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Article

Peroxide-Free Bleaching Gel: Effect on the Surface and Mechanical Properties of Nano- and Micro-Hybrid Restorative Composite Materials

by
Aftab Ahmed Khan
1,*,
Abdulaziz Abdullah Alkhureif
1,
Leonel S. J. Bautista
2,
Hanan Alsunbul
3 and
Sajith Vellappally
1
1
Dental Health Department, College of Applied Medical Sciences, King Saud University, Riyadh 11451, Saudi Arabia
2
Dental and Oral Rehabilitation Department, College of Applied Medical Sciences, King Saud University, Riyadh 11451, Saudi Arabia
3
Restorative Dentistry Department, College of Dentistry, King Saud University, Riyadh 11451, Saudi Arabia
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(10), 5935; https://doi.org/10.3390/app13105935
Submission received: 11 April 2023 / Revised: 8 May 2023 / Accepted: 9 May 2023 / Published: 11 May 2023
(This article belongs to the Special Issue Applied Sciences in Oral Health and Clinical Dentistry)
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Abstract

:
This laboratory investigation was designed to test the influence of a novel bleaching formulation based on phthalimidoperoxycaproic acid (PAP) with additives on the surface and mechanical properties of nano- and micro-hybrid restorative composites. Twenty-four bar-shaped and twelve disk-shaped samples from each restorative composite were prepared. The samples from each restorative composite were randomly divided into two groups according to the treatment, i.e., experimental and control. The treated groups went through the bleaching process: by Opalescence Regular or novel PAP+-containing gel (HiSmile™). The treated group underwent a bleaching process for seven consecutive days (a 10-min session of bleaching application every day) before the properties were tested. A paired sample t-test was performed to compare the results between the experimental and the control groups. The level of significance was set at 0.05. The surface roughness of the nanohybrid composite using Opalescence Regular (p < 0.05) was significant. Additionally, a significant difference in nanohardness and elastic modulus between the experimental and the control groups of the microhybrid composite using Opalescence Regular was observed: p = 0.041 and p = 0.023, respectively. While a marked difference in flexural strength was observed in the experimental and control groups using Opalescence Regular, Hismile™ bleaching gel caused a diminutive and insignificant reduction in tested properties (p > 0.05). It was found that Opalescence Regular bleaching gel affects the surface and bulk properties of restorative composite materials, whereas the novel PAP+ formulation has no deleterious effect on either nano- or micro-hybrid restorative composites.

1. Introduction

Dental bleaching is a process of chemical breakdown of chromogens. The recent demand for tooth whitening has increased steeply, making it one of the most sought-after cosmetic dental treatments [1]. The bleaching products are mainly composed of carbamide peroxide (CP) and hydrogen peroxide (HP) compounds as potent oxidizing agents [2]. Despite having a slightly different chemical formulation from HP, CP has a comparable mechanism of action and produces substances that are known to be powerful bleaching agents [3]. The oxidation of chromophores found in enamel and dentin and the breakdown of the extracellular matrix are two of the effects of bleaching. Both of these substances have localized negative effects on the oral mucosa and tooth structures [4].
Due to quick and effective results, vital teeth whitening procedures are currently among the most sought-after dental procedures [5]. Bleaching procedures can be performed in-office as well as at-home [6]; however, at-home teeth whitening is a common and viable treatment option among patients because of its ease and low cost [7]. The extended and repeated application of over-the-counter bleaching products has been linked to tooth sensitivity, oral mucosal irritation, oral infections, and surface and morphological changes in teeth [8,9,10].
Like clinical studies, laboratory investigations have also demonstrated the adverse effects of bleaching agents. Earlier research has advocated that bleaching agents dramatically diminish the surface gloss of resin composites, affecting the aesthetic quality of restorations [11,12]. These earlier studies have contemplated the damaging effect of home bleaching gels on the surface roughness [13], microhardness [11,14], and flexural properties [15,16] of restorative composites.
The mechanical properties are considered vital attributes for restorative composites’ long-term clinical survivability [17]. Recently, investigators have shifted their interest to employing organic peroxides such as phthalimidoperoxycaproic acid (PAP) as the active component in bleaching chemicals, as opposed to alternatives such as HP or CP. PAP is a non-toxic and readily biodegradable agent [18]. An investigation showed that PAP-containing gel caused etched enamel with reduced microhardness [9]. To address these issues, a novel PAP formulation designated PAP+ has been marketed. The formulation of PAP+ includes ingredients such as hydroxyapatite nanopowder and potassium citrate; both of these elicit an effective citrate buffering mechanism that maintains the pH near to neutral during the treatment [18].
This laboratory study was envisaged to ascertain the consequence of a novel PAP+ bleaching gel on two widely used all-purpose nanohybrid and microhybrid dental composite systems recommended for anterior and posterior restorations [19]. It considered the importance of the surface roughness of a restoration, which could exacerbate periodontal and caries disease [20], nanohardness, which is a valuable method for quantifying the unit area of an indented surface at the nanoscale [21], and high flexural strength and diametral tensile strength for stress-bearing restorations [22]. Taking into account these things, this study aimed to determine the effect of two different home bleaching systems, one based on free radical formulation and the other not, on the organic matrix of the restorative composite material in terms of nanohardness and elastic modulus, as well as to evaluate the surface roughness, flexural strength, and diametral tensile strength of the composite materials. It was hypothesized that the variables (the tested properties of the composite material) would be affected by the bleaching procedure.

