Effect of Coffee on Color Stability and Surface Roughness of Newly Introduced Single Shade Resin Composite Materials.

Abstract

Background

Dentists started to follow the era of using single shade resin composite restorations to avoid color shade selection. Our study was done to evaluate and compare color stability of two single shade resin composite materials.

Methods

sixty samples were randomly allocated into two main groups (n = 30) according to the composite resin used: Group O: (Omnichroma) samples and Group V: (Venus Peral) samples. Each group was then divided into two subgroups (n = 15): group O1 and V1: samples immersed in coffee. Group O2 and V2: samples immersed in distilled water. Color changes (Δ E) and roughness values (Ra) were evaluated at baseline, 1st, and 14th days of immersion. Color change was assessed using Vita Easy Shade V while surface roughness was assessed using, profilometer and Atomic Force Microscope (AFM), respectively. Data were collected and statistically analyzed using two-way variance analysis (ANOVA) and Tukeys post-hoc test (p < 0.05).

Results

Group O1 and V1 recorded the highest Δ E (P = 0.0002, 0.001, respectively) and Ra values (P < 0.001) no significant difference between both materials at 14 days

Conclusion

Single shade resin composite with smart chromatic material technology has dramatically color change and surface roughness that sacrifice esthetic success.

1. Background

Demand for ideal esthetic material in restoring teeth had a direct impact on both materials and techniques.¹ Recently; Dentists prefer to use ceramic and resin-containing restorative materials ² on the basis of their esthetic and biological properties. ³ The Esthetic successes of dental resin composite restorations depend primarily on their surface properties and color stability.

Using nanotechnology in dentistry, now manufacturers are introducing resin composite materials with single-shade systems in place of more complex color systems. It is stated that these materials are consisting of nanofillers (nanomer) and nanomer groups (nanocluster) providing more effective color harmony with dental tissues because of their “chameleon effect” properties. In recent times, single-shade resin composite, which can be used for all tooth shades, has been introduced to the dentist's use. Advantage of its color-matching ability eliminates the need for a shade-taking procedure and reduces composite inventory, minimizing chair time for patient and the wastage of unused composite shades.⁴

Color stability and surface roughness of composite resins remain important requirements for esthetic success. ⁵ Color changes have been associated with diet, chemical reactions, water absorption and poor oral hygiene.⁵ Consumption of certain beverages may affect the esthetic and physical properties of the resin composite, thereby destabilization the quality of restorations may occur.⁶ Beverages such as coffee, tea, cola, and wine cause different degrees of discoloration of resinous restorative materials.⁴ It was reported that a surface roughness value below 0.15 µm., decreases the adhesion of streptococcus mutans while when this values is above 0.2 µm create an accessible retention area for the attachment of the bacterial plaque.⁷

In order to assess the color stability of restorative materials, many instrumental techniques could be used such as; Digital cameras, Spectrophotometers, or colorimeters. Evaluating (ΔE) is referred to Commission International De L’éclairage (CIE) system. ⁴

Surface roughness is considered as one of the reasons for exterior discoloration. ⁸ Wear of dental resin composites denoting debonding of inorganic fillers from the resin matrix which result in leaving voids, increasing the surface roughness and forming a surface susceptible to exterior stain. ⁸ Mechanical, and Optical profilometers, SEM (scanning electron microscope), and AFM (atomic force microscope) are widely used device to measure and evaluate the surface roughness of restorative materials. Dental experts preferred profilometers as no preparation is required on samples to measure surface roughness, and repeated measurements are enabled. ⁹ Moreover, AFM can obtain 3D nanometric images with high-resolution on the material surface offering a complete surface quantification. ¹⁰

The aim of our study is to examine the color stability and surface roughness of smart chromatic resin composite after exposing them to commonly consumed beverages; coffee for 14 days using Vita Easy Shade V, a contact stylus profilometer, and AFM. The null hypothesis was that there is no difference in the Δ E and Ra of both single-shade composite resin after immersing in coffee for 14 days.

2. Materials And Methods

Materials:

• Resin Composite Materials: (Omnichroma/Venus pearl) (table 1)

• The beverages used were coffee (Nescafe classic, Nestle, Switzerland), and distilled water (Pharmapack, Egypt).

