Have you ever thought it might be your impression/casting and not the denture acrylic? Just one old guy's opinion. I have had similar issues with Lucitone 199. I don't use it any more. Make sure to leave your (assuming you are using heat cure) clamped casings stand for about a half hour under compression before dropping into the heat tank. Also one more thing to consider, is that if a patient has an impression taken at the end of the day the mucosa may be dehydrated and not at full shape. Have the patient come in first thing in the morning without wearing the dentures the night before, then take your impression. Use a good POLYETHER impresseion material like impregum. Polyvinyl siloxane doesn't cut it for me, and neither does a rubber base. Don't let anyone tell you otherwise. Impregum is better... (we had a meeting). Proper fit is all about compression. Compression of the tissue during impression, compression of the bite during occlusal registration, Compression during bite checks, and especially compression of the material in the flask. Another thing to consider is the patient's oral and general health. Are they taking Diuretic medication? Are they diabetic? Do they take any medications which effect blood pressure? These factors can greatly effect the day to day fit of a denture. If you put a denture in and it drops immediately. Don't panic. Let it settle into place for a while, sometimes it can take a few days for the muscles and tissues to settle and seal around the denture. Lastly, if that still doesn't work. Don't be afreaid to use a good chairside "reline filler" to capture detail such as Tokayama (not sure if thats how ya spell it) rebase. Excellent product. I also recommend Diamond D by Keystone. Fantastic acrylic to work with. Stay away from 20 minute curing of any kind. And be sure to bench cool and not shock cooling it in water after curing in heat. Remember basic chemistry... heat expands stuff, cooling constricts stuff. If you flash cool a flask full of hot acrylic, a thicker denture will shrink more within the flask because there is more acrylic to shrink. (duh').