Effect of Charcoal Toothpastes on the Microhardness and Surface Roughness of Nano - Filled Composites

Introduction

One of the most significant facial characteristic that influences a person's social and psychological well-being and motivates patients to seek dental care is an appealing smile.¹ A perfect aesthetic appearance is in high demand as people look out for teeth that are white and healthy and resemble their ideal smile.² Various aesthetic materials are now available in the market to meet these demands such as Glass ionomer cements, Composite resins, Ceramics, and Zirconia. However, composite resin is the preferred material for direct restorations because of properties such as excellent initial aesthetics, good adhesive bonding, high compressive strength, and unique formulations.³

Resin composites are composed of Urethane dimethacrylate (UDMA), or semi-crystalline polyceram, BISGMA (bisphenol A glycidyl methacrylate), an inorganic filler like silicon dioxide (silica), and a coupling agent like silane. Based on the type of filler particle and particle size, composites can be of different types like the macrofilled, microfilled, hybrid, nanofilled, bulk filled, and nano hybrid.

Material elements that affect longevity include the type of photoinitiator system, deterioration of the resin matrix, and inadequate irradiation of the light curing unit utilised for polymerization. In addition, there are other factors that play a part in the ecology of the oral cavity, such as the salivary buffering effect, exposure to food and drink, and certain external factors like brushing. These factors can make the restoration susceptible to staining or discoloration, eventually leading to restoration wear out.⁴

Composites with improved characteristics have been introduced to address these issues. One such material is nanocomposite. The nanocomposites have distinct nanoparticles of sizes ranging from 40 to 50 nm as the dispersed phase along with milled glass fiber. In comparison to hybrid composite, they show enhanced mechanical strength and surface finish.⁵

In today’s time, toothpaste with activated charcoal has gained immense popularity. This is because activated charcoal has high porosity and a large surface area (>1000 m² /g) due to which they can actively absorb stains by binding and removing them, thus preventing discoloration of teeth.⁶

Toothbrushing is a daily activity that can alter the smoothness and roughness of the resin composite. The reason for this is that the dentifrice's abrasiveness can cause the resin composite to become more vulnerable to surface roughness. Additionally, the bristles from the toothbrush may potentially harm the composite restoration and its interface with the tooth surface. Furthermore, the charcoal particles can remain in the sulcular gingiva, accumulate in deep pits and fissures, and cause surface or marginal restoration flaws. All of this compromises the aesthetics of the tooth-coloured restorations.⁷

The current study's null hypothesis asserts that exposure to charcoal toothpaste has no influence on the nanohardness and surface roughness of nano-filled composite materials.

Thus, comparing the impact of two charcoal toothpastes on the surface roughness and microhardness of the composite material was the goal of this study.

Materials and Methods

Two different composite resins, Z250 (Filtek Z250 XT) and bulk- fill (Tetric-N - Ceram) all in A3 shade were used. Table 1 lists the composite resins that were employed in this investigation.

Three dentifrices, Colgate total, Colgate total charcoal deep clean, and Healthvit activated charcoal were used and are listed in Table 2

Sample size estimation

Referencing data (mean and SD) from a prior study (Bragança GF et al., 2022) and taking into account α = 0.05, β = 0.2, and power = 80%, the study included a sample size of 30 per group for microhardness and seven per group for surface hardness.

Specimen preparation

Two distinct nano-filled composites were used to create a total of 132 disc-shaped samples.

A polylactic acid (PLA) mould of 8 mm width and 2 mm height was used to manufacture the specimens in two steps. For forty seconds, the Turbo bee cool light curing unit was turned on after the first increment was set. The second placement phase involved placing a mylar strip on the composite resin surface. A glass slab was placed on the mould's surface once the specimens had solidified. A water irrigation system was used to polish the specimens using silicon carbide paper. To ensure full composite polymerization, the samples were removed from the moulds and placed in distilled water at 37˚C for a whole day prior to brushing.⁸

Baseline analysis (Sample distribution)

Specimens were randomly grouped into three [n= 30] for microhardness and for surface roughness [n=7].

