* صناعة نظري / ثاني اسنان كركوكد.حسن20/11/2017 103
Impression Trays Definition: A device that is used to carry, confine and control impression material while making an impression.*
1- Impression tray must be rigid. Flexible trays cause distortion of the impression. 2- It should be dimensionally stable. 3- It should provide uniform space for impression material. 4- It should be smooth to avoid injury to oral structure. 5- It should not distort the tissue in the vestibular areas. 6- It should support set impression materials when removed from mouth.
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Classification:
I- Based on whether they are prefabricated or individualized 1- Prefabricated trays/stock trays: * Perforated trays. * Non perforated trays.2- Individualized trays/custom trays/special trays: * Close fitting special trays. * Loose fitting or spacer special trays.
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Classification:
II- Based on use of impression trays Dentulous trays. Edentulous trays. Combination trays.III- Based on whether it can be reused again or not Disposable trays. Non disposable trays.
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Classification:
IV- Based on material used for fabrication of impression trays Metallic trays. Non metallic trays.*
I- Materials used for fabrication of stock trays: 1- Metal * Tin-lead alloy. * Stainless steel. 2- Plastic
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I- Stock trays: 1- Rigid and support the set impression material. 2- Dimensionally stable. 3- Tray is smooth. So, no injury to the tissue. 4- Multiple set in several patients.
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A- Tray acrylic special trays: 1- Easy to fabricate. 2- Require no special equipment. 3- Sufficient dimensional stable. 4- Can be made thin but reasonably rigid. 5- Modified easily, by grinding with acrylic bur.
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I- Stock trays: 1- Dimensionally accurate impression is difficult to make with stock trays. 2- No uniform space available for impression material. 3- Flanges of these trays may be over or under extended.
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A- Tray acrylic special trays: * Dimensional stability is less due to polymerization shrinkage.
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I- Based on type of impression. 1- Diagnostic impression= stock trays. 2- Primary impression= stock trays. 3- Secondary impression= custom trays.
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