Yes, you can claim the dental expenses for your sons braces if you itemize and the expenses are more than 7.5% of your Adjusted Gross Income. Don't worry, just enter the dental expenses and TurboTax will figure it out for you!
To enter medical expenses see here - Where do I enter my medical expenses?
You can also read the following TurboTax faq for more information:
https://ttlc.intuit.com/replies/3301457
