A method for planning a root canal treatment of a tooth which includes a cavity of a patient. The method includes measuring a surface of the cavity with an optical three-dimensional method to generate three-dimensional measurement data of the cavity. A 3D-model of a guide template is planned based on the generated three-dimensional measurement data. The 3-D model is designed in its dimensions as a counterpart to the cavity. Three-dimensional volume data of the tooth is displayed. A position and an orientation of a root canal of the tooth is determined based on the three-dimensional volume data of the tooth. A guide opening for a tool is planned to expose the root canal. The guide opening is arranged within the guide template so that the guide opening points at an entry point of the root canal and in an entry direction of the root canal.
