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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 7  |  Issue : 2  |  Page : 37-41

Effect of artificial saliva on the mechanical and tribological behavior of nano-/micro-filled biocomposite materials for biomedical applications


Department of Mechanical Engineering, Faculty of Engineering, Kilis 7 Aralık University, Kilis, Turkey

Date of Submission13-Mar-2020
Date of Decision07-Apr-2020
Date of Acceptance27-Apr-2020
Date of Web Publication20-Jun-2020

Correspondence Address:
Efe Çetin Yilmaz
Department of Mechanical Engineering, Faculty of Engineering, Kilis 7 Aralik University, Kilis
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdrr.jdrr_19_20

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  Abstract 


Aim: The purpose of this study is to investigate the effect of artificial saliva storage time of composite materials with different filler structure (micro/nanofiller) on the mechanical and tribological behavior. Material and Method: Mechanical and tribological behaviors of composite materials were investigated with storage in artificial saliva for the control group, 1 day, and 7 days. Composite materials were subjected to direct contact wear tests (80 N wear force, 100.000 wear cycles, 1.8 Hz wear frequency, and 37°C ambient temperature) with a computer-controlled dual-axis abrasion device. The surface hardness of composite materials after each artificial saliva test procedure was determined using the Vicker's Hardness method. Results: In this study, it was concluded that the waiting process in artificial saliva increases the tribological behavior of the composite material. Conclusion: However, for the composite test materials in this study considered, correlations between the contact-wear resistance and surface hardness were found to be statistically insignificant.

Keywords: Biomedical application, composite material, hardness, volume loss


How to cite this article:
Yilmaz EÇ. Effect of artificial saliva on the mechanical and tribological behavior of nano-/micro-filled biocomposite materials for biomedical applications. J Dent Res Rev 2020;7:37-41

How to cite this URL:
Yilmaz EÇ. Effect of artificial saliva on the mechanical and tribological behavior of nano-/micro-filled biocomposite materials for biomedical applications. J Dent Res Rev [serial online] 2020 [cited 2020 Sep 25];7:37-41. Available from: http://www.jdrr.org/text.asp?2020/7/2/37/287333




  Introduction Top


The intraoral tribological process has a very complex and continuous structure. It is important to determine the mechanical and aesthetic behavior of biomaterials placed in this structure over time, because the correct estimation of the mechanical and esthetic behavior of a biomaterial placed in the mouth during the time period will contribute to the formation of a satisfactory treatment process. Manyin vivo andin vitro test methods have been developed in the literature to predict the mechanical and esthetic behavior of biomaterials.[1],[2],[3] In addition, researchers have tended to work towardin vitro testing methods due to the long duration, high costs, and ethical reasons ofin vivo studies. It is important to model the complex and continuous structure of the human oral tribological process inin vitro test parameters. For example, the bite force occurring during the chewing movement is a continuously variable and continuous parameter. There are many studies in the literature that perform the two-body and three-body abrasion test mechanisms on various biomaterialsin vitro laboratory environment.[4],[5],[6],[7] In the contact wear method, while the antagonist material and the composite test material are in direct contact, there is a third structure in the contact range of the contact-free wear mechanism. İntraoral tribology process, both wear mechanisms, can occur many times during chewing. Therefore, it is important to be able toin vitro simulation, these wear mechanisms in a laboratory environment and to determine the tribological behavior of composite materials.

It is a complex fluid structure of human saliva and contains various organic and inorganic structures. Dental composite materials placed in the mouth are constantly in contact with human saliva fluid. In the literature, the effect of artificial saliva and different fluids on dental composite materials has been investigatedin vitro simulation.[8] It is also known that artificial saliva fluid has a lubricating effect on the dental and dental composite materials. In recent years, the use of composite materials has been increasing in different filler structures capable of being polarized by blue light technology.[9] Dental composite materials are usually heterogeneous materials with resin matrix, inorganic fillers, and a silane coupling agent.[10] The amount and size of filler particles included in the composite resin matrix can determine each composite type and ultimately the most advantageous clinical application. It has been reported that damage to composite materials on living tissue may result from the deterioration of matrix and filler materials or may result from mechanical and environmental loads, microcracking, or filler particle breakage, which may reduce the possibility of composite restorations survivingin vivo ambient.[11] In the literature, composites classifications in some sources focus on properties that define the viscosity and stability of the composite material (e.g. flowable or packable), while considering the mechanical properties of dental composites in other sources, microstructure classifications are taken into account (such as microfilled, nanofilled, and micro/nanohybrid) [Figure 1].[12]
Figure 1: Schematic structure microstructural differences between various resin-based dental composites classes (a) Micro-filled, (b) Hybrid, (c) Micro/nanohybrid, (d) Nanofilled; (e) Short fiber reinforced[12]

