Technical Note: A Newly Designed Intraoral Device with Enclosed Spring for Controlled Mouth Opening in TMJ Hypermobility

Background: Temporomandibular joint (TMJ) hypermobility is a functional disorder characterized by excessive anterior translation of the mandibular condyle, often resulting in recurrent subluxation or dislocation. Traditional post-treatment immobilization meth- ods—such as intermaxillary fixation or external bandages—restrict mandibular movement but often compromise speech, nutrition, hygiene, and patient comfort. There is a grow- ing need for noninvasive, function-preserving intraoral solutions. Objective: This study introduces a structurally refined intraoral appliance that restricts mouth opening within a therapeutic range (33.5–41.5 mm) while preserving full mandibular function. The device incorporates a telescopic rod system enclosing a nickel-titanium spring, offering dynamic restrictions concerning anatomical integration and patient comfort. Materials and Methods: The prototype consists of custom 3D-printed bands cemented to the maxillary and mandibular premolars and molars. These anchor a telescopic rod with an internally en- closed spring system that generates reverse force during excessive opening. The system was tested in vitro on 3D-printed dental models simulating normal occlusion, evaluating verti- cal restriction, lateral and protrusive-retrusive mobility, and device stability. This design builds upon a previously patented prototype (TR 2023 005375 B), for which an international application has also been submitted to the European Patent Office (EPO Application No: EP23841576.4). The current structurally enhanced version is under a new national patent application (No: 2024/014422). Results: A functional simulation confirmed that the device restricts vertical mandibular opening without compromising lateral, protrusive, or retru- sive movement. The spring resistance began at 30 mm and gradually increased until the structural stop range was reached (33.5–41.5 mm). The appliance remained stable during testing, with no deformation, misalignment, or occlusal interference. Its enclosed design reduced soft tissue contact, improved hygiene, and enhanced long-term tolerability. Conclusion: This intraoral device offers a mechanically effective, removable, hygienic alternative to conventional immobilization methods in the conservative management of TMJ hypermo- bility. Its dynamic spring-loaded restrictions, compact intraoral profile, and preservation of functional mandibular movements position it as a promising adjunct following conservative or surgical treatment. Further in vivo studies and finite element analysis (FEA) will as- sess these materials’ biomechanical performance, internal stress distribution, and long-term structural integrity. Trial registration: Not applicable – This study involved no human participants and did not require trial registration.