As a visiting researcher or clinician you have two possibilities:
- Attending/ watching clinical and laboratory procedures
- Participating in clinical or laboratory research (without working on patients)
Your professional and academic requirements are a finished academic education in dentistry and/or a field of natural science or technology (e.g.: physics; chemistry; biology; medical technology; etc.)
You length of stay can be several months to several years.
You may need an tourist visa / passport according to the official/federal regulations.
Furthermore you should cross-check the general requirements listed here.