A profilometric and scanning electron microscopic analysis of tooth surface abrasion caused by rotary/oscillatory, linear motion, sonic, and ultrasonic toothbrushes: An in vitro study.

BACKGROUND: Adequate plaque control facilitates good gingival and periodontal health, prevents tooth decay, and preserves oral health. Toothbrushing is the primary method of removing plaque and can be classified into powered and manual toothbrushes. AIM: The primary objective was to compare the abrasiveness and surface roughness caused by four different power-driven toothbrushes with a different mode of action, on tooth surfaces in vitro.
MATERIALS AND METHODS: An in vitro experiment was conducted on eighty freshly extracted tooth specimens which were equally divided into four groups. Each group was brushed with the specifically assigned electric toothbrush to that group, but keeping parameters such as force applied during brushing, storage of tooth before and after brushing, and toothbrushing time same. A total of the 2-month study was done on each tooth specimen. Tooth surface roughness was recorded before and after the toothbrushing experiment to check the difference between surface roughness readings. Scanning electron microscopic (SEM) analysis was done afterward to analyse the surface topography of each group specimens. STATISTICAL ANALYSIS USED: Paired t-test used for intergroup analysis and intragroup analysis was done using Kruskal-Wallis test.
RESULTS: After comparing the baseline and final readings of each group, it has been found that the mean difference between values is highly significant in Group 1 (rotary/oscillatory). The mean rank of Group 1 was least in all four groups, which showed the highest tooth surface abrasion in that group. SEM analysis also revealed that Group 1 tooth specimens had deeper scratches/lines comparatively to other groups.
CONCLUSION: Rotary/oscillatory toothbrush caused the highest tooth surface abrasion when compared with other electronic toothbrushes. Copyright:

INTRODUCTION

Dental plaque is considered the single most important easily demonstrable local etiological factor playing an important role in the initiation and progression of periodontal disease. There is a high correlation between the poor oral hygiene, the presence of plaque, and the prevalence and severity of gingival and periodontal disease.[1] Adequate plaque control facilitates good gingival and periodontal health, prevents tooth decay, and preserves oral health. Although there are various methods including mechanical and other chemical methods for plaque removal, toothbrushing is the most widely accepted and is the primary method of removing plaque.[2]

Toothbrushes are often classified as manual and power-driven and are available in numerous variations (head size, type, bristle type, tuft rows, etc.). The effectualness of the manual toothbrush depends on the number of things together with toothbrushing methodology, duration, frequency, bristle texture, toothbrush style, and user deftness that reason effective oral hygiene becomes comparatively tedious, time overwhelming, and for several people, troublesome to master. On the opposite hand, for power-driven toothbrushes, the individual solely guides the top of the toothbrush round the dentition; the mechanical cleaning action being provided electrically by the replaceable batteries or rechargeable battery.[2]

Power-driven toothbrushes were initially created for patients with limited motor skills and for patients with a fixed orthodontic appliance.[3] Power-driven toothbrushes are also recommended for elderly patients, handicapped, and severely retarded children dependent on care providers, adolescents, and for patients with low oral hygiene compliance because these devices require minimal hand motion and coordination skills. Powered toothbrushes are a substitute for manual toothbrushes. Working principle of power-driven toothbrushes is mechanical contact between bristles and the tooth to get rid of the plaque. The addition of low frequency acoustic energy-generated dynamic fluid movements provides cleaning slightly away from the bristle tips. The vibrations inhibit the adherence of bacterial deposits to oral surfaces. Power-driven toothbrushes create hydrodynamic shear forces which disrupt plaque, a short distance from the bristle tips, providing additional interproximal plaque removal.[4] So far, many studies[5678] have been done on abrasive effects caused by manual toothbrushing, but very few studies have been performed to analyse the side effects of different types of powered toothbrushes on tooth surface. The study was aimed at comparative evaluation of abrasiveness and surface roughness caused by four different power-driven toothbrushes.

MATERIALS AND METHODS

Eighty freshly extracted single-rooted teeth, which were indicated for extraction by depatment of orthodontics were collected for this study from patients aged between 15 and 35 years. Tooth with any abnormalities such as hypoplasia, fluorosis, decalcification, crack, fracture, caries, restoration, abrasion, attrition, and erosion was excluded from the study.

