Doing braces for a tooth line, when the tooth has a large area of loss, the filling can not get enough retention force, the tooth needs to be prepared for the tooth, the production of metal porcelain or all-ceramic crown restoration. If the affected tooth has pulpitis or periapical periodontitis due to deep cavities, the first step is to remove the pulp, followed by root canal disinfection and completion of root canal treatment. For large missing posterior teeth, the filling is prone to fracture and dislodgement, and it is necessary to utilize the root canal to produce the core of the stump to fix the position, and then produce a full crown restoration, otherwise the tooth is prone to fracture along the neck of the tooth, resulting in failure of the restoration.