This is a combination beauty and health tip, but recently I've been experiencing some gum pain, and my (much older) doctor told me that one of her greatest regrets is that for over 40 years she used a very hard-bristle toothbrush and essentially put undue pressure on her gums every time she brushed her teeth. This later led to receding gum lines. Scary stuff, and just goes to show that you shouldn't ever blindly listen to dentists' recommendations! Her recommendation is to go with soft bristle brushes, and to use the sensitive setting on electric toothbrushes to avoid destroying the gums.
I wanted to expand that a little further by touching upon my own experience with a deep-cleaning, which was both unnecessary and in retrospect far more damaging than beneficial. My dentist scared me with the idea of things growing under my gum line, so I proceeded to go forth with a deep cleaning. That certainly led to receding gum lines, especially in my rightmost front tooth. The gum line, especially behind the tooth, is noticeably deeper now, and occasionally causes discomfort.
Please note that as a disclosure I am not a dental expert, and I'm sure some people have benefited from deep-cleaning procedures. But if I could go back, I wish someone would have shared this with me and let me understand the full risks, especially as I'm young and honestly it's done more harm than good.