“…Severe bone loss, deep PDs, furcation involvement, tooth mobility, unfavourable crown–root ratio, root proximity or presence of abscess have been used to categorize teeth as hopeless (Becker, Becker, et al, ; McGuire & Nunn, ). Despite extraction being proposed as the treatment of choice, 77% of non‐extracted hopeless teeth were retained after a mean period of 5.25 years (Becker, Becker, et al, ) without loss of attachment of the adjacent sites (Machtei & Hirsch, ), and lower probability of tooth loss was reported for greater intrabony components (Muzzi et al, ). Regeneration, especially when combined with advancements in flap design, represented a landmark improvement towards preservation of natural dentition.…”