This is a set of 3 mouthpieces, as one was used. They will be shipped in a box of 2 cases. Contents: - 3 Mouthpieces - Instruction Manual The following is quoted from the product website: 【Materials】 Main Body: EVA resin, Case: PP resin 【Size】 Free size (can be customized by cutting with scissors) ■ Recommended for: Those concerned about teeth grinding, clenching, temporomandibular joint disorders, or snoring. It reduces the burden on teeth and jaws, and also alleviates shoulder stiffness and headaches caused by teeth grinding. It protects the jaw joint muscles and can be used as a mouthpiece to prevent temporomandibular joint disorders. ■ You can easily create your own custom mouthpiece Simply soak it in hot water and bite down to easily mold it to the shape of your upper teeth and gums. Mouthpieces that are molded to your teeth fit perfectly, providing a comfortable fit. ■ How to use 1. Place the mouthpiece in approximately 80°C (176°F) hot water for about 60 seconds. 2. Take out the mouthpiece and let it cool slightly, then, looking in a mirror, align the center indentation of the mouthpiece with the center of your teeth and place it over your upper teeth. 3. Bite down firmly and press it against your teeth and gums to set it. ※ If you don't get a good mold, you can redo it. Repeat steps 1-3. 【Molding Required】 It molds to your own teeth shape, providing an excellent fit with zero discomfort. To make it, simply put it in hot water to soften it and mold it to your teeth. You can remake and fine-tune it, so it won't come out.