thanks for the question. Firstly, there are several reasons for the teeth to appear squarish, which prompt people to seek treatment in order to have a set of teeth with nicer dimensions.
With the right diagnosis, dentists will be in a better position to advise the chances of relapse.
They key term to predict whether the gum will relapse after gum contouring treatment is "Biological Width". The gum needs to be about 3mm away from the bone underneath.
A good way to predict whether the gum will relapse is through a technique called "bone sounding".
X-rays may be helpful to check where the bone level is, and if needed, bone can be removed to ensure the gum has less chance to grow back.
Based on my experiences with laser for gum contouring treatment of altered passive erupted teeth, the gum may bounce back slightly after the 1st treatment due to the amount of gum we may need to contour away for a nicer dimensioned teeth on the 1st visit. In these cases, I will do a touch up about 2 weeks later where I contour a lesser amount of gum tissue. So far, the results have been stable.
Hope that helps, and have a great journey to a nicer smile!
