Efficacy of a mouthrinse based on hydroxyapatite to reduce initial bacterial colonisation in situ

Objective: The present in situ -investigation aimed to specify the impact of pure hydroxyapatite microclusters on initial bioadhesion and bacterial colonization at the tooth surface. Design: Pellicle formation was carried out in situ on bovine enamel slabs (9 subjects). After 1 min of pellicle formation rinses with 8 ml of hydroxyapatite (HA) microclusters (5%) in bidestilled water or chlorhexidine 0.2% were performed. As negative control no rinse was adopted. In situ biofilm formation was promoted by the intraoral slab exposure for 8 h overnight. Afterwards initial bacterial adhesion was quantified by DAN staining and bacterial viability was determined in vivo/in vitro by live/dead-staining (BacLight). SEM analysis evaluated the efficacy of the mouthrinse to accumulate hydroxyapatite microclusters at the specimens' surface and spit-out samples of the testsolution were investigated by TEM. Results: Compared to the control (2.36 x 10(6) 2.01 x 10(6) bacteria/cm(2)), significantly reduced amounts of adherent bacteria were detected on specimens rinsed with chlorhexidine 0.2% (8.73 x 10(4) +/- 1.37 x 10(5) bacteria/cm(2)) and likewise after rinses with the hydroxyapatite testsolution (2.08 x 10(5) +/- 2.85 x 10(5) bacteria/cm(2), p < 0.001). No demonstrable effect of HA-particles on Streptococcus mutans viability could be shown. SEM analysis confirmed the temporary adsorption of hydroxyapatite microclusters at the tooth surface. Adhesive interactions of HA-particles with oral bacteria were shown by TEM. Conclusion: Hydroxyapatite microclusters reduced initial bacterial adhesion to enamel in situ considerably and could therefore sensibly supplement current approaches in dental prophylaxis. (C) 2017 Elsevier Ltd. All rights reserved.