Comparative In Vitro Study of Color Stability of Nanofilled, Microhybrid and Nanohybrid Resin Composites Exposed to Commonly Consumed Beverages

Resin composites are widely used for direct esthetic restorations because they combine conservative tooth preparation with favorable handling characteristics and acceptable mechanical performance [1-3]. However, long-term color stability remains one of the most important determinants of patient satisfaction and restoration longevity, since visible discoloration may lead to repolishing, repair or replacement [4-6].

Discoloration of resin composites is multifactorial. Intrinsic factors include the composition of the resin matrix, the degree of conversion, oxidation of residual monomers and degradation at the resin-filler interface [4-10]. Extrinsic factors include adsorption and absorption of pigments from beverages, dietary agents and tobacco products [4,6-8]. Surface roughness and water sorption further modify the susceptibility of composites to staining [11-13].

The three materials evaluated in the present study differ in filler technology and matrix formulation. Filtek Z350 XT is a nanofilled composite designed to provide a smoother polishable surface, Filtek Z250 is a microhybrid composite with larger filler particles and Tetric N-Ceram is a nanohybrid composite intended to balance polish retention with mechanical strength [14-16]. These compositional differences may influence staining behavior by altering surface texture, water uptake and pigment retention [11,14,15].

Commonly consumed beverages such as coffee, tea, cola and berry-based juices can affect restorative color through different mechanisms. Coffee and tea contain chromogenic polyphenols, cola has low pH that may increase surface susceptibility to staining and raspberry juice contains anthocyanin pigments that can penetrate and discolor resin surfaces [17-22]. The clinical relevance of color change is commonly interpreted using DeltaE values, with DeltaE>3.3 generally considered clinically unacceptable [18,19].

Although many studies have evaluated composite discoloration, fewer investigations have compared contemporary nanofilled, microhybrid and nanohybrid materials under the same staining conditions and at multiple time points [23-30]. Therefore, this in-vitro study compared the color stability of three commercially available composites after immersion in coffee, black tea, cola, raspberry juice and distilled water over 30 days. The primary objective was to compare composite categories, whereas secondary objectives were to compare beverages and immersion time. The null hypothesis was that neither composite type nor immersion medium would significantly influence color stability.

Study Design and Sample Preparation

This laboratory-based comparative in-vitro study evaluated color stability in three resin composite categories. Three commercially available A2-shade materials were selected: nanofilled composite (Filtek Z350 XT, 3M ESPE, St. Paul, MN, USA), microhybrid composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA) and nanohybrid composite (Tetric N-Ceram, Ivoclar Vivadent, Schaan, Liechtenstein). G*Power software (version 3.1.9.7) was used for sample size estimation with an effect size of 0.40, alpha of 0.05 and power of 80%, giving a minimum of 10 specimens per subgroup. A total of 150 disc-shaped specimens were prepared, yielding 50 specimens per composite and 10 specimens for each immersion subgroup. Any discrepancy in earlier counts has been corrected here for transparency.

Specimen Fabrication and Polishing

Specimens were fabricated in a standardized Teflon mold (10 mm internal diameter x 2 mm thickness). Composite was inserted in a single increment, covered with a Mylar strip and glass slide and light-cured with an LED curing unit (Elipar DeepCure-S, 3M ESPE; 1470 mW/cm2) positioned 1 mm from the specimen surface. Defective specimens were discarded and replaced before randomization. Specimens were polished sequentially with Sof-Lex aluminum oxide discs from coarse to superfine grit under water cooling according to the manufacturer instructions, then stored in distilled water at 37°C for 24 hours before baseline measurement.

Immersion Media and Allocation

Five immersion media were used: coffee, black tea, cola, raspberry juice and distilled water. Coffee was prepared by dissolving 3.6 g instant coffee in 300 mL boiling distilled water. Black tea was prepared by immersing two tea bags in 300 mL boiling distilled water for 10 minutes. Cola was used as supplied. Raspberry juice was used as the staining medium provided in the original experimental protocol; however, pH and detailed compositional analysis were not measured and this has been acknowledged as a limitation. Specimens were allocated by computer-generated randomization to five subgroups (n = 10) within each composite category and stored in 20 mL of solution at 37°C in sealed containers. Solutions were renewed every 24 hours. The continuous immersion protocol represented an accelerated staining model rather than a simulation of routine daily beverage intake.

