Teeth with Short Roots and Braces?

My 9 year old son's front teeth has short roots. The teeth are protruding and he's overbite so he needs braces. We saw 2 orthodontists with different approaches. What is correct - long treatment and light forces or short treatment with more force? The cause of short roots seems to be genetics, no trauma but thumb sucking til 3 years old. He also grinds his teeth at night. What should I do to prepare him for orthodontic treatments. I can provide copy of x-ray if needed. Thank you