Digital design and fabrication of direct-printed twin block appliances

Abstract

This paper presents a fully digital protocol for the design and in-house manufacturing of Twin Block and Reverse Twin Block appliances. The protocol is carried out using an open-source CAD program (FreeCAD) and Medit Link (Medit Apps). The digital workflow includes intraoral scanning, appliance and bite block design, 3D printing, and post-processing. Intraoral scanning and digital construction bite recording are conducted with the Medit i700 scanner. The designs of the direct-printed Twin Block and Reverse Twin Block are based on splints and are created with Medit Apps. The bite blocks are designed using FreeCAD. The appliance design starts with the creation of splint baseplates and cutouts to provide space for the blocks. The splint baseplate is united with the bite blocks, and the inner surface is prepared for an accurate fit. The 3D printing is carried out on the Formlabs Form 3B+ using LT Clear V2 resin. The post-processing step includes washing, curing, finishing, and polishing. The digital design allows for the optimization of retention, efficient use of undercuts, accurate reproduction of the mandibular advancement, and an integral fit between the bite blocks. This is an easily reproducible chairside workflow that is cost-effective, saves clinical time, reduces waste, and offers fast production and same-day replacement.