Development and Characterization of Novel CAD/CAM Composite Resins Infused with Nano-Hydroxyapatite for Minimizing Secondary Caries
CAD/CAM composite, silanized nanohydroxyapatite (nHAp), high-pressure hightemperature (HPHT) polymerization.
AuthorsAbstractIntroduction: Secondary caries at the restoration margin remains the primary clinical reason why resin-based restorations fail. While factorypolymerized computer-aided design and computer-aided manufacturing (CAD/CAM) composite blocks offer excellent baseline mechanical properties, they are biologically passive. This study developed and characterized a novel CAD/CAM composite resin infused with silanized nano-hydroxyapatite (nHAp) to introduce targeted bioactive and antimicrobial actions without compromising structural integrity. Methodology: Experimental CAD/CAM composite blocks were synthesized using a 1:1 weight ratio of Bis-GMA and TEGDMA monomers, incorporated with 0% (Control), 1%, 2%, and 5% weight fractions of \gamma-MPTS silanized nHAp (purity greater than 99%, particle size less than 100 nm). Homogenization was performed via planetary mixing and ultra-sonication, followed by high-pressure, high-temperature (HPHT) polymerization (180°C, 150 MPa, 60 minutes). Specimens (total sample size = 204) were prepared to evaluate three-point flexural strength, Vickers microhardness, degree of conversion (via FTIR), calcium/phosphate ion release (via ICPOES), and biofilm metabolic activity against Streptococcus mutans. Data were evaluated using One-way ANOVA and Tukey's post-hoc tests (p < 0.05). Results: The 1% and 2% nHAp groups maintained flexural strength values (142.3 MPa and 135.6 MPa, respectively) well above the ISO 4049 threshold of 100 MPa, whereas the 5% group dropped significantly to 89.4 MPa (p < 0.01). Vickers microhardness increased incrementally with filler load. The 2% and 5% groups exhibited continuous, statistically significant releases of calcium and phosphate ions under simulated cariogenic conditions (pH 5.5). Furthermore, biofilm metabolic activity and lactic acid production were significantly reduced in the 2% group (p = 0.024) compared to the control. Conclusions: Incorporating 2% wt silanized nHAp into an experimental HPHT resin matrix successfully produces a bioactive CAD/CAM composite block. This specific formulation inhibits cariogenic biofilm activity and releases essential mineral ions while preserving the mechanical performance required for high-stress posterior restorations.
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