Group 1: Control group - brushed with Colgate total

Group 2: Brushed with Colgate total charcoal

Group 3: Brushed with Healthvit activated charcoal

Abrasive challenge

The samples were brushed with an electric toothbrush for seven days. Every day, the toothbrush head was loaded with a pea-sized amount of toothpaste from each group. It was then held up to the specimen and brushed for 30 seconds. The samples were set up on a raised surface that was maintained on a platform above a table to keep them steady while they were being brushed. After each brushing cycle, each sample was rinsed with running tap water to remove any toothpaste residue, and it was then kept in distilled water at 37˚C until the analysis was finished.⁹

Microhardness testing

Forty five samples from each composite resin were subsequently divided into three groups based on the dentifrice (n=30). The specimens in this study were tested for microhardness using a Vickers microhardness tester of 136˚ pyramidal diamond indent at room temperature with a weight of 10N. Using a precisely calibrated test force, the indenter was driven into the sample for a predetermined dwell period of 15 seconds. The two diagonals of the surface indent were measured optically to establish the indent's size. The test forces divided by the indent's surface area yielded the VHN (Vickers hardness number). The two diagonals were averaged to determine the Vickers microhardness values.³

Surface roughness testing

Of the eleven specimens from each composite resin, three groups were further divided based on the dentifrices (n=7). Using a portable surface profile metre with a contact stylus gauge, the sample's surface roughness was measured. The device estimates the depth of the surrounding peaks using a pointed, cone-shaped probe in order to determine the surface roughness. The device was calibrated to zero point for each sample. When a beep sound was heard, a value displays on the screen. The device was then moved to another place, and the profile was recognized by measuring the difference in the height between the profile minimum and maximum (valley-to-peak). For every sample, three separate points were recorded at each point.³

Statistical analysis

Shapiro-Wilk tests were employed to evaluate the normality of data. To analyze the gathered data, a social science statistical program (SPSS version 22, IBM New York, USA) was employed. The surface roughness and microhardness mean and standard deviation were compared before and after the exposure by repeated measures ANOVA and the paired "t" test.

Results

Figure 1 shows the mean baseline and post-exposure microhardness values (SD of microhardness) of the composite resins. The microhardness of composite resins varied substantially from the beginning. In comparison to Filtex Z 250 XT, Tetric-N-Ceram displayed greater baseline values. The values indicated that Healthvit activated charcoal toothpaste showed decreased microhardness followed by Colgate total charcoal deep clean toothpaste, whereas Colgate total toothpaste showed the least change in microhardness. When the studied samples were brushed with Colgate total charcoal deep clean and Healthvit activated charcoal toothpastes, there was a significant variation (P <0.05) in the microhardness of the samples. In contrast to Tetric-N-Ceram, Filtek Z250 XT showed the least amount of microhardness change after a seven-day brushing routine with all three dentifrices. Nevertheless, brushing with Colgate total toothpaste did not result in a significant difference amongst the groups.

Figure 2 shows mean baseline and post-exposure surface roughness values (SD of surface roughness) of the composite resins. Each of the composite resins had considerable variations in surface roughness from early on. Tetric- N -Ceram showed a higher baseline value when compared with Filtek Z250 XT. The values indicated that Colgate total charcoal deep clean resulted in increased surface roughness followed by Healthvit activated charcoal. Whereas Colgate total showed the least increase in surface roughness. There was a significant difference among the tested samples when brushed with Colgate charcoal deep clean and Healthvit-activated charcoal toothpaste (P <0.05), whereas brushing with Colgate total toothpaste did not create a significant change in surface roughness among the groups. Filtek Z 250 XT showed the least increase in surface roughness after brushing with all the three dentifrices for seven days when compared to Tetric- N- Ceram.

Discussion

In today’s world, people are placing a high value on their aesthetics, especially their smile. Moreover, the color of a person’s teeth and smile has an important influence on their emotional condition. To remove stains from their teeth and get a more radiant smile, many people use abrasive toothpastes at home. However, using these toothpastes over an aesthetic restoration may conflict with the benefits it might provide as a whitening agent.¹

The purpose of this research was to compare the microhardness and surface roughness of a composite resin restoration brushed with toothpaste containing charcoal to see if there are any changes (if any) in these parameters.

