Effect of Preheating on Mechanical Properties of Different Commercially Available Dental Resin Composites

International Journal of Biomedicine 13(4) (2023) 317-322 http://dx.doi.org/10.21103/Article13(4)_OA14 ORIGINAL ARTICLE INTERNATIONAL JOURNAL OF BIOMEDICINE Dentistry Effect of Preheating on Mechanical Properties of Different Commercially Available Dental Resin Composites Timur V. Melkumyan1,2, Surayo Sh. Sheraliava1, Elena Ju. Mendosa4, Zurab S. Khabadze2, Maria K. Makeeva2,3, Nuriddin Kh. Kamilov1, Shahnoza K. Musoshayhova1, Angela D. Dadamova1, Shukhrat M. Shakirov5, Azad A. Mukhamedov5 Tashkent State Dental Institute, Tashkent, Uzbekistan Peoples’ Friendship University of Russia (RUDN University), Moscow, Russia 3 Sechenov University, Moscow, Russia 4 Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Moscow, Russia 5 Tashkent State Technical University, Tashkent, Uzbekistan 1 2 Abstract Background: This study aimed to reveal the effect of preheating on the surface microhardness and shear strength of composite materials used in the restoration of posterior teeth. Methods and Results: There were 3 composite materials under the study: Estelite Posterior, Harmonize and Filtek Z550. To make static and dynamic tests of them, 120 filling samples were prepared. Of those, 60 samples were for surface hardness measurements and 60 samples were used to evaluate the shear strength of composite materials. We formed 12 study groups with 10 filling samples in each. Samples made off Estelite Posterior, Harmonize™, and Filtek™ were designated with E, H, and F capital letters, respectively; the «VH» abbreviation indicated static Vickers hardness testing and «SS» was assigned for dynamic shear testing; mark (°) was used when preheating was applied. Filling samples were made of heated (up to 60°C) and room-temperature (23-25°C) composite materials. The filling samples of EVH, EºVH, HVH, HºVH, FVH, and FºVH groups were subjected to a surface microhardness test. The samples of ESS, EºSS, HSS, HºSS, FSS, and FºSS groups were subjected to shear-strength assessment of materials. The surface microhardness of filling samples was measured using a ПMT-3 Vickers hardness tester and the Vickers hardness number (VHN) was calculated. Dynamic tests were carried out using an UltraTester machine (Ultradent, Inc., USA) and shear test method until the shear-strength filling sample had completely failed. After analysis of the obtained results, it was found that preheating had enhanced the surface hardness and mechanical strength of the composite materials used in the study. However, the positive influence of preheating was significant only in the EVH-EºVH, ESS-EºSS, HSS-HºSS, and FSS-FºSS groups in 1.48, 1.09, 1.33, and 1.16 times, respectively. In the HVH-HºVH and FVH-FºVH groups, the identified differences were not of significance despite the improvement in mean values at 1.1 and 1.1 times. Conclusion: Preheating of light-curing resin-based composites is not equally effective for static and dynamic mechanical properties of materials for dental restoration. Preliminary laboratory tests could have helped before their clinical use.(International Journal of Biomedicine. 2023;13(4):317-322.) Keywords: composite materials • preheating • Vickers hardness • shear strength For citation: Melkumyan TV, Sheraliava SSh, Mendosa EYu, Khabadze ZS, Makeeva MK, Kamilov NKh, Musoshayhova ShK, Dadamova AD, Shakirov ShM, Mukhamedov AA. Effect of Preheating on Mechanical Properties of Different Commercially Available Dental Resin Composites. International Journal of Biomedicine. 2023;13(4):317-322. doi:10.21103/ Article13(4)_OA14. Abbreviations VH, Vickers hardness; VHN, Vickers hardness number; SS, shear strength. 318 T. V. Melkumyan et al. / International Journal of Biomedicine 13(4) (2023) 317-322 Introduction The limited lifespan of tooth-colored composite restorations caused by their early failure is one of the pressing problems in contemporary dentistry. This situation is multifactorial and may arise from the technological subtleties in the manufacturing process up to the unfavorable interplay of monomers, fillers, and photoinitiators in the composition of restorative systems. Sometimes, direct restoration of teeth can be technically sensitive, not to mention individual characteristics of mandible biomechanics and even minor aberrations in occlusion or tooth position in the arch of each patient.(1-7) Many commercially available composites already have excellent physical properties, chemical stability, and functional and cosmetic characteristics, allowing them to act as a good alternative to expensive ceramic restorations. However, the insufficient strength of resin-based materials is the subject of constant study to improve them.(8-10) In this regard, for more than half a century, studies have searched for better monomers or mixtures. Also, great attention is paid to the size and shape of filler particles with silane-coupling agents and their total weight and volumetric load. In the end, the proper compositions for new materials with exceptional physical properties may be found and used in restoring teeth in areas of high occlusal load.(11,12) It is known that the physicochemical properties of composite restoration largely depend on the quality of the polymer matrix, and the amount of residual bonds is highly influenced by light and thermal energy. It has also been noted that heating composite materials before photoactivation can increase their degree of conversion by reducing the viscosity of loaded polymers and increasing the mobility of free radicals. At the same time, reducing the percentage of remaining double bonds in composite restorations will help to improve their chemical stability and mechanical strength.(12-14) On the contrary, the increase in the conversion degree of double bonds may also be accompanied by high values of polymer volumetric shrinkage, which may cause marginal gap formation and microleakage of restorations. Furthermore, the high rate of polymerization in heated resin-based composites during photoactivation may contribute to the formation of polymer stress, which in turn has a negative effect on the physical properties of the final restoration.(13-17) Most resin-based materials available on the market mainly contain bisphenol-A-glycidyl methacrylate (BisGMA), urethane dimethacrylate (UDMA), triethylene glycol dimethacrylate (TEGDMA), and bisphenol-A-ethoxylatedglycidyl dimethacrylate (Bis-EMA). The properties of these monomers have been well studied separately and are not of particular interest. However, their mixtures are the subject of ongoing research.(18) Besides the organic matrix, the strength of a composite filling is predetermined by the amount and size of filler particles. In particular, the improvement in the mechanical properties of composite materials with high filler load has been confirmed by the results of static and dynamic tests.(19) The main objective of other studies was to assess the influence of filler particle shape on the shrin (...truncated)