Dewaxing of Complete Denture Procedure Quiz and Flashcards

Study Notes

Dewaxing and Packing Procedure of Complete Denture

After setting of gypsum, wax elimination procedure is done by placing the flask in boiling water for 5-7 minutes, separating the two parts of the flask, and removing the shellac base plate and wax using boiled water and detergent.
The flask is then dried and cooled in open air to remove all wax residues, as acrylic resin will not adhere to a surface coated with wax.
Any residual wax will contaminate the acrylic resin and prevent bonding between teeth and the denture base.

Acrylic Packing Procedure

Isolate the gypsum of the flasking by using physical or chemical separators, such as tin foil or a solution of alginate (cold mold seal).
Tin foil substitute is painted over the complete mold surface to prevent the resin from adhering to the stone, using a large brush to cover the cast and the open area of the upper half of the flask.
A small brush is used to carry the foil substitute around the teeth, avoiding covering the teeth to prevent a void in the completed denture.
The cold mold seal should be thin and even on all parts of the mold, except the teeth, which should not be separated.

Characterizing Denture Bases

A small amount of colored acrylic is placed over the neck of each tooth to give a pleasing appearance to the denture, resulting in a lighted area of the gingiva.

Mixing Acrylic Resin

Acrylic resin is a resinous plastic material of various esters of acrylic acid, used as a denture base material.
It is formed of a powder and liquid, with a ratio of 3 to 1 by volume for an average-sized denture.
The stages of acrylic mixing include a sandy stage, where a fluid mass occurs, and a stringy or fibrous stage, where the monomer starts to attack the polymer.
The mold is full when the acrylic is pressed smooth and dense.

Curing of Acrylic

The packed mold is heated (cured) in an oven or water bath, with controlled temperature and time.
Two water bath heating techniques can be used: heating the flask in a special bath of water, or heating the flask in an ordinary water bath.
The curing process should be controlled to prevent distortion and excessive free monomer.

Cooling of the Flask

After curing, the flask is cooled slowly on the bench in its water bath to relieve internal stresses caused by the difference in contraction between the acrylic and the mold material.

De-flasking Procedure

The flask is opened carefully after curing of acrylic resin to prevent breakage of the denture.
The steps include removing the flask from the clamp, removing the upper and lower lids, separating the two parts of the flask, and liberating the denture with its model.

Processing Problems

Powder/liquid ratio: too much polymer can result in a weak material, while too much monomer will result in excessive polymerization shrinkage and loss of fit.
Contraction porosity: associated with polymerization shrinkage, minimized by using a powder/liquid system between 5 and 8%, which should give rise to a linear shrinkage between 1.5 and 2%.
Gaseous porosity: caused by the boiling of the monomer, particularly if too much has been added to the dough or if the temperature is raised too quickly.
Processing strains: restricting the dimensional change during cooling results in internal strains, which can cause warpage, crazing, or distortion.

Description

Test your knowledge on the dewaxing and packing procedure of complete dentures in the third stage of 16th week lecture by Shurooq Falih. Questions cover steps such as wax elimination, flask boiling, flask separation, and cleaning. Practice to improve your understanding of the process.