Inspections conducted by the Ministry of Health from 2006 to 2008 found that recommendations regarding the sterilization of rotary instrument holders (RIHs) between patients were not being followed in several dental offices within the outpatient consultation and care units (UCSA) of correctional facilities. In July 2008, the French Institute for Public Health Surveillance (InVS) received a request to analyze the risk of bloodborne virus transmission under these conditions. Since other recent investigations also suggested that these violations were not limited solely to UCSA units, the risk assessment was also extended to private dental practices. From September to December 2008, the French Institute for Public Health Surveillance convened a working group comprising several experts in dental surgery, hospital hygiene, infectious disease epidemiology, and biostatistics. A modeling approach was adopted to assess the probability of HIV, HCV, or HBV transmission during a dental procedure. This probability depends on the likelihood of the PIR becoming contaminated during a procedure, the likelihood of viral transmission during a procedure involving a contaminated PIR that is reused without sterilization, and the proportion of susceptible individuals for the virus in question. The multiplicative models used were based on parameters derived from literature data or determined by experts in the absence of published data. Several scenarios considered varying probabilities of viral contamination persistence in the PIR. For each of the three viruses, and for an intermediate scenario of gradual decline in viral contamination, the following were calculated: the probability of having at least one case of viral transmission within a cohort of 1,000 patients who visited a dental office over the course of a year, and the annual number of transmissions of each of these viruses in the general population, taking into account the number of dental treatment sessions performed each year in France. In the general population, the average individual risk of contracting an infection following dental care in the absence of sterilization of dental instruments between patients is lowest for HIV at 1 in 420 million and highest for HBV at 1 in 516,000. The estimated risk in the prison population is approximately eight times higher. Given the large number of procedures performed in France each year, this failure to sterilize sharp instruments between patients—which does not comply with national recommendations—could result in fewer than 1 HIV infection, fewer than 2 HCV infections, and nearly 200 HBV infections annually in the general population. The number of such infections in the prison population could not be estimated due to a lack of available activity data. The working group therefore recommends strict adherence to standard precautions and good sterilization practices in dentistry, as well as enhanced hygiene training for dental professionals. Research should be promoted to strengthen the basis for instrument sterilization recommendations. The decision to inform patients who have undergone dental treatment in a practice that does not comply with these recommendations for sterilizing PIRs between patients should not be systematic but should be made on a case-by-case basis, taking into account this assessment and any other observed deviations from best practices. Given the prevalence of these viruses and their other possible modes of transmission, the potential detection of one of these infections in a person who has undergone dental care would not, on its own, allow for the conclusion that it is linked to the care provided. (R.A.)