A Comprehensive Review: Influence of Hexagonal Boron Nitride and Mesoporous Silica Nanoparticles on Dental Composite.

The use of mesoporous silica nanoparticles (MSN) within dental composites as fillers, especially with the addition of hexagonal boron nitride (HBN), is a positive trend in restorative dental materials. The application of such nanofillers has some of the most positive impacts that overcome the traditional composites’ most negative features, such as microbial intrusion, insufficient mechanical properties, and low resistance. While HBN has a well-known thermal conductivity, chemical stability, and mechanical strength, MSN possesses high surface area, which enhances the dispersion of fillers and the bactericidal activity. This review evaluates the influence of HBN and MSN on the morphological and mechanical structure, thermal resistance, and antimicrobial activity of the dental composites. In the research carried out by Kaptan Usul et al. (2024), the authors methodically studied the processes developed for the dental composites containing HBN and MSN filler portions of 5% and 10% by weight in a Bis-GMA/TEGDMA polymer matrix. The use of advanced bonding procedures together with FTIR, EDS, SEM, X-ray Interferometry, and Thermogravimetric analysis made it possible to improve the structure and thermal stability of the composite, which achieved the critical structural bonds.Staphylococcus aureus and Escherichia coli, alongside Saccharomyces cerevisiae, exhibited promising actions with minimum inhibition concentration values of 1-5 mg/mL. There are, however, no long-term stability monitoring and triobological evaluation, as well as exhaustive biocompatibility assessment, which are the challenges for clinical application. More efforts are required to address the issues of mass production, wear resistance, and cytotoxicity. Incorporating HBN and MSN into dental composites would aid in the development of restorative materials that can sustain stress, possess antimicrobial characteristics, and show clinical longevity, which is of utmost importance.   1. Introduction ________________________________________1.1. The Evolution of Dental Composites:________________________________________ In the Twentieth Century, there has been a drastic evolution to the form of dental composites as they were used towards the middle of that century. Economic cost and longevity of dental amalgam restorations meant they were the most widely used material by dentists. Nevertheless, the need to replace resin-based composites due to mercury toxicity and lack of appeal dictated their use. Although these materials were more appealing and biocompatible, they suffered from low toughness and were prone to shrinkage and contamination. (Kaptan Usul et al., 2024, p. 2296). 1.1.1. The Early Stages of Composite Developments: Initially, the dental composites achieved modernity with the use of an inorganic quartz or silica filler mixture along with a bisphenol A-glycidyl methacrylate (Bis-GMA) matrix and triethylene glycol dimethacrylate (TEGDMA) resin. While there was further enhancement of the aesthetic properties of dental composites, much more work was still needed regarding curing shrinkage. Researchers responded to this by developing hybrid composites that used plastic fillers to enhance mechanical strength. 1.1.2. Difficulties Encountered in the Use of Traditional Composites: Even though progress continues to be made, conventional composites are still faced with the following major difficulties: Mechanical Degradation: Dental composites are subject to wear, cracking, and chipping over time because of the repetitive loading forces during mastication. Microbial Infiltration: Within the cavity, composite materials interface with tooth structure, leading the cavity to be afflicted by the interface that allows the biofilm to accumulate and eventually results in secondary caries and affect the restoration. Hydrolytic Instability: Absorption of water means dental composites undergo hydrolytic degradation which leads to swelling that cracks and finally fails. Thermal and Chemical Instability: Substance dissolution in the oral cavity, with its changing temperature and pH, speeds up material destruction. To address the above issues, newer dental materials with high mechanical strength, resistance to microbes, and stability to the environment are required.________________________________________ 1.2. The Application of Nanotechnology In Dentistry: The integration of nanotechnology into dental materials composite technology has replaced the problems of traditional composite materials. The addition of some other new fillers like hexagonal boron nitride (HBN) nanoparticles and mesoporous silica MSN nanoparticles (HBN) has demonstrated improved mechanicals as well as antimicrobial properties (Niu et al., 2020; Mohammed et al., 2020). 1.2.1. Properties of Nanofillers: Nanofillers are considered the most efficient elements that take care of functional enhancement of dental composites by improving the adhesion of the filler to the polymer matrix. Polymerization shrinkage is reduced, wear resistance is enhanced, and optical properties are improved. With these two features, HBN and MSN are exceptionally good candidates: Hexagonal Boron Nitride (HBN): Like graphene, HBN has a layered crystalline structure. Its thermal conductivity is higher, and it is more chemically stable and mechanically stronger. Apart from these properties, its HBN's natural lubricating features, owing to its wear resistance, make it appropriate for use at high mechanical loads, like in dental restoration. Mesoporous Silica Nanoparticles (MSN): MSN exhibits exceptionally high surface areas, is porous, and is biocompatible. These features guarantee adequate dispersion in the composite matrix and enable the incorporation of antibacterial substances that help in the control of biofilms and bacterial growth (Wang et al., 2020). Mechanical Performance and Load-Bearing Capacity: The composite’s mechanical properties improved significantly with the use of nanotechnology (in comparison to their components) (Xu et al., 2021). Studies show that HBN increases compressive strength, while MSN is efficacious for crack resistance and wear resistance (Borges et al., 2019; Sharma et al. 2021). 