Teeth whitening process, a process that is quite successful, especially within  the yellow coloring.

But in a color close to purple  or gray tooth whitening is more difficult then in  yellow teeth,

Gray coloring may occur as a result of root canal therapy, and in fact as this process will be applied to 1-2 teeth it is quite easy to apply. But in the teeth, if you have a greyness or bruise, it becomes more difficult based on the treatment process  and operation lasts longer.