My Son 16yrs Spasmodically His Jaw Clicks In And Out,

My son 16yrs spasmodically his jaw clicks in and out, generally returns within the day, its been 3 days and he cant open his mouth at a wide distance. Relaxed mouth no pain, once he extends the pain increases. Physio say its not there area. we have used heat packs and voltaran cream, any other suggestion please