CC BY
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CHEMICAL PROBLEMS 2024 no. 1 (22) ISSN 2221-8688
115
UDC 54.057:547.995.1
EFFECTS OF ADDITION OF CHITOSAN AND DICARBOXYLIC ACID ON PROPERTIES OF 3D PRINTABLE ACRYLIC RESIN DENTURE BASE
112 Ihssan F. Al-Takai *, Luma AL-Nema , Fawzi H. Jabrail
Department of Prosthetic Dentistry, College of Dentistry, University of Mosul, Mosul, Iraq.
2Department of Polymer Chemistry, College of Science, University of Mosul, Mosul, Iraq.
*Corresponding Author: Ihsan20H@,uomosul. edu. iq
Received 07.11.2023 Accepted 25.01.2024
Abstract: 3D-printing has gained popularity in recent years due to the many advantages it offers over the traditional approaches for instance this technology reduces the time a dentist needs to create and fit dentures to just 2-3 sessions. Fumaric, maleic, and adipic acids with the percentage (0.1 wt.%) were added to chitosan solution (2 wt.%) and the final composite was added to the 3D printable acrylic resin. The specimens were examined for several chemical analyses (XRD, SEM, FTIR) and mechanical tests (impact strength and surface hardness tests), where the total number (115) of specimens used in the study was specimens divided into five groups. In chemical analysis, one specimen was constructed for each modified group and one specimen was used as the control group (3d printable resin without addition (non-modified) for each test. For mechanical tests ten specimens were constructed for each modified group and ten specimens were used as the control group (3dprintable resin without addition (non-modified) for each test. The results of chemical analysis showed improvement in the properties of modified 3d printable acrylic denture base resin, additionally the mechanical test results showed that the (Fumaric acid and Maliec acid with Chitosan) specimens have the highest properties in comparison with other specimens, while the lowest properties were for specimens of 3D printable acrylic resin with chitosan. The chemical and mechanical properties of the modified 3D-printed denture base are improved when chitosan is modified with dicarboxylic acids. Conversely, if chitosan alone is used to modify the 3D-printedpolymers, the mechanical and chemical properties would be decreased.
Keywords: Acrylic resin, Chitosan, Dicarboxylic acids, Fumaric acid, Maleic acid, Adipic acid. DOI: 10.32737/2221-8688-2024-1-115-132
1. Introduction
The most popular fabrication techniques that employ the "subtractive" method, in which a solid block of material is cut piece by piece to create the desired object, are casting, molding, forming, and machining. Subtractive methods have evolved significantly over the ages, leading to increased production efficiency and better final product quality [1, 2].
The first chair-side CAD/CAM machines were used in labs and dental offices in the late 1980s. By doing away with the need for impressions, this technology's primary advantage over traditional restorative dentistry techniques was a reduction in chair time.
However, the widespread use of dental CAD/CAMs was hindered by the high cost of the equipment and limitations on producing prostheses with precise anatomical details [3,4].
Ciraud created a method for powder deposition of meltable materials in 1972 [2, 5]. Housholder developed a laser-assisted powder sintering technique in 1979 using a similar methodology [6]. In contrast to subtractive techniques, these methods use an additive process whereby the objects are constructed layer by layer. 3D Systems Corporation unveiled the first additive manufacturing (AM) equipment in the late 1980s. Since then, AM has
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CHEMICAL PROBLEMS 2024 no. 1 (22)
seen a constant rise in applications, primarily in the automotive, aerospace, and medical sectors [7].
Additive manufacturing (AM), known as three-dimensional printing, is a method of creating objects by layer-by-layer material deposition. Aerospace, engineering,
construction, and medical are just a few of the industries that use 3D printing. Metals, polymers, and resins are among the many materials that can be used for 3D printing. These substances could be powder, liquid resins, or filaments. 3D printing is being used more and more in biomedical applications, especially in dental and craniofacial applications. Digital dentistry is made possible by the use of 3D printing methods to create patient-specific equipment, such as stereolithography (SLA), fused deposition modeling (FDM), and selective laser sintering. 3D printing for dentistry offers several advantages, including mass and individual customization, precise fit, speedy turnaround times, and accurate clinical results. The most popular type of 3D printable material for dental applications is photo-curable resin. With SLA technology, liquid resin is cured using a scanning laser so that objects can be built layer by layer. LED (light-emitting diode) projectors are used in digital light processing technology to cure the resin. Permanent and temporary crowns, gingiva masks, dental models, surgical guides, and custom impression trays are all made from liquid resin materials processed in SLA or DLP [8].
Photopolymer resin is cured using a projector in the digital light processing (DLP) 3D printing method. The sole distinction between it and Stereolithography (SLA) is that safe-light, or a light bulb, is used to cure the photopolymer resin rather than a UV laser in the SLA 3D printing method [9]. Heat-cured acrylic resin is the material of choice for the construction of complete dentures due to its desirable properties, although it has some disadvantages as its susceptibility to fracture. Several methods and materials are used to reinforce the acrylic resin denture base. One of these methods is reinforcement by using fibers. In this study, visible light cure fiber framework is used as reinforcement material and compared
with reinforcement with glass fiber [10].
Compared to heat-polymerized PMMA, the mechanical strength of 3D-printed resin was lower. When CAD/CAM (milled or 3D-printed) materials were compared to conventional denture base material, Prpic' et al. (2020) found that the 3D-printed PMMA had the lowest flexural strength of all the materials tested [11]. This outcome might be the result of the material composition since conventional acrylic resins have a higher double bond conversion rate than the monomer used in 3D printing, which is based on acrylic esters [12].
