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Article
Effect of Adding some Additives and Drying Method on Compressive Strength of Gypsum Products

Authors: Wael Abdul Razak وائل عبد الرزاق --- Ihab N. Yassin ايهاب ياسين --- Firas Abd Kati فراس عبد كاطع
Journal: Tikrit Journal for Dental Sciences مجلة تكريت لعلوم طب الاسنان ISSN: 20731213 Year: 2017 Volume: 5 Issue: 2 Pages: 25-32
Publisher: Tikrit University جامعة تكريت

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Abstract

Gypsum products (dental plaster and stone) are widely used indentistry. However, the main problem with any gypsum productsis reproduction of fine details and dimensional stability. Thecurrent study was conducted to assess the effect of incorporatingvarious additives (i.e. cured resin, pulverised stone, pulverisedplaster, and glass fibers) and drying method on compressivestrength of gypsum products. A total of 160 specimens weredivided into 2 groups according to the method of drying (air andmicrowave). For each drying method, each group was subdivideddepending on the type of material used into 2 groups; dentalplaster and dental stone. Variuos additives were used forreinforcement; cured resin, pulverised plaster, pulverised stone,and glass fibers. The unmodified group was considered as control.The specimens were dried and the compressive strength test wasapplied on all specimens. All specimens' data were statisticallyanalysed via ANOVA, Tukey and independent T tests.Thecompressive strength of gypsum products was significantlyinfluenced by the type of additive used. The specimens reinforcedwith glass fibers, cured resin, pulverised plaster, and stone had agreater value of mean compressive strength compared withunmodified groups. Statistically, highly significant differenceswere observed among all dried groups (P≤0.001). As well, themicrowave specimens were more resistant to compressiveloadings than air dried specimens. No significant differences,however, were recorded between the two drying methods(P>0.05).The glass fibers have a significant effect on compressivestrength of gypsum products. The pulverised particles and curedresin can be added at 1 % by weight to enhance the mechanicalproperties of plaster and stone. Microwave drying for 5 minutescan fasten the drying time and permit early manipulation of plasterand stone models.


Article
Evaluation of some adhesive materials for repairing gypsum models

Author: Radhwan H Hasan
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2005 Volume: 5 Issue: 6 Pages: 185-191
Publisher: Mosul University جامعة الموصل

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Abstract

The aim of this study was to evaluate some adhesive materialsthat are used in dentistry for repairing of gypsum cast.The specimens were prepared with dimensions 121×16×10mm length, width and thickness, respectively. The total numberof specimens was 96 (48 specimens for dental plaster,while the other 48 specimens were for dental stone). The lengthof each specimen was measured and recorded on its surface,then the specimens were fractured into two pieces and reattachedtogether with one of the three adhesive materials, reattachmentwas done either immediately (time= 0) or after 4minutes of adhesive application. These specimens were dividedinto six groups for each gypsum product, which involved:Group 1: Control, unrepaired specimens; group 2: Polycarboxylatecement, time= 0; group 3: Polyacrylic acid solution,time= 0; group 4: Polyacrylic acid solution, time= 4 minutes;group 5: Cyanoacrylate adhesive, time= 0; group 6: Cyanoacrylateadhesive, time= 4 minutes. The length of each specimenwas measured again and differences in length for each repairedspecimen was measured. Then all specimens were subjectedto the flexure of transverse strength test. Data were analyzedusing analysis of variance and Duncan’s Multiple RangeTest.The results indicated that using of cyanoacrylate adhesive,time= 0 and polyacrylic acid solution, time = 4 minuteshad significantly higher transverse strength providing maximumadhesion for each gypsum product. The results of this studyalso showed that there were dimensional changes with polycarboxylatecement adhesive and such changes not observedwith cyanoacrylate and polyacrylic acid solution adhesives.


Article
Effect of disinfectant agents on certain physical and mechanical properties of type IV dental stone

Authors: Hanan Abdul- Rahman Khalaf حنان عبد الرحمن خلف --- Mithaq Radhi Mohammed ميثاق راضي محمد
Journal: Journal of baghdad college of dentistry مجلة كلية طب الاسنان بغداد ISSN: 16800087 Year: 2014 Volume: 26 Issue: 1 Pages: 24-31
Publisher: Baghdad University جامعة بغداد

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Abstract

Background: Dental stone casts come into contact with impression materials and becomes susceptible to cross contamination from saliva and blood. This study was done to evaluate the physical and mechanical properties of dental stone type IV after treatments with various disinfecting agents and regimes (methods).Materials and Methods: Type IV dental stone and different types of disinfecting agents were used and divided into seven groups: G1: dental stone without disinfection (control group), G2: dental stone mixed with silver nitrate powder 0.5% , G3: dental stone mixed with silver nitrate powder 1%, G4: dental stone mixed with copper sulfate powder 0.5%, G5: dental stone mixed with copper sulfate powder 1% ,G6: dental stone immersed in propanol 70% and G7: dental stone immersed in ethanol 70%.Setting time, linear setting expansion, surface detail reproduction, compressive strength of type IV dental stone as well as compatibility with auto mixing addition silicone impression material were evaluated. The statistical analysis were conducted by ANOVA test followed by LSD test (p<0.05), also chi square test was used.Results: The compressive strength, linear setting expansion, surface detail reproduction and compatibility of stone specimens was affected to a higher extent by mixing with silver nitrate powder 1%, copper sulfate powder 1% while treating the stone specimens with the disinfecting powders at low concentrations as well as immersion of stone specimens in either ethanol or propanol for 15 minutes produce less effect on the previous tested properties. Conclusion: Silver nitrate 0.5%, copper sulfate 0.5% powders as well as 15 minutes immersion in 70% ethanol or 70% propanol did not promote adverse alterations in most of evaluated properties of type IV dental stone


