Clinical Complete Dentures

COMPLETE DENTURES

22. ADDENDUM
Questions and Answers

Question:: What is the euphemism for slaughterhouse and toilet? (See Section 6. Talking to Your Patient, "How to Speak to the Patient")
Answer:: Abattoir and powder room.

Question:: Why does a patient with an oral infection have to clean their dentures differently?
Answer:: In the polymerization of methyl-methacrylate, the release of gases causes microscopic pores and cracks. The pathogens reside in these invisible imperfections and serve as a reservoir for reinfection. Keeping the denture looking perfectly clean by using soap and water is not enough.

Question:: For complete denture construction, why do you make a primary model?
Answer:: We want to make a custom (personalized) tray that will fit accurately on this particular patient.

Question:: A faculty member saw a student in the clinic putting rubber base adhesive on the secondary tray with a brush that was attached to the cap of the bottle of adhesive. The instructor removed the brush and told the student to use a Q-tip. Why?
Answer:: When the brush touches the tray, the brush is now contaminated with the patient's bacteria. When the brush is returned to the bottle, then the entire bottle is contaminated. It is best to pour some adhesive on the tray then spread it with a Q-tip. The Q-tip will never touch the bottle. (Did you know that the "Q" in Q-tip stands for quality?)

Question:: Knowing that the impression material for secondary edentulous impressions should be 1/2 to 1mm thick, the student placed a thin sheet of wax over the primary model before making the impression tray. Was this a good idea and why?
Answer:: It was an extraordinarily bad idea. Because the tray is now so inexact, the student cannot correctly seat the tray in the patient's mouth. (Because of the "wax space" there is no seat.) Thus the borders of the tray cannot be shortened correctly. If the tray is properly made on the primary model, and firmly seated, the viscosity of the impression material will allow for 1/2 to 1mm thickness. (To be sure in other techniques there will be a need for relief under the tray. There will also be a need for tissue stops. )

Question:: What type of impression material did you use to take the edentulous secondary impression?
Answer:: You used rubber base impression material.

Question:: What are the two basic physical differences between a secondary tray and a recording base?
Answer:: A recording base does not have a handle. The borders of the recording base simulate that of the final denture. They are not purposely shortened.

Question:: What is the purpose of shortening the borders of the secondary impression tray (in complete denture construction)?
Answer:: You want to perfect the borders of the tray on the patient. Softened compound is added to the tray to capture the mucobuccal and mucolingual folds. It is easy to remove and add compound so the procedure can be repeated until the borders are correctly captured.

Question:: What temperature do you set your compound heater to anneal the compound?
Answer:: 140 degrees Fahrenheit. (60 degrees Centigrade)
Look under Section 11. Secondary Impression, "Using the Compound Heater" to get a more detailed answer.

Question:: How long should you leave the rubber base impression material to set in the mouth? on a typodent?
Answer:: In the mouth you need 6 to 7 minutes. If it is on a typodent you will need 10 minutes. Body heat makes the material set faster.

Question:: When pouring up an impression why is it permissible to invert a primary impression on a mound of stone or plaster, while you are not permitted to invert the secondary impression?
Answer:: The primary impression is not as important. So if changes occur while inverting then the secondary tray will change slightly. This error will be corrected in the final impression. We want the secondary model to be as accurate as possible. If you invert the secondary impression, the stone may pull away from the impression due to gravity resulting in a distortion. Then the final denture will be distorted.

Question:: Give two reason why you should bead and box secondary complete denture impressions.
Answer:: When you bead and box you can pour a base on the secondary impression without inverting. Inverting can sometimes cause the stone in the impression to move. Beading and boxing helps you define the useful portions of your impression. It ensures that you will capture the mucobuccal and mucolingual borders of your impression. When you vibrate the stone into your impression the heavier particles fall to the bottom. This means the tissue surface of your model will be stronger. The more watery mix will now be on the base of your cast which is now up top. You can trim down the base after the stone hardens.

Question:: Show by an equation the relationship between rest vertical dimension, occlusal vertical dimension, and free way space.
Answer:: RVD=OVD + FWS