See as a dentist myself I think it is due to trauma 2 some nerve while he gave u block[shot].Secondly when u have habit of bruxism or clenching of teeth in night the teeth gets attrited i,e vertical dimension of teeth is decreased so upper n lower teeth cant close with perfect grip.As a result MPDS develops[myuofunctional pain dysfunction syndrome].But it is usually associated with popping sound in TMJ and very rarely closing of mouth.Also u go for OPG if there is third molar involvement.[most common cause of lock jaw]if any problem contact me with
details.molarindia@yahoo.co.in