Full denture impressions

So at my new job I've started to make dentures again. My first job had a prosthetist making all the dentures and my next job didn't offer denture services. The last full denture I made was probably 4 years ago in dental school. Starting to make dentures again is an exciting prospect because they were a part of dental school that I quite enjoyed. I am finding that I am remembering small tips here and there and learning new ones as I go along.

Dentures are the most aesthetic restorations we can provide as we have full control over tooth shape, size, position and shade as well as gingival aesthetics. Each surface of a denture is important for different reasons.
-The fitting surface is obvious important for a good fit against the soft tissues with no trauma to specific areas.
-The peripheries are important in achieving a border seal to exclude air to allow a suction effect for retention.
-The vertical aspects of the flanges seat against the ridges for resistance to horizontal movement
- The occlusal surface is important for function and to fit against the opposing dentition. It should be balanced to allow stability of the denture
-The palatal and lingual areas should be thick enough to allow strength to the denture but thin enough for comfort and tongue space.
- The labial areas of the dentures should be well contoured to provide lip support for facial aesthetics and the teeth should be in the right position to provide dental aesthetics and phonetics.

Some tips for full denture primary impressions:
-Place periphery wax around the whole tray. Most edentulous impression trays are flared at the borders which will result in an overextended impression into the buccal space. However because of the flaring, there is often not enough extension of the tray vertically into the sulcus. Placing a stiff brand of periphery wax around the tray will allow the material to be supported at the periphery and lead to less distortion.
-Use tray adhesive and allow it to dry for the recommended time before taking the impression. Dentures are not comfortable to wear at the best of times and any step you can take to make them more accurate will be beneficial. If the material pulls away from the tray the entire impression will be distorted and avoidable retakes are a waste of time.
-Fill the tray to the brim. Insufficient impression material may not cover the entire full denture bearing area and you will have to retake the impression.
-Dentures aren't supposed to cover the entire surface of the impression. Even in well adapting trays, primary impression material will inevitably displace non attached tissues and make the denture bearing surface appear larger than it really is. Take an indelible marker and trace out on your primary impression the border of the attached tissues. This is "eyeballed" to a certain extent. To check the buccal extensions pull the cheek up and move it buccolingually back and forth. The tissue that doesn't move will be the extent of the buccal flange. To check the lingual area place your finger in the sublingual area and get the patient to raise their tongue to the roof of their mouth. Over extension into this area will result in a denture that jumps up every time the patient moves their tongue. The indelible ink will be transferred onto the primary cast. The technician can then take the special tray to just short of this mark.

Some tips for full dentures secondary impressions:
-Double check the fit of the tray against the primary cast. Overextended trays should be cut back, feel the intaglio surface of the tray with your finger and remove any sharp spots. These sharp spots will cut the mucosa when you seat the tray. Undercut ridges may lock the tray in place and should be relieved. Look for smooth areas on the stone that look as though the tray is scraping against it. These will impede proper seating of the tray.
-The prosthetist at work showed me how he gets his trays ready before the patient arrives. He wets the primary cast, dries the special tray, places heated greenstick around the whole periphery and seats it onto the cast adapting the greenstick into the sulcus of the model. When the patient arrives he can heat the whole tray in hot water and adapts the whole tray to the patient's mouth in one go.
-Impression material should be placed onto the tray in a thin wash. Train your dental assistant to do this. Move the impression material in one direction because back and forth motions will incorporate bubbles.
-When seating the tray rotate it into the mouth. Seat the tray vertically onto the tissue surface and press very firmly to extrude as much of the material as you can. Maxillary impressions put a few fingers under each side of the tray around the premolar area, stand behind the patient and lean your whole body back to get as much pressure as possible. For mandibular impressions, use your index and middle finger around the premolar area and thumbs under the mandible.
-For the maxillary impression pull the cheek and lip outwards and downwards only. Get the patient to purse their lips (like a kiss) to record the muscle extensions and get them to close slightly and move their mandible side to side to record the coronoid process space. For mandibular impressions tell the patient to lift their tongue up and try to lick their nose. Then get them to touch the tip of their tongue to each cheek.
-If you are having trouble removing the impression due to the suction effect firstly congratulations. Secondly, don't force it out. Get the patient to close their lips around the tray handle and puff their cheeks out. This will break the seal and force air under the impression and it will just drop off their tissues. Alternatively you can try and get a finger under the periphery of the impression and lever it off but this risks distorting the impression.
-Optionally you can warm some periphery wax lightly in a flame and stick it around the impression just shy of the sulcus. Seal the wax against the impression with a warm wax knife. This will make the pouring up of the impression easier for the technician.
-To try in the impression if you have added a post dam area, trim the excess, insert the tray and press upwards firmly. You can check the quality of retention this way.