Color Measurement and DeltaE Calculation

Color was measured at baseline, day 7, day 14 and day 30 using a reflectance spectrophotometer (VITA Easyshade V, VITA Zahnfabrik, Bad Sackingen, Germany) against a standardized white background [18]. Before each reading, specimens were rinsed with distilled water for 30 seconds and gently dried with absorbent paper to standardize surface conditions. Three readings were taken at the center of each specimen and averaged for L*, a* and b* coordinates. Color difference was calculated using the standard formula: DeltaE = Square root of [(DeltaL*)^2+(Deltaa*)^2+ (Deltab*)^2] [18]. DeltaE values were interpreted as imperceptible (<1.0), clinically acceptable (1.0-3.3) or clinically unacceptable (>3.3) [18,19].

Statistical Analysis

Data were analyzed using SPSS version 26.0 (IBM Corp., Armonk, NY, USA). Shapiro-Wilk and Levene tests were used to assess normality and homogeneity of variance. Two-way ANOVA examined the effects of composite type and immersion medium on color change and repeated-measures ANOVA evaluated time-related changes. Tukey HSD was used for post-hoc comparisons. A p-value <0.05 was considered statistically significant. Effect sizes and confidence intervals were not reported in the original dataset and are therefore identified as areas for improvement in future work.

Ethics, Funding and Reporting

As an in-vitro materials study, formal human-subject ethics approval was not required; however, the manuscript now clarifies this point for transparency. No external funding or manufacturer support was reported. The author declares no conflict of interest. A brief data availability statement has been added below.

All specimens demonstrated measurable color change after immersion, with beverage-exposed groups showing greater discoloration than the distilled water control. Overall, the 30 day ranking for color stability was Filtek Z350 XT (best), Tetric N-Ceram (intermediate) and Filtek Z250 (worst). Across beverages, the staining potential ranked raspberry juice>coffee>black tea>cola>distilled water.

At day 30, raspberry juice produced the highest mean DeltaE values in all three materials (8.94+0.87 for nanofilled, 12.67+1.23 for microhybrid and 11.34+1.08 for nanohybrid), whereas cola produced the lowest beverage-related staining values. Distilled water remained within clinically acceptable limits throughout the study.

Color change increased significantly with time in all beverage groups. In the accelerated continuous immersion model, some groups exceeded the clinical acceptability threshold as early as day 7 or day 14, whereas by day 30 all beverage-exposed groups had become clinically unacceptable (Table 1-3).

Two-way ANOVA demonstrated significant main effects of composite type, immersion medium and time, as well as a significant interaction effect, indicating that the degree of staining depended on the combination of restorative material and beverage exposure. Post-hoc comparisons showed that the nanofilled composite had significantly lower DeltaE values than the microhybrid and nanohybrid materials in most staining media.

Table 1: Mean Color Change (DeltaE+SD) Values at 30 Days by Composite Type and Immersion Medium

Table 2: Mean Color Change (DeltaE+SD) Values by Composite Type and Immersion Time

Table 3: Percentage of Specimens Exceeding the Clinical Acceptability Threshold (DeltaE>3.3)

The present study showed that both the restorative material and the immersion medium significantly influenced color stability. Nanofilled composite demonstrated the greatest resistance to discoloration, whereas microhybrid composite showed the greatest susceptibility. These findings support the view that filler architecture, resin matrix composition and polish retention influence the uptake and retention of staining pigments [14,15,23,24,29].

Raspberry juice produced the greatest color change in all materials. A plausible explanation is the combined effect of highly chromogenic anthocyanin pigments and acidic conditions, which may facilitate pigment adsorption and absorption [17]. Coffee and black tea also caused substantial staining, consistent with their known chromogen content [20-22,30]. Cola produced the lowest beverage-related color change but even cola resulted in clinically unacceptable discoloration after prolonged continuous immersion [21,22,30].

The superior behavior of Filtek Z350 XT may be related to its nanofilled architecture, which is associated with improved surface smoothness and better polish retention [14,15]. In contrast, the higher staining values seen with Filtek Z250 may reflect the behavior of larger filler particles and a matrix more prone to water sorption and pigment retention [6,8,9,27]. Tetric N-Ceram showed intermediate performance, suggesting partial benefit from nanohybrid formulation without matching the behavior of the nanofilled composite [14,16].

The time-dependent increase in DeltaE across all beverages indicates progressive cumulative staining [19-26,28-30]. However, these findings should be interpreted within the limits of the study design. Continuous immersion at 37°C represents accelerated exposure rather than normal clinical consumption. In daily life, staining is influenced by intermittent beverage contact, saliva, pellicle formation, oral hygiene, brushing abrasion and thermal fluctuation [11,12,21,26]. Because thermocycling and mechanical aging were not included, the present model does not fully reproduce oral conditions [26].

