Flossing, scaling and bugs in the blood

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Some of the evidence used to in the formulation of the NICE guidance on antibiotic prophylaxis for invasive dental procedures that we discussed yesterday was the recognition that everyday oral activities cause bacteraemia (Dental Elf  10th May 2011). This new cross-sectional study by Zhang et al looked the bacteraemia caused by flossing compared with scaling and root planing (SRP)

30 volunteers with chronic periodontitis received either full mouth flossing or one quadrant of SRP at separate appointments one week apart. Flossing and SRP was performed by one of the authors. Blood samples were obtained at baseline, 5 minutes after the start of treatment and 30 seconds and 10 minutes after completion. Total bacteraemia and viridans streptococcal bacteraemia (VSB) were investigated.

  • The 30 participants included 2 males and 18 females with a mean age of 47 (±9.5) years.  5 were current smokers, 8 former smokers and 21 never smokers. All fulfilled the criteria for severe chronic periodontitis
  • Total bacteraemia incidence was 30% for flossing and 43.3% for SRP (no significant difference; p = 0.21).
  • Flossing and SRP caused the same incidence of VSB (26.7%).
  • Flossing caused a higher mean magnitude of total and VSB bacteraemia than SRP, but the difference was not significant.
  • Viridans streptococci comprised 11.4% of flossing bacteraemia isolates and 7.6% in SRP.
  • Gingival inflammation was significantly associated with incidence of total bacteraemia.

The authors concluded

No differences were found between flossing and SRP in the incidence or magnitude of total bacteraemia or VSB. This finding is important in the ongoing re-evaluation of antibiotic prophylaxis to prevent infective endocarditis.


This studies finding suggests that flossing produces the same level of bacteraemia, as does SRP. It is also worth noting that in 5 participants their baseline samples were found to be positive for bacteraemia (not VSB) of oral origin  (two prior to flossing and 3 prior to SRP) and were excluded when analysing total bacteraemia.


Zhang W, Daly CG, Mitchell D, Curtis B. Incidence and magnitude of bacteraemia caused by flossing and by scaling and root planing. J Clin Periodontol. 2013 Jan;40(1):41-52. doi: 10.1111/jcpe.12029. Epub 2012 Nov 9. PubMed PMID: 23137266.

Dental Elf 10th May 2011 – Bacteraemia due to everyday oral activities.

Dental Elf 8th Jan 2013 – Costs of routine antibiotic prophylaxis prescribing to dental patients in the USA

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Derek Richards

Derek Richards is a specialist in dental public health, Director of the Centre for Evidence-Based Dentistry and Specialist Advisor to the Scottish Dental Clinical Effectiveness Programme (SDCEP) Development Team. A former editor of the Evidence-Based Dentistry Journal and chief blogger for the Dental Elf website until December 2023. Derek has been involved with a wide range of evidence-based initiatives both nationally and internationally since 1994. Derek retired from the NHS in 2019 remaining as a part-time senior lecturer at Dundee Dental School until the end of 2023.

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