Surface characteristics were the primary determinant in the selection of denture base materials. Surface properties like surface topography and roughness can affect discoloration, water absorption, microbial adhesion, and even oral hygiene [13]. For clinical applicability, the surface characteristics of 3D-printed DBRs should be evaluated. When compared to traditional heat-polymerized Dentures Base Resins (DBRs), the 3D-printed DBRs had poorer surface characteristics [14].
Many efforts have therefore been undertaken to enhance the mechanical and physical characteristics of printable acrylic resins, and this agrees with Biswas et a/.,[15] who stated the addition of Filler and nanoparticle-based reinforcing additives to acrylic base resins[16,17]. Chitosan filler is a polycationic polymer that has active "amino" and "hydroxyl" functional groups [18-22]. Moreover, chitosan also has a high resistance to heat due to its intramolecular hydrogen bonds [20, 21], so it can be used safely with printable and thermoplastic resin.
When acrylic resin was mixed with chitosan only, the tensile strength of the resin decreased, but it was still within an acceptable range when compared to the control group that did not add chitosan. These results were consistent with those of other studies that examined the size, aspect ratio, degree of filler dispersion, and adding other filler or materials to the composite [23-25]. This network strengthens the composite material and raises the stress distribution and modulus of elasticity [26] and this might be due to reinforcement and the enhanced interfacial bonding effect of chitosan composites which dispersed in resin
due to their high surface area, producing a network-like structure and restrict polymer chain mobility in the resin matrix, increasing the stiffness and modulus of elasticity [26-28].
The acrylic resin without mixture (control) had the largest average number of pores compared with the acrylic resin mixed with chitosan and acrylic acid at 1 and 2% concentrations. This phenomenon occurred because even after the polymerization of acrylic resin without a mixture, some monomers did not bind to the polymer and instead formed pores. Meanwhile, acrylic acid can function as a coupling agent to form bonds between acrylic resin and chitosan; hence, the monomers contained in the acrylic resin can be bonded during polymerization [29].
This finding was confirmed by the decreased residual monomer quantity in the acrylic resin mixtures with 1 and 2% chitosan and acrylic acid [30]. Therefore, this polymerization can reduce the formation of pores. The decrease in the amount of residual monomer can reduce the formation of space known as porosity [29]. A large pore size will allow the easy absorption of liquid, which in turn will reduce the density and other mechanical properties of the acrylic resin [31, 32].
This study aimed to evaluate the effects of adding chitosan, both pure chitosan solution and the composite of chitosan with a dicarboxylic acid, on the various characteristics of a 3D printable acrylic resin denture base.
2. Materials and methods
2.1. Materials. description are tabulated below (Table 1).
The materials with their origin state and short
_Table 1. Materials used in the study_
Chitosan powder (Shrimp source, China ),DD=75-85%; M.Wt=190-310KDa;glacial acetic acid
was supplied by Darmstadt, Germany_
Fumaric acid (glacial 100%, pro-analysis) was purchased from Merck (Darmstadt, Germany).
Adipic acid (glacial 100%, pro analysis) was obtained from Sigma-Aldrich (USA)._
Maleic acid (glacial 100%, pro-analysis) was purchased from Sigma Al-drich (USA)_
Poly(vinyl alcohol) (PVA Fluka), Honeywell Fluka, M.Wt=195 Kg mol-1
Ultrapure water (Maxima UltraPure Water, Elga-Prima Corp, UK) with resistivity > 18 Mfl/cm 3d printable acrylic resin (DENTABASE 3D+ denture base material (ASIGA , Australia)
2.2. Preparation
2.2.1. Chitosan Solution preparation. A
commercial supplier provided the chitosan solution. With a deacetylation percentage (DD) of 75-85% from chitin that will be processed, a local company sold shrimp source chitosan powder (China). Every solution was prepared using ultra-pure water. Every experiment used freshly made solutions, and no additional purification was applied to any of the chemicals. An oven was used to dry the chitosan until a consistent weight was reached. Dry chitosan (0.1 g) was dissolved in (2 wt%) of acetic acid solution in Ultra-pure water.
The solution was stirred and heated to 60 degrees Celsius for (I hour) and after completely dissolved, the solution was filtered for removal of air bubbles and undissolved materials [33].
2.2.2. Chitosan with dicarboxylic acid solutions. Dry chitosan solution (1.0g) was dissolved in the following acid solutions (2wt%) adipic acid, maleic acid, fumaric acid, then gently stirred, and heated to approximately 55°C in an oven for an entire night for dissolving and then filtered to get rid of any remaining dust and other contaminants and left two hours at room temperature for removal air bubbles from the solutions [33].
Subsequently, 0.1ml of each modified Chitosan acid solution was added to the main weight of the 3D printable acrylic resin (Asiga washing and curing machine; Australia). The designs are saved as STL files, and after the base and support are added to the 3D-designed samples, the printer settings and slicing are adjusted before the samples are exported to the
printer. Additionally, the study's recommendations for slice thickness, specimen cleaning, and drying were all followed [34, 35].
The specimens were ready for chemical and physical testing following the modification procedures. Thus, approximately 115 specimens were used in the study. ANOVA, Duncan's multiple range tests, mean and standard deviation, and p<0.01 were used to identify significant differences between the tested groups.
