Multirooted teeth with FI present some of the biggest challenges in periodontal therapy despite a large arsenal of therapeutic techniques. Guided tissue regeneration has improved the long-term prognosis of many deep grade II lesions but has not always shown consistent predictability. With improved barrier techniques and the development of effective growth factors, however, guided tissue regeneration may well become the treatment of choice for all grade II and III FI. Until that time, early diagnosis and treatment are critical to long-term success. Even strategically important teeth with more advanced FI often have a much better long-term prognosis than previously believed and can survive for many years, even with closed scaling and root planning and frequent, long-term maintenance. Before condemning molars with severe FI, clinicians should consider their experience in treating advanced periodontal diseases and seek consultation with a specialist when in doubt as to the prognosis and treatment of teeth with significant FI.