Custom Tray Purpose — NDEB AFK MCQ
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Correct answer: E — To provide a uniform, controlled thickness of impression material (2-3 mm) for improved dimensional accuracy and reduced distortion
A custom tray (fabricated on a diagnostic cast with cold-cure or light-cure acrylic) provides uniform impression material thickness (2-3 mm) around the prepared teeth. This uniform thickness minimises dimensional changes during setting (polymerisation shrinkage, thermal contraction) and ensures consistent elastic recovery during removal. Stock trays often result in variable, excessive impression material thickness, which can compromise accuracy, especially with less dimensionally stable materials (polysulfide, condensation silicone).
Reference: Anusavice – Phillips' Science of Dental Materials, 13th ed., 2022