I have a 3-4 mm gap for the extraction spaces for which the braces can't close. What are my options?

Based on your description of events, it doesn't sound like bonding would be the best option for you.  It would be the cheapest option, but not the best.  This is because the large space would require significant bonding that would be very likely to break off in just a few months following the procedure.  Cosmetic bonding to close spaces on the sides of teeth are not very durable for use on molars and premolar teeth.  I would highly suggest getting crowns for those two spaces (one on each side).  This fix will cost you about $2,500 total (depending on the region of the country you're in and which dentist does the work.  However, you have something that will last you 20 or 30 years if the crown is placed properly.  There are several financing options and payment schedule options that many dentist offer, so don't let money prevent you from getting the treatment that's best for your case.I hope this helps.  Follow me if you have more questions for me.Sarah Thompson, DMD

Three to four millimeters is a huge gap and would be difficult to close with direct bonding, although it can be done.  The problem being is that it is very difficult to close a premolar gap of that size with direct composite bonding making those teeth normal in proportion to your other teeth.  Also, since that is a side area where you generally bite and chew hard, it is more likely to fail by breaking off.  Two choices that would be stronger, look better and last much longer would be either full porcelain crowns or partial veneer-onlay combinations, that latter would be the one I would recommend as the best alternative.A bicuspid is generally 7mm in width, so you only got half of the space of the extracted tooth filled with your braces.  If it were larger a bridge, or cantilever bridge would be another option, however with the smaller space it is my opinion that neither of those restorative/cosmetic alternatives would be viable in your situation.

The reason you have excess space after extracting premolars is because the amount of space you needed to straighten your teeth was much less than what was created by extracting four teeth. I would strongly suggest that you not continue to try to close the gaps because your teeth will be even more overly retracted which will adversely affect your lip support and facial aesthetics. Depending on your age, you may get some natural closure over time as you have constant forward thrust from your second molar teeth that could possibly close some of the space. Hopefully the gaps are consolidated on the backside of your canine teeth where the spaces are less noticeable.Putting crowns on healthy teeth to close gaps created by extracting teeth is a bad idea. I would recommend cosmetic bonding to close the gaps if you don't want to wait to see if they will close naturally over time.Good luck!