The Restoration

The Restoration was, according to one account, the quality which allowed the Eighth Doctor to regenerate after he used the Moment to time lock the Last Great Time War and destroy the Time Lords and the Daleks, even though the Moment's nature should have made his existence fixed and prevented him from changing ever again.

On the last day of the Time War, a woman gave the Restoration to the Doctor with a kiss shortly before her death. As he regenerated, the Doctor reflected that he might one day pass the gift on to another. (PROSE: Doctor Who and the Time War) Indeed, the Ninth Doctor later saved Rose Tyler from the Bad Wolf entity with a similar kiss, triggering his regeneration into the Tenth Doctor. (TV: The Parting of the Ways)

By another account, it was the War Doctor who ended the Time War and regenerated into the Ninth Doctor, (TV: The Day of the Doctor) and the Doctor didn't receive a new regeneration cycle until the end of his eleventh incarnation. (TV: The Time of the Doctor)