Table (1): Composition of the restorative materials used in this study:

Abbreviations: UDMA=urethane dimethacrylate; TEGDMA=triethylene glycol dimethacrylate; TCD: Tricyclodecanurethane

Methods:

Study Design

Sixty samples were randomly allocated into two main groups (n = 30) according to the composite resin used: Group O: samples were obtained using single-shade composite resins (Omnichroma) and Group V: samples were obtained using single-shade composite resins (Venus Peral). Each group was then divided into two subgroups (n = 15): group O1 and V1: samples immersed in coffee. Group O2 and V2: samples immersed in distilled water. The color change (Δ E) and roughness values (Ra) were evaluated for all samples at baseline (before immersion), and on the 1st, and 14th days of immersion. Color assessments were measured using Vita Easy Shade V while surface roughness was measured using a contact stylus profilometer and AFM. The study proposal was reviewed and approved by the Research Ethics Committees (REC) of the Faculty of Dentistry, Cairo University, Egypt on 29/3/2022. With approval number 30.3.22.

Sample Size Calculation

Sample size calculated depending on a previous study (Aydın, et al) ⁴ as reference. According to this study, the response within each subject group was normally distributed with a standard deviation of 1.4. If the true difference in the experimental and control means is 1.8, minimally the study needed 11 subjects in each group to be able to reject the null hypothesis that the population means of the experimental and control groups are equal with probability (power) 0.8. The Type I error probability associated with this test of this null hypothesis is 0.05. The total sample size increased to 15 subjects per group to compensate 20% dropout.

Samples preparation:

Resin composite specimens’ preparation:

Thirty cylindrical disk-shaped specimens (6 mm diameter and 2 mm thickness) were prepared using a customized Teflon mold, rendering a total of 60 specimens for the two resin composite materials used. A Teflon mold and copper ring were fabricated with 2 mm thickness and 20 mm diameter with a centralized hole of (6mm diameter and 2 mm thickness) in which the resin composite was bulk packed as one increment. ⁴

According to the manufacturer’s recommendations, the resin composite materials were dispensed, manipulated, and polymerized. A nylon thread was incorporated into the specimen before polymerization to allow their easy handling and their suspension in the immersion solutions during all aging periods. The resin composite was bulk packed inside the central hole of the split Teflon ring. For ensuring that specimens would have flat polymerized surfaces free of bubble formation after curing, both top and bottom surfaces were each covered with transparent polyester matrix strips (TOR VM, Moscow, Russia) and a glass microscopic slide (1mm thickness) .⁴

Compressed specimens were polymerized for 20 seconds exposure time on the top and bottom surfaces respectively using a light-emitting diode polymerizing unit (LED COXO DB-686 MOCHA) through the glass slide and the polyester matrix strip. LED light curing unit was used in standardized mode, emitting 1200mW/cm2 irradiance as measured with a radiometer (Kerr manufacturing product). Then the two wings of the ring were opened to remove the specimens. The dimensions of the specimens were checked with a caliper (Pirmadent Germany SS). All samples were finished and polished using Sof-Lex disks (three-step system) starting with medium grit, then fine grit, and finally superfine grit all in a dry media for 15 seconds, then rinsing and drying with a water/air syringe for a total of 6 seconds. ¹¹ Specimens were stored in distilled water in tight vials for 24 hours at 37° C before the immersion procedures in incubator.⁴

Test solution preparation:

With each type of resin composite, the 30 specimens were randomly allocated into two subgroups (n = 15 per subgroup), according to the immersion solution to be investigated. The two immersion solutions used were: distilled water (control solution) and coffee. The coffee solution was prepared by adding 3.6 g of coffee using a digital spoon scale to 300 ml distilled water then boiling for 10 minutes to have a standardized concentration.¹² Filter paper was used to remove any impurities of the prepared coffee before being poured into vials and left to be cooled. Specimens were immersed through suspension with the nylon thread of 5 ml of an immersion solution. The immersion solutions were changed daily till the last assessment period. After placing specimens, the vial was sealed tightly with its cap to prevent any evaporation of the immersion solutions. ⁴ The containers were stored at 37°C by placing them in a thermal control unit. After each storage period, the specimens were removed from immersion solutions and allowed to dry before color assessments. Then after assessments, the same specimens were stored again in the vials containing daily fresh solutions for the next storage period. ⁴

