The Study Of Effects Of Gypsum Surface Hardener On Dental Stone

Background:The preparation of oral casts plays an important role in stomatology medical treatment, especially in prosthetic dentistry. The model preparation is directly related to the results of prosthetic restorations. Gypsum models must be able to replicate teeth and soft tissues in oral cavity. In this way, the restorations produced on these models can fit soft and hard tissues in oral cavity. Nowadays, there are many kinds of model materials, but dental stone is still the most widely used cast material. Some properties for dental stone are very important, such as fracture strength, dimentional stability, abrasion resistance, surface hardness and detail replication. In these properties, surface hardness and abrasion resistance are more important for technician and should be improved. When the dental laboratory technician carves wax patterns on the dies, abrasion and stress can be delivered to the dies by the instruments and tools, so the hardness and abrasion resistance of dies should be have adequate hardness and abrasion resistance. There are several methods that can be used to improve these two properties and surface hardener is extensively used because its ease of use.Purpose:The purpose of this study was to evaluate surface hardness silicone resin and abrasion resistance of 3 commonly used dental stone die materials with and without the application of a new gypsum surface hardener.Materials and methods: 1 .Hardness testA stainless block mould was made by machine. Its inner dimention is 20mm×10mm×10mm. Three dental stone materials were mixed with distilled water according to manufacture's recommendations and then were poured into the block mould, twenty specimens of each dental stone were fabricated .In all, 60 blocks were made. Twenty specimens of each dental stone were randomly assigned to two groups. One group were not coated with surface hardener as control group, the other were coated with surface hardener 24 hours before test. Each group were tested with a hardness (Akashi MVK-H21 Hardness Test Machine tester) and results were recorded. Statistical analysis was executed by SPSS 13.0 software, significant level a=0.05. 2. Abrasion resistance testSixty specimens were prepared as in the hardness test. Each group were tested with a abrasion device. Mass loss of each specimen was determined using an analytical balance. Statistical analysis was executed by SPSS13.0 software, significant level a=0.05.Result:1. The two-sample t-test for independent samples revealed an interaction between treated group and control group. For each dental stone, the result was significant (p<0.05). Group treated with surface hardener have higher hardness than that of control group.2. The two-sample t-test for independent samples revealed an interaction between treated group and control group. For each dental stone, the result was significant (p<0.05). Treated group have less mass loss than control group.Conclusion:Gypsum hardener silicone resin can improve hardness and abrasion resistance of dental stone.