KR20200083890A - Evaluation method of structural and mechanical properties of aerosol-deposited bioceramic films for orthodontic brackets - Google Patents

Abstract

Disclosed is a method for evaluating structural and mechanical properties of aerosol-deposited bioceramic films for an orthodontic bracket. Four kinds of bioceramic films (Al_2O_3, SiO_2, hydroxyapatite (HA), and brushite) are used in a simple aerosol deposition (AD) process at room temperature of 23°C, and the structural and mechanical properties are compared in order to validate potential for being used as the orthodontic bracket. As a result thereof, the HA and brushite films show very high deposition rate as compared with other coating techniques. Furthermore, the crystallite sizes of all the samples are largely reduced to 100 nm or less, which can increase biological efficacy and the mechanical properties of the bioceramic film. In addition, the HA and brushite films have optimal mechanical properties, i.e. adhesive strength and shear bond strength, of the bioceramic film for an orthodontic bracket.

Description

Evaluation method of structural and mechanical properties of aerosol-deposited bioceramic films for orthodontic brackets

The present invention relates to a method for evaluating the structure and mechanical properties of aerosol-deposited bioceramic films for orthodontic brackets.

This research is supported by research fund of Kwangwoon University in 2019, advanced research technology of renewable energy and electric vehicle power semiconductor technology by Korea Research Foundation (NRF) (Task No. 2017R1C1B5017013) and Korea Energy Technology Evaluation Institute (KETEP) funded by Ministry of Science and Technology Supported by track (task number 20174010201290).

1. Background technology

As the number of patients with dental problems continues to increase, orthodontic treatment has received considerable attention over the past 20 years [1-5]. Until now, metal biomaterials have been frequently used for dental applications such as passive replacement of hard tissue and fracture treatment aids due to their excellent mechanical strength and chemical stability [6-8] ]. However, diffusion of metal ions and toxic particles can cause detrimental effects on cells and bone tissues through corrosion or abrasion processes. To overcome these problems, bioceramics with high clinical potential have been widely investigated in recent dental treatments due to their excellent biocompatibility and structural and chemical similarity to human teeth and bones [9 ,10]. As described above, although bioceramic materials have many advantages, (1) mechanical properties, (2) surface roughness, and (3) crystallite Some specific concerns, such as size), are still studied by investigators and should be considered further [11-15].

Because orthodontic treatment typically handles misalignment of teeth and proper positioning of jaws, tooth movement is solely biomechanical properties such as adhesive strength and shear bond strength. According to [16,17]. The most important point of orthodontic treatment is the separation of the orthodontic brace bracket from the tooth, as well as the prevention of stress resulting from foreseen or unexpected forces, resulting in high binding during the orthodontic treatment period. It maintains high bonding strength. In addition, the clinical success of orthodontic brackets relies heavily on mechanical systems that can effectively achieve the durable coupling of dental brackets to teeth and benefit both medical staff and patients [11]. Therefore, the optimal bonding strength of orthodontic brackets requires stability to tissues and teeth, and unfavorable strength sometimes degrades biological performance and Cause traumatic dental injury.

For the recent production of brackets, it is necessary to consider surface topologies and degree of crystallite size for biological stability and effectiveness of dental treatment. For serpentine ceramic surfaces where the surface lubricity of the ceramic coating affects the substantial reduction in shear bond strength, a high shear bond strength between the ceramic coating and the resin This may be acceptable, as surface morphology, including surface roughness, is important in determining the micro-mechanical strength of the interface between the ceramic coating and the resin. Plays a role [19]. Regarding the effect of crystal size, the authors have shown that nanophase biocompatible ceramics with crystal size less than 100 nm adhere more firmly and osteoblasts than those with crystal size greater than 100 nm. It is asserted that it can promote the improvement of long-term function of osteoblasts (14,20).

In consideration of the above interest, various types of technologies have been tried to form an optimal bioceramic coating layer. Plasma spraying, one of the representative methods of bioceramic coating, has been widely commercialized due to its effectiveness and economic advantages [21-23]. However, due to the high temperature of the plasma, undesirable effects such as phase transformation, residual stress, easy debonding, high porosity, and gas leakage have appeared. In this article, although glass ionomer cement adhesives were used for successful bonding of orthodontic brackets, defects of lower bonding strength occurred. It became [24,25]. Moreover, some researchers and companies have provided a standard mesh base, supermesh base, and integral to provide mechanical interlocking, an important factor for higher bonding strength. Attempts have been made to add auxiliary mechanical preservation to bracket-base designs, such as integral bases and laser-structured bases [26-28]. However, existing methods increase the economic cost of complex and time-consuming procedures and processes.

In order to overcome the drawbacks such as the above-mentioned problems, special techniques are required to manufacture more improved orthodontic brackets and take full advantage of the advantages. Based on high-speed powder spraying, the aerosol deposition process (AD process) is a very attractive and has been used successfully as an alternative coating method, which is a vacuum without specific heat treatment (in This is because it enables formation of ceramic coating layers at room temperature (23°C, vacuum) [29,30]. Basically, the AD principle is that solid ceramic powder particles strongly collide with the target substrate to easily form a well-bonded ceramic coating layer, thereby providing fine nanophase particles and high adhesion strength on the substrate. It enables coating layers with bonding strength [31]. Poor adhesion strength due to inadequate experimental conditions, such as broad nozzle orifice and low gas consumption, even with a wide range of work on aerosol-deposited bioceramic films Poor bonding strength and high surface roughness occur [21, 32].

Patent Application No. 10-2018-0024067 (application date February 27, 2018), "Adhesive method of aluminum oxide and copper composite film through aerosol deposition process for application of film resistance", Kwangwoon University Industry-Academic Cooperation Foundation

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An object of the present invention for solving the above problems is to provide a method for evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets.

