
==== Front
BMC Oral Health
BMC Oral Health
BMC Oral Health
1472-6831
BioMed Central London

4876
10.1186/s12903-024-04876-5
Research
Effect of carbamide peroxide treatment on the ion release of different dental restorative materials
Yilmaz Merve Nur 1
Gul Pinar opinargul@gmail.com

2
1 https://ror.org/01x1kqx83 grid.411082.e 0000 0001 0720 3140 Department of Restorative Dentistry, Faculty of Dentistry, Bolu Abant Izzet Baysal University, Bolu, Turkey
2 https://ror.org/03je5c526 grid.411445.1 0000 0001 0775 759X Department of Restorative Dentistry, Faculty of Dentistry, Atatürk University, Erzurum, Turkey
14 9 2024
14 9 2024
2024
24 10899 7 2024
6 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
Background

To predict the long-term performance of restorative materials in the oral environment, it is important to evaluate their resistance to chemical and mechanical degradation and to know the toxic potential of the type and amount of ions eluted from the filling material. In this study, home bleaching was applied to dental materials with different contents and it was aimed to determine the type and amount of ions released from these materials.

Methods

In this study, amalgam, posterior composite resin, anterior composite resin, bulk fill composite resin, indirect composite resin, hybrid ceramic and all-ceramic were used as restorative materials. 10 specimens of each material were prepared according to the manufacturer’s instructions. Each material group was divided into two subgroups as the bleached group and the control group. After bleaching, all specimens were stored in 1 ml of 75% ethanol/water solution. Solutions were renewed after 1, 14 and 28 days. The type and amount of ions released from the materials were determined using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Data were analyzed using the Friedman, Wilcoxon Signed Ranks, and Mann-Whitney U tests (α = 0.05).

Results

It was determined that the amount of ions release from the restorative materials decreased over time (p < 0.05). According to the results of the Mann-Whitney U test, there was no difference between the bleaching and control groups in most of the restorative materials (p > 0.05).

Conclusion

Within the limits of this study, home bleaching system does not have a significant effect on ion release from restorative materials.

Keywords

Amalgam
Bleaching
Composite resin
Dental ceramic
Ion release
Research Fund of Atatürk UniversityTSA-2021-9427 TSA-2021-9427 issue-copyright-statement© BioMed Central Ltd., part of Springer Nature 2024
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pmcIntroduction

Today, with the increase in esthetic expectations and the development of adhesive systems, the production and use of restorative materials with different contents has increased in dentistry. Although the materials used are thought to be very stable structurally, these materials can deteriorate with environmental factors and the ions in the structure of the material can be released into the oral environment. It is thought that one of these release-increasing factors is bleaching agents, which are very popular in use today. The bleaching process can be applied by the dentist in the office with products containing high concentrations of hydrogen peroxide (HP), or it can be applied by the patient at home with products containing low concentrations of carbamide peroxide (CP) [1, 2]. The American Dental Association (ADA) and the European Scientific Committee for Consumer Products (SCCP) recommend using low concentration bleaching agents [3, 4]. Home bleaching has advantages such as providing a safe bleaching due to the use of low doses, a lower incidence of tooth sensitivity, obtaining similar bleaching results with bleaching agents containing higher concentrations, being more economical and less time spent in the clinic. One study reported that 10% CP application (8–10 h per day for 14 days) provided more effective whitening than 35% HP application (30 min once a week for 2 weeks), and this was confirmed by another clinical study [5–7]. In another study, it was reported that carbamide peroxide at a concentration greater than 10% caused a decrease in enamel surface hardness and did not cause serious side effects in soft tissues below this concentration [8].

Although home bleaching has all these advantages, there is a possibility that it may contact the restorations in the patient’s mouth during application and affect the restoration surfaces. The ability of bleaching agents to affect the physico-chemical properties of materials may cause deterioration of restorative materials. A wide range of restorative materials can be found in the mouth, from amalgam to composite materials and even ceramic materials. In the literature, the effects of bleaching on the surface properties such as hardness and roughness of the materials have been investigated, but there is no detailed information on the effect on the elution of ions from many other filling materials, especially CAD/CAM materials [9–12].

To predict the long-term performance of restorative materials in the oral environment, it is also important to evaluate their resistance to chemical and mechanical degradation and to know the toxic potential of the type and amount of ions eluted from the filling material because these ions can pass directly into body fluids in the oral environment.

In this study, it was aimed to determine the type and amount of ions released from dental materials with different contents applied at home bleaching.

The the hypothesis of the study is “bleaching treatment increases ionic release of restorative materials”.

Materials & methods

In this study, the type and amount of ions released from seven different restorative materials (Cavex Avalloy, Clearfil Majesty Posterior, Clearfil Majesty Estetic, FiltekBulk Fill Posterior, GrandioSO, Vita Enamic and Vitablocs Mark II) that were bleached were investigated. Information on the restorative materials used and their contents are given in Table 1.

Table 1 Information of the materials used in the study and their contents

Material	Type	Content	Manufacturer	LOT	
Cavex Avalloy	Amalgam	45% Ag, 30.5% Sn, 24% Cu and 0.5% Zn (10 parts of alloy mixed with 10.3 parts of Hg)	Cavex Holland Bv, Haarlem, Holland	836944	
Clearfil Majesty Posterior	Posterior composite	BISGMA, TEGDMA,

silanated ceramic, alumina microfillers

	Kuraray Co.,Ltd, Osaka, Japan	480070	
Clearfil Majesty Esthetic	Anterior composite	BISGMA, silanated Ba	Kuraray Co.,Ltd, Osaka, Japan	7A0191	
FiltekBulk Fill Posterior	Bulkfill composite	Aromatic UDMA, UDMA, silanized ceramics, silica and zirconia	3 M ESPE, MN, USA	N994343	
GrandioSO	Indirect composite	TEGDMA, BISGMA,

BISEMA

	Voco, Cuxhaven, Germany	1945406	
Vita Enamic	Hybrid ceramic	UDMA, TEGDMA, ceramic particles, SiO2, Al2O3, Na2O, K2O, B2O3, CaO, TiO2	VITA Zahnfabrik, Germany	54230	
Vitablocs Mark II	Full ceramic	SiO2, Al2O3, Na2O, K2O, CaO, TiO2	VITA Zahnfabrik, Germany	47620	
BISGMA: Bisphenol A glycerolate dimethacrylate, UDMA: Urethane dimethacrylate, TEGDMA: Triethylene glycol dimethacrylate, BISEMA: Bisphenol A ethoxylate dimethacrylate

Sample size determination

G*Power 3.1.9.4 software (Heinrich-Heine Dusseldorf University, Dusseldorf, Germany) was used to determine the sample size based on using the following parameters: 95% power, 0.27 effect size, and a error at 0.05. It was determined that the minimum number of specimens required for 7 groups was 70.

