Orthodontists receive an additional 2-3 years of education after dental school (during their residencies). They were also in the top 5-10% of their dental school classes. After that every patient that walks in the door is an orthodontic patient compared to the general dentist who sees a...
If your teeth are unusually small, it may not be aesthetically appealing to you to simply close the spaces. However, if they are narrow and all of your teeth are also smaller than typical, it may be perfectly acceptable for you to have the spaces closed.
If certain of your teeth are small...
Invisalign responded to cases JUST like this, and came out with Invisalign Express. If the case can be completed in 10 aligners or less (~5 months) the fee is less. Usually ~$2500 to $3000, but fees will vary from office to office, city to city.