What Type of Retainer Should I Use After Closing my 5mm Diastema with Invisalign?

With a 5 mm diastema there is a strong relapse potential; even if you wear a clear Invisalign type retainer there will be a tendency for the space to open up if you wear the retainer less than full time.  To prevent this, a small metal bar bonded on the tongue side of the two front teeth is the preferred retainer ... in addition to the clear plastic one worn at night.  One potential problem with this type of retianer is if the lower teeth contact the back side of the upper front teeth in a "deep bite" or "overbite" type of way there may not be any room for the bonded retainer.  Hopefully Invisalign has successfully reduced the overbite so this is not an issue.

I prefer to use the retainers supplied by Invisalign called Vivera Retainers.  They send you four new sets over the course of a year which should be plenty.  Of course, how well they work depends on whether you are diligent in wearing them.  Another option would be to bond a wire on the back of the teeth but you need to make sure there is room to do so when you bite together.  A wire is harder to keep clean but it is there all the time so you don't need to always remember to wear your retainer.