tooth-ache
齭 centers on toothache: pain localized in a tooth. The given meaning is specific and does not extend to broader dental conditions.
齭 combines 齒 (tooth) with 所, which likely contributes the sound. The character is a phono-semantic compound specifically for toothache.
The left side 齒 is a tooth, and the right side 所 looks like a place. Imagine a tooth that has become a place of pain: a toothache.
For ショ, picture a sore tooth that makes you say 'show' when you point to it: show -> ショ, and the toothache is on display.