1 Volume 23 2024 e242664 Original Research Braz J Oral Sci. 2024;23:e242664http://dx.doi.org/10.20396/bjos.v23i00.8672664 1 School of Dental Sciences, Health Campus, Universiti Sains Malaysia, Kubang Kerian, 16150 Kota Bharu, Kelantan, Malaysia. Corresponding author: Raja Azman Raja Awang Tel: +609-767-5808 Fax: +609-767-5505 E-mail: rjazman@usm.my Editor: Dr. Altair A. Del Bel Cury Received: February 11, 2023 Accepted: March 4, 2024 Characterisation and properties of Nanohybrid Dental Composite (NhDC) reinforced with zirconia and alumina Nurul Najwa Mohd Nordin1 , Noor Huda Ismail1 , Dasmawati Mohamad1 , Mohd Firdaus Yhaya1 , Raja Azman Raja Awang1* A trial nanohybrid dental composite (NHDC) was developed using silica extracted from biowaste rice. Aim: This study aims to test the effect of mixture of the silica and other filler which is zirconia and alumina, focusing on the characterization and their properties. Nano-silica obtained from rice husk was used as NHDC filler. Methods: Nanosilica white powder, derived from rice husk, was used. There were three groups: Group I, Zr (2%) and Al (3%); group II, Zr (3%) and Al (2%); and group III, Zr (3%). The distribution of filler particles and the chemical structure of filler particles were determined by FESEM images and FTIR test. Then, testing on Vickers hardness (VHN) and fracture strength (FS) of the samples was performed. Results: The distribution of filler particles showed a uniform distribution, and each peak element of the fillers was shown in the FTIR spectrum images. There was significantly increased on VHN and FS after addition of zirconia and alumina. Conclusion: This study concluded that zirconia and alumina strengthen the NHDC properties with addition of zirconia and alumina filler. Keywords: Composite resins. Aluminum oxide. Zirconium. Spectroscopy, fourier transform infrared. Flexual strength. https://orcid.org/0000-0003-1479-4908 https://orcid.org/0000-0002-5018-6048 https://orcid.org/0000-0001-8746-3742 https://orcid.org/0000-0001-8725-3489 https://orcid.org/0000-0001-6106-3839 2 Nordin et al. Braz J Oral Sci. 2024;23:e242664 Introduction Prior research improved dental composites in filler development till the 1990s. Filler sizes1 and composition of dental fillers have changed dramatically over the years. Along with filler size and composition, the amount of filler2 has been varied throughout a wide range3. Nowadays, resin composite consists of organic resins, inorganic fillers and initiator systems4. As coupling agents, silane derivatives are covalently linked to inorganic fillers to increase filler particle bonding5,6. The material of dental composite advancement can be classified into three catego- ries: development of the filler phase, modification of resin monomers or introduction of new monomer systems7, development of the initiator system8 and introduction of new monomer systems9,10. The majority of dental composites used in dental resto- rations are made up of a resin matrix and silane-treated nonporous inorganic fillers in a variety of sizes and shapes11. In 1985, the average size of the inorganic filler was used to classify composite filling materials, and it remained the standard in subse- quent studies12. In this study, we are employing zirconia and alumina as fillers in the reinforcement of dental composite, which is a limited study found. The characteristics of fillers were established using FTIR and FESEM equipment, and the properties will be evaluated using Vickers hardness and fracture strength. Materials and Methods i-Materials and Reagents The experimental nanohybrid composite was prepared using resin matrix and filler at a 52/48 ratio. For the resin matrix, 