Surface characterization and optical properties of zirconia-reinforced lithium silicate ceramics against different mouthwashes and thermocycling

Aim: To evaluate color stability (ΔE 00 ), translucency (TP), and surface roughness (Ra) of zirconia-reinforced lithium silicate (ZLS) with lithium disilicate (LS) against different mouth rinses after thermocycling. Methods: A total of 270 specimens were prepared: LS (IPS Emax CAD (group EC)), ZLS-1 (Vita Suprinity (group VS)), and ZLS-2 (Celtra Duo (group CD)). For each specimen, ΔE 00 , TP, and Ra measurements were recorded with a clinical spectrophotometer (CM-3600A) and a 3D non-contact profilometer (AEP Nanomap-1000WLI), respectively, between baseline and after 10000 cycles of thermal cycling. Each group was divided into six subgroups (n=15) according to the immersion solution: five mouthwashes (Meridol, Klorhex, Listerine Cool Mint, Listerine Healthy White Natural Lemon&Salt, and Curasept ADS 212), and distilled water for 72 hours. Statistical analysis was performed by using a three-way robust ANOVA with Tukey HSD test (α=0.05) . Results: Listerine Lemon&Salt and Cool M int caused the highest ΔE 00 and Ra values, while TP values of tested mouthwashes were similar ( p =0.051). Group EC had the highest ΔE 00 and Ra values with the lowest TP values against mouthwashes ( p <0.05). Conclusion: Prolonged use of mouthwashes may cause color change and increased surface roughness in LS more than ZLS. Patients should be advised to use alcohol-containing mouthwashes with caution in daily use.


Introduction
The correct selection of restoration material plays an important role in ensuring clinical success (1).Computeraided design and computer-aided manufacturing (CAD-CAM) systems allow dental clinicians to provide toothcolored and esthetic restorations with various ceramics that have advanced optical and mechanical properties (2)(3)(4)(5).Lithium disilicate-based ceramics (LS) are among the examples of materials of this type and have begun to be used frequently in today's dental clinics (6).
Optical properties of glass-ceramics such as translucency (TP) are critical from an esthetic point of view, and color stability is an important parameter for a long-lasting restoration (17,18).Because color change may affect the quality of the restoration, discoloration has been reported to be one of the main clinical reasons (38%) for prosthesis replacement (19)(20)(21).Surface texture, as well as color and TP, play a role in achieving successful results in prosthetic dentistry (22).It has been reported in the literature that the optical properties of restorative materials are affected by the surface texture, material structure, thickness, background and material color, fabrication technique, adhesive material, and aging (23)(24)(25).The reflection and spread of light from a rough and irregular surface changes the color of the restoration (26).In addition, the rough surface has an impact on plaque accumulation, shade matching, wear on opposing teeth or restoration materials, and the patient's tactile perception.27 Well-finished surfaces were reported to cause fewer technical and esthetic problems by giving the material harder, brighter, and more stable TP and color (3,27).Therefore, to achieve clinical success, it is necessary to have information about the color stability, TP, and surface properties of ZLS ceramics.
Restorative materials are exposed to intrinsic and/or extrinsic factors that may be associated with discoloration during use in the oral environment.While external discoloration occurs as a result of absorption or adsorption of solutions that stain the oral environment, such as beverages (tea, coffee, etc.) and mouthwashes, internal factors are related to the composition of restorative materials (28).Mouthwashes are widely used in various clinical situations to prevent periodontal diseases and improve oral health (29).Although these solutions have some clinical advantages, such as reducing the amount of supragingival plaque and the risk of gingivitis and preventing bad breath thanks to their bactericidal properties, they also have adverse effects, such as discoloration of restorative materials, erosion of teeth and mucosa, and taste disorder (28).Various components such as antimicrobial substances, salts, dyes, organic acids, and sometimes alcohol consisting of hydroxyl groups in the composition of mouthwashes are responsible for these adverse effects, and the duration of use of the mouthwash also affects the clinical results (28,30).Therefore, although this is a criterion that should be taken into consideration when choosing restorative materials or antiseptic solutions in the aesthetic area, it appears that there are not enough studies in the literature evaluating the exposure of ZLS materials to various mouthwashes.Thus, this deficiency was one of the driving forces in the emergence of the current study.
Another feature that affects the clinical performance of restorative materials is aging, and this phenomenon is inevitable (17).Ceramic materials used in the production of restorations wear out during use, and in glass-ceramic materials, this occurs by dissolution during use, as they are predominantly made of silica glass structure with the inclusion of various other cations that disrupt the silica network (17).With this aim, thermal cycling, which simulates environmental variables in the mouth to reflect the clinical use of ZLS materials, was applied in this study for aging purposes with the combined effect of mouthwash solutions.
The objectives of this study were to investigate the color stability, TP, and surface roughness of two ZLS materials exposed to the aging process and different types of mouthwashes and to compare them with LS.The null hypotheses were that (i) ceramic type and mouthwash solution would not affect discoloration, (ii) ceramic type and mouthwash solution would not affect TP, (iii) ceramic type and mouthwash solution would not affect surface roughness.

