Biomedical Research Journal

ORIGINAL ARTICLE
Year
: 2020  |  Volume : 7  |  Issue : 1  |  Page : 17--22

Effect of contact load upon attrition-corrosion wear behavior of bio-composite materials: In vitro off-axis sliding contact-chewing simulation


Efe Cetin Yilmaz 
 Department of Mechanical Engineering, Faculty of Engineering, Kilis 7 Aralik University, Kilis, Turkey

Correspondence Address:
Dr. Efe Cetin Yilmaz
Department of Mechanical Engineering, Faculty of Engineering, Kilis 7 Aralik University, Kilis
Turkey

Abstract

Background: In recent years, the use of composite materials as biomaterials has been increasing in dentistry. It is important to perform in vitro experiments of biomaterials before living tissue. Aim: The purpose of this work was to examine the effect of contact load upon attrition-corrosion wear behavior of bio-composite materials: in vitro off-axis sliding contact chewing simulation. Material and Method: In this study, 2 mm × 12 mm (weight × diameter) cylindrical test specimens were prepared from Filtek Supreme and Clearfil AP-X bio-composite materials with different filler structure. The surface roughness and Vicker's Hardness values of the bio-composites were measured before the wear test procedures. Then, the test specimens were subjected to off-sliding abrasion test procedures under different mechanical loads in artificial saliva and citric acid medium. Wear volume loss of bio-composite materials was determined after wear test procedures using the three-dimensional noncontact profilometer. Results: As the mechanical loading increased, the loss of wear volume in both composite materials increased irrespective of test medium. However, this increase in wear volume loss in test specimens was more pronounced in the citric acid environment. Conclusion: As a result of, the organic matrix structure (such as Ba glass particle) of the composite material contributes to more volume loss in corrosive environment.



How to cite this article:
Yilmaz EC. Effect of contact load upon attrition-corrosion wear behavior of bio-composite materials: In vitro off-axis sliding contact-chewing simulation.Biomed Res J 2020;7:17-22


How to cite this URL:
Yilmaz EC. Effect of contact load upon attrition-corrosion wear behavior of bio-composite materials: In vitro off-axis sliding contact-chewing simulation. Biomed Res J [serial online] 2020 [cited 2020 Dec 4 ];7:17-22
Available from: https://www.brjnmims.org/text.asp?2020/7/1/17/286558


Full Text



 Introduction



There are three main classes of materials used to treat the tissues and organs of living organisms such as biomaterials (including alloys), polymers (including bio-composites), and ceramics, or to interact with physiological systems.[1] Superior mechanical and esthetic behaviors are expected from the biomaterials placed in the living tissue. For example, sufficient wear behavior is expected from the biomaterials placed in the oral tribology environment because of inevitable-chewing movement. The wear of teeth and dental materials in the oral tribological process can be defined as the net volume loss of the material. It is possible to say that four basic wear mechanisms occur during human-chewing movement. These wear mechanisms are called attrition (two-body), abrasion (three-body), fatigue, and corrosive wear mechanism. Attrition-corrosion wear mechanism is one of the tooth wear type in this process and includes tooth-to-tooth contact in the presence of acids and accordingly contain both mechanical and chemical effects. It is important to understand the nature, mechanical, and chemical behavior of biomaterials as long as it remains in the oral tribology process.[2] Bio-composite materials have been developed continuously and successfully over the past decade.[3] However, it has been reported in the literature that composite materials are still damaged due to insufficient mechanical behavior.[3] For example, about 6.1% of these damages were reported to be due to insufficient wear resistance of the composite materials.[4] Therefore, it is important to be able to determine the wear behavior of composite materials before clinical treatment. In literature, many articles onin vitro wear of composite resins have been published over the years, using various different devices to simulate two and/or three-body wear mechanism process.[5],[6],[7],[8] In order to increase the correlation in the test results of the materials tested inin vitro experiments under laboratory ambient conditions, fixed size test samples are used. In the literature, the test fixed the samples to a certain extent duringin vitro chewing test procedures.[5] In order to determine only the wear resistance of composite materials, the anatomical structure in the living tissue is ignored within the scope of this study.

