Composite Resins with Different Polishing Types Immersed in Two Pigmenting Solutions: An in Vitro Study

ABSTRACT

Objective:  To compare the colour variation of the composite resins Forma, Z350XT, and Vittra APS at different exposure times in tea and chicha de jora solutions, and with different polishing techniques.

Material and Methods:  In this in vitro experimental study, the sample consisted of 90 resin discs, 30 of the Forma brand [15 with CP and 15 with CPG, divided into 3 subgroups of 5 each: Tea subgroup, Chicha de Jora subgroup, and Control group (saline solution)], 30 of the Filtek Z350 XT (15 with CP and 15 with CPG), and 30 of the Vittra APS brand (15 with CP and 15 with CPG), similarly divided into 3 subgroups.

Results:  A significant colour variation was found in the Forma, Z350 XT, and Vittra APS resins with the polishing techniques, pigmenting solutions, and at different times: 7 days (p<0.05), 14 days (p<0.05), 21 days (p<0.05), and 28 days (p<0.05).

Conclusion:  All resins showed colour changes due to the pigments, with Z350 XT showing the least variation in tea and chicha de jora with the Sof-Lex disc technique plus glycerine at 7, 14, 21, and 28 days.

Keywords:
Composite Resins; Fermented Beverages; Glycerol; In Vitro Techniques.

Introduction

The increasing demand for dental aesthetics has driven the development of dental restorations that closely mimic natural tooth color [¹]. These advancements have been facilitated by technological progress and contemporary scientific knowledge in dentistry, transforming clinical practice toward greater precision and effectiveness in replicating natural features in dental restorations [²].

In recent years, dental professionals have increasingly turned to resin-based restorative materials due to their ability to blend with natural tooth color, meeting patients' aesthetic expectations [³]. Finishing and polishing procedures are crucial, as they shape and refine the three-dimensional texture of the restoration, closely emulating the characteristics of natural teeth [⁴]. In addition to enhancing aesthetics, these procedures contribute to oral health by preventing discoloration, often caused by extrinsic stains on teeth, which can negatively impact the appearance of the smile [⁵].

There has been a significant shift in recent years among the population towards caring for their oral health and aesthetics, necessitating that dental professionals be prepared to meet this demand [⁶]. Dental resins (dental composites) are synthetic materials used in teeth with caries or deterioration, available in various shades that match dental tissues, resulting in pleasing, aesthetic restorations [⁷,⁸].

Composite resins are cutting-edge materials in restorative treatments due to their excellent mimicry and ease of manipulation, resulting in highly aesthetic outcomes. However, colour stability is a major issue, as it is an undesired effect in resins exposed to various pigmenting substances [⁹].

In our region, it is common to consume beverages such as tea, coffee, soft drinks, and fermented drinks like chicha de jora. These are the most consumed beverages in the Cajamarca region and northern Peru. This iconic Peruvian beverage has been cherished since Incan times and is still prepared artisanally [¹⁰]. Camellia Sinensis tea (containing theine) is prepared with boiling water [¹¹]. Previous studies evaluating colour stability have shown that beverages such as coffee, tea, red wine, and soft drinks can cause varying degrees of pigmentation in resins [¹²].

Composite resins provide high translucency and are used in both the anterior and posterior parts of the mouth. The inclusion of filler particles in the matrix enhances their mechanical properties: the smaller the filler particles, the lower the modulus of elasticity [¹³].

Upon completing restorations, excess material is removed with diamond and carbide burs, rubber tips and cups, abrasive strips, aluminium-coated discs, polishing pastes, and light-curing sealants. Finishing and polishing reduce exogenous discolouration of restorations by preventing plaque biofilm accumulation, thus providing shine, aesthetics, and functionality [¹⁴,¹⁵]. However, all composites have some disadvantages, such as degree of polymerisation and contraction, marginal colour loss, microleakage, and pigmentation [¹⁶,¹⁷].

This research provides the dental community with theoretical and practical knowledge from an in vitro study comparing the colour of three commercial composite resins when exposed to commonly consumed beverages, given that composite colour stability may vary due to other factors. The methodological justification involves using calibrated equipment, such as the digital spectrophotometer (VITA Easy Shade), which quantitatively evaluates the luminosity and opacity of the resins and can be employed in future similar investigations.

