FONTANA (CBS) — A Fontana dental office is cleaning up after an arsonist set a fire causing more than $1 million in damage, the latest in a string of arson fires.

The fire was reported at 3:22 a.m. on June 14 at Western Dental Center, 10144 Sierra Avenue, about a block south of Kaiser Hospital, the Riverside Press-Enterprise reported.

There were three other instances of dental offices being set on fire in March. Those offices were all along Sierra Avenue between Interstates 10 and 210, the newspaper reported.

None of the first three fires were at a Western Dental offices, but investigators believe all the fires are related.

“The ignition sources were all similar,” fire department spokeswoman Tracey Martinez told the Press-Enterprise.