I’ve talked to alot of my reptile owner friends and they all say It’s mbd. I’ve been feeding her calciulm but I just recently realised It’s without D3. I’m buying her new calcium today.Have you been providing calcium and vitamin D3 to your gecko? I don't really know for sure, but based on the picture of the whole gecko, it's possible that the mouth is open because the gecko has weak bones due to MBD (metabolic bone disease). I highly recommend a reptile vet visit.