![]() ![]() It is easy to adjust but is brittle, may distort at relatively low temperatures and is less easy to use. Shellac is a form of wax which softens on heating. ![]() However, although self-curing acrylic resin is cheap, it has limited working time and easily distorts during curing. They are more expensive than self-curing acrylic. They are supplied in a uniform thickness and are dimensionally stable on curing and in storage. Light-curing composite blanks are the most common and easy to use materials for tray construction. This should transfer to the model on casting. ![]() This is drawn on the primary impression by the clinician with an indelible pencil for alginate or a permanent marker pen for silicone. The outline (peripheral extension) required for the custom-made tray.The information you should find on the prescription card and impression is as follows: There are few indications in complete denture prosthetics for the use of such high viscosity materials for working impressions. Spacing is also required for stiff (high viscosity) impression materials because unless there is some spacing between the tray and the tissues it is difficult to seat the tray without using considerable force. A weak material such as alginate requires more spacing than a tough material such as silicone. The amount depends on the amount of undercut to be recorded, the elastic limit and tear strength of the chosen impression material. When undercuts are present, spacing is required. In edentulous cases, the majority of denture-bearing areas are free from large undercuts and impressions may be taken in close-fitting trays using impression materials which are rigid (non-elastic) when set, i.e. Retain its shape throughout the impression procedure and during model production.Allow pressure to be applied by the clinician on selected areas of the denturebearing area.Support the impression material in contact with the oral tissues.The design of the tray will depend on the amount of undercut present and the type of impression material being used. Like stock trays, they are used to support and transport the impression material to the mouth and once set, to the laboratory. Their design and accurate fit allows for better control of impression materials that are fluid and must be guided into place. They are custom-made to fit the denture-bearing area on the primary model. Overview of custom impression traysĬustom impression trays are used to overcome the inaccuracies associated with primary impressions. Primary impressions are discussed in the previous chapter, here we will begin with the manufacture of a customised tray. (Note: The clinical stages are indicated in bold, and those conducted in the dental laboratory in italics.) ![]()
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