Evaluation of the Effect of Saudi Coffee Consumption in Comparison to Various Types of Coffees on the Color of Novel Aesthetic Dental Ceramics

Abstract

The aim of this study was to evaluate the effect of Saudi coffee consumption in comparison to various types of commonly used coffees (instant black, Turkish, and espresso) on the color of novel aesthetic dental ceramics. A total of 144 flat cylindrical discs with an 8-mm diameter and 0.5-mm thickness were created using CAD/CAM technology. Three ceramic materials were used: Lithium disilicate (Emax) and two ultra-translucent monolithic zirconia ceramics; Aidite and Cercon Xt (Cer). The specimens were immersed in six coffee solutions: Saudi coffee from eastern region (ES), Saudi coffee from northern region (SN), Saudi coffee from middle region (SM), instant black coffee (Ne), Turkish coffee (Tk) and espresso coffee (Es). All specimens (n = 8) were immersed for a period of 15 days. The color of all specimens was measured before and after immersion, and the CIE L*a* b* coordinates were obtained with a spectrophotometer. Values for the translucency parameter (TP), contrast ratio (CR) and color change (ΔE) for each specimen were calculated. Data were analyzed using paired sample t-test and one-way ANOVA and post hoc testing. Color coordinates L*, a* and b* significantly changed after immersion in all coffee solutions relative to pre-immersion values, with a noticeable decrease in lightness (L*) (P < .05). A significant color change (∆E) was observed in all tested materials in all coffee solutions after immersion, with ∆E values exceeding 5.26 (P < 0.05). Color changes (∆E) for specimens immersed in the three formulations of Saudi coffee were significantly less than those immersed in the other coffee solutions (P < 0.05). Saudi coffee with formulations from the northern region resulted in more color changes in Emax in comparisons to the other two Saudi coffee formulations from the middle and eastern regions. Aidite and Cer ceramics showed less TP values than Emax. Consumption of coffee for a period of simulated 1 year has significantly altered the color of ceramic materials to a level above the threshold at which the clinical perception of color change occurred (> 3.3). Saudi coffee consumption caused less changes in the color of tested ceramics in comparison to the consumption of commonly used coffees (instant black, turkish, and espresso).

Introduction

Coffee is considered one of the most widely consumed beverages in the world with more than 400 billion cups consumed each year according to data from earlier years (World population review 2025). Coffee has always been a major part of Arab culture in general, and a traditional symbol of hospitality in Saudi culture. The Saudi coffee, known as Alqahwa, is typically made using green coffee beans that have been lightly roasted. In fact, Khawlani coffee beans, specific for Jazan region in the southwestern of Saudi Arabia, holds a huge place in the country’s farming and cultural tradition with contributing to 85% of coffee production in Saudi Arabia (Hassen et al. 2023). The taste of Saudi coffee varies among the different regions of the country due to the differences in the added spices. Often, it contains cardamom and may include other spices such as clove, ginger and saffron. These spices are added in small quantities for distinct aroma and taste.

Coffee consumption has been growing massively in the past few years. Although drinking coffee has become an integral part of people’s life, its effect on the color of teeth should not be overlooked. Tooth discoloration has been associated with regular coffee drinking (Kim et al. 2024). In an earlier in-vitro study, it was found that 90% of the natural teeth immersed in different types of coffees demonstrated tooth staining. However, the degree of tooth discoloration was type dependent (Kim et al. 2024). Turkish coffee showed the highest teeth stainability, while Arabic coffee, which is quite close to the ingredients of Saudi coffee, showed mild stainability (Al-Qarni et al. 2021). Another study demonstrated that teeth immersed in black coffee resulted in significant reduction in color lightness compared to teeth immersed in Arabic coffee and therefore, suggesting that Arabic coffee could be an alternative to black coffee after teeth bleaching (Borzangy et al. 2018).

The influence of drinking coffee on existing direct tooth-colored restorations have also been investigated earlier (Al-Qarni et al. 2021; Al-Shalawi et al. 2017; Paolone et al. 2022). Color stability of resin-based composite materials have been affected after exposure to commonly used types of coffee (Al-Qarni et al. 2021). The effect of these drinks was related to the type, concentration, and period of exposure. It has been documented that espresso coffee resulted in noticeable color change in tested resin-based materials followed by Turkish then American coffee. While Saudi coffee, on the other hand, displayed minimum changes in the color of the same materials tested (Paolone et al. 2022).