The purpose of this paper was to create and characterize four types of bioceramic coating layers through the AD process. The sapphire bracket chose the substrate because it has the advantages of color stability, biocompatibility, corrosion resistance, and non-toxicity. The deposition rate of each film was evaluated and changes in crystal size of the bioceramic films deposited-stained from the starting particles were analyzed. Subsequently, the mechanical properties for the orthodontic bracket, i.e., the adhesive strength and shear bond strength of the bioceramic films are measured to realize the feasibility of the bioceramic films for the mechanical properties of the orthodontic bracket. Confirmed. Finally, considering the properties and formation process of aerosol-deposited bioceramic films, film formation mechanisms for each bioceramic film were proposed.

In order to achieve the object of the present invention, a method for evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets, at room temperature, using an AD device, a sapphire bracket and a sapphire substrate by an aerosol deposition process (AD process) Depositing bioceramic particles on to form a nanostructured bioceramic coating layer; And measuring the mechanical properties of the aerosol-deposited bio-ceramic film for orthodontic brackets, namely surface roughness, deposition rate and adhesive strength.

The bioceramic coating layer is characterized by being a bioceramic film in which any one of bioceramic particles of Al ₂ O ₃ , SiO ₂ , HA (hydroxyapatite), or brushite is deposited.

The crystal size of the four types of bioceramic films is 100 nm or less from XRD data.

The AD device includes a vacuum system having a rotary pump and a mechanical booster pump, an aerosol chamber, a moving X-Y stage, a deposition chamber, a carrier gas, and a flow controller.

In the aerosol deposition process of step (a), bioceramic powders are dried in a drying oven at 80° C. for 8 hours using the AD device, and a fine sieve network is used. Moisture is removed or collected through, and the bioceramic powders are placed in an aerosol chamber, and a carrier gas is injected to supply the powder to drive the deposition chamber, and the bioceramic powders are supplied through a tube to a nozzle. Delivered; And film deposition includes forming the bioceramic coating layer using a nozzle orifice such that a dense film having a higher deposition rate and film hardness is formed in an AD process than a direct injection method.

Prior to the injection of the carrier gas, the deposition chamber is pre-evacuated at ~3.2 Torr by two types of vacuum pumps to maintain the accelerated powder velocity from the nozzle and helium (purity 99.99%). This carrier gas is used.

The nozzle orifice uses a 1.5×1.5 mm ² nozzle orifice having a deposition rate 7 times higher than that of a 10×0.4 mm ² nozzle orifice.

)가 각각 2㎛ 및 50㎛의 입자 크기를 갖는다. HA(hydroxyapatite) and brushite(

) Has particle sizes of 2 μm and 50 μm, respectively.

In the AD process, the bioceramic coating uses shadow mask patterning using a check-pattern on a sapphire bracket, and a check-patterned film is used. The brushite film has excellent mechanical properties and deposition rates, and has a shear bond strength that is more than twice that of the mesh-patterned film.

The surface properties of the aerosol-deposited bioceramic films were measured by atomic force microscopy, while the RMS roughness of the SiO ₂ film showed the lowest value, while the RMS roughness of the brushite and HA films showed the highest value, and strong ceramic-to- Resin bonding typically relies on micro-mechanical interlocking and chemical bonding, where an appropriately rough surface is effective for effective bonding strength between a ceramic coating and a soft resin. bonding strength),

The average surface roughness of the four types of aerosol-deposited bioceramic films has a desirable surface roughness for dental applications.

The HA (hydroxyapatite) and brushite films are SiO ₂ and Al ₂ O ₃ It has a larger deposition rate than the film.

In the HA (hydroxyapatite) and brushite film, SiO ₂ and Al ₂ O ₃ films had a shear bond strength value between 6 MPa and 8 MPa, and the HA and brushite film had a shear bond strength value greater than 10 MPa,

Optimal adhesion strength values were observed compared to the SiO ₂ and Al ₂ O ₃ films, and the HA and brushite films had a shear bond strength 1.5 times higher than that of the SiO ₂ and Al ₂ O ₃ films.

In the bio ceramic film, the HA (hydroxyapatite) and brushite films are used in the orthodontic bracket.

The present invention proposed a method for evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets. Four types of bioceramic films (Al ₂ O ₃ , SiO ₂ , HA (hydroxyapatite), and brushite) were used for a simple aerosol deposition (AD) process at room temperature of 23° C., orthodontic bracket The structure and mechanical properties were compared to verify the potential for use as brackets. As a result, HA (hydroxyapatite, hydroxyapatite) and brushite films showed significantly higher deposition rates compared to other coating techniques. Moreover, the crystal size of all samples was greatly reduced to less than 100 nm, which can improve the biological efficacy and mechanical properties of the bioceramic film. In addition, HA and brushite films have the optimal mechanical properties of bioceramic films for orthodontic brackets, namely adhesive strength and shear bond strength. These two important mechanical properties have been achieved by strong mechanical interlocking at the ceramic-to-resin interface, as well as thicker bumps with high deposition rates. This study confirmed that AD-provided HA and brushite films have high potential for application to orthodontic brackets.

As a result, four types of bioceramic films [Al ₂ O ₃ , SiO ₂ , HA (hydroxyapatite, hydroxyapatite), and brushite], HA (hydroxyapatite, hydroxyapatite) and brushite films are SiO ₂ and Al ₂ O ₃ It was shown to have a significantly higher deposition rate than the film. By comparing mechanical properties with SiO ₂ and Al ₂ O ₃ films, optimal adhesion strength values were observed for HA and brushite films. SiO ₂ and Al ₂ O ₃ films had a shear bond strength value between 6 MPa and 8 MPa, and the HA and brushite films observed shear bond strength values greater than 10 MPa. In addition, HA and brushite films showed 1.5 times higher shear bond strength than both SiO ₂ and Al ₂ O ₃ films, which is a result of higher bump thickness and sufficient RMS roughness. Inferred, can be used for orthodontic brackets.