2.3. Chemical analysis
2.3.1. Field Emission Scanning Electron Microscopy (SEM). The surface structure and distribution of the nanoparticles were assessed using a scanning electron microscope (SEM) with a spatial resolution of 1.5 nm (Mira 3 Tescan FESEM, Czech). Using a sputter coating machine, a 20 |im layer of gold was applied to all 3D printed samples to make them electroconductive and suitable for SEM imaging scanning. (15 KeV) is the accelerating voltage, and the magnification power will range from 2000 to 5000 X [36].
2.3.2. Fourier Transform Infrared Spectroscopy (FTIR). Fourier Transform Infrared Spectroscopy of a CL Alpha-PFTIR
spectrophotometer with a wavenumber range of 400-4000 cm-1 and a resolution of 2 cm-1 will be used to perform FTIR. 2.3.3. X- Ray Diffraction (XRD). An XRD instrument with CuKa tube operating at 40 kV and 30 mA produces X-rays with a wavelength of X=1.54060A; the scan mode is continuous scan, and the scanning speed is 5deg/min. 2.4. Mechanical test 2.4.1. Impact Strength
An impact strength test was performed using a Charpy impact tester. The test specimens were prepared following the ISO standard No. 179, measuring 55*10*10±0.2mm for length, width, and height, respectively, and featuring a V-shaped notch. The specimen's notch measured 2.5 mm in depth, with an effective depth of 7.5 mm below the notch throughout its 10 mm width. The specimen was fixed horizontally using two support arms spaced 40 mm apart. It was then struck by a 75.8 kg free-swinging pendulum that was released from a fixed height at the midpoint on the opposite side of the notch. The impact strength of each specimen was measured in kJ/m2 using the formula below [37, 38]:
Impact strength = E/b*d
(here, E: absorbed energy, b: sample width, d: sample thickness). 2.4.2. Surface Hardness:
The following dimensions
(10x10x3.3±0.2 mm for length, width, and height, respectively) will be prepared for each group's specimens. Every specimen had five measurements made on various parts of it, from which the mean value was determined [39].
The Microhardness Vickers tester (HV-1000A, Korea) will be used to measure the specimen's surface hardness. The hard materials are fitted with an indenter, which is a 1.25 mm-
diameter round steel ball [40].
The apparatus's solid plane will hold the specimen, and the needle is positioned 12 mm from the specimen's edge. A constant minor load of 44.5N was applied to the specimens. The apparatus automatically converted the tester's measurement of the indenter's relative movement, which is measured immediately after each indentation, into a scale with a graduation of 0 to 100 units. After the load is applied for one second, the final hardness value will be determined by visually interpreting the analog.
3. Results and discussions
3.1 Field Emission Scanning Electron Microscopy (SEM).
In this test, the SEM images showed that chitosan samples only form an irregular morphological surfaces with folds and voids
with high porosity and the chitosan surfaces show high roughness which means high shape factors with whiten spots or edges mean they had course surfaces, while with the addition of 2% w/w chitosan to dicarboxylic acids (adipic,
fumaric, and maleic acids) SEM images shows a homogenous structure after addition of chitosan and dicarboxylic acid materials more than that of the control samples and the chitosan samples alone (Figure 1).
The morphology of the examined samples studied by SEM shows major morphologic features and a microstructure overview were observed at low magnification, precise
morphological features was observed at medium magnification, and microstructural details were observed at high magnification [41].
The 3D printable acrylic resin was analyzed using FESEM. The modified resin with chitosan alone and chitosan with dicarboxylic acids caused observable morphological changes.
Fig. 1. A representatiove images of Field Emission Scanning Electron Microscopy of (A) Control group; (B) Chitosan group; (C) Adipic acid group; (D) Fumaric acid group; (E) Maleic acid group.
The large-sized particles of the modified samples had irregular surface morphology, while the surface of the unmodified control sample was rough. The surface morphology of the control samples showed pores, which suggested that the material had not been compacted with fatigue composite.
The control sample's surface morphology showed 42 pores, which increased when chitosan was added, showing chitosan particles with less dispersion of 3d printable acrylic resin.
The SEM image of 2% w/w chitosan alone showed that the chitosan particles had embedded themselves in the denture base resin. This could have an impact on the physical or mechanical bond that can form because of size differences between the chitosan and the resin; this could be because the resin is unable to bind with all of the chitosan particles, and the voids in the polymerized resin can cause the strength
to decrease as the chitosan percentage increases [42].
SEM pictures were used to support the conclusions. Furthermore, the dispersion of particles in space and the development of multilayer coupling agents surrounding the particles may limit the availability of functional groups for monomer reactions.
When analyzing various concentrations of different denture base composites, the earlier studies [24; 43-46] observed a decrease in flexural strength due to non-uniform distribution and insufficient binding of composite particles in the resin matrix. The extended hydrocarbon chain of adipic acid may be the reason for the increased adhesion and homogeneity of 3D printable resin particles observed in the FESEM images of the chitosan: adipic acid group.
FESEM images of the chitosan: fumaric acid samples revealed that the particles had a
more spherical, crystalline structure, which indicates that the cohesiveness of the 3D-printed resin particles increased and the overall material structure became more compact.
The maleic acid group displayed the most compact and homogenous morphological surface in the FESEM images, and the modified polymer demonstrated extremely high strength and compactness figures owing to its configuration. In line with [41] who claimed that a compact microstructure generated by PMMA particles diffusing toward one another to form strong connection necks because of the photopolymerization process in the PMMA sample, the dicarboxylic acid samples used in this study had a compact microstructure generated by 3D printable PMMA resin particles diffusing toward one another, leading to the holes and voids decreasing, increasing overall resistance and compactness, and forming strong connection necks following a successful and flawless photopolymerization process.
