Impact of simulated toothbrushing and dentifrice abrasiveness on the surface roughness, gloss, and microhardness of CAD/CAM hybrid restorative materialsAbstract
Aim This study investigated the impact of toothpaste abrasiveness on the surface roughness, gloss, and microhardness of resin composite and CAD/CAM hybrid materials.
Methods A 4x3 factorial design was utilized. The substrate was divided into 4 groups: Vita Enamic Hybrid Ceramic (VE), SHOFU Block HC Hybrid Ceramics (SH), Grandio Blocs CAD/CAM Nano-Hybrid Resin Block (GB), and dental enamel (ESM). The factor abrasiveness of toothpaste presented 3 levels: Low-36 (L), Medium-78 (M), and extra-high-175 (EH). Before and after brushing represented the repetition factor. Specimens (n=15 per group) measuring 6mm X 2mm were prepared and submitted to brushing aging. Surface gloss, roughness, and microhardness were evaluated before and after the brushing simulation. Three-way repeated measures ANOVA and the Tukey’s test (p<0.05) were used for statistical analysis.
Results Gloss measurements indicated a significant increase after brushing ESM with the M toothpaste, while GB material significantly reduced gloss overall. The use of EH increased the roughness of the ESM group only. An increase in microhardness was detected using L and M for VE, while a decrease was observed in ESM specimens.
Conclusion The tested protocols influenced the surface gloss, and the roughness was similar in the groups, except in the ESM group. The EH abrasive dentifrice was the only one that did not demonstrate statistical differences for microhardness in brushing protocols for these materials.
Keywords
Dental restoration wear; Computer-aided design; Toothbrushing; Organically modified ceramics
Introduction
The influence of social media has led to an increase in demand for dental treatments that improve the aesthetics of smiles. Dentists can choose from a variety of restoration materials to suit these objectives. The use of resin materials is highly suggested since they provide predictability, great cosmetic results, a conservative approach, and clinical longevity.
There is also an increasing demand for rapid treatments, and materials made using CAD/CAM technology can be an intriguing alternative. Furthermore, the desire for whiter teeth have driven the pharmaceutical sector to produce a wide array of toothpaste formulas with varying abrasives1-3.
In clinical practice, abrasion is identified as a key factor impacting the aesthetics and lifespan of dental restorations. Abrasion from a variety of factors, including masticatory pressures, eating habits, and dental hygiene routines, presents a considerable obstacle to long-term restorative integrity. The cosmetic component of restorations may be jeopardized since abrasion causes surface roughness, wear, and discoloration, disrupting visual harmony within the oral cavity. Furthermore, the durability of restorations is jeopardized as abrasion gradually diminishes material volume and modifies surface properties, threatening structural integrity and functional lifespan. Understanding the basic processes that promote abrasion and devising measures to limit its deleterious consequences are thus critical in assuring the effectiveness and sustainability of dental restorations in clinical practice4,5.
Materials that may endure abrasion ceramics are the most used therapeutically for indirect restorations due to their great biocompatibility and wear resilience, despite their low tensile strength. Resin-based materials have lately emerged as a therapeutic option because of their mechanical capabilities, optical behavior, and aesthetic qualities. As a result, hybrid CAD/CAM materials offer a mix of ceramic mechanical performance and the incorporation of composites, intending to deliver useful and long-lasting qualities6-8.
To understand the abrasion resistance of materials, surface roughness, and gloss loss are critical indicators that can be used for comparing materials and dental enamel. The gloss of restorative material correlates with surface roughness, with rougher surfaces exhibiting lower brightness and consequently facilitating a greater accumulation of biofilm. Smooth restorative surfaces are vital for clinical success, preventing biofilm buildup and surface staining. Studies indicate that average roughness values exceeding 20 µm can lead to increased biofilm formation9-16.
Considering ceramics might undergo abrasive degradation while using pastes with different abrasiveness, the use of hybrid materials presents some advantages over ceramics, the surface behavior after abrasion with kinds of toothpaste with different abrasiveness is not yet known5.
