Question

what makes the high-pitched whine on a dental drill?

Answer 1

Short answer: the whine mostly comes from the tiny turbine (or motor) spinning at extremely high speed and the air flow through and around it. That creates aerodynamic tonal noise plus vibration of the metal parts, which you hear as a high-pitched whine.

A bit more detail:
- High-speed “air‑turbine” handpieces use compressed air to drive a tiny rotor that spins on bearings at hundreds of thousands of rpm. Fast rotating blades and the periodic passage of blades past stationary parts produce strong pressure fluctuations (the “blade‑pass” frequency) and harmonics in the audible range. Turbulent air flow through small passages adds broadband high‑frequency noise.
- The blade‑pass frequency ≈ (rpm/60) × number_of_blades. Example: 300,000 rpm = 5,000 revolutions/second; with 3 rotor blades that gives 15,000 Hz — a very high, sharp pitch.
- Structural vibration: the rotor and head can vibrate and radiate sound; worn bearings, imbalance or damage make the noise louder or change its pitch.
- Load and water affect the sound: when the bur meets a tooth the turbine slows a bit (pitch drops), and the water spray/air jet can damp or change the timbre.
- Electric micromotor handpieces run at much lower speeds or different gearing and produce a deeper, less piercing sound than air turbines.

So the characteristic whine is fundamentally aeroacoustic (fast blades + air flow) plus mechanical vibration, not just the bur cutting the tooth.