50% urethane dimethacrylate (UDMA) (Merck KGaA, Germany) was used as a base-monomer and 50% TEDGMA (Sigma Aldrich, Germany) as a diluent. Three types of fillers were used in the study which were silica (SiO2), zirco- nium oxide (ZrO2) and aluminium oxide (Al2O3). This study used a sol-gel technique as in past study13, nano-sized zirconia was purchased from US Research Nanomaterials (USA) and macro-sized alumina was purchased from Merck KgaA (Germany). Cam- phorquinone (CQ) (Merck Schuchardt OHG, Germany) and DMAEMA (Merck, Germany) also were added as visible light photo-initiator and co-initiator, respectively. ii-Extraction of silica powder and silanisation Rice husks were gently washed with water and dried in a 110°C hot air oven overnight14. The dried rice husks were treated to 1M HCl solution in a hot water bath for 90 minutes and dried again in a hot air oven. Then, 10% NaOH solution was added in the dried husk at 90°C to extract silica as described from a previous study15. All fillers were dried at 80°C in oven after silanisation using 6 wt.% γ-MPS. FTIR analysis was used for characterization. iii-Fabrication of NHDC Camphorquinone (0.01 wt.%) and DMAEMA (0.01 wt.%) was mixed in a matrix resin (UDMA/TEGDMA, 50/50 wt.%). The silanated fillers were added to the mixture and blended homogeneously. 3 Nordin et al. Braz J Oral Sci. 2024;23:e242664 The trial nanohybrid dental composite (NHDC) was grouped into three groups depend- ing on the percentage of zirconia and alumina component: Group I, Zr (2%) Al (3%); Group II, Zr (3%) Al (2%); and Group III, Zr (3%) Al (0%). A negative control group was no addition of filler other than silica whereby commercial Z250XT (3M ESPE, St. Paul, MN, USA) was a positive control group. iv- Characterisation and mechanical tests The NHDCs were characterised using Fourier Transform Infrared Spectroscopy (FTIR), IRTracer 100 (Shimadzu, Japan) and FESEM (FEI Nova NanoSEM 450, US), followed by their mechanical tests. Fracture Strength (FS) Test To test FS, a split stainless steel mould (25 × 2 × 2 mm)16-18 was used to prepare n=6 samples per group. All samples were cured using the light-emitting diode curing unit (Elipar™ Freelight 2 LED, 3 M ESPE). The samples were tested at a crosshead speed of 0.75 mm/min14 using a universal testing machine (Model AG-X Plus Series Shimadzu, Japan) for FS test. Vickers Hardness (VHN) Test To test VHN, an acrylic mould (5 mm diameter and 2 mm thick) was used to prepare n=6 samples per group. All samples were tested for VHN using a Vickers’ hardness tester (Model VM 50, FIE) with 1 kg load 15 seconds dwelling time19. Results Characterisation of Silica Powder from Rice Husk i-FESEM (a) unsilaned silica powder (left) (b) silaned silica powder (right) Figure 1. FESEM images of silica powder 4 Nordin et al. Braz J Oral Sci. 2024;23:e242664 ii-FTIR Tr an sm itt an ce (% ) Wavenumber (1/cm) 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 800 600 4001200 1000 Tr an sm itt an ce (% ) Wavenumber (1/cm) 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 800 600 4001200 1000 Tr an sm itt an ce (% ) Wavenumber (1/cm) 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 4000 3800 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 800 600 4001200 1000 (b) Zirconium oxide (ZrO2) nanoparticles (c) Alumina (Al2O3) microparticles Figure 2. FTIR spectra of fillers (a) Silica (SiO2) nanoparticles 5 Nordin et al. Braz J Oral Sci. 2024;23:e242664 Fracture Strength Table 1.Fracture strength evaluation of experimental NHDC NHDC Mean, MPa (SD) F statistic (df) p-value No reinforced filler 73.387 (23.401)π Reinforced Zr (3%) & Al (2%) 70.003 (3.453)π Reinforced Zr (2%) & Al (3%) 80.943 (12.317)π 