Color measurements testing

Color shade assessment using Commission International de L’Eclainge (CIELab) color system (L*, a* and b* values) at baseline before immersion, after one day, and after 14 days by digital spectrometer device Vita Easyshade V (VITA Zahnfabrik, Bad Säckingen, Germany). It is a portable spectrophotometer and a new fifth generation of Easyshade with a handpiece of fiber optic probe assembly for illuminating and receiving the reflected light from the sample and results appear through a LED screen. The base unit has the calibration block into which the handpiece is seated in. The Easyshade handpiece has a 5mm diameter stainless steel probe. ¹³ Procedures of measurements by Vita Easyshade started with a calibration process that was performed as per the manufacturers’ instructions. ¹³ The probe was perpendicular to the recorded specimen before pressing the measurement on and the results were displayed. According to the manufacturers’ instructions, two successive measurements were done and reported for each sample. ¹³

The color differences (∆E) between the three measurements were calculated by using Hunter’s equation: ΔE = [(ΔL) 2 +(Δa)2 +(Δb)2 ]1/2 ΔE represents the overall color difference, ΔL* is the difference in the lightness, Δa* is the difference in the axis a* of chroma and Δb* is the difference in axis of b* of chroma. ΔE ˃3.3 is considered unacceptable clinically; ΔE < 3.3 clinically acceptable color alteration and ΔE < 1 relates to color alterations not detected by the human eye. ¹⁴

Surface roughness testing

The surface roughness of the materials was tested using a contact stylus profilometer (SJ- 210 Surface roughness tester Mitutyoyo Japan). Each specimen was fitted to the specimen holder in which the surface was to be measured in the horizontal direction, then the specimen holder moves in a vertical direction up to the specimen surface just touching the measuring tip. Device calibration is done according to the manufacturer's instructions before use. ¹⁵ Five readings were recorded for each specimen at a distance of 500 microns each

Testing parameters:

1. Measuring distance 4 mm

2. Measuring Speed 0.5 mm/s. Returning 1mm/s

3. Measuring force 0.75 mN

4. Stylus profile: tip radius 2-micron, tip angle 60 degree

5. Evaluation parameter Ra values expressed in microns

Surface morphology analysis using Atomic Force Microscope (AFM)

Surface morphology analysis was gained using the Atomic Force Microscope (Tosca 200 AFM - Anton Paar GmbH – Germany, tapping mode − 500 um increment - rate 1 line/second) in ‘contact’ mode. Four various regions were chosen to have different images which can be scanned by software (Mountains® 8.2 Software - Digital Surf, Besançon, France).

Statistical Analysis:

All data were presented as mean &standard deviation. Data were presented in 1 table &1 graph. Statistical analysis was performed with SPSS 16 ® (Statistical Package for Scientific Studies), Graph pad prism & windows excel.

Exploration of the given data was performed using the Shapiro-Wilk test and Kolmogorov-Smirnov test for normality which revealed that the significant level (P-value) was insignificant as P-value > 0.05 which indicated that the alternative hypothesis was rejected, and the concluded data originated from a normal distribution (parametric data) resembling normal Bell curve.

The color values changes (ΔE) were obtained by calculating the difference in the color of the specimens against black and white backgrounds using the following formula:

3. Results

Color measurements results

a: Comparison between different materials:

Comparison between different materials was performed by using the One Way ANOVA test which revealed a significant difference between different groups after 1 day and after 14 days as P < 0.05, followed by Tukey`s Post Hoc test for multiple comparisons which represented that after 1 day, V1 was significantly the highest color changes (22.32 ± 6.51), then O1 (16.35 ± 2.53), while there was insignificant differences between V2 (3.30 ± 1.19) and O2 (3.63 ± 1.39). After 14 days, V1 (31.65 ± 6.41) and O1 (30.72 ± 10.74) were significantly the highest with insignificant difference between them, then V2 (5.23 ± 1.03) and O2 (2.38 ± 1.72) was significantly the lowest with insignificant difference between them, as presented in table (2) and figure (1).

b: Comparison between color changes after 1 day and after 14 days:

Comparison between Δ E after 1 day and after 14 days was performed by using Paired t-test which revealed a significant increase in color changes after14 days in all groups as presented in table (2) and figure (1).

