Cerium chloride pretreatment reduces initial biofilm attachment on hydroxyapatite: a scanning electron microscopy study

The incorporation of cerium instead of calcium into the crystal lattice of hydroxyapatite appears to increase the resistance of dental hard tissues to caries lesion initiation and progression. The effect on initial biofilm formation is yet unknown. The aim of this study was to assess the effect of cerium(III)chloride (50%CeCl₃) pretreatment of hydroxyapatite (HA) discs on subsequent growth of an initial 3 species caries-biofilm. Twelve 9.5 mm diameter hydroxyapatite discs were divided into three groups (<i>n</i> = 4) and treated for 1 min with either 50% CeCl₃, ultrapure water (Control), or 0.02% chlorhexidine gluconate (CHX) and washed twice in ultrapure water for 1 min. Samples were incubated in artificial saliva (21 °C, 120 min) for pellicle formation and then placed in an active attachment caries biofilm model comprising <i>Actinomyces naeslundii</i>, <i>Schaalia odontolytica</i>, and <i>Streptococcus mutans</i>, cultured anaerobically at 37 °C for 4 h before being fixed in 2.5% glutaraldehyde and examined using scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) in high-vacuum mode. SEM-micrographs at up to 50,000× showed net-like or spherical precipitates on the surface of all CeCl₃-samples but not on the Control or CHX-samples. CeCl₃-samples also showed signs of acid attack possibly due to the low pH (2.6) of the CeCl₃ solution. Rods and cocci were found on all Control, but only on 2 of 4 CHX samples. On CeCl₃ samples, only one harbored isolated cocci but no rods were observed. EDX-analyses confirmed the presence of Cerium in all CeCl₃ samples with atomic percent (At%) ranging from 0.1 to 0.4 for areas without visible precipitates and up to 4.1 for areas with precipitates. CeCl₃-treatment before pellicle formation results in the development of precipitates on the surface of HA and appears to have potential to inhibit initial biofilm growth on HA compared to CHX treated or untreated controls.