Clenching and grinding is a habit - a bad one - and like any habit, it can be broken and replaced with a good one. It is a matter of getting the right message to the subconscious mind.
During the day, you can consciously get the right message to you subconscious mind by repeating "Lips together, teeth apart...from this position do not depart".
At night, you can unconsciously get the right message to you subconscious mind by listening to this audio file.
It takes 21 days to break a bad habit and replace it with a good one.
Bitesplints are definitely helpful and sometimes still needed, and protect against the bad effects of clenching/grinding, however it does not address the cause which has a subconscious mind/cebtral nervous system basis. These exercises address that.