, (b)

, (c) HA, (d) 브러시 라이트.
도 3은 본 연구에서 사용 된 다른 바이오 세라믹 분말(bioceramic powders)의 침착 속도(μm / min)를 보여주는 그래프.
도 4는 AD 공정에 의해 사파이어 기판 위에 증착 된 각 분말 및 바이오 세라믹 박막의 XRD 패턴.
도 5는 (a)와 (ai)

막, (b)와 (b)

막, (c)와 (ci) HA 막, 그리고 (c) 희토류 금속 산화물 박막의 표면 마이크로 구조물의 광학 현미경 사진. (d) 및 (d) 브러시 타트 필름을 포함한다.
도 6은 AFM에 의한 실험 그룹에서 각 바이오 세라믹 필름의 표면 형태(Surface morphologies)와 표면 거칠기(surface roughness) 측정 결과.
도 7은 사파이어 기판에서 바이오 세라믹 코팅층(bioceramic coating layers)의 탈착에 대한 내성을 확인하기 위한 4 가지 타입의 바이오 세라믹 필름의 접착 강도(Adhesive strength) 측정.
도 8은 4-META/MMA-TBB 에폭시 수지(META/MMA-TBB epoxy resin)를 사용하여 사파이어 브라켓(sapphire bracket)과 에나멜(enamel) 사이의 전단 결합 강도(shear bond strength) 그래프.
도 9는 위의 측정 데이터를 고려한 각 바이오 세라믹 박막의 막 형성 메커니즘(Film formation mechanisms of each bioceramic film). 그림과 관련된 그래프는 각 바이오 세라믹 필름(bioceramic film)의 평균 두께 (Ta)와 RMS 거칠기(RMS roughness)를 보여준다.1 is a schematic diagram of an aerosol deposition apparatus.
Figure 2 is a SEM micrograph of bioceramic powders prepared before the AD process (AD precess): (a)

, (b)

, (c) HA, (d) brush light.
3 is a graph showing the deposition rate (μm / min) of other bioceramic powders (bioceramic powders) used in this study.
4 is an XRD pattern of each powder and bioceramic thin film deposited on a sapphire substrate by an AD process.
5(a) and (ai)

Membranes, (b) and (b)

Optical micrographs of the surface microstructures of the membranes, (c) and (ci) HA membranes, and (c) rare earth metal oxide thin films. (d) and (d) brush tart films.
6 is a surface group (surface morphologies) and surface roughness (surface roughness) measurement results of each bio-ceramic film in the experimental group by AFM.
7 is a measure of the adhesive strength (Adhesive strength) of four types of bio-ceramic films to confirm the resistance to desorption of bio-ceramic coating layers on a sapphire substrate.
FIG. 8 is a graph of shear bond strength between a sapphire bracket and an enamel using 4-META/MMA-TBB epoxy resin.
9 is a film formation mechanism of each bioceramic thin film considering the above measurement data (Film formation mechanisms of each bioceramic film). The graph associated with the figure shows the average thickness (Ta) and RMS roughness of each bioceramic film.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail the configuration and operation of the invention.

The present invention provides a method for evaluating the structure and mechanical properties of aerosol-deposited bioceramic films for orthodontic brackets. Four types of bioceramic films (Al ₂ O ₃ , SiO ₂ , HA (hydroxyapatite, hydroxyapatite), and brushite) were used for a simple aerosol deposition (AD) process at room temperature of 23° C. The structure and mechanical properties were compared to verify the potential for use as orthodontic brackets. As a result, HA (hydroxyapatite, hydroxyapatite) and brushite films showed significantly higher deposition rates compared to other coating techniques than films using Al ₂ O ₃ and SiO ₂ . Moreover, the crystal size of all samples was greatly reduced to less than 100 nm, which can improve the biological efficacy and mechanical properties of the bioceramic film. In addition, HA and brushite films have the optimum mechanical properties of bioceramic films, namely adhesive strength and shear bond strength. These two important mechanical properties have been achieved by strong mechanical interlocking at the ceramic-to-resin interface, as well as thicker bumps with high deposition rates. This study confirmed that AD-provided HA and brushite films have high potential for application to orthodontic brackets.

2. Materials and methods

(1) Selection of bioceramic powders

Four biocompatible bioceramic powders were used in this study, (a) SiO ₂ (SUNSIL-130NP, SUNJIN Chemical Ltd., Ansan, Korea), (b) Al ₂ O ₃ (Showa Denko Co., Ltd. , Tokyo, Japan), (c) Hydroxyapatite (HA, hydroxyapatite) (Dio, Co. Ltd., Busan, Korea), and (d) Brushite (Dio, Co. Ltd., Busan, Korea). SiO ₂ is a promising material in biotechnology because it is widely abundant in nature as well as in medicine [34]. In addition, aluminum oxide Al ₂ O ₃ is widely known as a ceramic biocompatible material that has been used in implants and bone filling for over 30 years. HA (Hydroxyapatite) showed excellent effects for dental implants in various previous studies because of its similarity to human teeth and bones [7,35]. In addition, Brushite films have been studied in many dental and bone applications in the clinical field [36]. Therefore, an AD process was performed using four types of these selected powders.

(2) Bioceramic coating process

Bioceramic coating films were prepared on flat sapphire substrates and sapphire brackets by the AD process. The surface roughness of the sapphire bracket was approximately 19 nm.