Table (2): Mean & standard deviation of color changes (Δ E after 1 day and after 14 days) in all groups:

N: Count *: Significant difference as P < 0.05.

Means with the same superscript letters in the same column were insignificantly different as P > 0.05

Means with different superscript letters in the same column were significantly different as P < 0.05

Surface roughness results

a: Comparison between different intervals (effect of time) table (3) and figure (2):

Comparison between different intervals was performed by using the One-Way ANOVA test which revealed a significant difference in all groups as P < 0.05, followed by Tukey`s Post Hoc test for multiple comparisons which revealed that:

• In Group O1 and V1 there was a significant difference between all intervals (significant increase as all with different superscript letters)

• In Group O2 and V2 there was as insignificant difference between baseline and after 1 day, while after 2 weeks was significantly the highest.
  

Table (3): Descriptive statistics of all groups regarding surface roughness at baseline, after 1day and after 14 days and comparison between different intervals within each group:

• Min: minimum Max: maximum M: mean SD: standard deviation
• *Significant difference as P < 0.05
• Means with different superscript letters were significantly different as P < 0.05
• Means with the same superscript letters were insignificantly different as P > 0.05

b: Comparisons between different groups table (4) and figure (3):

Comparison between different intervals was performed by using the One-Way ANOVA test which revealed a significant difference in all groups as P < 0.05, followed by Tukey`s Post Hoc test for multiple comparisons which revealed that:

• At baseline: Group O1 and O2 were significantly the lowest with insignificant difference between them (same have letter a), while Group V1 and Group V2 were significantly the highest with insignificant difference between them (same have letter b).

• After 1 day: Group O2 and V2 were significantly the lowest with insignificant difference between them (same have letter c), then Group O1, while Group V2 was significantly the highest.

• After 14 days: Group O1 and V1 were significantly the highest with insignificant difference between them (both have letter a), while Group O2 and V2 were significantly the lowest with insignificant difference between them (same have letter b)

Table (4): Mean and standard deviation of roughness at baseline, after 1day and after 14 days and comparison between different groups:

• M: mean SD: standard deviation *Significant difference as P < 0.05
• Means with different superscript letters were significantly different as P < 0.05
• Means with the same superscript letters were insignificantly different as P > 0.05

Correlation between color changes and surface roughness:

Correlation between surface roughness and color changes was calculated using Pearson`s Correlation Coefficient (r) which revealed a very strong (r > 0.8), positive (+), significant (P < 0.05) correlation between them in both groups (table 5).

Table (5): Correlation between color changes (Δ E) and surface roughness after 1 day and after 14 days in both groups:

Atomic Force Microscope results

The surface roughness results measured by the contact stylus profilometer explained and proved by the AFM analysis (Fig. 4–7).

4. Discussion

The wide use of the different shades of adhesive composite as esthetic restoration in anterior and posterior teeth paid attention to its multiple steps and the time consumption that produced challenges for dentists.¹⁶ Recently, many manufacturers introduced a new single-shade resin composite as it has the advantage of reducing chair time and reducing the time of shade selection. ¹⁶ Moreover, it was reported that any discoloration in the resin composite will affect the aesthetic ^{17, 18} so, the current study presented the problems of color stability of resin composite after exposure to commonly consumed drinks of different storage periods. The null hypothesis in this study was totally rejected due to statistically significant differences in color and surface roughness values of both resin composite materials before and after immersion at evaluation with the Vita easy shade, profilometer, and AFM.

