2025 Volume 67 Issue 1 Pages 1-4
Purpose: This study compares the ability of extrinsic stain removal and surface roughness changes on tooth surfaces after using two different types of dental air polishing powder: Sodium bicarbonate and novel eggshell powder.
Methods: For the study of extrinsic stain removal, twenty bovine teeth were soaked in coffee for extrinsic stain formation. Group 1 and Group 2 were polished with sodium bicarbonate powder and novel eggshell powder, respectively. The acquired stains of teeth were recorded as baseline, and color changes after cleaning with two different powders were also measured by colorimeter. Sixteen samples from eight human posterior teeth were used for the surface roughness test. Surface roughness values (Sa) of two groups (sodium bicarbonate and novel eggshell powder) were measured by a contact-type profilometer before and after polishing with two types of powders.
Results: The data showed that the average ΔE* value of the sodium bicarbonate group was higher than that of the novel eggshell powder group (P < 0.05). The average ΔSa value of the sodium bicarbonate group was higher than that of the novel eggshell powder group (P < 0.05).
Conclusion: Sodium bicarbonate powder showed higher stain removal ability and surface roughness changes than the novel eggshell powder.
Biofilm is the main etiological factor in periodontal disease and dental caries. It accumulates on tooth surfaces as bacterial dental plaque [1]. Periodontal disease and dental caries are prevented with regular self-performed oral hygiene and professional removal of supragingival and subgingival biofilm biannually [2,3,4,5]. Over recent years, there have been many professional teeth cleaning methods for dental plaque or biofilm removal, calculus elimination, and stain erasing. Conventional teeth cleaning methods use hand instruments, sonic and ultrasonic scalers, and air polishing. Although hand and ultrasonic instruments are the most common tools, they usually cause patient discomfort and pain during and after treatment [6,7,8].
Air polishing was first introduced to dentistry in the late 1970s to remove extrinsic stains and soft debris quickly and easily on tooth surfaces [9]. Recently, many types of air polishing powder have appeared that are different in grain size and shape. The types of air polishing powder used in air-powder polishing depend on the amount of stain deposition and areas of tooth surfaces such as enamel, cementum, and dentin.
Sodium bicarbonate is the original material used in air polishing powders. It is intended for heavy stain removal due to the grain structure and size. Its particle size is around 60-120 microns, according to manufacturing companies. The new formula for sodium bicarbonate powders is just 40 microns, and it can be used to remove extrinsic stains as efficiently as a 65-micron powder [10]. However, the cost of air polishing, including polishing powder, is greater than conventional methods, such as a rubber cup with pumice, which presents an additional cost for patients in alternative treatments.
Over the years, waste products from agricultural and industrial processes have been increasing. Eggshells are interesting waste products and can be an essential alternative source of calcium carbonate (CaCO3). Therefore, many researchers have been studying recycling eggshells to use in the field of dentistry as abrasives and polishing pastes to increase economic value and decrease eggshell waste products [11,12]. For this study, eggshells were prepared from chicken eggshells.
Novel eggshell or calcium carbonate powders were prepared from chicken eggshells (Fig. 1). Eggshells were cleaned and dried in a hot air oven (FD240, Binder, Tuttlingen, Germany) at 100°C for 24 h, fifty grams of eggshells were milled with the grinding machine (Pulverizing machine, Rong Tsong Precision Technology Co., Taichung, Taiwan, ROC) for three rounds (2 min per round with 25,000 rpm) (Fig. 2) and sieved with mesh (45 microns) to filtrate the particle size of eggshell powder (Fig. 3). The average particle size of eggshell powders was about 32 microns measured by particle size analyzer (Mastersizer 2000, Malvern Instruments Ltd., Worcestershire, UK). The shapes of particles were investigated using scanning electron microscopy (SEM) with a magnification of 1,000 times (Fig. 4).