2. Materials and Methods

2.1. Materials

In this experimental laboratory-based study, a quantitative research method was followed. A G-power calculator was used to compute the sample size for each study group. Each subgroup utilized 6 samples per group using α = 0.05 and β = 80%.
Two different restorative composite materials with A2 shade were selected (Table 1). Twenty-four rectangular bar-shaped samples with dimensions 30 mm × 2 mm × 1.5 mm were prepared from each composite material using a silicon mold. However, 12 disk-shaped samples from each composite material with dimensions 6.0 mm in diameter × 3.0 mm in height were fabricated using a silicon mold. The disk-shaped samples were intended for use in non-destructive techniques, i.e., surface roughness, nanohardness, and elastic modulus. Therefore, the same samples were used for pre- and post-bleaching evaluation.
The composite material was inserted, added carefully up to the brim of the mold, and pressed gently with a glass slide. The samples for surface roughness, nanohardness, elastic modulus, diametral tensile, and flexural strength were light-cured according to the manufacturer’s instructions. A mark was made on the untreated side of each sample to identify the surface type. A hand-held LED curing device Elipar Freelight 2 (3M ESPE, Seefeld, Germany) with a 430–480 nm and light intensity of 900 mW/cm2 was used to polymerize the samples. After polymerization, the samples were stored in an incubator at 37 °C for 24 h.
Next, Sof-Lex polishing disks (3M ESPE) were used to polish the samples in descending order of granulation. Each disk was utilized for 10 s at a slow speed. The samples were then submerged for 24 h at 37 °C in distilled water to ensure full polymerization. Half of the samples (n = 6) from each composite material underwent the below-mentioned tests to obtain the baseline (control) readings of flexural strength and diametral tensile strength. In contrast, surface roughness and nanoindentation were the non-destructive techniques. Therefore, the baseline (control) readings and final (experimental) readings were obtained from the same samples.

2.2. Bleaching Process

The remaining half of the samples were randomly divided into two groups according to the home bleaching gel used (n = 6/group). Two different bleaching systems were evaluated, i.e., Opalescence Regular, a widely used bleaching product, and HiSmile™, with a novel bleaching system containing PAP+ as an active ingredient. The bleaching products were applied with a syringe on the surface of the samples to standardize the amount of gel. Each day, the bleaching gel was uniformly dispersed and left to remain on the sample surface for 10 min according to the manufacturer’s recommendations. Afterward, the samples were thoroughly rinsed with distilled water for 30 s. For seven consecutive days, the bleaching application was performed on the samples. The samples were incubated in distilled water at 37 °C after each bleaching application until the next bleaching session.

2.3. Surface Roughness Test

On the 7th day after bleaching, the surface roughness from each group was examined with a 3D optical non-contact surface profilometer (ContourGT, Bruker, Campbell, CA, USA). The Ra (the so-called arithmetical average value of all absolute distances of the roughness profile from the center line within the measuring length) was evaluated based on non-contact scanning white light interferometry with an objective standard camera of a 5× magnification. The scanning area was situated at the center part of the surface. Vision64 (v 5.30) application software (Bruker, Campbell, CA, USA) was used to control the precision and the measurements of surface roughness parameters. The initial (before bleaching application) and the final (after bleaching application) readings were taken from the same targeted area.

