1.Cleaning of calculus and plaque: In order to ensure the health of periodontal tissues and gingival margin and the accuracy of impressions, the calculus and plaque must be cleaned before veneering to maintain good oral hygiene. 2.Treatment of caries: All the caries found in the examination should be treated by filling. If the caries invades the pulp, the pulp treatment should be done. 3.Treatment of periodontitis: If there are symptoms of periodontitis such as gum congestion, swelling, pus overflowing from periodontal pockets, periodontal treatment should be done first, and the teeth should be set after the inflammation subsides. 4, in addition to bad restorations: improperly designed restorations, or restorations that have lost function and stimulate the surrounding tissue and can not be corrected should be removed. 5.Extraction of loose teeth and roots that cannot be retained.