Ideal dental bio-composite materials provide wear resistance similar to dental tissues. In order to increase the wear resistance of bio-composite materials and to minimize flaking during filler processes, the shape, size, and volume of the filler have been extensively changed in recent years.[9] In the field of dentistry, the classification of composite materials focuses on properties that define viscosity and consistency (e.g. flowable or packable), it is best to consider the mechanical properties of composites and their microstructure classifications.[10] In the manufacture process, new composite materials such as nanohybrid and microhybrid were obtained with reducing the particle size in the inorganic filler structure of the composite materials. The aim of this work was to examine the effect of contact load upon attrition-corrosion wear behavior of nanofilled Supreme and hybrid-filled Clearfil AP-X bio-composite materials;in vitro off-axis sliding contact-chewing simulation.

 Materials and Methods



The mechanical and chemical properties of Supreme with nano filler and Clearfil AP-X composite with hybrid filler tested in this study are shown in [Table 1]. Test samples with a diameter of 12 mm were produced from flowing composite tubes using cylindrical aluminum sample holders. During the preparation of the test samples, hardening process using conventional QTH polymerization device was performed under the conditions determined by the manufacturer (Elipar TriLight, 3M ESPE, 750 mW/cm2). The wear surfaces of the composite materials were polished with 1000 and 600 grit SiC abrasive paper and then embedded in 14 mm diameter size acrylic resin. [Figure 1] shows an example of bio-composite test sample prepared for wear test mechanisms.{Table 1}{Figure 1}

Computer-controlled test mechanism was designed and manufactured to evaluate both off sliding (30° angle on lateral) and contact load upon attrition-corrosion wear mechanism. [Figure 2] shows schematics of the dual-axis off sliding wear simulation test mechanism. Composite test specimens were subjected to 100.000 mechanical loading, 3000 thermal cycles (minimum 5°C and maximum 55°C), and 0.3 mm lateral movement mechanism under different wear forces both artificial saliva and citric acid medium. The pH values of these solutions were measured as about 5.7 and 3.2, respectively. [Table 2] shows the artificial saliva (Fusayama-Meyer) chemical solution in this study used.[11] In each wear test procedure, 6 mm diameter steatite balls were used as antagonist-abrasive material.{Figure 2}{Table 2}

Composite test specimens Vicker's hardness values determined before the wear test procedures. A load of about 19.355 N was applied for 30 s using a pyramidal mold; the depth of the measure represents the hardness of the specimen. Surface roughness of composite test specimens determined the before wear test procedure using atomic force microscopy (Hitachi 5100N). Wear volume loss of composite materials were determined afterin vitro wear test procedures using the three-dimensional (3D) noncontact profilometer (Bruker-Contour GT 3D Vision64). Composite materials microstructure analyses were evaluated using the scanning electron microscopy (Zeiss Sigma 300).

 Results



[Table 3] shows Vicker's hardness and surface roughness values before wear test procedures of tested composite materials. Clearfil AP-X composite material exhibited higher Vicker's hardness and surface roughness behavior than Filtek Supreme. It is possible to say that the hard Ba glass particles contained in the monomer structure of the Clearfil AP-X composite material increased matrix hardness. [Table 4] shows that mean wear volume loss values after off-sliding wear test procedures of in this study tested composite materials.{Table 3}{Table 4}

[Figure 3] shows noncontact two-dimensional and 3D profilometer image examples in the off-sliding wear mechanism of the composite material. It has been obtained that the wear depth increases in the composite material from the area where the bite force is to the off-sliding (30° angle sliding direction) wear area region. In addition, as the abrasive antagonist ball moves in the same coordinate along the lateral movement, the wear width [Figure 3]a and [Figure 3]c has not changed through chewing cycle tests. Particle transport was observed along the wear area in the direction of lateral movement [Figure 3]b and [Figure 3]d.{Figure 3}