Preparation of tooth specimen

Teeth were extracted with caution to avoid any damage to the coronal morphology. Following extraction, the teeth were washed under running tap water and etched with citric acid (2.3 pH) to remove the smear layer, then were stored in the artificial saliva until required. Extracted teeth were examined under stereomicroscope [Figure 1a] for smooth enamel morphology.

Figure 1

(a) Stereo microscope used to study enamel morphology; (b) Olympus microscope to measure bristle diameter; (c) Scanning electron microscope used to analyse the topography of tooth specimen after toothbrushing experiment

Eighty teeth samples were equally divided into four groups and were stored separately in artificial saliva.

Group 1: The specimens were brushed with Brushpoint™ Deepclean Oscillating Toothbrush Figure 2a (bristle diameter: 0.13 mm)

Figure 2

(a) Rotary/oscillatory toothbrush; (b) Linear motion toothbrush; (c) Sonic toothbrush; (d) Ultrasonic toothbrush

Group 2: The specimens were brushed with Dr. Fresh™ Velocity Linear Motion Toothbrush Figure 2b (bristle diameter: 0.18 mm)

Group 3: The specimens were brushed with Sonic-FX™ Sonic Toothbrush Figure 2c (bristle diameter: 0.16 mm)

Group 4: The specimens were brushed with Pro-Medic™ Professional Ultrasonic Toothbrush Figure 2d (bristle diameter: 0.17 mm).

Softness of each toothbrush was determined by the diameter of the bristle filament [Figure 3], which was measured through Olympus U-TV0.5XC-3 microscope [Figure 1b].

Figure 3

(a) Bristle size of Group 1 rotary/oscillatory toothbrush; (b) Bristle size of Group 2 linear motion toothbrush; (c) Bristle size of Group 3 sonic toothbrush; (d) Bristle size of Group 4 ultrasonic toothbrush

Before starting the brushing experiment for each group, the present surface roughness of each tooth was measured by surface profilometer [Figure 4f] to get the baseline record. Custom-made acrylic resin blocks were made for each tooth sample to ensure the exact repositioning of the specimens during every brushing cycle in the brushing machine [Figure 4a] and were stored in artificial saliva before and after the experiment.

Figure 4

(a) Custom-made wooden brushing machine; (b) force gauge; (c) armamentarium used; (d) tooth specimen mounted in its acrylic block and toothbrush fixed in brushing machine; (e) 250 g of force applied on toothbrush; (f) profilometer used to read surface roughness readings

In vitro abrasion experiment

A total of 2-month study was performed on each tooth specimen, in which 2 min of brushing was done on each tooth/day for 60 days. Brushing cycles were divided into four cycles/day. Each cycle consisted of a 30 s of toothbrushing and a 30 s of storage in artificial saliva [Figure 4c]

The tooth specimen was taken out of the artificial saliva and was then mounted in its respective custom-made acrylic block to ensure the same position of the tooth during each brushing cycle. After that, it was placed on the custom-made wooden brushing machine [Figure 2a]. Radicular part of the tooth specimen was covered with a transpore surgical tape up to the level of cementoenamel junction leaving the coronal part (test side) of the tooth specimen exposed. Toothpaste slurry was applied on the tooth sample

The toothbrushes were fixed in the holder of the brushing machine by tightening the screws, allowing the placement of the toothbrush head perpendicular to the surface of the coronal part of the tooth specimen. The force gauge [Figure 4b] head was fixed over the head of the toothbrush, allowing a load of 250 g on the toothbrush head during brushing [Figure 4d and e]. After applying force, brushing was performed for 30 s which was followed by placement of that sample in artificial saliva for 30 s, thus making it a complete one brushing cycle

After completing the four brushing cycles, the specimens were rinsed under running water and then again stored in artificial saliva until the next day of brushing cycle.

After the completion of 2 months study, each specimen was reevaluated under profilometer for final surface roughness readings.

Scanning electron microscopy analysis

After the final profilometric readings, all specimens were sectioned carefully with the fine diamond cutting disc at the most convex surface of tooth specimen to analyse the surface topography, in which any vertical, horizontal, and oblique scratches/lines produced by the abrasive strokes of the toothbrushes can be appreciated and compared under scanning electron microscope (SEM) [Figure 1c].

RESULTS

The purpose of this study was to compare the abrasiveness and surface roughness caused by different types of powered toothbrushes on tooth surfaces on eighty freshly extracted single-rooted teeth.