Preparation of specimens

A total of 70 specimens, 10 of each material, were prepared using square shaped metal molds (5 × 5 × 2 mm). The composite materials (A2 color) were placed in a metal mold with a transparent tape (Mylar strip) on the top and bottom and sandwiched between two glasses. The material was then cured for 20 s using a visible blue LED light device (Elipar Freelight II, 3 M Oral Care, St. Paul, MN, USA) at a wavelength of 430–480 nm (light intensity:1200 mW/cm2). Light intensity was controlled using radiometer. In addition, IsoMet Diamond Wafering Blades (Buehler, Lake Bluff, IL, USA) cutting device was used under water cooling to obtain 5 × 5 × 2 mm specimens from CAD/CAM blocks. After the prepared specimens were kept in distilled water for 24 h, their surfaces were polished using medium, fine and superfine aluminum oxide discs (Sof-Lex, 3 M ESPE, St. Paul, MN, USA).

One commercially available dental amalgam was selected for this study. The chemical composition of this alloy was summarized in Table 1. The amalgam capsules were automatically mixed in a dental amalgamator (SDI, Bayswater, Victoria, Australia) according to the manufacturers’ instructions. The freshly prepared mix was condensed into mold using hand condensers. The specimens were left in the molds for 60 min, then they were removed and placed in distilled water. Twenty-four hours later, the specimens were polished using standard silicone polishers (Shofu Amalgam Polishing Kit, Shofu Inc, Kyoto, Japan) mounted on a slow-speed contra angle [13].

Bleaching process

Each material group was divided into two subgroups as the bleached group and the control group. Opalescence PF (Ultradent Products INC, South Jordan, Utah, USA) bleaching gel containing 16% Carbamide Peroxide (CP) was applied to the bleaching group according to the manufacturer’s instructions. In the study, a 14-day application cycle of 4 h a day was applied as a treatment protocol in order to ensure maximum surface contact in terms of ion release. The bleaching agent was applied to the upper surface of the specimen and a mark was made on the edge to identify the upper surface of the specimens. After bleaching the specimens, the specimens were washed with tap water for one minute and dried. Then, the specimens were transferred to glass tubes containing 1 ml of 75% ethanol/water mixture. During the periods when the bleaching processes were applied to the specimens, the control group specimens were also removed from the ethanol/water solution in parallel with these times (4 h every day for 14 days) and stored in a dry environment. Following the bleaching process, the specimens in the experimental and control groups were put back into the ethanol/water solution and this cycle was repeated throughout the bleaching sessions. Solutions were renewed 1, 14 and 28 days after bleaching. The obtained solutions were kept at + 4 ºC until ions analysis.

Ion analysis

The type and amount of ions released from the materials used in this study were determined using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). The analyzed ions are Si, Li, Ba, Al, B, Sr, Zr, Ca, Na, Fe, Ti, K, Zn, Sn, Cu, Ag and Hg.

Sample preparation

Ethanol/water solutions were decomposed with a microwave system before ion analysis. For this process, 0.5 ml of ethanol/water mixture samples were taken and transferred into Teflon containers. 9 ml of HNO3 and 1 ml of H2O2 solution were added to them, and the containers and segments forming the system were closed and placed in the microwave. Decomposition of the samples was carried out using the Milestone connect ETHOS UP microwave system (Milestone, Sorisole, Italy), which reached 190 °C within 15 min and then held at 190 °C for 15 min. As a result of decomposition, 5 ml ultrapure water was added to the 10 ml samples and diluted. The samples were filtered using a 0.45 μm syringe filter and read by giving them to the device without any second dilution.

Analysis process

Ion analysis of ethanol/water samples was performed using an ICP-MS instrument (Agilent 7800 series, Agilent Technologies, Japan). The ICP-MS device contains a glass MikroMist nebulizer (U-series, Australia) used to load samples into the system and a quartz spray chamber (double pass, USA). The plasma part consists of an inert sample input kit containing a quartz torch (2.5 mm, Japan), and a sample cone and skinner cone (for x-lens, USA) made of nickel material.

Before starting the analysis, the device was purged with helium gas for 45 min. After setting the device parameters such as plasma gas: 15 L/min, auxiliary gas: 1 L/min, carrier gas: 1 L/min, makeup/dilution gas: L/min and carrier gas pressure 1.45 kPa, the device is activated. After the device was activated, torch axis, resolution axis, EM, standard lenses tune, plasma corection, full spectrum and performance report tests were performed, respectively. Afterwards, the device was calibrated with a tuning solution (1 µg/l Ce, Co, Li, Mg, Tl, Y). The values obtained as a result of the tune process were checked and it was determined whether there was any deviation in the device. Standard solutions prepared using stock solutions were read and the calibration curves were checked. After checking the calibration curves, the samples were loaded into the device by the autosampler and analyzed. The autosampler and tubing were washed with 2% HNO3 and ultrapure water, and the probe part was washed with 1% HCl solution and made ready for the next injection. Measurements were made at 1200 W RF power, 1 L/min carrier gas flow and 0.30 rps nebulizer pump speed, and argon gas was used as carrier gas.

Statistical analysis

The obtained data were analyzed using SPSS 20 (IBM, Chicago, IL, USA) statistical package program. Kolmogorov-Smirnov test was used to detect the distribution of data. Analysis of the amount of ions released from materials over time was done using the Friedman and Wilcoxon Signed Ranks tests. In addition, the bleaching and control groups for each material were compared using the Mann-Whitney U test. All statistical analyzes were performed separately for each ions type. p < 0.05 value was considered statistically significant.

Results

In the present study, the amounts of Si, Li, Ba, Al, B, Sr, Zr, Ca, Na, Fe, Ti, K, Zn, Sn, Cu, Ag and Hg ions released over time after bleaching processes were applied to seven different restorative materials were analyzed. The types and amounts (µg/ml) of ions released from each restorative material were given in Tables 2, 3, 4, 5, 6, 7 and 8.