2.4. Nanoindentation Test

Nanoindentations of the samples were performed using a nanomechanical device (UMT1, Bruker, CA, USA) equipped with a Berkovich diamond indenter nanotip. The tests were executed at a room temperature of 23 ± 1 °C, with loading and unloading rates of 0.5 mN/s and a 10 s dwell time. The maximal load was set to 20.0 mN. A total of 3 readings was obtained from each sample and the mean value was calculated for the individual sample [23]. The initial (before bleaching application) and the final (after bleaching application) readings were taken from the same targeted area. The nanohardness and elastic modulus values were determined in gigapascal (GPa) with the help of proprietary software.

2.5. Flexural Strength Test

The 3-point bending test was performed on the experimental and control groups samples according to the ISO 4049 specifications in such a way that the diameter for both supports and the loading piston was 2 mm and the span in between supports was 20 mm. A universal testing machine (Model no. 3369 Instron, Canton, MI, USA) was used with a crosshead speed of 1.0 mm/min and a load cell of 5 kN. The maximum load at fracture and the flexural strength (in MPa) were automatically recorded by the proprietary software (Bluehill ver. 2.4).

2.6. Diametral Tensile Strength Test

Diametral tensile strength was evaluated on samples in accordance with the American Dental Association (ADA) Specification no. 27. From each group, six cylindrical-shaped samples were selected. To apply the load on the specimens’ diameter, the study samples were positioned such that their flat ends were perpendicular to the base plate of the universal testing machine (Model no. 3369 Instron, Canton, MI, USA). At a crosshead speed of 1.0 mm/min and with a load cell of 5 kN, a compressive force was applied. The compressive force was applied until the sample fractured. The proprietary software (Bluehill ver. 2.4) was used to calculate the diametral tensile strength in megapascals (MPa).

2.7. Statistical Analysis

The normality of the data was verified using a non-parametric test, i.e., the Shapiro–Wilk test. The descriptive statistic was performed to summarize the data while inferential statistics were performed to compare the differences between the treatment groups. The Statistical Package for the Social Sciences (SPSS ver. 28, IBM, New York, NY, USA) was used. A paired t-test was performed to evaluate the difference between two variables for the same subject. A p value of less than 0.05 was considered significant.

3. Results

Figure 1 graphically illustrates the surface roughness (Ra) values of the study groups before and after the bleaching application. Both bleaching systems exhibited a deleterious effect on the surface roughness. However, the deleterious effect was observed to be significant only in the nanohybrid composite using the Opalescence Regular bleaching system. The highest increase in surface roughness was observed in the nanohybrid composite using Opalescence Regular (0.58 µm in control and 0.76 µm in experimental; p = 0.000), while the lowest increase in surface roughness was observed in the microhybrid composite using HiSmile™ (0.66 µm in control and 0.68 µm in experimental; p = 0.192). The p-value of the control and experimental groups in the microhybrid composite using Opalescence Regular and in the nanohybrid composite using HiSmile™ were also observed as insignificant, i.e., 0.071 and 0.092, respectively.
Table 2 displays the nanohardness data of the study groups. The highest nanohardness (in GPa) was observed in the control group of the microhybrid composite using Opalescence Regular (0.24 ± 0.02 GPa), while the lowest nanohardness was witnessed in the experimental group of the nanohybrid composite using HiSmile™ (0.20 ± 0.02 GPa). The paired t-test outcome suggests a statistical difference between the control and experimental groups of the microhybrid composite using Opalescence Regular (p = 0.041). However, the bleaching application caused a reduction in nanohardness in other remaining groups. However, the difference was observed as insignificant (p > 0.05).
Table 3 displays the elastic modulus data of the study groups. The highest elastic modulus (in GPa) was observed in the control group of the microhybrid composite using Opalescence Regular (9.67 ± 1.46 GPa), while the lowest elastic modulus was witnessed in the experimental group of the microhybrid composite using Opalescence Regular (7.7 ± 1.2 GPa). The paired t-test suggests the statistical difference between the control and experimental groups of the microhybrid composite using Opalescence Regular (p = 0.023).
Figure 2 shows the load–displacement nanoindentation behavior exhibited by the resin of the nanohybrid composite after the bleaching regime at a loading and unloading rate of 0.5 mN/s at 23 ± 1 °C.
Table 4 displays the flexural strength of the study groups. The highest flexural strength (in MPa) was observed in the control group of the microhybrid composite using HiSmile™ (82.18 ± 5.22 MPa), while the lowest flexural strength was witnessed in the experimental group of the nanohybrid composite using Opalescence Regular (71.75 ± 4.75 MPa). Each study group exhibited a reduction in flexural strength after the bleaching application. The paired t-test outcome suggests no statistical difference between the control and experimental groups (p > 0.05).
Figure 3 graphically illustrates the diametral tensile strength (MPa) values of the study groups, i.e., before and after the bleaching application. Both bleaching systems exhibited a deleterious effect on the diametral tensile strength, although the deleterious effect was not significant when using any type of bleaching system, irrespective of the restorative composite used. However, a decrease in diametral tensile strength was observed as more pronounced with the use of Opalescence Regular compared to HiSmile™. The highest change in diametral tensile strength was observed in the nanohybrid composite using Opalescence Regular (44.21 MPa before bleaching and 39.24 MPa after bleaching), while the lowest change in diametral tensile strength was observed in the microhybrid composite using HiSmile™ (41.38 MPa before bleaching and 39.2 MPa after bleaching).