Mean roughness score of Group 1 at the baseline was 3.472 ± 0.763 and after toothbrushing was 2.969 ± 0.682, and the mean difference is 0.503 ± 0.159. The comparison between the baseline and final readings (after toothbrushing) is highly significant [Table 1 and Figure 5]. Mean roughness score of Group 2 at the baseline was 3.391 ± 0.322 and after toothbrushing was 3.351 ± 0.315 and the mean difference is 0.039 ± 0.082. The comparison between the baseline and final readings (after toothbrushing) is significant [Table 2 and Figure 6]. Mean roughness score of Group 3 at the baseline was 3.586 ± 0.356 and after toothbrushing was 3.535 ± 0.378, and the mean difference is 0.052 ± 0.065. The comparison between the baseline and final readings (after toothbrushing) is significant [Table 3 and Figure 7]. Mean roughness score of Group 4 at the baseline was 3.488 ± 0.375 and after toothbrushing was 3.487 ± 0.375, and the mean difference is 0.002 ± 0.003. The comparison between the baseline and final readings (after toothbrushing) is nonsignificant [Table 4 and Figure 8].

Table 1

Rotary oscillatory

Rotary oscillatory	Mean±SD	SEM	95% CI of the difference
			Lower	Upper
Baseline	3.472±0.763	0.171	0.429	0.578
Final	2.969±0.682	0.152
Rotary oscillatory	Mean differences		t-test	P
Baseline - final	0.503±0.159		14.20	0.001 (HS)

P<0.05 considered significant. SD – Standard deviation; SEM – Standard error mean; HS – High significant; CI – Confidence interval; P – Level of significance

Figure 5

Comparison of baseline and final values of Group 1

Table 2

Linear motion

Linear motion	Mean±SD	SEM	95% CI of the difference
			Lower	Upper
Baseline	3.391±0.322	0.072	0.001	0.078
Final	3.351±0.315	0.071
Linear motion	Mean differences		t-test	P
Baseline - final	0.039±0.082		2.17	0.043 (S)

P<0.05 considered significant. SD – Standard deviation; SEM – Standard error mean; S – Significant; CI – Confidence interval; P – Level of significance

Figure 6

Comparison of baseline and final values of Group 2

Table 3

Sonic

Sonic	Mean±SD	SEM	95% CI of the difference
			Lower	Upper
Baseline	3.586±0.356	0.080	0.021	0.083
Final	3.535±0.378	0.085
Sonic	Mean differences		t-test	P
Baseline - final	0.052±0.065		3.55	0.01 (S)

P<0.05 considered significant. SD – Standard deviation; SEM – Standard error mean; S – Significant; CI – Confidence interval; P – Level of significance

Figure 7

Comparison of baseline and final values of Group 3

Table 4

Ultrasonic

Ultrasonic	Mean±SD	SEM	95% CI of the difference
			Lower	Upper
Baseline	3.488±0.375	0.084	0.001	0.003
Final	3.487±0.375	0.084
Ultrasonic	Mean differences		t-test	P
Baseline - final	0.002±0.003		1.83	0.083 (NS)

P<0.05 considered significant. SD – Standard deviation; SEM – Standard error mean; NS – Not significant; CI – Confidence interval; P – Level of significance

Figure 8

Comparison of baseline and final values of Group 4

After comparing the baseline and final readings of each group, it has been found that the mean difference between values is highly significant in Group 1 (P = 0.001). The mean difference in values of Group 2 (P = 0.043) and Group 3 (P = 0.01) is significant; however, the mean difference between the values of Group 4 (P = 0.083) is found to be nonsignificant.

Table 5 and Figure 9 show the comparison of the mean rank of Group 1, Group 2, Group 3, and Group 4. After comparing the mean rank of all groups, it has been shown that the comparison of all four groups is statistically significant and Group 1 has the least mean rank, which shows that the Group 1 has the highest abrasion among all four groups. Table 6 shows the intergroup comparison of mean scores of all four groups. In comparison to Group 1, Group 2 and Group 3 show significant difference with a P value of 0.028 and 0.031, respectively, and Group 4 shows a highly significant difference (P = 0.001). In comparison to Group 2, Group 3 shows nonsignificant difference (P = 0.106) and Group 4 shows significant difference (P = 0.049). In comparison to Group 3, Group 4 shows a significant difference (P = 0.048).