Table 2 Type and mean (µg/ml) amounts of ions released from bleaching and control groups for Cavex Avalloy material

Ions	Groups	1 DAY	14 DAYS	28 DAYS	p	
Mean	SD		Mean	SD		Mean	SD		
Li	PF	0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.135	
B		0.04	0.05	A	0.03	0.06	A	0.01	0.02	A	0.035	
Na		0.66	1.47	A	20.12	1.45	B	0.17	0.29	AB	0.015*	
Al		0.25	0.40	A	0.00	0.00	A	0.03	0.06	A	0.174	
Si		4.55	0.98	A	4.20	0.51	AB	9.25	3.28	B	0.022*	
K		1.74	1.11	AB	6.63	0.64	A	0.58	0.20	B	0.007*	
Ca		0.09	0.15	A	0.06	0.08	A	0.00	0.00	A	0.232	
Ti		0.00	0.00	A	0.01	0.02	B	0.00	0.00	AB	0.029*	
Fe		0.26	0.41	A	0.07	0.09	A	0.06	0.13	A	0.819	
Cu		5.33	11.84	A	0.24	0.27	A	0.04	0.05	A	0.165	
Zn		0.44	0.76	A	2.38	1.07	B	0.09	0.09	AB	0.022*	
Sr		0.00	0.01	AB	0.01	0.00	A	0.00	0.00	B	0.021*	
Zr		0.00	0.00	A	0.00	0.01	A	0.00	0.00	A	0.627	
Ag		16.51	36.84	A	0.40	0.87	A	0.08	0.14	A	0.819	
Sn		6.71	14.96	A	1.27	1.13	A	6.87	2.17	A	0.091	
Ba		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.486	
Hg		27.66	60.73	A	0.67	1.26	A	0.15	0.22	A	0.819	
Li	CONTROL	0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.018	
B		0.00	0.00	A	0.00	0.00	A	0.09	0.06	A	0.018	
Na		0.50	0.69	A	13.19	6.45	A	0.53	1.19	A	0.012	
Al		0.00	0.00	A	0.72	1.22	A	0.02	0.03	A	0.068	
Si		4.19	0.21	A	6.53	1.85	A	7.24	3.45	A	0.074	
K		3.42	2.78	AB	8.54	3.35	A	0.53	0.18	B	0.015*	
Ca		0.17	0.28	A	0.58	0.26	A	0.18	0.23	A	0.196	
Ti		0.00	0.01	A	0.07	0.08	B	0.01	0.01	AB	0.015*	
Fe		0.00	0.00	A	0.93	1.26	A	0.06	0.08	A	0.113	
Cu		5.96	8.24	AB	6.42	7.71	A	0.05	0.06	B	0.022*	
Zn		0.59	0.38	A	3.01	0.44	B	0.56	0.09	AB	0.022*	
Sr		0.02	0.01	A	0.01	0.01	AB	0.00	0.00	B	0.022*	
Zr		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.607	
Ag		19.26	25.79	A	13.75	13.93	A	0.11	0.20	A	0.247	
Sn		7.57	8.96	A	11.66	7.58	A	12.91	6.01	A	0.549	
Ba		0.00	0.00	A	0.01	0.01	B	0.00	0.00	AB	0.008*	
Hg		30.37	39.42	A	30.79	38.34	A	0.17	0.31	A	0.074	
p: Friedman test, SD: Standard Deviation. *p < 0.05; statistically significant. Different capital letters on the same row shows statistically significant difference

Table 3 Type and mean (µg/ml) amounts of ions released from bleaching and control groups for Clearfil Majesty Posterior

Ions	Groups	1 DAY	14 DAYS	28 DAYS	p	
Mean	SD		Mean	SD		Mean	SD		
Li	PF	3.03	0.79	AB	12.49	1.32	A	2.14	0.53	B	0.015*	
B		3.71	1.58	A	7.62	1.51	B	5.25	0.68	AB	0.015*	
Na		2.67	5.41	A	24.08	11.32	B	4.17	0.99	AB	0.015*	
Al		0.25	0.24	AB	5.89	4.74	A	0.13	0.15	B	0.015*	
Si		6.73	2.77	A	16.58	7.28	B	7.78	2.71	AB	0.041*	
K		0.32	0.23	AB	2.05	0.83	A	0.18	0.17	B	0.015*	
Ca		0.82	1.84	A	1.80	0.96	A	0.08	0.18	A	0.056	
Ti		0.03	0.07	A	0.06	0.05	A	0.01	0.01	A	0.196	
Fe		0.00	0.00	A	0.00	0.00	A	0.03	0.04	A	0.135	
Cu		0.00	0.00	A	0.04	0.01	A	0.00	0.00	A	0.012	
Zn		0.08	0.14	AB	0.75	0.52	A	0.00	0.00	B	0.010*	
Sr		0.01	0.01	AB	0.11	0.04	A	0.01	0.00	B	0.015*	
Zr		0.05	0.04	AB	0.48	0.41	A	0.01	0.03	B	0.015*	
Ag		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.038	
Sn		0.41	0.92	A	4.22	4.16	A	6.40	1.39	A	0.069	
Ba		0.03	0.02	AB	0.31	0.25	A	0.01	0.00	B	0.015*	
Hg		0.00	0.00	A	0.00	0.01	A	0.00	0.00	A	0.232	
Li	CONTROL	3.01	0.15	AB	6.58	0.40	A	1.80	0.11	B	0.007*	
B		3.34	0.39	A	6.01	0.88	B	5.13	0.50	AB	0.015*	
Na		1.25	2.42	A	10.73	4.74	B	1.88	1.39	AB	0.022*	
Al		0.94	0.61	AB	16.90	5.99	A	0.02	0.04	B	0.007*	
Si		6.11	0.99	A	24.02	6.71	B	7.04	0.71	AB	0.015*	
K		0.41	0.14	AB	0.86	0.21	A	0.34	0.04	B	0.022*	
Ca		0.05	0.07	AB	1.13	0.68	A	0.00	0.00	B	0.010*	
Ti		0.00	0.01	AB	0.03	0.02	A	0.00	0.00	B	0.029*	
Fe		0.04	0.05	A	0.00	0.00	A	0.00	0.00	A	0.050	
Cu		0.00	0.00	A	0.01	0.01	A	0.00	0.00	A	0.076	
Zn		0.04	0.06	AB	1.56	0.59	A	0.00	0.00	B	0.010*	
Sr		0.05	0.05	AB	0.25	0.14	A	0.00	0.00	B	0.007*	
Zr		0.07	0.04	AB	1.08	0.44	A	0.03	0.04	B	0.015*	
Ag		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.036	
Sn		0.00	0.00	A	0.00	0.00	A	7.37	4.37	A	0.007	
Ba		0.03	0.02	AB	0.12	0.03	A	0.00	0.00	B	0.007*	
Hg		0.00	0.00	A	0.00	0.00	B	0.00	0.00	AB	0.010*	
p: Friedman test, SD: Standard Deviation. *p < 0.05; statistically significant. Different capital letters on the same row shows statistically significant difference

