Effects of thermal cycling on mechanical and antibacterial durability of bioactive low-shrinkage-stress nanocomposite.

OBJECTIVES: Recent studies developed low-shrinkage-stress composite with remineralizing and antibacterial properties to combat secondary caries and increase restoration longevity. However, their long-term durability in thermal cycling is unclear. The objectives of this study were to develop an antibacterial, remineralizing and low-shrinkage-stress composite, and to investigate its durability in thermal cycling for 20,000 cycles, equivalent to two years of clinical life. METHODS: The resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE). Composites were made with 5% dimethylaminohexadecyl methacrylate (DMAHDM) and 20% of nanoparticles of amorphous calcium phosphate (NACP). Composites were thermal cycled at 5°C and 55°C for 20,000 cycles. A human salivary biofilm model was used to evaluate antibiofilm activity before and after thermal cycling. RESULTS: After 20,000 cycles, the flexural strength of bioactive low-shrinkage-stress composite matched commercial control with no antibacterial activity (p > 0.05). Surface roughness was clinically acceptable at less than 0.2 µm. UV+NACP+DMAHDM composite reduced the total microorganisms, total streptococci, and mutans streptococci by 2-5 logs, compared to commercial composite. Biofilm lactic acid production was reduced by 11 folds. The antibacterial performance was maintained after thermal cycling, with no decrease after 20,000 cycles. CONCLUSIONS: Bioactive low-shrinkage-stress composite possessed good mechanical properties that matched commercial composite both before and after thermal cycling. The new composite had potent antibacterial activity, which was maintained and did not decrease after thermal cycling. CLINICAL SIGNIFICANCE: The new bioactive low-shrinkage-stress composite could reduce polymerization shrinkage stress and release calcium and phosphate ions, with good mechanical properties and strong antibacterial function that were durable after thermal cycling. These properties indicate great potential for inhibiting recurrent caries and increasing the restoration longevity.

Novel low-shrinkage-stress bioactive nanocomposite with anti-biofilm and remineralization capabilities to inhibit caries.

Background/purpose: A common reason for dental composite restoration failure is recurrent caries at the margins. Our objectives were to: (1) develop a novel low-shrinkage-stress, antibacterial and remineralizing resin composite; (2) evaluate the effects of dimethylaminohexadecyl methacrylate (DMAHDM) on mechanical properties, biofilm inhibition, calcium (Ca) and phosphate (P) ion release, degree of conversion, and shrinkage stress on the new low-shrinkage-stress resin composite for the first time. Material and methods: The resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE) with high resistance to salivary hydrolytic degradation. Composites were made with 0%-8% of DMAHDM for antibacterial activity, and 20% of nanoparticles of amorphous calcium phosphate (NACP) for remineralization. Mechanical properties and Streptococcus mutans biofilm growth on composites were assessed. Ca and P ion releases, degree of conversion and shrinkage stress were evaluated. Results: Adding 2-5% DMAHDM and 20% NACP into the low-shrinkage-stress composite did not compromise the mechanical properties (p > 0.05). The incorporation of DMAHDM greatly reduced S. mutans biofilm colony-forming units by 2-5 log and lactic acid production by 7 folds, compared to a commercial composite (p < 0.05). Adding 5% DMAHDM did not compromise the Ca and P ion release. The low-shrinkage-stress composite maintained a high degree of conversion of approximately 70%, while reducing the shrinkage stress by 37%, compared to a commercial control (p < 0.05). Conclusion: The bioactive low-shrinkage-stress composite reduced the polymerization shrinkage stress, without compromising other properties. Increasing the DMAHDM content increased the antibacterial effect in a dose-dependent manner.

Minimally-invasive dentistry via dual-function novel bioactive low-shrinkage-stress flowable nanocomposites.

The objectives of this in vitro study were to develop a novel low-shrinkage-stress flowable nanocomposite with antibacterial properties through the incorporation of dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP), and investigate the mechanical and oral biofilm properties, to be used in minimally-invasive techniques. METHODS: The light-cured low-shrinkage-stress flowable resin was formulated by mixing urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE) at a 1:1 mass ratio. Different mass fractions of glass, and either 5% DMAHDM or 20%NACP or both were incorporated. Paste flowability, ultimate micro tensile strength and surface roughness were evaluated. The antibacterial response of DMAHDM resin was assessed by using biofilms of human saliva-derived microcosm model. Virtuoso flowable composite was used as a control. RESULTS: (45% resin+5% DMAHDM+20% NACP+30% glass) formula yielded the needed outcomes. It had flow rate within the range of ISO requirement. The micro tensile strength was (39.1 ± 4.3) MPa, similar to (40.1 ± 4.0) MPa for commercial control (p > 0.05). The surface roughness values of the novel composite (0.079 ± 0.01) µm similar to commercial composite (0.09 ± 0.02) µm (p > 0.05). Salivary microcosm biofilm colony forming unit values were reduced by 5-6 logs (p < 0.05). Biofilm metabolic activity was also substantially reduced, compared to control composite (p < 0.05). SIGNIFICANCE: The novel bioactive flowable nanocomposite achieved strong antibacterial activities without compromising the mechanical properties. It is promising to be used as pit and fissure sealants, and as fillings in conservative cavities to inhibit recurrent caries and increase restoration longevity.