While previous research revealed less color deterioration in teeth and resin-based composite restorations in response to Saudi coffee consumption (Al-Qarni et al. 2021; Al-Shalawi et al. 2017), tooth staining remains one of the biggest concerns among people who care about their facial beauty and seek beautiful smiles. Patients’ concern about aesthetics has grown rapidly in the past years, therefore, demanding more natural looking dental restorations that cannot be distinguished from adjacent teeth but the same time, having the ability to withstand the extreme oral conditions. Such cosmetic need has necessitated the dental material manufacturers to develop new restorative materials with optimum cosmetic features that meets patients’ needs and satisfies their urge for natural beauty. The employment of computer-aided design/computer-assisted manufacturing (CAD-CAM) technologies have expanded the range of restorative materials available, including ceramic restorations, and material manufacturers are broadening their range of offerings to achieve optimal levels of accuracy and aesthetics while minimizing armchair operating times (Aziz et al. 2020; Marchesi et al. 2021). Ceramic materials in dentistry are massively being advocated as physically strong, tooth-colored materials for prosthetic dental restorations.

Lithium disilicate glass ceramic has gained immense popularity and is now preferred over other glass-matrix ceramics for veneer restorations due to its high translucency and superior optical properties (Chen et al. 2021). The improved development in physical and mechanical characteristics and advanced biocompatibility, together with excellent aesthetic features, has led the use of zirconia ceramic prosthesis not only in the posterior region, but also in the anterior posterior region (Zhang and Lawn 2018). Those CAD/CAM milled ceramics are known for their superior resistance to discoloration and ability to maintain color stability during clinical use, resulting in a seamless color match (Adawi et al. 2021). Despite their stain-resistant properties, restorative and prosthetic materials in the oral cavity can still be affected by external factors such as temperature and humidity changes, as well as exposure to food, beverages, and smoking, which could lead to extrinsic discoloration of these materials (Paravina et al. 2015).

Alongside the introduction of recent ultra-translucent monolithic zirconia ceramic materials, substantial research has taken place (Alnassar 2022) to investigate the effect of various oral conditions on the aesthetic aspect of these materials. Visually perceived color change thresholds can be implemented as a quality control method to provide guidelines for choosing cosmetic dental materials (Colombo et al. 2017). Additionally, although newly produced innovative ultra-translucent zirconia ceramics have displayed aesthetically attractive features and the capability to resemble the of natural teeth color, the stability of their color after exposure to intraoral stimuli such as coffee drinking remains a concern.

Therefore, the aim of this in-vitro cross sectional study was to evaluate the effect of Saudi coffee consumption in comparison to various types of commonly used coffees (Turkish, instant black and espresso) on the color of novel ultra-translucent monolithic zirconia materials recently launched into the market in comparison to the commonly used lithium-disilicate ceramic veneers.

The null hypotheses were:

1. There is no color change in the ceramic materials immersed in different coffee solutions.

2. There is no difference in color change with consumption of Saudi coffee in comparison to commonly used coffees (instant black, turkish and espresso)

Matereials and methods

Fabrication of test specimens

A total number of 144 specimens were fabricated in the shape of flat cylindrical disks measuring 8 mm in diameter and 0.5 mm thickness (Fig. 1). The samples were constructed following manufacturer instructions using computer aided design/computer aided manufacturing CAD/CAM technology. Three ceramic materials were used (48 specimen from each material): Lithium disilicate (Emax) and two ultra-translucent monolithic zirconia ceramics; Aidite (Aid) and Cercon Xt (Cer) (Table 1). Shade A1 was used to construct the specimens which were then exposed to one glazing cycle at a temperature instructed by the manufacturer using glaze paste (FLUO; IPS Ivoclar Glaze Paste). Specimens were then maintained in separate containers until testing. Each material group (n = 48) has undergone color measurement using spectrophotometer at baseline before immersion (Pre) in coffee solutions and then measured again after immersion (Post).

Fig. 1.

Ceramic specimen in the form of cylindrical disk

Table 1.

