Can oral appliances cause tightness in neck and shoulder muscles?

I have been using a SomnoDent oral device for the past 4 months. Very good fit and comfortable. I keep it in for about 6-7 hours every night. Works well, no snoring, breathing issues, etc., but when the setting gets over about 5 mm, I notice that my neck and shoulder muscles get tight and stay this way for many hours. My sleep dentist would like me to get to 7-8 mm, but each time I try to get the advancement around 4.5 to 5.0 mm., the tightness returns. My jaw pain is NIL. I DO NOT faithfully use the AM aligner with exercises, so maybe this would help here. The only problem is tight neck and shoulder muscles (Upper Trapezius and Sternocleidomastoid). I am doing exercises to strengthen them.
Maybe I can only increase the advancement 1 turn every other day or so. Or is the 4-5 mm. advancement setting adequate for me? I have mild to moderate OSA, with a score of 16. My sleep dentist has moved away, and getting a new one soon. ANY ADVICE and/or COMMENTS are welcome.

I am a dentist working in dental sleep medicine. Unfortunately, there is just no way to answer that question long distance and without examining you. Your original sleep dentist should and probably did record the maximal protrusion you were capable of before treatment. Without knowing that measurement you are flying blind.I will say that your body does have ways to alert you when you are overdoing the protrusion level. It may be that you are maxed out at 4-5mm. If you are asymptomatic, it may be that the 4-5 mm is sufficient for you. The only official way to know is to have either a home sleep test or a lab sleep test with the oral appliance in place. If your AHI is low or nil, you may be finished with adjustments. You absolutely need to use your AM aligner with exercises faithfully. As to the tight neck and shoulder muscles, strengthening exercises may not be your answer. That would actually tend to make them tighter. The more logical answer is that they need to be loosened up and stretched. Oftentimes a Licensed Massage Therapist or a Physical Therapist familiar with the head, neck, and TMJ area can be very helpful with that. They can often loosen up your muscles enough so that you can do more protrusion without muscular or tmj symptoms. Basically though, you need to wait for your new sleep dentist to discuss all of these things and let him or her supervise the titration of your appliance. I wouldn't suggest do-it- yourself for this. Better just stay at 4-5 mm until you have professional guidance again. Arthur B. Luisi, Jr., D.M.D.