Sodium bicarbonate powderSodium bicarbonate powder (Classic powder, Saterec, Merignac, France) was applied to clean extrinsic stains on tooth surfaces according to the manufacturer’s instructions. The particle shapes were recorded using SEM with a magnification of 1,000 times (Fig. 5).
Air polishing deviceIn this study, the dental air polishing device (AIR-N-GO, Saterec) was used according to the manufacturer’s instructions (Fig. 6).
Twenty extracted bovine teeth (anterior teeth, sound enamel) were stored in sterile water at 4°C and changed weekly (the teeth will be kept no more than 6 months). After cleaning with pumice and removing the pulp, all teeth were filled to the root apex with resin composite (Filtek Z350 XT, 3M, St. Paul, MN, USA) and coated with three layers of nail varnish (Quick dry top coat, Revlon, Jakarta, Indonesia) on the root surface. Marking the position for the testing area as a 1 × 1 cm square, the testing area is selected between the cervical to the middle one-third of the buccal surface of the crown. Then, all teeth were soaked with coffee (Gold selection, Tchibo, Hamburg, Germany) for 5 days at 37°C, and the coffee was changed daily. Specimens were divided into two groups equally; each group comprised ten specimens. The baseline color measurement of all specimens was recorded and repeated three times with a spectrophotometer (Ultrascan Pro, Hunter Associates Laboratory, Inc., Reston, VA, USA) and a 7 mm port diameter using The Commission Internationale de l’Eclairage L*a*b* (CIE L*a*b*). Then, the three values were averages. After baseline measurement, group 1 was cleaned with sodium bicarbonate powder, and group 2 was cleaned with eggshell powder using an air-polishing device. Each sample was polished for 1 min (at a 45-degree angulation of the handpiece and a 5 mm distance from the tooth surface). The color change after cleaning was recorded and repeated three times compared with the baseline by spectrophotometer. The calculation of the color change ΔE* between the baseline and after polishing in the 3-d CIE L*a*b* color space is as follows [13].
ΔEab* = [(L1*-L2*)2 + (a1*-a2*)2 + (b1*-b2*)2]1/2
The surface roughness testEight extracted human teeth (posterior teeth with sound enamel, no restoration, and no defects on the testing area) were stored in sterile water at 4°C and changed weekly (the teeth will be kept no more than 6 months). All teeth were cleaned with pumice by using a rubber cup. Only the crown part of each tooth was divided into two pieces: buccal and lingual. All samples marked the position for the testing area as a 3 × 3 mm square, and each sample was fixed on the acrylic plate before cleaning with an ultrasonic cleaner in sterile water. Samples were separated into two groups; each group was composed of eight specimens, and all samples measured surface roughness (Sa) for three randomized positions as the baseline using a contact profilometer (Talyscan150, Taylor Hobson, Leicester, UK). After baseline measurement, group 1 was polished with sodium bicarbonate powder, and group 2 was polished with eggshell powder using an air-polishing device. Each sample was polished for 15 s (at a 45-degree angulation of the handpiece and a 5 mm distance from the tooth surface). All specimens were cleaned with an ultrasonic cleaner in sterile water to remove the remaining abrasive powders on tooth surfaces. Surface roughness changes were recorded for three randomized positions using a contact profilometer compared to the baseline.
Statistical analysisThe sample size was determined by n4studies from the pilot study after preparing five prototypes of bovine teeth for the color change test and three prototypes of extracted human teeth for the surface roughness test. The sample size was calculated assuming an independent sample test with α = 0.05 and β = 0.2, giving a sample size of n = 6 for the color change test and n = 3 for the surface roughness test. Finally, the study was considered to conduct the experiment with a sample size of n = 10 and n = 8 for the color change and the surface roughness test, respectively. The obtained data were analyzed using a statistical software program (SPSS Version 22.0; IBM, Chicago, IL, USA), with the Shapiro-Wilk test used to verify normal distribution. The statistically significant differences between groups were identified using the Mann-Whitney U test in the color change test and the independent sample t-test in the surface roughness test. A P-value <0.05 was considered statistically significant.
