Studies On The Model Qualities Affected By Operative Factors In Clinical Practice

The accuracy of models and dies are the foundation of various prosthetics. The casts poured from the impressions should be the exact replicas of the oral structures to ensure the fit of dentures to abutments and oral tissues. On the other hand, the disinfection of alginate is related to the safety of medical treatment. There are one hundred million HBV carriers in China, and the impressions are often contaminated with saliva and blood containing HBV. Consequently, working models become a potential source of contamination to cause cross infection.Nowadays, conventional impression materials (alginate) and model materials (dental stone) are well developed to ensure the qualities of model. However, these materials are usually not used correctly according to the directions of manufacture in clinic such as improper disinfection means and wrong W/P ratio of alginate and die stone. These problems reduce the accuracy of models and result in the failure of some dentures .This study investigated the practical W/P ratios of alginate and die stone that used in clinic, evaluated the antivirus effects of five methods that often used to disinfect impressions and chose good means. Then a mandible metal full arch was used as a master model, with four marks on it to represent two canine teeth and two first molar concavities. Some alginate impressions and die stone models were made in different conditions according to the W/P ratios and disinfections separately. Then the lines between the marks onstones models were measured and compared.1 The effect of water/power ratio and pouring time on accuracy and dimensional stability of alginate impressions. Study show that: (1)to mix alginate materials with the W/P ratio at will affects the accuracy of models greatly. (2)the W/P ratio of alginate material should be in the range from 23g:10g to 30g:10g , or the impression will deformation.(3)the time of pouring(15min and 30min) generated negative dimensional shrink(P<0.01).2 The effect of different disinfectant methods to alginate impression and dimensional changes after disinfection. Study show that: (1)HBsAg can be inactived by these means: a 10min soak in 1500mg/L sodium hypochlorite or 25 min wait after spraying of impression with this solution; a lOmin immersion in 2% glutaraldehyde. While these means have not effect: a 60min immersion in 2% glutaraldehyde or placing in ozone for 60min.(2)these measure will affect the accuracy of impression(P<0.05): immersing impressions in 2% glutaraldehyde for 50min and 60min;wait 45min after spraying of impression with 1500mg/L sodium hypochlorite.(3)these means have good and virus effected and don't change the accuracy of impression: a 10-30min soak in 1500mg/L sodium hypochlorite or 25-35 min wait after spraying of impression with this solution; a 40min immersion in 2% glutaraldehyde.3 The effect of water/power ratio on accuracy and hardness of alginate impressions. Study show that:(1)the water/power ratio of mixing die stone changed from 22g:100g to 25:100g doesn't affect the accuracy of models. (2) The surface hardness and abrasion resistance of models decreased greatly when the W/P ratio of mixing die stone changed from 22g:100g to 25:100g(P<0.05).