The Study Of Accurate Control Of The Dosage And Water Powder Ratio Of Die Stone When Pouring Oral Casts

The preparation of oral casts plans an important role in stomatology medical treatment. Work model qualities are directly related to the restorative effect of various dentures that determine the degree of satisfaction for sufferers. As work model material reaches its all capability standards, it is possible to reproduce the form of oral tissues accurately so that the high quality dentures can be made to fit the abutments and oral soft tissues.Though there are so many kinds of modern oral cast materials, die stone is the most popular work model material in clinical use. Nowadays, the type IV gypsum products are well developed to ensure the qualities of casts. However, some nonstandard manipulations exist in the preparation of work model, of which wrong W/P ratio is the most familiar and most important one. The operators just mix a certain amount of water and powder by experience to pour the casts, at the same time they often increase the W/P ratio of die stone for better fluidity, longer work time and convenient handling. These will result in lower qualities of work model that influence the final restorative effect in clinic. The fact that the dosage of water and powder of die stone is uncertain not only affects the qualities of casts but induces the waste of materials.By researching the above clinical problems, the purpose of this study is to explore a handy and applied method for quantitative controlof W/P ratio of die stone during pouring work model in order to ensure the qualities of work model and save materials. The specific idea is to measure the water and powder of die stone quantificationally by using some kind of metage container. Therefore, this study investigated and classified the dosage of die stone of clinical work model through weighing the models. Then according to the results of practical verification, the final classification was fixed and meanwhile the distinguishing and use of the classification was mastered. Further, on the base of mensuration of packing density of die stone, the feasibility and particular method of rationing the powder by container were discussed. After knowing the packing density of the powder, six spoons with different cubage were made. On investigating the W/P ratio of both clinic and spoon control, with surface hardness as a indication, the effects of different W/P ratio on the properties of work model were compared. By primary study, the following conclusions can be obtained:1. The classification of dosage of die stone of work model is as follows: the increase group (~70g), the larger group (~60g), the large group (~50g), the middle group (~40g), the small group (~ 30g) and the smaller group (10~20g). Usually the mean dispersion of dosage of die stone of work model between maxilla and mandible is about 10g.2. The tray types and the size of jaw dental arch as indications on classification have relativity because the dosage of die stone of clinical work model is determined by multifold factors. When using the classification by synthetic estimation and pouring the working face of work model at first, the amount of die stone is just enough and not wasteful.3. Rationing the powder of die stone by spoon is feasible, but the method of packing filling must be keeped firmly.4. Correspond to 6 sorts, 6 hemispherical spoons with different cubage were made on the experiment data and the water was measured by a20ml syringe.5. Though the W/P ratio of die stone in clinic is about 25ml: 100g, itcan be controlled within 21ml:100g~23ml:100g by using spoons.This control was proved effective with surface hardness as aindication, so the qualities of work model can be ensured.