9.560 (4,25) p = 0.0001* Reinforced Zr (3%) only 81.512 (16.253)π Commercial FiltekTM Z250XT 127.325 (26.911)* Statistical significance of differences among groups was determined using One-way ANOVA, followed by post-hoc Tukey Test. *Significance level set at p = 0.05. The asterisk symbol (*) represents a statistically significant difference when compared to no reinforced filler NHDC (negative control). The pi constant symbol (π) represents a statistically significant difference when compared to Commercial FiltekTM Z250XT (positive control). SD = standard deviation; Zr = zirconia; Al = alumina Vickers Hardness Table 2. Vickers hardness evaluation of experimental NHDC NHDC Mean, HV (SD) F statistic (df) p-value No reinforced filler 24.310 (4.040)π 22.77 (4,25) p = 0. 0001* Reinforced Zr (3%) & Al (2%) 29.250 (7.910)π Reinforced Zr (2%) & Al (3%) 34.400 (11.080)π Reinforced Zr (3%) only 34.560 (2.730)π,* Commercial FiltekTM Z250XT 61.760 (8.360)* Statistical significance of differences among groups was determined using One-way ANOVA, followed by post-hoc Tukey Test. *Significance level set at p = 0.05. The asterisk symbol (*) represents a statistically significant difference when compared to no reinforced filler NHDC (negative control). The pi constant symbol (π) represents a statistically significant difference when compared to Commercial FiltekTM Z250XT (positive control). SD = standard deviation; Zr = zirconia; Al = alumina Discussion Characterisation of Silica Powder from Rice Husk i-FESEM Figure 1 shows SEM images of the synthesized nanosilica before and after silanization at 50,000x magnification. Figure 1a (unsilane silica powder) shows that the surface silica is agglomerated and heterogeneous before silanization, while Figure 1b (silanized silica powder) shows that the treated silica surface is uniform and widely distributed. ii-FTIR Figure 2 depicts the FTIR spectra of the coupling silane agent γ-methacryloyltrime- thoxypropylsilane (γ-MPS) (A), the filler untreated γ-MPS (B), and the filler treated 6 Nordin et al. Braz J Oral Sci. 2024;23:e242664 with γ-MPS (C). Figure 2a depicts the silica’s FT-IR spectrum. The intense peak at 1722 cm-1 in the γ-MPS spectrum reflects hydrogen bonding between silanol groups, and the band at 2945cm-1 represents the stretching vibrations of the CH3 and CH2 groups (Figure 2a A). The spectra of SiO2 nanoparticles (Figure 2a B) showed the symmetrical stretching vibration of the siloxane bond, Si-O-Si, at 1055 cm−1. The silanol Si-OH symmetry stretching and bending vibration bands, which are found at 802.4 cm-1 and 464.8 cm-1, respectively. The findings of Halvorson et al.20(2003) are compatible with the SiO2 spectrum20. The presence of the stretching vibrations of C-H at 2945 cm-1 and C=O at 1722 cm-1, in the spectra of the treated silica nanoparticles served as evidence that silica silanisation with γ-MPS was effective (Figure 2a C). The strong peak at 1722 cm-1 points to hydrogen bonds between γ-MPS silanol groups (Fig. 2b A) in particles of zirconia. The symmetric and asymmetric stretch- ing vibrations of γ-MPS’s alkyl groups, CH3 and CH2, can be linked to the band at 2945 cm-1. As mentioned by Zidan et al.21(2021) the peak between 3650 to 3200 cm-1 were attributed to O–H (hydroxy group) bending vibration on the nanozirconia particles21. According to Patel et al.22(2017), the absorption at the lower peaks are due to Zr–O and Zr–O2–Zr vibrational stretch, respectively22. The stretching vibra- tion C=O (carbonyl group) at 1722 cm-1 corresponds to Zr-O bending vibration, which confirms the successful of treated ZrO2 nanoparticles with γ-MPS (figure 2b C). Meanwhile, the silanisation for alumina was