Materials used in the study

Material	Material Type	Trade Name	Manufacturer	Chemical Composition
Emax	Lithium disilicate block	IPS E.max CAD,	Ivoclar Vivadent, Schaan, Liechtenstein	Li2Si2O5 70%, ZrO2 4%
Aidite	Ultra-translucent multilayer monolithic zirconia block	Aidite 3D Pro Zir	Aidite, Bracon Digital Dental Products, UK	ZrO2 90%−95%, Y2O3 4%−10%, Al2O3 < 0.5%, other oxides < 0.5%
Cercon Xt	Ultra-translucent multilayer monolithic zirconia block	Cercon Xt Extra-translucent	Cercon Xt, Dentsply DeguDent, Hanau-Wolfgang, Germany	ZrO2,Y2O3 9%; HfO2 < 3%; Al2O3, SiO2 < 1%

Immersion in coffee solutions:

Specimens from each material group was stored in their designated container filled with distilled water and maintained in an incubator at 37° for 24 h before starting the immersion cycle. Each material was divided into six subgroups according to coffee immersion solution (n = 8):

1. Saudi coffee with formulation from eastern province (SE): 800 ml of water, 40 g of ground coffee medium roast (Khawlani Saudi Coffee Beans, Baja, Saudi Arabia), 30 g of cardamom ground, and little amount of saffron

2. Saudi coffee with formulation from northern province (SN): 800 ml of water, 40 g of ground coffee dark roast (Khawlani Saudi Coffee Beans, Baja, Saudi Arabia), 30 g of cardamom ground

3. Saudi coffee with formulation from central/middle province (SM): 800 ml of water, 40 g of ground coffee medium roast (Khawlani Saudi Coffee Beans, Baja, Saudi Arabia), 30 g cardamom ground, little amount of saffron, and 0.5 g of clove

4. Instant black coffee (Nescafe) (Ne): 180 ml of water and 1 teaspoon (2 g) of coffee powder (Nescafe Classic, Nestle, Brazil)

5. Turkish coffee (Tk): 200 ml of water and 2 teaspoons (4 g) of coffee powder (Baja Plain Turkish Coffee, Saudi Arabia)

6. Espresso coffee (Es): 40 ml of water mixed with 12 g of coffee powder (Lavazza Espresso Italiano Classico, Torino, Italy)

The water was boiled at 100 °C, then kept boiling for 15 s. Ground coffee powder was added to the boiled water following the above ingredients and was stirred, then was kept on low heat for 2 min without stirring. All coffee solutions were prepared in the same day of immersion and the solution pH was measured immediately after preparation using pH meter (Guang Ying ZD) (Table 2).

Table 2.

pH measurement after preparation of each coffee solution

Coffee solution	pH
SE	4.82
SN	4.78
SM	4.81
Ne	4.33
Tk	4.47
Es	4.33

Each specimen was submerged in 2 ml of coffee solution within a 3 × 3 cm plastic container (Fig. 2) for fifteen days (Aldosari et al. 2021; Alzahrani et al.2022) as the total immersion period to simulate a one year of coffee consumption. Specimens were taken after 24 h from their containers, rinsed with running water and placed again in freshly made coffee solution. The coffee was made fresh and replenished every day. Specimens were maintained at 37 °C in an incubator.

Fig. 2.

Ceramic specimen immersed in 2 ml of coffee solution within plastic container

Color evaluation

Color assessment was performed before and after coffee immersion. For assessment of color, the the CIE L*a* b* color coordinates values for each specimen was measured using a spectrophotometer (LabScan XE^®, HunterLab, Sunset Hills Road, Reston, Virginia, USA) against a black and a white background at three different angles. For each specimen, the readings were taken three times. The following equations were used to compute the color chage delta E value (ΔE), translucency parameter (TP) and contrast ratio (CR).

$$\mathrm{\Delta }E=\left[\left(L_1^{\ast },-,L_2^{\ast }\right)_{}^2,+,\left(a_1^{\ast },-,a_2^{\ast }\right)_{}^2,+,\left(b_1^{\ast },-,b_2^{\ast }\right)_{}^2\right]_{}^{1/2}$$

where the subscripts 1 and 2 indicate the readings before and after immersion respectively, L* indicates lightness, a* indicates the green (a) and red (+ a) axes, and b* indicates the blue (b) and yellow (+ b) axes.

$$TP=\left[\left(L_b^{\ast },-,L_w^{\ast }\right)_{}^2,+,\left(a_b^{\ast },-,a_w^{\ast }\right)_{}^2,+,\left(b_b^{\ast },-,b_w^{\ast }\right)_{}^2\right]_{}^{1/2}$$

where the subscripts b and w indicate the black and white backgrounds, respectively.

$$\begin{array}{cc}CR=\frac{Y_B}{Y_w}& \text{while}Y={\left(\frac{L+16}{116}\right)}^3\text{x}{\text{Y}}_{\text{n}}\end{array}$$

where Yn is equal to 100, and the subscripts B and W represent the black and white backgrounds, respectively.