Table 4 Type and mean (µg/ml) amounts of ions released from bleaching and control groups for Clearfil Majesty Esthetic

Ions	Groups	1 DAY	14 DAYS	28 DAYS	p	
Mean	SD		Mean	SD		Mean	SD		
Li	PF	0.19	0.15	A	0.13	0.05	AB	0.02	0.00	B	0.022*	
B		6.31	4.47	A	10.02	0.80	A	5.88	0.61	A	0.074	
Na		2.65	3.19	A	33.29	11.04	B	4.28	5.52	AB	0.022*	
Al		0.46	0.49	A	0.44	0.28	A	0.00	0.00	A	0.066	
Si		10.49	3.74	AB	10.30	1.34	A	7.16	1.25	B	0.022*	
K		1.09	0.83	A	8.51	3.20	B	0.98	0.45	AB	0.022*	
Ca		1.22	1.50	A	0.00	0.00	A	0.00	0.00	A	0.023	
Ti		0.01	0.01	A	0.00	0.00	A	0.00	0.00	A	0.099	
Fe		0.01	0.03	A	0.41	0.90	A	0.00	0.00	A	0.368	
Cu		0.01	0.01	A	0.01	0.01	A	0.00	0.00	A	0.036	
Zn		0.09	0.11	AB	0.19	0.14	A	0.00	0.00	B	0.021*	
Sr		0.07	0.06	AB	0.06	0.02	A	0.01	0.00	B	0.022*	
Zr		0.01	0.01	A	0.05	0.03	A	0.00	0.00	A	0.056	
Ag		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.068	
Sn		3.96	7.23	A	7.91	4.04	A	6.20	2.73	A	0.247	
Ba		3.11	3.01	AB	3.77	1.28	A	0.22	0.07	B	0.015*	
Hg		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.007	
Li	CONTROL	0.13	0.07	AB	0.17	0.12	A	0.02	0.00	B	0.015*	
B		4.67	0.47	A	10.19	1.27	B	6.05	0.28	AB	0.007*	
Na		1.63	2.07	A	14.34	8.48	A	6.08	1.91	A	0.165	
Al		0.44	0.61	A	2.51	1.77	A	0.01	0.03	A	0.056	
Si		9.88	2.24	AB	22.00	9.59	A	7.37	0.98	B	0.041*	
K		1.10	0.70	A	6.84	3.24	A	0.93	0.15	A	0.074	
Ca		0.85	0.59	A	1.43	2.12	A	0.39	0.58	A	0.692	
Ti		0.01	0.01	A	0.00	0.01	A	0.01	0.01	A	0.143	
Fe		0.09	0.20	A	0.14	0.30	A	0.27	0.50	A	0.497	
Cu		0.01	0.01	A	0.01	0.01	A	0.01	0.01	A	0.449	
Zn		0.00	0.00	A	0.28	0.26	A	0.00	0.00	A	0.024	
Sr		0.11	0.06	AB	0.46	0.13	A	0.02	0.00	B	0.007*	
Zr		0.01	0.03	A	0.08	0.08	A	0.00	0.00	A	0.069	
Ag		0.00	0.01	A	0.00	0.00	A	0.00	0.00	A	0.305	
Sn		3.73	2.70	AB	2.99	4.24	A	6.23	2.79	B	0.041*	
Ba		2.67	1.06	AB	17.54	7.01	A	0.66	0.13	B	0.007*	
Hg		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.092	
p: Friedman test, SD: Standard Deviation. p < 0.05; statistically significant. Different capital letters on the same row shows statistically significant difference

Table 5 Type and mean (µg/ml) amounts of ions released from bleaching and control groups for Filtek Bulk fill posterior

Ions	Groups	1 DAY	14 DAYS	28 DAYS	p	
Mean	SD		Mean	SD		Mean	SD		
Li	PF	0.04	0.01	AB	0.06	0.00	A	0.02	0.00	B	0.007*	
B		3.73	0.28	A	8.84	0.66	B	5.61	0.73	AB	0.007*	
Na		2.99	2.81	A	28.15	2.10	B	8.48	2.60	AB	0.007*	
Al		0.18	0.24	A	0.38	0.53	A	0.01	0.01	A	0.249	
Si		12.11	2.12	A	13.41	8.76	AB	7.61	0.56	B	0.015*	
K		0.44	0.19	A	2.25	0.17	B	0.50	0.13	AB	0.022*	
Ca		0.04	0.09	A	0.09	0.12	AB	0.84	0.48	B	0.010*	
Ti		0.07	0.02	A	0.04	0.02	AB	0.01	0.01	B	0.015*	
Fe		0.20	0.45	A	0.03	0.04	A	0.10	0.23	A	0.779	
Cu		0.01	0.01	A	0.02	0.01	A	0.01	0.00	A	0.165	
Zn		0.00	0.00	A	0.06	0.03	B	0.00	0.01	AB	0.009*	
Sr		0.08	0.07	AB	0.20	0.08	A	0.01	0.00	B	0.015*	
Zr		3.01	1.00	A	0.24	0.07	AB	0.00	0.01	B	0.007*	
Ag		0.01	0.00	A	0.00	0.00	AB	0.00	0.00	B	0.015*	
Sn		9.66	1.57	A	5.54	12.39	A	2.60	2.30	A	0.074	
Ba		0.16	0.09	A	0.15	0.03	AB	0.03	0.02	B	0.022*	
Hg		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.056	
Li	CONTROL	0.05	0.01	A	0.04	0.01	A	0.02	0.01	A	0.074	
B		3.59	0.56	A	6.28	0.71	B	5.84	0.36	AB	0.015*	
Na		8.11	4.61	A	7.93	2.38	A	7.27	1.00	A	0.819	
Al		0.49	0.34	A	0.03	0.06	B	0.03	0.04	AB	0.015*	
Si		14.69	4.03	A	12.58	3.80	AB	8.20	0.94	B	0.015*	
K		0.90	0.72	AB	0.69	0.12	A	0.41	0.07	B	0.015*	
Ca		1.27	1.45	A	0.08	0.18	A	0.90	0.46	A	0.056	
Ti		0.09	0.04	A	0.00	0.01	B	0.01	0.01	AB	0.015*	
Fe		0.00	0.00	A	0.00	0.00	A	0.05	0.12	A	0.368	
Cu		0.01	0.01	A	0.00	0.00	B	0.00	0.00	AB	0.007*	
Zn		0.07	0.14	A	0.05	0.08	A	0.01	0.01	A	0.420	
Sr		0.38	0.26	A	0.15	0.09	AB	0.05	0.03	B	0.007*	
Zr		3.96	1.86	A	0.24	0.25	AB	0.05	0.07	B	0.007*	
Ag		0.01	0.01	A	0.00	0.00	B	0.00	0.00	AB	0.022*	
Sn		17.89	5.48	A	6.55	3.16	A	7.27	4.90	A	0.247	
Ba		0.55	0.31	A	0.14	0.05	AB	0.08	0.03	B	0.007*	
Hg		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.023	
p: Friedman test, SD: Standard Deviation. p < 0.05; statistically significant. Different capital letters on the same row shows statistically significant difference

