Biomedical Research Journal

: 2021  |  Volume : 8  |  Issue : 1  |  Page : 14--19

Effect of different thermal change tests of micro tensile strength behavior bio-composite materials; In vitro study

Efe Çetin Yilmaz1, Recep Sadeler2,  
1 Department of Control Systems Electrical and Electronic Engineering, Faculty of Engineering and Architecture, Kilis 7 Aralık University, Kilis, Turkey
2 Department of Mechanical Engineering, Faculty of Engineering, Ataturk University, Erzurum, Turkey

Correspondence Address:
Prof. Efe Çetin Yilmaz
Department of Control Systems Electrical and Electronic Engineering, Faculty of Engineering and Architecture, Kilis 7 Aralık University, Kilis


Background: The thermal changes in environments that composite materials are exposed to has a great effect on fatigue and wear behavior. Aim: Micro-cracks and interfacial deformations occur in the composite material structure because of heating and cooling environments occurring on material surfaces. Considering the environment to which bio-composite materials used in the human body are exposed, it is inevitable that they are exposed to a thermal change cycle environment. Material and Method: In this study, the mechanical behaviors of Silorane, X-Trafil and Valux-Plus bio-composite materials were examined after being exposed to thermal cycles in an artificial mouth environment in the temperature range of minimum 5 °C and maximum 65 °C. Micro-tensile strengths of bio-composite materials after thermal cycle test procedures were determined using a universal micro tensile tester device. In addition, microstructural analyzes of bio-composite materials were evaluated using scanning electron microscopy (SEM). Results: Within the scope of the data obtained as a result of this study, it was concluded that the thermal changes in environments significantly affects the micro-shrinkage behavior of bio-composite materials. Conclusion: The behavior of the matrix structure of the composite material significantly affected the formation of micro cracks.

How to cite this article:
Yilmaz EÇ, Sadeler R. Effect of different thermal change tests of micro tensile strength behavior bio-composite materials; In vitro study.Biomed Res J 2021;8:14-19

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Yilmaz EÇ, Sadeler R. Effect of different thermal change tests of micro tensile strength behavior bio-composite materials; In vitro study. Biomed Res J [serial online] 2021 [cited 2023 Dec 2 ];8:14-19
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In vitro testing remains an essential method for the initial screening of dental materials. Thermal cycling is one of the most widely used procedures in clinical practice to simulate physiological aging experienced by biomaterials.[1] In vitro test mechanisms in the laboratory environment are of great importance due to the various difficulties encountered in studies on in vivo studies. The data obtained from thermal cycle tests in a laboratory environment contribute greatly to in vivo studies. Literature shows that many authors have simulated various in vitro test mechanisms such as artificial aging, three-body wear, two-body wear, etc.[2],[3],[4],[5] The data obtained from these studies can give information about the mechanical and esthetic behavior of a material during its stay on living tissue. Restorative materials should be resistant to environmental conditions that vary from patient to patient.[6] For example, mastication forces, occlusal lives, dietary factors, humidity, and temperature fluctuations contribute to uncontrollable factors that can affect the life of materials.[6]

Thermal cycling has been used extensively in dental research for about 70 years, when it was observed that cooled, restored teeth produce an “exudate” from the restoration edges when teeth are heated.[1] This system has traditionally been used to simulate in vivo aging of restorative materials by repeated cyclical exposures to hot and cold temperatures in a water bath to reproduce thermal changes occurring in oral cavity.[1] It is very important to select minimum and maximum temperatures in thermal cycle tests performed in the laboratory environment. [Figure 1] gives examples of the temperatures of the absorbed fluids and the resulting average minimum and maximum tooth surface temperatures.[7] Human saliva is a liquid of complex composition, which includes organic and inorganic groups and microorganisms. Dental composites must be able to withstand contact between the oral cavity and saliva. In literature, authors have also investigated the effect of liquids (artificial saliva and deionized water) on the mechanical properties of resin-based composites.[8] It is known that artificial saliva has a lubricating effect on dental and dental composites. In recent years, composite materials have been used in various structures of fillers that can be polarized using blue light technology.[9] Dental composite materials are usually heterogeneous materials with a polymer matrix, inorganic fillers, and a silane-matrix coupling.[2] The amount and size of filler particles included in the composite resin matrix can determine each type of composite and ultimately the most beneficial clinical application. It has been reported that damage to composite materials on living tissues may result from degradation of the matrix and filler materials, or it may be the result of mechanical and external stress, microcracks, or destruction of filler particles, which may reduce the likelihood of composite restorations being retained in in vivo ambient.[10]{Figure 1}

