The Effect of Prophylactic Powders on the Surface Roughness of Enamel

Review of the literature establishes air polishing as an effective method of removing extrinsic stain from teeth,^3,4 with less chairtime required and less subsequent fatiguing of the operator. Conventional rubber-cup polishing with prophylactic paste is a convenient method of plaque removal that is often used in conjunction with scaling. It is typically effective as a prophylactic treatment, although it often leaves organic debris within the fissures of teeth.² The AP remedy involves the propulsion of sodium bicarbonate (NaHCO₃) powder, water, and air into the developmental fissures of the tooth, allowing for debris removal on the entirety of the tooth surface.

Both rubber-cup and air-abrasive prophylaxis may result in alterations of the smooth enamel surface by creating voids and scratches, or by generating an overall rough surface more prone to the accumulation of biofilm.⁵ However, while some studies suggest that various methods of dental prophylaxis have a profound effect on surface roughness, others maintain that the result is not of clinical significance, with the surface alterations being minimal in nature.^3,4,6 As an alternative to sodium bicarbonate, a recently developed powder composed of calcium carbonate (CaCO₃) in a spherical arrangement has been theorized to increase the efficacy and speed of typical AP prophylactic treatment. However, studies have shown that use of this type of powder has demonstrated deeper irregularities in root surface structure than other powders used with equivalent air-polishing devices.¹

In this study, different dental prophylaxis media that are currently used in professional oral hygiene practice were observed with respect to the degree of aggression they exhibit on human enamel. The null hypothesis was that the different treatment protocols did not have a significant effect on the surface roughness of enamel.

A total of 150 enamel specimens were sectioned from 50 non-carious human molars using a rotating diamond wheel under consistent water cooling. These samples were trimmed using a high-speed diamond bur into sections of approximately 5 mm in diameter. They were then mounted in orthodontic resin bases with heated greenstick compound and stored at room temperature in distilled water. The embedded teeth were ground to a smooth surface on a rotating MetaServ® (Buehler, www.buehler.com) polisher with polishing paper of sizes 250, 600, 800, 1000, and 2000 µm for 4 minutes on each subsequent grit size.

The experiment was separated into two parts. In the first, the samples were divided into eight groups of 15 samples each: six groups were treated with air-abrasive prophylactic treatments; the seventh group of samples was subjected to rubber-cup polishing with prophylactic paste; and the eighth was used as a control and underwent no prophylactic treatment. The air-abrasive devices were mounted in a metallic holder to allow the spray to contact the surface of each sample at an angle of 45 degrees with the head of the device positioned 5 mm above the enamel. Each sample was polished for 30 seconds, during which time the sample was moved rapidly under the fixed handpiece to allow for even distribution of abrasive powder. Two different air-abrasive devices were used—the LM-ProPower AirLED (LM Instruments, www.lm-dental.com) air polisher and the Air-Flow® Handy 2 (EMS, https://new.ems-company.com)—in conjunction with two abrasive powders: sodium bicarbonate (LM-ProPower Air Polishing Powder, LM Instruments) and microsphere calcium carbonate (Pixie Pearls™, Germiphene Corporation, www.germiphene.com).

The LM-ProPower AirLED has two operating modes that control the flow of air and water: Working Mode 1, with 60% of the power limit; and Working Mode 2, with 100% of the power limit. In this study, the handpiece was calibrated for the optimum polishing function, as described in the operating manual, before each working mode was tested with the various powders. Four sample groups were tested with the LM device: two at Working Mode 1 with each type of abrasive powder (1LMC and 1LMP), and two at Working Mode 2 (2LMC and 2LMP). Between each sample, the machine was air-purged to prevent clogging. Two sample groups, one for each powder, were subjected to air polishing for 30 seconds by the EMS unit (EMSC and EMSP), which was set to operate at an air pressure of 0.35 Mpa and a water pressure of 0.2 Mpa. For both air-polishing units, the powder capsule was refilled to maximum after the treatment of each sample to ensure performance consistency. The last group of samples was treated to conventional prophylaxis with rubber-cup application of both medium- and fine-grit Oral-B® prophy paste (PP) (Procter & Gamble, www.pg.com). Each sample was subjected to 0.05 grams of medium-grit polishing paste for 15 seconds, and then an equal amount of fine-grit paste for an additional 15 seconds, for a total treatment time of 30 seconds, under a load of 250 grams and a speed of 1500 rpm.

