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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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