Will Filing Teeth for Invisalign Affect Teeth Strength?

Sometimes, after Invisalign, I will do some contouring of the teeth to idealize aesthetics. This contouring should be very slight. Oftentimes, I will use a Sharpie pen to black out the tiny bit (edge) that I plan to remove. When you look in the mirror you can't see the line, but you can see what the finished result will look like.

We all do that to finish a case up and make it look better. When the teeth were crooked, they wore differently, so now that they are straight, they need to be evened up. They will also bite better this way and are not harmed by the polishing.

What you are referring to is Inter proximal reduction (IPR). This is done routinely for orthodontic readons to align your teeth for long term stability. A very small amount (less than .3 mm) of enamel is filed. It doesn't render your teeth weak or predispose your teeth to any caries etc. I usually give flouride treatment after that.