This is in line with Qin et al. [47], who stated that the interaction of chitosan with other
biomaterials, like nanodiamonds, is important to improve its biological and mechanical properties for clinical applications where these interactions showed higher color stability compared with other materials. Additionally, the interaction of chitosan with other biomaterials, like dicarboxylic acids, is important to improve its biological and mechanical properties for clinical applications.
3.2. Fourier Transform Infrared Spectroscopy (FTIR).
The FTIR spectrum of control samples which represent the acrylic resin, shows absorption bands at 2955cm-1 and 2872cm-1 are related to aliphatic u(C-H) groups. The strong absorption bands at 1715cm-1 and 1082cm-1 represent the u(C=O) group and the u(C-O) group, respectively. The strong absorption bands at 3369cm-1 were belong to the hydroxyl group u(O-H) group, in addition, the absorption bands at 1405 cm-1 and 1387cm-1 are related to ô(-CH2) groups of acrylic resin (Figure 2).
Fig. 2. A representative images of Fourier Transform Infrared Spectroscopy (A) Control group; (B) acrylic resin modified only with 2%(w/w) Chitosan alone; (C) acrylic resin modified with chitosan and adipic acid; (D) acrylic resin modified with chitosan and fumaric acid; (E) acrylic resin
modified with chitosan and maleic acid
The FTIR spectrum of acrylic resin modified only with 2%(w/w) Chitosan alone shows absorption bands at 2955 cm-1 and
2871cm-1 are related to the aliphatic u(C-H) group. The strong absorption bands at 1715 cm-1 and 1510 cm-1 represent the u(C=O) group and
u(N-H) group of amide-I and amide-II of chitosan. The absorption frequency at 1101cm-1 belongs to u(C-O) and that at 3360 cm-1 represent the hydroxyl group u(O-H) group in acrylic resin and chitosan. Those bands at 1405 cm-1 and 1377 cm-1 are related to ô(-CH2) groups of acrylic resin.
The FTIR spectrum of acrylic resin modified with chitosan and adipic acid shows absorption bands at 2955 cm-1 and 2872 cm-1 are related to the aliphatic group u(C-H). The absorption bands at 1713 cm-1 and 1510 cm-1 are representing the u(C=O) group and u(N-H) group of amide-I and amide-II of chitosan respectively. The absorption bands at 1101cm-1 and 3368 cm-1 for u(C-O) and u(O-H) groups, respectively. The absorption bands at 1384 cm-1 and 1366 cm-1 are related to ô(-CH2) groups of acrylic resin.
The FTIR spectrum of acrylic resin modified with chitosan and fumaric acid shows absorption bands at 2955 cm-1 and 2872 cm-1 are related to the aliphatic group u(C-H). The absorption bands at 1714 cm-1 and 1510 cm-1 represent the u(C=O) and u(N-H) groups of amide-I and amide-II of chitosan respectively. The absorption bands at 1103 cm-1 and 3374 cm-1 belong to u (C-O) and u(O-H) groups respectively. In addition, the absorption bands at 1404 cm-1 and 1367 cm-1 are related to the 5(-CH2) group of acrylic resin.
The FTIR spectrum of acrylic resin modified with chitosan and maleic acid shows absorption bands at 2954 cm-1 and 2872 cm-1 are related to the aliphatic group u(C-H). The absorption bands at 1713 cm-1 and 1510 cm-1 represent the u(C=O) and u(N-H) groups of amide-I and amide-II of chitosan, respectively. The absorption bands at 1101 cm-1 and 3380 cm-1 belong to u (C-O) and u(O-H) groups, respectively. In addition, the absorption bands at 1384 cm-1 and 1366 cm-1 are related to the 5(-CH2) group of acrylic resin.
FTIR analysis was employed to determine whether epoxy groups are present in acrylic latex and to investigate the interaction of chitosan and acrylic latex during the mixing process [48]. When engineered chitosan polysaccharide interacts with dicarboxylic acids, functional group modifications are monitored through FTIR studies. Comparing the
dicarboxylic acid spectrum to the chitosan group alone revealed few discernible changes. The result of superposed -OH was a broad, strong absorption in the 3380-3368 cm-1 region. The aliphatic group u(C-H) is connected to the absorption bands at 2954 cm-1 and 2872 cm-1.
The presence of asymmetric -COO-stretching is indicated by absorptions in the 1713-1715 cm-1 range. The peak that was seen between 1510 and 1500 cm-1 was caused by stretching of the symmetric N-H bend. Further absorption peaks at 1387, 1082, and 1405 cm-1 were similar to the chitosan 2% spectrum, suggesting that the main structural backbone of the chitosan structure did not change [49].
FTIR analyses confirm the interaction of dicarboxylic acids with chitosan and the results suggested that the concentration of dicarboxylic acids, increases the degree of cross-linking with chitosan and this agrees with Sailakshmi et al. [50] who stated that FTIR spectral analyses confirm the interaction of dicarboxylic acids with chitosan polysaccharide and the results suggested that increase in the concentration of DCA (0.05%-0.5%), increases the degree of cross-linking up to 0.4% concentration and about 60%-65% cross-linking was observed with 0.2% DCA with chitosan
3.3. X- Ray Diffraction (XRD)
The XRD pattern showed that the maxima of the control group occurred at (16.561 degrees) along the 20 axis with a width of maxima (0.161) and a height of maxima (468) which improved that the samples of the control group had an amorphous shape, while the maxima of the chitosan samples added alone present at (18.62 degrees) along the 20 axis with more height of maxima (449)and width of maxima was (0.086) which less than that of the control samples, and this means that the chitosan group had more crystalline behavior than the control group and all other group used in the study (Table 2, Figure 3).
