Although there is a strong emphasis on prevention of bacteremia in the dental office setting, the relative risk for IE from dental procedures versus routine daily events such as tooth brushing is unknown. Bacteria commonly gain entrance to the circulation through ulcerated gingival crevicular tissue surrounding the teeth.23
While dental extractions are among the most likely of dental procedures to cause bacteremia, tooth brushing may disrupt a far larger surface area of gingival crevicular tissue. While brushing does not appear to have the same incidence, duration, nature, and therefore magnitude of bacteremia as a dental extraction, we found a substantial incidence of bacteremia (23%) of IE-causing species from this common daily oral hygiene activity. In addition, the brushing group had a larger percentage of positive cultures at 60 minutes (9% vs. 2% respectively). This suggests that brushing poses a risk for bacteremia similar to a dental extraction, given professional guidelines that recommend tooth brushing at least twice per day. Therefore, there is the potential for bacteremia from tooth brushing alone to occur over two hundred times per year, by comparison with an average of less than two dental office visits per year per person in the United States.29
Although amoxicillin has a significant impact on bacteremia from a dental extraction, a notable number the extraction patients who received prophylaxis in this study nonetheless showed evidence of bacteremia, including IE-related species. This lack of 100% efficacy alters the per-dose risk-benefit ratio, increasing the number needed to treat to avert a distant site infection.
The duration of bacteremia likely reflects the nature and number of bacteria that enter the circulation, as well as multiple other host factors such as immune responses. Although it is not clear what role duration has on the risk for bacterial seeding of cardiac valves, our data demonstrate that bacteria are cleared rapidly, particularly in the presence of amoxicillin. However, some pathogenic species persisted for at least 60 min. following brushing and extraction without antibiotic.
The human oral cavity is colonized by a larger variety of bacterial flora than any other anatomical area. Over 700 species of bacteria have already been identified, 400 of which were found in the periodontal pocket adjacent to teeth.30
Streptococci represent a significant proportion of the flora around the teeth, especially in the supragingival plaque, and they are frequently associated with IE. An extensive search of the literature yields a common list of 126 individual bacteria reported in blood cultures following extractions (N=131) or tooth brushing (N=26), all identified by conventional clinical laboratory methods. However, data on the incidence, duration, nature and magnitude of bacteremia from non-IE-associated species, and bacteria identified by non-molecular means, are of little or no help to clinicians or policy makers.31
We focused on the 32 bacterial species identified in the present study that were also on the list of 275 bacteria reported to cause IE, 11 (32%) of which have not been reported previously in studies of brushing or extractions. Finally, we identified 71 species and subspecies of bacteria not previously reported in blood cultures following extractions or tooth brushing, 30 of which are novel.
It is difficult to quantitate the magnitude of bacteria that initially gain entrance to the circulation following dental procedures due to factors such as heart rate, blood volume, proximity of the blood collection site to the source of the bacteremia, and the rapid bacterial clearance by the reticuloendothelial system. Although animal model data have established that the rate of infection of damaged heart valves is dependent upon the inoculum size of the bacterial challenge, with larger inocula yielding higher infection rates, there are no data indicating the range of inocula which result in endocarditis in vulnerable patients. Although we were able to reliably detect and therefore quantitate a bacteria in blood at or above a concentration between 103 and 104 CFU/mL, the magnitude from extractions and tooth brushing was below this level in all samples examined. Therefore, all we can say is that the magnitude of bacteria in the blood cultures was below 104 CFU/ml.
We have over twice the number of complex extractions in the extraction – placebo group (19 vs. 9) which, although not statistically significant, suggests that 20% of the placebo group vs. 9% of the amoxicillin group had a more invasive procedure. This might contribute to the increased incidence and duration of bacteremia in the placebo group, and this would likely explain the (non-significant) increased extraction time for the placebo group. If this is the case, there is less of an impact from Amoxicillin than suggests.
There are potential limitations to this study. First, since all subjects were seen at a hospital-based clinic, and all needed an extraction, they may have been demographically distinct from, and had a greater burden of dental disease than, the general population. Our population was similar to the US population in gender distribution (56% male in the study vs. 49% male nationally), but was different in racial/ethnic break-down (69% African –American in the study vs. 12% nationally and 28% locally) [US Census Bureau, American Community Survey, 2006].32
We are not aware of any differences between racial groups in terms of oral bacterial flora in disease or health, and we therefore feel that these data are easily extrapolated to other racial and ethnic groups. Second, although the number of bacterial CFU per ml of blood was always below 10,000, this does not exclude the possibility of significant differences in CFU/ml below this threshold between the three groups, which might be important in terms of risk of heart valve colonization. Our data suggest that brushing and single tooth extraction, generally thought to be at different ends of the spectrum of invasiveness, are similar from the standpoint of magnitude.
There is ongoing debate concerning the health risks, cost-effectiveness, and practicality of the routine use of prophylactic antibiotics.3, 4, 33-35
The lack of efficacy data for this practice has to be weighed against risk factors (e.g., drug reactions), potential for resistant strains and various economic costs to society from the routine use of antibiotics for common dental procedures. Although the 2007 AHA recommendations call for far fewer people to receive antibiotic prophylaxis than earlier guidelines, these recommendations have been adopted for over 20 groups of noncardiac patients as well.36
The incidence, duration, nature and magnitude and daily occurrence of bacteremia from tooth brushing and other routine daily events (e.g., chewing food) calls into question the appropriateness and emphasis on prophylaxis for periodic dental procedures. Given the unfeasible concept of advocating antibiotic coverage for tooth brushing, we suggest that a controlled clinical trial is indicated to resolve this longstanding issue. In the meantime, there should be a greater focus on avoidance of dental disease in patients at risk for distant site infection in general, and IE in particular.