1 shows a schematic diagram of an AD device. AD devices are mainly vacuum systems (rotary pumps and mechanical booster pumps), aerosol chambers, mobile XY stages, deposition chambers, carrier gases, and mass flow controllers. ). The bioceramic powders were dried in a drying oven at about 80° C. for 8 hours, and permeated through a fine sieve net to remove or collect moisture. These powders are placed in an aerosol chamber, and the deposition chamber is driven by supplying a carrier gas as powder. The powders are then delivered through a tube to a converging nozzle. Prior to the injection of carrier gas, the deposition chamber was pre-evacuated at ~3.2 Torr by two types of vacuum pumps to maintain the accelerated powder velocity from the nozzle. Helium (99.99% purity) was used as a carrier gas, because a light inert gas had a sufficiently high rate to increase the particle impact rate, resulting in strong adhesion between the film and the substrate. The substrate was positioned 5 mm from the nozzle. The mass flow of the carrier gas was set to 10 L/min, and the characteristic time ( τ _g ) of the surrounding flow was determined by the following equation; τ _g = D/ μ _{g , exit} , where D is the nozzle exit diameter and μ _{g , exit} is the gas speed [37]. The bioceramic powders delivered through the nozzle to the deposition chamber formed dense ceramic films by violently colliding with the substrate and converting sufficient kinetic energy into thermal energy upon impact [38]. The detailed experimental conditions are summarized in Table 1.

The main advantages of the experimental setup can be divided into two factors:

Film deposition utilizes a check-pattern mask rather than a direct injection method and utilizes an optimized nozzle orifice of 1.5 × 1.5 mm ² [39].

First, in a previous study, the effect of nozzle size on deposition rate and film hardness in the AD process was investigated. This study suggested that dense films with high deposition rates and high hardness were achieved simultaneously when using a nozzle orifice of 1.5 x 1.5 mm ² . In addition, it has been reported that a nozzle orifice of 1.5 x 1.5 mm ² has a deposition rate approximately 7 times higher than a nozzle orifice of 10 x 0.4 mm ² .

Secondly, two coating methods have been proposed for the AD process: one is to form a mesh-patterned film, which directly writes through nozzle movement, and the other is a sapphire bracket. Shadow mask patterning using check-pattern on a sapphire bracket. As a result, the check-patterned brushite film showed excellent properties in terms of mechanical properties and aerosol deposition rate, while the mesh-patterned brushite film showed low deposition rate ( low deposition rate and weak shear bond strength [36]. In the study, the check-patterned brushite film showed a shear bond strength more than twice that of the mesh-patterned film. Therefore, in this study, two factors were reflected as important experimental parameters to optimize and highly improve the deposition thickness and mechanical performance for aerosol-deposited bioceramic films. A metal shadow mask was fixed on the sapphire bracket to more stably deposit bioceramic particles.

(3) Characteristics

The shape and size of the bioceramic powders and the surface microstructure of the coating layer were applied to a field-emission scanning electron microscopy (FE-SEM, S-470, HITACHI LTD., Japan) at 10 kV. Was observed by. Bio by using X-ray diffraction (XRD, X'Pert PRO dirrfactometer, PANalytical, USA) using ~1.5406 Cu Cu Kα radiation for the 2 θ range of 10-60° in increments of 0.02° (2 θ ) The crystallinity of the ceramic powders and the coating layer was evaluated.

The thickness of the bioceramic coating layer was measured using a surface roughness meter (XP-1, Ambios Tech, USA), and an area of 40 ⅹ 40 µm ² using an atomic force microscope (atomic force microscopy: AFM, N8 NEOS, Brucker, Germany) The root mean square (RMS) surface roughness and morphologies were investigated.

The adhesive strength between the sapphire substrate and the aerosol-deposited bioceramic coating layer was measured using a universal tester (UTM, DUT-300CM, Daekyung engineering Corp., Korea). Became. Epoxy resin (4-META/MMA-TBB) and cylindrical rods were attached in stages to the bioceramic films, and the maximum load was until the bioceramic films were fully debonded from the substrate. Pulled up at a loading speed of 5 mm/min. Thereafter, the adhesion was estimated.

To evaluate the shear bond strength, a ceramic with a bioceramic coating layer using a knife-edge blade with a crosshead speed of 1 mm/min. It was applied to the interface between the bracket (ceramic bracket) and enamel (enamel, human premolar).

The maximum load for debonding was measured in ratios of Newtons and converted to megapascals (MPa) as the ratio of Newtons to the surface area of the bracket base. .

3. Results

3.1 Formation of dense nanostructured bioceramic films by the AD process

2 shows an SEM micrograph of each bioceramic powder.

)가, 도 2(c) 및 (d)에 도시된 바와 같이, 각각 2㎛ 및 50㎛의 입자 크기가 선택되었다. 2(a) and (b), an average particle diameter of ˜0.5 μm was used for SiO ₂ and Al ₂ O ₃ . In a previous study, we investigated the effect of Al ₂ O ₃ on the deposition properties through the AD process, so that Al ₂ O ₃ It was confirmed that the shape and size of the powder had better properties in both surface roughness and deposition rate [40]. As a result, when using Al ₂ O ₃ having an average particle size of 0.5 μm, while adequate surface roughness and highest deposition rate are simultaneously achieved, Al ₂ O ₃ larger than 0.5 μm. The particles (Al ₂ O ₃ particles) not only formed excessively deteriorated surfaces but also showed a significantly reduced deposition rate. Surface roughness is an important factor in orthodontic brackets, as it has an important relationship with bonding strength, so excessively high surface roughness enamels during debonding. ) While adequate roughness indicates that the desired shear bond strength is achieved [41, 42]. Moreover, since the thickness of the ceramic film for dental brace brackets must be composed of tens of micrometers to obtain excellent shear bond strength, the deposition rate is also an important parameter for the bracket. Indeed, previous studies on aerosol-deposited brushite films showed that the shear bond strength increased gradually with increasing thickness. Therefore, SiO ₂ and Al ₂ O ₃ having a particle size of ˜0.5 μm were chosen for high mechanical performance in the body. Additionally, HA (hydroxyapatite, hydroxyapatite) and brushite (which appear to be oriented parallel to a particular direction)

), as shown in Figures 2 (c) and (d), particle sizes of 2 μm and 50 μm, respectively, were selected.

