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