I cannot remember what study to quote, so I will just explain the mechanics and my opinion. The pulp that is exposed has an outward flow. the blood vessels in the pulp exert a positive pressure and so the pulp fluid will flow outward and tend to "wash out" bacteria. A pulp polyp is an example of a chronically exposed pulp that has remained vital. What is sounds like you are explaining is a NON-Carious, traumatic exposure. In this case there was no previous pulpal inflammation (the pulp was absolutely healthy prior to the trauma). This pulp has the ability to heal itself. Therefore, the pulp can remain vital for "who knows how long." This is different in a Carious tooth that has been constantly battered with microbial toxins and then after cutting into it with a bur at high speed has a small exposure (the ability of this pulp to heal itself is much less than the aforementioned). If a patient came into my office with a fractured tooth with a pulp exposure that occured two weeks ago. I would begin a Cvek pulpotomy and if the pulp bled when I removed the inflamed tissue then I would finish the Cvek pulpotomy and chances are it would be just fine. If it did fail you would go ahead and do endo. like you had planned. You lose nothing with trying the Cvek.