My husband (non custodial parent) and I am paying for his son's braces. The cost is roughly $2500. We don't have a choice since the mother (custodial parent) does not want to pay for braces. It's for the well being of the kid. Of course it's a chunk of money that we could use elsewhere. But we don't have a choice since the "mother" refuses to pay. I think by law you could split the cost 50/50 but what can you do if the other parent doesn't want to pay. After all.. It's your kid. Your responsibility.
The non-custodial parent must pay child support to the parent that does have custody. That parent must pay for the braces from the child support payment..that is why it is called child support. However, and this is a big however, it appears that all the money is being used elsewhere and that your child is in need of braces. Please keep in mind that it is not the child's fault that the custodial parent can not (or will not) pay to have the child's teeth fixed. If you can afford this, please give some consideration to helping your child with this problem. Straight teeth and a good bite are not just a cosmetic thing. Over all health can (and is) involved and nice teeth are even a boost when that child reaches the age of searching for a job. So, if you can find it in your heart to do this, it would be a very nice thing for you to do. But, no, I do not believe you are obligated unless it was stipulated in the divorce decree that you are responsible for all medical. Even then, it would be questionable if teeth straightening would be considered medical. You may need to consult with an attorney if your EX pushes this issue and you can not (or will not) do this for your child.