The color change of stained teeth after polishing with two different types of powder was evaluated in terms of ΔE (Table 1). The Shapiro-Wilk test displayed a non-normal distribution: sodium bicarbonate powder (P = 0.474) and novel eggshell powder (P = 0.039). According to the Mann-Whitney U test results, sodium bicarbonate powder and the novel eggshell powder were statistically significant (P < 0.05). Median ΔE* values, interquartile range of color differences, and P-value are listed in Table 1. Sodium bicarbonate powders showed higher ΔE* values than the novel eggshell powder (P < 0.05).
| Sodium bicarbonate powder (n = 10) |
Novel eggshell powder (n = 10) |
P-value | |
|---|---|---|---|
| ΔE | 34.90 ± 11.00 | 29.40 ± 21.86 | 0.034 |
Median (± interquartile range) of color change (ΔE) and differences between groups
Surface roughness test (Sa)
The surface roughness was determined in terms of Sa (Table 2). The Shapiro-Wilk test displayed the normal distribution of each group: sodium bicarbonate powder (P = 0.230) and novel eggshell powder (P = 0.100). According to the independent sample t-test results, sodium bicarbonate powder and the novel eggshell powder were statistically significant (P < 0.05). Mean ΔSa, standard deviation of surface roughness differences, P-value, and 95% confidence interval of the difference (CI) are listed in Table 2. Sodium bicarbonate powders showed higher ΔSa values than the novel eggshell powder (P < 0.05).
| Sodium bicarbonate powder (n = 8) |
Novel eggshell powder (n = 8) |
P-value | 95% Confidence interval of the difference | ||
|---|---|---|---|---|---|
| lower | upper | ||||
| ΔSa | 0.096 ± 0.051 | 0.045 ± 0.032 | 0.033 | 0.004829 | 0.096171 |
Mean (± standard deviation) of surface roughness change (ΔSa) and differences between groups
The objectives of the study were to compare the ability of extrinsic stain removal on tooth surfaces and the surface roughness of enamel surface after using the novel eggshell and the sodium bicarbonate air polishing powder. Both null hypotheses were rejected. There are statistically significant differences in the ability of extrinsic stain removal and the surface roughness between sodium bicarbonate and novel eggshell powder.
Eggshells are an alternative source of calcium carbonate, and they become waste products from households, agriculture, and industries. Many waste products from eggshells can be recycled to use in dentistry as a polishing paste [12], but there have been no reports on using eggshells for air polishing powder. Eggshells are easily obtainable, especially from households, compared to duck eggs or shells. In this study, all eggshells from the same farm were used, and sterilization was performed at 100°C for 24 h. Several pieces of evidence show that heat treatment for 20 min at 80°C, 85°C, and 95°C effectively inactivates tuberculosis specimens [14].
Numerous studies have shown that there are many methods for removing dental biofilm. Air-polishing methods are recommended due to their effectiveness and efficiency in new powders [15]. The ability to clean plaque and stains depends on many factors, such as particle sizes and shapes of particles [16]. However, large particle sizes of air-polishing powders affect tooth abrasion [17]. The consideration of powder types is essential in properly removing plaque and extrinsic stains. In some cases, sodium bicarbonate powders should not be recommended for use on patients with histories of hypertension, sodium-restricted diets, or medications affecting the electrolyte balance. Therefore, calcium carbonate powder is recommended as an alternative powder [18].
Furthermore, different exposure times, distances, angulation of air-polishing tip are crucial factors affecting surface roughness and stain removal effectiveness [16,19]. In this study, these factors are controlled under the same conditions. However, the hardness of sodium bicarbonate and calcium carbonate (2.5 and 3, respectively, on the Mohs hardness scale) cause different outcomes of surface roughness (enamel, dentin, cementum = 5, 3, and 2, respectively, on the Mohs hardness scale). In addition, the difference in the solubility in water between sodium bicarbonate and calcium carbonate could influence the surface abrasion. The greater amount of undissolved particles of calcium carbonate in a water-air mixture could contribute to an increase in surface roughness [20].
