Comparison of surface abrasion produced on the enamel surface by a standard dentifrice using three different toothbrush bristle designs: A profilometric in vitro study.

AIM: The aim was to assess, in vitro, the effect on surface abrasivity of enamel surface caused by three different types (flat trim, zig-zag, bi-level) of toothbrush bristle design.
MATERIALS AND METHODS: Twenty-four freshly extracted, sound, human incisor teeth were collected for this study. The enamel slab was prepared, which were mounted, on separate acrylic bases followed by subjected to profilometric analysis. The surface roughness was measured using the profilometer. The specimen were divided into three groups, each group containing eight mounted specimens, wherein, Group 1 specimens were brushed with flat trim toothbrush; Group 2 brushed with zig-zag and Group 3 with bi-level bristle design. A commercially available dentifrice was used throughout the study. A single specimen was brushed for 2 times daily for 2 min period for 1 week using a customized brushing apparatus. The pre- and post-roughness value change were analyzed and recorded. STATISTICAL TEST: Kruskal-Wallis test and Mann-Whitney U-test. RESULT: The results showed that surface abrasion was produced on each specimen, in all the three groups, which were subjected to brushing cycle. However, the bi-level bristle design (350% increase in roughness, P = 0.021) and zig-zag bristle design (160% increase in roughness, P = 0.050) showed significantly higher surface abrasion when compared with flat trim bristle design toothbrush.
CONCLUSION: Flat trim toothbrush bristle produces least surface abrasion and is relatively safe for use.

INTRODUCTION

Ever since its invention, the toothbrush has played a vital role in the maintenance of oral health and dental hygiene. Therefore, dentists throughout the world advocate the regular use of the toothbrush to maintain oral hygiene.[1] The use of toothbrush with dentifrice improves the mechanical control of dental plaque.[2] However, if brushing of the teeth is not done judiciously, it could results in trauma to the soft tissue as well as hard tissue of the oral cavity.

The wearing of the tooth surface caused by friction of tooth with a foreign object is called “abrasion.”[3] Buccal surfaces of teeth are more prone to abrasion due to overzealous brushing.[3] Abrasion is most commonly associated with toothbrushing on the cervical margins of teeth.[4] Various studies have shown that different variables influence toothbrush abrasion. These variables include brushing technique, force of brushing, duration and frequency of brushing, and type of brush, in particular filament stiffness.[5] Regular toothbrushing with dentifrices has been considered an etiological factor in gingival recession and tooth wear as reported by various studies.[67]

Profilometer is a device used for measuring surface roughness. In vitro studies, have used profilometric analysis to measure change in surface roughness after subjecting the specimens to toothbrushing.[8910]

There are various types of toothbrushes with different bristle design available in the market. Depending on the diameter of the bristles, toothbrushes have been categorized as soft (0.2 mm), medium (0.3 mm) and hard (0.4 mm).[1112] In general, toothbrush bristles vary in size and design as well as in length, hardness and arrangement. The stiffness of bristles varies based upon its diameter, length, number of filaments in a tuft, and curvature of filaments.[12]

Some of the common bristle designs available in the Indian market include flat trim design, zig-zag pattern, and bi-level bristles. Toothbrush with different bristle design can affect surface abrasivity. In describing the optimal characteristics of a toothbrush, Bass[13] recommended that each filament should be end-rounded to minimize trauma. However, subsequent clinical studies by Hine,[14] showed that the shape of the ends of nylon filaments is unimportant and that round-ended bristles are no safer than cut-ended bristles. However, many dentists still recommend the use of round bristle tips as they cause fewer traumas than bristles with sharp edges.

The mechanism is unclear as to how different bristle designs affect abrasion of the tooth surface as reported by various studies done in different parts of the world. To the best of authors’ knowledge, there have been no such studies reported in India, to assess the effect of harmful effects produced by different bristle designs on the tooth surface. A reason that can be cited is that we need to apply a uniform force on the tooth surface, which cannot be done manually and requires construction of a customized brushing apparatus, which will deliver uniform force and involves technical complications. Therefore, this study was undertaken with the objective to assess, in vitro, the effect on surface abrasivity of enamel surface caused by three different types (flat trim/zig-zag/bi-level) of bristle design along with the use of standard dentifrice and application of uniform force by a specially designed customized toothbrushing machine.

