Removed braces, does swollen gum cause gap in between the teeth?

I have recently removed my braces, and i noticed there's a tiny gap in between my front teeth. My dentist advised that it is due to my swollen gum, and it will get better when my gum is back to normal, and by then depends on the condition might need to redo retainer to fix it. Is it true that swollen gum might caused the gap? Or i shld insist my dentist to fix it now. Thanks.

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