The color stability and surface characteristics of the two single-shade resin composites used depends on the different compositions; fillers, particle size, and distributed resin matrix. A commercially available supra-nanofiller resin composite (omnichroma) was compared against a nanohybrid resin composite (Venus pearl). Nanotechnology applications introduced in the fillers size range within 0.1- 100nm to improve properties ¹⁹. Studies that evaluated the stability of single structured resin composite are severely lacking the limit proper assert its chemical performance. It was stated that details of the fabrication conditions for the organic filler distributed inside the Omnichroma resin are not clear. ²⁰

The esthetic and mechanical properties of resin composite are influenced not only by their chemical composition but also by the environment to which they are exposed such as chemical agents found in saliva, foods, and beverages either intermittently or continuously. Coffee is a strong stain popular ^4,21 and favorable drink used daily by most of the population. So, it was chosen as one of the experimental immersing solutions. While distilled water was used as a control to investigate the behavior of the resin composite itself. ¹⁴ It is worth mentioning that artificial saliva and distilled water have the same effect on resin composite. ²²

In this study each step was made to standardize the methodology; the specimens’ thickness of 2mm for the light cure unit and the curing time was adjusted to 40sec with 20sec exposure time for the top and 20sec for the bottom respectively ²³, miller strip and the standardized finishing and polishing procedures. Specimens were immersed in distilled water for 24 hours before immersion in the tested solutions to complete polymerization. ¹⁷

In the current in-vitro study, a static immersion was done for all specimens for one day and 14 days which was equivalent to one month and 14 months of consumption, respectively. ¹⁷ The increase in temperature will accelerate color change in the restoration ²⁴, specimens were incubated in to adjust the temperature at 37⸰c all the storage time to simulate the oral environment. Coffee was replaced with a new proportion every 24 hours to minimize bacterial growth.

Visual perception of color is a psychological point-view and unfortunately depends on the observer’s skill. ¹⁴ In order to overcome the problem of visual assessment of the color, many color-evaluating devices have been used as Colorimeters and Spectrophotometers that are more precise than the naked eye. ¹⁴ Color assessments in our study were done using a digital spectrometer device Vita Easy shade V. This device is considered a reliable tool to measure the color change not only in clinical applications but also for research purposes in evaluating color interactions of human teeth and dental materials. ²⁵

Color measurement is usually done by using the CIELAB color system. ¹⁴ CIEL*a*b system is very popular and it provides a standardized technique with useful analysis of ΔE* values accurately. This system can define small color changes accurately and have many advantages including, objectivity, repeatability, and sensitivity. ¹⁴

Surface roughness refers to the finer irregularities of the surface texture that refers to the action of the production process or the material’s features.⁸ Currently several available methods are present to measure the surface texture of any material including contact stylus tracing, scanning electron microscopy, laser reflectivity, non-contact laser metrology, and atomic force microscopy. Contact stylus tracing was used in the current study because it was fast, simple, and reliable for the comparative assessment of surface roughness properties of both tested single-shade composite resins. ²⁶Atomic force microscopy (AFM) is a technique for analyzing the topography of the surface. It is an effective technique for characterizing nanoparticles and nanomaterials because it offers qualitative and quantitative information on several physical properties such as size, shape, surface texture, and roughness with a demonstrating image for any surface type, including polymers, ceramics, composites, glass, and biological materials.²⁷

A strong and positive correlation between color stability and surface roughness results in our study was explained by the structure and chemical composition of both resin composite materials used. Based on the fact that composite resins with smaller filler size exhibit smoother surface property ²⁸ and less color change ⁴, both resin composite materials exhibited statistically significant difference behavior regarding surface roughness at baseline. The O groups showed superior surface smoothness than the V groups which could be related to the lower filler size ⁴ and higher filler loading ²⁹as mentioned in table (1). The specimens immersed in the coffee solution reported greater color change and surface roughness when compared to the specimens immersed in distilled water. This could be due to both adsorption and absorption of the yellow stains which have low polarity. This low polarity of yellow stain has the ability to penetrate into deeper layers of resin composite ¹⁴, in agreement with many studies. ^{(4, 17)} On the opposite side, a study found an acceptable color change after immersion in coffee for 48 hours E < 3.3, this may be due to difference in immersion solution preparation methods and concentration. ³⁰

