Good elastic property and reproduces most undercut areas. Good recovery from distortion. Non hydrophobic. Palatable and well tolerated. Can be reused.
Alginate 32 Willium Wilding s introduced. Glycol - small amount - To make powder dustless 8. Chemical indicators - small amount pH changes from alkaline to neutral to indicate different stages in manipulation Violet — during spatulation Pink - ready to load White - ready for insertion into mouth 9. Disinfectants ammonia salts and CHX - small amount 35 USES 1.
Mouth protectors 3. Study models and working casts 4. Type II — Normal setting. Gelation occurs by a chemical reaction. This will also lead to reduced working time 48 The required quantity of powder and water are dispensed in a bowl.
Spatulation is carried out until a smooth creamy mix of alginate is obtained. This results in a superior mix than obtained manually. A plastic scoop and cylinder is provided. These systems consist of a mixing unit that mixes - an aqueous base paste — sodium alginate polyacrylic acid - an organic initiator paste - calcium sulphate- hemihydrate and sodium phosphate. Materials stored for one month at 65 degree Celsius are unstable for use as they do not set at all or set too rapidly for any practical use.
Afterwards it is placed in a humidator while stone hardens. Stone cast or die should be kept in contact with the impression preferably for 60 minutes or for a minimum of 30 minutes. A base is added only after the first application of stone sets.
This method protects against volume change of the irreversible hydrocolloid impression material and distortion of the unsupported portions of the impression.
Elastic recovery : Reproduction of tissue details : lower than agar. ADA Sp. Requires material to reproduce a line that is 0. Dimensional stability: poor 7. Storage : cool, dry, tightly closed lid. In another way the clinician can safely influence gelation time by altering the temperature of water used to mix the impression material.
However using water cooler than C and warmer than 54 c is not recommended. To ensure maximum surface hardness, methods employed are : 1. Immersing the impression in a solution containing an accelerator for setting of gypsum products before pouring impression with gypsum. This acts by two ways a accelerates setting of gypsum.
Incorporating a plastic hardener or accelerator in the material by the manufacturer. Potassium titanium fluoride is most commonly used hardening agent. In general a hardening solution is not required unless specified by the manufacturer as most of the commercially available alginates contain a hardener in them.
In the form of a sol, containing the water. A reactor of plaster of Paris is supplied separately. Paste system, one containing the alginate sol, the second the calcium reactor. These materials are said to contain silicone and have superior tear resistance. Packaged for all automatic mixing machines. Perfectly defined margins. Trim excess alginate from non-critical areas to decrease amount of Microbial contamination. Spray the entire impression surface and the reverse side of the tray as well.
Biomechanics of rpd. What to Upload to SlideShare. Related Books Free with a 30 day trial from Scribd. Dry: A Memoir Augusten Burroughs. Related Audiobooks Free with a 30 day trial from Scribd. Empath Up! Keerthi Lenka. Khant Shyam. Kirti Komal. Manpreet Kaur. Yazid Abu Rabia. Samer Younan. Anjana S Rajan. Ikra Chahel. Show More. Views Total views. Actions Shares. No notes for slide. Impression materials agar and alginate 1.
Impression trays can be separated into two main categories- stock trays and special trays. It is a sulphuric ester of linear polymer of glactose. They break at increasing temperature to sol form. This helps in using agar as an impression material. Agar is useful as an ingredient in desserts in the Asian region, but it is commonly used as a solid substrate containing culture media for microbiological work.
It is also useful as a laxative, as an appetite suppressant, as a vegetarian substitute for gelatin, as a thickener for soups, as an ingredient in fruit preserves, ice cream, and other forms of desserts, and as a clarifying agent in brewing. It is also occasionally useful for sizing paper and fabrics. The component that causes the jelly-like nature in agar is the unbranched polysaccharide, which is obtained from the cell walls of some species of red algae. However, for commercial applications, agar is obtained primarily from ogonori.
Agarose is a polymer material a linear polymer containing the repeating units of agarobiose. Agarobiose is a disaccharide made of D-galactose and 3,6-anhydro-L-galactopyranose. On the other hand, agaropectin contains alternating units of D-galactose and L-galactose that are modified with acidic side groups.
Alginate is the conjugate base of alginic acid. Alginic acid is a polysaccharide that occurs in the cell walls of brown algae. This substance is hydrophilic, and it can form a viscous gum upon hydrating. It can form salts such as sodium alginate and calcium alginate with metal ions.
The appearance of this material can range from white to yellowish-brown. The alginate we know at present is a developed structure that is useful as a substitute for agar when agar became uncommon during World War II.
Typically, this material is commonly used than agar, mainly in dental impression at present due to the ease of use.
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