My child has no problems with eating or drinking, but grinds his teeth until I want to grind mine! His dentist says it's common in kids with Down syndrome. I saw your teeth grinding items and wondered if they might help? He is 5 years old, does not speak much – he imitates sounds, growls and whale noises from his favorite movies, but has no interest in forming words. He is in speech therapy through school.
Teeth grinding is generally used to help children with special needs to organize their bodies or to calm down; they are seeking stimulation to the temporomandibular joint (TMJ). This joint is where the upper jaw and lower jaw meet right below the ears. Babies suckle their thumbs or suckle on a pacifier to get the same needed stimulation. As your dentist noted, teeth grinding is common in children with the diagnosis of Down syndrome, but there are reasons and a treatment protocol. Because your son is not talking, I suspect he has weakness in the masseter muscles (muscles of the jaw) as related to his diagnosis, he too may need that additional stimulation to the TMJ.
This is such a huge issue that I have written a book on the subject called, Assessment and Treatment of the Jaw.
There is a whole chapter on why kids grind their teeth or have other habits that provide direct stimulation to the TMJ. I encourage you to read the book before you invest in any therapy tools, as it will help you identify what tools and activities would most benefit your son.
In addition, if there is a gap between what your son understands and what he can say, then his jaw weakness may be a primary factor in keeping him from using oral language. You may want to look into having him evaluated by an SLP in your area who is familiar with Oral Placement Therapy. Many SLPs have taken our introduction classes and would be able to work with your son if there are muscle-based deficits related to his difficulty in learning to talk.