![]() ![]() Plastic impression trays are generally single use (disposable).Īnother special type of plastic impression tray is the “dual-arch” tray. This is frequently required in “open tray” procedures which need a hole at implant transfers to unscrew the transfers through the impression tray. ![]() The main benefit of plastic impression trays is the ease with which holes can be made in them. These trays may be perforated or non-perforated and offer more or less mechanical retention. Standard plastic impression trays come in various types. The choice of correct tray size must be determined intraorally using a special compass. Schreinemaker impression trays are shaped and flanged to suit the specific anatomies of edentulous patients. These trays come in various upper and lower sizes and in different arch shapes. “Schreinemaker” trays (9) are special metal impression trays intended for use with edentulous patients. In the absence of mechanical retention, chemical adhesion between the tray and the impression material is essential. Impression trays with no form of mechanical retention (holes or rim locks) need to be coated with a special adhesive to retain the impression material (8). Because the material tends to come out from the holes, however, the same pressure (vis a tergo) applied using a non-perforated tray may not be achieved. When removed from the oral cavity, perforated trays with rim locks offer excellent mechanical retention for the impression material which is therefore unlikely to become detached from the tray or distort. Metal impression trays can be perforated or non-perforated and come with or without rim locks. (7) Rigid impression trays are to be preferred whenever a good degree of accuracy is required, as they do not flex during positioning or during removal of the impression. Metal impression trays are more rigid and therefore offer greater accuracy and precision than flexible plastic alternatives. Standard impression trays can be made from metal or plastic. Still others, referred to as sectional trays, cover only a specific section of the arch such as, for example, the anterior group (second and fifth sextant). Some impression trays cover the entire arch of the patient while others cover only a semi-arch (quadrant). Alternatively trays (and especially plastic trays) may be marked with sizes xs, s, m, l and xl. Standard impression trays come in 6 sizes numbered from 1 to 6, starting with the smallest diameter and progressing to the largest. There are various ways to determine the correct size for an impression tray: you can try one out directly in the patient’s oral cavity or you can use a special compass to determine the diameter of the arch intraorally and then select the most suitable size of tray. Anatomical differences play a fundamental role in the choice of impression tray, which may need to be larger or smaller depending on the patient from whom the impression is to be taken. The first factor determining variation in impression trays is the anatomy of the individual patient, which can vary significantly. Let us take a look at the main differences between them. There are various types of standard impression tray on the market. based on standard arch measurements and shapes. Standard impression trays, on the other hand, are ready made, i.e. Impression trays can easily be flanged for use with edentulous patients or drilled at the location of implant transfers for use in “open tray” procedures. Before the impression can be taken, therefore, a film of adhesive specially formulated for use with impression material must be applied. Conventional techniques are still the most commonly used today: a coating of resin is applied to a spaced stone model, the excess is removed, the handle formed and the tray is cured.Ĭustom impression trays do not provide any mechanical retention for the impression material, unless holes have been made in them with a bur. (4)Ĭustom impression trays produced using conventional methods are normally made from resin (5), while those produced using digital CAD/CAM software are typically made from PLA (polyactide) by means of 3D printing (6). Compared to standard, stock impression trays, custom versions offer the advantage of allowing a controlled and constant thickness to be achieved in the impression material. Impression trays can be produced using conventional, stone model based techniques (2) or using digital techniques (3). Having an impression tray that accurately reflects the anatomy of the patient’s arch is a great advantage as the material used to take the impression will be distributed more accurately and more evenly over the relevant areas. are produced specifically for an individual patient. Custom impression trays are individually made, i.e. ![]()
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