shown in figure 2 C. The formation of the Al2O3 structure is confirmed by the peak at 1722 cm-1 corresponding to the Al-O bending mode. A strong peak at 1722 cm-1 indicates hydrogen bonding between γ-MPS silanol groups. Symmetric and asymmetric stretches (alkyl groups) of γ-MPS can be determined at the band of 2945 cm-1. Fracture strength Fracture strength (FS) testing provides a reliable predictor of clinical durability23. Experimental NHDCs with a reinforced Zr and Al fillers significantly rise the fracture strength values (p<0.05) compared to the control group (control group). However, it is still inferior to the Z250XT on the market. No reinforcing filler, reinforcing Zr (3%) and Al (2%) were less than 80 MPa. A lower fracture strength may be due to poor inter- facial interaction preventing an efficient stress transfer between the components. In such cases, adding filler particles is expected to increase the number of weak links6,24. The incorporation of alumina25-26 and zirconia as a filler in the composite could help in increase fracture strength27-29. The contents of nanoparticles and microparticle fillers can have a significant effect in increasing the fracture strength of dental composites26. Vickers hardness Hardness was used to determine how easy it was to complete the restoration and how long it lasted30. The hardness values of the experimental NHDC reinforced Zr (3%) & Al (2) were significantly higher than the no reinforced filler (control group) (Table 3) (p < 0.05). Addition of Al2O3 filler31-32 into composites increases the hardness of the composites, as suggested by Kiran et al.32 (2018). Furthermore, the zirconia filler reinforcement significantly improved the Vickers hardness33-34. This advantage 7 Nordin et al. Braz J Oral Sci. 2024;23:e242664 is likely due to the properties of the ZrO2 particles and the interfacial shear strength between the nanofiller and the resin matrix35. It can be concluded that an ideal dental composite resin should have low Vickers hardness and high fracture strength to be clinically suggestive of long-term suc- cess in dental restorations. Adding zirconia and alumina fillers to nanohybrid dental composites was shown to increase the Vickers hardness and fracture strength of the composites. Acknowledgements The authors would like to dedicate our deepest gratitude to Universiti Sains Malaysia (USM) for research university grant scheme no. 1001/PPSG/8012215 for the financial support and provides the facilities of lab for works. Authors also thanks to USM staff MDL lab, Kubang Kerian for the technical support. Conflicts of Interest None. Data Availability Datasets related to this article will be article upon request to the corresponding author. Author Contribution Nurul Najwa Mohd Nordin: Conceptualization, Methodology, Investigation, For- mal analysis, Writing- Original draft. Noor Huda Ismail: Validation, Visualization. Dasmawati Mohamad: Validation, Visualization. Mohd Firdaus Yhaya: Supervision, Validation. Raja Azman Raja Awang: Supervision, Writing- Reviewing and Editing. All authors actively participated in discussing the manuscript’s findings and have revised and approved the final version of the manuscript. References 1. Rodríguez HA, Kriven WM, Casanova H. Development of mechanical properties in dental resin composite: effect of filler size and filler aggregation state. Mater Sci Eng C Mater Biol Appl. 2019 Aug;101:274-82. doi: 10.1016/j.msec.2019.03.090. 2. Bociong K, Szczesio A, Krasowski M, Sokolowski J. The influence of filler amount on selected properties of new experimental resin dental composite. Open Chem. 2018;16(1):905-11. doi: 10.1515/chem-2018-0090. 