ABSTRACT
Objectives
To study the influence of nanoparticles of hydroxyapatite, zirconia, and glass on the wear and the microhardness of the organic matrix of experimental dental composite resin.
Materials and methods
The dental composite resin matrix was fabricated from bisphenol A-glycidyl methacrylate (Bis-GMA) (40 wt%), triethylene glycol dimethacrylate (TEGDMA) (36 wt%), and camphorquinone (0.4 wt%). Nanohydroxyapatite, glass, and zirconia fillers were silane treated. Nano-hydroxyapatite, glass, and zirconia were incorporated at three different concentrations. The polymerization of the dental composite resin was done using a light curing unit. Experimental dental composite resins were evaluated for wear and microhardness. The data were analyzed by one-way analysis of variance (ANOVA) test.
Results
The experimental dental composite resin composed of 32% of nanohydroxyapatite, 27% of zirconia, and 19% of glass as filler showed the minimum amount of wear. The Vickers hardness (VHN) number was observed to be minimum for the experimental dental composite resin composed of 24.1% of nanohydroxyapatite, 22% of zirconia, and 14.5% of glass.
Conclusion
The inclusion of 32% nanohydroxyapatite, 27% of zirconia, and 19% of glass as filler into the experimental dental composite resin decreased the wear and increased the hardness.
How to cite this article
Mirajkar CK, Winnier J, Hambire U. Effect of Nanohydroxyapatite, Zirconia and Glass Filler Particles on the Wear and Microhardness of Experimental Dental Composite Resin. Int J Clin Pediatr Dent 2023;16(S-1):S81–S84.
Keywords: Compressive strength, Dental caries, Nanofilled composite
Introduction
Dental composite resin is an esthetic restorative material gaining popularity due to increasing demands for tooth-colored fillings. Occlusal wear of the material has been one of the major causes of failure. Wear is caused by abrasion, adhesion, and adhesive effects between two contacting surfaces. The inclusion of nano biofillers in the polymer matrix of bioDental composite resins brought a fundamental change in the field of restorative dentistry. Different types of inorganic, as well as organic fillers, have been incorporated to enhance the engineering properties of bioDental material. Fillers are added to decrease water sorption, enhance engineering parameters, reduce abrasion, and enhance microhardness.
The dimension of the filler particle loading ranges between millimeters to nanometers. Various studies have shown that the nanosized filler particles have an important influence on the engineering parameters of bioDental composites. The surface area, physical property, chemical reactivity, and hardness of the filler particles can be changed by reducing the dimensions of the filler loading to nanometers from the micrometer.
Recently hydroxyapatite in nanoscale has been added as an inorganic filler in dental composite resins. They have been shown to improve the properties of the experimental dental composite. The literature review suggests that the effect of the combination of zirconia, glass, and hydroxyapatite nanofillers on the wear and the microhardness of dental composite resins are unknown. The analysis was conducted to evaluate the influence of nanoparticles of hydroxyapatite, zirconia, and glass on the wear and microhardness of the organic matrix of experimental bioDental composite resin. Null hypothesis suggests with inclusion of nanohydroxyapatite, zirconia, and glass will not influence the wear and microhardness of the experimental dental composite resins.
Materials and Methods
Bisphenol A-glycidyl methacrylate (Bis-GMA), which is manufactured by Sigma Aldrich with a density of 1.161 g/mL at 25°C, TEGDMA, (85%, Sigma-Aldrich) containing 80–120 ppm of monomethyl ether of hydroquinone as an inhibitor with a density of 1.092 g/mL at 25°C, TEGDMA (98%, Sigma-Aldrich) containing 90-110 ppm of monomethyl ether hydroquinone as an inhibitor, camphorquinone (97%, Sigma-Aldrich) and acetone were used as supplied by the manufacturer without further processing. They were added in the proportion of 45 wt% Bis-GMA, 28 wt% of TEGDMA, and 27 wt% of TEGDMA to prepare the organic phase. The nanohydroxyapatite particles, zirconia, and glass were silanized to increase the coupling between the filler particles and the matrix. This was done using 5 wt% of silane and 95 wt% of acetone. The evaporation of the solvent was done, keeping the experimental composite specimens in the dark room for 24 hours at 37°C. The material used was weighted on an advanced electronic balance (Aczet Pvt Ltd, Mumbai). The components were thoroughly mixed with the help of ultrasonic homogenizers (BR Biochem Life Sciences Pvt Ltd, New Delhi). The activation of the monomer was done with the help of a light-cure unit (Coltene Spec 3 LED Curing Light).