4. Discussion

Considering the results obtained, the hypothesis tested was partially rejected: The surface properties of the tested composite materials were affected by CP-based Opalescence Regular bleaching gel, while the bulk properties were insignificantly affected when using Opalescence Regular gel. In contrast, PAP+-based bleaching gel did not affect the surface and bulk properties of the composite materials. To avoid plaque accumulation, a smooth restorative surface is vital [20]. However, we observed that the active and other added agents in the Opalescence regular bleaching system may compromise the structural integrity of the restorative composite surface. A significant increase in surface roughness of the microhybrid restorative composite using Opalescence Regular insinuates that the resin matrix of the composite is susceptible to chemical erosion due to multi-component acidic and oxidizing bleaching chemicals [24]. The irreversible changes in the restorative composite might have an effect on the durability and clinical life of the restorative material. In contrast, the insignificant increase in surface roughness after bleaching in the HiSmile™ group might hint towards a mild effect on the resin matrix system of both restorative composite systems.
The nanoindentation test is considered a reliable and valid method for gauging any changes at the nanoscale [21,25]. A significant decrease in nanohardness of the resin matrix with Opalescence Regular using the microhybrid composite indicates the detrimental effect of carbamide peroxide on the resin matrix of the microhybrid composite. Carbamide peroxide breaks down into HP and urea. HP is a powerful oxidant that produces free radicals and causes oxidation and has high reactivity and extensive ability to diffuse into an organic component of the composite [26]. Free radicals have the potential to impact the resin–filler interface and result in filler–matrix debonding [27]. In contrast, a statistically insignificant nanohardness reduction in the nanohybrid composite group might be explained by the lower resin matrix ratio and higher content of inorganic fillers in the composition.
Although the peroxide-free experimental bleaching product reduced the nanohardness both in the microhybrid and nanohybrid composite groups, the reduction was not statistically significant. This diminutive reduction could be due to the vulnerability of the resin matrix to chemical alteration. Another cause might be that the resin matrix of the composite material absorbs water, which transforms into plasticizing molecules inside the resin matrix. The presence of hydroxyapatite and potassium citrate for buffering in formulation maintains a near-neutral pH during application [18]. The near-neutral effect of pH is shown to be undamaging on the resin matrix system of the restorative composite materials.
The data of the elastic modulus are interesting and interpretive, and they corroborate well with the nanohardness results. The restorative composites with high elastic modulus perform better clinically [28]. The significant decrease in elastic modulus of the microhybrid composite strongly indicates the depletion due to the pH or diffusion gradient of the Opalescence Regular components with lower molecular weight into the resin matrix system of the restorative composite material [29]. However, the bleaching session from each bleaching product was limited to 10 min for seven consecutive days and the samples were incubated in distilled water at 37 °C after each bleaching session until the next bleaching procedure. Depending on the polarity of the molecular structure, the restorative composites absorbed water to varying degrees [29]. The water uptake might have affected the elastic modulus of the restorative composite. The insignificant elastic modulus reduction in the remaining three groups, in particular to HiSmile™ bleaching on the microhybrid composite, might suggest a mild and innocuous effect of this new peroxide-free bleaching product. Recent studies also claim that the presence of nano-hydroxyapatite in the formulation helps in remineralizing the enamel surface more effectively [30,31]. In the case of the resin matrix, these nano-hydroxyapatite fillers might have filled in the tiny pits created due to the bleaching process and made the resin matrix resilient and stiff.
