This is directly from the HTM01-05 document
Dental handpieces
4.7 Practices can seek the advice on the
decontamination of handpieces from the handpiece
manufacturer. Dental handpieces are constructed
with a number of features that are difficult to clean
and steriliize. The use of a validated washerdisinfector
may be successful provided that the
handpiece and washer-disinfector are compatible.
Where this is established, sterilization using a type
B or type S sterilizer is likely to be useful, although
it should be accepted that it is unlikely that sterility
will be achieved – whatever sterilizer is used – due
to the presence of lubricating materials. The
information above should be used by practices to
make an informed decision on the choice of
sterilizer (Type B, S or N).
4.8 If no validated and compatible washer-disinfector is
available, steam sterilization will generate a
reduction in contamination. Accordingly, progress
towards best practice may be seen as a further risk
reduction measure in this context.
Also this link explains it nicely as well. Steam sterilisation is the preferred method, but vacuum is ok too.
www.isopharm.co.uk/dental/sterilisation
