The Effect of Adding a Stone Base on the Accuracy of Working Casts Using

Gypsum has been widely used in the field of prosthodontics wherein they are used for the preparation of stone cast. Stone cast are used for molding oral and maxillofacial structures. Another use of gypsum is the production of dental prostheses in dental laboratory.Gypsums is in the form of calcium sulfate hemihydrate which is used in different purposes in dentistry, in which case a gypsum product used for casting and dies may be different from another molding wherein accuracy and stability is different with another gypsum product.

Classification of gypsum are: 1. Impression plaster, 2. for model plaster, 3. dental stone, 4. for dental stone, high strength and low expansion, and dental stone, high in strength and expansion. An example of on the specific classification is type 4 where it is widely used in making working cast and dies in the art of wax technique. Removable die is used more often to aid in the manipulation of dies during fixed prosthesis fabrication. Die pins are then integrated into die stone cast after which a stone base is poured to mesh with the cast that contains the die pins, this is done for reference on the placement of the dies. When cured the dies can be adjusted and can even be placed back to the stone base for other adjustments. This however does not guarantee 100% accuracy as the stone expands it may affect die position. It is important starting from the casting that fitting should be accurate to avoid problems when turned over to the laboratory. This minimizes the time it takes from the laboratory to fabricate but also the cost involved when repeat is needed.

In this article a tool maker microscope or also known as measuring microscope was used in conjuction with a surveyor parallelometer from Ney. The Ney surveyor-parallelometer marked and cut flat in a parallel manner which allows better measurement of the tool maker microsope making it more accurate. These were the lower posterior of the teeth, for better impression and easier measurement. Using teeth 21, 28, 30 and d18 as reference points and assigned as A, B, C, and D respectively. Using a tool maker microscope measurement were taken and recorded after which the stone base was poured. Sectioning and seating were done afterwards wherein each die was again measured using a tool maker microscope.

There is a significant difference in the measurement obtained by the tool maker microscope. Measurement before and after sectioning the difference is evident in reference from teeth 21, 28, 30 and 18. Although there was a limitation in the study due to the restriction from model used and the materials which was limiting still the result were conclusive; that difference was noted in the average measurements of the solid cast again on teeth 21, 28, 30 and 18. Also a difference in master model and LP in measurement between the two casts was noted. That difference bases will produce different result but those result will show no significant difference and smallest margin of error which is tolerable. Read more on this