3. Shah PK, Stansbury JW. Role of filler and functional group conversion in the evolution of properties in polymeric dental restoratives. Dent Mater. 2014 May;30(5):586-93. doi: 10.1016/j.dental.2014.02.015. 4. Aydınoğlu A, Yoruç ABH. Effects of silane-modified fillers on properties of dental composite resin. Mater Sci Eng C Mater Biol Appl. 2017 Oct;79:382-9. doi: 10.1016/j.msec.2017.04.151. 5. Habib E, Wang R, Wang Y, Zhu M, Zhu XX. Inorganic fillers for dental resin composites: present and future. ACS Biomater Sci Eng. 2016 Jan;2(1):1-11. doi: 10.1021/acsbiomaterials.5b00401. Epub 2015 Dec 17. 8 Nordin et al. Braz J Oral Sci. 2024;23:e242664 6. Kundie F, Azhari CH, Muchtar A, Ahmad ZA. Effects of filler size on the mechanical properties of polymer-filled dental composites: a review of recent developments. J Phys Sci. 2018;29(1):141-65. doi: 10.21315/jps2018.29.1.10. 7. Peutzfeldt A. Resin composites in dentistry: the monomer systems. Eur J Oral Sci. 1997 Apr;105(2):97-116. doi: 10.1111/j.1600-0722.1997.tb00188.x. 8. Miao X, Zhu M, Li Y, Zhang Q, Wang H. Synthesis of dental resins using diatomite and nano-sized SiO2 and TiO2. Prog Nat Sci Mater Int. 2012;22(2):94-9. doi: 10.1016/j.pnsc.2012.03.006. 9. Atai M, Pahlavan A, Moin N. Nano-porous thermally sintered nano silica as novel fillers for dental composites. Dent Mater. 2012 Feb;28(2):133-45. doi: 10.1016/j.dental.2011.10.015. Epub 2011 Dec 3. 10. Elfakhri F, Alkahtani R, Li C, Khaliq J. Influence of filler characteristics on the performance of dental composites: a comprehensive review. Ceram Int. 2022;48(19):27280-94. doi: 10.1016/j.ceramint.2022.06.314. 11. Samuel SP, Li S, Mukherjee I, Guo Y, Patel AC, Baran G, et al. Mechanical properties of experimental dental composites containing a combination of mesoporous and nonporous spherical silica as fillers. Dent Mater. 2009 Mar;25(3):296-301. doi: 10.1016/j.dental.2008.07.012. Epub 2008 Sep 19. 12. Mota EG, Weiss A, Spohr AM, Oshima HMS, de Carvalho LMN. Relationship between filler content and selected mechanical properties of six microhybrid composites. Rev Odonto Cienc. 2011;26(2):151-5. doi: 10.1590/S1980-65232011000200010. 13. Che Zulkifli NS, Ab Rahman I, Mohamad D, Husein A. A green sol-gel route for the synthesis of structurally controlled silica particles from rice husk for dental composite filler. Ceram Int. 2013;39(4):4559-67. doi: 10.1016/j.ceramint.2012.11.052. 14. Noushad M, Ab Rahman I, Husein A, Mohamad D. Nanohybrid dental composite using silica from biomass waste. Powder Technol. 2016;299:19-25. doi: 10.1016/j.powtec.2016.05.035. 15. Noushad M, Zulkifli NSC, Ab Rahman I, Husein A, Mohamad D, Ismail AR. Nanosilica from rice husk as fillers in dental nanocomposites - a preliminary study. In: International Conference on Advanced Nanomaterials and Emerging Engineering Technologies. IEEE; 2013 Jul 24-26. p. 91-4. doi: 10.1109/ICANMEET.2013.6609243. 16. Chung SM, Yap AU, Chandra SP, Lim CT. Flexural strength of dental composite restoratives: comparison of biaxial and three-point bending test. J Biomed Mater Res B Appl Biomater. 2004 Nov;71(2):278-83. doi: 10.1002/jbm.b.30103. 17. Yap AU, Teoh SH. Comparison of flexural properties of composite restoratives using the ISO and mini-flexural tests. J Oral Rehabil. 2003 Feb;30(2):171-7. doi: 10.1046/j.1365-2842.2003.01004.x. 18. S Sharafeddin F, Motamedi M, Fattah Z. Effect of preheating and precooling on the flexural strength and modulus of elasticity of nanohybrid and silorane-based composite. J Dent (Shiraz). 2015 Sep;16(3 Suppl):224-9. 19. Yusoff NM, Johari Y, Rahman IA, Mohamad D, Khamis MF, Husein A, et al. Hardness of flowable resin composite from rice husk. 2018;5(2):181-90. doi: 10.1016/j.jmrt.2019.04.014. 