The XRD pattern also showed that the maxima of adipic acid samples occurred at (17.439 degrees) along the 20 axis with a width of maxima (0.262) and height of maxima (275) which improve that the samples of adipic acid had an amorphous shape more than that of the control group and only chitosan group 2% w/w. The XRD pattern also showed that the
maxima of fumaric acid samples occurred at (17.730 degrees) along the 20 axis with a width of maxima (0.315) and height of maxima (454) which improved that the samples of fumaric acid had highly amorphous texture more than that of all other group used in the study. The XRD pattern also showed that the
maxima of maleic acid samples occurred at (16.830 degrees) along the 20 axis with a width of maxima (0.297) and height of maxima (354) which improved that the samples of maleic acid had highly amorphous texture more than that of all other group used in the study except fumaric acid group.
Table 2. Peak Search Report (1 Peaks, Max P/N=4.0) for tested groups.
Groups 2-Theta d (spacing) BG Height I% Area I% FWHM (width)
Control 16.561 5.3485 1395 468 100 9436 100 0.161
Chitosan 18.620 4.7614 1351 449 100 4854 100 0.086
Adipic acid 17.439 5.0812 929 275 100 9247 100 0.262
Fumaric acid 17.730 4.9983 1466 454 100 17883 100 0.315
Maleic acid 16.830 5.2636 1520 354 100 13131 100 0.297
PEAK: 47-pts/Parabolic Filter, Threshold=3.0, Cutoff=2.0%, BG=3/1.0, Peak-Top=Summit
The degree of crystallinity, element proportions in the mixture, and crystallinity of the specimens are all determined by XRD analysis. Part of the ray may be transmitted through atomic planes when an X-ray interacts
with a material; the remaining portion is absorbed, refracted, scattered, and diffracted by the specimens. Depending on the atomic arrangement and type, materials' X-ray diffraction patterns vary for each element [51].
À A Ac B
K c À ' V D V
Fig. 3. Representative images of X-Ray Diffraction of (A) Control group; (B) Chitosan group; (C) Adipic acid group; (D) Fumaric acid group; (E) Maleic acid group.
Since XRD displays the normal order of crystalline phases of the materials under investigation, it was utilized to analyze the impact of the incorporated polymers on the PMMA crystallinity behavior [52, 53]. The XRD pattern of control samples showed a single diffraction peak, signifying the material's
amorphous nature. The control group samples had an amorphous shape that corresponded to the amorphous region of the material, as evidenced by the broad diffraction peak at 16.561 degrees along the 20 axis, with width of maxima (0.161) and height of maxima (468) [54]. The XRD pattern of chitosan samples
alone had more intensity and sharpness with narrower diffraction peaks than those of the control group in the amorphous region, indicating that the addition of chitosan to polymer improved the crystallinity and structural configuration of PMMA, which had a direct impact on its mechanical, biological, and physical properties. However, chitosan samples alone at (18.62 degrees) along the 20 axis with more height of maxima (449) and width of maxima (0.086) was less than that of the control group. These results agree with Salman et al. [40] reported that the XRD graph displayed narrower peaks and increased intensity as the polymer's crystallinity increased.
The XRD pattern of dicarboxylic acid with chitosan showed a broader diffraction peaks with less intensity and sharpness than that appeared in the XRD pattern of control group, indicating that the addition of dicarboxylic acid with chitosan to 3D printable acrylic resin confirms that there was no apparent chemical interaction between the blended material and there was only physical (electrostatic) interaction between the added agent which could form amorphous architectural build with 3D printable acrylic resin due to the formation of interpenetrating network among the blended composite [55-57]. So, that the XRD pattern improved that control group and the group of dicadboxylic acid with chitosan 2% w/w were highly amorphous and with no any crystalline maxima.
3.2 Mechanical test results and discussion.
3.2.1. Impact strength. The impact test mean and standard deviation values for the
control, experimental, and modified groups. According to the results, the control sample's impact was greater than that of the experimental group modified with only 2 wt % chitosan and less than that of the experimental sample modified with the dicarboxylic acid used in the study (adipic, fumaric, and maleic acid and chitosan). The modification by the maleic acid group resulted in the highest impact value (18.7). This study revealed a highly significant statistical difference between the impact of the modified groups and the control group, with P-value<0.01(Table 3).
Using Duncan's multiple range values showed that the impact value of the 3D printable acrylic denture base modified with Chitosan (12.4) was lower than that of the control group (15.9), whereas the impact value of the base modified with dicarboxylic acid (Adipic, Fumaric, and Malic acid) + Chitosan (16, 18.7, and 18.7) was higher. The 3D printable acrylics modified with Chitosan samples showed a statistically significant difference from the control group (Table 4). Additionally, there was a statistically significant difference between the control sample and the sample of fumaric acid and maleic acid on one side, as well as a statistically significant difference between the samples of fumaric acid and maleic acid on one side and the Chitosan sample on the other side. However, there was no statistically significant difference between the control group and the samples of 3D printable acrylics modified with adipic acid, nor between the samples of fumaric acid and maleic acid on the other.