Table 5

Mean rank of all four groups

Ranks			Kruskal-Wallis test
Groups	n	Mean rank	χ2	P
Rotary oscillatory	20	24.23	15.977	0.001
Linear motion	20	47.38
Sonic	20	39.08
Ultrasonic	20	51.33
Total	80

P<0.05 considered significant. P – Level of significance. n – Number of samples. χ2 – Symbol of Kruskal-wallis test

Figure 9

Comparison of the mean rank of all four groups

Table 6

Intergroup comparison of all four groups

Groups	Mean difference	P	Significant
Group 1
Group 2	−0.38±0.36	0.028	S
Group 3	−0.56±0.30	0.031	S
Group 4	−0.52±2.81	0.001	HS
Group 2
Group 3	−0.18±0.06	0.106	NS
Group 4	−0.14±3.17	0.049	S
Group 3
Group 4	0.04±3.11	0.048	S

P<0.05 considered significant. NS – Not significant; HS – High significant; S – Significant; P – Level of significance

DISCUSSION

Cleaning of teeth can be traced back to the ancient times long before the relationship between the plaque and gingival health was established.[5] The toothbrush is the principal instrument in general use for accomplishing plaque removal as a necessary part of disease control. The evolution of toothbrushes has led to the development of four distinct technologies, manual, electromechanical, sonic, and ultrasonic brushes.[9] Manual toothbrushing is relatively tedious, time consuming for many individuals. Therefore, electric/mechanical toothbrushes offer an alternative to manual toothbrushes.[2610] The powered toothbrushes appear to be helpful in improving the oral health of physically and mentally handicapped individuals and children because these devices require minimal hand motion and coordination skills.[11] However, besides having potential benefits of dental plaque biofilm removal and improving oral health, the injudicious use of toothbrush in causing injuries to dental hard and soft tissues has also been documented; abrasion is the most common among them.[7]

Dental abrasion is the pathologic wearing of teeth as a result of abnormal processes, habit, or abrasive substance.[8] Toothbrushing abrasion is determined by the abrasivity and concentration of the toothpaste, the kind of toothbrush used, and the brushing force.[12]

This study was done on eighty single-rooted teeth and was collected from patients undergoing orthodontics treatment aged between 18 and 35 years. The reason for selecting this age group was twofold: (a) the detrimental effect of the toothbrush is minimal. (b) Morphological details on the naturally enamel surface are well preserved for observation.

In the present study, the rotary/oscillatory toothbrush (Brushpoint™ Deepclean Oscillating Soft Toothbrush) with a bristle diameter of 0.13 mm was used. The whole head of toothbrush with individual tufts move in counterclockwise direction at the frequency of 7500 strokes/min. As a secondary cleansing action, rotaries that generate a high-frequency pulsing motion are able to remove plaque at a distance beyond where their bristles actually touch. The linear motion toothbrush (Dr. Fresh™ Velocity Linear Motion Soft Toothbrush) with bristle diameter of 0.18 mm was used in the present study, which works at 5500 strokes/min. The mechanical motion of toothbrush is single vibration motion produced by a motor inside the toothbrush. The sonic toothbrush (Sonic-FX™ Sonic Soft Toothbrush) with bristle diameter of 0.16 mm was used in the present study, which works at the frequency of 33,000 strokes/min. In addition to the effect of mechanical brushing, sonic toothbrush uses the concept of utilizing low-frequency acoustic energy to generate dynamic fluid activity and perhaps a mild cavitation effect has been developed to provide a beyond the bristle tip cleaning activity. The ultrasonic toothbrush is a toothbrush with a Piezo-electric ultrasonic emitter embedded in the brush head. The transducer contracts and expands volumetrically in tune with the impulses provided by the power supply, converting the electric energy into ultrasonic waves. The ultrasonic waves are transmitted from the transducer to the brush head and the bristles. The bristle vibration amplitude is microscopic and does not provide any tactile feedback to the user. The ultrasonic toothbrush (Pro-Medic™ Professional Soft Toothbrush) with bristle diameter of 0.17 mm was used in the present study. It works with the help of a macro oscillator, which produces the ultrasonic frequency of 6000 rpm.

