If you or your partner notice that you grind your teeth while sleeping, it's important to know that this is a dangerous habit that needs to be remedied, otherwise there are two main consequences.
When you grind you are wearing away precious enamel from your teeth, which is your best line of defence against decay, and also is what gives teeth their beautiful full shape, whereas your teeth may start looking 'stumpy', short, non-proportional and a little ugly.
You could be causing chronic damage to your tempro-mandibular joint (TMJ) which is the joint that connects the lower jaw to the base of the skull. In the TMJ there is a delicate piece of cartilage that when exposed to repeated and high forces, such as when you grind your teeth at night, will start to change shape initially, and then eventually be worn right away. In the early stages this can present as just an annoying 'crackling' noice whenever you talk or eat, or you can notice your jaw 'clicking'. In the latter stages, especially when most of your cartilage is worn away you will experience extreme pain as bone rubs on bone everytime you chew or talk.
A night bite splint helps prevent both these processes, and is very easy to make. You sleep with it every night, either until the habit disappears, or some people just pop it in and go to sleep every night and they don't have anymore problems.
An example of a bite splint worn while you sleep