Materials and Methods
In the present study, one type of LS (IPS Emax CAD (Ivoclar Vivadent, Schaan, Liechtenstein) (group EC), and two types of ZLS were evaluated, including Vita Suprinity (Vita Zahnfabrick, Bad Säckingen, Germany) (group VS), and Celtra Duo (Dentsply, Hanau-Wolfgang, Germany) (group CD).The details and compositions of the ceramic materials and mouthwashes used in the present study are displayed in Table 1.The sample size for the groups (n=72 per group) was determined based on an initial power analysis (PS software; Dupont and Plummer, 1997), which was estimated based on similar previous studies (5% significance level and mean gamma count with 80% power) (11,17).

Specimens Preparation
A total of 270 square-shaped specimens (90 samples of each ceramic) (10 mm×10 mm×1.2 mm) were prepared with a low-speed diamond saw (Isomet 4000, Buehler, Lake Bluff, IL, USA) under a water-cooling system at a speed of 2500 rpm and a feeding rate of 14.4 mm/min, and the thickness was measured using a digital caliper (Digimatic Micrometer; Mitutoyo Corp., Tokyo, Japan).One side of each sample was designated as the test surface, and the remaining surfaces were covered with transparent nail polish (Nail Enamel-301, Glass Effect, Flormar, Milano, Italy).Surfaces were finished and polished using silicon carbide grinding paper (Buehler-Met II Silicon carbide grinding paper P400/600, Buehler, Lake Bluff, IL, USA) from 600 to 1200 grit under running water at 300 rpm (Mecatech 264, Presi, Eybens, France), followed by the application of polishing paste (Renfert Polish LiSi2, Renfert GmbH Company, Hilzingen, Germany).Finishing and polishing were performed in one direction with standard pressure, time, and the same operator, according to the manufacturers' instructions.The samples were then thoroughly cleaned ultrasonically for 15 minutes (Eurosonic Micro, Euronda, Vicenza, Italy) and air-dried for 30 seconds.The surfaces were checked for cracks or irregularities using a magnifying loupe (HR ×2.5, 420 mm/16", Heine, Germany), and a final check for the dimensions of the samples was performed using a digital caliper.

Measurements for Optical Properties
Optical measurements of all samples were made at the baseline, after the aging process and after being exposed to mouthwash.
These measurements were performed in "tooth single" mode using a clinical spectrophotometer (CM-3600A; Konica Minolta Inc, Tokyo, Japan) according to CIEDE2000 color coordinates.The interval wavelength at which the measurements were taken was between 360 and 740 nm in an 8 mm diameter illumination area.Before the measurements, the spectrophotometer was calibrated at the intervals specified by the manufacturer.Measurements were performed on the polished surfaces of the specimens using D65 standard illumination under an observer angle of 10° and a light source angle of 45° (22).The same time of day was preferred for measurements, and each sample was measured three times on two different backgrounds.Color difference values obtained under experimental conditions were calculated with the following formula of CIEDE2000(ΔE00) (31): The parametric factors of the CIEDE2000 color difference formula were considered as 1.The perceptibility threshold was accepted as ΔE00 ≤ 0.81, and the acceptability threshold was accepted as ΔE00 > 1.77 (32).

