Design of a Custom Tray for Final Impression for Complete Denture

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

Certain area of the edentulous jaw is covered by masticatory mucosa that can bear the masticatory load. Masticatory mucosa covers the hard palate, attached gingiva and dorsal surface of tongue. They have resiliency, their surface texture feels rubbery, and they provide a firm base for complete dentures. Histologically, they show keratinized epithelium and interdigitated interface with many rete ridges and CT papillae with a thin layer of submucosa or sometimes none.  

Stress bearing area of upper and lower edentulous jaw 

The areas that can bear the masticatory load are divided into two types: They are

1. Primary stress bearing areas
2. Secondary stress bearing areas

Primary supporting areas

They are the main load bearers. They are

1. Hard palate
2. Posterior-lateral slopes of residual ridge

Stress bearing areas of the upper edentulous jaw

Secondary stress bearing areas

They bear less load. They are

1. Residual ridge
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

1. Incisive papilla
2. Median palatine raphe
3. Torus palatinus
4. Sharp spiny processes
5. Cuspid eminence
6. 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