Thus, this article aims to assess the impact of the abrasiveness of toothpaste on the surface roughness, gloss, and microhardness of composite resins and hybrid resins, commonly used in the fabrication of indirect restorations, in comparison to enamel. The null hypothesis is that the dentifrices do not alter the microhardness, gloss, and roughness of the tested materials.
Material and Methods
This study employed a 4x3 factorial design (with n=15 specimens for group) considering the following experimental factors: Substrate at 4 groups - Hybrid ceramic (Vita Enamic; Vita Zahnfabrik, Bad Säckingen, Germany – VE group), Nano-hybrid resin with fluorine release and recharge (HC SHOFU; Shofu Dental GmbH, Ratingen, Germany – SH group), Hybrid nano-ceramic CAD/CAM Block (Grandio Blocs; VOCO GmbH, Cuxhaven, Germany – GB group), and Dental Enamel (ESM) (table 1); and the toothpaste abrasiveness factor at three levels - B (Low abrasiveness with RDA= 36 - Sensodyne ProNamel; GlaxoSmithKline, Brentford, UK), M (Average abrasiveness with RDA= 78 - Colgate-Palmolive, New York, NY, USA), and XA (Extra-high abrasiveness with RDA = 175 - Colgate Luminous White; Colgate-Palmolive, New York, NY, USA) (table 2). Time was the final factor, with readings before and after. The study assessed roughness, gloss, and microhardness (Figure 1).
Chemical composition of restorative materials. It includes the specific percentages of key components. The information provided outlines the primary ingredients and their respective proportions used in each material.
Chemical composition of toothpastes with different abrasiveness levels. This table provides detailed information on the composition including the percentages of key chemical components and the abrasiveness factor (RDA value) for each toothpaste is also indicated.
The substrates under study were obtained using a 6mm diameter trephine bur and cut into 2mm thickness, resulting in 180 specimens. These were divided into 3 groups for each dentifrice (n=15). Initial readings of gloss, roughness, and microhardness were conducted as described, and the specimens were subjected to a brushing machine with slurry at a 1:3 ratio of deionized water for 100,000 cycles at a frequency of 2Hz and a load of 2N5, that simulates 10 years of clinical wear. Each cycle utilized a different level of abrasiveness, starting with low abrasive dentifrice (B=36), medium (M=78), and extra-high abrasive (XA=175). Following brushing, final readings were taken.
180 discs (6mm diameter, 2mm thick) with n=15 each, were fabricated from CAD/CAM blocks using a custom-made diamond-coated trephine drill bit adapted to a circular cutting machine. Subsequently, they underwent cutting in a serial cutting machine (Labcut 1010; Extec Technologies Inc., Enfield, CT, USA) with diamond discs at a lower velocity and ample cooling. The specimens were polished on both sides using a polisher (Polipan-U; Panambra, São Paulo, Brazil) at 600rpm and silicon carbide sandpaper (Silicon Carbide; Extec Corp, Enfield, CT, USA) with decreasing grain sizes: 15 µm (P1200 - 30 seconds), 10 µm (P2400 - 60 seconds), and 5 µm (P4000 - 120 seconds), all while being continuously cooled with water. Between sandpaper changes and at the end of the polishing procedure, the specimens were cleaned in an ultrasonic bath for 10 minutes.
Gloss analysis was conducted both before and after brushing using a gloss meter (Novo-Curve; Rhopoint Instruments, East Sussex, UK) with a 2x2 mm area and a 60-degree light incidence. The values were expressed in Brightness Units (UB). To prevent ambient light interference, the specimens were shielded with a black opaque plastic cover. Three readings were taken for each specimen, and the average was used for statistical analysis.
Surface roughness was assessed using a contact profilometer (MaxSurf XT 20; Mahr GmbH, Göttingen, Germany), with three scans covering a length of 4.2 mm and spaced 0.25 mm apart. The average surface roughness (Ra) was determined with a cutoff value of 0.25 mm and a scan speed of 0.1 mm/s. Roughness measurements were taken both before and after the brushing simulation.