CR values are ranged from 0 to 1, where 0 represents a transparent material and 1 indicates an opaque one. The ΔE, TP, and CR were measured for each sample before and after immersion in the coffee solutions.

Statistical analysis

Data were analyzed using IBM SPSS Statistical software for Windows version 26.0 (IBM Corp., Armonk, N.Y., USA). Levene’s test of homogeneity was applied, and data were found to be normally distributed. Descriptive statistics (mean, standard deviation, minimum & maximum) were used to describe the outcome variables (L*, a*, b*, ΔE, TP and CR). The Student’s paired t-test for single sample was used to compare the difference of the mean L*, a*, b*, TP and CR values between pre and post immersion within each coffee solution and each material. The one-way analysis of variance followed by post-hoc test (Tukey’s test) was used to compare the mean values of ΔE, TP and CR among the 6 groups of coffee solutions within each material. One-way ANOVA followed by Tukey’s post hoc test was also applied to compare the mean values of ΔE, TP and CR among the three ceramic materials within each solution. A p-value of < 0.05 was used to report the statistical significance of results.

Results

Descriptive data for the mean and standard deviation of color coordinates L*, a* and b* obtained from the spectrophotometer reading for the three tested materials pre- and post- immersion in the six coffee solutions are displayed in Table 3. Paired sample t-test have demonstrated significant decrease in L* values for the three tested materials after immersion in all coffee solutions (P < 0.05) indicating decrease in material lightness. The biggest drop in the L* value was recorded in the Aidite after immersion in Ne solution (P < 0.05).

Table 3.

Mean and standard deviation (SD) values of the L*, a* and b* color coordinates obtained from the spectrophotometer for the three test materials before (Pre) and after (Post) immersion in the six coffee solutions

* P value was significant at P < 0.05 for comparisons between pre and post immersion readings within each coffee solution

It was evident from Table 3 that the Emax and Cer ceramics demonstrated significant changes (P < 0.05) in the a* color coordinate leaning toward the red zone of the red-green axis after immersion in Ne, Tk and Es coffee solutions. Emax disks immersed Saudi coffee solutions, on the other hand, have demonstrated a significant change in a* parameter, however, the shift was toward the green zone (P < 0.05). Cer, on the other hand, have demonstrated a significant (P < 0.05) shift toward the red zone of the red-green axis after immersion in the three types of Saudi coffee solutions (SE, SN, and SM). In contrary, immersion of Aidite ceramics in Ne, Tk and Es coffee solutions have shifted their color towards the red zone of the red-green axis. This was statistically significant in the Ne solution (P < 0.05).

Table 3 showed significant increase in b* color coordinate in Emax disks immersed in SE and SM shifting their color toward the yellow zone of the yellow-blue axis (P < 0.05). Similarily, immersion of Emax disks in Ne and Es solutions have increased the b* value making these disks yellower. This shift towards the yellow zone was statistically significant in the Ne solution (P < 0.05). It was noticeable from Table 1 that Aidite ceramics have shifted toward blue zone on the yellow-blue axis with significant decrease in b* value after immersion in Ne, Tk, and Es coffee solutions (P < 0.05), while Aidite disks immersed in SM Saudi coffee has shifted towards the yellow zone (P < 0.05). On the other hand, Cer ceramics have become yellower after immersion in all coffee solutions. This was statistically significant in SE, Ne and Es solutions (P < 0.05). Interestingly, ceramic disks from the three materials that were immersed in SN Saudi coffee did not have noticeable change in the b* parameter (P > 0.05).

