While not suffering from periodontitis, I certainly get mouth ulcers within a week of packing in smoking tobacco- without fail.
I have been led to believe that this is due to the lack of the antibacterial nature of tobacco smoke, and the increased quantity of bacteria in the mouth therefore leading to ulceration.
I may be wrong but periodontitis is also caused by bacteria? So perhaps a high strength antibac mouthwash like Corsodyl will do the trick.
Hope it gets better,
SJ