No study group exhibited a significant decrease in flexural strength of the restorative composite. We can assume that the bleaching treatment did not affect the bulk properties of the restorative composites. The obtained results suggest Opalescence Regular had a deleterious effect on the flexural properties of the microhybrid composite. This could be because of the higher vulnerability to water sorption and material disintegration due to the higher amount of organic resin matrix in the microhybrid composite [32,33]. A p-value close to 0.05 in the Opalescence Regular microhybrid composite may argue that unprotected double bonds at the resin–filler interface were oxidized by free radicals generated due to the bleaching process [15,34]. In contrast, the flexural strength of the restorative composites using HiSmile™ was less affected. We believe that since the surface properties were mildly affected using this novel bleaching system, the effect on bulk properties was insignificant and diminutive only, while incubation of samples in distilled water at 37 °C after each bleaching session of 7 consecutive days might have caused water sorption at the filler–resin interface. Consequently, the flexural strength and integrity of these materials were reduced in each study group. The findings of our study are in line with the previous studies that have advocated the insignificant effect of home-bleaching gels on the flexural properties of the dental composites [7,35].
Similarly, no significant difference in the evaluation of diametral tensile strength was observed between the tested bleaching groups. This might suggest that the effect of CP is confined to the material’s surface only, resulting in only a significant change in surface properties such as roughness, nanohardness, and the elastic modulus of the material, while the insignificant decrease in flexural and diametral tensile strength tests might hint toward undamaged bulk material due to the shorter duration of the bleaching procedure.
Phthalimidoperoxycaproic acid (PAP+), the new bleaching agent under investigation, is an organic acid with a high oxidation potential. The bleaching process requires oxidation because it breaks down the organic double bonds that result in tooth discolorations. PAP+, however, does not depend on HP being released [18]. The results of earlier research have demonstrated that free radicals are mostly responsible for the inorganic and organic components of the tooth surface degrading and the reduction of the surface and mechanical properties of the restorative materials [18]. Unlike the previous formulation of PAP that etched and reduced the enamel microhardness [10], the manufacturer claims that their new formulation (designated as PAP+) is optimal and non-acidic [18]. The presence of nano-hydroxyapatite might help during the bleaching process by filling in the damaged areas of the resin matrix. The present study confirms the mild influence of the novel bleaching system on the tested properties of the restorative composites. This suggests that individuals can achieve bleaching without risking damage to their dental composite restorations. Hence, the clinical life of the composite restorations would not be affected using this novel bleaching system.
Our results are consistent with earlier studies that have indicated that even low concentrations of CP can have harmful effects on the surface roughness [13], hardness [13,14], and flexural properties [15,16] of restorative composites. However, our findings contradict with the result of Zuryati et al. [14] which claimed no adverse effect on the surface roughness of all three composite resins using Opalescence regular. This study evaluated the efficacy of a novel PAP+-based bleaching gel. To the best of our knowledge, this material has not been previously tested on restorative composites. Therefore, direct comparison and contrast with previous studies are not possible. Nevertheless, the results obtained in this study provide valuable insights into the performance of the new bleaching material, which can serve as a benchmark for future research on this bleaching material.
The present study might have some drawbacks, such as controlled laboratory conditions that cannot simulate the exact oral conditions and may not reproduce the findings. Due to the complexity of the oral cavity, the performance of restorative composites in conjunction with bleaching agents may vary clinically. The laboratory studies may not reflect the long-term effectiveness and safety of home-based bleaching gel. It is important to conduct long-term clinical studies to evaluate the long-term effects of these products. Additionally, only a single type of 20% CP-based bleaching agent was compared and contrasted with a novel PAP+-based bleaching agent. Therefore, the results need to be cautiously interpreted. In future studies, multiple commercially available at-home bleaching products need to be compared and contrasted. Clinical studies are strongly recommended for the validity and reliability of the findings. Further research in this area can lead to the development of safer and more effective bleaching agents for clinical use. In this regard, studies related to active ingredients for teeth bleaching that are less likely to cause sensitivity or damage to dental restorations and developing nanotechnology-based teeth bleaching products that can penetrate the tooth enamel more effectively, resulting in a more even and long-lasting whitening effect, would be interesting.