Figure 3 demonstrated a significant change in color (∆E) observed in all tested materials after immersion in all coffee solutions, with ∆E values exceeding 5.26 (P < 0.05). These changes in color were above the threshold at which the clinical perception of color change occurred (> 3.3), and therefore were observed clinically with the naked eye (Fig. 4). The ∆E value was the highest in Aidite zirconia after immersion in Ne solution (14.72), and the smallest color change was seen in the Emax after immersion in SE coffee solution (5.26) (Fig. 3). It was evident from Fig. 3 that all ceramic disks immersed in Saudi coffee solutions (SE, SN, and SM) demonstrated less ∆E values in comparison to the other tested coffee solutions (Ne, Tk, and Es) (P < 0.05). SN Saudi coffee demonstrated higher ∆E values in comparison to the other two formulations of Saudi coffee (SE and SM) which was statistically significant within the Emax disks (P < 0.05).

Fig. 3.

Color differences (∆E) between pre and post immersion of the three ceramic materials in the six coffee solutions. * Significance at (p < 0.5) for Saudi coffees relative to other coffee solutions (Ne, Tk, Es), § Significance at (p < 0.05) for Emax within Saudi coffee formulations (SE, SN, SM). † Significance at (p < 0.05) for Aidite in Ne relative to other coffee solutions. ★ Significance at (p < 0.5) for Cer in Tk relative to other coffee solutions

Fig. 4.

Aidite zirconia ceramic discs before (PRE) and after immersion in six coffee solutions

Figure 5 displays the calculated TP values of the three test ceramic materials before, (Pre) and after immersion in the six coffee solutions. Emax translucency pre-immersion was significantly higher (18.56) than the other two zirconia ceramics, Aidite and Cer (P < 0.05). The translucency of all tested ceramic materials has significantly decreased after immersion in all coffee solutions (P < 0.05). The highest TP values after immersion were recorded for SN coffee for Emax material (17.01), while the lowest translucency for Emax disks was recorded for discs immersed in Ne coffee (14.30) (P < 0.05). The TP values of Aidite ceramics immersed in the three formulations of Saudi coffee (SE, SN, SM) were higher than those immersed in the other coffee solutions (NE, Tk, Es) with statistical significance of (P < 0.05) relative to Tk coffee solutions which showed the least TP values within Aidite ceramics (9.65). For Cer, specimens immersed in NE coffee demonstrated the lowest TP values (10.77).

Fig. 5.

Translucency parameter (TP) of the three ceramic materials before (PRE) and after immersion in six coffee solutions. * Significance at (P < 0.05) in all groups after immersion in all coffee solutions. ★ Significance at (P < 0.05) for Emax relative to other materials. † Significance at (P < 0.05) for Emax in Ne relative to all other coffee solutions. § Significance at (P < 0.05) for Emax in SN relative to Emax in Es. ♀ Significance at (P < 0.05) for Aidite in ES relative to Aidite in the three Saudi coffees (SE, SN, SM). ✦ Significant at (P < 0.05) for Aidite in Tk relative to Aidite in Saudi coffees SN and SM

The calculated contrast ratio values of the three test ceramic materials before, (Pre) and after immersion in the six coffee solutions are displayed in Fig. 6. Although there were changes in CR values after immersion, these changes were not significantly different from the pre-immersion (PRE) values (P > 0.05) except for the Aidite discs immersed in Es coffee which showed significant increase in CR values post immersion (P < 0.05). The increase in CR values of Aidite ceramic immersed in Tk coffee was significantly higher than the increase in CR values of the same material after immersion SE, SN and Ne coffee solutions (P < 0.05). Cer discs immersed in Ne coffee, on the other hand, demonstrated higher CR values compared to Cer discs immersed in SE, SM and Es coffee solutions (P < 0.05).

Fig. 6.

Contrast Ratio (CR) of the three ceramic materials before (PRE) and after immersion in six coffee solutions. * Significance at (P < 0.5) for Aidite in Es relative to PRE values. † Significance at (P < 0.5) for Aidite in Tk relative to Aidite in SE, SN, and Ne. ✦ Significance at (P < 0.5) for Cer in SE, SM, Es relative to Cer in Ne

Discussion

The newly introduced ultra-translucent multilayer monolithic zirconia ceramics for veneer restorations were tested in comparison to the dominantly employed aesthetic lithium disilicate ceramic material in the present study to assess the effect of consumption of different types of commonly used coffee on the color and optical properties of these aesthetic ceramic materials. According to the results, the two null hypotheses which stated that there is no color change in the ceramic materials immersed in different coffee solutions and there is no difference in color change with consumption of Saudi coffee in comparison to commonly used coffees (instant black, turkish and espresso) were rejected.

