Besides muscle strain, what secondary effect stems from the friction of the standard regulator mouthpiece on oral tissues?

Irritation, inflammation, or shallow sores on the gums, cheeks, and palate.

The mechanical interaction between the diver and the regulator involves more than just jaw mechanics; the mouthpiece itself is a source of localized trauma. Constant contact, friction, and pressure exerted by the standard hard rubber or silicone mouthpiece against the delicate tissues inside the mouth contribute significantly to soft tissue symptoms of DMS. This ongoing mechanical stress can cause irritation and inflammation where the material contacts the gums, the inside linings of the cheeks, and the roof of the mouth (palate). Over time, especially for new divers or those wearing ill-fitting gear, this friction can lead to the formation of shallow sores, adding to the overall discomfort associated with DMS.