Flasking ,Wax elimination Packing and Processing Dr.Mohammad Ibrahim Al Sayed

Flasking: Is the process of investing the cast with the waxed denture in a flask to make a sectional mold that is used to form the acrylic resin denture base.

Preparation of the cast: Procedure: The following procedure is applied to both maxillary and mandibular dentures Preparation of the cast: 1. Remove the mounting from the articulator, separate the casts from the plaster mountings. Save the plaster mounting as it will be used to reposition the cast on the articulator after the dentures are processed. 2. Try the casts in the bottom half of the flasks. At least ¼ inch of space should exist between the occlusal surfaces and incisal edge of the teeth and the top of the flask. Trim the casts if necessary but you must retain the index groove. 3. Soak the casts and waxed dentures in water for a few minutes.

Flasking: 1. Coat the inner surface of the flasks with vaseline. 2 .First pour: This pour is made of a mix of plaster of paris. a. Test the cast in its place. Spatulate a heavy mix of plaster and stone and fill the lower half of the flask till about one-third. b. Seat the cast until the land area is flush with the rim of the flask. Remove excess plaster, smooth the remaining *No undercuts should be present in the plaster * Be sure that all the portion of the metal rim are free from any plaster c. For the lower cast , bring a small amount of plaster in the tongue space to eliminate the undercut in the region of the retromylohyoid fossa Allow the investment to set then proceed to the second investment

3.Second pour: 1.Position the second part of the flask and ensure that the two halves are contacting metal to metal. 2.Place a thin film of vaseline on the surface of the set stone in the lower half of the flask. 3.Position the second part of the flask in place. 4.Spatulate a thin mix of half plaster and half stone and pour it over the teeth from one corner of the flask. Avoid entrapping air in the mix. 5.Bring the stone to the occlusal surface of the invested teeth leaving exposed occlusal surface of the posterior teeth and the incisal edge of the anterior teeth.

4.Thid pour: 1.Apply separating medium on the set plaster and stone (i.e. second pour) 2.Complete the investment using a mix of stone .Stone will resist more pressure than a mix of plaster and stone. 3.Fill the flask with the mix, place the lid of the flask in position, some stone should pass through the holes of the lid. 4.Allow the stone to set at least one hour before wax elimination.

Preparation of the mold Wax elimination 1. After flasking , allow the stone to set completely. Then place the flask in boiling water for 5 minutes. *This will soften the waxed denture base which can be easily removed from the mold when the flask is opened. 2. Open the flask through the provided openings. 3. Carefully remove the softened wax. All teeth should remain in the top half of the flask 4. If any of the teeth have been pulled loose they should be replaced in position. 5. Using hot water flush out all the remaining wax and any residue that may be present. 6. Flush the flask again with hot water to which a detergent has been added. Use a small paint brush to thoroughly clean the stone and teeth from any residues of wax. 7. The final flushing is done is done with clean hot water to remove all traces of the detergent solution. It is essential to remove all wax residue since acrylic resin will not adhere to a surface coated with wax. Any residual wax will contaminate the acrylic resin and prevent bonding between the teeth and the denture base.

Application of tin-foil substitute: 1.Stand the flask on its side and allows it to dry . a. while the mold is still warm paint all the portions of the exposed stone with a separating medium.( tin-foil substitute such as alginate solution). This is done to make the surface of the mold nonabsorbent to avoid penetration of the liquid acrylic resin (monomer) into the stone during processing. If liquid acrylic resin penetrates the mold surface the finished denture will have a crust of acrylic resin and stone or plaster. This layer has to be removed during finishing. The result is improperly contoured and hence an unaesthetic and poor fitting denture base.

Allow the first coat of separating medium to dry then apply a second coat and allow it to dry. The separating medium should be placed around the teeth and over the surface of plaster or stone. The procedure should produce a smooth and shiny mold surface.