Therefore, the objective of this study was to compare the colour variation of the three different composite resins at different exposure times to Tea and Chicha de jora with different polishing techniques in vitro.

Material and Methods

Study Design and Ethical Approval

The study was experimental, longitudinal, prospective, and analytical. Authorisation was obtained from the Ethics Committee of the Professional School of Stomatology at Cesar Vallejo University (No. 0143-2024-/UCV/P). However, as it was a laboratory analysis, biosecurity protocols were followed, and proper waste management procedures were implemented.

Sampling and Sample Size

The sample consisted of 90 composite resin discs, divided as follows: 30 from Forma (Ultradent Products Inc., South Jordan, UT, USA) (15 with conventional polishing (CP) and 15 with conventional polishing plus glycerine (CPG)), 30 from Filtek Z350XT (3M ESPE, St. Paul, MN, USA) (15 with CP and 15 with CPG), and 30 from Vittra APS (FGM Dental Group, Joinville, SC, Brazil) (15 with CP and 15 with CPG). The sampling was non-probabilistic and convenience-based.

Inclusion and Exclusion Criteria

Resin discs measuring 8 mm in diameter and 2 mm in height from the Forma, Vittra APS, and Filtek Z350XT brands were included. These discs were manually fabricated using the incremental technique or according to the manufacturer's recommendations for the polymerisation process. Discs with rough surfaces that could affect the study were excluded, as were those of a different size than those selected for the research, and resin discs that did not comply with the soaking times in the pigmenting substances.

Procedure and Technique

Access was granted to the laboratory facilities at Cesar Vallejo University, Piura branch, where the resin discs were fabricated, and colour measurements were taken using the VITA (Easy Shade) digital spectrophotometer.

Resin discs of A2 enamel colour from the Forma, Vittra APS, and Filtek Z350XT brands were fabricated in circular polycarbonate moulds measuring 8 mm in diameter and 2 mm in height using the incremental technique to avoid polymerisation distortion. The discs were placed on a glass slide to remove excess material and form smooth surfaces. Polymerisation was then performed using a Woodpecker LED.D lamp with a wavelength range of 440 nm to 490 nm and an intensity of 1000 mW to 1700 mW/cm², applying light curing to the surface of each disc in 20-second intervals.

Polishing of the resin discs was performed after 24 hours. Initially, excess resin was removed with a 12-blade carbide bur using an NSK PANA-MAX (NSK-Nakanishi Inc., Kanuma, Tochigi, Japan) push-button handpiece. Polishing was performed with the Sof-Lex discs (3M ESPE, St. Paul, MN, USA) polishing system using an NSK PANA-MAX EX 203 (NSK-Nakanishi Inc., Kanuma, Tochigi, Japan) contra-angle and micromotor. The discs were then rinsed and dried with a triple syringe, and the Sof-Lex disc sequence was followed. The discs were polished with medium discs at 1000 rpm for 10 seconds, followed by fine and extra-fine discs at 30,000 rpm for 15 seconds in a dry field.

The discs were then stored in saline solution for 24 hours at 37 °C to simulate oral cavity humidity in a POL-EKO incubator (POL-EKO-APARATURA, Wodzisław Śląski, Poland). Subsequently, the initial colour measurements of the resin discs from each group were taken with the VITA (Easy Shade) digital spectrophotometer (VITA Zahnfabrik H. Rauter GmbH & Co. KG, Bad Säckingen, Germany) before immersion in the pigmenting substances. Each disc was randomly removed with tweezers from the jars containing the pigmenting substances (chicha de jora and tea) in a proportional number for each resin brand and then hermetically sealed. The discs were removed only for colour measurements at 7, 14, 21, and 28 days.

Statistical Analysis

For data analysis, SPSS (Statistical Package for the Social Sciences Inc., IBM, NY, USA) version 28.0 was used. For descriptive statistics, the mean, median, standard deviation, and interquartile range were calculated. For inferential statistics, normality and homoscedasticity of the data were checked using the Shapiro-Wilk test and Levene’s test, respectively. According to these results, the data did not show normality, so the nonparametric Mann-Whitney U test and the Kruskal-Wallis test were used to compare two and three independent groups, respectively. To compare more than two paired measures, the Friedman test was used. Additionally, the Bonferroni post hoc test was applied if significant differences were detected in both the Kruskal-Wallis and Friedman tests. The level of significance was set at p<0.05.

