In a journal which has been out of print for several (10?) years, there was an
article which showed that if a contaminated instrument tip was left in place
on a three-way air/water syringe after use, and left undisturbed for 48 hours,
the handpiece itself would be contaminated. The article was in a journal
called Clinical Prevention, published by Williams and Wilkinson, in the late
1970s (1976?).

        If someone could point me in the right direction (via the Internet,
preferably) to acquire this article, I would be indebted to you. You can reach