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.

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

Birr says students used the device during a classroom exercise last Thursday. Toward the end of the period, 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 was released from jail after posting $2,000 bail. The Salem-Keizer School District placed him on leave.

Birr says the markings had mostly faded by Tuesday.