In the current research, simulated one year of coffee consumption has resulted in remarkable change in the color of all ceramic materials tested regardless of the type of coffee. This finding was in line with previous investigations (Al Ahmari et al. 2022; Al-Samadani 2013; Elsaka et al. 2022; Haralur et al. 2019; Hutami et al. 2018) which confirmed that coffee is one of the strongest staining beverages as it contains traces of chromogenic substances such as tannin and chlorogenic acid (Al Ahmari et al. 2022; Hutami et al. 2018). Additionally, the pH of the prepared coffee in the current study ranged from 4.3 to 4.8, which contributed to the observed discoloration (Al Ahmari et al. 2022; Hutami et al. 2018).

Assessment of the above demonstrated color changes was carried out utilizing the CIE L* a* b* “Commission Internationale de l’Eclairage” numeric color system whereby the L* a* b* coordinates were recorded using a spectrophotometer. The widespread utilization of spectrophotometer for obtaining the CIE-L*a*b* color values has been documented in previous investigations confirming its reliability as a color testing tool of various dental materials (Alghazali et al. 2019; Alrabeah et al. 2023a, b, c; Hardan et al. 2022; Pop-Ciutrila et al. 2015; Turgut and Bagis 2011). A recent study investigating the effect coffee consumption of several CAD/CAM ceramic systems (Al Ahmari 2022) has used the same color measurement formula as the present research and have demonstrated ΔE of 2.63 for the lithium disilicate samples (IPS Emax CAD) and 2.99 for multilayer zirconia after immersion in Arabic coffee (Qahwa) which is far from the observed color difference (ΔE = 5.26–8.93) in the current in-vitro investigation for the lithium disilicate group Emax and monolithic zirconia. The difference in the magnitude of ΔE between the two studies could be attributed to the difference in specimen thickness which was 2 mm in the previous study (Al Ahmari 2022) while the thickness of specimens in the current study was 0.5 mm representing typical veneer thickness. It is logical to notice more color changes in materials if the thickness is decreased (Alrabeah et al. 2023a, b, c). The ∆E values of the current research after immersion in various color solutions were at a level above the threshold at which the clinical perception of color change occurs (> 3.3) (Funt and Roshan 2021; Lindsey and Wee 2007). Such high ∆E values were also observed on the work of Hutami et al., in which exposure to different coffee solutions resulted in color changes of ∆E values ranging from 7.42 to 14.74 (Hutami et al. 2018). The authors explained such variations in ∆E values between the coffee solutions tested to be related to the degree of roasting of different coffees. Darker roasts (as seen in espresso, Turkish, and instant black coffee) undergo more intense thermal processing, which leads to the Maillard reaction and caramelization of sugars. These processes produce a high concentration of melanoidins, which are dark-colored, high-molecular-weight polymers known to bind strongly to surfaces, including dental substrates (Kim et al. 2025; Lu et al. 2023). Additionally, dark roasting reduces the pH of the beverage, increasing acidity and potentially promoting surface roughness or microstructural degradation of ceramics, which in turn enhances stain absorption (Abu Ramadan et al. 2025; Alencar-Silva et al. 2019) This could explain the present finding in which immersion of the ceramic discs in the commonly consumed coffees (Ne, Tk, Es) resulted in color changes higher than the changes observed when ceramic discs were exposed to the Saudi coffee formulations (SE, SN, SM). Saudi coffee distinguishes itself from widely consumed coffees though lighter roasting process of its coffee beans resulting in lighter color of the final coffee beverage. The lighter beverage color and transparency in Saudi coffee correlate with a lower optical density and chromophore intensity, consistent with the reduced ΔE values observed in this study.

As mentioned earlier, the degree of coffee bean roasting is known to alter the content of chromogenic substances and chlorogenic acid present in coffee which play a role in the development of darker color, stronger flavour and aroma of coffee solutions (Hutami et al. 2018). This could also explain the difference in ∆E between the three formulations of Saudi coffee where the SN formulation with its darker degree of roasting had increased color changes compared to formulations from the eastern and central regions of Saudi Arabia. These formulations (SE and SM) made from lightly to medium roasted green coffee beans, have a lower melanoidin and polyphenol concentration, than darker roasting coffee types (Al-Shami et al. 2023). The reduced degradation of chlorogenic acids during light roasting may limit both pigment concentration and acidic etching, thereby decreasing the risk of surface alteration and staining (Kim et al. 2025).

