The custom trays are fabricated so that the final impression of the patient’s edentulous mouth can be taken accurately with proper border extension of the complete denture and with correct pressure over the selected soft tissues. The selective pressure technique helps in making the impression in such a way that when the dentures are finished and worn by a patient, they exert pressure only on those areas that are able to 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 in 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. We will learn here as to how to make a special tray on a cast that has been made from impression compound.
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
This topic is covered in another article. To read the article, click at the link.
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