Untitled Quiz

Impression Trays

• Impression trays are devices used to hold impression material in the mouth.
• They maintain the material's position while it sets and during removal, as well as during the casting process.
• Trays consist of a body and a handle.
• The body comprises a floor and flanges.
• Upper trays have a palatal portion, while lower trays have lingual flanges.
• Impression trays must be strong and rigid to prevent distortion during removal.

Requirements of Impression Trays

• Trays need to be smooth and clean, and sterilizable if not disposable.
• They must confine the impression material and hold it in the right position to cover the whole jaw area.
• The trays must allow for equal thickness of impression material.
• Flanges must reach the sulci and frena without causing displacement.
• Mechanical locking (rim-lock undercuts or perforations) or adhesives are used to secure elastic impression materials.

Stock Trays

• Stock trays are pre-made trays available in various sizes and shapes.
• They are inexpensive and meant for preliminary impressions.
• Sizes and shapes are adjusted to accommodate different arch sizes and types of patients (dentulous, edentulous, or partially edentulous cases).
• Stock trays are available in various materials including nickel silver, stainless steel, aluminum tin, and plastics.
• Plastic stock trays are disposable.
• Incorrect tray selection results in distorted impressions.

Dentulous Patients (teeth present)

• Trays designed for patients with teeth have flat floors, high flanges, and the handle aligns with the floor.
• Perforated or Rim-lock trays are often chosen for these patients.

Edentulous Patients (no teeth)

• Trays for toothless patients have rounded floors and short flanges that accommodate the ridge shape.
• Handles are often L-shaped, enabling border moulding in the labial areas of the impression.

Partially Edentulous Patients (some teeth)

• Trays for these patients have a flat floor and high flanges in the area with remaining teeth, with a rounded floor and short flanges in the toothless areas.

Construction of Primary or Study Cast

• A cast is a positive reproduction of the upper or lower arch tissue captured in an impression.
• The study cast is made from a preliminary impression.
• The working cast is created from the final impression.
• Denture bases or other dental restorations are fabricated using the working cast.
• Plaster of Paris mixes need to be poured in stages to avoid air trapping.
• The casting and finishing processes are often required to complete the cast.