Complex sentence: As irreversible pulpitis generates an apical abscess, the character of the toothache may simply change without any pain free period, i.e. the pain becomes well localized, and biting on the tooth becomes painful.
Split into simpler sentences: As irreversible pulpitis generates an apical abscess, the character of the toothache may simply change without any pain-free period. For instance, the pain becomes well localized, and biting on the tooth becomes painful.