Low-shrinkage-stress nanocomposite: An insight into shrinkage stress, antibacterial, and ion release properties.

The aims are: (a) To develop the first low-shrinkage-stress nanocomposite with antibacterial and remineralization capabilities through the incorporation of dimethylaminododecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP); (b) to investigate the effects of the new composite on biofilm inhibition, mechanical properties, shrinkage stress, and calcium (Ca) and phosphate (P) ion releases. The low-shrinkage-stress resin consisted of urethane dimethacrylate and triethylene glycol divinylbenzyl ether. Composite was formulated with 3% DMAHDM and 20% NACP. Mechanical properties, shrinkage stress, and degree of conversion were evaluated. Streptococcus mutans biofilm growth on composites was assessed. Ca and P ion releases were measured. The shrinkage stress of the low-shrinkage-stress composite containing 3% DMAHDM and 20% NACP was 36% lower than that of traditional composite control (p < 0.05), with similar degrees of conversion of 73.9%. The new composite decreased the biofilm colony-forming unit by 4 log orders and substantially reduced biofilm lactic acid production compared to control composite (p < 0.05). Incorporating DMAHDM to the low-shrinkage-stress composite did not adversely affect the Ca and P ion release. A novel bioactive nanocomposite was developed with low shrinkage stress, strong antibiofilm activity, and high levels of ion release for remineralization, without undermining the mechanical properties and degree of conversion.

Long-term antibacterial activity and cytocompatibility of novel low-shrinkage-stress, remineralizing composites.

A low-shrinkage-stress (LSS), antibacterial and remineralizing nanocomposite was recently developed; however, validation of its long-term antibacterial potency in modulating human salivary-derived biofilm is an unmet need. This study aimed to evaluate the antibacterial effect of the bioactive LSS composite before and after aging in acidic solution for 90 days using a multi-species biofilm model, and to evaluate its cytotoxicity. The LSS composite consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE), 3% dimethylaminohexadecyl methacrylate (DMAHDM) and 20% nanoparticles of amorphous calcium phosphate (NACP). Biofilm colony-forming units (CFU), lactic acid production, and confocal laser scanning microscopy (3D biofilm) were evaluated before and after three months of aging. Cytotoxicity was assessed against human gingival fibroblasts (HGF). The new LSS composite presented the lowest biofilm CFU, lactic acid and biofilm biomass, compared to controls (n = 6, p < 0.05). Importantly, the new composite exhibited no significant difference in antibacterial performance before and after 90-day-aging, demonstrating long-term antibacterial activity (p > 0.1). The LSS antibacterial and remineralizing composite presented a low cell viability at original extract that has increased with further dilutions. In conclusion, this study spotlighted that the new bioactive composite not only had a low shrinkage stress, but also down-regulated the growth of oral biofilms, reduced acid production, maintained antibacterial activity after the 90-day-aging, and did not compromise the cytocompatibility.

Bioactive low-shrinkage-stress nanocomposite suppresses S. mutans biofilm and preserves tooth dentin hardness.