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  Materials and Methods Top


In this study, wear test specimens were prepared from nanofilled Supreme and micro-filled Heliomolar composite materials (2 mm wide × 13 mm diameter cylindrical). The chemical and mechanical properties of the composite test sample provided by the manufacturer are shown in [Table 1]. The test specimens were divided into three groups as control group, 1-day and 7-day artificial saliva storage procedurein vitro ambient. The chemical components of the artificial saliva fluid used in test environments are shown in [Table 2].[13] The surface hardness values of the composite test samples were determined using the “Vicker's Hardness” method after artificial saliva storage test process. In this method, a load of approximately 19.355 N was applied to the sample surface for 30 s using a mold in pyramid geometry. This method is also known that the depth of the measurement indicates the hardness of the test specimen. Composite test samples were subjected to contact wear mechanism under 80 N wear force, 100.000 wear cycles, 1.8 Hz wear frequency, and 37°C ambient temperature using a wear device with 30° lateral movement. Each wear test procedure 6 mm diameter Al2O3 ball used as antagonist material. [Figure 2] shows the systematic of the contact wear mechanism with a 30° lateral movement. Microstructural analysis of test samples was performed using scanning electron microscopy. The wear volume depth of the test specimens was determined, with scanning the measuring speed of 8 μm on the x-axis, 12 μm on the y-axis, and 1000 μm on the wear surface using the Bruker-Contour GT three-dimensional (3D) Vision 64 simulation software.
Table 1: Chemical and mechanical properties of tested composite materials

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Table 2: Chemical components of artificial saliva test medium

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Figure 2: Systematic of the contact wear mechanism with 30° lateral movement

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  Results Top


The Vicker's Hardness and wear volume loss of the composite materials tested in this study after the artificial saliva procedure are shown in [Table 3]. It has been observed that the immersion in artificial saliva for 1-day process improves the contact-wear resistance of both composite materials. However, it has been observed that immersed in artificial saliva for 7-day process does not have a significant effect on the hardness and wear resistance of composite materials. As a result, it can be thought that the immersed time in artificial saliva for 1 day is an optimum time for the composite materials tested in this study. [Figure 3] shows an example of noncontact 3D profilometer analysis taken from the wear surface of the composite material after wear test procedures. When it is an examined example of noncontact 3D profilometer analysis, the composite material was generally observed to exhibit a homogeneous wear behavior. [Figure 4] and [Figure 5] show microstructure of heliomolar and supreme composite materials after wear test procedures, respectively (for control group immersed artificial saliva medium). It has been observed that particle transport of lateral movement direction and microcracks occur on the wear surface of both composite materials.
Table 3: The Vicker's Hardness and wear volume loss of the composite materials tested in this study after the artificial saliva procedure

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Figure 3: Example of noncontact three-dimensional profilometer analysis taken from the wear surface of the composite material after wear test procedures

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Figure 4: Microstructure of heliomolar composite material after the wear test procedures (a: wea surface, b: particle transport area and c: particle crack area)

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Figure 5: Microstructure of supreme composite material after the wear test procedures (a: wea surface, b: particle transport area and c: particle crack area)

