![]() The removal of any unsupported excess alginate with a scalpel will reduce the chance of distortion, as the impression is packed for transport. Gentle wiggling or gradual unseating can cause viscous flow and limit the elastic recovery and accuracy of the impression. After a full set, the alginate impression should be removed with a sharp snap movement. It can be beneficial if alginate is smeared deeply into the occlusal fissures of the teeth ( Fig. This happens most commonly if the pellicle is removed from the tooth when multiple sequential impressions are taken. If the teeth are over-dried, the alginate can form a chemical bond to the hydroxyapatite crystals. Over-drying with 3-in-1 air should be avoided. ![]() 15 The teeth should be gently dried with suction or gauze. Mouth preparation should be carried out before making your alginate impression to achieve enhanced surface detail. It can be tempting to use wax for this purpose, as it is cheap and fast to use, but it is flexible and can be easily distorted. A better technique is to modify the stock tray to increase its length with a rigid material, such as an impression compound ( Fig. In an attempt to capture the most posterior teeth, the clinician will often seat the tray too far back, resulting in the anterior teeth perforating through the impression material as the tray is rotated upwards. Stock trays of adequate width will often not be long enough to capture the full length of the arch. Tray perforations through the alginate can lead to inaccurate impressions and ideally should be avoided, particularly in key areas ( Fig. There should be good material support around the full arch and 3-5 mm clearance from the teeth around all aspects of the tray to allow adequate alginate thickness. Sizing the tray appropriately is essential. 11 When using alginate, universal plastic stock trays provide adequate rigidity. In reality, the studies that have investigated this have been concerned with high viscosity silicone putty, not alginate. This was born out of concerns about the rigidity of newer plastic stock trays, which were thought to flex and then rebound on impression removal. Classically, metal rim lock trays were recognised to be the gold standard. The tray is the foundation of an accurate impression. For the best results, cold water is recommended. There is some evidence to suggest that higher temperature water results in less dimensionally accurate impressions. By increasing or decreasing the temperature of the water, the setting time can be manipulated. Most setting times are based on 22 ☌ tap water and average 2-3 minutes. 8 Setting time of alginates can vary considerably between manufacturers. Altering the powder-water ratio by up to 25% does not affect the accuracy of the impression. For the best results, it is best to maintain the volume of powder and vary the amount of water. This article will aim to outline a simple and evidence-based summary of how to execute the stages above to a high standard.īy altering the powder-to-water ratio when mixing alginate, it is possible to manipulate the consistency. Recording a centric relation record (CRR) Recording impressions to achieve high-quality study casts The stages to produce accurately mounted study casts include: They are not always necessary but are invaluable when executing complex tooth wear cases. The production of articulated study casts comes at significant expense and must provide added value. They are also useful in the production of guides and stents. Duplicated study casts can be modified with mock equilibrations, tooth removal, or additive waxing, to simulate proposed treatment plans. They can be used to examine the static and dynamic occlusal contacts without muscular guarding or the visual limitation of the soft tissues. 1, 2, 3, 4, 5, 6, 7 The use of digital techniques will be discussed in a separate article within this series.Īrticulated study casts serve as a medico-legal record of the patients' pre-treatment presentation. ![]() The use of analogue techniques to produce articulated study casts is well documented. Articulated study casts can form an integral part of the treatment planning process for patients with complex tooth wear.
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