This study provides clinically relevant guidance for restorative material selection and patient counseling. Patients with frequent intake of berry juices, coffee or tea may benefit from selection of materials with better stain resistance and from reinforcement of maintenance measures such as periodic polishing and dietary advice [4,21-23,26,29,30]. Nevertheless, the study did not evaluate surface roughness, stain removability or repolishing efficacy, so mechanistic interpretation remains limited [4,11,12].

The main limitations were the in-vitro disc model, absence of thermocycling and toothbrushing abrasion, lack of pH and chemical characterization of the raspberry juice, restriction to shade A2 and lack of surface roughness or microscopic analysis [12,18,26]. Future studies should combine intermittent immersion with artificial saliva, thermal cycling, abrasion and surface analysis to improve clinical simulation [11,21,26].

Within the limitations of this accelerated in-vitro immersion model, commonly consumed beverages adversely affected the color stability of all tested resin composites.

Raspberry juice showed the highest staining potential, followed by coffee, black tea and cola. Filtek Z350 XT demonstrated the best color stability, Filtek Z250 the worst and Tetric N-Ceram intermediate behavior.

By day 30, all beverage-exposed groups exceeded the clinical acceptability threshold for color change, whereas distilled water remained acceptable.

These findings support patient dietary counseling and material selection based on staining risk but clinical extrapolation should be cautious because thermocycling, abrasion and restoration anatomy were not simulated. Future studies should evaluate stain removal and more realistic oral aging models.

