Offer Valid: 4/1/13 - 6/30/13 Buy any 3 Stones, Get 1 Free! Print promo code PATTERSONJAN2013 on invoice. Fax your proof of purchase 888-727-2614 or email and attach a pdf of your proof of purchase to kerrpromo@kerrdental.com.The required purchase from Patterson must be on one invoice dated 4/1/13-6/30/13. Please indicate choice of free goods (of equal or lesser value). Incomplete or illegible invoices will not be honored. Invoices received after 7/31/13 will not be honored. Multiple redemptions on a single invoice are valid. Offer cannot be combined with any other Kerr or Patterson special. Offers not valid in Puerto Rico.