Table 6 Type and mean (µg/ml) amounts of ions released from bleaching and control groups for GrandioSO

Ions	Groups	1 DAY	14 DAYS	28 DAYS	p	
Mean	SD		Mean	SD		Mean	SD		
Li	PF	0.02	0.01	A	0.02	0.01	A	0.02	0.01	A	0.165	
B		7.29	1.91	A	14.33	4.43	A	7.37	0.88	A	0.074	
Na		12.43	2.47	AB	24.92	11.71	A	6.60	0.71	B	0.015*	
Al		1.72	1.14	A	0.17	0.21	AB	0.00	0.01	B	0.009*	
Si		34.50	14.13	A	15.95	4.35	A	88.74	78.51	A	0.549	
K		0.85	0.32	A	2.62	1.33	A	1.07	0.48	A	0.074	
Ca		1.91	2.61	A	0.10	0.22	A	0.51	0.54	A	0.066	
Ti		0.02	0.01	A	0.04	0.02	A	0.01	0.01	A	0.247	
Fe		0.00	0.00	A	0.03	0.07	A	0.68	1.48	A	0.174	
Cu		0.02	0.03	A	0.01	0.01	A	0.01	0.01	A	0.247	
Zn		0.12	0.23	A	0.05	0.07	A	0.04	0.05	A	0.007*	
Sr		0.09	0.05	A	0.04	0.02	AB	0.00	0.00	B	0.022*	
Zr		0.02	0.01	A	0.01	0.01	AB	0.00	0.00	B	0.015*	
Ag		0.02	0.04	A	0.00	0.00	A	0.00	0.00	A	0.091	
Sn		16.40	3.74	A	0.05	0.11	B	7.11	3.00	AB	0.007*	
Ba		7.64	5.33	A	2.81	1.01	AB	0.06	0.02	B	0.015*	
Hg		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.232	
Li	CONTROL	0.03	0.01	A	0.02	0.01	A	0.02	0.00	A	0.449	
B		11.30	5.41	AB	14.99	2.61	A	7.45	0.37	B	0.041*	
Na		11.59	3.27	A	6.90	1.94	AB	5.71	1.34	B	0.022*	
Al		4.23	3.47	A	0.14	0.11	AB	0.00	0.00	B	0.007*	
Si		47.72	30.91	A	11.51	2.84	B	24.54	6.17	AB	0.015*	
K		0.90	0.21	A	0.75	0.13	A	0.70	0.12	A	0.165	
Ca		0.02	0.03	A	0.68	1.25	A	0.04	0.10	A	0.497	
Ti		0.03	0.02	A	0.02	0.01	A	0.02	0.02	A	0.819	
Fe		0.00	0.00	A	0.02	0.03	A	0.40	0.72	A	0.144	
Cu		0.00	0.00	A	0.00	0.00	A	0.01	0.00	A	0.549	
Zn		0.00	0.00	A	0.03	0.05	A	0.00	0.00	A	0.368	
Sr		0.25	0.19	A	0.09	0.03	AB	0.02	0.02	B	0.007*	
Zr		0.05	0.04	A	0.01	0.01	AB	0.00	0.00	B	0.015*	
Ag		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.050	
Sn		15.51	7.32	A	0.00	0.00	B	6.78	2.90	AB	0.015*	
Ba		20.45	16.64	A	3.31	0.56	AB	0.73	0.44	B	0.007*	
Hg		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.050	
p: Friedman test, SD: Standard Deviation. p < 0.05; statistically significant. Different capital letters on the same row shows statistically significant difference

Table 7 Type and mean (µg/ml) amounts of ions released from bleaching and control groups for Vita Enamic

Ions	Groups	1 DAY	14 DAYS	28 DAYS	p	
Mean	SD		Mean	SD		Mean	SD		
Li	PF	0.01	0.01	AB	0.01	0.01	A	0.03	0.01	B	0.022*	
B		4.86	0.46	A	7.18	0.67	A	5.54	0.73	A	0.074	
Na		5.45	6.46	A	18.73	10.15	A	6.50	5.31	A	0.247	
Al		0.12	0.17	A	0.16	0.16	A	0.09	0.09	A	0.678	
Si		6.39	0.88	A	7.53	1.11	A	8.02	3.28	A	0.549	
K		0.56	0.25	AB	2.25	0.85	A	0.23	0.12	B	0.007*	
Ca		0.00	0.00	A	0.25	0.38	A	0.00	0.00	A	0.135	
Ti		0.00	0.00	A	0.02	0.02	A	0.02	0.02	A	0.040	
Fe		0.05	0.08	A	0.20	0.16	A	0.10	0.15	A	0.241	
Cu		0.02	0.01	AB	0.04	0.01	A	0.00	0.00	B	0.021*	
Zn		0.04	0.04	A	0.01	0.02	A	0.00	0.00	A	0.174	
Sr		0.00	0.00	AB	0.01	0.01	A	0.00	0.00	B	0.041*	
Zr		0.00	0.00	AB	0.07	0.15	A	0.00	0.00	B	0.010*	
Ag		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.148	
Sn		0.00	0.00	A	0.41	0.91	AB	10.93	1.12	B	0.009*	
Ba		0.05	0.01	AB	0.17	0.12	A	0.04	0.01	B	0.015*	
Hg		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.368	
Li	CONTROL	0.01	0.01	A	0.01	0.01	A	0.03	0.00	A	0.074	
B		4.92	0.56	A	6.47	1.40	A	5.01	0.41	A	0.165	
Na		7.43	7.14	A	5.69	3.01	A	4.57	1.81	A	0.819	
Al		1.51	2.04	A	0.01	0.01	A	0.06	0.07	A	0.179	
Si		9.22	4.51	A	7.94	2.24	A	9.71	4.52	A	0.819	
K		0.84	0.88	AB	0.88	0.27	A	0.17	0.07	B	0.022*	
Ca		0.03	0.06	A	0.51	0.81	A	0.09	0.13	A	0.529	
Ti		0.00	0.00	A	0.00	0.00	A	0.00	0.01	A	0.061	
Fe		0.12	0.27	A	4.63	10.06	A	0.08	0.10	A	0.913	
Cu		0.01	0.01	AB	0.08	0.08	A	0.00	0.00	B	0.007*	
Zn		0.06	0.13	A	0.00	0.00	A	0.00	0.00	A	0.368	
Sr		0.00	0.00	A	0.01	0.01	A	0.00	0.00	A	0.074	
Zr		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.032	
Ag		0.01	0.02	A	0.00	0.01	A	0.00	0.00	A	0.368	
Sn		0.22	0.45	AB	0.13	0.28	A	8.18	2.24	B	0.015*	
Ba		0.09	0.04	A	0.07	0.06	A	0.04	0.02	A	0.074	
Hg		0.18	0.41	A	0.12	0.26	A	0.00	0.00	A	0.368	
p: Friedman test, SD: Standard Deviation. p < 0.05; statistically significant. Different capital letters on the same row shows statistically significant difference

