyether[easy]
Hydrophobic- polysulfide,polyvinyl siloxanes, condensation silicones
2. Viscosity
Light body polysulfide & Con. Silicone- Low viscousHeavy body polysulfide- High viscous[putty]
3. Cost
Custom tray fabricationCustom tray fabrication
Custom trays are most commonly made from acrylic resin tray
material. These materials should not be directly applied to the casts
since impression material used in the tray requires room to flow.
Trays made for alginate require more relief {0.6cm} than for
elastomeric impression materials, which require less relief {0.3cm}.
Requirements:
1] Rigid- The custom tray should be rigid throughout the impression procedures.
2] Retain shape- The custom tray should retain its shape since low fusing materials and other impression materials has to be applied over it.
3] Simple- The tray should be simple so that it can be easily made and should be should cost less.
4] Possible to trim- The tray should be able to trim since the extensions of the tray have to be adjusted. 5] Smooth borders- The borders of the tray should be smooth since sharp borders will injure the soft tissue.
Types of materials available for fabricating the custom tray:
1] cold cure or Self-cure acrylic.
2] Heat cure acrylic.
3] Thermo set vinyl {vacuum adapted}.
Fabrication procedures:
A] Dough method.
B] Sprinkle on method.
Dough method:
1] Outline the extent of the tray on the cast by a lead pencil.
2] Adapt relief wax above the cast and paint it with tinfoil substitute.
3] Tray material is assembled with spatula, tray formers, measuring
devices and separating medium.
4] Tray formers are made by using base plate and forming a stone investment around them. So two molds can be prepared for maxillary and mandibular tray.
5] Measure and mix the powder and liquid, which should be, thin and pour it into the mould which is already lubricated with petroleum jelly.
6] After mold is filled with resin allow it to set until it becomes plastic. 7] After setting remove it and adapt on the cast using the fingers and hold it. 8] Excess material is used to make a handle in front of the tray.
9] Trim the borders of the tray and check it by placing on the cast and
finally polish it with pumice.
10] Perforations are made on the tray for adherence of impression
material with the tray.
Sprinkle on method:
This is the conventional method by adding liquid to the powder directly
on the cast.
• Rigid & made 6hrs in advance.
•3 occlusal stops(3mm/3mm holes)made.•Wax spacer (2mm) & aluminium foil adapted.•Handles and wings are made.
Vacuum former unit
Close adaptation
Time saving
Expensive
CLASSIFICATION
1. ELASTOMERIC IMPRESSION TECHNIQUE STOCK AND CUSTOM TRAY (A) Putty reline technique. (B) Double,single mix technique (C) machine mix technique.[Pentamix} 2. IMPRESSION FOR POST&CORE
3. DOUBLE ARCH METHOD
4. COPPER BAND
CONVENTIONAL TECHNIQUE
A. PUTTY RELINE TECHNIQUE I
•Tray adhesive (Poly siloxane with ethyl silicate) is applied on Stock tray
•Poly vinyl siloxane – Loaded in stock tray
•Impression made
•Scraping done
•Light body impression material – Expressed on prepared teeth
•Final impression made
1 2
3 4
5 6
7 8
FINAL IMPRESSION
Adhesive (polysiloxane with ethyl silicate) is coated.
Polyvinyl siloxane loaded in the stock tray
cellophane strip adapted on prepared teeth.
The impression is obtained and the strip is removed.
Light body impression material is applied and final impression
done.
Impression is held for 7 min.
PUTTY RELINE TECHNIQUE II
1 2
3 4
1 2
3
1 2
3 4
B. DOUBLE MIX TECHNIQUE
Custom tray coated with adhesive
Light body material is loaded in syringe
Medium / heavy body material is loaded in custom tray
Retraction cords removed and syringe material expressed on
prepared teeth
Custom tray with medium / heavy body seated in
patient’s mouth
Impression held for 7 minutes
PREPARED TEETH IN FULL MOUTH REHABILITATION (OCCLUSAL VIEW)
RETRACTION CORDS PLACED
IMPRESSION OF MAXILLARY ARCH
( FULL MOUTH REHABILITATION)
SINGLE MIX TECHNIQUE
* 7.5 inches of polyether base and acclerator paste is expressed.
* The mix is spatulated for 1 min.
* Tray is loaded and syringe material is kept ready.
* Retraction cords are removed.
* Syringe material applied on prepared teeth.
* Tray is seated in the mouth for 4 min.
C. MACHINE MIX, PENTAMIX
2. IMPRESSION FOR POST&CORE
INDIRECT TECHNIQUE
Root canal is widened and impression is made byOrthodontic wire coated with elastomeric impression material Or Burn out plastic can be used for impression of post
Light body impression material injected around the burn out plastic post
Impression made with medium body elastomeric impression material or putty
LIGHT BODY IMPRESSION MATERIAL
AROUND THE BURN OUT PLASTIC POST
POST IN THE WIDENED ROOT CANAL
LIGHT BODY IMPRESSION MATERIAL AROUND THE POST
SEATING THE TRAY
IMPRESSION OF THE WIDENED ROOT CANAL
3. DUAL ARCH METHOD
• Tray inserted to determine clearance laterally and distally [cross bar distal to last tooth in arch]
• Complete closure in centric position
• Tray removed smoothly
• Wax used to block out the undercuts surrounding die
• Impression boxed before poring
• Verticulator used for articulation
THANK YOU
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