Impression Trays PDF

IMPRESSION TRAYS  The impression tray is a device used to carry the impression material into the mouth, maintaining it in position during setting, and supporting it during removal from the mouth and when casting the impression The tray consists of a body and a handle ...

IMPRESSION TRAYS  The impression tray is a device used to carry the impression material into the mouth, maintaining it in position during setting, and supporting it during removal from the mouth and when casting the impression The tray consists of a body and a handle  Floor Flanges The body consists of a floor and flanges. The difference between the upper and lower trays is that the upper has a palatal portion while the lower has lingual flanges Palatal Portion Lingual Flange Requirements Of Impression Trays  Requirements Of Impression Trays Strong and rigid to avoid distortion of the impression on removal. Smooth, clean and can be sterilized if they are not disposable.  Confine the impression material and hold it in correct position in the mouth and cover the whole area of the jaw which is required for the impression. Allow for equal thickness of impression material. The flanges of the tray must reach the functional position of the sulci and frena but not displace them.  provide for mechanical locking of the impression material to the tray through rim-lock undercut or perforation. Otherwise, adhesives should be used for the elastic impression materials. The stock trays should be available in different size and shapes. Sizes and shapes They must be inexpensive. Types of impression trays Types of impression trays Stock trays Special, individual or custom trays.  I- Stock Trays These are ready- made trays available in different shapes and sizes They are supplied in small, medium, large and extra large sizes The shape of the tray differs according to the case whether it is dentulous, edentulous or partially edentulous  For Dentulous Patients The tray has flat floors, high flanges and the handle is in-line with the floor of the tray For Dentulous Patients may be perforated, rim-lock trays or water-cooled trays The rim-lock tray is the tray of choice because it is rigid and it confines the impression material, helping to force it into all the areas to be included in the impression. Although, perforated trays are rigid, they don’t confine the material as the rim- lock tray  For Edentulous Patients The trays having round floor and short flanges to conform the shape of the ridge For Edentulous Patients The handle is bent in the form of L-shaped and joined at right angle to the floor of the tray to clear the lip and allows proper border moulding in the labial portion of the impression For Partially-edentulous Patients part of the tray has flat floor and high flanges in the dentulous area and the other part has rounded floor and short flanges in the edentulous area For Partially-edentulous Patients  The stock tray materials The stock trays can be made from different materials as nickel silver, stainless steel, aluminum tin or plastics. The stock tray materials The plastic stock trays are usually disposable The stock trays are used for making the.preliminary impression. The tray must be selected to conform nearly the shape and size of the arch Incorrect selection of the tray results in a distorted impression. If a tray with long flanges is used the oral vestibules will be distorted and result in over-extended impressions  If a short tray is used the impression material leaves the tissue and will be unsupported These impressions give an inaccurate cast and cause discomfort to the patient. Some dentists prefer to modify stock trays to improve their fitness. These modifications include bending the flanges to provide adequate space for impression material, or cut the flanges to accommodate for labial or buccal frena or to reduce over extended flanges Construction Of Primary Or Study Cast A cast or model is a positive reproduction of the form of the tissue of the upper or lower arch, which is made in an impression  Construction Of Primary Or Study Cast The study cast is made from the preliminary impression and the working cast is made from the final impression, and over which denture bases or other dental restoration may be fabricated. The study cast working cast  The study cast is made by pouring the mixed plaster of paris into a preliminary impression. The plaster of Paris is mixed with water (approximately one part water to two parts plaster) and poured to one end of the impression and vibrated to eliminate the air bubbles.  Plaster mix is always added to the same area to avoid trapping of air until the impression is filled. Excess plaster is poured over a glass slab and filled impression is inverted over it. The border is then smoothed and shaped by the use of spatula. After setting of the plaster the impression is removed from the plaster cast then the periphery of the cast is trimmed.