Table 8 Type and mean (µg/ml) amounts of ions released from bleaching and control groups for Vitablocs Mark II

Ions	Groups	1 DAY	14 DAYS	28 DAYS	p	
Mean	SD		Mean	SD		Mean	SD		
Li	PF	0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.007	
B		0.01	0.01	A	0.01	0.02	AB	0.05	0.02	B	0.009*	
Na		0.00	0.00	A	19.45	4.89	B	0.87	1.04	AB	0.008*	
Al		0.00	0.00	A	0.04	0.06	A	0.04	0.07	A	0.178	
Si		3.05	0.51	A	4.79	0.56	AB	5.47	1.43	B	0.022*	
K		0.87	0.42	A	6.88	1.76	B	0.61	0.17	AB	0.022*	
Ca		0.21	0.26	A	0.27	0.34	A	0.23	0.20	A	0.854	
Ti		0.00	0.00	A	0.02	0.01	B	0.01	0.00	AB	0.041*	
Fe		0.00	0.00	A	0.00	0.00	A	0.04	0.03	A	0.007	
Cu		0.02	0.01	A	0.02	0.01	A	0.01	0.01	A	0.247	
Zn		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	1.000	
Sr		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.202	
Zr		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.368	
Ag		0.00	0.01	A	0.01	0.01	A	0.01	0.01	A	0.549	
Sn		0.00	0.00	A	3.22	2.05	AB	9.45	3.91	B	0.021*	
Ba		0.00	0.00	A	0.01	0.01	A	0.00	0.00	A	0.091	
Hg		0.01	0.02	A	0.01	0.01	A	0.02	0.03	A	0.692	
Li	CONTROL	0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.066	
B		0.00	0.00	A	0.00	0.00	A	0.03	0.02	A	0.007	
Na		0.37	0.83	A	9.29	2.27	B	0.53	0.78	AB	0.016*	
Al		0.83	1.85	A	0.11	0.24	A	0.05	0.05	A	0.424	
Si		5.77	4.41	A	4.52	0.60	A	4.85	1.08	A	1.000	
K		3.13	1.36	AB	6.72	1.55	A	0.81	0.59	B	0.007*	
Ca		0.18	0.21	A	0.89	0.40	B	0.28	0.13	AB	0.041*	
Ti		0.01	0.00	A	0.01	0.02	A	0.01	0.00	A	0.549	
Fe		0.01	0.03	A	0.75	1.69	A	0.14	0.24	A	0.056	
Cu		0.05	0.02	AB	0.15	0.20	A	0.01	0.00	B	0.015*	
Zn		0.00	0.00	A	0.00	0.01	A	0.00	0.00	A	0.368	
Sr		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.247	
Zr		0.01	0.01	A	0.00	0.00	A	0.00	0.00	A	0.779	
Ag		0.01	0.01	A	0.23	0.51	A	0.00	0.00	A	0.368	
Sn		1.02	1.08	A	0.00	0.00	AB	10.91	2.57	B	0.009*	
Ba		0.00	0.00	A	0.00	0.00	A	0.00	0.00	A	0.035	
Hg		0.02	0.05	AB	0.36	0.78	A	0.00	0.00	B	0.029*	
p: Friedman test, SD: Standard Deviation. p < 0.05; statistically significant. Different capital letters on the same row shows statistically significant difference

According to the Friedman and Wilcoxon Signed Ranks test results, there were statistically significant differences between the groups in terms of the amount of ions released from the restorative materials over time (p < 0.05). Ion release in restorative materials was mostly high in the first day and the release decreased over time (p < 0.05).

The comparison of the control and bleaching groups in terms of the total amount of ions released from each restorative material and the statistical analysis results were given in Table 9. According to the results of the Mann-Whitney U test, there was no difference between the bleaching and control groups in most of the restorative materials (p > 0.05). Although it was observed that the release of some ions increased after bleaching in a few groups with significant differences, it was found that bleaching did not affect the release of the main ions contained in the materials (p > 0.05). Although not statistically significant, the amount of ions released from the bleaching groups was mostly higher than the control group.

