Secondary caries at the
restoration margins remains the main reason for failure. Although
calcium phosphate (CaP) composites are promising for caries inhibition,
there has been no report of CaP composite to inhibit caries in situ. The
objectives of this study were to investigate the caries-inhibition
effect of nanocomposite containing nanoparticles of amorphous calcium
phosphate (NACP) in a human in situ model for the first time, and to
determine colony-forming units (CFU) and Ca and P ion concentrations of
biofilms on the composite restorations.
NACP with a mean particle size of 116nm
were synthesized via a spray-drying technique. Two composites were
fabricated: NACP nanocomposite, and control composite filled with glass
particles. Twenty-five volunteers wore palatal devices containing bovine
enamel slabs with cavities restored with NACP or control composite.
After 14 days, the adherent biofilms were collected for analyses.
Transverse microradiography determined the enamel mineral profiles at
the margins, and the enamel mineral loss ΔZ was measured.
NACP nanocomposite released Ca and P ions and the release significantly increased at cariogenic low pH (p<0.05). Biofilms on NACP nanocomposite contained higher Ca (p=0.007) and P ions (p=0.005) than those of control (n=25). There was no significant difference in biofilm CFU between the two composites (p>0.1).
Microradiographs showed typical subsurface lesions in enamel next to
control composite, but much less lesion around NACP nanocomposite.
Enamel mineral loss ΔZ (mean±sd; n=25) around NACP nanocomposite was 13.8±9.3μm, much less than 33.5±19.0μm of the control (p=0.001).
NACP nanocomposite substantially reduced caries formation in a human in
situ model for the first time. Enamel mineral loss at the margins
around NACP nanocomposite was less than half of the mineral loss around
control composite. Therefore, the Ca and P ion-releasing NACP
nanocomposite is promising for caries-inhibiting restorations.