Think it's time to make a petition to the govt to tell banks to allow this, helps bring in more economy to the country and banks and makes it simple for dtv holders a win win situation, otherwise till then use alternate sources like wise
Anonymous participant sure the dentist usually won't be sure of what documents needed but you can try, also if your feeling a bit paranoid and traveling long distance would recommend maybe getting an established agency to do the paperwork for you, they mite charge a bit but will help you a great deal
Best to give as much evidence as possible, so if you can visit a dentist in your home country, get an exray -Quote for all the work to be done, connect with a Thai dentist exchange emails with them get a quote from them arrange for appointment times book a stay for long close to dentist, if you have some idea how you'll spend your free time show that, show bank statement that you have enough money for treatment and to live, possibly add a cover letter why your looking to get treatment in Thailand