Surface Roughness Measurements and Surface Observation
The surface roughness (Ra) values of the study surfaces were measured by the 3D non-contact profilometer (AEP Nanomap-1000WLI; AEP Technology, Santa Clara, CA, USA) with an optical resolution of 550 nm.The Ra value, which is the arithmetic mean value of the absolute values of the roughness profile of the folds (surface heights) followed from top to bottom, was measured for this aim (33).
Values of the Ra were calculated for each group and subgroup at the baseline, before and after thermocycling and mouthwash simulation.The average of Ra values was computed with SPIP software (Image Metrology A/S, Lyngby, Denmark) using three single individual measurements, according to ISO 4287.
Further evaluation of the structural surface topography of each group was performed under a scanning electron microscope (SEM) (Carl Zeiss EVO LS 10; Carl Zeiss NTS, Oberkochen, Germany) at 250x magnification after sputter coating with gold.

Aging process
Samples underwent an aging process with a 30 s dwell and 6 s transition time before mouthwash simulation by using a thermocycling machine under the condition of 5-55°C with a heating and cooling system by a programmable logic (Automated Thermocycling Machine; Gökçeler Machines, Sivas, Türkiye).Each specimen was tested for 10,000 cycles to simulate approximately one year of in vivo use (34).

Mouthwash simulation
Specimens of each ceramic group were divided into five mouthwash groups (MERIDOL, Klorhex, LISTERINE Cool Mint, LISTERINE Healthy White Natural Lemon&Salt, Curasept ADS 212) and distilled water for the control (n=15).
Mouthwash solutions were kept in vials with a cover to prevent evaporation at 37°C for the test period of 72 hours, which is equivalent to six years of mouthwash use when the solution is used twice a day for one minute each time (35).
All the specimens were immersed in 20 ml mouthwash or distilled water for 2 minutes, and test solutions were changed twice daily.

Statistical analysis
Statistical analysis was carried out using the WRS2 package with R Program (R Core Team; R Foundation for Statistical Computing, Vienna, Austria).
Conformity with normal distribution was examined with skewness -kurtosis (±2) values.A three-way robust ANOVA (analysis of variance) test was used to compare TP values that did not comply with normal distribution according to solution, material, and time, and multiple comparisons were performed with Bonferroni Correction.
Three-way ANOVA was used to compare L, a, b, and ΔE values, and the Tukey HSD test was applied for multiple comparisons.Analysis results were presented as median (minimum-maximum).The significance level was considered as p<0.05.

ΔE 00
For color difference ΔE00, a statistically significant interaction was observed among the group, solution, and time (p<0.001)(Table 2).
All groups subjected to the aging process showed greater discoloration than after immersing mouthwash solutions in all groups (p<0.05).A significant difference between the ΔE00 values of the groups was detected, regardless of the solution and time effect (p<0.001).Average ΔE00 values varied depending on the solutions (p=0.020), and the lowest value was obtained in distilled water (0.54±0.32) (Table 3).

TP
For TP, the solution's main effect was not found to be statistically significant on TP median values (p=0.051), while a significant interaction was detected among the group and time (p<0.05)(Table 4).The highest TP value was found in the group VS (20.1(12.42-23.51))and the lowest TP value belonged to group EC (15.66 (12.25-21.45))(Table 5).
Solution and material interaction was found to be statistically significant on TP average values (p=0.001).The highest average value was found in group VS with Meridol mouthwash material (20.97 (16.43-23.51))(Table 5).
Material and time interaction was found to be statistically significant on TP mean values (p=0.002).The highest average TP value was obtained after mouthwashing in the group VS (20.64 (12.82-23.51)),and the lowest value occurred in the group EC (15.48 (12.25-19.1))after the aging process (Table 5).Median (minimum -maximum); a-c: There is no difference between main effects with the same letter; AH: There is no difference between interactions with the same letter.TC: Thermal cycling; MW: Mouthwashing

Ra
For Ra, a statistically significant interaction was found among the group, solution, and time (p=0.022),while the effect of the material on Ra values was not found to be significant (p=0.051)(Table 6).The highest Ra median value was obtained after group EC was immersed in Lemon/Salt mouthwash (0.27) and after immersing in Cool Mint mouthwash (0.27) (Table 7).