Wear Test
Six cylindrical specimens of 10 mm diameter and 3 mm length were prepared along the block of acrylic resin of 80 mm length and thickness of 5 mm. The experimental composite resin was packed into the cylindrical cavities and the upper part was covered with acetate matrix strips. The photoactivation of the samples was performed for 60 seconds. The light-cured samples were polished with polishing disks. A group of 10 specimens were made and a total of 30 specimens were used for the wear test. The specimen was kept in mineral water for 24 hours at 37°C before the wear test. The wear test was performed with a linear reciprocating tribometer. A frequency of 2 Hz and a load of 10–15–20 was used. EN31 was used for testing. The tests were performed using standard ASTMG99. The cylindrical specimens were slid on the fixed rectangular surface.
The wear loss is calculated using the equation below:
Wear rate = (Δm*103)/(ρ*L*F) mm3/N-m.
Where, Δm = total mass loss in gm.
ρ = density of composite in g/cc.
L = sliding distance in meter.
F = applied load in Newton.
Microhardness Test
The microhardness test was performed using the VHN test. The micro Vickers Hardness Testing System HM-101 (Mitutoyo, Japan) with test forces of 098.07–9807 mN was used. The tests were performed using standard ASTM E384-06. A load of 500 gm was applied for 15 seconds. A diamond indenter was used. The indentations obtained on the specimens were observed under the microscope. The indentation was started in the center of the sample. Three indentations with a distance of 3 mm between each of them were made, as shown in Figure 1. The calculation of VHN was done by measuring the indentation made. The diagonal length was measured. The formula used was:
Fig. 1.
Schematic representation of the 3 mm distance between indentations of Vickers microhardness
VHN = 1.854 f/d2
In above equation connotes the force applied and d is the distance of the indentation made.
Statistical Analysis
The one-way ANOVA (version 21.0, Statistical Package for the Social Sciences, Inc., Illinois, United States of America) was performed to assess the amounts of wear and microhardness. Significant differences were considered at p < 0.05.
Regression analysis was performed to obtain the relationship between the volume content of the three fillers and their correlation with the wear. The volume percentages of nanohydroxyapatite, zirconia, and glass were evaluated and correlated to abrasive wear to develop a mathematical model. By using multiple linear regressions mathematically, the regression equation was evaluated. The regression model was validated using the Minitab package simulation technique.
The regression equation is evaluated by the multivariable technique of optimization:
WR = 6623−670H + 288Z + 35476G + 22.67HZ−3.66ZG + 17.2G2−2.3Z2
Taguchi's optimization technique is to be employed for further evaluation and optimization of the variables
Taguchi's method uses the signal-to-noise ratio, also called the S/N ratio, for evaluating the minimum variation in the output characteristics. An attempt is made to keep the abrasive wear of the experimental dental composite to a minimum. So, the theory of the smaller the better is employed to evaluate the signal-to-noise ratio.
S/N ratio = −10 Log10 (mean of the sum of squares of abrasive wear)
Discussion and Results
The major components of dental composite are filler and matrix. In this study, the natural hydroxyapatite nanofiller particles were used in combination with zirconia and glass. The variables used for abrasive load are summarized in Table 1. The wear was tested using samples made with varying percentages of filler. The variation in filler volume percentage is summarized in Table 2. Taguchi's optimization technique was employed for further evaluation and optimization of the variables.1–4
Table 1.
Input variables for the wear analysis
| Serial no | Variables | Unit | |
|---|---|---|---|
| 1 | Load (force) | n | 700 |
| 2 | Velocity | rpm | 1200 |
| 3 | Distance of slide | m | 60 |
Table 2.
Variation on filler volume percentage
| Process Variables | Variations | ||
|---|---|---|---|
| Sample 1 | Sample 2 | Sample 3 | |
| Nanohydroxyapatite % | 24.7 | 26.7 | 32 |
| Zirconia % | 22.1 | 26 | 27 |
| Glass % | 14.5 | 17 | 19 |
An attempt is made to keep the abrasive wear of the experimental dental composite to a minimum. So, the theory the smaller, the better is employed to evaluate the signal-to-noise ratio.
S/N ratio = −10 Log10 (mean of the sum of squares of abrasive wear)
The results of the abrasive wear are summarized in Tables 3 to 5. It was observed that sample 3, composed of 32% of nanohydroxyapatite, 27% of zirconia, and 19% of glass, showed a minimum amount of wear. The maximum amount of wear was shown by sample 1, composed of 24.1% of nanohydroxyapatite, 22% of zirconia, and 14.5% of glass. When nanohydroxyapatite is used with glass and zirconia, the abrasive wear reduces with a uniform dispersion of filler in the matrix. The filler volume percentage is varied to study the variation in the wear properties. Figure 2 depicts that as the volumetric percentage of nanohydroxyapatite is varied, the abrasive wear increases to 26.7% and then goes on decreasing progressively. Figure 3 shows that as the zirconia volume increases, the wear decreases to 26% and then again goes on to increase. Figure 4 shows that as the glass percentage increases the wear increases to 17%, and then the rate of increase of wear decreases. Figure 5 is plotted to study the combined effect of the three fillers on the abrasive wear properties. The filler percentage where we can obtain optimum wear is achieved by Taguchi's optimization technique and shown in conclusion.
