Since August 2009, members of the Primary Care Dentistry Research Forum (http://www.dentistryresearch.org) have taken part in an online vote to identify questions in day-to-day practice that they felt most needed to be answered with conclusive research. The question which receives the most votes each month forms the subject of a critical appraisal of the relevant literature. Each month a new round of voting takes place to decide which further questions will be reviewed. Dental practitioners and dental care professionals are encouraged to take part in the voting and submit their own questions to be included in the vote by joining the website.The paper below details a summary of the findings of the seventh critical appraisal. In conclusion, the critical appraisal identified no evidence on the epidemiological scale of cross-infection caused in dental practices and therefore also of the cost impact of cross-infection caused in primary dental practices. As a result, no 'cost of illness', or cost-benefit assessment, exists or is feasible at this time.