Test in 15/9 Subgroup Mean±SD
Impact Test Control, n=10 15.9±0.7b
Chitosan, n=10 12.4±0.7a
Adipic, n=10 16±0.6b
Fumaric, n=10 18.7±0.7c
Maleic, n=10 18.7±0.8c
Same letter=non-significant difference (p>0.05) Different letter=significant difference (p<0.05)
Table 3. Impact of control and experimental groups which modified with a dicarboxylic acid (Adipic, Fumaric, and Maleic acid and Chitosan) and with only Chitosan 2 wt%.
Table 4. Impact of control and experimental groups which modified with a dicarboxylic acid (Adipic, Fumaric, and Maleic acid and Chitosan ) and with only Chitosan 2 wt%.
Sum of Squares Df Mean Square F Sig.
Between Groups 268.021 4 67.005 140.767 0.000**
Within Groups 21.420 45 .476
Total 289.441 49
** Highly Significant at P-Value < 0.01, ANOVA test
In terms of the modified materials' mechanical properties, these are essential characteristics of any biomaterial from an application standpoint [50]. The foundation materials for dentures should be sufficiently impact-resistant to withstand fracture in the event of an unintentional drop. Maxillary denture fractures are mostly caused by impact and fatigue forces, whereas impact forces account for 80% of mandibular denture fractures. Using the Charpy or Izod configurations, impact strength tests are frequently used to assess the amount of energy absorbed by materials before fracture [45, 58, 59].
The maximum augmentation in the impact strength was achieved after the addition of maleic fumaric and adipic acids respectively (18.7, 18.66, and 16 KJ/m2). The difference in impact strength decreased between the fumaric acid samples and maleic acid samples which was in the range of impact strength values which were approximately the same, so that there was no statistically significant difference.
The impact strength obtained from a mixture of a dicarboxylic acid with a concentration of 0.1% with resin matrix containing chitosan 2 wt %was found to be higher than that of the standard 3D printable acrylic resin without modification (control) and the only chitosan samples. This can be attributed to the fact that the mixture of two added materials can produce a mixture of materials containing the properties of the two components such that other properties tend to make the mixture material into a matrix with better strength properties.
This can be seen in the 3d acrylic resin matrix mixture with chitosan and dicarboxylic acid which shows an increase in impact strength and this agrees with Sailakshmi et al. [50] who approved that the most preferable mechanical properties were observed at 0.2% concentration
of dicarboxylic acid and any additional increase in DCA concentration results in the reduction in mechanical properties. The crossed carbon double bonds react with the oligomer during the reaction as it polymerized, forming bonds with the filler into a polymer matrix. This bond can add strength to the nature of physical strength, namely impact strength [31].
The noteworthy association between impact strength variables and residual monomer variables provides an additional explanation. The impact strength variable and the residual monomer variable had a correlation coefficient of -0.6682. The opposite relationship between the two variables is indicated by a negative correlation coefficient. The impact strength decreases with increasing residual monomer concentration and vice versa. According to Feng et al. [60], the acrylic resin may become more plastic and lose impact strength due to the leftover monomer acting as a plasticizer, so that the results of this study suggest that the addition of carboxylic acid to acrylic resin lead to decrease the residual monomer elution and this point lead to increase the impact strength of the modified dicarboxylic samples.
A statistically significant increase in the impact strength of the modified groups compared to the control group was confirmed by One Way Analysis of Variance at p<0.01. The findings showed that the presence of acidic content enhanced the mechanical properties (impact strength) of the resulting polymer and that chitosan and dicarboxylic acids increased the chain's length and strength. The carboxyl derivatives of diacid interacted with the NH2 group of chitosan through covalent or physical linkage, improving the mechanical properties over those of the control samples, even though all of these observations showed the cross-linking ability of dicarboxylic acid with chitosan [50, 61].
This agrees with Prajwala et al. [62] who approved that the impact strength of the resin matrix improved when it was incorporated by rubbery particles as the crack propagation was decelerated when reached the rubber interface. This also was in agreement with Gad and Abualsaud [63] who reported that the properties of composites are greatly influenced by the interactions between the polymer matrix and the incorporated fillers.
Ayaz and Durkan [64] asserted that the high strength of compatibility between the components of the crosslinked polymeric blend was disrupted by the excess polymer incorporated or that the increase in porosity was the cause. This is supported by the observation of a decrease in the impact strength of 3D PMMA along with the addition of chitosan alone. This result could be attributed to supersaturation of the polymer matrix and the excess of added chitosan filler. Denture fractures were found to be primarily caused by porosity and stress concentration [65]. This is consistent with the findings of Anjali et al. [66], who discovered that the impact strength of the composite is mainly determined by the filler particle distribution within the matrix. Furthermore, the outcomes supported the findings of Spasojevic et al. [67], who linked the decreased impact strength of modified resin materials to the emergence of microdefects in the polymer matrix, which act as a stress concentrator and crack accelerator.
3.2.2. Surface Hardness. According to the findings, the control group's surface hardness was higher than that of the experimental samples modified with chitosan 2 wt % alone and lowers than that of the experimental samples modified with the dicarboxylic acid used in the study (adipic, fumaric, and malic acid) and chitosan. With the addition of the fumaric acid samples, the maximum surface hardness value of 48.20 was attained. The surface roughness of the modified samples differed statistically significantly from the control samples at p value<0.01 (Table 5).
