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Modification of Gypsum Products (Part III): Practical Application of Modified Gypsum Products

Authors: Mohammed A Abdullah --- Isam K Al-Khayat --- Nadira A Hatim
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2010 Volume: 10 Issue: 15 Pages: 17-24
Publisher: Mosul University جامعة الموصل

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Abstract

Aims: To determine the suitability of new modified Iraqi plaster and modified Plaster of Paris as a cast in microwave curing of acrylic denture base material, and microwave and open air drying methods on the surface roughness and dimensional accuracy of the cast. Materials and methods: Two types of gypsum products were used in this study {(Iraqi plaster, Plaster of Paris) with the combined additives (Gum Arabic 0.5%, calcium oxide 0.75%, and ferric oxide 0.2%), and Type III stone Plaster/Stone 3:1} that incorporated within the two gypsum products. The effects of drying method and combined additives on the surface roughness and dimensional accuracy of the experimental gypsum products, and acrylic denture base pro-duced from the modified gypsum casts have been evaluated. Mean, standard deviation, variance (ANOVA), and Duncan's multiple range tests were used to analyze the measurements. Results: ANOVA test showed that there was a significant difference in the surface roughness and dimensional accuracy between Iraqi plaster and plaster of Paris with or without additives dried in open air and microwave techniques. Conclu-sion: There was slight dimensional change in the gypsum cast with additives of clinical importance to compensate the polymer shrinkage of the acrylic denture base after cooling. There was no significant dif-ference in the average roughness of acrylic resin cured by microwave oven as a curing method. Keywords: acrylic, roughness, dimensional accuracy.

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Article
Modification of Gypsum Products (Part II): The Effect of Drying Methods on The Compressive Strength and Surface Hardness of Modified Gypsum Products

Authors: Mohammed A. Abdullah --- Isam K. Al-Khayat --- Nadira A. Hatim
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2009 Volume: 9 Issue: 14 Pages: 162-167
Publisher: Mosul University جامعة الموصل

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Abstract

Aims: Studying the effect of microwave drying on the physical and mechanical properties of modified
Iraqi plaster and modified Plaster of Paris in comparison with open air drying method. Materials and
methods: Two types of gypsum products were used in this study (Iraqi plaster, Plaster of Paris) with
the combined additives (gum arabic 0.5%, calcium oxide 0.75%, and ferric oxide 0.2%) that incorporated
within the two gypsum products. Physical and mechanical properties of the experimental gypsum
products have been evaluated by measuring the compressive strength, surface hardness, and surface
roughness. Mean, standard deviation, analysis of variance (ANOVA), and Duncan's multiple range
statistical test were used to analyze the data. Results: ANOVA analysis showed that there was a significant
difference in the compressive strength, surface hardness, and surface roughness between Iraqi
plaster (I.P) and Plaster of Paris (P.O.P) with or without additives. Conclusions: At two hours time
interval microwave oven drying, Iraqi plaster and Plaster of Paris samples were stronger than air dried
samples; and microwave oven at 10 minutes for 800 Watt not only increased the strength of gypsum
products samples, but also save time.

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Article
Evaluating the effect of new denture cleaners on the surface roughness of acrylic resin denture base material (An in vitro study)

Authors: Nadira A Hatim --- Salem A Al–Samarraie --- Isam K Al–Khayat
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2003 Volume: 3 Issue: 1 Pages: 31-38
Publisher: Mosul University جامعة الموصل

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Abstract

Three newly prepared denture cleaner solutions from materials available in our country [namely; oxalic, citric and tartaric acids dissolved in isopropyl alcohol (5% w/v)] were studied for their effect on 110 specimens of heat cure acrylic resin prepared according to ADA Specification for 7 days, 1 month, 6 months, and 12 months, compared with Steradent denture cleaner by two techniques (immersion and brushing techniques). The concentration (5% w/v) was selected according to the results of pilot study. The results of this study showed that oxalic and tartaric acids have nearly the same effect on surface roughness in relation to Steradent by immersion technique for six months, but this result was increased to show high rough surface of samples treated by citric acid for one year. Treatment with the four solutions led to reduction in weight (0.03 mg) except citric acid (0.49 mg). Statistical analysis was performed using F–test two–sample. The results revealed that there was a significant difference at levels 1% and 5% between the brushing and immersion techniques, roughness of the surfaces, and period of using each solution Changes in weight in relation to surface area were ranged between 0.01– 0.03 mg/cm2 for Steradent and oxalic acid in immersion technique, while the result was 0.05–0.23 mg/cm2 for brushing technique of the other solutions except citric acid. Oxalic acid showed complete removing of the stain within 8–10 minutes, Steradent and tartaric acid need 6–8 hours, while citric acid did not show the same result.

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