Properties of boron nitride nanosheet-reinforced resin-matrix ceramics

Abstract

BACKGROUND: Boron nitride nanosheets have demonstrated remarkable advantages in enhancing the properties of dental materials. However, the current research on boron nitride nanosheets-reinforced resin-matrix ceramic materials is still in the preliminary exploration stage. OBJECTIVE: To investigate the effect of boron nitride nanosheet addition on the properties of resin-matrix ceramics. METHODS: 60% bisphenol A glycidyl methacrylate and 40% triethylene glycol dimethacrylate were used as the resin matrix, and barium glass powder was used as the inorganic filler. Resin-matrix ceramics were prepared by mixing 83% (mass fraction) of the resin matrix with 17% (mass fraction) of the barium glass powder. Meanwhile, boron nitride nanosheets were added to replace the barium glass powder at mass fractions of 0.3%, 0.5%, 0.7%, and 0.9% to prepare 0.3%, 0.5%, 0.7%, and 0.9% (mass fractions) of boron nitride nanosheet/resin-matrix ceramics, respectively. Resin-matrix ceramics were co-cultured with extracts of 0.3%, 0.5%, 0.7%, and 0.9% boron nitride nanosheet/resin-matrix ceramics and mouse fibroblast L929 cells (or human umbilical vein endothelial cells). CCK-8 assay was used to detect the survival rate of the two cells, and live/dead staining was used to detect L929 cell activity. The wettability, mechanical properties, and wear properties of resin-matrix ceramics and 0.3%, 0.5%, 0.7%, and 0.9% boron nitride nanosheet/resin-matrix ceramics were tested. RESULTS AND CONCLUSION: (1) After co-culture with resin-matrix ceramics and extracts of 0.3%, 0.5%, 0.7%, and 0.9% boron nitride nanosheet/resin-matrix ceramics, the survival rates of L929 cells and human umbilical vein endothelial cells all exceeded 85%, with no obvious cytotoxicity; live/dead staining showed that the extracts of resin-matrix ceramics and 0.3%, 0.5%, 0.7%, and 0.9% boron nitride nanosheet/resin-matrix ceramics did not affect L929 cell activity. (2) With the increase of boron nitride nanosheet mass fraction in the material, the water contact angle of resin-matrix ceramics increased, and the flexural strength and microhardness first increased and then decreased, among which 0.5% boron nitride nanosheet/resin-matrix ceramics had the highest flexural strength and microhardness. After 60,000 cycles, with the increase of boron nitride nanosheet mass fraction, the wear depth and wear volume of resin-matrix ceramics gradually increased; after 120,000 cycles, with the increase of boron nitride nanosheet mass fraction, the wear depth and wear volume of resin-matrix ceramics first decreased and then increased. The results show that appropriate addition of boron nitride nanosheets can significantly improve the comprehensive properties of resin-matrix ceramics.

1. Introduction

Dental restorative materials, as key elements for oral functional reconstruction, must not only possess excellent physicochemical properties to adapt to the complex oral environment [1], but also match the mechanical properties of natural enamel to achieve durable and stable restoration [2]. In recent years, resin-matrix ceramics have been widely used in dental restoration due to their unique performance advantages [3]. These materials combine the processability of traditional resin materials with the high strength of ceramic materials [4], achieving optimized performance. Compositionally, resin-matrix ceramics mainly consist of an organic matrix and inorganic fillers [5]. The addition of inorganic fillers not only significantly enhances the mechanical properties [6] and wear resistance [7] but also effectively reduces polymerization shrinkage [8-9], significantly improving the comprehensive performance and clinical application value of the material in dental restoration [10].

Studies have shown that adding nano- and micron-sized particles to resin-matrix ceramics can effectively enhance the mechanical strength of the material under masticatory load [11]. Boron nitride nanosheets are a new type of two-dimensional nanomaterial with a structure similar to graphene [12], in which the original carbon atoms of graphene are completely replaced by boron and nitrogen atoms arranged in a hexagonal lattice with strong covalent bonds [13]. Compared with graphene and other two-dimensional materials, boron nitride nanosheets possess unique advantages [14]. Their biological inertness stems from stable B-N bonds, which can effectively reduce reactive oxygen species-induced cytotoxicity and inflammatory risks [15-16]. Furthermore, compared with silica particles, boron nitride nanosheets have higher interfacial compatibility and toughening ability [17], while avoiding stress concentration issues caused by silica [18]. These characteristics make boron nitride nanosheets more promising for applications in dental resin composites and ceramic materials [19-20]. Research has proven that adding a small amount of boron nitride nanosheets can significantly enhance the flexural strength and hardness of dental resin composites and dental zirconia materials [21-22]. For example, LI et al. [19] added boron nitride nanosheets to polymethyl methacrylate, increasing its flexural strength by 56.7% and compressive strength by 53%; LEE et al. [23] added boron nitride nanosheets to zirconia, increasing its flexural strength by 27.3% and fracture toughness by 37.5%. These findings fully confirm the significant effectiveness of boron nitride nanosheets as a reinforcing phase in polymer-based and ceramic materials, laying a theoretical and practical foundation for further research.

Given that resin-matrix ceramics are in long-term contact with gingiva and dental pulp, the biocompatibility of the material is particularly critical [24]. Regarding the biocompatibility of boron nitride nanosheets,