5. Conclusions

This laboratory study uncovered that the use of HP-based bleaching gel affects the surface properties of a material, if not the bulk, while PAP+-based home bleaching gel did not exert a negative influence on the surface and bulk properties of restorative composites. It is concluded that a patient with composite restorations can use PAP+ home bleaching gel without damaging them.

Author Contributions

Conceptualization, A.A.K. and S.V.; Methodology, S.V.; Software, H.A.; Validation, L.S.J.B., A.A.K. and A.A.A.; Formal Analysis, A.A.K.; Investigation, L.S.J.B.; Resources, H.A.; Data Curation, L.S.J.B.; Writing—Original Draft Preparation, A.A.K.; Writing—Review and Editing, A.A.A.; Visualization, S.V.; Supervision, A.A.A.; Project Administration, H.A.; Funding Acquisition, A.A.A. All authors have read and agreed to the published version of the manuscript.

Funding

Researchers Supporting Project number (RSP2023R31), King Saud University, Riyadh, Saudi Arabia.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

All the authors declare no conflict of interest.

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Applsci 13 05935 g001 550
Figure 1. Graphical representation of surface roughness of the control and experimental groups: (A) surface roughness using Opalescence Regular bleaching gel on microhybrid and nanohybrid restorative composites. (B) depicts the surface roughness using HiSmile™ bleaching gel on microhybrid and nanohybrid restorative composites.
Figure 1. Graphical representation of surface roughness of the control and experimental groups: (A) surface roughness using Opalescence Regular bleaching gel on microhybrid and nanohybrid restorative composites. (B) depicts the surface roughness using HiSmile™ bleaching gel on microhybrid and nanohybrid restorative composites.
Applsci 13 05935 g001
Applsci 13 05935 g002 550
Figure 2. Load–displacement nanoindentation curve for resin in the experimental group of nanohybrid composite material at a loading and unloading rate of 0.5 mN/s.
Figure 2. Load–displacement nanoindentation curve for resin in the experimental group of nanohybrid composite material at a loading and unloading rate of 0.5 mN/s.
Applsci 13 05935 g002
Applsci 13 05935 g003 550
Figure 3. Graphical representation of diametral tensile strength of the control and experimental groups: (A) Diametral tensile strength using Opalescence Regular bleaching gel on microhybrid and nanohybrid restorative composites; (B) depicts the diametral tensile strength using HiSmile™ bleaching gel on microhybrid and nanohybrid restorative composites.
Figure 3. Graphical representation of diametral tensile strength of the control and experimental groups: (A) Diametral tensile strength using Opalescence Regular bleaching gel on microhybrid and nanohybrid restorative composites; (B) depicts the diametral tensile strength using HiSmile™ bleaching gel on microhybrid and nanohybrid restorative composites.
Applsci 13 05935 g003
Table
Table 1. Materials used in the laboratory study.
Table 1. Materials used in the laboratory study.
MaterialCompositionManufacturerLOT No.
Saremco microhybrid compositeInorganic filler (barium glass & silica 76% wt., 52% by volume) particle size from 4 to 3000 nm, bisGMA, bisEMA, TEGDMA, catalysts, inhibitors, pigmentsSaremco Dental AG, Rebstein, SwitzerlandA990
Nanohybrid Light Cure Compositecrystalline and fumed silicon dioxide 80–90% wt., bisGMA, TEGDMA, catalysts, inhibitors, pigmentsMEDENTAL International Inc., Vista, CA, USA13092378