1.2.2. Advantages of Nanotechnology in Dental Materials: The application of nanotechnology in dental composites has a number of obvious advantages. Advanced Mechanical Properties: Added nanofillers in a dental composite result to an increase in compressive strength, elastic modulus, and even fracture toughness because they minimize stress concentrations and crack propagation. Improved Aesthetics: As a result of enhanced optical properties, composites can replicate the natural translucency of enamel due to the submicroscopic size of nanofillers. Antimicrobial Activity: The use of MSN incorporated antimicrobial agents nanofillers is said to decrease bacterial colonization and biofilm formation.Long-Term Durability: The extended life span of restorations is said to be better with the use of nanofillers due to their enhancing effect on thermal, chemical, and hydrolytic stability. This makes dental construction more convenient and easier for the patients and dentists therefor saves time and money. These advantages underscore the transformative potential of nanotechnology-based dental composites.________________________________________ 1.3. Research Scope and Objectives: Because of the very convincing use of nanofillers HBN and MSN, this review set out to fully analyze their effects on the structural, mechanical, thermal, and antimicrobial properties of dental composites. The focus of the analysis is on the systematic analysis done by Kaptan Usul et al. (2024) that studied combination of HBN and MSN in a bis-gma tegdma polymer matrix at different weight fractions 5 % and 10 %. 1.3.1. Major Areas of Concern in Research: As with any review, a few key research questions have been set forth: Structural Integrity: In what ways do HBN and MSN affect the bonding, crystallinity, and dispersion relativities of the dental composites? Thermal Stability: How much do these nanofillers increase the thermal and glass transition temperatures of the dental composites? Mechanical Performance: In what way do HBN and MSN affect the compressive strength, elastic modulus and fracture toughness of the composites? Antimicrobial Efficacy: To what degree do the composites interact with the most aggressive oral biofilm pathogens and what level of biofilm resistance do the composites provide? Long Term Durability: How resistant are HBN- and MSN-based composites to hydrolytic degradation, chemical erosion and wear in the oral environment? 1.3.2. Research Goals: The aims of this review are as follows: • Examine Structural Features: Study the molecular bonding, crystallinity, and the dispersion of the nanoparticles. • Assess Other Associated Mechanical Properties: Evaluate load-bearing capacity, thermal stability, and deep time durability. • Investigate Effects on Microorganisms: Measure antimicrobial activity with MIC, MBC, and biofilm inhibition tests. • Note Existing Knowledge Deficits: Indicate inactive problems such as wear resistance, cytotoxicity, and the ability to mass produce the composites. • Recommend Subsequent Research: Suggest to other researcher’s functionalization of the advanced nanoparticles along with biocompatibility and clinical testing.________________________________________ Accomplishing objectives gives this review greater depth with regards to HBN and MSN-based dental composites. Their scope may extend to restorative dentistry, where the development of next generation composites with enhanced functionality, mechanical durability, and improved clinical outcomes is highly desired. 2. Methodological Framework ________________________________________2.1. Composite Fabrication:________________________________________Dental composites were created by incorporating HBN and MSN at weight percentages of 5 and 10, respectively into a bisphenol A glycidyl methacrylate (Bis-GMA)/TEGDMA polymer matrix. During the curing process, photopolymerization was employed to facilitate proper dispersion and avoid agglomeration (Kaptan Usul et al., 2024, p. 2297).________________________________________ 2.2. Analytical Techniques: 2.2.1. Structural and Morphological Analysis: FTIR Spectroscopy: Validated the chemical interaction between the fillers and the polymer matrix.XRD: Provided information on the crystalline structure and phase composition.SEM-EDS: Confirmed the fillers were well distributed in the resin material with little to no gaps.TGA and DSC: Demonstrated significant thermal stability and a high glass transition temperature (Kaptan Usul et al., 2024).________________________________________   2.2.2. Thermal Characterization: TGA Analysis: The composites with MSN counterparts showed thermal stability of up to 1000°C with a weight loss of 1.44% (Kaptan Usul et al., 2024, Fig. 5). DSC Analysis: DM10 sample due to better filler-matrix interaction achieved the highest glass transition temperature (Tg) of 218°C (Kaptan Usul et al., 2024, Fig. 6).