Group O2 and V2 demonstrated unacceptable color change (˃3.3) after 14 days of immersion in distilled water which was in consistent with a study that had an unacceptable color change of resin composite after immersion in distilled water for 5 days. ¹⁴ Moreover, it has been reported that the water absorption of composite resins reaches its highest level in 7–60 days. ¹⁷ In contrast to Farah and Elwi who found that immersion in distilled water for 7 days resulted in imperceptible color changes (ΔE ≤ 1). ³¹

It was stated that, when inorganic fillers de-bond from the resin matrix this may lead to leaving voids, resulting in an increase in the surface roughness forming a surface susceptible to external stains. ^{8, 32}Additionally, the resin matrix plays an important role in staining susceptibility. ^14,33,34 Many studies stated that the ability of resin composite to discolor depends on the hydrophilicity of the resin matrix and the ability of a material to absorb water. 32, 35Both materials have matrix composition based on triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA). It was reported that TEGDMA monomer is responsible for color change due to high water absorption and an increase in coloration. ^4,17 In agreement with a study where the most color change was related to the nanofilled single shade resin composite (Omnichroma) after immersion in coffee for 1 day in comparison to multi-shade resin composite that could be due to TEGDMA in its composition. ⁴ Different opposite study in findings, they stated that no correlation between color and roughness. ³⁶

Nanohybrid (Venus Pearl) composite was more color unstable than nano-filled composite (Omnichroma). According to the data provided by the manufacturer (Kulzer GmbH) who claimed that, Venus Pearl with novel low shrinkage composition of tricyclodecane (TCD)-urethane monomer which is characterized by big molecular size that demonstrate good chemical stability. ³ Although nanohybrid (Venus Pearl) contains tricyclodecane TCD urethane-based monomer, which in turn gives high resistance to discoloration ³, its lower filler content and presence of agglomerated particles (nanoclusters) could be the reason for the less color resistant in comparison to the nanofilled resin composite (Omnichroma). This agreed with another study which concluded that nanohybrid resin composite has inferior color stability and surface roughness compared to nanofill type.^{8, 9} This explains that the staining process of dental composite is a multifactorial issue. It depends not only on the type of resin matrix but also on filler size, degree of polymerization, water sorption, degree of smoothness, type, and exposure time to staining solution. Moreover, environmental factors such as pH and temperature play roles in the staining process. ¹⁷

The mean color values and surface roughness after 14 days period was the highest for both Groups O1 and V1. This could be due to increase the interaction between the resin and the chemicals. More penetration of water inside resin with staining substances of the coffee solution occurred. These conclusions agree with many previous studies. ^{4, 9}, ^{14, 17}

Although the present study confirmed the detrimental effects of tested solutions on single-shade resin composite material, there are several limitations in our study. Similarly, to other in vitro studies, there are factors affecting the restorations in the oral cavity: microbiota, saliva circulation, temperature, and pH changes. Therefore, the oral cavity could not be imitated exactly. ¹⁷

5. Conclusions

Based on the results gained from this study, we concluded that;

1- Type of resin composite, immersion periods have an obvious effect on color stability and surface roughness of single shade resin composite.

2- The single-shade resin composite tested showed an "extremely unacceptable" color change in surface roughness even with distilled water.

3- More studies are needed to dig in-depth into the behavior of such materials.

Abbreviations

Declarations

Ethics approval and consent to participate

The study proposal was reviewed and approved by the Research Ethics Committees (REC) of the Faculty of Dentistry, Cairo University, Egypt on 29/3/2022. With approval number 30.3.22.

No consent as no biological or human samples were used in this study.

Consent for Publication

Not applicable.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Competing interests

The authors declare that they have no competing interests

Funding

No funding was obtained for this study.

Author contributions

ShR: Conceptualization, methodology, investigation, resources, writing the original draft. HMT: Methodology, visualization, formal analysis, writing—review, and editing. RK: Methodology, visualization, formal analysis, writing—review, and editing. All authors reviewed the manuscript and gave final approval.

• Raghda 

Acknowledgments

Not applicable.

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