A novel resin cement to improve bonding interface durability

Abstract

Bonding failure is one of the main causes of failure of dental restorations. The bonding strength, aging resistance, and polymerization shrinkage of cement can affect the stability of the bonding interface and lead to marginal microleakage. To reduce the bonding failure rate of restorations, a novel polyurethane (PU) cement was designed to improve the mechanical properties, hydrophobicity, degree of conversion (DC), polymerization shrinkage, bond strength and aging resistance of cement by introducing isophorone diisocyanate (IPDI) and hydroxyethyl methacrylate (HEMA) and adjusting the polyester : polyether ratio to increase the degree of cross-linking. Experimental results verified that the novel PU could increase the mechanical properties and thermal stability of the cement, reduce polymerization shrinkage during the curing reaction, improve the bonding performance and DC, endow the cement with hydrophobic properties, and improve its ability to resist aging in the salivary environment to maintain the long-term stability of interfacial bonding under the influence of comprehensive factors. The results of this study provide a new direction and insights to reduce microleakage and improve the success rate of restorations.

Fig. 1. (A) ¹H NMR spectra of PU based on polyester polyol. (B) ¹H NMR spectra of PU based on the polyether polyol. (C) FT-IR spectra of PU based on polyester polyol. (D) FT-IR spectra of PU based on the polyether polyol.

Fig. 2. Tensile testing. Tensile strength and elongation at break for PUs with different molar ratios of PDGPA to PPO that could be suitable for application in dental cements.

Fig. 3. Characterization of the PU and MS cements. (A) Water sorption. (B) Water solubility. (C) Contact angle of five different cements and representative images of the cement surface. (D) Influence of different PUs on the degree of conversion of the experimental and commercial cements (mean ± SD, n = 5).

Fig. 4. Thermal characterization of four kinds of PUs.

Fig. 5. Mechanical properties of the cements after 24 h and 10 000 thermocycles. (A) Flexible strength (B) elastic modulus (C) compressive strength (D) hardness (mean ± SD, n = 8).

Fig. 6. Polymerization shrinkage and kinetics of the resin cements: (A) polymerization volume shrinkage, (B) polymerization strain, (C) rate of shrinkage, and (D) gel point (mean ± SD, n = 5).

Fig. 7. Representative images of (A), (B) CLSM and (C), (D) SEM showing the interfacial characteristics; comparatively few short resin tags (rt) underneath the hybrid layer (hl) are well defined. rc, resin cement; rt, resin tag; hl, hybrid layer.

Fig. 8. Microtensile strength of PUs and MS after 24 h and 10 000 thermocycles. Different capital letters represent statistically significant differences within each cement group (p < 0.05; horizontal comparisons). Lowercase letters represent statistically significant differences within each cement group before and after 10 000 thermocycles (p < 0.05; vertical comparisons) (mean ± SD, n = 20).

Fig. 9. Distribution of three fracture modes after 24 h and 10 000 thermocycles.

Fig. 10. Representative microleakage images between the tooth and ceramic inlay after 10 000 thermocycles. (A) MS; (B) PU1; (C) PU2; (D) PU3; (E) PU4.

Fig. 11. (A) Cytotoxicity of the control, MS and PU cements in different dilutions with culture medium at 24 h, 48 h, and 72 h determined by CCK-8 assay. The RGR was calculated. (B) Live/dead fluorescence cell staining after L929 cells were cultured for 24 h in culture medium with the control, MS and PUs. Living cells were stained with calcium-AM (green), and dead cells were stained with PI (red).