According to Duncan's multiple range values, the modified 3D printable acrylic denture base with chitosan 2 wt % alone had a lower surface hardness (20.659) compared to the control samples (30.650); on the other hand, the modified 3D printable acrylic denture base with dicarboxylic acid (Adipic, Fumaric, and Malic acid) and Chitosan had a higher surface hardness (32.440, 41.220, and 39.100), respectively and all modified samples—aside from the samples that was modified with adipic acid showed a statistically significant difference in surface hardness from the control samples. The study also showed a statistically significant difference in surface hardness among all modified samples, with the exception of the groups that were modified with fumaric and maleic acids, which showed no statistically significant difference in surface hardness between them (Table 6).
Table 5. Surface hardness of tested groups.
Test Subgroup Mean±SD
Hardness Results Control, n=10 30.7±5.9b
Chitosan, n=10 20.7±6.7a
Adipic, n=10 32.5±3.1b
Fumaric, n=10 41.2±7.3c
Maliec, n=10 39.1±4.7c
Same letter=non-significant difference (p>0.05) Different letter=significant difference (p<0.05)
Sum of Squares Df Mean Square F Sig.
Between Groups 2627.414 4 656.854 19.889 0.000**
Within Groups 1486.201 45 33.027
Total 4113.615 49
Table 6. Surface hardness of control and experimental groups which modified with dicarboxylic acid (Adipic, Fumaric and Maleic acid and Chitosan ) and with Chitosan 2wt % alone.
** Highly Significant at P-Value < 0.01, ANOVA test
The results of surface hardness can be explained by stating that according to the result of FESEM images which shows an increased adhesion and homogeneity of the chitosan-adipic acid samples, and revealed that in the chitosan-furmaric acid samples the particles had a more spherical, crystalline structure, which indicates that the cohesiveness of the 3D-printed resin particles increased and the overall material structure became more compact. The maleic acid group displayed the most compact and homogenous morphological surface in the FESEM images, and the modified polymer demonstrated extremely high strength and compactness owing to its configuration. The dicarboxylic acid samples used in this study had a compact microstructure generated by 3D printable PMMA resin particles diffusing toward one another, which led to the holes and voids decreasing, increasing overall resistance and compactness, and forming strong connection necks following a successful and flawless photopolymerization process. This is consistent with another study [41] who claimed that a compact microstructure generated by PMMA particles diffusing toward one another to form strong connection necks because of the photopolymerization process in the PMMA sample, while certain voids were discovered at the fracture site of the 3D-printed specimens with chitosan 2% alone, according to SEM results. These gaps could weaken the bonding layers between surfaces, which could cause delamination and fractures. As a result, it was determined that voids had a role in the printed resin's decreased mechanical performance. Furthermore, the kind of failure observed depends on where the voids are located. If a void is in the center of the specimen, it will function as a flaw; if it is on the edges of the specimen, it may function as the fracture's
starting point and reduce hardness [68, 69].
Another explanation was that the complex mixture was intended to be reinforced by the addition of dicarboxylic acid (DCA). Chitosan and acrylic resin may bind actively to the hydroxyl group of acrylic acid. Double bonds (C = O) and two carboxylic acids (COOH) were present in dicarboxylic acid (DCA). If there is any residual monomer left over from the reaction of an acrylic resin mixture between a polymer and a monomer, it will be reduced by adding chitosan and dicarboxylic acid. Acidic carboxylates react with NH2 from base chitosan, while the acrylic acid double bond (C=O) reacts with acrylic resin monomers, the residual monomer showed a decrease in the percentage of residual monomer. This was due to the acrylic resin's monomers binding to form polymer bonds during polymerization. The residual monomer decreased as the degree of bond conversion increased under UV light and by the addition of additive to acrylic resin and this finding agrees with Al-Ali et al. [70] who stated that the degree of bond conversion increased when curing was done under high temperatures as in microwave or heat curing method and the light cure resin showed the highest degree of bond conversion and agree with Hasan and Abdulla [71] whom stated that the application of fiber to polymer during mixing to form a polymer monomer matrix, the monomer seems to be reduced, so the level of tested residual monomer seems to be the low level in groups of heat and miocrowaved reinforced resin with fibers than the non-reinforced resins. Residual monomers can also lessen the mechanical strength and surface hardness of acrylic resins and these finding agree with Anusavice et al. [72] and Chaves et al. [73].
4. Conclusions
The chemical and mechanical properties of the modified 3D-printed denture base are improved when 2 wt.% chitosan is modified with fumaric acid + 2wt.% chitosan and maleic acid+2 wt.% chitosan groups have the highest
mechanical properties than other groups in the study. When chitosan 2 wt.% alone was used to modify the 3D-printed polymers, the mechanical and chemical properties would be decreased.
The FTIR spectrum shows that the chitosan cross-linked dicarboxylic acids blend the acrylic resin. Moreover, SEM images show homogeneous structures after blending with observable morphological changes, while a 3D printable acrylic resin after blending with chitosan alone shows an irregular surface morphology.
The degree of crystallinity was improved after blending especially in the case of fumaric and maleic acid cross-linked chitosan additive.
The impact strength and surface hardness were increased significantly and improved for 3D printable acrylic resin after modification especially in case of fumaric and maleic acid cross-linked chitosan additive.
Acknowledgements
The authors acknowledge the College of Dentistry, Mosul University in Iraq for providing support in performing this research.