MATERIALS AND METHODS

The study was undertaken in September and October 2012 in a private dental institution in India. Prior to the study institutional clearance to conduct the study was taken. A total of 24 freshly extracted teeth were collected from various camps. The teeth, which were extracted were immediately immersed in formalin solution and transported to the institution. Teeth that showed signs of hypoplasia, fluorosis, caries, fracture, decalcification, and restoration were not considered in this study and were discarded.

Gross trimming of all the surfaces of the extracted teeth was done using a lathe machine (Baldor 340 Dental lathe), so that only labial surface remained intact. The labial surface was selected and subjected to toothbrushing cycle because under normal circumstances, in the oral cavity, the labial or buccal surfaces of teeth are more prone to harmful effects of vigorous toothbrushing. The net labial surface area that remained after gross trimming was approximately 9 mm2. The specimens were then mounted, on separate acrylic bases (Meliodent Cold). Hence, a total of 24 mounted specimens were made. The acrylic was allowed to dry completely. All stains and food debris adhering to the prepared specimens were cleared off. Following this, all the 24 acrylic slabs with the mounted enamel specimens were subjected to profilometric analysis (Taylor Hobson Precision SURTRONIC 3+).

Profilometric analysis

A profilometer is a device used to measure the surface roughness. The profilometer produces a tracing using digital and analog hardware and software, and calculates the average surface roughness (Ra) value for the resultant tracing.[15] The surface roughness was measured using the profilometer (Taylor Hobson Precision SURTRONIC 3+), for each specimen and values were recorded.

Customized brushing model

A custom made brushing apparatus was constructed by the expert consultation. The brushing apparatus was designed to deliver uniform force and uniform unidirectional motion to the tooth surface.

The customized brushing apparatus consists of the following parts:

Motor: (Wexco) To deliver a uniform force and move toothbrush in back and forth direction.

Handle: To which toothbrush can be attached.

Base: To support the whole apparatus.

Three different commercially available toothbrushes of the same company (Oral-B) and same bristle diameter (medium) with different bristle orientations (flat trim, zig-zag and bi-level) were used in the study. Toothbrushes were mounted on the brushing apparatus and fixed firmly, so that there was no lateral movement during brushing. The apparatus was so designed that it facilitated easy replacement of one type of toothbrush with another. The mounted enamel slabs were firmly fixed in position during brushing. Using Dontrix gauge (GAC International, Inc., Bohemia, NY, USA) the tension of the spring was adjusted to 90 ± 10 g[11] as this was found to be normal pressure range, which people apply manually during toothbrushing. During the brushing cycle, the tension was adjusted periodically.

Dentifrice slurry

A commercially available standard dentifrice (Colgate, India) was used throughout the study. Toothpaste in pea shape was squeezed over the mounted specimens following that they were subjected to brushing cycle.

Brushing regimen

The mounted enamel specimens were randomly divided into three groups: Group 1, Group 2, and Group 3. Each group contained eight mounted specimens. Group 1 specimens were brushed with flat trim bristle design, Group 2 with zig-zag pattern and Group 3 with bi-level bristle design toothbrushes. All the three toothbrushes used were of medium type. The brushing regimen was carried out, in a direction, perpendicular to long axis of the tooth, with a uniform force as it naturally happens in oral cavity. A single specimen was brushed for 2 min period, twice daily, for 1 week. After the brushing regimen was over, the surface roughness of all the 24 mounted specimens were calculated using profilometer.

Statistical analysis

Pre- and post-brushing surface hardness values were recorded. The change in surface hardness was measured. All statistical analysis was performed using SPSS version 16 (SPSS Inc, Chicago, USA). Kolmogorov–Smirnov test was performed to check for skewness. Kruskal–Wallis test and Mann–Whitney U-test were performed to compare between the groups.

RESULTS

Kolmogorov–Smirnov test was performed, which showed that the data was unevenly distributed. Hence, Kruskal–Wallis test was performed to compare the change in surface roughness among the three groups. The results showed that the change in surface roughness (post- and pre-roughness) was statistically significant between the three groups [Table 1].

Table 1

Comparison of surface abrasion produced by three different toothbrush bristle design using a standard dentifrice

When two different groups were compared, it was found that there was a significant difference in surface roughness change (post- and pre-roughness) when Group 2 (zig-zag bristles) was compared with Group 1 (flat trim) and Group 3 (bi-level) was compared to Group 1 (flat trim) [Table 2].

