Can you explain the difference between the Midwest Stylus ATC 890 and the Midwest Stylus ATC 990 handpieces?

Yes, both are new handpieces from DENTSPLY Professional. They are air-driven handpieces with an “Adaptive Torque Control,” a system which monitors the bur load and changes the air pressure to adjust the torque for peak power over a broad range of speeds. The Stylus ATC 890 has a mid-sized head, and the Stylus ATC 990 has a mini-sized head.