In the current study, a powered toothbrush was used to standardize the brushing pattern of strokes. According to a study by Zarrrani et al. (2017), the hardness of the toothbrush can change the surface properties of tooth-colored restorative materials. To prevent any unfavourable effects, a toothbrush with gentle bristles was used.⁴

Instead of using artificial saliva, which could influence the surface qualities and build a protective layer on the composite, the prepared samples were submerged and preserved in distilled water.¹

The microhardness of the test material was determined using the VHN indentation test because its calculations are not affected by the indenter's size. Furthermore, it is recommended and frequently utilised for assessing dental materials' macro- and microhardness (Bahbeshi et al., 2020).⁶

The degree of monomer to polymer conversion, shape and size, and volume of the filler particle, and composite matrix composition, all affect surface properties.

In this study, the microhardness of nanofilled composite resin brushed with charcoal toothpastes had more decreased values. This is also in accordance with the study by Jin J et al. which explained the fact that due to the difference in the microhardness of the composite, there will be a difference in the microhardness of the material. Among the composites, Tetric - N - Ceram showed decreased microhardness when compared to Z250 XT as the latter had 68% volume of fillers and BISGMA, UDMA, ethoxylated bisphenol A dimethacrylate (BISEMA), polyethylene glycol dimethacrylate (PEGDMA) and triethylene glycol dimethacrylate (TEGDMA) as its monomers.³

Similarly, discs brushed with Healthvit activated charcoal (5.98) showed decreased microhardness when compared with discs brushed with Colgate total charcoal deep clean toothpaste (7.44). This can be attributed to the fact that Colgate toothpaste contained charcoal powder as one of its ingredients.

In this investigation, surface roughness was measured, and both composites exposed to two different charcoal toothpastes have shown a significant increase in surface roughness compared to the discs subjected to the control toothpaste.⁵

Larger projecting filler particles that are present in the matrix and are exposed as a result of surrounding fillers being displaced by toothbrush abrasion are responsible for surface roughness (Ra). This results in the formation and spread of microcracks, which separate the filler particles and raise surface roughness. This result is consistent with the research findings of Oliveria et al. and Monteiro et al.⁷

In the current study, Tetric- N-Ceram showed increased surface roughness in comparison to Filtek Z250 XT, when brushed with charcoal-containing toothpastes. This is due to the presence of larger particle size of the fillers (3 microns) in Tetric - N - Ceram as compared to Z250 XT filler size.

Similarly, discs brushed with Colgate total charcoal deep clean (1.07) showed increased surface roughness when compared to discs brushed with Healthvit-activated charcoal toothpaste (0.95). This can be attributed to mica, a component of Colgate toothpaste.

The results of this investigation demonstrated that toothbrush abrasion and dentifrices had varying effects on the surface roughness and decreased microhardness of the nano-filled composite. Overall, the kind of material had a greater impact on the surface characteristics than the kind of dentifrices; the results were comparable in both cases.

Thus, it is advised that the kind of polymer composite material is essential for its long-term surface qualities, and oral factors such as nutrition, dentifrice use, parafunctions, and oral hygiene maintenance will affect the properties of the nano-filled polymer.⁸

The study's limitations are that the tests were conducted in an in vitro environment and that the samples were only brushed for a period of seven days.

Conclusion

Within the parameters of the research, it can be concluded that Tetric - N Ceram showed decreased microhardness and increased surface roughness before and after the dentifrice exposure.

Among the charcoal toothpastes, it was inferred that Colgate charcoal toothpaste increased surface roughness when compared to Healthvit-activated charcoal toothpaste. Whereas in terms of microhardness, Healthvit activated charcoal toothpaste showed decreased microhardness when compared with Colgate charcoal deep clean toothpaste.

An upsurge in surface roughness can lead to plaque accumulation, which can degrade the quality of the restoration. The restoration's ability to withstand fractures could be compromised by its diminished microhardness. To see greater variations in the surface characteristics of the sample, it could be brushed for a longer duration of time.

Conflict of Interest

Nil