Bacterial Adhesion Forces Mediating Biofilm Formation to Orthodontic Materials

  • Dr Li Mei, Department of Biomedical Engineering/Orthodontics, University Medical Center Groningen, University of Groningen, The Netherlands
  • Prof Yijin Ren, University Medical Center Groningen, The Netherlands
  • Prof Henny Van der Mei, Department of Biomedical Engineering, University Medical Center Groningen, University of Groningen, The Netherlands
  • Prof Henk Busscher, Department of Biomedical Engineering, University Medical Center Groningen, University of Groningen, The Netherlands

Introduction: The biofilm on bracket-adhesive-enamel junctions causes enamel decalcification, affecting about 50% of all patients undergoing orthodontic treatment. The forces by which bacteria adhere to these materials are determinant for their ease of removal, e.g. by brushing.
Objective: To directly measure the adhesion forces of oral bacteria to the surfaces constituting the bracket-adhesive-enamel junction.
Methods: Adhesion forces were measured by atomic force microscopy (AFM) at room temperature in adhesion buffer (pH 6.8). Ten force measurements were made at each site; three locations were randomly selected on each sample. Adhesion times ranged from 0-120 s.
Results: 1In the absence of a saliva-coating, strongest bacterial adhesion forces were measured to the adhesive surface (-2.9 to -6.9 nN), while the lowest were found on enamel (-0.8 to -2.7 nN). 2In the presence of a saliva-coating, the enamel surface exerted stronger adhesion forces (-0.6 to -0.7 nN) than stainless steel and adhesive surfaces (-0.4 to -0.5 nN) 3Saliva-coating strongly reduced the adhesion forces to less than 1 nN on the included orthodontic material surfaces 4Streptococcal bond strengthening was observed. Streptococcal adhesion forces increased upon increasing the adhesion time from 0 to 120 s. (Note, attractive forces are indicated as negative forces by convention.)
Conclusion: Bacteria adhere stronger to adhesive and stainless steel than to enamel surfaces in the absence of a saliva-coating. Bacterial adhesion forces significantly decreased after coated with saliva, and increased with adhesion times.