In particular, brushite powder with a particle size larger than the previous three types of powder was used in this study because, in the previous study, aerosol-deposited brushite film with a particle size larger than 50 μm (aerosol) This is because -deposited brushite film) showed good mechanical properties and deposition rate [36].

From the aerosol-deposited bioceramic films, the deposition rates of four types of powders were first investigated as shown in FIG. 3. Deposition rate was measured through a surface profiler and calculated as the deposition thickness per scanning time. The deposition rate was defined as how thick the coating layer was formed over the scanning time: (a) SiO ₂ : 0.38 μm/min, (b) Al ₂ O ₃ : 0.75 μm/min, (b) HA: 22 μm/min , And (d) Brushite: 27 μm/min. For HA (hydroxyapatite, hydroxyapatite) and brushite films, a significantly higher deposition rate was achieved compared to current surface coating methods. In the AD process, the difference in deposition rate is known to be due to the surface energy, density, shape, size, etc. of raw powder [43,44]. ].

This study considered why the deposition rate of each material is different by focusing on the surface energy, shape, and basic structure of the pure powder. It is known that the surface energy of each material has the following numerical values: SiO ₂ ; 5.02 J/m ² [45], Al ₂ O ₃ ; 1.01 J/m ² [46], HA; 0.025 to 0.076 J/m ² [47], and brushite; 0.386 J/m ² [48]. First, the inversely proportional relationship between deposition rate and surface energy is established. This effective phenomenon is closely related to the agglomeration behavior of the ceramic powder in the aerosol chamber. In general, if the surface energy of the powder has a low value, the particles tend to push away from each other in the aerosol chamber and tend to disperse more [44], which means that at higher deposition rates more aerosols are delivered to the deposition chamber. And an effective bioceramic film is formed. However, particles with high surface energy tend to aggregate themselves in the aerosol chamber to dissipate this energy, and for this reason, aerosolization to reach the sapphire substrate- The aerosolized-powders ability is reduced for dispersed-particles. Because of the effect on the difference in surface energy properties of the main particles, the deposition rate can be defined as shown in FIG. 3.

Second, unlike SiO ₂ and Al ₂ O ₃ , HA and brushite powders have significantly different properties, as shown in FIG. 2, in that they have a flat structure as well as much larger particle sizes. Because the structure of brushite powders generally tends to flatten along the 010 face and mainly consists of a fairly thin and brittle plate [49,50], it is often easy to produce a large number of impacts on the substrate, each particle This results in active bonding with Wah. Similarly, HA is parallel to the crystallographic direction (001) of the starting powder, so that HA is easily broken into small pieces [51]. For these two reasons, it can be inferred that the best deposition rate was achieved when using HA and brushite powders.

4 shows XRD patterns of raw powders and as-deposited bioceramic films. Compared to other surface coating processes, the AD process offers great potential due to room temperature aerosol deposition processing at 23°C. For example, in this study, XRD patterns of aerosol deposited bioceramic films did not show a phase transition as shown in FIG. 4. The peaks of the four types of bioceramic films were weak and wide compared to the four types of starting powders. The crystal sizes of the 4 types of deposited films were determined by the Debye-Scherrer equation, D = Κλ / β cosθ , where D is the average grain size, λ is the wavelength of the X-ray (Cu Kα emission: 1.5406 ÅA), β is FWHM (full width at half maximum), and θ is the diffraction angle [52]. From the calculation results derived from the Debye-Scherrer equation, the crystal sizes of SiO ₂ , Al ₂ O ₃ , HA (hydroxyapatite, hydroxyapatite) and brushite films are (100), (104), (110) and (020). Corresponding to the surfaces, it was predicted to be approximately 1748 nm, 24.93 nm, 43.77 nm and 77.98 nm, respectively, which is substantially reduced compared to the respective starting particle size. This phenomenon can be directly related to shock-loading solidification, which is known to be the basic mechanism in AD. When the ceramic particles strongly collide with the sapphire substrate during the AD process, grain pulverization of the starting particles is induced upon their impact on the hard sapphire substrate. , It becomes a fine nanocrystalline structure.

Nanocrystallites smaller than 100 nm may be beneficial in biotechnology for dental brackets, implants, and bioactivity. In previous studies, conventional ceramics, such as Al ₂ O ₃ and HA with grain sizes greater than 100 nm, resulted in clinical failure and non-ideal dental effects due to defects in bonding strength [53]. In contrast, nanophase ceramics provide improved long-term functions for implant osteoblasts, cell population motility, cell proliferation, and the like.

In view of the foregoing, nanocrystalline bioceramic films have great potential, particularly with respect to improved bonding strength between the orthodontic bracket and the tooth. Will maintain, which will result in high dental bracket efficiency.

