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This study aimed to provide evidence that phosphoric acid pre-etching is necessary for the chemisorption between enamel and 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing universal adhesives. Three MDP-containing universal adhesives: Single Bond Universal (SBU), All Bond Universal (ABU), and Clearfil Universal Bond Quick (CBQ), as well as an experimental MDP-containing adhesive (EX) were investigated. Clearfil SE Bond (CSE) was a control and untreated enamel (UE) was another control. Self-etch (SE) and etch-and-rinse (ER) bonding modes were employed for universal adhesives. The enamel surfaces with different treatments were observed with a scanning electron microscope (SEM). The chemical bonds in the enamel reactants were determined using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR). The charge changes with phosphoric acid pre-etching or without were characterized by ζ-potential. FTIR confirmed the chemisorption between enamel and MDP-containing adhesives. XPS and 31P NMR studies detected improved chemical affinity to the phosphoric acid etching + MDP-containing universal adhesives applied with enamel. The ζ-potential of MDP-containing universal adhesives absorbed with enamel, with or without etching became more negative compared with that of UE (P < 0.05). Furthermore, single etching created a negative ζ-potential with a higher absolute value (P = 0.009). Phosphoric acid pre-etching can increase the negative charge on the enamel surface and facilitate the chemical reactions of MDP and hydroxyapatite (HAp) to produce more calcium salts, thus improving the chemisorption between enamel and MDP-containing universal adhesives.

Background Mesoporous calcium-silicate nanoparticles (MCSNs) have good prospects in the medical field due to their great physicochemical characteristics, antibacterial activity and drug delivery capacity. This study was to analyze the antibiofilm activity and mechanisms of silver (Ag) and zinc (Zn) incorporated MCSNs (Ag/Zn-MCSNs) with different percentages of Ag and Zn. Methods Ag/Zn(1:9, molar ratio)-MCSNs and Ag/Zn(9:1, molar ratio)-MCSNs were prepared and characterized. Endocytosis of nanoparticles by Enterococcus faecalis (E. faecalis) treated with Ag/Zn-MCSNs was observed using TEM to explore the antibacterial mechanisms. The antibiofilm activity of Ag/Zn-MCSNs with different ratios of Ag and Zn was tested by E. faecalis biofilm model in human roots. The human roots pretreated by different Ag/Zn-MCSNs were cultured with E. faecalis. Then, SEM and CLSM were used to observe the survival of E. faecalis on the root canal wall. Cytotoxicity of the nanoparticles was tested by CCK8 kits. Results The Ag/Zn-MCSNs release Ag+ and destroy the cell membranes to kill bacteria. The MCSNs containing Ag showed antibacterial activity against E. faecalis biofilms in different degrees, and they can adhere to dentin surfaces to get a continuous antibacterial effect. However, MTA, MCSNs and Zn-MCSNs could not disrupt the bacterial biofilms obviously. MCSNs, Ag/Zn(1:1, molar ratio)-MCSNs and Ag/Zn(1:9)-MCSNs showed no obvious cytotoxicity, while Ag-MCSNs and Ag/Zn(9:1)-MCSNs showed cytotoxicity. Zn-MCSNs can slightly promote cell proliferation. Conclusion Ag/Zn-MCSNs have good antibiofilm activity. They might achieve an appropriate balance between the antibacterial activity and cytotoxicity by adjusting the ratio of Ag and Zn. Ag/Zn-MCSNs are expected to be a new type of root canal disinfectant or sealer for root canal treatment.

Background: Silver (Ag) and/or zinc (Zn) incorporated mesoporous calcium-silicate nanoparticles (MCSNs) have good physicochemical characteristics and can be advanced materials for root canal filling. This study was to analyze the antibacterial properties and mechanism of Ag/Zn-MCSNs with different percentage of Ag and Zn.Methods: The antibacterial properties and the cytotoxicity of them were evaluated. Human root canals were inoculated with E. faecalis for 4 weeks to establish bacterial biofilm model. The E. faecalis biofilms were treated with MCSNs, Ag-MCSNs, Zn-MCSNs, Ag/Zn-MCSNs, calcium hydroxide (CH) and mineral trioxide aggregate (MTA) for 7 days. The ultrastructure and distribution of viable bacteria of the specimens were evaluated using SEM and CLSM. Human root canals were pretreated with CH, MCSNs, Ag-MCSNs, Zn-MCSNs and Ag/Zn-MCSNs, then the root canals were immersed in E. faecalis suspension for 7 days. The adhesion and colonization of E. faecalis on the root canal walls were observed using SEM and CLSM. Endocytosis of E. Faecalis treated by Ag-MCSNs and Ag/Zn-MCSNs were observed using TEM. Results: The MCSNs containing Ag showed better antibacterial properties than MCSNs and Zn-MCSNs (PP>0.05), while Ag-MCSNs and Ag/Zn(9:1)-MCSNs showed cytostatic effects. Zn-MCSNs slightly promote cell proliferation (PE. faecalis biofilm in different degree, and can adhere to dentin surfaces to get a continuous antibacterial effect, but MTA, MCSNs and Zn-MCSNs could not disrupt the bacterial biofilm obviously. The Ag-MCSNs and Ag/Zn-MCSNs release Ag+ and destroy the cell membranes to kill bacteria. Conclusions: The antibacterial effects and cytotoxicity of Ag/Zn-MCSNs are related to Ag content, while Zn reduce cytotoxicity and promote cell proliferation.

Mesoporous calcium-silicate nanoparticles (MCSNs) are advanced biomaterials for drug delivery and mineralization induction. They can load silver and exhibit significantly antibacterial effects. However, the effects of MCSNs and silver-loaded MCSNs on dentin are unknown. The silver (Ag) and/or zinc (Zn) incorporated MCSNs (Ag-Zn-MCSNs) were prepared by a template method, and their characterizations were tested. Then the nanoparticles were filled into root canals and their effects on the dentin were investigated. Ag-Zn-MCSNs showed characteristics of mesoporous materials and sustained release of ions over time. Ag-Zn-MCSNs adhered well to the root canal walls and infiltrated into the dentinal tubules after ultrasound activation. Ag-Zn-MCSNs showed no significantly negative effects on either the flexural strength or the modulus of elasticity of dentin, while CH decreased the flexural strength of dentin significantly (P