Hugh Pickens writes: "Although the first electric dental drill was patented in 1875 and modern drills grind the diseased portions of teeth away at up to 500,000 rpm, dentists have recently been seeking less invasive ways of wiping out stubborn, tooth-decaying bacteria. Now Live Science reports that bacteria-killing jets of plasma could soon replace the drills used to treat cavities in our teeth after researchers recently demonstrated that a small, blowtorch-like device emitting a relatively cool beam of purple plasma could eliminate oral bacteria in cavities, leaving more tooth structure intact than a drill does. "I think plasma will provide additional advantages [in treating cavities], namely by not drilling into or removing dentin so deeply," says Stefan Rupf at Saarland University. To test how well "cold" plasma jets sterilize tooth material, researchers took slices of dentin from extracted human molars, doused them with bacteria, and torched them with the plasma jet. An inspection of the damage done to the germs via a scanning electron microscope shows bacterial remnants had holes in their cell walls, or exterior skin-like structures because when the plasma jet fires, it charges oxygen gas in the surrounding air, creating highly reactive molecules that can break down the bacteria's defenses. "What we think is that the reactive oxygen species are able to penetrate and to destroy bacterial walls," says Rupf adding that he expects the technique to be available to general dentistry in three to five years."