3.2 Surface properties of aerosol-deposited bioceramic films

In addition to the significant effect of crystal size fluctuations after the AD process, the surface structure must be carefully considered for orthodontic bracket applications, which is essential for proper tooth movement and biological performance, coefficient of friction ( friction coefficient). Additionally, the bonding strength of films is affected by the shape, sharpness, and depth of surface flaws or defets of the surface defects or defects [54,55]. From the SEM micrograph results as shown in Figure 5, SiO ₂ Film and Al ₂ O ₃ While all films exhibited a fairly smooth surface than other bioceramic films, HA (hydroxyapatite) films and brushite films showed severely damaged surfaces after the impact of particles on the substrate. Although the initial particle sizes of SiO ₂ , Al ₂ O ₃ , and HA powder have similar values, SiO ₂ The film had the most visible flat and uniform surface among them. The cause of the inconsistency in the surface structure may be due to the difference between the Vickers hardness and the surface energy of each raw material. First, the average values of Vickers hardness for SiO ₂ , Al ₂ O ₃ , and HA (hydroxyapatite) are known as 8.20 GPa [56], 15.71 GPa [57], and 4.03 GPa [58], respectively. During the AD process, Al ₂ O ₃ , which is known as one of the highest hardness materials among ceramics, can transmit a large impact to the substrate. This environment is obviously Al ₂ O ₃ Between particles and Al ₂ O ₃ Although it can result in an organically tight bond between the particles and the substrate, the internal microstructure of the surface was slightly rough due to the continuous minor etching effect due to the strong impact stress on the substrate [ 59]. Secondly, as presented in Section 3.1, considering that HA and brushite have a large particle size and unique shape, these particles give a greater impact on the film deposited during the aerosol deposition process (AD process). , It is clear that it will cause surface deterioration due to repetitive impact. Therefore, for HA (hydroxyapatite) and brushite films, morphologies can be considered to be dominantly controlled by their basic structure in a straight line with the same crystallographic direction and their angular shape. have.

In order to investigate the surface roughness of each bioceramic film in more detail, atomic force microscopy was performed to confirm surface morphologies and RMS roughness. The measurement of the RMS roughness value is considered a major factor in orthodontic systems because it is closely related to the ceramic-to-resin bond strength. Thus, a strong and robust ceramic-to-resin bond can improve marginal adaptation and limit microleakage avoidance. Strong ceramic-to-resin bonding typically relies on micro-mechanical interlocking and chemical bonding, which is due to the soft properties of the resin, which makes it suitable for the ceramic surface. It requires roughening [60]. That is, a properly rough surface is a prerequisite for achieving effective bonding strength between the ceramic coating and the resin.

6, the RMS roughness of the SiO ₂ film showed the lowest value, while the RMS roughness of the brushite and HA films showed the highest value. Excessive roughening of surfaces over a few micrometers caused ceramic damage during debonding of the bracket, so specific surface treatments were performed in some previous studies. . Nevertheless, the four types of bioceramic films appeared to have adequate RMS roughness without special surface treatments.

Therefore, although the brushite film or HA film shows some craters on the surface, the average surface roughness of all four types of aerosol-deposited bioceramic films used in this study roughness) showed a desirable value for dental applications.

3.3 Tensile and shear mechanical properties between ceramic coating and sapphire bracket as deposition mechanism

The adhesive strength and shear bond strength between the ceramic coating for the orthodontic bracket and the sapphire bracket are the external forces during the orthodontic procedure. It should be enough to support. Therefore, the adhesion strength in vitro was first measured, and as a result, numerical values of the applied force required to debond each bioceramic coating layer from the sapphire substrate are shown.

As shown in FIG. 7, the SiO ₂ film, Al ₂ O ₃ film, HA film, and brushite film withstand 5 MPa, 14.5 MPa, 9.5 MPa, and 9.2 MPa, respectively. According to other studies, the bond strength should be greater than approximately 6-8 MPa to avoid adhesion failure and improve mechanical properties [62, 63]. Therefore, the aerosol-deposited SiO ₂ film was slightly insufficient for dental brackets due to the low adhesive strength during the procedure. However, AD process (AD process) for the high strength (high strength) and the Al ₂ O ₃ particles (Al ₂ O ₃ particles) having a high hardness (high hardness) is formed basically strong binding after impact on the substrate Therefore, the Al ₂ O ₃ film recorded the highest adhesive strength value. However, if the bond strength is too high, such as an Al ₂ O ₃ film, it can damage enamel during debonding and lead to deformation of the tooth structure [64, 65].

Suitable bond strength values were measured for HA and brushite films. Therefore, bioceramic films with optimum adhesive strength can be formed by the AD process when HA and brushite powders are used rather than SiO ₂ and Al ₂ O ₃ powders.

Next, we measured the shear bond strength of the orthodontic brackets, which is an important factor in dealing with the transfer of forces to the bonded interface and tooth structures. Brackets and enamels were bonded with 4-META/MMA-TBB epoxy resin.

As shown in FIG. 8 with red, blue, and black lines, it was confirmed that aerosol-deposited bioceramic films had reliability and durability by testing shear bond strength three times for each sample. From the measurement results, both the SiO ₂ and Al ₂ O ₃ films had a shear bond strength value between 6 MPa and 8 MPa. HA and brushite films showed shear bond strength values greater than 10 MPa, much larger than SiO ₂ and Al ₂ O ₃ films. The tendency of the shear bond strength was proportional to the RMS roughness value analyzed in FIG. 6. As indicated by the HA and brushite films, coarse surface properties are desirable to achieve micro-mechanical interlocking with the resin and are not easily debonded even with high shear forces. Moreover, it is believed that the difference in the in vitro shear bond strength between the four types of bioceramic films is more closely related to the deposited-film thickness than the physical properties of each material [38]. This means that dense ceramic nanostructured films with large thickness act to support the shear force because thicker bumps provide strong macro-mechanical interlocking. From the two rectification mechanical tests, HA and brucite films showed statistically higher adhesion strength and shear bond strength, which is practically suitable for dental applications, while SiO ₂ and Al ₂ O ₃ films are insufficient. It has a bonding strength.