High content of chlorogenic acid also reduces the pH value of the coffee beverage. The pH values of the three coffee beverages (Ne, Tk, Es) tested in the present study had lower pH values compared to those of the Saudi coffee formulations (SE, SN, SM). The earlier work of Awliya et al. corroborates with the present findings in which the discoloration produced with the consumption of instant black coffee (Ne), Turkish coffee (Tk) and Espresso coffee (Es) was higher in comparison to Saudi coffee (Awliya et al. 2010). The authors explained their results to be related to the dark color and concentration of coffee beverages (Ne, Tk, Es) in comparison to the lighter color and lower concentration of Arabic coffee (Awliya et al. 2010). However, Arabic coffee in the work of Awliya et al. did not induce significant color changes (∆E < 2.55) which disagrees with the present findings. This could be due to the composition of Arabic coffee which lacked the spices present in the different formulations of the Saudi coffee in the current study. The Saudi coffee prepared currently contained various amounts of saffron, cardamom and cloves. Saffron contains carotenoids such as crocin, which are yellow-orange in nature, while cardamom contains essential oils as cineole and limonene with relatively light coloration. Clove, on the other hand, is rich in eugenol, which has a distinct aroma and mild pigmentation. Although it may have some staining potential, its chromogenic load is significantly lower than that of coffee polyphenols (Safy and Elgamily 2019). AlSamadani have examined the effect of Arabic coffee containing cardamom and cloves on the color composite resin disks and have found that Arabic coffee has shifted the color from yellowness to blueness and justified this finding due to the presence of cardamoms and cloves in the component of the Arabic coffee (Al-Samadani 2013). In the present study, the immersion of Emax ceramics in Saudi coffee (SE, SN, SM) resulted in discoloration more noticeably in the green–red axis shifting towards green which could be assumed to be related to the presence cardamoms and cloves as explained earlier (Al-Samadani 2013), however, oils in cardamom are volatile, light-colored and aromatic, and do not contribute significantly to staining. Some studies even suggest a mild cleansing or surfactant effect that could reduce pigment adherence (Al-Samadani 2013; Noumi et al. 2018). Similarly, saffron is highly water-soluble and used in small concentrations in Saudi coffee and its ability to cause surface discoloration is minimal compared to melanoidins and tannins typical of dark roasted coffee (Sánchez and Winterhalter 2013). These biochemical differences support the observation that Saudi coffee formulations resulted in lower ΔE values compared to commonly consumed dark-roast coffees. While commonly used coffee beverages present a high risk for esthetic compromise of restorations, Saudi coffee’s unique composition and preparation method may make it a less harmful alternative from a dental material perspective.

