The root canal orifice is the junction between the pulp chamber and the root canal, or the migration of the pulp chamber floor and the root canal. The positioning of the root canal orifice is a critical step in the correct positioning of each root canal. In single canal teeth, the pulp chamber and root canal are continuous canals and it is difficult to identify the root canal orifice morphologically; in multi-rooted teeth, there is a funnel-shaped root canal orifice, but the root canal orifice can only be found after careful treatment of the contents of the pulp chamber in the crown of the tooth. Clinically, if there is difficulty in finding the root canal orifice in a multi-canal tooth for some reasons, the following methods can be used in combination to help find the root canal orifice in addition to applying knowledge of the anatomical morphology of the tooth pulp chamber. 1, multiple root canal teeth often due to ageing changes or restorative dentin deposition, or pulp stone, or pulp cavity calcification, or root canal morphology variation, and so on, and make the root canal mouth is not easy to find, with the help of the three-dimensional anatomical morphology of the tooth, from all directions and positions to understand and see the anatomical morphology of the pulp cavity; and the use of a variety of angular projection method taken by the X-ray film to understand and point out the number of roots and root canals, shape, location, direction and curvature; and The number, shape, position, direction and curvature of the roots and root canals, the relationship between the roots and the crowns, and the possible variations of the root and root canal anatomy. 2.Remove the dentin collar blocking the root canal opening in the cervical part of the pulp chamber of the molar, so as to fully expose the root canal opening at the bottom of the pulp chamber. 3.After using a root canal irrigant that can dissolve and remove necrotic tissue in the pulp chamber to thoroughly clean the pulp chamber, the root canal opening is likely to be detected. 4.When probing the root canal opening, attention should be paid to the dentin and restorative dentin covering the top of the bone in the darker part of the pulp chamber for thorough probing. Attention should also be paid to the direction of the root canal for exploration. 5. There are several developmental grooves in the pulp chamber floor, which are related to the direction of the root canal opening, i.e., the developmental grooves along the pulp chamber floor migrate to the root canal opening. Therefore, if a very sharp root canal probe is used to scratch along the developmental groove, it is expected to open the tighter root canal opening. When a root canal has been pointed out, the possible location of the remaining root canals can be estimated, and if necessary, a small amount of dentin can be removed with a small ball drill in the developmental sulcus where the root canal is likely or expected to be located, and then a sharp probe is used to try to puncture the calcified area to find the root canal opening and remove the dentin collar from the neck of the tooth to expose the location of the root canal opening. Be careful not to excessively deepen or flatten the developmental sulcus when drilling and grinding to avoid losing these natural markers and grinding laterally or puncturing the root bifurcation area. 7.Apply tincture of iodine at the bottom of the pulp chamber, and then use a slightly dry alcohol cotton ball to rub over the bottom of the pulp to remove the iodine; the darker coloring is often the root canal opening or the developmental groove. 8.Transillumination method: Using the light source of the optical fiber diagnostic instrument to illuminate the hard tissue of the buccolingual crown, the light enters the pulp chamber through the enamel and dentin, and the root canal mouth can be seen as a black spot; while the light source is illuminated from the soft tissue near the root protrusion, the light enters the pulp chamber through the soft tissue, bone and dentin, and the root canal mouth is shown to be brighter than the nearby pulp chamber.