How to approach this niche?
You could focus on the actual teeth whitening as a service or on teeth whitening products.
Although the generic terms around teeth whitening have a lot of competition, there is huge potential around its longtail:
1. The localized approach
It is shown before in this article, but it’s such a good method for lead generation or rank and rent. See the screenshot below for the (growing) search volume of teeth whitening near me and a competition of 0. True that it is kind of logical, given its local intent, but let us guide you through it.