Table 9 Comparison of bleaching (B) and control (C) groups in terms of total ion amount

Ions
(B-C)	CA	CMP	CME	FBP	GSO	VE	VMII	
Li	0.00		6.28	*	0.02		0.01		-0.01		0.00		0.00		
B	-0.01		2.10		1.31		2.47	*	-4.76		1.17		0.03		
Na	6.72		17.06		18.17	*	16.32	*	19.75	*	13.00	*	10.13	*	
Al	-0.46		-11.58	*	-2.07	*	0.03		-2.49		-1.20		-0.90		
Si	0.04		-6.07		-11.29	*	-2.34		55.41		-4.94		-1.82		
K	-3.53		0.93		1.71		1.19		2.18	*	1.15		-2.31		
Ca	-0.78	*	1.53		-1.45		-1.28		1.76		-0.38		-0.65		
Ti	-0.07		0.06		-0.01		0.02		0.00		0.03	*	0.01		
Fe	-0.59		-0.02		-0.08		0.28		0.29		-4.49		-0.86		
Cu	-6.82		0.03	*	0.00		0.02		0.03		-0.04		-0.15	*	
Zn	-1.25		-0.77		0.00		-0.06		0.18		-0.01		0.00		
Sr	-0.02	*	-0.18		-0.45	*	-0.28		-0.23	*	0.00		0.00		
Zr	0.00		-0.63		-0.05		-1.00		-0.03		0.07		-0.01		
Ag	-16.12		0.00		0.00		0.00		0.02		-0.01		-0.22		
Sn	-17.29		3.67		5.10		-13.92		1.26		2.81		0.75		
Ba	-0.01		0.20	*	-13.76	*	-0.43	*	-13.97		0.07		0.00		
Hg	-32.86		0.00		0.00		0.00		0.00		-0.30		-0.35		
CA: Cavex Avalloy, CMP: Clearfil Majesty Posterior, CME: Clearfil Majesty Estetic, FBF: Filtek Bulk Fill Posterior, GSO: GrandioSO, VE: Vita Enamic, VMII: Vitablocs Mark II, *p < 0.05: Mann-Whitney U test

When the total amount of ions released from all materials was considered, the highest released ion was found to be Si (38.59 µg/ml). It was followed by Na (25.16 µg /ml), Sn (16.87 µg /ml) and B (14.65 µg /ml), Hg (6.47 µg /ml), K (5.79 µg /ml), Ba (4.65 µg /ml), Ag (3.6 µg /ml), Al (2.81 µg /ml), Li (2.16 µg /ml), Cu (1.33 µg /ml), Ca (1.3 µg /ml), Zn (0.76 µg /ml), Fe (0.72 µg /ml), Zr (0.68 µg /ml), Sr (0.18 µg /ml) and Ti (0.06 µg /ml), respectively (Fig. 1).

Fig. 1 Mean values of released total ions from restorative materials

Discussion

In this study, the amount of ions released from different filling materials treated with bleaching agent did not differ significantly with the control groups. Therefore, the hypothesis of the study was rejected.

Previous studies have reported that measuring the release of certain ions was more valuable than assessing the total mass loss of restorative materials [14, 15]. For this reason, in this study, the amount of released ions was compared instead of weight measurements of restorative materials. The ICP-MS method, which is used to determine the ion amount, was preferred because of its excellent sensitivity in ion measurement.

It is stated that hydrogen peroxide can also be used at 3%, 5% and 6% concentrations for home bleaching [16]. 10–16% CP which decomposes into 3–5% HP and 7–10% urea when the bleaching agent interacts with the oral environment are mostly used in the home bleaching method [16]. HP decomposes into OH- and O- free radicals, which are strong oxidizing agents and promotes changes in the surfaces of restorations, creating a potential source for ion release [17].

The restorative material tends to dissolve when in contact with water, and the amount of dissolution varies with storage time [18]. The longer the filling materials are exposed to CP, the greater the dissolution and the greater the release of ions are expected. For this reason, in the present study, in order to obtain the highest ions elution in accordance with the manufacturer’s instructions, a home bleaching system, which is used according to the procedure of bleaching for 4 h every day for 14 days, was used. Bleaching agents may degrade the surface of the restorative material, causing the baseline release of ions to be higher and therefore less release in other period measurements. However, the released products are not always in the ionic state, but can also be found in the form of a series of chemical compounds consisting of these ions. Restorative material products in compound form can also break down over time and be released from the material. Therefore, although baseline release was high, it persisted at other follow-up intervals.

Several studies have been performed to determine the influence of the type of solvent on the release of substances from resin composites. The leaching of organic components from commercial dental composites was investigated in terms of inorganic ions from commercial composites after aging in ethanol, water, and artificial saliva solutions and under other various conditions, as indicated in the literature [19–22]. However, the contents of commercial dental composites may vary depending on the manufacturer. This complexity makes it harder to study the chemical degradation in commercial dental composites. Ferracane [23] reported a weak correlation between conversion rates and eluted ingredients in water. A better correlation was found if an ethanol–water mixture was applied. Especially, the 75% ethanol–water mixture (v/v), which has been recommended by the US Food and Drug Administration as a food-simulating fluid, was used by various authors. Ferracane stated that the intraoral fluids represent solvents probably somewhere between the more aggressive organic solvents and water, which is less effective than pure ethanol [24]. Jakovac et al. [14] reported that acids were an excellent test medium compared to saliva or distilled water because they cause faster material dissolution, thus allowing the long-term stability of dental ceramics to be evaluated. Ferreira et al. [25] reported that amalgam was more affected by bleaching than composite and that in both types of restorative materials, the deterioration caused by bleaching causes the separation of ions and the formation of roughness in the material, which negatively affects the physical and biological properties of the material. For this reason, they reported that aggressive environments should be used to detect degradation in materials in vitro. In this study, 75% ethanol/water solution recommended by the US Food and Drug Association (FDA) was used as the solvent medium, since it is the liquid that best mimics the oral environment [23].

When the amalgam and released ions were examined, it was reported in the literature that there was an increase in mercury (Hg) levels on the bleached amalgam surface [17, 26]. In this study, it was determined that other ions such as silver, copper and tin were released in addition to mercury ions in all amalgam samples, but no significant difference was found between the groups (p > 0.05, Table 9). Rotstein et al. [26], reported a significant increase in Hg levels released from the specimens after a 14-day application with a bleaching agent containing 10% CP, and researchers reported that prolonged contact with bleaching agents may cause microstructural changes on amalgam surfaces. Similarly, Oskoee et al. [17], found that the Hg levels released when a bleaching agent containing CP was applied to the specimens for 6 h a day were significantly higher. Similar to the findings of the present study, Al-Salehi et al. [27], reported that Hg release from specimens did not increase after treatment with a bleaching agent containing 10% CP. In the present study, it was determined that eluted Hg from amalgam was similar to the control group in the 1-day period, but less than the control group in the 14-day period. We think that the differences in these studies may be due to the different content ratios of the amalgam restorative materials used or the washing process performed after the bleaching process.

Regarding the polishing of amalgam fillings, several studies have found higher concentrations of Hg in solution in unpolished amalgam specimens compared to polished amalgam specimens, and it has been reported that bleach causes lower corrosion potential for polished amalgam compared to unpolished ones [28–30]. Corrosion in amalgam is an oxidation-reduction reaction in which the metals in the material react with the non-metallic ions in the environment and form chemical compounds [31]. Such redox reactions also occur at the amalgam and bleaching agent interface. Unpolished surfaces lead to active oxidation [29, 30]. To eliminate this situation, in the present study the specimens were polished after 1 day and ion release was measured after 24 h.