Table 2

Comparison of surface abrasion produced between two groups of different toothbrush bristle design using a standard dentifrice

DISCUSSION

Numerous toothbrushes of various designs and specifications are available today for the removal of bacterial plaque and food debris. For the most part, the choice of a toothbrush is a personal decision based on individual preferences.[16] There are various designs of toothbrushes available in Indian market, and over decades they have undergone technical modifications also but still there is no data available equivocally that one design is better than the other. Simultaneously, the injudicious use of these toothbrushes can cause trauma and mechanical wear of the tooth surface.

Various types of toothbrushes available in the market keep the buyer in a state of dilemma as to which one to choose, due to lack of information about the “quality” of it.[17] Various epidemiological surveys conducted in Indian population have shown that a greater proportion of Indian population use medium to hard toothbrush.[1819] The authors are of the opinion that the lack of knowledge and awareness regarding the correct selection might be the cause for the majority of them to select incorrect toothbrush without knowing the adverse outcomes. Various studies have shown that medium and hard toothbrushes cause higher proportion of abrasions compared with soft toothbrushes.[2021] However, in these studies the effect of different bristles designs have not been evaluated. With the paucity of data to evaluate the harmful effects of different bristle designs of toothbrush on hard tissue, this in vitro study was undertaken wherein three different bristle designs (flat trim, zig-zag and bi-level) were compared using a medium toothbrush.

The surface abrasion can be evaluated using a profilometer. Various studies have used profilometric analysis to evaluate change in surface roughness.[8910] The Ra of a specimen is the arithmetic average height of roughness component irregularities from the mean line measured within the sampling length. The recordings of profilometer were made by placing the tip of the profilometer at the center of each mounted specimen which was embedded in acrylic base.

In this study, for carrying out the brushing cycle, a customized brushing apparatus was constructed. A number of, in vitro studies, have reported the use of commercially available automated brushing machine.[2223] However, due to the high cost of these machines, their use is restricted to large scale pharmaceutical and optical testing companies. Hence in thisstudy, a customized brushing apparatus was designed, which allowed brushing at consistent brush stroke speed and brush head pressure (90 ± 10 g)[10] which is within normal pressure range was applied manually during toothbrushing.

In this study, the surface abrasivity produced on the mounted enamel specimen produced by three different toothbrush bristle design was evaluated. The bristle diameters for all the three designs of toothbrushes were same (medium) and in order to minimize differences, toothbrushes of same company (Oral-B) were selected. In order to minimize surface abrasivity caused by use of different dentifrices, standardized dentifrice was used in all cases. The results of current study showed that surface abrasion was produced on each specimen, in all the three groups, which were subjected to brushing cycle. However, the bi-level bristle design and zig-zag bristle design showed significantly higher surface abrasion when compared to flat trim bristle design toothbrush. Similar findings were reported by Drisko et al.,[24] and Bass[13] wherein they found that sharp-pointed bristles cause more of surface abrasion. However, in a study done by Hine,[14] there was no differences found between different toothbrush bristle designs. The results were also contrary to the findings of Sripriya and Shaik Hyder Ali[25] wherein their study, they found that that there is no single superior design of manual toothbrush. Though minor and some site differences in favor of the brushes were seen, they were not statistically significant differences observed.

Irrespective of type of bristle design, surface abrasion was produced in all the three groups. However, the flat trim bristle design was found to be relatively safe compared to other designs. Toothbrush design, brushing frequency, brushing pressure and abrasivity of dentifrice, all affect the degree of cervical abrasion observed among individuals. However, in this study only the bristle design was evaluated by keeping other factors constant. This type of, in vitro study, helps in evaluating surface abrasion caused due to different bristle design before planning expensive and time consuming clinical trials.

In this study, the effect of saliva was not taken into consideration. Saliva is essential for a lifelong conservation of the dentition. Various functions of saliva are implicated in the maintenance of oral health and the protection of our teeth.[26] Previous studies carried out by Hila Hajizadeh et al.,[27] Zuryati et al.,[28] Kaur and Nandlal[29] have evaluated abrasion produced on dental materials. However, these studies also had the limitation that the effect of saliva was not evaluated. Hence, the authors recommend that further studies should be conducted wherein the role of saliva on abrasion should be evaluated to determine any clinical implication.

CONCLUSION

The flat end bristle design was found to cause less surface abrasion. Hence, the use of flat end bristle design is recommended based on the findings, as it was found to be relatively safe in not causing tooth wear. However, further long-term longitudinal and clinical studies are needed to clarify the relationship of the different designs of toothbrush bristles and soft- and hard-tissue abrasion.