Is there a reason why sun exposure is not recommended after visiting the dentist?

There is no reason you cannot have sun exposure after dental implant therapy. Sun exposure has no effect on the intraoral dental procedure.  However, it is normal to be prescribed a short course of antibiotics after the implant procedure and there are some antibiotics that can be associated with increased sensitivity to the sun.  That being said, the typical antibiotics that are prescribed with dental implant procedures are not associated with photosensitivity and you should have nothing to worry about.  Enjoy Mexico! 

Thank you for your question. It is recommended that you consult your treating Doctors for instructions.

The only reason I can think of is possible photosensitivity from antibiotics. Being in the sun for a long time right after a surgical procedure probably isn’t the best idea however.

I’m not aware of any reason that sun exposure would be detrimental following dental implant placement.
The only possibility that I can think of is if they will be prescribing medication that makes you photosensitive.
In that case, you would need to stay out of direct sun exposure.
I hope you found this information to be helpful,
Dr. Champagne

I've never heard that recommendation. If you have extensive surgery, the doctor will discuss your post operative instructions in detail. For most dental surgery, sun exposure is fine afterwards. 

That isn't typical as a dental post-op recommendation. Now depending on the procedure, if you're having extensive dental surgery, it may not be best to hang out in the sun afterwards since it could wear you down to a degree. That, however, isn't because you had a typical dental visit. On a different note, be careful where you get your implants internationally. I've seen some pretty unusual things done on patients which then needed to be addressed here. Sometimes cheaper isn't the best way to go.