Conflicts of interest: There is no Conflict of interest
Ethical approval and consent to participate: REC reference no. UOM. Dent. 23/38
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XiTOZAN VO DiKARBON TUR§ULARININ OLAVOLORlNiN Di§ PROTEZLORlNiN 3D CAPINDA iSTlFADO OLUNAN AKRlL QATRANININ XASSOLORlNO TOSiRl
ihsan F. Ol-Takai1*, Luma Ol-Nema1, Fauzi H. Cabrayil2
1 Mosul Universiteti, Stomatologiya Kolleci, Protez Di§ Mualicssi Departamenti, Mosul, iraq.
2Mosul Universiteti, Elmlsr Kolleci, Polimer Kimyasi Departamenti, Mosul, iraq. *e-mail: Ihsan2011@uomosul.edu.iq
Xulasa: 3D 9ap texnologiyasi ananavi yana§malarla muqayisada bir 9ox ustunluklara gora son illarda populyarliq qazanmi§dir. Masalan, bu texnologiya di§ hakiminin di§ protezlarinin hazirlanmasi u9un lazim olan vaxti 2-3 seansa qadar azaldir. Fumar, malein va adipin tur§ulari (0.1 kutla %) xitozan mahluluna (2 kutla %), son kompozit isa 3D 9ap u9un uygun olan akril qatranina alava edilir. Numunalar bir ne9a kimyavi analiz (XRD, SEM, FTIR) va mexaniki sinaqlarla (zarbaya davamliliq va sathi mohkamlik testlari) xarakteriza edilmi§dir. Bu tadqiqatda istifada edilan numunalarin umumi sayi (115) be§ qrupa bolunmu^dur. Kimyavi analiz u9un bir numuna
hazirlanmi§ va bir nümuna nazarat qrupu kimi istifada edilmi§dir (har test ü9ün alavasiz 3D 9ap qatrani (dayi§dirilmami§)). Mexaniki sinaq ü9ün har bir dayi§dirilmi§ qrup ü9ün on nümuna hazirlanmi§ va on nümuna nazarat qrupu kimi istifada edilmi§dir (har sinaq ü9ün alavalarsiz 3D 9ap qatrani (dayi§iklik edilmami§). Kimyavi analizlarin naticalarinda dayi§dirilmi§ akril 3D 9ap qatraninin takmilla§dirilmi§ xüsusiyyatlari mü§ahida olunmu§dur. Bundan alava, mexaniki sinaqlarin naticalari göstarmi§dir ki, nümunalari digar nümunalarla müqayisada fumar tur§usu va xitoanli malein tur§usu an yüksak xassalara, an a§agi xüsusiyyatlar isa 3D 9ap ü9ün nazarda tutulmu§ xitozanli akril qatrandan hazirlanmi§ nümunalara aiddir. £ap protezlari xitozan istifada edilmakla takmilla§dirilmi§ va dikarbon tur§ularla modifikasiya edilmi§dir. öksina, 3D 9ap edilmi§ polimerlari dayi§dirmak ü9ün yalniz xitozan istifada edilarsa, mexaniki va kimyavi xassalari azalacaq.
A?ar sözlari: akril qatrani, xitosan, dikarbon tur§ulari, fumarin tur§usu, malein tur§usu, adipin tur§usu.
ВЛИЯНИЕ ДОБАВКИ ХИТОЗАНА И ДИКАРБОНОВЫХ КИСЛОТ НА СВОЙСТВА АКРИЛОВОЙ СМОЛЫ ДЛЯ 3D ПЕЧАТИ ОСНОВАНИЯ ЗУБНЫХ ПРОТЕЗОВ
11 2 Ихсан Ф. Аль-Такай *, Лума Аль-Нема , Фаузи Х. Джабраил
1 Кафедра ортопедической стоматологии, Стоматологический колледж, Университет Мосула,
Мосул, Ирак.
2Кафедра химии полимеров, Научный колледжМосульского университета, Мосул, Ирак.
*e-mail: Ihsan20H@uomosul.edu.iq
Аннотация: ЗБ-печать приобрела популярность в последние годы благодаря множеству преимуществ, которые она предлагает по сравнению с традиционными подходами. Например, эта технология сокращает время, необходимое стоматологу для создания и установки зубных протезов, до 2-3 сеансов. Фумаровую, малеиновую и адипиновую кислоты в процентном соотношении (0.1 мас.%) добавляли к раствору хитозана (2 мас.%), а конечный композит добавляли к акриловой смоле, пригодной для 3Б-печати. Образцы были подвергнуты нескольким химическим анализам (XRD, SEM, FTIR) и механическим испытаниям (испытания на ударную вязкость и поверхностную твердость), где общее количество (115) образцов, использованных в исследовании, представляло собой образцы, разделенные на пять групп. При химическом анализе был изготовлен один образец для каждой модифицированной группы, и один образец использовался в качестве контрольной группы (смола для 3Б-печати без добавок (немодифицированная) для каждого испытания). Для механических испытаний было изготовлено десять образцов для каждой модифицированной группы и десять образцов были использованы в качестве контрольной группы (смола для 3Б-печати без добавок (немодифицированная) для каждого теста. Результаты химического анализа показали улучшение свойств модифицированной акриловой смолы для 3Б-печати, кроме того, результаты механических испытаний показали, что (фумаровая кислоты и малеиновой кислоты с хитозаном) образцы имеют самые высокие свойства по сравнению с другими образцами, а самые низкие свойства были у образцов из акриловой смолы с хитозаном, предназначенной для 3Б-печати. Химические и механические свойства модифицированного 3Б-печатного протеза улучшаются при использовании хитозана. Модифицируется дикарбоновыми кислотами. И наоборот, если для модификации полимеров, напечатанных на 3 D-принтере, использовать только хитозан, механические и химические свойства будут снижены.
Ключевые слова: акриловая смола, хитозан, дикарбоновые кислоты, фумаровая кислота, малеиновая кислота, адипиновая кислота.