[Figure 4] shows microstructure analyses of in this study tested composite materials under 60 N wear force in artificial saliva and citric acid medium chewing condition (A, a and C, c: Clearfil AP-X and B, b and D, d: Filtek Supreme). In these figures, significant wear tracks were detected in the Clearfil AP-X composite material in the direction of the axial wear mechanism. These wear tracks continued to form deformation mechanisms along the wear area. The thermal cycling mechanism used in the chewing test procedure prevented the particles carried from the wear surface of the composite material to form a third-abrasive surface. Therefore, intra-oral tribology two-body (direct contact impact) wear mechanism can be simulated in a more complex structure. In both tested in this study composite materials, two-body wear tests performed in citric acid environment revealed more significant wear surface deformations than artificial saliva environment. As a result, it can be said that artificial saliva wear environment has a chemical lubricant effect through chewing test procedures.{Figure 4}

 Discussion



In this study, nanohybrid-filled Clearfil AP-X and nano-filled Supreme dental bio-composite materials were analyzed with wear structural analysis, surface roughness, and hardness measurements usingin vitro off-axis sliding contact chewing simulation. Filtek Supreme composite material contained the nano-silica zirconia-silica nanoclusters filler structure monomer, whereas the Clearfil AP-X composite contained silanated barium glass, silanated colloidal SiO2, and silanated SiO2 filler structure monomer. The different monomer structure of the composite materials contributed to their different two-body wear behavior in chewing test procedures. Furthermore, increasing the inorganic filler particle size of the composite material negatively affected the two-body wear resistance in chewing test procedures. Bio-composite as use dental materials exhibit a particular wear pattern because many properties related to their composition directly affect wear resistance. In general, the loading force applied to the composite material during chewing is completely transferred from the matrix to the filler particles. Therefore, the mechanical behavior of the cross-link in the matrix structure of the composite material will significantly affect the abrasion resistance. In this study, it can be said that the nano-silica zirconia-silica nanoclusters contained in the Filtek Supreme composite material contribute to the two-body wear resistance in the chewing test procedures. The size, shape and hardness of the fillers, the quality of the bond between the fillers and the polymer matrix, and the polymerization dynamics of the polymer have an effect on the wear properties of a dental bio-composite. In the literature, it has been reported that G-aenial Universal Flo has better wear resistance as it contains smaller filler particles than the G-aenial posterior.[12] In addition, Bayne et al.[13] suggested that the presence of large particles could theoretically lead to further erosion of the restorative material in wear test procedures.[13] When the restoration is subjected to chewing forces, the stress spreads through the resin-filler particles to the resin matrix. This results in an easy removal of these particles from the surface, exposing the organic matrix, and accelerating wear.[12]

One suggestion for increasing the wear resistance of composites is to increase the abrasive resistance of the resin matrix rather than to increase the hardness of the filler particles.[14],[15] The dominant base monomer used in commercial dental composites was bis-GMA mixed with other dimethacrylates such as triethylene glycol dimethacrylate (TEGDMA) because of its high viscosity. Urethane dimethacrylate (UDMA) refers to another alternative organic matrix composition and is often found in the present compositions. In the literature, Söderholm et al.[16] suggested that after 3 years ofin vivo clinical studies, urethane-based composites had a significantly higher wear resistance than bisGMA-based composite materials.[16] In this study, it is possible to say that the urethane-based monomer structure contained in the supreme composite material contributes to better two-body wear resistance than the Clearfil AP-X composite material in chewing test procedures. Thus, the filler and volume of the filler affect the wear rate. The low elastic modulus in the material results in wider contact areas and thus lower pressures. Large filler particles are, in theory, related to the high friction coefficient in the high polymeric matrix and are associated with higher internal shear stress. In literature according to some studies, the wear resistance of the composites in the oral cavity depends on the gap between the filler particles which provide protection against the food bolus. The presence of smaller filler particles increases the wear resistance by reducing the particulate hole in the composite.[13],[17],[18] Bio-composite material manufacturers are trying new composites with different formulations to overcome the shortcomings; however, furtherin vitro investigation is needed to assess whether these changes provide superior mechanical properties in the chewing test procedures. The improvements in the component structure of dental composite materials are called micro- and nano-structures as chemical structures. These materials are called micro- or nanohybrid resin composites depending on the size and content of micro- or nano-particle.[6] In addition, such resin composites are called universal. It is difficult to distinguish these structures in commercial composite materials because of both the microstructure and mechanical properties tend to be similar.[6] The tested dental composite materials in this study are available at the market and widely used in the dental treatment.

