Dental Asia Mar/Apr 2020

By Guido Testa Behind the Scenes 58 DENTAL ASIA MARCH / APRIL 2020 S andblasting As an apprentice dental technician in northern Italy in 1979, Guido Testa was trained in traditional methods such as casting of metal crowns using the lost-wax technique. With the advent of technology, he started to implement new tools into his workflow, such as the 3D microscope from Renfert, which allows him to see even the smallest details inside a crown. Testa came up with the idea of using the sandblasting device as a method of material removal after he heard German dental technician Oliver Brix’s technique of carving the occlusal surface of CAD/CAM manufactured lithium disilicate units via sandblasting. “My therory is based on experience. Lithium disilicate is mainly used for restorations on anterior teeth. Their anatomical shape means the preparation usually has a narrow incisal area,” said Testa. “In many cases, the CAD/CAM milling or grinding tools in the milling devices cannot reach these areas well. If you allow the cutter or diamond bur to mill all the way to the end of the preparation, depending on the diameter of the bur, too much material could be removed.” If more material than neccessary is removed and the wall thickness is maintained, it reduces the space available for aesthetic individualisation and characterisation. Another option is to mill the material in the machine with small instruments, but this process takes much longer. To ensure the restoration fits perfectly on the die, it is possible to grind the inner surface of the crown manually with a diamond bur and handpiece. An innovative way would be using a sandblasting device. Preparing the crown Before fitting the crown in place, the outer surface of the die is coated with a surface marker (Fig. 1). Any interfering contacts can then be seen on the inner surfaces of the crown (Fig. 2). The crown is then checked using the video microscope EASY view 3D from Renfert with an enlargement factor of 15 or 20, in both 2D and 3D to view the starting situation. Next, the individual areas are sandblasted with a fine sandblasting device. A prerequisite for this method is that the sandblasting device is equipped with an immediate stop function, because maximum precision is needed in this material removal method. The nozzle should have a diameter of 0.4 mm, while the blasting sand used should be Cobra 25 mμ at 1.0 Bar. an al ternat i ve to cutters or burs