Offer Valid: 4/1/13 - 6/30/13 Buy (4) 200ct mix n' match boxes of Disposable Prophy Angles, Get 1 box of 200 Free! To receive your free good, please send a copy of your Patterson invoice to: Young Dental, Algonquin, IL 60102 or fax to 888-771-7573. Requests must be received by 7/31/13. Qualifying purchase(s) must be on one invoice. Offer cannot be combined.