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  Discussion Top


Thein vitro result obtained in this study showed that the artificial saliva environment improves the mechanical and tribological behavior of composite materials. When [Table 3] is examined, it will be seen that the mechanical and tribology resistances of both tested composite materials increase after 1-day artificial saliva environment process. The mechanical and esthetic behavior of composite materials, which are preferred as biomaterials in the field of dentistry, can be improved as time progress. The particle size improvements in the monomer structure of the dental composite material formed the chemical composition of two different particle structures. The filling structure of the composite material can be called nano or micro according to the particle size.[7] The developments in the filler structure of composite materials have brought superior mechanical and tribological behaviors to these materials. In the literature, many studies have investigated the effects of parameters such as chewing force, thermal change, and wear mechanism of composite materials on mechanical and tribological behavior.[1],[3],[14] However, in these studies, the effect of storage in the artificial saliva environment on the mechanical and tribological behavior of the composite material was ignored. Therefore, the aim of this study is to investigate the effect of artificial saliva storage time of composite materials with different filler structure (micro/nanofiller) on the mechanical and tribological behavior. In this study, water and artificial saliva were used to simulate the physiological condition. Human saliva is expected to be more reactive than artificial saliva due to the presence of certain bacterial enzymes, such as cholinesterase, which can break down composite materials.[15] However, within the scope of this study, the completion of the experiment periods in a long time made it impossible to use human saliva throughin vitro study process. For this reason, artificial saliva medium, whose chemical components are given in the literature, was prepared in a laboratory environment. Since the urea medium in the artificial saliva was estimated to accelerate the degradation, the media of artificial saliva media was replaced with a new one every 24 h throughin vitro study process. Although the Vicker's hardness of the composites decreased after storage in 1-day artificial saliva process due to matrix softening, the wear resistance of the composites increased.

In this study, particle transport direction of lateral movement was observed on the wear surfaces of composite materials after the wear test procedure [Figure 4] and [Figure 5]. The material exhibited elastic and plastic behavior during the contact of the composite material and the antagonist material (step 1 direct contact). Then, with the start of the lateral movement mechanism, the shattered pieces of plastic behavior began to be carried on the wear surface (step 2 lateral movement mechanism). Finally, the contact surface between the composite and the counter material has disappeared (step 3 unloading vertical movement). Thus, particle transport on the wear surface of the composite material has ended. The composite composition can affect physical and mechanical properties, such as bending strength, fracture toughness, Vickers hardness, and elasticity module,[16] and these properties can affect the direct-contact wear of composite materials. In this study, the Heliomolar biocomposite material showed lower hardness than supreme composite material, but it has better two-body abrasion resistance after wear test procedures irrespectively artificial saliva storage process. In the literature, there was no linear relationship between the surface hardness and loss of wear volume between five biocomposite materials after wear testing procedures.[17] In this study, there was no linear relationship between Vicker's hardness and wear volume loss. In addition, the characteristic of the wear mechanism in the wear movement can also affect the wear resistance of the composite material. Researchers have focused onin vitro test experiments in the laboratory, because living tissuesin vivo test experiments are very long, costly, and ethical problems.[7],[18],[19] However, the human body has a very complex and constantly changing structure. For this reason, it is very important that the experimental conditions applied in the laboratory environment can simulate the parameters in the living tissue. In the literature, mechanical and chemical tests of biomaterials are performed by manyin vitro test methods.[4],[7],[20] In these test methods, variable parameters on living tissue are simulated on the test mechanism. For example, biting force and thermal change during the chewing movement are some parameters in the mouth. In the literature, it has been reported that teeth and dental materials are subject to continuous mechanical loads between 20 N and 120 N during the chewing movement.[21] It has been reported inin vivo studies that the average chewing movement of a person varies between 300 and 700 per day.[17] It has also been reported that chewing simulators can load 50,000–1,200,000 mechanics forin vitro wear testing.[17] 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 regarding the selection of antagonist abrasive materials duringin vitro chewing test protocols.[18]


  Conclusion Top


In this study, it was concluded that the waiting process in artificial saliva increases the tribological behavior of the composite material. However, for the composite test materials in this study considered, correlations between the contact-wear resistance and surface hardness were found to be insignificant. It has been observed that the immersion in artificial saliva for 1-day process improves the contact-wear resistance of both composite materials. However, it has been observed that immersed in artificial saliva for 7-day process does not have a significant effect on the hardness and wear resistance of composite materials. As a result, it can be thought that the immersed time in artificial saliva for 1 day is an optimum time for the composite materials.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Sutiman DM, Mareci D, Nechita TM, Iordache I, Rosca JC. The electrochemical behaviour of some unnoble alloys in fusayama artificial saliva. Maced J Chem Chem Eng 2007;26:57-63.  Back to cited text no. 13
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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