What is the main purpose of using a custom impression tray?

The main purpose of using a custom impression tray is to ensure correct impression thickness. Custom trays are designed to fit the individual contours of a patient's mouth, which helps achieve the ideal thickness of the impression material. This is crucial for a few reasons: it provides greater accuracy in capturing the details of the oral structures, which is important for the fit of any prosthetic devices that will be made from the impressions. Additionally, having consistent and appropriate thickness can prevent distortion that might occur if the material is too thin or too thick.

When using a pre-fabricated tray, it may not provide the precise fit needed for certain cases, leading to inconsistencies in the impression. Hence, custom trays play a vital role in enhancing the quality of the impressions and, subsequently, the prosthetics fabricated from them.