Yes you can definitely continue the treatment here in US. The cost of braces tightening here is $100 to $200 depending upon the qualification of a dentist (whether  a general dentist or a specialized dentist) and the cost of living of the city. Make sure that both the dentists i.e. in India and In US are communicating with each other regarding the treatment. Alsp when you will be coming here in US, get all the treatment related documents with you. For more info on braces treatment visit the link....http://www.identalhub.com/article_average-cost-of-braces-for-teeth-431.aspx