Effect of contact time between alginate impression and type III dental stone on cast model properties

Objective: To measure the effect of different contact time between the alginate impression and type III dental stone on cast model properties in the terms of dimension stability, hardness and surface details reproduction. Material and methods: Sixty-seven cast models were obtained from stainless steel cylinder using alginate impression material and type III dental stone. Thirty-seven cast models were separated after one hour (control group) and 30 cast models were separated from impressions after 9 hours. The samples were evaluated under light microscope for surface details, measured by digital caliper for dimension stability and hardness was tested by making indentation on the cast then measuring the depth using digital caliper. Results: The dimension stability of cast models was not affected by increasing contact time between type III dental stone and alginate impression while surface details decreased. In the meanwhile, hardness was improved with increasing contact time. Conclusion: According to the results of this study, pouring of impression up to 9 hours can negatively affect the cast model properties in the term of details richness.

A study on the contact angle and wettability of the dental stones / 대한치과보철학회지

The purpose of this study was to investigate the contact angles and wettability of conventional dental stones and improved dental stones and newly developed dental stones on several impression materials. Materials included in this study were several dental stones and newly developed dental stone; 2 type III stones (Snow Rock, New Diastone), 6 type IV stones(Crystal Rock, Vel Mix, Fuji Rock, Tuff Rock, Resin Rock and newly developed dental stone) and 1 type V stone (Die Keen). Contact angles on the impression materials were measured with contact angle measuring device. Ten specimens for each material, total 180 specimens were made on void entrapment model. The two impression materials (Handae, GC) were used to produce 9 groups of die stone casts form void entrapment model. Voids in the stone casts were counted under a stereoscopic microscope. The grad for the reproduction ability of each materials on the void entrapment model was calculated from the casts by one examiner. From the experiment, the following results were obtained : 1. The newly developed stones showed smallest contact angle. Type III dental stone had larger contact angles than type IV and V stones. Contact angle was much affected by the impression materials. 2. Resin containing die materials such as Tuff Rock and Resin Rock had smallest void number than any other groups. 3. In comparing reproduction parameters, Tuff Rock and Resin Rock presented superior results, while Vel Mix showed lowest reproduction ability.

A Study on the Abrasion Resistance and Surface Roughness of the Dental Stones / 대한치과보철학회지

The purpose of this study was to investigate the abrasion resistance and surface roughness of conventional dental stones and improved dental stones and newly developed dental stones. Materials included in this study were several dental stones and newly developed dental stone; 2 type III, 6 type IV(including newly developed dental stone),1 type V Ten specimens for each material,total ninety specimens were made. Each specimen was subjected to 50 complete cycle abrasion under constant load 0.42N at speed of 6mm per sec.The depth after abrasion test was measured for each specimen. Surface roughness before and after abrasion test was compared.The results were as follows ; 1.The resin containing die materials such as Tuff Rock and Resin Rock had superior abrasion resistance. 2.Type IV,V Surface roughnessdental stone exhibited greater abrasion resistance than Type IIIdental stone. 3.The results of the surface roughness showed similar pattern with the abrasion resistance.