Which instrument is described as a flat plastic instrument?

• A. Mouth mirror
• B. Flat plastic
• C. Amalgam plugger
• D. Excavator

Answer: (B)

In dentistry, the material and shape of an instrument reveal its job. A flat plastic instrument has a flat blade and is made of non‑metallic plastic, which makes it ideal for spreading, smoothing, and placing viscous or putty‑like materials without scratching tooth surfaces or leaving metal marks. The flat blade lets you create an even, smooth layer across a cavity floor, a matrix, or a base material, and being plastic means it’s often disposable and easy to handle for materials like bases, impression compounds, or temporary filling materials.

In contrast, tools like a mouth mirror are used for indirect vision and illumination and are typically metal with a mirrored head; an amalgam plugger is a metal tool designed to condense amalgam into a cavity; an excavator is a metal, spoon‑shaped instrument used for removing carious dentine and shaping cavities. Their shapes and materials point to different functions, not to spreading or smoothing plastic materials. Therefore, the flat plastic instrument best matches the description.