Mercury vapor release from amalgam fillings
All solids have a certain vapor pressure, and if this vapor pressure exceeds the atmospheric pressure, then evaporation of the solid occurs. Some of the solid turns into gas. More specifically, it's the uppermost layer of the solid that evaporates. 


  What would cause vapour release from elemental mercury? Would it be
  pressure, friction...


Friction could definitely increase the kinetic energy of the mercury particles and increase the solid's vapor pressure. An increase in pressure could also increase the temperature and therefore kinetic energy of the solid's constituent mercury atoms. 


  could one stop the vapour release through cooling the mercury?


Yes, that would decrease the kinetic energy of the particles and lower the solid's vapor pressure. Here's a chart relating temperature (in Kelvins) to vapor pressure. At physiological temperatures, we're still talking about an extremely low vapor pressure. 



http://www.physics.rutgers.edu/~eandrei/389/NISTIR.6643.pdf