Profile evaluation and surface observation
Optical profilometry images of the groups based on the solution were described in Figures 1, 2, and 3.After mouthwashing with distilled water, all groups' surfaces appeared relatively smooth and uniform.Regarding 2D and 3D observations and profile evaluation of the surfaces after mouthwashing, Lemon/Salt and Meridol displayed the most irregular surface among all solutions for groups CD (Fig. 1) and EC (Fig. 2).It was also observed that the solution that caused the formation of the most irregular surfaces for group VS was Lemon/Salt (Fig. 3).Median(minimum-maximum); a-c: There is no difference between main effects with the same letter; A-I: There is no difference between interactions with the same letter.MW: Mouthwashing

Discussion
The present study evaluated the performance of two different ZLS materials based on ΔE00, TP, and Ra by comparing them with LS.The overall results of this study showed mouthwash solution and ceramic type were effective on ΔE00 and Ra values, while TP values were affected only by the material type.Thus, while the first and second null hypotheses of this study were rejected, the third null hypothesis was partially rejected.
Color stability during the clinical survival period of the prosthetic restoration is as important as the mechanical strength of the dental material, and changes in the color affect the lifespan and quality of the restoration (36).There are studies in the literature evaluating the effect of various coloring solutions (artificial saliva, orange juice, cola, coffee, and red wine) on the color of dental materials, but studies investigating the discoloring effect of mouthwashes on prosthetic dental materials are less common (37)(38)(39)(40)(41).In these studies, it is observed that they generally examine the effects of mouthwashes on composites, compomers, acrylic resins, resin-modified glass ionomers, and hybrid composites, and it is understood that there are not enough studies on LS ceramics (40).For this reason, in the present study, the effect of new-generation mouthwashes on both discoloration and optical and surface properties of LS and ZLS CAD/CAM restorative materials was comprehensively investigated.
Mouthwashes are frequently used to eliminate the pathogenic microorganisms that cause tooth decay, periodontal diseases, and bad breath, and their duration of use varies depending on the patient and indication (42).The duration of use of mouthwashes is increased in patients undergoing chemotherapy and radiotherapy, in the presence of osteoradionecrosis and osteonecrosis, in the treatment of osteomyelitis, and in cases where patients with mental or physical disabilities can't maintain oral hygiene (43).Considering the use of mouthwashes in daily life, it has been reported that a one-year application of mouthwash for one minute twice a day is equivalent to a 12-hour test evaluation period (44).In this study, to evaluate the long-term effect of mouthwashes, the samples were kept in the mouthwashes for 72 hours, in other words, equivalent to 6 years of restoration clinical use.
Besides mouthwashes, the clinical performance of dental restorations is affected by aging, and thermal aging of dental restorations is a natural phenomenon (17).The artificial aging method with thermal cycling, which reflects the temperature changes in the oral environment, is one of the most common methods used in experimental studies, and all samples in our study were first subjected to thermal cycling and then mouthwashing to imitate the oral environment (45).It has been reported in the literature that the thermal cycle applied for 10000 cycles between 5-55 ℃ temperatures corresponds to 1 year of restoration in clinical use, and this period was taken as the basis in the current study (46).
In all the ceramic groups, immersion in LISTERINE Cool Mint and Lemon&Salt led to the highest discoloration, and distilled water provided the lowest ΔE00 values for all groups (Table 3).In the present study, while there was no difference between the ΔE00 values in the groups CD and EC after immersing mouthwashes, the lowest value was measured in the group VS and all values were below the visual perceptibility threshold value (ΔE00≤0.81).The ΔE00 findings of the present study about Listerine Cool Mint (0.75 ± 0.37) and Lemon&Salt (0.75 ± 0.32) mouthwashes agreed with the findings of other previous studies that evaluated all ceramics and reported greater discoloration than after being immersed in Klorhex (22).In other studies where resin nano ceramics, polymer-infiltrated ceramic networks, feldspathic ceramics, LS, and zirconia were evaluated, it was observed that results parallel to the present study were obtained and the most discoloration was in the Listerine mouthwashes than chlorhexidine solutions (22,47).This difference could be attributed to the alcohol content of Listerine mouthwashes (21.6% ethanol, LISTERINE Cool Mint; 14.58% ethanol, LISTERINE Lemon&Salt) as some studies have reported that mouthwashes with high alcohol content increase color changes on bioceramic material due to alcohol having a higher absorption and solubility effect on the material by causing chemical changes such as volumetric change, hydrolysis, and oxidation (22,40,48).It is also stated in the literature that mouthwashes not only have high alcohol content and low pH values but also contain preservative and coloring components, which cause color changes in the restorative materials.Thus, the discoloration or esthetical properties of CAD/CAM all ceramic materials may be evaluated in future studies based on different pH values.
