New keratin and bone is growing under those white patches. The white is old, dead bone that was exposed when the keratin was chewed off. The new keratin won't look like the old keratin, and he'll always have a sort of bumpy look to him, not nice and smooth like his original keratin surface, but it will be healthy and protect him just as well. The new growth takes a very long time...over a year. You will eventually start seeing those white spots starting to lift as he grows under them, and they eventually pop off.
There is no special care required. It's old damage.