In recent years, the high biocompatibility, mechanical, and esthetic behavior of composite materials have increased their use in the field of health. It is one of the common conditions, in which the tooth is demineralized due to the acidic environment created by the degradation products released by microorganisms in the oral cavity.[11] The strategy of treating dental caries that causes tooth destruction often involves the removal of caries and composite filling to restore the function, integrity, and morphology of the missing structure.[12],[13] Significant progress in nanometer-scale process technology and the application of nanohybrid composites led to a substantial improvement in the properties of resin-based composites.[11],[14] The particle size distribution of reinforced fillers such as alumina, zirconia, silicon oxide, silicate glasses, and others in composite resins ranges from macrofilled or conventional composites (up to 50.0μm) to nanofilled composites (0.005–0.04μm).[11] Silane-treated fillers are often used to improve the bonding between resin and filler. However, the improvement of mechanical properties by most microfillers for resin-based composites is not suitable for stress-bearing areas and is therefore often used in nonstress areas, frontal areas, or a sandwich technique.[11] Therefore, high aspect ratio materials such as Si<Subscript>3</Subscript>N<Subscript>4</Subscript>, SiC whiskers, tetrapod whiskers, inorganic fibers, halloysite nanotubes, and polymer fibers are incorporated into composite resins to improve the mechanical strength of composites.[11],[15]

 Materials and Methods

In this study, the mechanical behaviors of Silorane, X-Trafil, and Valux-Plus bio-composite materials were examined after being exposed to thermal cycles in an artificial mouth environment in the temperature range of minimum 5°C and maximum 65°C. [Table 1] shows the mechanical and chemical properties of biocomposite materials tested in this study. The monomer structures of the composite materials are different from each other. The reason for choosing these composite materials is to evaluate the effect of thermal cycle experiments on different monomer structures. The surface temperatures of the test samples were detected by the thermal sensor with a frequency of 50 Hz. It was decided to change the ambient temperature of the test sample by processing the data received by the microprocessor. Thus, temperature changes on the test sample are instantly processed as real-time data. [Figure 2] shows the electronic circuit systematics of the thermal cycle test. During the preparation of test samples, the hardening process using a conventional Quartz-Tungsten-Halogen (QTH) polymerization device was performed under conditions determined by the manufacturer (Elipar TriLight, 3M ESPE, 750 mW/cm2). Composite materials were exposed to the control group, 3000, 6000, and 12,000 thermal cycle and temperature dwell time 30 sn in artificial saliva ambient. The chemical components of the artificial saliva fluid used in thermal cycle test environments are shown in [Table 2].[16] The artificial saliva fluid was recreated in 24 h periods because of chemical degradation. The mechanical behavior of the composite material was determined using a microtensile device after each thermal cycle test group. In this study, composite materials, 1 × 1 mm2 sized stick-shaped samples were prepared for the microtensile test which was subjected to a water-cooled cutting device (BIS Co JAPAN). [Table 3] summarizes the one-way ANOVA results of analysis of microhardness composite materials with changes in thermal environments. The test specimens were in a pulled single axis with a microtensile tester up to the fracture mechanism. Fi[gure 2] shows an example of a cutting and microtensile test device mechanism. Micro analyses were performed from the fractured surfaces of the test specimen using scanning electron microscopy after thermal cycle test procedures.{Table 1}{Figure 2}{Table 2}{Table 3}


The mechanical behavior of composite materials after thermal cycle tests is shown in [Figure 3]. As can be seen, Silorane, X-Trafill, and Valux-Plus composite materials have shown the highest mechanical behavior in the control group test procedure. It can be considered that silane whiskers in a matrix structure in Silorane composite are provided with the highest mechanical behavior. All composite materials showed lower mechanical behavior with an increase in the number of thermal cycles. As a result, it is possible to say that the matrix structure of composite materials weakens with the increase in the number of thermal cycles. It has also been reported that the mechanical and esthetic behavior of composite materials changes after thermal cycle tests.[3],[17],[18] [Figure 4] shows the microtensile strength behavior of composite material after different thermal cycle test procedures. When the number of thermal cycling tests increased, the fracture resistance of composite materials decreased in artificial saliva ambient test procedures. [Figure 5] shows microstructure analyses of composite materials after 12,000 thermal cycle test procedures in artificial saliva ambient. [Figure 5] depicts the images of microstructure taken from the fractured surfaces of composite materials. The study showed that thermal cycle procedures caused deformation in the microstructure. It is known that microfractures on the surfaces of composite materials occur as a result of thermal expansion. Different monomer structure of composite materials has varying effects of the thermal expansion of the material. This is because temperature changes in the environment cause the composite material to exhibit different behaviors within the monomer structure. The size of the cracks formed after 12,000 cycles negatively affected the microtensile bond strength value. The reason why Silorane dental filling material has a higher microtensile bond strength value compared to the other two materials can be explained by the smaller crack lengths. As a result, it may be concluded that the thermal changes in environments cause different rates of expansion within the composite material.{Figure 3}{Figure 4}{Figure 5}