Table 3.
L9 orthogonal array for sample 1
| Serial no |
Load
(N) |
Speed
(rpm) |
Sliding distance
(m) |
Wear rate
(gm/m) x 10 −4 |
|---|---|---|---|---|
| 1 | 29.43 | 400 | 600 | 0.2198 |
| 2 | 29.43 | 500 | 800 | 0.3256 |
| 3 | 29.43 | 600 | 1000 | 0.3413 |
| 4 | 39.24 | 400 | 800 | 0.3872 |
| 5 | 39.24 | 500 | 1000 | 0.4137 |
| 6 | 39.24 | 600 | 600 | 0.4417 |
| 7 | 49.05 | 400 | 1000 | 0.4463 |
| 8 | 49.05 | 500 | 600 | 0.4923 |
| 9 | 49.05 | 600 | 800 | 0.5079 |
Table 5.
L9 orthogonal array for sample 3
| Serial no |
Load
(N) |
Speed
(rpm) |
Sliding distance
(m) |
Wear rate (gm/m)
x 10 −4 |
|---|---|---|---|---|
| 1 | 29.43 | 400 | 600 | 0.1352 |
| 2 | 29.43 | 500 | 800 | 0.1385 |
| 3 | 29.43 | 600 | 1000 | 0.1483 |
| 4 | 39.24 | 400 | 800 | 0.1397 |
| 5 | 39.24 | 500 | 1000 | 0.1478 |
| 6 | 39.24 | 600 | 600 | 0.1376 |
| 7 | 49.05 | 400 | 1000 | 0.1493 |
| 8 | 49.05 | 500 | 600 | 0.1379 |
| 9 | 49.05 | 600 | 800 | 0.1513 |
Fig. 2.
Variation in the wear with nanohydroxyapatite filler volume
Fig. 3.
Variation in the wear with zirconia filler volume
Fig. 4.
Variation in the wear with glass filler volume
Fig. 5.
Combined effect plot of wear variation with volumetric filler percentage
Table 4.
L9 orthogonal array for sample 2
| Serial no | Load (N) | Speed (rpm) | Sliding distance (m) | Wear rate (gm/m) × 10 −4 |
|---|---|---|---|---|
| 1 | 29.43 | 400 | 600 | 0.4008 |
| 2 | 29.43 | 500 | 800 | 0.4123 |
| 3 | 29.43 | 600 | 1000 | 0.5113 |
| 4 | 39.24 | 400 | 800 | 0.4872 |
| 5 | 39.24 | 500 | 1000 | 0.5137 |
| 6 | 39.24 | 600 | 600 | 0.4917 |
| 7 | 49.05 | 400 | 1000 | 0.5463 |
| 8 | 49.05 | 500 | 600 | 0.4923 |
| 9 | 49.05 | 600 | 800 | 0.5479 |
The observed analysis is in conformity with the studies done, which show that nanoparticles improve the engineering properties of ceramic-polymer restorative material.5,6 The filler loading of 70–80% by volume and 65–75% by weight fraction has been shown to enhance the wear properties.7
The mean values of Vickers microhardness are summarized in Table 6. Sample 3 (81.76 ± 4.56 VHN) exhibits the highest VHN (harder), followed by sample 2 (61.90 ± 5.35 VHN) and sample 1 (42.16 ± 4.57 VHN). In this study, we found that specimens made from experimental composite (sample 3) showed significantly higher microhardness values.
Table 6.
VHN of experimental composite resins
| Experimental composite | Vickers microhardness (mean ± standard deviation) |
|---|---|
| Sample 1 | 42.16 ± 4.57 |
| Sample 2 | 61.90 ± 5.35 |
| Sample 3 | 81.76 ± 4.56 |
Conclusion
An attempt is made to fabricate bioDental composite resins using natural hydroxyapatite, zirconia, and glass as nanofiller particles. The results of our study showed that the experimental dental composite resin with 32% of nanohydroxyapatite, 27% of zirconia, and 19% of glass showed the minimum amount of wear and a higher value of microhardness. L9 array was employed for the statistical analysis of the Taguchi's optimization technique for the analysis of abrasive wear
Orcid
Chaitali Mirajkar https://orcid.org/0000-0001-7672-0184
Umesh Hambire https://orcid.org/0000-0002-7707-6869
Footnotes
Source of support: Nil
Conflict of interest: None
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