In the second part of the experiment, the remaining 30 samples were split into two groups of 15 each. Both groups were subjected to air-abrasion treatment with the LM unit at Working Mode 2 (100% of the power limit). The first group was treated with microsphere calcium carbonate (2LM5C), and the second with the sodium bicarbonate powder (2LM5P). The methodology for this section of the experiment was identical to that mentioned above; however, a treatment time of 5 seconds was applied for the specimens in these groups.

In order to assess the surface roughness of the enamel specimens, each sample was evaluated using a Mitutoyo mechanical stylus profilometer (Mitutoyo, www.mitutoyo.com) both before and after treatment. The unit was set to collect six readings for each specimen at a linear displacement of 0.4 mm, three 1 mm apart parallel to one another, and another three taken with the sample rotated 90 degrees counterclockwise. The values obtained by this method were a record of the mean surface roughness (Ra) for each sample measured in microns. This data was organized into tables and subjected to statistical analysis using two-way ANOVA and a Tukey HSD (honest significant difference) rank order test at P = 0.05.

One sample from each test group, that which had the highest Ra result, was dehydrated in a desiccator and then air-dried. The specimens were mounted on aluminum stubs and then sputter-coated with gold and subjected to scanning electron microscopy (SEM) at 5.0 kV.

The two-way ANOVA and Tukey HSD rank order test at P = 0.05 were applied to the data and the results tabulated. The results for the average surface roughness (Ra) in micrometer (μm) for each group of samples as determined by the mechanical stylus profilometer are summarized in Table 1.

It was determined that the distribution of the values obtained for a number of the sample groups differed statistically from one another. Each of the air-polishing devices, when used with the microsphere calcium carbonate for a 30-second treatment, resulted in surface roughness values that were the most significantly increased when compared to those of the PP and control groups. The same treatments, when completed with the standard sodium bicarbonate powder (LM-ProPower powder), were also significantly more abrasive to enamel surfaces than the corresponding treatment conducted with rubber-cup polishing. However, they resulted in a lesser increase in surface roughness than the microsphere calcium carbonate.

In the second part of the experiment, statistical analysis of the data found that treatment with the LM unit, in conjunction with both powders for only 5 seconds, resulted in a surface roughness of enamel that had no statistically significant difference to a 30-second treatment with prophylactic paste.

SEM analysis showed an overall smooth surface for the samples in the control group, since each was treated to polishing prior to prophylactic treatment (Figure 1a and Figure 1b). However, as was expected, a few developmental anomalies remained. Each of the remaining samples revealed some form of alteration to the surface of the enamel. The sample that was subjected to the prophylactic paste and rubber-cup polishing displayed scratches consistent with the rotating action of the head of the handpiece and the abrasive nature of the paste. These anomalies were seen most clearly at a lower (250X) magnification (Figure 2a), compared to the 1000X magnification (Figure 2b). Figure 3 and Figure 4 show the SEM examination of the LM unit with sodium bicarbonate jet. They include the 30-second treatment at 250X magnification (Figure 3a) and 1000X magnification (Figure 3b) as well as the 5-second treatment at 250X (Figure 4a) and 1000X magnification (Figure 4b). There is a noticeable difference in the surface texture of the samples when the 5-second treatment is used. Thirty-second EMS unit treatment with sodium carbonate powder and microsphere calcium carbonate, respectively, are shown in Figure 5 and Figure 6. The sodium bicarbonate powder SEM is seen at 250X magnification in Figure 5a and at 1000X magnification in Figure 5b. The EMS unit with microsphere calcium carbonate powder at 250X magnification is seen in Figure 6a, and at 1000X in Figure 6b. Both sets of images reveal the presence of powder residue on the surface of the enamel along with various scratches.

The 30-second treatment time for the first part of the experiment was chosen as a result of a review of the literature ^2,5,6 and in order to correspond with the minimum time commonly used clinically when rubber-cup polishing is employed.⁶ In the second part of the experiment, the 5-second treatment time was chosen in accordance with the minimum effective air-polishing time, as described by the manufacturer of the calcium carbonate. The 45-degree working angle was established to fit within the recommended range of 30 to 60 degrees.⁷ This range was selected to avoid damaging gingival tissue during the clinical use of the AP.^3,7

The results of this study showed that each type of prophylactic method caused some alteration to the surface of the enamel specimens, as interpreted through the surface roughness measurement and corresponding SEM analysis. This result was supported by previous studies.^5,8,9 The roughness of the enamel surface increased with the application of each treatment, most significantly with a 30-second air abrasion treatment with either of the APs and the calcium carbonate powder.