It is of great importance to determine the thermal behavior of composite materials, as it is inevitable that these materials can be exposed to thermal cycling environments on living tissue. Therefore, many test mechanisms that can simulate the thermal cycling environment have been developed.[1],[3],[17],[19] In the simulations performed in the laboratory environment, it is of great importance that the test parameters are included in the system in a short time and the system responds quickly in terms of accuracy of the test results. In this study, sensing the thermal environment with a thermometer at 50 Hz frequency response time without contact increased the sensitivity of the thermal exchanges in environments. In addition, the control of the system components by the 16FXX microprocessor increased the sensitivity in the application of the experiment parameters. Finally, the experimental data received from the 16FXX microprocessor was transferred to the computer environment through a parallel port, and the data were processed instantly. Thus, the thermal change data during the experiment were analyzed in real time. The creation of the test system with computer-controlled real-time data analysis enabled the same parameters to be applied to the specimen during the thermal test cycle.

Dental composite resins based on microfillers and conventional nanofillers have led to increased polish retention and are often used to maximize esthetics in the anterior region.[20] However, the posterior region is a pressure-bearing region and nanophase often offer insufficient power due to the particle cluster (aggregate) phenomenon.[20] Composites are blended with large microfillers to increase strength, but they may present a relatively less polished appearance due to their fragility and thus obtain a matte appearance rather than a glossy surface.[21] Therefore, the combined properties of proper strength and durability are considerations when choosing materials for restoration. These composites are desirable as they offer better esthetic properties and require a more minimal space design.[11] Saliva is a complex liquid-containing organic and inorganic groups and microorganisms. Dental composites must withstand the oral environment upon contact with saliva.[8] Several studies have reported that mechanical properties of composites stored in artificial saliva are improved (e.g., Vicker hardness stored for 7 days in artificial saliva). Lubricants such as artificial saliva reduce the coefficient of friction, thereby reducing wear. In addition, artificial circulation of saliva performed during the experiment can remove worn particles from the area of material wear. Therefore, the selection of artificial saliva media in experimental environments will affect the mechanical behavior of composite materials. In order to increase the mechanical behavior of composite materials, it has been proposed that particles in the filler structure should be selected with a harder structure particle.[22],[23] The predominant base monomer used in commercial dental composites was bis-GMA mixed with other dimethacrylates such as TEGDMA due to its high viscosity. UDMA monomer structure refers to another alternative organic matrix composition and is often found in existing compositions. Söderholm et al.[24] suggested that, after 3 years of in vivo clinical studies, urethane-based composites have significantly higher wear resistance than bisGMA-based composite materials.[24] The mechanical and esthetic behavior of composite materials, which are preferred as biomaterials in the field of dentistry, can be improved as time progresses. Improvements in particle size in the monomer structure of the dental composite material created the chemical composition of two different particle structures. The filling structure of the composite material can be named as nano or micro depending on the particle size.[4] Advances in the filling structure of composite materials have given these materials superior mechanical and tribological behavior. There are many studies in the literature investigating the effects of parameters such as chewing force, thermal change, and wear mechanism on the mechanical and tribological behavior on composite materials.[4],[11],[25],[26]

The composite materials tested in this study showed lower fracture resistance as the number of thermal cycles increased. It is possible to say that the thermal cycling process contributes to the occurrence of various deformations in the monomer structure of composite materials. Silorane and X-Trafill composite materials showed similar fracture behavior resistance after thermal cycle procedures. The Valux-Plus composite material showed lower fracture resistance behavior in the control group and thermal cycle tests than Silorane and X-Trail composite material. It has been reported that the monomer organic matrix structure of the composite material has an increasing effect on hydrolytic degradation.[2] The data obtained within the scope of this study showed a decrease in the fracture behavior resistance of composite materials after 6000 thermal cycle test procedures. It can be concluded that the rate of deformation in the monomer structure of the composite material increases after 6000 thermal cycles.


Within the scope of the data obtained as a result of this study, it was concluded that the thermal changes in environments significantly affects the microshrinkage behavior of biocomposite materials. The behavior of the matrix structure of the composite material significantly affected the formation of microcracks. The study showed that thermal cycle tests affect different deformation mechanisms in the composite material monomer structure. Therefore, it is important to consider the thermal cycle parameter in wear and fatigue test experiments conducted in a laboratory.

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Conflicts of interest

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