A night guard is a retainer-like plastic piece that can be hard or soft. It covers the biting surfaces and can be worn on either the bottom or top set of teeth. Since patients have different teeth patterns, a night guard is custom-made for each patient by molding it to fit your teeth without the risk of being uncomfortable or unnecessarily bulky. It has many names; therefore, when you hear dentists talk about a mouthguard, occlusal guard, gum shields, bite splint, dental guard, or nocturnal bite plate, they refer to the same thing.

Typically, a soft or a hybrid night guard is recommended for wearing over your crown. This helps protect the crown while avoiding the chance of loosening or pulling out your crown. The hard night guard, which is made from a more rigid material, may exert more force on your crown (especially when taking the night guard off), causing the crown to loosen.
If you’re wearing a night guard over the opposing teeth to your crown (e.g. you have a crown on a lower tooth and you’re wearing a night guard over your upper teeth), then you should be fine to get either a soft, hybrid, or a hard night guard. Be sure to check with your dentist for a recommendation for your specific situation.
How to Get a Night Guard for Crowns
You absolutely should wear a night guard if you have crowns. When you protect your crowns with a night guard every night, you reduce the chance you’ll need to get them replaced due to damage.
Importance of Getting the Right Night Guard
Prevent Plaque Development
Despite the similarity in names, you should not confuse a sports mouth guard with the one designed for preventing teeth grinding and clenching. A sports mouth guard will do more harm than good. It covers the teeth and gums as it is meant to protect them from blunt force trauma. If worn at night, it traps bacteria on the gum’s surface while you sleep since saliva can’t get to the gums while wearing a sports mouth guard.
Saliva helps to neutralize acids that can cause cavities and washes away food particles hence preventing plaque development. Therefore, it is best to consult an oral hygiene professional when looking for a night guard to avoid damaging your teeth. It is important to note that some night guards come with holes to allow saliva to access your teeth. Thus, a dentist will provide you with the right design depending on the condition of your teeth.
What can i use as a temporary mouth guard?
Your custom night guard should feel snug. When you first put it on, the night guard may feel tight, but it needs to fit securely to stay on your teeth without being held in place with assistance from your jaw. The snug fit will keep the custom night guard in place so that it does not fall out during the night. If your custom mouth guard does not fit your teeth or if it falls off, then it has not been fitted correctly or has been damaged and you need to visit your dentist to have it repaired.
Source: Colgate.com