HiSMiLE™Sorbitol, water, phthalimoperoxycaproic acid, propylene glycol, glycerin, potassium nitrate, PEG-8, hydroxyapatite, cellulose gum, hydroxyethylcellulose, xanthan gumHismile Pty Ltd., Burleigh Waters, Australia012102020
Opalescence RegularGlycerin, water, carbamide peroxide, xylitol, carbomer, PEG-300, sodium hydroxide, EDTA, potassium nitrate, sodium fluorideUltradent Products, Inc., South Jordan, UT, USABFSDM
Key: bisGMA = bisphenol A-glycidyl methacrylate, bisEMA = bisphenol A ethoxylated dimethacrylate, TEGDMA = triethylene glycol dimethacrylate, PEG-8 = polyethylene glycol with molecular weight 8 g/mol, PEG-300 = polyethylene glycol with molecular weight 300 g/mol, EDTA = ethylenediaminetetraacetic acid, nm = nanometer.
Table
Table 2. Mean nanohardness (in GPa) of the two composite materials distributed according to two different treatments.
Table 2. Mean nanohardness (in GPa) of the two composite materials distributed according to two different treatments.
Bleaching GelCompositeTreatmentMeanStd. Dev.p
Opalescence RegularMicrohybridcontrol0.240.020.041 *
experimental0.230.07
Nanohybridcontrol0.210.020.080
experimental0.210.02
Hismile™Microhybridcontrol0.230.030.064
experimental0.220.02
Nanohybridcontrol0.210.020.104
experimental0.200.02
Note: p < 0.05, * = significance between two variables, GPa = gigapascal.
Table
Table 3. Mean elastic modulus (in GPa) of the two composite materials distributed according to two different treatments.
Table 3. Mean elastic modulus (in GPa) of the two composite materials distributed according to two different treatments.
Bleaching GelCompositeTreatmentMeanStd. Dev.p
Opalescence RegularMicrohybridcontrol9.671.46
experimental8.130.540.023 *
Nanohybridcontrol8.42380.92651
experimental7.69871.221210.072
Hismile™MicrohybridControl8.85251.39031
experimental8.27381.061880.089
NanohybridControl8.37380.80534
experimental7.73001.431710.096
Note: p < 0.05, * = significance between two variables, GPa = gigapascal.
Table
Table 4. Mean flexural strength (in MPa) of the two composite materials distributed according to two different treatments.
Table 4. Mean flexural strength (in MPa) of the two composite materials distributed according to two different treatments.
Bleaching GelCompositeTreatmentMeanStd. Dev.p
Opalescence RegularMicrohybridControl81.184.500.056
experimental75.365.14
NanohybridControl75.923.490.067
experimental71.754.75
HismileMicrohybridcontrol82.185.220.082
experimental77.863.30
Nanohybridcontrol74.942.960.092
experimental72.323.75
Note: p < 0.05, MPa = megapascal.
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Khan, A.A.; Abdullah Alkhureif, A.; Bautista, L.S.J.; Alsunbul, H.; Vellappally, S. Peroxide-Free Bleaching Gel: Effect on the Surface and Mechanical Properties of Nano- and Micro-Hybrid Restorative Composite Materials. Appl. Sci. 2023, 13, 5935. https://doi.org/10.3390/app13105935

AMA Style

Khan AA, Abdullah Alkhureif A, Bautista LSJ, Alsunbul H, Vellappally S. Peroxide-Free Bleaching Gel: Effect on the Surface and Mechanical Properties of Nano- and Micro-Hybrid Restorative Composite Materials. Applied Sciences. 2023; 13(10):5935. https://doi.org/10.3390/app13105935

Chicago/Turabian Style

Khan, Aftab Ahmed, Abdulaziz Abdullah Alkhureif, Leonel S. J. Bautista, Hanan Alsunbul, and Sajith Vellappally. 2023. "Peroxide-Free Bleaching Gel: Effect on the Surface and Mechanical Properties of Nano- and Micro-Hybrid Restorative Composite Materials" Applied Sciences 13, no. 10: 5935. https://doi.org/10.3390/app13105935

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