Another reason why Listerine Lemon&Salt causes more discoloration than other mouthwashes may be the sodium fluoride (NaF) content (0.02%) that is not found in other mouthwashes.NaF is added to the mouthwash formula as an anti-caries ingredient, and it was stated that the fluoride content caused changes in the surface roughness and color of different dental ceramics (49)(50)(51).Although this NaF content supports the discoloring effect of Listerine Lemon&Salt than other evaluated mouthwashes in the present study, no difference was found in the color change effect of Listerine Cool Mint and Lemon&Salt, warranting future studies.
There are not enough studies to allow comparing the results of the current study with Meridol, which was included in this study and contains amine fluoride and stannous fluoride as active ingredients (Table 1).In the present study, it was measured that Meridol produced a lower total ΔE00 value (0.73 ± 0.29) than Listerine group mouthwashes (Cool Mint, 0.75 ± 0.37; Lemon&Salt, 0.75 ± 0.32) and higher ΔE00 values than Klorhex (0.71 ± 0.34) and Curasept (0.65 ± 0.36) mouthwashes for all study groups.In a study with a similar setup to the current study evaluating composite materials, it was found that the color change caused by the Meridol group was significantly less than other solutions (Listerine Total Care Zero and Andorex), and the color change caused by mouthwash groups other than the Meridol was not statistically different from the control group (52).In this study, excluding the control group, the Curosept group was determined to have the lowest total ΔE00 value (0.65 ± 0.36) compared to the solutions.A statistically significant difference was detected between the total ΔE00 values of the ceramic groups, and the highest discoloration was measured in the group EC (0.85 ± 0.35) (p<0.001).This result may be thought to be due to the difference in the content of LS ceramics from ZLS (3).Another point worth noting is that thermal cycling (0.92 ± 0.26) caused more color change than exposure to mouthwash (0.53 ± 0.28) in all groups, regardless of the material.This can be attributed to the knowledge that small-sized particles Show changes in distribution due to the decrease in particles after aging, which may be related to changes on the surface (53).Therefore, it is recommended that clinicians pay attention to periodic follow-ups to clinically reduce the discoloration problems of restorations produced from LS and ZLS materials.
The TP value of the material affects the aesthetics of dental ceramics as much as the color (53).It has been shown in the literature that the TP value of human teeth varies approximately between 15 and 19 at 1 mm thickness, and the TP values of restorative materials can reach up to 25 (54).The initial average TP values of the samples prepared with 1.2 mm thickness in this study were measured as 17.79 (14.86-19.65)for Celtra Duo, 15.86 (12.35-19.14)for Emax CAD and 19.96 (13.84-23.2) for Vita Suprinity, respectively (Table 5).When the TP values obtained from all materials included in the study were compared, no statistically significant difference was seen at the beginning and after the thermal cycle, while the values after immersion in mouthwash were found to have a higher TP distribution.This may be attributed to the effects of the mouthwash ingredients, pH levels, or alcohol content on the material, and is consistent with the results of studies from Soygun et al. and Lee et al. (40,47).
In the current study, while the main effect of the mouthwash solution on TP values was not found to be statistically significant, the material effect was found to be significant (p<0.001).TP median values obtained from all materials differ from each other, and the lowest value was measured in the group EC after mouthwashing (15.66(12.25-21.45))(Table 5).This situation is compatible with the data obtained from various studies that ZLS material shows higher TP than resin nanoceramics, polymer-infiltrated ceramics, feldspathic ceramics, and LS ceramics (5,55,56).TP values of dental ceramics are affected by factors such as the crystal structure, dimensions, structural differences, pigments, size and distribution of defect areas contained in the material, and the crystal size of ZLS has been reported to be 4 to 8 times smaller than the crystals contained in LS (3,(57)(58)(59).Although TP depends on the properties of the material, surface roughness, and thickness also affect this parameter (3).In Kanchanavasita et al.'s study, it was reported that reducing the thickness of the material increased the TP value (60).Therefore, in this study, the thickness of the samples was determined as 1.2 mm to be similar to the prosthetic restoration thicknesses applied in the clinic.The processes applied to the surface of the ceramic material as well as the material thickness affect its TP (54).To prevent this effect from affecting the study results and to ensure standardization, mechanical polishing was applied to the surfaces of the samples.As there are studies in the literature reporting that LS and ZLS restorations with polished surfaces exhibit sufficient tribological properties in terms of plaque retention and wear when compared to those with glazed surfaces value (61,62).
