Denture Base Sealing Quiz: Contraction and Gaseous Porosity Denture

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Questions and Answers

What is the purpose of packing acrylic resin into the mold?

To increase the vertical dimension of occlusion

To accelerate the curing process

To reduce the pressure applied on the acrylic

To prevent shrinkage and porosity after polymerization (correct)

Why should pressure be applied gradually during the packing of a denture?

To speed up the curing process

To decrease the accuracy of detail in the final prosthesis

To increase the risk of porosity in the final prosthesis

To allow the resin to flow within the mold (correct)

What are the consequences of adding acrylic resin too early into the mold?

Prevents shrinkage and porosity in the final prosthesis

Leads to an increase in vertical dimension of occlusion

Results in a dense and well-packed prosthesis

Causes porosity in the final prosthesis (correct)

When is it considered too late to pack acrylic resin into the mold?

Stage IV Signup and view all the answers

What method is used to press the flask when packing a denture?

Using a pneumatic press Signup and view all the answers

Why should acrylic flash be trimmed away during the packing process?

To ensure even pressure distribution Signup and view all the answers

What should be done to the teeth in the mold when applying cold mold seal?

Ensure they are not separated and not covered by the cold mold seal Signup and view all the answers

Which component is used to characterize denture bases and create a lifelike appearance?

Colored acrylic placed over the gums Signup and view all the answers

In what ratio are the powder and liquid mixed for an average-sized denture when using acrylic resin?

3 parts powder to 1 part liquid Signup and view all the answers

During which stage of acrylic mixing does the mix become tacky, sticky, and adhere to the sides of the jar?

Stringy or fibrous stage Signup and view all the answers

Why is it important for the cold mold seal to be thin and even on all parts of the mold?

To prevent adherence of the denture base to the mold Signup and view all the answers

Which component acts as a cross-linking agent in acrylic resin?

Cross-linking agent - ethylene glycol dimethacrylate Signup and view all the answers

What is the primary cause of inadequate softening of the powder by the monomer in denture processing?

Too much polymer Signup and view all the answers

What is the main consequence of too much monomer in denture processing?

Excessive polymerization shrinkage Signup and view all the answers

What is the primary reason for contraction porosity in dentures?

Linear shrinkage Signup and view all the answers

Which factor is crucial in minimizing contraction porosity during denture processing?

Powder/liquid system with 5-8% ratio Signup and view all the answers

What is the main reason for the linear contraction observed during denture processing?

Thermal factors Signup and view all the answers

How does excessive monomer affect the potential outcomes in denture processing?

Increased polymerization shrinkage Signup and view all the answers

What is the purpose of slowly cooling the flask on the bench?

To relieve internal stresses caused by contraction differences Signup and view all the answers

Which step is NOT part of the de-flasking procedure?

Pressing the acrylic smooth and dense Signup and view all the answers

What is the potential issue with heating the flask in an ordinary water bath as described?

Higher likelihood of distortion during deflasking Signup and view all the answers

Why should temperature and time be controlled during the curing of acrylic?

To prevent overheating and ensure proper polymerization Signup and view all the answers

In which heating technique does the temperature rise to boiling after reaching 72°C?

The special bath heating technique Signup and view all the answers

What should be done to prevent breakage of the denture during de-flasking?

Cool the flask slowly on the bench in its water bath Signup and view all the answers

What is the term used to describe the volatilization of the monomer due to temperature rises above the boiling point?

Gaseous porosity Signup and view all the answers

How can the potential problem of gaseous porosity be eliminated during denture processing?

Utilizing a long curing period with a hold period at 70°C Signup and view all the answers

What is the consequence of restricting dimensional change during cooling in denture processing?

Internal strains Signup and view all the answers

Why is it important to cool the flask slowly during denture processing?

To prevent internal strains Signup and view all the answers

What can cause gaseous porosity in denture material?

Exceeding the boiling point of the monomer during processing Signup and view all the answers

How do modern heat-cured acrylics behave if the correct powder/liquid ratio is achieved in denture processing?

Their flexibility remains consistent despite processing times Signup and view all the answers

Study Notes

Curing of Acrylic

The packed mold is heated (cured) in an oven or in water bath to control temperature and time.
Two water bath heating techniques can be used: heating the flask in a special bath of water or in an ordinary water bath.
The first technique takes 16 hours, while the second technique takes 2 hours to reach 72°C, then 1 hour at boiling temperature.
The second technique has a shorter time but may cause distortion during deflasking and increase the amount of free monomer.

Cooling of the Flask

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

De-flasking Procedure

The flask is removed from the clamp, and the upper and lower lids are removed.
The two parts of the flask are separated using a plaster knife, and the denture is liberated with its model.
The model is removed carefully, and if there is an undercut, it is split into two or three parts to remove them easily.
The excess of acrylic is removed using an acrylic bur.

Processing Problems

Powder/liquid ratio: too much polymer can result in a weak material, while too much monomer can result in excessive polymerization shrinkage, loss of fit, and gaseous porosity.
Contraction porosity: occurs due to polymerization shrinkage, which can be minimized by using a powder/liquid system between 5 and 8%.
Gaseous porosity: caused by the volatilization of the monomer, which can be eliminated by having a long curing period with a hold period at about 70°C.
Processing strains: occur due to the dimensional change during cooling, which can be minimized by cooling the flask slowly.

Stages of Acrylic Resin

Smooth dough-like stage: where the monomer diffuses into the polymer.
Rubber-like stage: where the monomer penetrates further into the polymer, making it too stiff to be packed or molded.
Stiff stage: where the acrylic resin becomes hard.

Packing of Acrylic

It is the procedure of applying acrylic resin into the mold and pressing the flask to compensate for the contraction of the acrylic after polymerization.
The acrylic resin should be placed in the mold and pressed in a clamp immediately.
Too early or too late application of the acrylic resin can result in porosity, loss of detail, or movement of teeth.

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.
Stages of acrylic mixing: sandy stage, stringy or fibrous stage, and a smooth, stiff stage.

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Test your knowledge on the process of sealing the cold mold seal on a denture base, and characterizing denture bases to make them look more lifelike. Questions may cover techniques such as spreading the seal, avoiding covering the teeth, and adding colored acrylic for a natural appearance.

Denture Base Sealing and Characterization Method Quiz

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