Matters needing attention in double nail replacement technology: (1) The plane of the model is parallel, 7~8mm away from the neck edge of the prepared tooth, so that the model is horseshoe-shaped. (2) The working model is often punched with a laser punch, and there should be enough distance between the nail holes. (3) Bonding substitute nail and fixing device: 1, blowing off the powder in the hole, and bonding with 502 glue. 2. Insert the plastic nail sheath into the metal substitute nail. (4) Adding a model base: sticking a wax ball with a diameter of 2-3mm on the tail of the replacement nail, and coating an isolating agent on the bottom surface of the model. (5) cutting instead: sawing with a U-shaped saw with a thickness of 0.2 mm, and the sawing direction is parallel to the longitudinal direction of the prepared blank; (6) Generation separation: applying pressure to the end of the generation nail at the base of the model with tools to separate the generation nail together with the generation nail from the model.