Comparative evaluation of enamel abrasivity by toothbrush and velcro: An in vitro scanning electron microscope study

Abstract

Context:

Plaque control has been shown to be pivotal in maintaining the optimal periodontal health. Mechanical plaque control is the most popular option for establishing the optimal oral health. Toothbrushes have been the novel tool for mechanical cleansing. However, the abrasive potential of the toothbrushes on the enamel surface is an area in gray.

Aims:

The aim of this in vitro study is to evaluate the abrasivity of the toothbrush versus the velcro fasteners.

Materials and Methods:

The mounted teeth of both the groups were subjected to abrasion test, and the tooth surfaces were observed for the possible abrasions from the oscillating strokes (toothbrush) and frictional contacts (hook and loop velcro) and examined under the scanning electron microscope.

Results:

Comparative assessment of both velcro (hook and loop) and toothbrush bristles did not reveal any evidence of abrasion on the tooth specimens.

Conclusions:

Veclro fasteners are safe and qualitatively at par to the manual toothbrush for their efficacy and efficiency in teeth cleansing

INTRODUCTION

Prevention has become the cornerstone of modern dental practice. Cleaning of teeth can be traced back to the ancient times long before the relationship between the plaque and gingival health was established. Evidence exists that preventive oral hygiene was practiced by Egyptians some 5000 years ago. Toothpicks made of bone and metal dates back to Roman times and by 15^th century advise was given that teeth should be cleaned with a small stick after every meal.

In 1728, it was recorded that dentists were aware of the toothbrushes made of horse hair and in late 1800, toothbrushes looked much the same as they are today.[1]

The classic study of experimental gingivitis by Loe in 1965 laid emphasis on the importance of plaque control to check and prevent gingival and periodontal diseases.[2] The first toothbrush got introduced in 1640.[3] Broadly two methods of plaque control are available: Mechanical and chemical. Mechanical method supervenes in its performance of which toothbrush has been cited as the primary aid to control the supragingival plaque. Toothbrush has ever since undergone several modifications in design to improve the plaque removing efficacy. In the 1960's, there was a major breakthrough in this direction by marketing the first electric toothbrush. From the numerous earlier studies with manual toothbrushes, it appeared that efficient plaque removal depended on less on any specific method or type of brush than on an individual having an effective technique of toothbrushing.[4]

Toothbrush regardless of the brushing method falls short of removing the interdental plaque accumulation secondary to the bristle design and configurations. This in vitro study was undertaken to assess and compare abrasivity of human enamel when subjected to toothbrush bristles and velcro fasteners as a possible plaque removing aid.

MATERIALS AND METHODS

Materials

Human maxillary first premolars

Extracted maxillary first premolars of the patients (12–14 years) undergoing orthodontic treatment were included in the study. The extracted teeth were examined under magnification for smooth enamel morphology. Teeth affected with dental caries, fluorosis, fracture, enamel hypoplasia were excluded from the study

Self-powered oscillating device

Specifications comprised of a power handle with pilot light and magnetic ring switch, recharger (110–240 V), voltage - 2.4 V, frequency 3,300 oscillations/min.

Abrasion testing equipment

A customized wooden board (a) with clamped accessories attached clamp (b) Diagonally placed and fixed at one end to hold self-powered oscillating device. Tooth holding adjustable platform (c) Clamped to hold the cylindrical plaster insert in which the tooth specimens were mounted (d) [Figure 1].

Figure 1.

Abrasion testing equipment

Oral devices

Toothbrush: Popular brand of a junior toothbrush with two rows of single-level flat bristle ended profile. Hook and loop velcro: Two strips of size 20 mm × 2.5 mm respectively (Velcro India).

Scanning electron microscope

Japan Electronics Laboratory make JSM-T200 with a provision of taking micrographs with the camera T-20 Camera Serial Interface attached to it [Figure 2].

Figure 2.

Scanning electron microscope

Negative films

Black and white panchromatic negative films of 120 size with 125 ASA (ORWO German Democratic Republic/Indu India).

Strain measuring devices

These comprised of: (a) Strain gage (7 mm × 4 mm) with resistance of 12 ohms (measurement group – Instrument division, Raleigh, USA) (b) Digital strain indicator (measurement group – Instrument division, Raleigh, USA) (c) Signal conditioning amplifier (Model no. 2310 - measurement group – Instrument division, Raleigh, USA) (d) Oscilloscope – Model no DTO-31002, frequency 100 mhz (BPL-India) (e) San-ei-Visilight – strain recorder – Model no. 5n (Japan) [Figure 3].

Figure 3.