In the first part of the experiment, where 30-second treatments with prophylactic paste and rubber-cup polishing were employed, a statistically significant increase in surface roughness was observed and confirmed, by SEM analysis, through the presence of scratches on the surface of the samples. The most prominent alteration of the enamel surface was observed with the AP treatments that were conducted for 30 seconds. However, when the samples were subjected to 5-second treatments with the APs, the surface roughness results were not statistically different from those of the prophylactic paste and rubber-cup polishing. This finding demonstrates the efficiency of the AP devices when compared to conventional treatment using polishing paste. It shows that with 5 seconds of application the clinician can obtain the same degree of abrasiveness compared to polishing pastes used during 30 seconds.

With regard to the AP devices, this study found no significant difference between the two devices where enamel surface roughness was concerned. Other studies have found that the use of different AP devices can produce different amounts of abrasion, even when consistent treatment times are employed.¹⁰ In this study, the EMS device resulted in higher surface roughness values compared to the LM device. However, they were not statistically different. For the results of this experiment, treatment time and the abrasive powder choice were more indicative of changes in surface roughness than was the AP itself.

Base on these findings, it can be suggested that when using APs for 30 seconds, there should be subsequent polishing of the tooth surface with PP in order to reduce the surface roughness. It is known that an increase of surface roughness leads to a buildup of plaque; therefore, in order to reduce the AP exposure, the plaque should be stained prior to tooth cleaning.

It should be clear that the surface roughness measurements are not the only criteria for selection of an optimal treatment/technique. It is also important to know the cleaning effectiveness, because the ultimate goal of selecting a technique is efficient removal of plaque and stain without damaging the teeth. However, the clinical efficiency of the treatments was not the subject of this study.

When considering the second portion of this experiment, the discrepancy in surface roughness that was observed between the two prophy powders during the first part of the study becomes negligible. This suggests that treatment time may be the most important variable when considering the relative abrasiveness of prophylactic methods. Clinically, it has been determined by previous studies that air-powder prophylaxis is more efficient in removing plaque and extrinsic stain than other conventional methods of prophylaxis, with less subsequent fatiguing of the operator.^3,11,12 Although the present study did not investigate this scenario, it is possible to correlate the previous studies’ findings^3,11,12 to the current study’s results since the abrasiveness of the prophylactic treatments is responsible for the removal of superficial stains. In the present study a 5-second treatment with an air-polishing device caused equivalent changes in surface roughness when compared to a 30-second rubber-cup polishing treatment.

The findings of many studies show that treatment with APs requires no subsequent polishing of enamel with prophylactic pastes when used for 5 seconds. Although in-vitro research should not be extrapolated to the clinic, it is likely that this prophylactic method is clinically safe and the surface alterations of enamel do not contraindicate this procedure, as no serious or irreversible damage to the enamel structure was observed.

Based on the methods and materials used to establish the surface roughness of enamel following two prophylactic methods, the authors can conclude the following:

• All prophylactic methods caused some alteration of the surface of the enamel specimens.

• All AP treatments conducted for 30 seconds produced enamel surfaces that were significantly rougher than the corresponding rubber-cup polishing.

• AP treatments conducted for 5 seconds produced enamel surfaces that had no statistical difference in surface roughness when compared to 30-second rubber-cup polishing treatments.

Melissa M. Fratolin, DDS
Schulich School of Medicine and Dentistry, The University Western Ontario, London, Ontario, Canada

Vinicius Capo Bianco, DDS, MSc, PhD
Bauru Dental School, University of Sao Paulo, Brazil

Maria Jacinta Moraes Coelho Santos, DDS, MSc, PhD
Assistant Professor, Division of Restorative Dentistry, Schulich School of Medicine and Dentistry, The University Western Ontario, London, Ontario, Canada

Amin S. Rizkalla, PhD, P. Eng.
Associate Professor, Division of Biomaterials Science, Schulich School of Medicine & Dentistry, The University Western Ontario, London, Ontario, Canada

Gildo Coelho Santos Jr, DDS, MSc, PhD
Associate Professor, Chair of the Division of Restorative Dentistry, Schulich School of Medicine and Dentistry, The University Western Ontario, London, Ontario, Canada

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