The Knoop microhardness (KHN) of the specimens was measured using a microdurometer (FM-700; Future-Tech Corp., Tokyo, Japan) with a programmed load of 0.245N applied for 10 seconds. To avoid interference with roughness measurements, three indentation marks were made on the bottom of the specimens, spaced 100 µm apart. The average value was used for statistical analysis.
The brushing procedure was carried out using an automatic brushing machine (MEV2; Odeme Dental Research, Luzerna, Brazil) with 100,000 cycles at a frequency of 2Hz and a brushing load of 2.5N applied by soft brushes with nylon bristles and rounded ends (Ultra Professional; Sanifill, São Paulo, Brazil), following the recommendations of ISO/TR 14569-1:2007. The brushing slurry was prepared by mixing distilled water and toothpaste in a 1:3 ratio. During brushing, a metallic strip with a center hole (2.5 mm high and 1.5 mm wide) was placed on the specimen to ensure that only the central area was brushed.
The results underwent statistical analysis, which included calculating the mean, standard deviation, median, and 1st and 3rd percentiles as part of descriptive statistics. Inferential statistics involved a three-way ANOVA of repeated measurements, with the repeated factor considering the initial and post-brushing measurements. The other two factors considered were the type of material and the type of toothpaste (abrasiveness) used for brushing. Multiple comparisons were conducted using Tukey’s test, and the significance level was set at 5%.
Results
In the initial gloss assessments, specimens from the GB group displayed superior results compared to other materials. However, in the final readings, significant variations in gloss were observed. It was noted that the only toothpaste that increased gloss was Colgate Total 12 when applied within the control group (Table 3).
Data referring to the initial and final gloss analysis, according to the materials and abrasives tested. Data presented as media and standard deviation (SD), or as median and percentiles. Different lowercase letters represent statistical differences analyzed within the columns (between groups at the initial time or within the final time). Capital letters represent differences between the beginning and end of each tested condition.
Regarding roughness, the initial readings of the CAD/CAM hybrid materials and the control group were similar. However, it can be observed in Table 2 that roughness increased in the control group with the use of the highest abrasive toothpaste studied (Table 4).
Data referring to the initial and final rugosity analysis, according to the materials and abrasives tested. Data presented as media and standard deviation (SD), or as median and percentiles. Different lowercase letters represent statistical differences analyzed within the columns (between groups at the initial time or within the final time). Capital letters represent differences between the beginning and end of each tested condition.
In the microhardness tests, both VE and GB materials showed higher initial hardness compared to the SH group. Among these, the EN specimens demonstrated a closer resemblance to the initial hardness of the control group. Following brushing, the VE group’s hardness increased when using Sensodyne Pro-Enamel and Colgate Total 12 toothpastes. However, all toothpastes studied led to a reduction in the hardness of the control group. (Table 5).
Data referring to the initial and final microhardness analysis, according to the materials and abrasives tested. Data presented as media and standard deviation (SD), or as median and percentiles. Different lowercase letters represent statistical differences analyzed within the columns (between groups at the initial time or within the final time). Capital letters represent differences between the beginning and end of each tested condition.
Discussion
Based on the results obtained from the parameters under study, it is feasible to discuss the implications of materials when exposed to varying levels of abrasiveness. Literature extensively explores the existence of microscopic and macroscopic irregularities in restorative materials resulting from brushing, leading to a decline in surface gloss13,17-19.
According to studies conducted by Kim et al.20, there is a correlation between surface roughness and increased biofilm accumulation .The roughness of restorative materials can be influenced by polishing protocols and daily brushing, which patients typically maintain as part of their oral hygiene routines. In this study, only Colgate Luminous White toothpaste, known for its higher abrasiveness, exhibited differences in roughness compared to the control group. Based on the obtained data, the null hypothesis cannot be accepted. This finding raises concerns regarding the long-term durability and performance of dental restorations over extended service periods.
As stated by Prakki et al.18, there exists a correlation between surface roughness and gloss. In the control group, gloss decreased when using low and extra-high abrasive dentifrices but increased with brushing using medium abrasive toothpaste. The only dentifrice that altered enamel roughness was Colgate Luminous White, while microhardness decreased in the enamel with all brushing protocols. This relationship between gloss and roughness was only noticeable in the control group.
