ADA Specifications For Dental Materials

ADA Specifications For Dental Materials

ADA specification, types, uses, manipulation, and setting process of gypsum products.
Answer:

Uses of Gypsum Products:

• As study models for the oral and maxillofacial structures.
• As cast and die material.
• As impression material.
• As investing material in flaking procedures for acrylic complete and partial denture processing.
• As investment material for the casting of metallic restorations.

Manipulation of Gypsum Products

• ProportioningFor attaining maximum strength water powder/ratio should be optimum.
• Recommended water/powder ratio for various gypsum products is:
  • Impression plaster: 0.50–0.75
  • Dental plaster: 0.45–0.50
  • Dental stone: 0.28–0.30
  • Die stone, Type 4: 0.22–0.24
  • Die stone, Type 5: 0.18–0.22.
• Instrument Used: It is a flexible rubber bowl and stiff bladed spatula.

Hand Mixing Procedure:

Water is taken first. The powder is then dispensed as per the proper water/powder ratio. The powder is sifted in water in rubber bowl. Now it is allowed to setting for 30 seconds and also to minimize air entrapment, stirring of the mix is done vigorously.

Inside of the bowl is wiped by a spatula so that there is wetting of powder and a breakdown of lumps. Mixing is continued until a smooth creamy mix is obtained. Spatulation is completed in 45 to 60 seconds.Vibration of mix is done either on the vibrator or by repeated tapping against a bench. Now the gypsum product is poured in the impression taking care not to entrap the air.

Mechanical Mixing:

It is done under the vacuum and this provides strong and dense casts. A uniform homogeneous creamy mix with the less incora portion of air is obtained by using an automated vacuum mixer. A good mix should have a glossy surface with smooth creamy consistency. The incorporation of air voids in the mix is reduced by use of vacuum mixers. The weighed powder is incorporated in 15 seconds by hand speculation in a special container, followed by 20 to 30 seconds of mechanical mixing of high frequency and low amplitude under a vacuum