Based on the measurement data, as shown in FIG. 9, the AD mechanism of the bioceramic films used in this study was categorized into four different phenomena. The four types of bioceramic films showed a common characteristic with a crystal size smaller than 100 nm after the AD deposition process. The two samples, except SiO ₂ and Al ₂ O ₃ , showed some visible craters on the sapphire substrate in enlarged SEM images, but the RMS roughness values were based on resin and ceramic coating. It could have been sufficient to form micro-mechanical interlocking between coatings, and would have served as a bonding advantage for dental brace brackets as suggested in previous studies.

In the case of SiO ₂ film as shown in FIG. 9(a), the deposition rate was relatively low due to the high surface energy, which is an inherent property, and the two types of mechanical properties were orthodontic. It was not suitable for the dragon bracket. While the Al ₂ O ₃ film showed extremely high adhesive strength, it could cause significant damage to the teeth when debonding the dental bracket, resulting in deformation of the tooth structure.

Another major issue with Al ₂ O _{3 included} a significantly lower deposition rate of less than 1 μm/min, lower than the HA film and brushite film, as shown in FIG. 9(b), which resulted in thin bumps. The lack of macro-mechanical interlocking from thin bumps resulted in low shear bond strength.

9(c) and (d), HA and brushite films, which gave the best results among the four types of bioceramic films in this study, did not have a heating process or surface treatment. The AD device has shown great potential in terms of high deposition rate and fairly effective mechanical properties due to proper surface roughness, which is the most useful in the use of orthodontic systems. Both shear bond strength and adhesive strength, considered important issues, were satisfied.

The method of evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets of the present invention, at room temperature, bioceramic particles on a sapphire bracket and a sapphire substrate by an aerosol deposition process (AD process) using an AD device Depositing to form a nanostructured bioceramic coating layer; And measuring the mechanical properties of the aerosol-deposited bio-ceramic film for orthodontic brackets, namely surface roughness, deposition rate and adhesive strength.

The bioceramic coating layer is characterized by being a bioceramic film in which any one of bioceramic particles of Al ₂ O ₃ , SiO ₂ , HA (hydroxyapatite), or brushite is deposited.

The crystal size of the four types of bioceramic films is 100 nm or less from XRD data.

The AD device includes a vacuum system having a rotary pump and a mechanical booster pump, an aerosol chamber, a moving X-Y stage, a deposition chamber, a carrier gas, and a flow controller.

In the aerosol deposition process of step (a), bioceramic powders are dried in a drying oven at 80° C. for 8 hours using the AD device, and a fine sieve network is used. Moisture is removed or collected through, and the bioceramic powders are placed in an aerosol chamber, and a carrier gas is injected to supply the powder to drive the deposition chamber, and the bioceramic powders are supplied through a tube to a nozzle. Delivered; And film deposition includes forming the bioceramic coating layer using a nozzle orifice such that a dense film having a higher deposition rate and film hardness is formed in an AD process than a direct injection method.

Prior to the injection of the carrier gas, the deposition chamber is pre-evacuated at ~3.2 Torr by two types of vacuum pumps to maintain the accelerated powder velocity from the nozzle and helium (purity 99.99%). This carrier gas is used.

The nozzle orifice uses a 1.5×1.5 mm ² nozzle orifice having a deposition rate 7 times higher than that of a 10×0.4 mm ² nozzle orifice.

In the AD process, the bioceramic coating uses shadow mask patterning using a check-pattern on a sapphire bracket, and a check-patterned film is used. The brushite film has excellent mechanical properties and deposition rates, and has a shear bond strength that is more than twice that of the mesh-patterned film.

The surface properties of the aerosol-deposited bioceramic films were measured by atomic force microscopy, while the RMS roughness of the SiO ₂ film showed the lowest value, while the RMS roughness of the brushite and HA films showed the highest value, and strong ceramic-to- Resin bonding typically relies on micro-mechanical interlocking and chemical bonding, where an appropriately rough surface is effective for effective bonding strength between a ceramic coating and a soft resin. bonding strength),

The average surface roughness of the four types of aerosol-deposited bioceramic films has a desirable surface roughness for dental applications.

The HA (hydroxyapatite) and brushite films are SiO ₂ and Al ₂ O ₃ It has a larger deposition rate than the film.

In the HA (hydroxyapatite) and brushite film, SiO ₂ and Al ₂ O ₃ films had a shear bond strength value between 6 MPa and 8 MPa, and the HA and brushite film had a shear bond strength value greater than 10 MPa,

Optimal adhesion strength values were observed compared to the SiO ₂ and Al ₂ O ₃ films, and the HA and brushite films had a shear bond strength 1.5 times higher than that of the SiO ₂ and Al ₂ O ₃ films.

In the bio ceramic film, the HA (hydroxyapatite) and brushite films are used in the orthodontic bracket.

4. Conclusion

By using four types of biocompatible bioceramic powders, nanostructured bioceramic coating layers were formed on sapphire brackets and sapphire substrates. The crystal size of all bioceramic films was calculated to be less than 100 nm from XRD data, and this method can be used for high efficacy orthodontic brackets such as successful treatment and improved bond strength.