1. Leinfelder, K.F. “Composite Resins.” Dental Clinics of North America, vol. 29, no. 2, 1985, pp. 359-371.
2. Zorzin, J. et al. “Modern Concepts of Esthetic Dentistry: Composite Resins.” Quintessence International, vol. 44, no. 6, 2013, pp. 431-442. https://doi.org/10.3290/j.qi.a29563.
3. Fahl, N., Jr. “Dental Composite Resins: An Update.” British Dental Journal, vol. 184, no. 5, 1998.
4. Mundim, F.M. et al. “Effect of Staining Solutions and Repolishing on Color Stability of Direct Composites.” Journal of Applied Oral Science, vol. 18, no. 3, 2010, pp. 249-254. https://doi.org/10.1590/S1678-77572010000300009.
5. Janda, R. et al. “Color Stability of Resin-Based Filling Materials after Aging When Cured with Plasma or Halogen Light.” European Journal of Oral Sciences, vol. 113, no. 3, 2005, pp. 251-257. https://doi.org/10.1111/j.1600-0722. 2005.00217.x.
6. Bagheri, R. et al. “Influence of Food-Simulating Solutions and Surface Finish on Susceptibility to Staining of Aesthetic Restorative Materials.” Journal of Dentistry, vol. 33, no. 5, 2005, pp. 389-398. https://doi.org/10.1016/j.jdent.2004. 10.018.
7. Patel, S.B. et al. “The Effect of Surface Finishing and Storage Solutions on the Color Stability of Resin-Based Composites.” Journal of the American Dental Association, vol. 135, no. 5, 2004, pp. 587-594. https://doi.org/10.14219/jada.archive. 2004.0246.
8. Vichi, A. et al. “Color and Opacity Variations in Three Different Resin-Based Composite Products after Water Aging.” Dental Materials, vol. 20, no. 6, 2004, pp. 530-534. https://doi.org/10.1016/j.dental.2002.11.001.
9. Asmussen, E. and A. Peutzfeldt. “Influence of UEDMA, BisGMA and TEGDMA on Selected Mechanical Properties of Experimental Resin Composites.” Dental Materials, vol. 14, no. 1, 1998, pp. 51-56. https://doi.org/10.1016/S0109-5641(98)00009-8.
10. Munoz, C.A. et al. “Effect of Pre-Heating on Depth of Cure and Surface Hardness of Light-Polymerized Resin Composites.” American Journal of Dentistry, vol. 21, no. 4, 2008, pp. 215-222.
11. Turssi, C.P. et al. “Abrasive Wear of Resin Composites as Related to Finishing and Polishing Procedures.” Dental Materials, vol. 21, no. 7, 2005, pp. 641-648. https://doi. org/10.1016/j.dental.2004.10.011.
12. Erdemir, U. et al. “Effects of Polishing Systems on the Surface Roughness of Tooth-Colored Materials.” Journal of Dental Sciences, vol. 8, no. 2, 2013, pp. 138-144. https://doi. org/10.1016/j.jds.2012.12.003.
13. Imamura, S. et al. “Effect of Filler Type and Polishing on the Discoloration of Composite Resin Artificial Teeth.” Dental Materials Journal, vol. 27, no. 6, 2008, pp. 802-808. https:// doi.org/10.4012/dmj.27.802.
14. Sideridou, I.D. et al. “Physical Properties of Current Dental Nanohybrid and Nanofill Light-Cured Resin Composites.” Dental Materials, vol. 27, no. 6, 2011, pp. 598-607. https:// doi.org/10.1016/j.dental.2011.02.015.
15. Mitra, S.B. et al. “An Application of Nanotechnology in Advanced Dental Materials.” Journal of the American Dental Association, vol. 134, no. 10, 2003, pp. 1382-1390. https:// doi.org/10.14219/jada.archive.2003.0054.
16. Ozturk, E. et al. “Effect of Resin Shades on Opacity of Nanohybrid Composites and Color Masking Ability Using Different Backgrounds.” European Journal of Dentistry, vol. 7, suppl. 1, 2013, pp. S55-S62. https://doi.org/10.4103/1305-7456.119074.
17. Khoo, H.E. et al. “Anthocyanidins and Anthocyanins: Colored Pigments as Food, Pharmaceutical Ingredients and the Potential Health Benefits.” Food & Nutrition Research, vol. 61, no. 1, 2017. https://doi.org/10.1080/16546628.2017. 1361779.
18. Commission Internationale de l’Eclairage. Colorimetry: Official Recommendations of the International Commission on Illumination. 1971.
19. Ruyter, I.E. et al. “Color Stability of Dental Composite Resin Materials for Crown and Bridge Veneers.” Dental Materials, vol. 3, no. 5, 1987, pp. 246-251. https://doi.org/10.1016/S01 09-5641(87)80081-7.
20. Um, C.M. and I.E. Ruyter. “Staining of Resin-Based Veneering Materials with Coffee and Tea.” Quintessence International, vol. 22, no. 5, 1991, pp. 377-386.
21. Guler, A.U. et al. “Effects of Different Drinks on Stainability of Resin Composite Provisional Restorative Materials.” Journal of Prosthetic Dentistry, vol. 94, no. 2, 2005, pp. 118-124. https://doi.org/10.1016/j.prosdent.2005.05.004.
22. Topcu, F.T. et al. “Effects of Different Drinks on Color Stability of Dental Resin Composites.” Journal of Dentistry, vol. 37, no. 2, 2009, pp. 128-132. https://doi.org/10.1016/j. jdent.2008.10.009.
23. Ardu, S. et al. “A Long-Term Laboratory Test on Staining Susceptibility of Esthetic Composite Resin Materials.” Quintessence International, vol. 41, no. 8, 2010, pp. 695-702.
24. Ozturk, E. et al. “Color Stability of Novel Resin Composites and Effects of Staining Solutions.” Journal of Esthetic and Restorative Dentistry, vol. 25, no. 4, 2013, pp. 254-264. https://doi.org/10.1111/jerd.12016.
25. Catelan, A. et al. “Color Stability of Sealed Composite Resin Restorative Materials after Ultraviolet Artificial Aging and Immersion in Staining Solutions.” Journal of Prosthetic Dentistry, vol. 105, no. 4, 2011, pp. 236-241. https://doi.org/ 10.1016/S0022-3913(11)60038-3.
26. Poggio, C. et al. “Color Stability of Esthetic Restorative Materials: A Spectrophotometric Analysis.” Acta Biomaterialia Odontologica Scandinavica, vol. 2, no. 1, 2016, pp. 95-101. https://doi.org/10.1080/23337931.2016. 1217416.
27. Ren, Y.F. et al. “Effects of Common Beverage Colorants on Color Stability of Dental Composite Resins: The Utility of a Thermocycling Stain Challenge Model in Vitro.” Journal of Dentistry, vol. 40, suppl. 1, 2012, pp. e48-e56. https://doi. org/10.1016/j.jdent.2012.04.017.
28. Alandia-Roman, C.C. et al. “Effect of Cigarette Smoke on Color Stability and Surface Roughness of Dental Composites.” Journal of Dentistry, vol. 41, suppl. 3, 2013, pp. e73-e79. https://doi.org/10.1016/j.jdent.2012.12.004.
29. Ardu, S. et al. “Color Stability of Contemporary Composite Resins.” Journal of Esthetic and Restorative Dentistry, vol. 23, no. 3, 2011, pp. 174-185. https://doi.org/10.1111/j.1708-8240.2011.00415.x.
30. Kobayashi, S. et al. “Discoloration Effects of Common Beverages on Composite Resins.” Odontology, vol. 106, no. 3, 2018, pp. 315-322. https://doi.org/10.1007/s10266-018-0337-3.