Dr. Mew always says in light contact or near contact. Also chewing applies pressure on the lower teeth to follow the upper ones.

From the beginning, my lower intermolar width has been wider than my upper intermolar width, but with my lower molars lingually tipped, preventing a cross bite. I am trying to expand my upper arch to be wider than my lower arch and then upright my lower molars. However, I find that my intercanine width is now wider on my upper arch than my lower arch so that there is a gap between the distal slopes of my lower canines and the mesial slopes of my upper canines. I also have some crowding of my lower incisors. So I would like to get some expansion of my lower intercanine width. Here's an old thread about this topic ( /community/community/main-forum/how-to-encourage-the-mandibular-arch-to-keep-up-with-expansion-of-the-maxillary-arch/# ). We discussed the impact of chewing to maintain occlusion after the upper arch expands, and we also talked about the potential role for appliances in mandibular expansion. For now, I am using a myobrace to try evening everything out after gaining about 6mm of upper intermolar width with a removable palate expander.