Streptococci used to be commonly isolated from Dental Unit Water Lines (DUWLs). Streptococci may be non-pathogenic and form part of the normal commensal flora. Streps are also required to produce Emmental (Swiss) cheese.

However other species (often the alpha-haemolytic) may be pathogenic and have been linked to meningitis, septicaemia, necrotising fasciitis,  pneumonia, endocarditis, erysipelas and pharyngitis.

Potential Issues with Dental Units

High Speed Drill

Since the adoption of anti-retraction valves by most manufacturers of dental handpieces in 1996, Steptococcal contamination of Dental Unit Water Lines (DUWLs) has become far less common. Prior to this when the high-speed dental drill was disengaged, some oral fluids were sucked back into the handpiece. This could be as much as 1ml of oral fluid, equivalent to 25,000 oral bacteria.

However the correct function of the valve depends upon effective maintenance of the handpieces, lubrication and regular servicing (and replacement when required).