These one-off explanations were especially weird. Like--Superman hides his clothes in a hollow tooth? When did he get a hollow tooth? Then there was some idiotic explanation of why everybody thinks Clark looks different--Hypnotism? Early on Superman could mould his face to change his appearance.
If it helps, this page nor the rest of the comic actually mentions a hollow tooth. Maybe the compressed costume was placed "between his cheek and gum"...
And to be more pendantic, this scene in Superman 296 was the second time Clark hid his costume in his mouth. The first time was in Superman 294.