However, differences in two properties, deposition rate and mechanical properties, were confirmed by comparing four types of bioceramic films [Al ₂ O ₃ , SiO ₂ , HA (hydroxyapatite, hydroxyapatite), and brushite]. . The mismatch of deposition rate between the four samples is due to the difference in the surface energy and the basic structure of each raw material. As a result, HA (hydroxyapatite, hydroxyapatite) and brushite films are SiO ₂ and Al ₂ O ₃ It was shown to have a significantly higher deposition rate than the film. Optimum adhesion strength values were observed for HA and brushite films compared to SiO ₂ and Al ₂ O ₃ films. In four types of bioceramic films, SiO ₂ and Al ₂ O ₃ films had shear bond strength values between 6 MPa and 8 MPa, and HA and brushite films had shear bond strength values greater than 10 MPa. In addition, HA and brushite films showed 1.5 times higher shear bond strength than both SiO ₂ and Al ₂ O ₃ films, which is a result of higher bump thickness and sufficient RMS roughness. Inferred, can be used for orthodontic brackets. These results facilitate the formation of bioceramic films with large-thickness nanocrystalline structures with high mechanical properties and encourage further utilization of an economical and simple AD process.

As described above, the present invention has been described with reference to preferred embodiments of the present invention, but the present invention is within the scope not departing from the technical spirit and scope of the present invention described in the following claims by those skilled in the art. It will be understood that various modifications or variations can be carried out.

Claims (13)

(A) forming a nanostructured bioceramic coating layer by depositing bioceramic particles on a sapphire bracket and a sapphire substrate by an aerosol deposition process (AD process) using an AD device at room temperature; And
(b) measuring the mechanical properties of the aerosol-deposited bioceramic film for orthodontic bracket, namely surface roughness, deposition rate and adhesive strength;
Method for evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets comprising a. According to claim 1,
The bioceramic coating layer
Structural and mechanical properties evaluation method of aerosol-deposited bioceramic film for orthodontic brackets, characterized in that it is a bioceramic film in which any one of Al ₂ O ₃ , SiO ₂ , HA (hydroxyapatite), or brushite is deposited. . According to claim 2,
Method for evaluating the structure and mechanical properties of aerosol-deposited bioceramic films for orthodontic brackets, wherein the crystal size of the four types of bioceramic films is 100 nm or less from XRD data. According to claim 1,
The AD device is a vacuum system having a rotary pump and a mechanical booster pump, the structure and mechanical properties of the aerosol-deposited bioceramic film for orthodontic brackets having an aerosol chamber, a moving XY stage, a deposition chamber, a carrier gas, and a flow controller. Assessment Methods. According to claim 4,
The aerosol deposition process (AD process) of step (a) is
Using the AD device, bioceramic powders are dried in a drying oven at 80° C. for 8 hours, soaked through a fine sieve net to remove or collect moisture, and the bioceramic powders ( powders) are placed in an aerosol chamber, driving a deposition chamber by injecting carrier gas and supplying the powder, and transferring the bioceramic powders to a nozzle through a tube; And
Film deposition comprises forming a bioceramic coating layer using a nozzle orifice such that a dense film having a higher deposition rate and hardness is formed in an AD process than a direct injection method;
Method for evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets comprising a. The method of claim 5,
Prior to the injection of the carrier gas, the deposition chamber is pre-evacuated at ~3.2 Torr by two types of vacuum pumps to maintain the accelerated powder velocity from the nozzle and helium (purity 99.99%). Method for evaluating the structure and mechanical properties of aerosol-deposited bioceramic films for orthodontic brackets, in which this carrier gas is used. The method of claim 5,
The nozzle orifice uses a 1.5 × 1.5 mm ² nozzle orifice having a deposition rate 7 times higher than that of a 10 × 0.4 mm ² nozzle orifice, a method for evaluating the structure and mechanical properties of an aerosol deposited bioceramic film for orthodontic brackets. According to claim 2,
HA(hydroxyapatite) and brushite(

) Has a particle size of 2㎛ and 50㎛ respectively, a method for evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets. The method of claim 5,
In the AD process, the bioceramic coating uses shadow mask patterning using a check-pattern on a sapphire bracket, and a check-patterned film is used. aerosol deposited bio for orthodontic brackets, which has excellent mechanical properties and excellent deposition rate, and has a shear bond strength that is more than twice that of mesh-patterned films. Method for evaluating the structure and mechanical properties of ceramic films. According to claim 2,
The surface properties of the aerosol-deposited bioceramic films were measured by atomic force microscopy, while the RMS roughness of the SiO ₂ film showed the lowest value, while the RMS roughness of the brushite and HA films showed the highest value, and strong ceramic-to- Resin bonding typically relies on micro-mechanical interlocking and chemical bonding, where an appropriately rough surface provides effective bonding strength between a ceramic coating and a soft resin,
The average surface roughness of the four types of aerosol-deposited bioceramic films has the desired surface roughness for dental applications, and the structure of the aerosol-deposited bioceramic film for orthodontic brackets And mechanical property evaluation methods. According to claim 2,
The HA (hydroxyapatite) and brushite films are SiO ₂ and Al ₂ O ₃ Method of evaluating the structure and mechanical properties of an aerosol-deposited bioceramic film for orthodontic brackets with a deposition rate greater than the film. According to claim 2,
The HA (hydroxyapatite) and brushite film
SiO ₂ and Al ₂ O ₃ films had a shear bond strength value between 6 MPa and 8 MPa, the HA and brushite films had a shear bond strength value greater than 10 MPa,
Optimal adhesive strength values were observed compared to the SiO ₂ and Al ₂ O ₃ films, and the HA and brushite films had a shear bond strength 1.5 times higher than that of the SiO ₂ and Al ₂ O ₃ films, orthodontic bracket. Method for evaluating the structure and mechanical properties of aerosol-deposited bioceramic films. According to claim 2,
The bio-ceramic film is a method for evaluating the structure and mechanical properties of the aerosol-deposited bio-ceramic film for the orthodontic bracket, wherein the HA (hydroxyapatite) and brushite films are used for the orthodontic bracket.

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