Study On Pouring Working Cast Model By Measuring Spoon To Calculate Dose And Clinical Factors That Affect Cast Quality

Stomatological treatment is impossible without the fabrication of cast. Precise replicating oral tissues depends on the quality of cast. Dental cast material should have low expansion coefficient and high compressive strength. The most widely used cast materials are: common gypsum, artificial stone and die stone. Among these, the die stone has been applied widely because of its lower expansion coefficient and better compressive strength. When using die stone to manufacture working cast model, we should operate normatively, mix strictly according to the water powder ratio which provided by the factory illustration, then we can guarantee the quality of working cast model. The impression material also has certain effects on the quality of working cast model, so we should select the gypsum material which is compatible with impression material, drawing of impression tray according to prescriptive time. Disinfecting the impression and the working cast models can avoid the cross infection effectively, but different method of disinfection working cast model has different effects on quality of cast. similar existence influence to it's quality. In the clinical operation, increasing or decreasing water powder ratio ad libitum often cause the drop of cast quality, and still there is no measuring spoon which can measure die stone powder to pour cast at present. Doctors select different impression material,drawing time of impression tray and disinfection methods. My research aims at developing measuring spoon which can measure water powder ratio and pouring working cast model with it, studying the relationship between influencing factor of impression and pouring cast and the kinds of restoration, selecting the best method of disinfection to improve cast quality.Objective:1. To calculae the mass of die stone powder of working cast model by weighing the cast of the denture, and classify cast according to the mass of die stone powder. Measuring spoon is developed with the classifying results to control the mass of die stone powder and the water powder ratio. The cast quality will be improved and material be saved in this way.2. The precision of working cast model affects the quality of restorations. At present, it is not studied fully of the effects of impression material on the precision of working cast model. This research studied the effects of four kinds of impression material and three different time of drawing impression on the precision of working cast model in order to instruct the fabrication of cast clinically.3. To observe the effects of high heat sterilization and immersion disinfection on precision of the working cast model and to select better disinfection method that can guarantee the quality of cast.Methods:1. The development method of measuring spoon:Selects the prosthetic working cast model made from the three kinds of impression tray which marked the small group, the middle group, the large group, through the survey,statistics the die stone powder amount used filled in mold in clinical, carried on statistical classification and tested it in clinical. Designed and manufactured a set of measuring spoon on this foundation, tested and adjusted it in clinical.The measuring spoon group and the skilled manpower hand work team as an experimental group, the standard lower jaw group as a control group, used the SPSS13.0 statistical software single sample T-test to carried comparison on the precision and the degree of hardness, by P<0.05 thought that has statistical significance.2. Using four kinds of dental impression materials (alginate impression material, agar-agar impression material, silica gel impression material and polyether impression material) commonly used in clinical, duplicated a standard lower jaw model under the same condition (the die stone modeling material was applied), three different drawing time of impression tray(2h, 6h and 12h), carries on to compare the precision each other, and observed the precision difference between its and the standard lower jaw model. The obtained datum carries on the group T-test with SPSS13.0 statistical software, by P<0.05 thought that the difference has statistical significance.3. Used 2% neutral strengthening glutaric dialdehyde disinfection fluid immersion and the high temperature high pressure (132℃, 232kpa) to disinfect the working cast model; after disinfection, compared the working cast model precision with the standard model, the obtained datum carried on the group T-test with SPSS13.0 statistical software, by P<0.05 thought that the difference has statistical significance.Results:1.The artificial denture prosthetic working cast model can divide into three kinds according to its die stone's amount used: the small working cast model needs the die stone powder≤45g; the middle working cast model is 46~55g; the large working cast model is 56~65g.The tested result of measuring spoon in clinical: all tested sample which amount the die stone powder used were in the sort area, the accordant sample number of the partial artificial denture impression which die stone powder amount used occupy the partial artificial denture impression sample total 88.89%.The accordant sample number of the fixed artificial denture impression which die stone powder amount used occupy the fixed artificial denture impression sample total 92.27%. Total accordant sample number of the impression which die stone powder amount used occupy the total impression sample 90.46%. Pass through the clinical trial, found all the samples were in sort area of die stone powder amount used.Measuring spoon designed as the hemispheroid, also divides into three kinds, the inside diameter size is in turn correspondingly 29.91mm,28.29mm and 26.46mm.There was no statistical significance between the measuring spoon group and the standard lower jaw model in precision and hardness (P>0.05), but there was statistical significance between the hand work group and the standard lower jaw model in precision and hardness (P<0.05).2.When drawing of impression tray after 6h there were no statistical significance between the polyether group,the silica gel group and the standard lower jaw model in precision (P>0.05); when drawing of impression after 12h there was no statistical significance between the agar-agar group and the standard lower jaw model in precision (P>0.05); but there was statistical significance between the alginate group and the standard lower jaw model in precision (P<0.05).3.There was no statistical significance between high heat sterilization method and the standard model in precision (P>0.05), but there was statistical significance between the immersion disinfection group and the standard model in precision (P<0.05).Conclusions:This experimental study proved that :1.The required mass of die stone powder of working cast model corresponds with the impression tray size and the dental arch size, it is proper to classify working cast model according to this. It is possible to pour cast precisely by controlling water powder ratio and the mass of die stone powder. Thus the hardness and precision of cast is guaranteed and the cast quality is improved.2. When the working cast model was drawn from polyether or silica gel impression material after it was poured for 6 hours, its precision can be guaranteed. The change of model size was the smallest and could be used to make precise restoration; When the working cast model was drawn from agar-agar impression material after it was poured for 12 hours, its precision can be guaranteed, its change rate of model size was the secondly and can be used to make cast of common restorations. When the working cast model was drawn from algal impression material even after it was poured for 12 hours, its precision cannot be guaranteed, its change of model size was the most and was not suitable to manufacture working cast model.3.The precision of working cast model disinfected by high heat sterilization method is higher than that did with the immersion disinfection method, sterilization by high heat can improve quality of the artificial denture.