20. Halvorson RH, Erickson RL, Davidson CL. The effect of filler and silane content on conversion of resin-based composite. Dent Mater. 2003 Jun;19(4):327-33. doi: 10.1016/s0109-5641(02)00062-3. 21. Zidan S, Silikas N, Al-Nasrawi S, Haider J, Alshabib A, Alshame A, et al. Chemical characterisation of silanised zirconia nanoparticles and their effects on the properties of PMMA-Zirconia Nanocomposites. Materials (Basel). 2021 Jun;14(12):3212. doi: 10.3390/ma14123212. 22. Patel SB, Baker N, Marques I, Hamlekhan A, Mathew MT, Takoudis C, et al. Transparent TiO2 nanotubes on zirconia for biomedical applications. RSC Adv. 2017;7(48):30397-410. doi: 10.1039/C7RA03940A. 9 Nordin et al. Braz J Oral Sci. 2024;23:e242664 23. Kramer MR, Edelhoff D, Stawarczyk B. Flexural strength of preheated resin composites and bonding properties to glass-ceramic and dentin. Materials (Basel). 2016 Jan;9(2):83. doi: 10.3390/ma9020083. 24. Foroutan F, Javadpour J, Atai M, Rezaie HR. Mechanical properties of dental composite materials reinforced with micro and nano-size Al2O3 filler particles. Iran J Mater Sci Eng. 2011;8(2):25-33. 25. Farhan AJ, Hussein WA. Effect of alumina contents on the some mechanical properties of alumina (Al2O3) reinforced polymer composites. NeuroQuantology. 2020;18(5):35-42. doi: 10.14704/nq.2020.18.5.NQ20165. 26. Kundie F, Azhari CH, Ahmad ZA. Effect of nano-and micro-alumina fillers on some properties of poly (methyl methacrylate) denture base composites. J Serbian Chem Soc. 2018;83(1):75-91. doi: 10.2298/JSC170118056K. 27. Ahmed MA, Ebrahim MI. Effect of zirconium oxide nano-fillers addition on the flexural strength, fracture toughness, and hardness of heat-polymerized acrylic resin. World J Nano Sci Eng. 2014;4(2):50-7. doi: 10.4236/wjnse.2014.42008. 28. Ismail NH, You LS, Jalil ANA, Ghani NBA, Awang RA. Physical and mechanical properties analyses of zirconia reinforced experimental nanohybrid dental composite (Nhdc) from rice husk. Malaysian J Microsc. 2020;16(2):77-88. 29. Chan KS, Nicolella D, Furman BR, Wellinghoff ST, Rawls HR, Pratsinis SE. Fracture toughness of zirconia nanoparticle-filled dental composites. 2009;6117-24. J Mater Sci. doi: 10.1007/s10853-009-3846-4. 30. Hashemikamangar SS, Meymand MZ, Kharazifard MJ, Valizadeh S. Surface microhardness of a self-adhesive composite in comparison with conventional composite resins. Dent Med Probl. 2020 Jul-Sep;57(3):247-53. doi: 10.17219/dmp/118123. 31. Alsharif SO, Bin Md Akil H, Abbas Abd El-Aziz N, Arifin Bin Ahmad Z. Effect of alumina particles loading on the mechanical properties of light-cured dental resin composites. Mater Des. 2014;54:430-5. doi: 10.1016/j.matdes.2013.07.069. 32. Kiran MD, Govindaraju HK, Jayaraju T, Kumar N. Review-effect of fillers on mechanical properties of polymer matrix composites. Mater Today Proc. 2018;5(10):22421-4. doi: 10.1016/j.matpr.2018.06.611. 33. Lin GSS, Ghani NRNA, Ismail NH, Singbal K, Noorani TY, Mamat N. New Experimental zirconia- reinforced rice husk nanohybrid composite and the outcome of its surface roughness and microhardness in comparison with commercialized nanofilled and microhybrid composite resins. Contemp Clin Dent. 2021 Jan-Mar;12(1):21-27. doi: 10.4103/ccd.ccd_298_20. 34. Wang T, Tsoi JK, Matinlinna JP. A novel zirconia fibre-reinforced resin composite for dental use. J Mech Behav Biomed Mater. 2016 Jan;53:151-60. doi: 10.1016/j.jmbbm.2015.08.018. Epub 2015 Aug 17. 35. El-Tamimi KM, Bayoumi DA, Ahmed MMZ, Albaijan I, El-Sayed ME. The Effect of salinized nano ZrO2 particles on the microstructure, hardness, and wear behavior of acrylic denture tooth nanocomposite. Polymers (Basel). 2022 Jan;14(2):302. doi: 10.3390/polym14020302.