Could having a too-small mouth cause any respiratory issues?

Likely not, but...: It may be a problem if you need surgery under general anesthesia. Patients with small mouths or the inability to open their mouth well may be present difficulty if a breathing tube must be inserted. This problem can be detected on a pre-surgical evaluation. Some patients have a small jaw which could lead to upper airway obstruction since the tongue is more likely to fall back into the airway.