SALEM, Ore. (AP) -- An Oregon science teacher who police say used a Tesla coil to burn the phrase "I love mom" into the arms of students has been charged with criminal mistreatment.

Samuel Dufner

Salem Police Lt. Steve Birr says 37-year-old Samuel Dufner was arrested Tuesday at South Salem High School.

Birr says students used the coil in an exercise last Thursday. Dufner noted it could also be used to mark the skin and asked for volunteers.

Dufner burned "I love mom" -- with a heart to symbolize the word love -- into their arms.

A parent complained Friday, starting the investigation.

Dufner posted $2,000 bail. The Salem-Keizer School District placed him on leave.

Birr says the markings had mostly faded.

The Tesla coil transmits electricity without wires at high frequency and high voltage levels.