Another parameter affecting TP is thermal cycling, and it has been determined that this process reduces TP values (17).This interaction is explained by the fact that the thermal cycle changes the optical properties of the material, increases the crystal size of the material, and changes the orientation of the crystals and the glass matrix (17,58,(63)(64)(65).In this study, although higher TP values were obtained in the ZLS groups (group CD, 17.68 (14.82-19.87); group VS, 19.58 (12.42-23.14))than in group EC (15.48 (12.25-19.1)as a result of aging with thermal cycling, no statistically significant difference was found in TP values before and after thermal cycling for all groups (Table 5).The current study gives similar results to previous studies in the literature focusing on the TP values of LS and ZLS samples, but it differs partially from the study of Porojan et al. (11,17,38,53,66).In the mentioned study, it was reported that LS samples had higher TP than ZLS samples, but the difference was not statistically significant (17).This difference can be due to the type and preparation of the materials used in the relevant study; only CAD/CAM materials were evaluated in the current study.In this study, it was also observed that the group VS had higher TP values than the group CD.It is thought that the difference between these groups with similar microstructure is due to the difference in crystal size.While group VS contains lithium metasilicate crystals of approximately 0.5 µm in size, group CD contains crystals of 1.0 µm in size (10).
The surface texture of dental materials affects their optical properties and TP (67,68).For the Ra value used to measure surface roughness, 0.20 µm has been determined as the critical threshold value for bacterial retention, and it has been reported that discoloration is observed in restorations with average Ra values more than 0.20 µm and has a negative effect on plaque accumulation on teeth TP (69).In the current study, the highest Ra values were obtained from the Listerine Lemon&Salt (0.25 (0.2-0.3)) and Meridol (0.25 (0.2-0.3)) mouthwash groups, while results similar to these values were observed in the Listerine Cool Mint (0.24 (0.2-0.3)) mouthwash (Table 7).The group with the lowest Ra values was the control group, and it showed similar results to the study in which feldspathic ceramic, polymer-infiltrated ceramic, and lithium disilicate glassceramic samples were examined and it was found that Listerine lemon/salt mouthwash increased the roughness (47).This can be attributed to the chemical composition of the mouthwash, as it has been reported that mouthwashes containing essential oils and alcohol cause higher surface roughness (70).Although the results of the present study are compatible with the data of a limited number of studies in the literature, they are not sufficient for clinical decision-making, needing future studies to confirm the data.
The surface properties of dental ceramics depend on the pH value of the solutions to which the material is exposed, and it has been determined that low pH values are effective in surface roughness (39).The mouthwashes and pH values used in the study are as follows: Meridol (pH: 3.88), Listerine Cool Mint (pH: 3.93), Klorhex (pH: 5.1-5.8),Listerine Lemon&Salt (pH: 6.56), and Curasept (pH: 5.7) (47).When these pH values are examined, the data of Cool Mint and Meridol mouthwashes are compatible with the Ra values obtained, while the fact that Lemon&Salt causes high Ra even though it has a higher pH value than these two mouthwashes.This difference is considered an interesting result of the present study and reveals the need for further studies.
According to the results of the current study, the type of ceramic material was effective on surface roughness, and LS (group EC: 0.25 (0.2-0.3)) samples had higher Ra values compared to ZLS samples (group CD: 0.22 (0.2-0.3), group VS: 0.22 (0.2-0.3)) after immersing mouthwash solutions (Table 7).The results of this study were consistent with a recent study that evaluated full and semi-stabilized zirconia, LS, ZLS, and hybrid ceramic materials and reported that the surface roughness in LS and hybrid ceramic samples was higher than in other material groups (71).One of the reasons for explaining the difference between these materials may be the difference in the 'crystal and glass phase ratio' in the structure of the materials.Another point worth noting is that these ceramics, which contain crystalline and glass phases, have a difference in the dissolution rates between phases, and the lithium metasilicate (Li2SiO3) in the LS content dissolves more slowly than the glass matrix content.This causes roughness on the material surface due to clinical use (72).
One of the limitations of this study was the lack of reproduction of the oral environment, as results may vary due to individual variations.Additional limitations of the present study that need to be investigated in the next studies are not including samples of different thicknesses, exposing the samples only to mouthwash and removing the effect of saliva, not taking cement color and thickness into account in measurements, not preparing the samples in crown shape, and applying only one type of aging process to samples (thermal cycling).Therefore, future studies are needed to confirm the findings of this study and should also investigate the longterm effect of the use of mouthwash solutions, which may contribute to a clear decision for the study.