Results

When comparing colour variation (∆E) after the composite resins Forma, Filtek, and Vittra, with different polishing techniques, were immersed in tea, chicha de jora, and saline solution (control), significant differences were observed at 7 days (p<0.05), 14 days (p<0.05), 21 days (p<0.05), and 28 days (p<0.05) between the pigmenting beverages and the saline solution. However, no significant differences were observed between chicha de jora and tea at the various time points for the three composite resins, regardless of the polishing technique used (p>0.05).

Additionally, it was noted that both chicha de jora and tea significantly altered the colour of the three composite resins with different polishing techniques over time (p<0.05), with these values exceeding the clinically acceptable threshold (∆E >3.3) (Table 1).

Table 1
Comparison of Colour Variation (∆E) over exposure time to different beverages, according to the type of composite resin with different polishing techniques.

Composite Resin	Polishing	Beverage	Day 7				Day 14				Day 21				Day 28				p-value**
			Mean	Median	IQR	p-value*	Mean	Median	IQR	p-value*	Mean	Median	IQR	p-value*	Mean	Median	IQR	p-value*
Forma	S	T	1.58	1.41 A	1.17	0.006*	6.77	6.70 A, B	1.03	0.002*	7.27	7.27 A	0.1	0.005*	7.62	7.87 A	1.47	0.006*	0.011**
		CJ	1.27	1.16 A, B	1.26		8.88	8.86 A	0.73		5.92	6.07 A, B	1.96		6.38	6.58 A, B	2.28		0.003**
		Control	0	0.00 B	0		1.36	1.16 B	1.28		1.03	1.11 B	0.22		1.2	0.93 B	0.68		0.026**
	S + G	T	4.83	5.46 A	2.45	0.002*	9.36	9.31 A	1.7	0.002*	7.95	7.42 A	1.48	0.005*	8.16	7.49 A	1.77	0.002*	0.007**
		CJ	2.1	2.15 A, B	0.31		5.66	5.61 A, B	1.12		4.65	2.60 A, B	5.17		3.2	3.00 A, B	0.56		0.014**
		Control	0	0.00 B	0		0.83	0.83 B	0.43		0.73	0.74 B	0.73		0.9	1.01 B	0.43		0.019**
Filtek Z350 XT	S	T	5.76	6.94 A	3.03	0.004*	12.89	12.50 A	0.17	0.007*	16.55	16.26 A	3.15	0.002*	17.7	18.78 A	5.19	0.002*	0.003**
		CJ	3.92	3.39 A, B	2.74		12.25	12.24 A, B	1.45		10.21	10.49 A, B	2.97		7.91	7.40 A, B	1.45		0.003**
		Control	0	0.00 B	0		0.6	0.58 B	0.29		0.49	0.46 B	0.33		0.46	0.46 B	0.29		0.014**
	S + G	T	1.75	1.83 A, B	1.68	0.002*	7.46	6.07 A, B	7.52	0.008*	18.83	17.52 A	21.41	0.004*	10.09	10.15 A	4.61	0.003*	0.011**
		CJ	4.16	4.08 A	1.07		8.74	8.65 A	1.74		6.16	6.13 A, B	2.21		6.52	6.32 A, B	2.63		0.004**
		Control	0.06	0.00 B	0.15		0.76	0.65 B	0.63		0.5	0.25 B	0.78		0.55	0.33 B	0.71		0.004**
Vittra APS	S	T	14.67	15.22 A	4.71	0.002*	24.18	23.84 A	7.35	0.002*	30.26	30.53 A	10.97	0.002*	30.96	30.85 A	9.12	0.007*	0.003**
		CJ	3.59	3.63 A, B	1.11		5.91	5.96 A, B	0.48		5.86	4.45 A, B	6.09		3.53	3.17 A, B	3.42		0.041**
		Control	0	0.00 B	0		0.88	1.01 B	0.74		0.7	0.65 B	0.61		2.21	1.20 B	3.19		0.003**
	S + G	T	1.18	1.20 A, B	0.37	0.002*	9.16	7.53 A, B	6.54	0.008*	16.13	16.07 A	10.81	0.006*	9.7	10.04 A	5.45	0.008*	0.004**
		CJ	3.68	4.17 A	1.49		10.99	9.96 A	3.8		11.82	11.47 A, B	1.18		7.93	8.22 A, B	6.5		0.012**
		Control	0	0.00 B	0		0.59	0.51 B	0.75		0.33	0.42 B	0.25		0.4	0.44 B	0.43		0.007**

