To maintain oral hygiene, toothbrushes and toothpastes are the most commonly used tools. An ideal toothpaste is expected to clean and remove external stains without damaging enamel and restorations. However, it is important to note that different properties added to these tools can cause permanent changes to teeth and restorations [20, 21]. This research compared the effects of four different toothpastes, which containes silica, blue covarin, activated carbon, and one conventional, on the surface roughness and colour values of CAD-CAM materials,. The null hypotheses were rejected as significant changes observed in roughness and colour of the materials.
All samples were treated with the same surface finishing procedures to eliminate surface irregularities and ensure standardisation. Literature have shown that surface roughness values exceeding 0.2 µm lead to biofilm formation on restoration surfaces, increased adsorption of colorant particles and material wear [22, 23]. A study reported that surface roughness values of 0.5 µm and above could be differentiated by the individual's tongue [24]. In this study, we obtained similar surface roughness values in all samples (CS = 0.28 ± 0.09, CD = 0.26 ± 0.07, CDC = 0.17 ± 0.04). Siam et al. [25] conducted a study on zirconium-reinforced lithium silicate specimens (Celtra Duo) which were divided into two subgroups, glazed and polished. No statistically significant difference was found between the two surfaces (p = 0.8204) when the surface roughness of the specimens was measured using an optical profilometer. Likewise, the surface roughness values of CD and CDC samples before brushing were not statistically different in our study.
Abrasions on the surface of restorations are a crucial factor affecting their clinical lifespan. Different ageing protocols are used for long-term evaluation of materials. The most commonly preferred ones are thermal cycling, mastication cycles and brushing simulations [26]. This study, observed an increase in surface roughness values for all materials after the ageing process with brushing. Similarly, Kim et al. [27], in their study investigating the surface properties of different CAD-CAM blocks, reported an increase in surface roughness values for Cerasmart and Celtra Duo blocks after thermal ageing. In contrast, Picolo et al. [28] found no significant difference in surface roughness after brushing for lithium silicate glass ceramics reinforced with zirconia. This variation is believed to be caused by differences in toothpaste types and dilution ratios, as well as the use of a soft toothbrush for brushing.
In a study evaluating the surface roughness of chairside CAD-CAM materials after brushing, the Cerasmart group showed the lowest surface roughness values before brushing and the highest roughness values after brushing when compared to leucite-based glass ceramic and polymer infiltrated glass ceramic blocks [29]. Sugiyama et al. [30] investigated the surface roughness of CAD-CAM blocks with different contents after mechanical cleaning. They found that the roughness values of composite blocks (Shofu Block) were higher than those of lithium silicate blocks (Celtra DUO). In our study, the surface roughness values of the CS group specimens brushed with Curaprox™ and Opalescence™ were significantly different from CD and CDC samples (p < 0.008). It is believed that this variation is a result of the lower hardness of resin blocks in comparison to ceramic-based materials.
When examining the post-brushing colour change values, a significant difference was found between the CS and CDC groups (p = 0.010, p = 0.018, respectively), while no difference was observed in the CD group (p = 0.669). Pouranfar et al. [5] investigated the colour change between ceramic polymer (Cerasmart, VITA Enamic) and lithium disilicate (IPS E-max CAD) after 12 years of brushing. Our results are consistent with their finding that the color change of ceramic polymers was greater. The amount of staining depends on the stain resistance of the material and the bleaching agent content. The higher degree of colour change in the CS group, compared to the CD group, can be attributed to the material's resin content. The reason for the CDC group's higher colour change than the CD group is believed to be due to the abrasion of the glaze material and the material's greater susceptibility to external factors.
In recent years, various teeth whitening products, including toothpaste and mouthwash, have been introduced to markets and pharmacies. The effectiveness and potential harms of these non-prescripted products are not yet clear. According to a study, toothpastes containing silica can erode the resin matrix, resulting in increased surface roughness. However, toothpastes with hydrated silica have lower abrasive properties [31]. The toothpastes included in this research contain different types of silica. Opalescence™ toothpaste contains silica, while Signal™ White Now, Colgate™ Max Fresh, and Curaprox™ Black in White toothpastes contain hydrated silica. The brushing process demonstrated a significant increase in the roughness values of CS samples brushed with Opalescence™, which may be attributed to its silica content.
Activated charcoal is added to toothpastes to enhance their whitening properties by absorbing coloring substances. While some studies suggest that it can effectively clean teeth due to its porous and large surface area, the literature on this topic is limited [32–34]. Palandi et al. [32] reported that charcoal-containing products do not have a whitening effect and may cause negative changes in enamel topography in their brushing study with bovine teeth. Thomas et al. [33] stated that charcoal-containing pastes showed lower whitening and higher abrasion than other alternatives. A study investigated the colour and surface properties of composite resin toothpastes containing whitening agents. The results showed that toothpastes containing activated carbon exhibited no statistical difference in colour change compared to conventional toothpastes [34]. Our study found that charcoal-containing pastes had similarly low whitening efficiency, but were the only group that caused a significant difference in surface roughness change values compared to other paste types.
The use of blue covarine in toothpastes creates a fine, translucent appearance on tooth enamel, reducing the yellowish color and making teeth appear whiter and brighter by shifting the shade on the scale towards white [35]. However, despite some studies in the literature not supporting this activity, no study on CAD-CAM ceramics has been found. A study was performed to examine the impact of whitening toothpastes and mouthwashes on bovine dentin. The study found that blue covarine content resulted in similar color change values to traditional fluoride toothpastes [36]. The results also showed that Signal™ White Now produced similar color changes to conventional toothpaste in all three material groups.
The scanning electron microscope (SEM) images confirmed the changes measured with the profilometer. The evaluation of these images revealed that brushing teeth with abrasive toothpastes caused more changes in surface morphology than conventional toothpaste. The CS samples brushed with Opalescence™ and Curaprox™ toothpastes showed deeper and more prominent lines.
Some of the limitations of this research include the inability to imitate the thermal and pH cycles of the mouth and the inability to reflect nutritional habits, saliva proteins and enzymes in the experiments. In addition, the fact that the samples have flat surfaces devoid of anatomical pits and fissures, as in the mouth, prevents the polishing and brushing processes from being fully simulated. Further studies in close-to-oral conditions with different toothpaste products and CAD-CAM materials will increase the accuracy of the results.