The highest amount of color change was recorded for the Aidite monolithic zirconia (∆E 14.7) after exposure to Ne instant black followed by the Cer monolithic zirconia (∆E 12.9) after exposure to Tk coffee. This increased color change in zirconia ceramics was also observed earlier in the work of Haralur et al. who demonstrated similar findings in which the highest ∆E values (5.60) were observed in the monolithic zirconia ceramics after immersion in Ne instant coffee (Haralur et al. 2019). Such variation in the values of ΔE among the materials tested in response to exposure to different coffee solutions could be attributed to material composition and structure, and that color stability is material dependent. Dental glass ceramics are materials that consist of a glass matrix and crystalline phase. The relationship between the crystal size and their distribution with the glassy matrix crystals influences the color and optical of these ceramic materials (Alrabeah et al. 2023a, b, c; Comba et al. 2022). The Aidite and Cer zirconia used in the present study are classified as partially-stabilized-zirconia, containing 5 mol% yttria (5Y-PSZ) with > 50% cubic-phase zirconia (Ban 2021; Zhang and Lawn 2018). This difference in crystal structure minimized the residual pores and impurities, which if exist, produce magnitudes of different refractive indices and lead to surface light scattering, which in turn affects the final color and induce inferior optical properties (Ziyad et al. 2021). Zhang and Lawn have explained that the inclusion of cubic-phase zirconia enhances the light transmittance (Alrabeah et al. 2023a,, b, c; Zhang and Lawn 2018)]. On the other, Emax glass ceramic, composes a dense and homogeneous distribution of crystalline structure of lithium disilicate (Li₂SiO₃) having 70% of crystal volume (Li₂SiO₃) embedded in a glassy matrix with a 0.2 to 1 μm diameter crystal size (Alrabeah et al. 2023a, b, c; Zhang and Lawn 2018). It’s been documented that the smaller the crystalline ratio, the better the color characteristics are to be observed (Zhao et al. 2018) which could explain the preferred response of the Emax ceramic in the present study in terms of ΔE in response to coffee exposure. Additionally, zirconia is known to undergo low thermal degradation (LTD) in which the tetragonal phase develops a gradual transformation into the monoclinic phase at low temperatures and in the presence of wet and humid conditions such as those present in the oral cavity when exposed to acidic food, beverages, and temperature changes (Almohammed et al. 2022; Alrabeah et al. 2024; Huang et al. 2024). This transformation influences the aging resistance and therefore affecting the ceramic’s long-term stability and durability (Almohammed et al. 2022; Huang et al. 2024). LTD can be reduced by adding alumina in small quantities, but in turn could affect the translucency (Almohammed et al. 2022; Alrabeah et al. 2024). Further aging of these yttria-partially stabilized zirconia (Y-PSZ) has been found to cause overall color changes, and this could explain the clinically noticeable color changes with Aidite and Cer in the present study (Huang et al. 2024).

From a clinical point of view, coffee would be categorized one of the strongest discoloring beverages for both the teeth and dental restorations including dental ceramics. Dental practitioners should instruct their patients to maintain their daily hygiene regime of teeth brushing to maintain the color stability of their existing restorations.

The lack of clinical simulation in the present study is a particular limitation. The presence of saliva could dilute the staining coffee solution and therefore minimize the final color change. Also the fact that the hard (teeth) and soft tissues (tongue and lips) that are normally present in the oral cavity were absent in the present study demonstrates another limitation which may become cause of some errors. Additionally, the absence of brushing procedure could have exaggerated the overall color change. Another limitation is that thermocycling was not conducted and the constant exposure of ceramics discs over 15 days of immersion could affect the degree of discoloration of the tested ceramics. In addition, a distilled water immersion group could have served as a control to isolate the intrinsic aging effect from extrinsic staining. Future work will incorporate this important control. Further research should also consider in-vivo situations and the effect of brushing on the color stability of all-ceramic restorations after exposure to coffee beverages.

Conclusion

Within the limitations of the present study, the following conclusions were found:

1. Consumption of all tested types of coffee altered the color of all tested ceramic materials to a level above the threshold at which the clinical perception of color change occurred (> 3.3).

2. Saudi coffee consumption caused less changes in the color of tested dental ceramics in comparison to the consumption of commonly used coffees (instant black, turkish, and espresso).

3. Saudi coffee with formulations from the northern region (SN) resulted in more color changes within the Emax material in comparisons to the other two Saudi coffee formulations from the middle and eastern regions (SM and SE).

4. The highest color change was observed in Aidite ceramics immersed in instant black coffee (Ne) followed by Cer ceramics immersed in Turkish Coffee (Tk).

5. Instant black coffee exposure caused the most reduction in translucency within the Emax, while Turkish coffee caused the most reduction in translucency within the Aidite material.

Author Contributions

Conceptualization, methodology, validation, and supervision: G.A..; formal analysis, G.A.; investigation, G.A., A.A, N.A., A.N.A., K.A.; resources, G.A.; data curation, A.A, N.A., A.N.A., K.A.; writing—original draft preparation, G.A., A.A, N.A., A.N.A., K.A.; writing—review and editing, G.A.; project administration, G.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the “Saudi coffee grants” program offered by the Saudi Ministry of Culture. All opinions expressed herein belong to the researchers and do not necessarily reflect those of the Ministry of Culture.

Data availability

Data are available on request from the corresponding author.

Declarations

Ethics Statement

No ethical approval was required. The study was conducted in accordance with the Declaration of Helsinki and approved by the College of Dentistry Research Center (Registration number IR-0494; Dated: 13–05-2024).

Consent for publication

All authors agree for publication of research.

Consent to participate

All authors consent to participate in the research.

Competing Interest

“The authors declare no conflicts of interest.”