• IQR: Interquartile Range;
• ^*
  Based on the Kruskal-Wallis test;
• ^**
  Based on the Friedman test, p<0.05 (significant differences); A and B: different letters in each column of the median indicate significant differences (p<0.05) based on the Bonferroni post hoc test. S: Polishing with 4-step Sof-Lex discs; S+G: Polishing with 4-step Sof-Lex discs + Glycerin; T: Tea beverage; CJ: Chicha de Jora beverage.

Furthermore, it was evident that only the Vittra composite resin immersed in tea and chicha de jora did not show significant colour variation (∆E) under both polishing techniques at all evaluated times (p>0.05). In contrast, the Forma resin polished with Sof-Lex discs and glycerine showed significantly greater colour variation (∆E) compared to the same resin polished without glycerine at different immersion times in tea (p<0.05). However, when this resin was immersed in chicha de jora, the greatest significant variation was observed in those polished without glycerine (p<0.05). Finally, regarding the Filtek resin, the most significant variation across immersion times, both in tea and chicha de jora, was observed in those polished without glycerine (p<0.05) (Table 2).

Table 2
Comparison of the Colour Variation (∆E) of each composite resin with different polishing techniques, at different times of immersion.

Beverage	Composite Resin	Polishing	Day 7			Day 14			Day 21			Day 28
			Median	IQR	p-value*	Median	IQR	p-value*	Median	IQR	p-value*	Median	IQR	p-value*
Tea	Forma	S	1.41	1.17	0.016*	6.70	1.03	0.008*	7.27	0.10	0.016*	7.87	1.47	0.548
		S + G	5.46	2.45		9.31	1.7		7.42	1.48		7.49	1.77
	Filtek Z350 XT	S	6.94	3.03	0.151	12.50	0.17	0.008*	16.26	3.15	0.31	18.78	5.19	0.008*
		S + G	1.83	1.68		6.07	7.52		17.52	21.41		10.15	4.61
	Vittra APS	S	15.22	4.71	1	23.84	7.35	0.222	30.53	10.97	0.31	30.85	9.12	0.548
		S + G	1.20	0.37		7.53	6.54		16.07	10.81		10.04	5.45
Chicha de Jora	Forma	S	1.16	1.26	0.016*	8.86	0.73	0.151	6.07	1.96	1	6.58	2.28	0.016*
		S + G	2.15	0.31		5.61	1.12		2.60	5.17		3.0	0.56
	Filtek Z350 XT	S	3.39	2.74	0.548	12.24	1.45	0.008*	10.49	2.97	0.008*	7.40	1.45	0.222
		S + G	4.08	1.07		8.65	1.74		6.13	2.21		6.32	2.63
	Vittra APS	S	3.63	1.11	0.31	5.96	0.48	0.69	4.45	6.09	0.548	3.17	3.42	1
		S + G	4.17	1.49		9.96	3.8		11.47	1.18		8.22	6.50
Control	Forma	S	0	0	0.008*	1.16	1.28	0.008*	1.11	0.22	0.016*	0.93	0.68	0.008*
		S + G	0	0		0.83	0.43		0.74	0.73		1.01	0.43
	Filtek Z350 XT	S	0	0	0.69	0.58	0.29	0.008*	0.46	0.33	0.032*	0.46	0.29	0.056
		S + G	0	0.15		0.65	0.63		0.25	0.78		0.33	0.71
	Vittra APS	S	0	0	1	1.01	0.74	0.31	0.65	0.61	0.095	1.20	3.19	0.008*
		S + G	0	0		0.51	0.75		0.42	0.25		0.44	0.43

• IQR: Interquartile Range;
• ^*
  Based on the Mann-Whitney U test, p<0.05 (significant differences); S: Polishing with 4-step Sof-Lex discs; S+G: Polishing with 4-step Sof-Lex discs + Glycerin.

