**Core Concept**
Rotary reamers are a type of surgical instrument used in endodontics to shape and enlarge the root canal. The classification of rotary reamers is crucial for determining their proper use and maintenance.

**Why the Correct Answer is Right**
Rotary reamers are classified based on their cutting efficiency and working length. They are categorized into two main types: **tapered and parallel**. Tapered rotary reamers are used for initial canal shaping, while parallel rotary reamers are used for final shaping and enlargement. The correct classification of rotary reamers helps in selecting the appropriate instrument for a specific procedure, ensuring efficient and safe root canal treatment.

**Why Each Wrong Option is Incorrect**
* **Option A:** Rotary reamers are not classified as drill bits, as they have a distinct cutting mechanism and are designed specifically for endodontic use.
* **Option B:** Rotary reamers are not classified as file systems, as they are a separate category of instruments with distinct characteristics and uses.
* **Option C:** Rotary reamers are not classified as ultrasonic instruments, as they operate at a different frequency and are not designed for ultrasonic use.

**Clinical Pearl / High-Yield Fact**
When selecting a rotary reamer, it is essential to consider the working length, canal curvature, and the desired shape of the canal. Using the correct type of rotary reamer can help prevent instrument breakage and ensure successful root canal therapy.

**Correct Answer: D. Tapered and parallel**