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General Impression Tray Selection Guidelines
Selecting an appropriate tray for the desired technique and materials
used is an extremely important, yet often overlooked, part of successful
impressions. Full arch perforated metal, rigid plastic or custom trays
are recommended for fixed or removable prosthetic restorations involving
three or more units (veneers and long span bridges). For all cases involving
only one or two simple restorations (single crowns, inlays and onlays),
small double-arch impression trays offer the advantage of capturing the
restorative impressions, opposing dentition/occlusion and bite registration
- all at once. Metal perforated, stock double arch trays are recommended
for patients with strong tongues or gag reflexes (these tend to exert
undesirable forces, especially on lower posterior impressions).
When selecting a tray, consider the following additional factors and
tips:
A. Tray Size
- Ensure stock or custom tray allows for a minimum material thickness
of 5 mm surrounding the preparation. If it's too thin, compression of
the material can result in deformation during removal.
- Potential exists for tearing if there is not enough space between
the equatorial line of the tooth and the side of the tray. Permanent
distortion may also occur due to strong distortion of the lower parts
of undercuts.
- Double Arch impression trays should be sufficiently sized to encompass
the canine tooth, ensuring proper occlusal registration.
- Try tray in mouth at full closure to assure proper relationships and
adequate space between the restoration pads and hamular notches.
- Ensure stock trays closely fit the arch form of the patient (reduces
amount of impression material required and facilitates seating the loaded
impression tray intraorally).
B. Distortion Resistance
- All trays (full arch on quadrant metal or plastic) must be rigid enough
to resist deformation. They should also be extensive enough to support
the impression material to cover all areas.
- Ensure selected tray is not distorted by the weight of stone bending
unsupported sections.
- If a plastic tray is used, ensure the lingual arm is not flexed by
the tongue (can cause distortion by inducing a spring back effect).
- Excessive pressure on the tray should be avoided during the final
set stage. Doing so might squeeze the material toward the tray wall,
which can then spring back after the pressure is removed.
- No heavy body material or high durometer putty has the strength to
overcome flexural errors caused by the tray.
CALL TOLL FREE 1-866-372-3786
24 HOUR TOLL FREE FAX 1-800-361-5088
Email: products@aurumgroup.com
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