(a) An order of disposition in a dependency proceeding shall continue in force until the purposes of the order have been accomplished.
(b) The court may terminate an order of disposition of a child adjudicated as a dependent child on or without an application of a party if it appears to the court that the purposes of the order have been
accomplished.
(c) When a child adjudicated as a dependent child reaches 18 years of age, all orders in connection with dependency proceedings affecting him or her then in force terminate and he or she shall be discharged from
further obligation or control.