________________________________________ 2.2.3. Mechanical and Antimicrobial Testing: Mechanical Strength: HMP presented the highest compressive strength of DM5 composites at 103.48 MPa compression, which is exceedingly higher than the superset of commercial composites like Filtek Supreme Ultra (Kaptan Usul et al., 2024, Fig. 8). Antimicrobial Efficacy: For the MIC test, HMP composites were able to mitigate E. coli and S. aureus growth at concentrations of 1-5 mg/mL (Kaptan Usul et al., 2024, Table 4).________________________________________ 3. Experimental Insights This part analyzes in detail the results of the experiments aiming at the structural, mechanical, thermal, and anti-microbial characteristic of the HBN and MSN modified dental composites. The clear morphological uniformity, mechanical integrity, chemical stability, and antimicrobial characteristics of the materials is explained by numerous advanced characterization techniques. ________________________________________3.1. Morphological and Structural Integrity________________________________________ 3.1.1. Intermolecular Forces and Chemical Bonds: An analysis of the Fourier transform infrared highlights spectroscopy (FTIR) indicates that the structural characterization assures some degree of success with regard to the incorporation of the nanofillers. The distinct peaks at 1327cm?¹ reported are due to B-N stretching vibrations from hexagonal boron nitride (HBN) confirming its chemical bonding within the Bis-GMA/TEGDMA polymer matrix. The other peaks appearing in the range of 1045-1100cm?¹ were due to stretching vibrations of Silicate mesoporous particles (MSN) silica that showed the existence of silicate frameworks that are stable. Because of this synergistic bonding a molecular network was formed which in turn greatly improved the rigidity as well as the chemical stability of the polymer matrix (Kaptan Usul et al. 2024, Fig 1). The degree of polymerization for the nanofillers and the resin matrix provided a chemical bond that prevented interfacial debonding which is characteristic of most other dental composites.________________________________________ 3.1.2. Composition of The Crystallinity and Other Phases: X ray diffraction (XRD) studies showed that the hexagonal crystalline configuration of HBN possessed characteristic sharp diffraction peaks at 26.8o (002 Plane) and 41.7o (100 Plane) which were previously identified. These peaks have sharpness, suggesting the existence of moderately ordered HBN crystallites. On the other side the dulling of intensity of the broad peaks indicate the predominating amorphous nature of the MSN This implies that MSN provides flexibility, which is mechanical, and HBN offers rigidity, which is structural (Kaptan Usul et al 2024 Fig 2) The hybrid structure effectively balanced mechanical strength with toughness, which is fundamental for load-stressed toothing restorable dentures. Dual-phase crystallinity was important in the improvement of resistance to cracking and the reduction of brittleness.________________________________________ 3.1.3. Microstructural Homogeneity: SEM/EDX imaging convinced us that the polymeric matrix contained uniformly distributed nanoparticles. Some degree of nanofillers agglomeration was observed, demonstrating that the pre-polymerization mixing step worked properly. Elemental mapping confirmed the presence of boron, nitrogen, and silicon, proving that both nanofillers were incorporated successfully (Kaptan Usul et al. 2024, Fig. 3). The uniformly dispersed nanoparticles inhibited micro voids formation that can weaken composites by providing sites for fracture propagation. This morphologic homogeneity increased resistance to mechanical erosion and deterioration of the composites, which are otherwise likely to fail prematurely.________________________________________ 3.2. Thermal Stability and Degradation Resistance________________________________________ Thermal Stability and Durability: HBN and MSN nanofillers are well known for their high thermal conductivity and hence, can be used in load bearing toothing dentures without any reservations (Singh et al., 2023). Also, the thermal stability of MSN reduces the rate of polymer degradation while in oral cavity (Lu et al., 2023). 3.2.1. Indicators for Thermal Stability: TGA confirmed that HBN-MSN composites exhibits superior thermal resistance. Even at aggressive temperatures near 1000 °C, the DM5 and DM10 composites suffered little weight loss (1.44%) when compared to traditional composites. The heightened weight resistance these composites exhibited was explained by HBN's hexagonal lattice structure and MSN's thermal barrier capabilities (Kaptan Usul et all, 2024, Fig. 5). Due to the inorganic makeup of these nanofillers, the composites are applicable for high temperature dental applications such as crowns and bridges as they do not experience thermal decomposition prematurely.________________________________________ 3.2.2. Glass Transition Temperature (Tg): DSC analysis showed marked increase in glass transition temperature (Tg) of 218 °C for the DM10 composite suggesting strong polymer cross linking as a result of filler matrix bonding. Improved interfacial adhesion between the nanofillers and polymer matrix resulted in greater restriction of segmental chain movement increasing Tg (Kaptan Usul et al., 2024, Fig 6). The aforementioned composite also has enhanced structural integrity which enables it to withstand long term clinical applications which includes exposure to fluctuating oral temperatures. The high Tg ensures that the polymer does not soften under functional stress.________________________________________ 3.3. Mechanical Properties and Load Capacity: Composites' mechanical features are said to be significantly enhanced with the addition of nanotechnology (Xu et al., 2021). Research indicates that while HBN improves compressive strength, MSN aids in wear and crack resistance (Borges et al., 2019; Sharma et al., 2021).