Several studies examined the surface roughness changes by using human teeth as specimens. However, many studies have prepared specimens using bovine teeth. The main reason that bovine teeth are widely considered to be used is that they are easily obtainable in large quantities. In addition, recent evidence indicates that bovine teeth are a suitable alternative to human teeth because of their similar chemical composition [21]. For surface roughness experiments, human teeth were used to imitate the tooth surface condition to resemble the real human teeth as much as possible.
The color measurement in this study was measured by a spectrophotometer (UltraScan Pro). The sample preparation process is limited by small port size and sensitive procedures. These are the important reasons for using bovine teeth in this experiment, as their anterior teeth are large and flat.
For this study, the statistical data showed that sodium bicarbonate powder is more effective in removing extrinsic stains from coffee, as measured by the spectrophotometer (ΔE). However, sodium bicarbonate powders abraded or destroyed tooth surfaces more than the novel eggshell powder measured by the profilometer or surface roughness test (Sa). The results from this study conform to previous studies, which showed the association between particle sizes of powders and the effectiveness of erasing stains. The particle size of sodium bicarbonate powders is about 76 microns. Its particle size is larger than the novel eggshell powder (32 microns), this is the crucial reason that sodium bicarbonate powders can remove stains efficiently compared to the novel eggshell powder, while the novel eggshell powders can preserve tooth structure or less abrasion on tooth surfaces after using air polisher.
The uses of air polishing powder are considered by many factors, such as areas on tooth surfaces (enamel, dentine, and cementum) and types of stains (heavy, moderate, and slight stains) [22,23]. Therefore, each type of powder is recommended to be used cautiously.
The present study focuses on removing external stains from coffee and investigates roughness changes, which are limited in human and bovine teeth. However, studying roughness changes after using eggshell air polishing powder on many types of materials used for restoration, such as composite resin, poly(methyl methacrylate) (PMMA), metal, and ceramic, is an interesting topic for further studies. Additionally, external stains from tobacco are commonly found during the prophylaxis procedure. Therefore, cleaning tobacco stains with eggshell powder is planned to be carried out for future research.
The findings of this study are summarized as follows.
CaCO3: calcium carbonate; SEM: scanning electron microscopy; PMMA: poly(methyl methacrylate)
The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the Faculty of Dentistry, Chulalongkorn University (HREC-DCU 2023-054).
The authors have no conflict of interest to declare. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Not applicable
VP: conceptualization, methodology, formal analysis, investigation, resources, data curation, writing original draft, writing review and editing; NT, KS, and AK: conceptualization, writing review and editing, supervision; CT: writing review and editing; WP: conceptualization, methodology, formal analysis, writing review and editing. All authors read and approved the final version of the manuscript.
1)VP: visaluk.pun@gmail.com, https://orcid.org/0000-0003-1152-6801
2)WP: wisarut.p@chula.ac.th, https://orcid.org/0009-0003-0709-875X
3)NT: niyom.t@chula.ac.th, https://orcid.org/0000-0001-8853-0089
4)KS: krisana.s@chula.ac.th, https://orcid.org/0000-0002-0142-3107
5)AK: dentton@hotmail.com, https://orcid.org/0000-0001-8719-5119
6)CT: cheewin23@live.com, https://orcid.org/0000-0001-5255-7247
The authors wish to thank Dr. Pornpen Siridamrong for advice and assistance in powder preparation. This study was supported by the Faculty Research Grant, Faculty of Dentistry, Chulalongkorn University, Thailand.
The data set used in the current study is available on request from Dr. Visaluk Punyawattananon.
