Professor Undt, based in Vienna, is a specialist for oral and maxillofacial surgery as well as for dental and oral medicine. Since 1992 he has specialised in the field of dysfunctions of the temporomandibular joint, or the TMJ. During his time at the Viennese University Dental Clinic he developed a particular interest in splint therapy and electronic recording of TMJ function. During his surgical training he covered the entire range of open and endoscopic maxillofacial surgery. He specialised very early on in the surgical treatment of functional TMJ diseases and of fractures to the condylar process of the mandible. Professor Undt has been performing arthroscopic TMJ surgery since 1994, gaining rich and varied experience in the wide range of arthroscopic microsurgical techniques, with instruction from international specialists.

Nowadays Professor Undt himself is among the world's leading specialists in the field of arthroscopic and reconstructive TMJ surgery. Not only does he perform surgery in Vienna, but also in university clinics all over the world as a guest professor. His numerous live-operations that are transmitted to international congresses and symposia have helped to familiarise a large group of specialists with minimally invasive surgical techniques for TMJ surgery. Since 2003 Professor Undt has held a TMJ surgery course in Vienna - this is now the most popular course in this specialist field worldwide, and has to date attracted over 400 participants from 50 nations from  all corners of the globe.

Since 2003 Professor Undt has also focused on the endoscopic treatment of salivary gland diseases. Diagnostic and interventional sialendoscopy allows salivary gland stones to be removed with minimally invasive microsurgery, rather than having to remove all or part of the salivary gland. More and more patients are coming to Vienna to undergo this specialist surgery.