Strain measuring device

Methods

Preparation of teeth

Teeth were extracted with caution to ensure minimal/no damage to the coronal morphology. Following extraction the teeth were washed under running tap water and stored in 10% formalin. The apices of the teeth were resected and sealed with resin. The teeth were immersed in n/100 as a standardized dilution of sodium hydroxide for 10 min and followed by rinsing with distilled water to remove the acquired pellicle. Teeth samples were dried and stored in labeled glass vial. They were later vertically mounted in the cylindrical plaster insert [Figure 4].

Figure 4.

Mounted maxillary first premolar teeth

Scanning of specimens

The selected forty maxillary teeth were subjected to pretreatment surface topography scanning under the scanning electron microscope (SEM). Buccal surface of each tooth being scanned was divided into nine imaginary zones A to I. The maximum convexity in both occlusocervical and mesiodistal directions was marked “zone E [Figure 5]. This zone was expected to receive the maximum strokes and thus the critical area to be studied for the SEM For standardization of the SEM scans, both before and after subjection to brush or Velcro techniques, two reference points R1 and R2 were marked on the buccal surface of each tooth. This ensured the projected SEM scan on screen with reference to R1 coinciding with the right hand top corner.

Figure 5.

Imaginary zones as divided on the buccal surface of maxillary first premolar

Grouping of specimens

Specimens were divided into two groups: A and B comprising 20 teeth each. Group A exposed to effects of abrasions resulting from the oscillating strokes from conventional nylon bristle ends of the toothbrush. Group B was divided into two subgroups B1 and B2 comprising of ten specimens each. B1 was exposed to frictional effects of hook velcro whereas subgroup B2 received frictional strokes from loop velcro.

Measurement of fixed tension

The forces exerted by the three oral hygiene devices used in the study were measured in the static and dynamic position. To measure the forces in a static position, a transducer with the resistance foil strain gage was fixed to the shaft assembly of the self-powered device. It thus enabled measuring the static and torque forces applied to the tooth in motion. In order to assess the relationship between the strain and increasing or decreasing loads appearing on the heads of the three devices, gradually increasing weights in the range of 50–300 g were applied to the heads and the strains produced were recorded by the transducer and the digital strain indicator [Tables 1 and 2]. Graphic plotting was done for the strain values against the known weights (forces). This imaginary line joining the different values followed a straight pathway throughout the range of different weights [Figure 6]. In order to record the forces in a dynamic position, the strain gage was connected to the signal coordinating amplifier and further the assembly was attached to the oscilloscope. Before recording the dynamic strain the signal coordinating amplifier balanced the readings at mark zero. The self-powered oscillating device was clamped to the board with the position of the oral devices in contact with the tooth surface. Oscilloscope read the strain values once the oscillation was started. Signal conditioning recorder was connected to the San-ei-Visilight recorder (SE-Recorder) for the graphical representation of the microstrain values. The SE – Recorder recorded the values on the ultraviolet ray sensitive paper. After 2 min of exposing the paper to the daylight, graphical wavy tracings were visible to the naked eye. The dynamic forces were found in the range of 145–170 g for hook velcro and 130–145 g for toothbrush and loop velcro.

Table 1.

Kilovoltage and magnifications at which teeth and devices were scanned during pre and post treatment phases

Table 2.

Applied loads on the device head and the resultant microstrain values

Figure 6.

Graph showing the strain values as applied against the load

Subjection of specimens to abrasive techniques

The total duration of the frictional exposure to the tooth specimens was 20 min. In order to control, the frictional heat generated each exposure was kept for 2 min with a 2 min interval. Distilled water was used as a coolant drop by drop at 30 s interval during each 2 min exposure. The overall oscillation data as interpreted was: 3,300 oscillations/min, 6,600 strokes to and fro/min with each oscillation, total number of abrasion strokes that each specimen (irrespective of the techniques, i.e. brush bristle or velcro) received was 132,000. The constant forces a maintained was in the range of 145–170 g for hook Velcro and 130–145 g for loop Velcro and brush bristle.

Scanning of specimens after abrasion

All the forty teeth specimens were subjected to posttreatment scanning, recording and comparison of surface topography with the pretreatment micrograph records. The objective criteria for assessing the micrographs (pre-and posttreatment) was: (a) Assessment of pretreatment width to the horizontally placed bright bands alternating with the perikymata and compare it with the posttreatment changes in the surface details. (b) Pre-and posttreatment assessment and comparison of the dimensional extent of the prominent landmark as mapped on the buccal surface. (c) Pre-and posttreatment comparative assessment of any dark vertical lines produced by the abrasive strokes.