Conclusion
Based on the findings of the present study, the following conclusions were drawn: 1.There was a significant difference between the average ΔE00 values according to the ceramic type, and the highest discoloration was observed in the group EC. 2. Average ΔE00 values varied depending on the applied mouthwash solutions, and the discoloration order was; Listerine Cool Mint = Listerine Lemon & Salt > Meridol> Klorhex> Curasept > Distilled water.All discoloration values were clinically acceptable.3.In all groups included in the study, regardless of the material, thermal cycling caused more discoloration than exposure to mouthwash.4. While the main effect of the mouthwash solution on TP values was not found to be statistically significant, the material effect was found to be significant.The lowest TP was measured in the group EC.
Readings were carried out by an expert operator and average values were calculated by the same operator.The CIELAB values were recorded on both white (W) (L* = 94.6, a* = 0.2, b* = −0.8)and black (B) (L* = 2.3, a* = 0.5, b* = 2.1) backgrounds.Further color measurements were performed on a neutral gray background, and the TP was determined as the color difference (ΔE00) between measurements against W and B backgrounds.

Figure 1 . 8 Figure 2 .
Figure 1.Optical profilometry images showing the 2D (a), 3D surface topography (b) and the profile roughness (c) for the line of Celtra Duo samples after immersing in selected mouthwashes.

Figure 3 .
Figure 3. Optical profilometry images showing the 2D (a), 3D surface topography (b) and the profile roughness (c) for the line of Vita Suprinity samples after immersing in selected mouthwashes.

Table 1 .
List of materials used in the study*

Table 3 .
Descriptive statistics of ΔE00 values and multiple comparison results

Table 4 .
Comparison of translucency parameters according to mouthwash, material and time Q: Three-Way Robust Anova test statistics

Table 5 .
Descriptive statistics and multiple comparison results of translucency values by solution, material and time.

Table 6 .
Comparison of Ra (surface roughness) values according to material, solution and time Q: Three-Way Robust Anova test statistics