Four upper front teeth are missing. Would it possible to have four distinct implants?

When you treatment plan the number of implants to fill a certain space you must always keep in mind that each implant needs to be 3 mm away from any other implant and at least 1-1.5mm away from any tooth.
Therefore if you have 4 implants (2 with 3mm diameter and 2 with 4 mm diameter) and the appropriate spacing between these implants your total space will exactly be 27mm therefore it is possible. 
However, study's will show that when you have two implants next to each other it is more difficult to mainatain the papilla or pink triangle that is in between the teeth. Often times a "black triangle" or space appears between these teeth and the results are not ideal.
As a result, a situation where a patient is missing their front four teeth is often treatment planned to have 2 implants and a bridge not just for reduction in costs but to increase in "pink esthetics"
This does not mean that 4 implants cannot be placed (as there is room although it is very tight). I would recommend seeing an implant specialist who understands both the restorative and surgical aspects to get the best results.
Try searching AAID and ABOI for best results.

Hi:It is very likely that you can have four possibly narrow implants in the space you have described.  I would like to see a photo of the missing teeth to give you more accurate advice.Best,Dr. Maddahi