Not all RCT treated teeth require crown. Those with significant loss of tooth structure do require crown to prevent further damage to the tooth structure and to restore proper shape and function of that particular tooth, most importantly in back teeth which are constantly under biting forces. Front teeth might not require crown if there is no substantial damage to the tooth structure. Just a minor procedure to preserve its shape and shade will do. Various types of crown materials like metal, porcelain fused to metal, zirconia(metal free) etc are prevalent. Would suggest a high strength metal free crown for back tooth.