The composition of the composite can affect physical and mechanical properties such as bending strength, fracture toughness, Vickers hardness, modulus of elasticity, curing depth[19] and these properties, in turn may influence two-body wear resistance of composite materials. In this study, Supreme bio-composite material showed lower hardness value than Clearfil AP-X composite material, but had better two-body wear resistance after chewing test procedures. In the literature, no linear relationship was found between surface hardness and wear volume loss among five bio-composite materials after wear test procedures.[12] In this study was not found linear relationship between Vicker's hardness and wear volume loss. In addition, the characteristic of the wear mechanism in the chewing movement may also affect the wear resistance of the composite material. The researchers concentrate on laboratoryin vitro test experiments due to the fact that living tissuein vivo test experiments were very long, costly, and ethical problems.[6],[20],[21] However, the human body has a very complex and constantly changing structure. Therefore, it is very important that the experimental conditions applied in the laboratory environment can simulation parameters in the living tissue. In the literature, mechanical and chemical tests of biomaterials are performed by manyin vitro test methods.[6],[22],[23] In these test methods, variable parameters on living tissue are simulated on the test mechanism. For example, bite force and thermal change occurred during chewing movement are some parameters in the mouth. In the literature, it has been reported that teeth and dental materials are subjected to continuous mechanical loads between 20 N and 120 N during chewing movement.[24] It has been reportedin vivo studies that the average chewing movement of a human varies between 300 and 700/day[12] It has also been reported that chewing simulators are capable of mechanical loading of 50,000–1,200,000 forin vitro wear testing.[12] As a result of this study, the selected 100.00 chewing cycles correspond to an average of 1 yearin vivo experiments. There is no agreement in the literature on the choice of antagonist abrasive material duringin vitro chewing test protocols.[20] In this study, 6 mm diameter ceramic abrasive antagonist balls which are frequently preferred in the literature were used chewing simulation test protocols.[20],[22],[25]

In the intraoral tribological process, the structure within the chewing cycle medium varies in a continuous and complex state that includes temperature and components such as saliva, salts, foods, liquids, and drugs. This variable medium structure can affect the two-body wear resistance of composite materials in chewing cycle process. Saliva is a liquid with a complex composition-containing organic and inorganic groups and microorganisms. Dental composite materials should withstand the oral cavity environment in contact with saliva.[18] In the studies in the literature, it has been reported that the mechanical properties of the composite materials stored in artificial saliva are improved (such as Vicker's hardness stored for 7 days in artificial saliva medium). Lubricants, such as artificial saliva, reduce the friction coefficient, thus reducing wear. Furthermore, artificial salivary circulations performed during the experiment can remove worn particles from the material wear area. In addition to, these particles may prevent them from being a third abrasive structure during the chewing test procedures. In this study, all composite materials tested exhibited better two-body wear resistance in artificial saliva environment than in citric acid environment. In the two-body wear tests in artificial saliva medium, composite materials exhibited a homogeneous wear microstructure behavior, while wear tracks (direction off-sliding wear mechanism) became more prominent in citric acid environment [Figure 4].

 Conclusion



Within the limitations of the presentin vitro study, the hardness of nano-hybrid-filled Clearfil AP-X bio-composite material was significantly greater than the nano-filled Filtek Supreme bio-composite material. All materials tested in this study showed higher wear resistance in the artificial saliva environment compared to in citric acid environment. As a result of it was thought that the artificial saliva medium produced a lubricating effect for bio-composite dental materials during the off-axis wear test process. The mean wear volume loss of Filtek Supreme composite test specimens was lower than the Clearfil AP-X composite material irrespective of wear ambient conditions. When the loading amount increased in the test procedure, the wear volume loss of composite materials increased. However, in this process, the matrix structure of the composite material was decisive in the formation of abrasion resistance.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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