Mydent - Perforated Plastic Impression Trays. Defend Impression Trays are made of a strong, rigid material that aids in the generation of consistent, distortion-free impressions. Compatible with a wide range of impression materials, these trays offer a system of holes and perforations to optimize flow and retention of materials. The disposable, preshaped trays can be easily trimmed or flame softened to adjust for a custom fit. In addition, Non-slip grips offer an easy, clean removal.