The custom trays also known as special trays are fabricated so that the final impression of the patient’s edentulous mouth can be taken accurately with proper border extension. The selective pressure technique helps in making the impression in such a way that when the newly fabricated dentures are worn by a patient, they exert pressure only on those areas of the mouth that can withstand the masticatory load. The selective pressure technique of impression making spares the non-pressure bearing area of the edentulous jaw and thus eliminate the possibility of trauma resulting in pain and ulceration in the mucosa. The special tray for selective pressure technique is made on the primary cast that has been prepared by pouring the impression made in alginate or impression compound. The impression taken in impression compound records the mucosa in a compressed state whereas the impression taken with alginate records the mucosa in a non-compressed state. From these two opposite states of mucosa record, a dentist proceeds to prepare a special tray that is used to make an impression with selective pressure. We will learn here as to how to make a special tray on a cast that has been made from impression compound.
Masticatory mucosa
Stress bearing area of upper and lower edentulous jaw
The areas that can bear the masticatory load are divided into two types: They are
2. Secondary stress bearing areas
Primary supporting areas
- Hard palate
- Posterior-lateral slopes of residual ridge
Secondary stress bearing areas
They bear less load. They are
2. Rugae area
3. Maxillary tuberosity
Relief area
The area that cannot bear load, and if overloaded, can dislodge the denture or become sore. They area
- Incisive papilla
- Median palatine raphe
- Torus palatinus
- Sharp spiny processes
- Cuspid eminence
- Zygomatic process
How to make a special tray
The wax spacer of specific thickness in a special tray is provided to accommodate the impression material being used to record the soft tissue state. Stoppers in a custom tray prevent it from sinking beyond a limit into the soft tissues, so that the impression material remains of a specific thickness to record proper functional or static state.
Maxillary custom tray-top view |
Maxillary custom tray-Transverse view |
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