It could be because the expansion is causing your teeth to shift, expansion gives more room for the teeth and they start shifting in place, or maybe the appliance is pushing on the front teeth?

@sinned Not using portion of appliance that pushes forward, only laterally.

@mewem143 do you have a photo of the expander (ideally mounted on your dental cast)

@limebike yeah check one of my previous posts 

@mewem143 This one, right?

 Well, from what it seems is that your incisors are very much shovel-shaped, i.e., they have a lot of "sideways undercut / sidecut :-)". Incidentally, the acrylic there is not trimmed off and goes right into the indentations of your incisor backs. As you expand, it is actively pulling the incisors apart. If you do not want that, you need to trim off the protruding bits of the acrylic that go into the indentations, but leave enough so your incisors do not retrude.

BTW, what is your intermolar width (measured between the insides of the first molars)?

@limebike low 40s I believe, and I already shaved off all the parts that hit my oncisors since my only goal is lateral expansion 

@mewem143 Despite the right canine which looks slightly rotated to the distal, it seems that you have a pretty well-developed arch already.

@limebike yea but not enough tong space, had braces :(

@mewem143 Interesting. Is your tongue more on the wider side? Mine is.

In this case, one would need a more wider, circular arch that sits more forward in the face.

@limebike yeah, any tips on achieving that? My plans just to expand and see how far I can go w my tongue.

@mewem143 If you expand, you will get gaps. You should close them by pushing all the teeth mesially to the front.

What is your plan for the fine adjustment after the expansion?

@limebike hmph, was pretty sure that the gaps closed themselves, going from previous posts on the forum reasoning that gums are elastic so the gaps would automatically close.

@mewem143 You originally had a bit of a pointy front of the arch. Maybe the gaps formed during your expansion so far resolved themselves by producing a more rounded out arch? How much are you planning on expanding?

@limebike don’t have a pre set goal but just to the point where I can fully fit my tongue. And no gaps have formed yet, just slight pain in my molars, incisors, and palate so far, also have expanded a few mm already since the day I got it (guess I was able to expand a bit w my tongue before it arrived).

@limebike Why would the incisors retrude without the acrylic on them? As far as lateral expansion with an expander I don't think this would influence the anterior teeth. Maybe if he were to undergo expansion via braces or invisalign they would retrude, since the teeth would all be moving in relation to one another.

@cliffbars It depends on the patient's tendency. If you have a tendency for your incisors to retrocline, having no acrylic support in the back (and also no other support, e.g., tongue), and having the lips exert pressure on the incisors, it may result in slight retrusion of the incisors until the incisors touch the acrylic.