________________________________________ 3.3.1. Compressive Strength and Elastic Modulus: The mechanical testing results highlighted a stunning increase in load-bearing capacity of composite materials. The DM5 composite recorded outstanding performance with a compressive strength of 103.48 MPa, which is higher than that of the commercial materials, such as Filtek Supreme Ultra. This enhancement was ascribed to the agglomeration and the strong interfacial bond between the fillers and matrix materials (Kaptan Usul et al., 2024, Fig. 8). Due to the nature of the elastic modulus increased with the of HBN in the matrix. On the over 10 % HBN the strength due to the in highly composites.________________________________________ and to The and composites exhibited increased fracture toughness, which is a result of the with the layered structure of The as mechanical and crack In particles of MSN the stress increased the mechanical strength (Kaptan Usul et al., 2024, p. These characteristics improved fracture toughness, the use of crowns and bridges for   Antimicrobial Activity: The composites inhibited the growth of microbial colonization of biofilm pathogens like Escherichia coli, aureus and Saccharomyces et al., 2020). Antimicrobial Efficacy: of MSN into dental composites improves the biofilm resistance of the composite which is important in secondary caries et al., 2020). More high like Escherichia coli and aureus et al., and Methodological Analytical of advanced characterization such as infrared spectroscopy X-ray diffraction with spectroscopy analysis and thermal analysis into a This to the structural, thermal, and mechanical of the composite and enhances the of the reduction (Kaptan Usul et al., 2024, p. 2297).________________________________________ The of HBN and MSN greatly enhanced the performance of the composites. crystalline material provided mechanical strength as well as thermal the MSN's high surface and for greater filler dispersion and improved antimicrobial These synergistic fillers the challenges presented by conventional filler (Kaptan Usul et al., 2024, p. of for Antimicrobial Activity: The composite was for antimicrobial activity traditional like and The results indicate that the composites demonstrated range toxicity like Escherichia coli, and Saccharomyces with an MIC range of 1-5 This superior the of the materials in the of biofilm and dental (Kaptan Usul et al., 2024, Table 4).________________________________________ of Mechanical Properties: The results of the mechanical testing provided clear of enhanced load-bearing and The DM5 composite commercial dental composites such as Filtek Supreme Ultra by a compressive strength of 103.48 This was due to which was above a level to cavity and stress concentration within the matrix (Kaptan Usul et al., 2024, Fig. of Structural and Thermal Stability: The composites also showed the thermal stability with the weight loss and the highest glass transition temperatures The use of MSN greater thermal resistance due to improved filler-matrix along with strong resistance to thermal The DM10 composite, which a Tg of 218 degree its towards the development of dental restorations (Kaptan Usul et al., 2024, Fig. 6).________________________________________   of and Testing: The of triobological testing is the wear resistance, surface and dental composites undergo actions from and with wear testing with known such as and wear would help the for Stability and Even though it was that water and thermal stability was the was in long term like hydrolytic degradation, thermal and chemical in These are fundamental to the of the composites and in the oral in and of the is the lack of in and biocompatibility testing with like and biocompatibility with would the of the composites for extended clinical with Other Composites: Even with the composites’ they were not alongside other used dental materials like Filtek Supreme and Ultra. A would set the materials their commercial counterparts in to and and of Insights for This not into the of the of materials, cost efficient and of such as and polymerization are to from results to and bond Strength The not the bonding strength of the composites with the enamel and Some adhesion for bond strength and micro bond strength would their in dental restorations such as cavity and Research focus the of biocompatibility to materials for clinical use with commercial also et al., and Testing: The and wear resistance of the materials and their surface together with be testing procedures such as These would the over with the aid bearing   and undergo stability like hydrolytic degradation, and as well as in with The would a of the composites’ stability over time within the oral of and dental and in biocompatibility is also to with and Dental to of clinical of Advanced The incorporation of or in the filler matrix would capabilities and also enhance antimicrobial and nanofillers are to properties even of Composite and Strength: properties be by means of adhesion of and bond strength The results their application in cavity and Studies of and are that further for and control would enable and The with over time be need to longevity of resistance to bacterial and and commercial dental composites would help the and their along with and with the form the of these challenges and these it is that HBN- and MSN-based dental composites have the potential to be and materials in the restorative and The combination of HBN and MSN modified dental composites which have increased mechanical durability, thermal resistance, and antibacterial activity. Research focus be at the durability, the of mass production, and clinical testing for application of the materials in