Discussion

This study showed that the Vittra APS resin polished with conventional polishing (CP) exhibited greater colour variation than the Forma and Filtek Z350 resins after immersion for 7, 14, 21, and 28 days in pigmenting substances, chicha de jora, and tea. All three resins, both CP and polished with conventional polishing plus glycerine (CPG), showed significant colour variation (p<0.05) between the pigmenting beverages, chicha de jora and tea, and the saline solution. These findings are consistent with those reported by Allccahuaman et al. [¹⁸], Şişmanoğlu and Sengez [¹⁹], Serin-Kalay [²⁰], and Mederos et al. [²¹]. This could be due to prolonged exposure to these solutions, such as tea and chicha de jora, which alter the colour stability of composite resins.

Our study found that the Filtek Z350 resin exhibited less colour variation when exposed to chicha de jora. The colour change in resin composites could be associated with their differing chemical formulations [²²]. The presence of triethylene glycol dimethacrylate (TEGDMA) in the resin composite composition may increase water absorption and staining rates, leading to hydrolytic degradation or detachment of the filler matrix [²³,²⁴].

The TEGDMA composition in Forma and Filtek Z350 XT resins could explain the clinically unacceptable colour changes observed in these resins at 7, 14, 21, and 28 days when immersed in chicha de jora, considering the small size of the filler particles in Filtek Z350 XT (5-20 nm) and Forma (5-50 nm). The size and distribution of fillers may be related to colour variation, the pH of chicha de jora (3.5 to 4.6), its fermentation over time, and the carbohydrates present in chicha de jora.

These findings are also consistent with those of Christiani et al. [²⁵], who found less colour variation in groups using the Viscovery sealant with other pigments such as coffee. Although coffee was not used in our study, tea was used, which contains 35-45% catechins (at various degrees of polymerisation) and 6% caffeine [²¹]. Due to these components and the presence of water, colour changes in resin composites occur, as water absorption by the polymers softens the matrix components, reducing corrosion resistance and leading to subsequent discolouration [²⁶].

The application of various polishing systems also resulted in colour variation in the Forma, Filtek Z350 XT, and Vittra APS resins, with the Sof-Lex disc polishing system providing the most shine and least roughness. This system is highly effective at forming smooth surfaces that are less susceptible to solubility than those produced by other polishing systems, and is easy to identify, available in four colours, with the darkest being coarser and the ultrafine being lighter [²⁷,²⁸].

Colour variation in resins may be related to surface roughness and integrity, as well as the polishing technique used. During polishing, the detachment of filler particles creates varying degrees of porosity, providing a medium for pigment accumulation and triggering colour changes. Using a sealant creates smooth surfaces by filling in any remaining irregularities. Although a sealant was not used in this study, glycerine was employed to prevent oxygen from entering, thereby reducing pigment infiltration. The spectrophotometer was used to objectively assess colour variation, thereby minimising information bias compared with visual colour assessment [²⁹,³⁰].

As limitations of the study, it must be acknowledged that findings from this in vitro study cannot be fully extrapolated to clinical settings due to various factors affecting the colour stability of restorative materials in the oral cavity, such as the presence of saliva, dental biofilm, and the effect of different foods and beverages. Additionally, prolonged sample immersion may have affected the results. Clinical randomised controlled trials are recommended to reflect the effects of both pigmenting substances in the oral cavity.

Conclusion

The colour of the Forma, Filtek Z350 XT, and Vittra APS resins varied when exposed to pigmenting solutions, with the Z350 XT showing the least colour change when exposed to tea and chicha de jora, using the Sof-Lex discs plus glycerine technique at 7, 14, 21, and 28 days.

• Financial Support
  None.

Data Availability

The data used to support the findings of this study can be made available upon request to the corresponding author.

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Edited by

• Academic Editor:
  Alessandro Leite Cavalcanti

Publication Dates

• Publication in this collection
  17 Apr 2026
• Date of issue
  2026

History

• Received
  10 Jan 2025
• Reviewed
  26 Aug 2025
• Accepted
  02 Sept 2025