My son is 5 ys.during sleeping i hear sound from his teeth .like a spasm.he also developed stone in the duct of lt submandibular gland?

Sounds like bruxism: It's common for young children to have bruxism or "teeth grinding" during sleep. Sometimes this goes away on its own. Sometimes it is associated with a dental abnormality or other problem. It might be helpful to have his dentist perform an examination. His pediatrician might be able to offer more specific advice on evaluation or treatment with an exam as well. Good luck!

Teeth grinding: Teeth grinding at night is common. It is nothing to worry about and does not need to be treated. The baby teeth may wear down, but adult teeth are much stronger and much less likely to wear down. The submandibular stone is not common in a 5 year old. You should go see your ENT doctor about this.