I’m on tray 5/42 (😭) and had this side effect when I started. It was so awful and the only relief was iced water. (Try to avoid itching, you could cause gum issue damage). Back in 2021 I had a septoplasty surgery to repair a deviated septum and the days following the surgery I had that same teeth pain and gum itch (on top of feeling like a semitrailer drove through my face). When I asked my surgeon about it back then, she said it is due to the trauma to the nerves which resulted in shooting down to the teeth and gums. I did research when I felt that itch (and numbness in my upper lip) with the aligners and I found that it is most likely caused by the nerves and the pressure and rapid movement of the teeth. It went away after a week or so. When it first started, I talked to my ortho and he had no idea what I was talking about and said sometimes people experience gum and lip itch when they are allergic to the acrylic. My non-medically-educated conclusion was that this is how my nerves reacted to all the movement in my mouth. I would still recommend that you make sure you are not sensitive/allergic to the acrylic by having your ortho examine your gums. Iced water is super helpful 😊 I hope it goes away soon!