The VE group exhibited an increase in microhardness following the use of low and medium-abrasiveness toothpaste. As noted by Ramos et al.19 (2016), there is a need for further studies to determine material properties that can predict the clinical performance of materials used in both direct and indirect restorations. However, this group did not demonstrate differences in gloss or rugosity.
Nevertheless, the gloss and roughness of this material were not affected by the different levels of abrasive protocols, indicating its resilience to abrasive challenges. Based on the results obtained in this study, this CAD/CAM hybrid material (VITA Enamic) could be considered a suitable choice for fabricating indirect restorations.
The SB group showed no alterations following the brushing protocols at different levels of abrasiveness, maintaining consistent values of gloss, roughness, and microhardness after the conducted tests. It is a material comprising 61% compacted nanoparticle-filled zirconium silicate, forming a uniform framework, a characteristic responsible for enhancing greater resistance and high hardness, as observed in these analyses.
Abad-Coronel et al.21, in their comparative study of CAD/CAM material volumetric analysis after dental brushing, demonstrated that the Shofu Block HC material exhibited a high wear rate. In its composition, large silica silicate and zirconia filling particles with a spherical shape and smaller surface area were found, which could be easily worn away during brushing. These characteristics were not observed in the protocols involving the studied dentifrices.
In the GB group, microhardness was not affected by these protocols and surface gloss decreased following brushing (Table 1) with all tested dentifrices. This observation holds significant importance as it may affect patient perception, causing aesthetic discomfort and necessitating more frequent periodic check-ups. However, this correlation wasn’t evident in this study since there was no alteration in the roughness of the tested materials19,21,22.
This change could potentially be attributed to the brushing protocol. These findings can be attributed to the material having a less resilient surface, which may have undergone structural changes due to brushing, resulting in relatively uniform wear and minimal influence on roughness. Additionally, variations in brushing techniques, such as the positioning of bristles, may have contributed to surface irregularities, which can be rationalized by the material’s inherently less resilient surface and the loss of surface structure may provide the most plausible explanation for these findings19,21,22.
In assessing gloss parameters, the GB group showed a significant difference exceeding the limit of perceptibility of 35.7 Gloss Units (GU). This implies that after the brushing procedure, there is a noticeable change in gloss in this material, which is considered noticeable and unacceptable by observers23.
However, with the remaining brushing protocols, the observed changes are noticeable but fall within an acceptable range. Notable changes in gloss are observed in enamel with the studied protocols, and these alterations are considered acceptable23. In terms of roughness, none of the materials exceed a difference of 20 micrometers, a threshold established in the literature for biofilm accumulation20,23-26.
In this study, all the toothpastes tested had a lower influence on abrasion resistance on CAD/CAM hybrid materials. The lack of observed influences in the present study highlights other properties of the materials used. SH presents fluoride in its composition and may enhance the treatment outcomes over time, considering its bioactive behavior. Clinical analyses are recommended to verify if the same parameters observed in this study are repeated in clinical practice and the possible influences of the bioactive properties of some of the tested materials.
In conclusion, the study highlights the significant impact of toothpaste composition on the properties of dental materials, particularly CAD/CAM hybrid material Grandio Blocs. Sensodyne toothpaste, along with other tested toothpaste, was found to reduce gloss and microhardness in Grandio Blocs. Interestingly, while roughness was not affected in most restorative materials, dental enamel showed changes when exposed to the extra-high toothpaste. Despite the superior performance of CAD/CAM materials over dental enamel in the study, these findings emphasize the need for further clinical analyses to validate the observed effects and to better understand the implications for dental practice.
Acknowledgments
We would like to express our profound gratitude to the São Paulo Research Foundation (FAPESP) for the invaluable support provided through the scientific initiation scholarship during our undergraduate studies (Grant #2021/11287-5). This funding was crucial for the development of our research project, enabling us to acquire new knowledge and essential skills for our academic and professional growth.
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Data availability:
Datasets related to this article will be available upon request to the corresponding author.
Edited by
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Editor:
Dr. Altair A. Del Bel Cury
Datasets related to this article will be available upon request to the corresponding author.
