In situ Evaluation of Calcium Phosphate Ion-releasing Nanofilled Restorative Materials

Concerns about recurrent caries at restoration margins have led to the development of calcium phosphate-resin composites that have been shown to remineralize enamel and dentin lesions.  Objectives:  This study assessed the antibacterial effects of amorphous calcium phosphate nanoparticle (NACP)-filled nanocomposites in an in situ model. Methods: A randomized, double-blind, split-mouth design was conducted in one phase of 14 days, during which 25 volunteers wore palatal devices containing six bovine enamel slabs.  Each slab was randomly restored with one of three composites: (1) nanocomposite containing 40% NACP + 20% glass fillers (NACP group); (2) nanocomposite containing 40% NACP + 20% tetracalcium phosphate (NACP/TTCP group); (3) Control composite containing 60% glass fillers.  Volunteers used non-fluoride-containing dentifrice 3x/day.  A 20% sucrose solution was dripped onto the slabs 8x/day. Biofilms formed on the slabs were submitted to biochemical and microbiological analyses.  Kruskal–Wallis and Student-Newman-Keuls tests were used to evaluate the results (α=5%).  Results: No significant differences were found between NACP, NACP/TTCP, and control group regarding the microbiota (mean±s.d. expressed in Log10):  For total streptococci, 6.01±0.67, 5.82±0.73, and 5.98±0.46 for the three groups, respectively (p=0.96). For mutans streptococci, 5.05±0.74, 4.94±0.98, 5.04±0.52 for the three groups, respectively (p=0.91).  For lactobacilli, 6.5±0.8, 6.6±1.0, 7.0±0.7 for the three groups, respectively (p=0.25). For calcium (Ca) concentrations (µg/mg) were 132.6±77.7, 116.8±83.2, 78.4±39.2, respectively. NACP and NACP/TTCP had significantly higher Ca than control composite (p<0.05). Phosphate-ion (Pi) concentrations (µg/mg) were 23.46±6.2, 20.59±10.8, 18.51±10.6, respectively; NACP had significantly higher Pi than control (p=0.01). Conclusions:   NACP and NACP/TTCP nanocomposites with calcium phosphate fillers did not show a significant antibacterial effect under the studied cariogenic exposure conditions, but suggested the ability to remineralize lesions by providing significantly higher Ca and Pi concentrations. Therefore, these nanocomposites indicated a remineralizing potential, and could be further improved by incorporating additional antibacterial agents to combat biofilm growth.