Imfeld T 1996 documented that artificial saliva contains calcium and phosphate in a supersaturated state, enabling replacement of mineral loss of tooth surface.[13] In the present study, all tooth specimens were stored in artificial saliva for remineralization until required. The same studies were done by, Rodrigues et al. 2001, Worschech et al. 2006, de Menezes et al. 2007, and Ionta et al. 2014, who stated that artificial saliva has a role in the remineralization of teeth.[14151617]

In the present study, the brushing force was kept constant by the construction of a customized brushing apparatus that helped to deliver uniform force during brushing, and the same dentifrice was used in all four groups. This was in accordance to studies done by Teche et al., 2011 and Ganss et al., 2009, who used the customized brushing apparatus to assess the role of toothbrush and toothpaste in abrasion process.[1819] Dabhi et al. 2016 also used a customized brushing apparatus to deliver the same force during brushing on all tooth specimens. van der Weijden et al., 2004 documented that some powered toothbrushes stop entirely or partially when excessive amounts of force are employed by the user (over 250 g).[820] Hence, in the present study, we used a constant 250 g of force during brushing for all tooth specimens.

The average time of toothbrushing with a powered toothbrush is 2 min, twice daily of an individual. Hence, in the present study, sufficient time is considered for the study that may cause abrasion by brushing each tooth specimen 2 min daily for 60 days. Kumar et al. 2015, Lagerweij et al. 2006, and Ganss et al. 2009 also performed in vitro studies to check the erosion and abrasion on tooth surface where they brushed all the samples daily for 2 min.[7181921]

In the present study, we used the same dentifrice (Colgate Total™) on all tooth specimens to ensure the homogeneity of the abrasive properties of toothpaste.

Wiegand et al. 2012 determined the toothbrush abrasion on dental hard tissues with the help of profilometer.[2223] The highest mean difference between baseline and final average roughness values shows greater abrasion on tooth surface in that group. In the present study, Ra value (average surface roughness) was calculated with profilometer and difference in Ra value before and after toothbrushing provided a proxy measure for assessing surface abrasion.

Dyer et al., 2001, performed a study to compare the abrasion caused by linear and rotary toothbrushes.[24] They found that rotation/oscillation toothbrush causes more abrasion than linear motion. It may be concluded that the area of substrate contacted by brush with the rotary action. The rotary motion brings into play a wider zone of the substrate than the linear motion. Wider brushes would, therefore, have more bulk of substrate to remove.[25] Furthermore, each unit area of substrate is exposed to brushing over less time because the rotary motion moves the brush on and off the peripheral areas of substrate. Wiegand et al., 2006, did the study to evaluate the susceptibility of sound and eroded dentin to brushing abrasion performed by sonic toothbrush and found that loss of sound and demineralized dentin was increased by sonic toothbrushes because frequency and brushing motion influence the abrasion and enhances the transportation of dentifrice to tooth surface. Terezhalmy et al., 1994, evaluated the efficacy and safety of an ultrasonic toothbrush and revealed that ultrasonic toothbrush did not cause any abrasion on tooth surface.[4]

Ojha et al. and Worawongvasu compared the surface topography of all tooth specimens with the help of SEM to evaluate the enamel abrasivity caused by toothbrushing.[5222526] Hence, in this study, all specimens were subjected to posttreatment SEM to record and compare the surface topography, in which any vertical, horizontal, and oblique scratches/lines produced by the abrasive strokes were compared. Tooth samples in Group 1 (rotary/oscillatory) showed the deep and generalized vertical, horizontal, and oblique scratches/lines produced by abrasive strokes [Figure 10a]. Group 2 (linear motion) [Figure 10b] and Group 3 (sonic) [Figure 10c] also showed such scratches/lines produced by abrasive strokes, but they were less prominent when compared with Group 1. Group 4 (ultrasonic) did not show any noticeable change in tooth surface [Figure 10d].

Figure 10

(a) Group 1 specimen showing deep and generalized vertical, horizontal, and oblique scratches/lines. (b and c) Less prominent scratches/lines as compared to Group 1. (d) Group 4 showing nonnoticeable change on tooth specimen

Wiegand et al. 2006 documented that, due to complex interaction of dentifrice and toothbrush during toothbrushing, it was assumed that the different operating systems (e.g., rotation/oscillation, linear motion, sonic, and ultrasonic) of the electric toothbrushes may lead to a modification of dentifrice transportation over the tooth surface and therefore to an alteration of toothbrush abrasion.[27]

CONCLUSION

The rotary/oscillatory toothbrush caused the highest tooth surface abrasion and ultrasonic toothbrush caused the least abrasion on tooth surface among all four power-driven toothbrushes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.