There is nothing unlawful about post-dating a check and both the bank of deposit and the payor (your) bank are responsible for noting and acting on the information on the check including the date.
It may be unlawful for the dentist to present the post-dated check to the bank for payment, but there is nothing wrong with your writing it.
In some states there is a criminal offense only when the bad check is given in exchange for property or for a present consideration.
In other states it is a criminal offense to issue a bad check with intent to defraud or with knowledge of insufficient funds.
A bank may in some cases pay a post-dated check before the date on the check unless the customer notifies the bank not to pay it.The prescribed numbers of days for the various states are:- 5 Days In many states the criminal provisions regarding bad checks do not apply to post-dated checks.Because post-dated checks are a promise to pay in the future, they are not technically viewed as checks.I understand that having the check in the hand means money in the bank.It does give the convenience of having the check in hand on the rent day.