Ibrahim Amna Adam, Alhajj Mohammed Nasser, Khalifa Nadia, Gilada Magdi Wadie
Department of Oral Rehabilitation, Faculty of Dentistry, Khartoum University, Khartoum, Sudan; Department of Prosthodontics, Faculty of Dentistry, Al-Gezira University, Wad Medani, Sudan.
Department of Oral Rehabilitation, Faculty of Dentistry, Khartoum University, Khartoum, Sudan; Department of Prosthodontics, Faculty of Dentistry, Thamar University, Dhamar, Yemen.
Compend Contin Educ Dent. 2017 Jun;38(6):e1-e4.
Alginate impression (irreversible hydrocolloid) material is commonly used in dental practice because it is easy to mix, low in cost, and well tolerated by patients. The material is not dimensionally stable, however; thus, it is necessary to pour the impression immediately after the molding is accomplished, or within 60 minutes if the impression is kept in 100% humidity. Excessive contact of the alginate impression with the cast model over time may affect the model's properties. In this study, the authors tested the effect of contact time between an alginate impression and type III dental stone on cast model properties. Sixty-seven cast models were obtained from a stainless steel cylinder by using irreversible hydrocolloid impression material and type III dental stone. Thirty-seven cast models were separated from the impression after 1 hour (control group) and 30 cast models were separated after 6 hours (study group). The samples were evaluated under light microscope for surface details and measured by digital caliper for dimensional stability. An indentation on the cast was made and the depth of the indentation was then measured with a digital caliper to measure hardness. The dimensional stability of the cast models was not affected when contact time was increased from 1 hour to 6 hours (P = .507). Surface details did not deteriorate when contact time was increased, as all of the samples could reproduce all details after the 1-hour and 6-hour interval periods. However, hardness was greater after 1 hour of contact time (P = .001) than after 6 hours of contact time. In conclusion, contact between alginate impression material and type III dental stone up to 6 hours did not affect the dimensional stability and richness of the surface; hardness, though, was significantly affected.
藻酸盐印模（不可逆水胶体）材料在牙科实践中常用，因为它易于混合、成本低且患者耐受性良好。然而，该材料尺寸不稳定；因此，印模完成后需立即灌注模型，若印模保存在100%湿度环境下，则需在60分钟内灌注。随着时间推移，藻酸盐印模与铸模模型过度接触可能会影响模型性能。在本研究中，作者测试了藻酸盐印模与III型牙科石膏接触时间对铸模模型性能的影响。通过使用不可逆水胶体印模材料和III型牙科石膏，从不锈钢圆柱体获得67个铸模模型。37个铸模模型在1小时后与印模分离（对照组），30个铸模模型在6小时后分离（研究组）。在光学显微镜下评估样本的表面细节，并用数字卡尺测量尺寸稳定性。在铸模上制作一个压痕，然后用数字卡尺测量压痕深度以测量硬度。当接触时间从1小时增加到6小时时，铸模模型的尺寸稳定性未受影响（P = 0.507）。随着接触时间增加，表面细节并未恶化，因为所有样本在1小时和6小时间隔期后都能重现所有细节。然而，接触1小时后的硬度（P = 0.001）大于接触6小时后的硬度。总之，藻酸盐印模材料与III型牙科石膏接触长达6小时不会影响尺寸稳定性和表面丰富度；不过，硬度受到显著影响。