Article
Examination of the particle’s shape, size and distribution of the commercial dental gypsum products

Authors: Lamia T Rejab --- Sawsan H Al–Jubori
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2003 Volume: 3 Issue: 2 Pages: 103-107
Publisher: Mosul University جامعة الموصل

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Abstract

Gypsum products used in dentistry are in the form of α and β calcium sulfate hemihydrate as dental stone and plaster. The aim of the study is examination of the particle’s shape, size and distribution of the different commercial dental gypsum products. The particle’s shape was examined microscopically with transmitted light microscope instead of reflected light microscope or electron microscope. Analysis of the particle’s size distribution and the measurement of the powder particle’s fineness was performed by sieving procedure using sieving machine. The data was collected and calculated and then compared with the ADA Specification No. 25 for gypsum products. The results showed that the microscopical examination with transmitted light microscope give clear accurate and precise image about the different shapes of the stone and plaster. The results of the analysis for particle’s size distribution showed that there is a difference in the distribution between the different tested commercial dental gypsum products and also showed that all products have particle’s size larger than the ADA Specification No. 25.


Article
Modification of gypsum products (Part I): physical and mechanical properties of adding some additives on different types of gypsum products

Author: Nadira A Hatim
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2007 Volume: 7 Issue: 10 Pages: 206-212
Publisher: Mosul University جامعة الموصل

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Abstract

Aims: A pilot study was done to evaluate the physical and mechanical properties of the Iraqi plaster (Al- Ahliya gypsum) and Plaster of Paris (British Gypsum), and to improve the quality by the incorporation of some additives. Materials and Methods: Two types of gypsum products were used in this study (Iraqi plaster, Plaster of Paris). Three types of additives {gum arabic at a concentration of (0.1%, 0.25%,0.35%, 0.50%), calcium oxide at a concentration of (0.1%, 0.25%, 0.35%, 0.50%, 0.75%), and ferric oxide acts as a pigment (blue or red) at a concentration of (0.1%, 0.2%)} were incorporated afterpreparation into the weighted dried gypsum powder. The effects of these additives on the physical andmechanical properties of the experimental gypsum products (Iraqi plaster and Plaster of Paris) have beenevaluated by measuring the water/powder ratio, setting time, linear setting expansion, and compressive strength. Four hundred sixty gypsum samples were prepared for this study. Mean, standard deviation, variance (ANOVA), and Duncan's multiple range tests were used to analyze the measurements. Results: ANOVA showed that there was a significant difference in the water/ powder ratio, setting time, linear setting expansion, and compressive strength between Iraqi plaster and Plaster of Paris depending upon the type and the concentration of each additive used. Conclusions: The last concentration of each additive (gum arabic 0.5%, calcium oxide 0.75%, or ferric oxide 0.2%) in all the experimental measurements that are incorporated within the two gypsum products showed


Article
Comparison of Some Properties between Commercially Available Gypsum Products

Author: Tameem K. Jassim تميم خضر جاسم
Journal: Tikrit Journal for Dental Sciences مجلة تكريت لعلوم طب الاسنان ISSN: 20731213 Year: 2012 Volume: 1 Issue: 2 Pages: 63-69
Publisher: Tikrit University جامعة تكريت

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Abstract

Gypsum models are often used in dental healthcare, and there is an increased need for manipulation of master casts in extensive reconstructions requiring a material that is not easily abraded or damaged with dimensional accuracy, accurate reproduction of details, and the use of a voids free surface master model. This study was conducted to compare between commercially available type III and type IV dental stones in some of their properties.Four groups were compared: Zhermack and Geastone of Type III dental stone, and Zhermack and Bluejey of Type IV improved dental stone. Ten specimens were fabricated for each material from a rubber ring with dimensions of 20mm height and 30mm diameter. Dimensional stability, reproduction of details, surface porosity, and surface hardness were evaluated for the different gypsum products.Results of this study show that for the dimensional stability there was an increase in dimension more than that of the test block and was only highly significant for groups Z3 and Z4. The surface hardness for groups Z3 and Z4 was significant higher than groups G3 and B4 in all of time intervals except after 24h for groups Z4 and B4 this was insignificant. Surface porosity test and reproduction of details test, both revealed no significant difference between the test groups.As conclusion the Zhermack dental stone products, type III & IV, showed higher surface hardness than Zeus dental stone products, type III & IV (Geastone and Bluejey). On the other hand we found that Zeus dental stone products showed good dimensional stability than the Zhermack dental stone products. All stone products provided similar scores for details reproduction, and were similar in relation to surface porosity.

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