RESULTS

The results of the study are based on pre-and posttreatment analysis of the topographic details of the enamel surface by SEM technique. The frictional contact of the toothbrush and Velcro was studied on forty tooth specimens through the scanned images as obtained. The accelerating kilo voltage value [Table 1] was chosen and ensured that the posttreatment scanning of each specimen corresponded to the pretreatment kV values at which it was scanned. The magnitude of the force as exerted by the three devices on the teeth surface while frictional contacts was recorded with the strain gage [Table 2]. A linear graph was plotted based on the different values as obtained [Figure 6] in the range of force values to which the tooth surface was subjected.

Based on the assessment criteria of the micrographs the study revealed: (1) The tooth surfaces details remained unaffected and without any observable change after being subjected to frictional contacts in all the three devices as studied (2) the width of the bright bands remained constant and no dimensional variation was observed. (3) The width of the corresponding perikymata remained unaffected after subjection to an equal number of frictional strokes irrespective of the devices used. (4) The horizontal pattern of perikymata arranged parallel to the cementoenamel junction remained undisturbed despite the frictional strokes. Tooth abrasion was not evident from any of the three methods used [Figures 7–10] (5) Comparative profiles of the three devices (toothbrush, hook and loop velcro) revealed that none of the three devices underwent any distortions [Figures 11].

Figure 7.

Pre (X) and post treatment (Y) micrographs of the specimens exposed to hook velcro (magnifications ×170)

Figure 10.

Pre and post treatment scanning electron microscope profiles of devices studied (a and b) = Hook velcro, (c and d) = Loop velcro, (e, f) = Toothbrush (a, c and e = Pre treatment, b, d and f = Post treatment)

Figure 11.

Micrographs showing abrasions (a and c) = before, (b and d) = After magnification (a and b) (×170) and (c and d) (×220)

Figure 8.

Corresponding insets X and Y as shown on the left side of specimens exposed to hook velcro (magnification ×220)

Figure 9.

Pre (X) and post treatment (Y) micrographs of the specimens exposed to toothbrush (magnification ×170)

DISCUSSION

This in vitro study has given a good estimate of the possible abrasive potential of the three devices when subjected to uniform application of well-controlled forces. This possibility is otherwise difficult in the clinical in vivo studies in the presence of the dynamic parameters, e.g., saliva and plaque. A good estimate of the abrasive potential of the devices in an in vivo environment cannot be established. The rationale behind this study was to assess if the toothbrush bristles or any other tooth cleaning device could induce abrasions or possible surface distortions in the enamel. Comparative pre and posttreatment SEM analysis on otherwise sound enamel surface under the effect of controlled frictional strokes of known magnitude of force and applied for a fixed duration were the endpoints of the study. SEM studies are known to read the minute details of any surface changes.

Considering the eruption pattern of premolars that is, 10–11 years, the age group as defined for the tooth specimens was 12–14 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.[5] The topographical landmarks as perikymata and the alternating bright bands were the guidelines of estimating the pre-and posttreatment changes. The reference points as marked on the buccal surface enabled the precise orientation for the pre-and posttreatment scanned micrographs. This being a pioneering proof of concept in vitro study to estimate the abrasive potential the 20 min duration was designed. The baseline observational criteria and the increased magnification range (175 × 225–220 × 330) enabled a larger surface area to be scanned on the tooth specimens. Scott and Wycoff[5] in their SEM study had concluded that frictional changes combined with the controlling variables of advancing age and proportionate exposure to abrasions lead to a formation of widening zones of bright band and perikymata. However, our study revealed constant width measurements in the pre-and posttreatment micrographs. Additionally, none of the three study devices rendered any abrasions secondary to the frictional strokes on the tooth surface after 20 min duration. Any evidence of abrasion if present would have been assessed by the presence of the linear black marks traversing at right angles to perikymata.

Anneroth and Popplemann[6] Klima[7] in their studies have pointed out the shortcoming of the manual toothbrush bristle configuration. Kitchen[8] and Sagnes and Sangnes[9,10] have demonstrated clinical abrasion of the tooth surface with manual toothbrushes and dentifrices. In an effort to search an improved device, Sharma[11] proposed the use of velcro, with its added advantage of providing smooth round end configuration, for tooth cleansing. His study had given an important dimension of the possibility of improved plaque removing efficacy of velcro. Based on these observations, the purpose of this study was to estimate the abrasive potential of velcro to that of a manual toothbrush.

CONCLUSION

This SEM study performed on the tooth specimens concluded as: No evidence of identifiable areas of suggestive abrasions on the pre-and posttreatment micrographs following controlled force and frictional strokes of velcro (hook and loop) and toothbrush bristles, hook and loop velcro fasteners qualify and appear safe as tooth cleansing device when compared to toothbrush and SEM profiles of the hook and loop velcro and toothbrush bristles did not reveal any significant change in shape, size or surface details. In a continuation to the documented literature, this pioneering in vitro study has added a dimension to the possible abrasivity potential of toothbrush and the velcro fasteners.