Figure 2. A and B, Design of the simple tubes and customized resin coverings on the setup model. C, Customized resin coverings were transferred onto the pretreatment models. D, Gingival simple tubes were placed on the printed model into the recesses receiving them, and transfer trays were fabricated by thermoforming. E, Occlusal simple tubes were placed into the recesses, thereby fixing the mesiodistal ends of the tubes in the transfer tray. F, Flowable resin was injected into the central recesses for customized resin coverings, which fixed the central part of the occlusal simple tubes.