Recurrent dental caries is one of the main reasons for resin composite restoration failures. This study aimed to: (1) develop a bioactive, low-shrinkage-stress, antibacterial and remineralizing composite and evaluate the sustainability of its antibacterial effect against Streptococcus mutans (S. mutans) biofilms; and (2) evaluate the remineralization and cariostatic potential of the composite containing nanoparticles of amorphous calcium phosphate (NACP) and dimethylaminohexadecyl methacrylate (DMAHDM), using dentin hardness measurement and a biofilm-induced recurrent caries model. The antibacterial and remineralizing low-shrinkage-stress composite consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE), 3% DMAHDM and 20% NACP. S. mutans biofilm was used to evaluate antibiofilm activity, before and after 3 months of composite aging in acidic solution. Human dentin was used to develop a recurrent caries biofilm-model. Adding DMAHDM and NACP into low shrinkage-stress composite did not compromise the flexural strength. The low-shrinkage-stress composite with DMAHDM achieved substantial reductions in biofilm colony-forming units (CFU), lactic acid production, and biofilm biomass (p < 0.05). The low-shrinkage-stress DMAHDM+NACP composite exhibited no significant difference in antibacterial performance before and after 3 months of aging, demonstrating long-term antibacterial activity. Under S. mutans biofilm acidic attack, dentin hardness (GPa) was 0.24 ± 0.04 for commercial control, and 0.23 ± 0.03 for experimental control, but significantly higher at 0.34 ± 0.03 for DMAHDM+NACP group (p < 0.05). At an instrumental compliance of 0.33 µm/N, the polymerization shrinkage stress of the new composite was 36% lower than that of a traditional composite (p < 0.05). The triple strategy of antibacterial, remineralization and lower shrinkage-stress has great potential to inhibit recurrent caries and increase restoration longevity. Statement of Significance Polymerization shrinkage stress, masticatory load over time as well as biochemical degradation can lead to marginal failure and secondary caries. The present study developed a new low-shrinkage-stress, antibacterial and remineralizing dental nanocomposite. Polymerization shrinkage stress was greatly reduced, biofilm acid production was inhibited, and tooth dentin mineral and hardness were preserved. The antibacterial composite possessed a long-lasting antibiofilm effect against cariogenic bacteria S. mutans. The new bioactive nanocomposite has the potential to suppress recurrent caries at the restoration margins, protects tooth structures, and increases restoration longevity.

Novel low-shrinkage-stress nanocomposite with remineralization and antibacterial abilities to protect marginal enamel under biofilm.

OBJECTIVES: Polymerization shrinkage stress may lead to marginal damage, microleakage and failure of composite restorations. The objectives of this study were to : (1) develop a novel nanocomposite with low-shrinkage-stress, antibacterial and remineralization properties to reduce marginal enamel demineralization under biofilms; (2) evaluate the mechanical properties of the composite and calcium (Ca) and phosphate (P) ion release; and (3) investigate the cytotoxicity of the new low-shrinkage-stress monomer in vitro. METHODS: The low-shrinkage-stress resin consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE), and 3 % dimethylaminohexadecyl methacrylate (DMAHDM) and 20 % calcium phosphate nanoparticles (NACP) were added. Mechanical properties, polymerization shrinkage stress, and degree of conversion were evaluated. The growth of Streptococcus mutans (S. mutans) on enamel slabs with different composites was assessed. Ca and P ion releases and monomer cytotoxicity were measured. RESULTS: Composite with DMAHDM and NACP had flexural strength of 84.9 ±â€¯10.3 MPa (n = 6), matching that of a commercial control composite. Adding 3 % DMAHDM did not negatively affect the composite ion release. Under S. mutans biofilm, the marginal enamel hardness was 1.2 ±â€¯0.1 GPa for the remineralizing and antibacterial group, more than 2-fold the 0.5 ±â€¯0.07 GPa for control (p < 0.05). The polymerization shrinkage stress of the new composite was 40 % lower than that of traditional composite control (p < 0.05). The new monomers had fibroblast viability similar to that of traditional monomer control (p > 0.1). CONCLUSION: A novel low-shrinkage-stress nanocomposite was developed with remineralizing and antibacterial properties. This new composite is promising to inhibit recurrent caries at the restoration margins by reducing polymerization stress and protecting enamel hardness.

Novel antibacterial calcium phosphate nanocomposite with long-term ion recharge and re-release to inhibit caries.

Short-term studies on calcium-phosphate (CaP) ion-rechargeable composites were reported. The long-term rechargeability is important but unknown. The objectives of this study were to investigate nanocomposite with strong antibacterial and ion-recharge capabilities containing dimethylaminododecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP), and evaluate long-term ion-recharge by testing for 12 cycles (taking 6 months to complete) for the first time. Three groups were tested: (1) Heliomolar control; (2) Resin+20%NACP+50%glass; (3) Resin+3%DMAHDM+20%NACP+50%glass. Biofilm acid and colony-forming units (CFU) were measured. Ion-recharge was tested for 12 cycles. NACP-DMAHDM composite reduced biofilm acid, and reduced CFU by 4 logs. High levels of ion releases were maintained throughout 12 cycles of recharge, maintaining steady-state releases without reduction in 6 months (p>0.1), representing long-term remineralization potential. Bioactive nanocomposite demonstrated long-term ion-rechargeability for the first time, showed remineralization and potent anti-biofilm functions, with promise for tooth restorations to combat caries.