It has been stated in literature that ion release from amalgams was proportional to the surface area of the specimen, and the levels of mercury released may be different even in different batches of the same amalgam type under the same conditions [32]. Al Salehi [27], reported that considering the surface area of an amalgam filling is approximately 5 mm x 5 mm, approximately 1.125 µg of mercury will be released from the filling. In addition, the World Health Organization has stated that the maximum acceptable daily mercury intake (ADI) should not exceed 40 µg and that mercury release from approximately 36 fillings should occur in order to exceed this limit [27]. In the present study, the surface areas of the amalgam specimens were prepared to be approximately 5 mm x 5 mm, and the release rate was below the maximum acceptable daily mercury intake of the World Health Organization. Although dental amalgam continues to be used in many countries, amalgam use has decreased recently due to the availability of safer alternatives and esthetic reasons.

When other ions released from the materials into the solution are examined, one of them was aluminum. As a result of aluminum forming fluoride complex ions such as AlF2+ and AlF2+ in aqueous solutions, the free fluoride level decreases [33]. Although the effect of this ion on health is questioned in terms of aluminum, it was reported that the consumption of water containing 1000 ppm aluminum does not adversely affect health [34, 35]. Silicon is usually released in oxygenated forms such as silicate, which has been reported to be beneficial for the circulatory system and safer in terms of toxicity [36]. When silicon is present as silicic acid, Si(OH)4 reacts with aluminum to form hydroxyaluminosilicate complexes, which results in the removal of harmful species from aqueous solutions, thus eliminating the biohazard of aluminum [37]. The aluminum contained in the glass filler particles replaces the silicon, forming Si-O-Al bonds, and this structure causes the formation of negative regions [38]. These negative fields cause the glass particles to become more susceptible to acid attack. Sodium is also attracted by these negative fields and sodium can also form Si-O-Na bonds that break the silica network. It has been stated that this return to basic pH may cause some cytotoxic effects on cells. Si and Al levels detected in the present study and they were low amounts.

Although dental ceramics are considered to be structurally very poorly soluble and generally biocompatible materials, there are also opinions to the contrary [14]. Kukiattrakoon et al. [39], evaluated the ion release of four types of porcelain in different solutions in their study. They could not find inert porcelain in acidic pH solutions. In addition, researchers reported more ion release than the ISO 6872 standard. In another study, the effect of bleaching agents on ion release in different aesthetic materials was examined and as a result, it was found that ceramic materials were not inert, but the weight loss was lower than the standards set by ISO 6872 [40]. In the present study, ion release was observed in both the bleached ceramic specimens and the control groups. However, in parallel with the studies in the literature, the least release was observed in ceramic group specimens compared to other restorative materials [14, 39, 40].

The composition, structure and chemical properties of the porcelain that make up the dental ceramics, as well as the environmental factors to which the material is exposed, are the main factors affecting the chemical stability of the material [41]. In a previous study, the ISO 6872 standard was used to evaluate the ion release and it was found that Na+ and K+ ions were more easily released than other ions [39]. In previous studies, it has been reported that divalent Mg+ 2, Ca+ 2, Zn+ 2 and Ba+ 2, trivalent Al+ 3 and immobile Zr ions cause an increase in chemical stability and a decrease in ion exchange [41, 42]. Similarly, in a study by ion and Karaokutan et al. [40], the most released ions were Na+ and K+, followed by Ca+ 2 and Al+ 3 ions. The least released ions are Zn+ 2 and Li+. These ion levels obtained for all restorative materials were found to be well below the daily dose according to the minimum risk level list reported by the Agency for Toxic Substances and Disease Registry. In a study on ion release in dental ceramics, they detected high amounts of sodium ions in the specimens, as opposed to listing no or very low sodium levels in the manufacturer’s declaration [14]. The products contained in the materials are reported in the Material Safety Data Sheets (MSDS). These documents are created in accordance with the current legislation and show that the necessary approval has been obtained for the material to be placed on the market. As a result, if the manufacturer does not always have to declare each component of the material, it is probably not listed in the MSDS. In the present study, Na + ion releases were unexpectedly high in all restorative materials. We think that this may be due to the fact that it is not given in the manufacturer’s information and that these ions can be released easily.

In current study the most released ions were Si, Na, Sn and B and these ions were followed by Hg, K, Ba, Ag, Al, Li, Cu, Ca, Zn, Fe, Zr, Sr and Ti ions. However, the amounts of these ions were below the daily dosage for all the restorative materials according to the minimal risk level list specified by the Agency for Toxic Substances and Disease Registry (The minimum risk level of ions is given as 600–2100 mg/day for Li, and 0.2 mg/kg/day for B, 2400 mg/day for Na, 50-1000 mg/day for Al, 3500 mg/day for K, 1000 mg/day for Ca, 0.02 mg/kg/day for Cu, 0.3 mg/kg/day for Zn, 2 mg/kg/day for Sr, 0.3 mg/kg/day for Sn and 0.2 mg/kg/day for Ba respectively) [40, 43].

The limitations of this study are that only one type and single dose of bleaching agent was examined and that the neutralizing effect of saliva against bleaching agents and the thermal and mechanical effects that the material is exposed to in the oral environment cannot be reflected in the samples due to the in vitro study.

Conclusions

Within the limits of this study, it was found that home bleaching did not significantly affect the structure of the materials used and did not change the ion release in the materials. Although the amount of ions released from all materials was found to be below minimal risk levels, this issue needs to be supported by clinical studies for a clearer understanding.

Acknowledgements

Not applicable.

Author contributions

PG designed the experiment. MNY performed samples preparation. MNY performed the practical experiment. PG carried out measurements, data collection and statistical analysis. PG and MNY wrote the manuscript writing. PG and MNY revised the manuscript.

Funding

This work was funded by the Research Fund of Atatürk University (Project number: TSA-2021-9427).

Data availability

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Abbreviations

ICP MS Inductively Coupled Plasma-Mass Spectrometer

ADA American Dental Association

SCCP Scientific Committee for Consumer Products

HP Hydrogen peroxide

CP Carbamide Peroxide

Hg Mercury

ADI Acceptable Daily Intake

MSDS Material Safety Data Sheets

FDA Food and Drug Association

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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