In Vitro Evaluation of Molar Teeth Occlusal Surface Roughness in Simulated Brushing

Cervical abrasion is a common form of non-carious cervical lesion (NCCL) characterized by the loss of tooth structure at the cervical margin. It is often attributed to mechanical factors such as tooth brushing habits. Understanding the impact of various brushing methods and tools on cervical abrasion is crucial to providing evidence-based preventive strategies.

DH is one of the most vexing dental problems, affecting people aged 20 to 50 [1]. The hydrodynamic theory explains the environmental, mechanical, thermal and chemical changes that cause fluid movement within the exposed dentinal tubules, stimulating the pulpal fibers and inducing transient sharp pain. Visual or tactile examination of the teeth is essential to elicit the characteristic DH by applying a stimulus to the affected tooth with standardized air-blast stimulation [1].

Morphological and histological features of the cervical region contribute to the region's disproportionately high rate of lesion development, where the tooth crown becomes more vulnerable to physical and chemical stimuli as the enamel thickness gradually decreases near the cementoenamel junction (CEJ) and the dentinoenamel junction. In its initial phases, the cervical abrasion appears clinically as a narrow horizontal groove on the buccal/labial surface of the tooth near the CEJ. It also has a polished surface with a glossy appearance, as well as tactile sensitivity to the path of the explorer [2].

Cervical Abrasion (CA) is defined as a pathological condition caused by abrasive agents on the tooth surface or any objects placed frequently between or on the teeth. Tooth wear‐attrition, abrasion and erosion are considered Non Carious Cervical Lesions (NCCLs), discomfort, sensitivity, pain and loss of tooth vitality [3]. The etiology of cervical abrasion is multifactorial involving a complex interaction of various factors such as overzealous brushing technique, use of an abrasive agent. Other factors such as erosion and abfraction also contribute to varying degrees [3].

Since the abrasive process is rather slow, there is formation of secondary and tertiary dentin to protect the pulp. Sclerotic dentin is another protective response that has treatment implications. Retention of dental plaque, sensitivity, pulp damage and periodontal disease progression are few of the undesirable effects of CA. Treatment is aimed toward managing the symptoms, restoring the morphology of the teeth and treating soft tissue pathology. If untreated, pulpal exposure and infection, as well as periodontal deterioration are possible. Therefore, CA must be managed appropriately with suitable restorative procedures [4].

Several biological, chemical and behavioral functions can hasten the process leading to structural and functional loss of teeth. The cementum and dentin are more likely to be severely affected [5]. These are a group of lesions called noncarious cervical lesions presented as a wedge or V-shaped defect on the cervical region of the tooth, associated with gingival recession [5].

Many variables, including rough tooth brushing and the use of dentifrice with a high-abrasive component, may lead to tooth abrasion. Brushing causes lesions that are more noticeable in the incisor, canine and premolar regions than they are in the molar region [7].

Maintaining proper oral hygiene is essential for the prevention of dental caries and periodontal conditions, with tooth brushing being a fundamental component of routine oral care. Nevertheless, both clinical and epidemiological evidence have highlighted concerns regarding the negative consequences of incorrect brushing practices, particularly the development of cervical abrasion. This condition involves the pathological loss of tooth structure at the cervical region (near the gumline) and is typically attributed to mechanical wear rather than decay. Contributing factors include the application of excessive brushing pressure, use of toothbrushes with hard bristles and highly abrasive toothpaste formulations.

Cervical abrasion has been observed in various demographic groups, affecting individuals across different age ranges. Although structural changes in the tooth related to aging-such as increased dentin exposure-may play a role, inappropriate brushing habits continue to be a significant and adjustable risk factor. Despite numerous studies investigating the mechanical aspects of brushing, there remains a lack of consensus on the most effective brushing method, duration and frequency that can adequately clean teeth while minimizing damage. Furthermore, the interaction between mechanical forces and chemical influences, including abrasive agents in toothpaste and acidic components in the diet, deserves closer examination.

One major difficulty in evaluating cervical abrasion lies in distinguishing it from other forms of Non-Carious Cervical Lesions (NCCLs), such as erosion and abfraction. While abrasion is primarily mechanical, erosion results from the chemical breakdown of tooth structure due to acid exposure and abfraction is believed to stem from stress-induced microcracks caused by occlusal forces. The overlapping characteristics of these conditions complicate efforts to isolate toothbrushing as a primary cause, highlighting the need for well-controlled clinical and laboratory-based investigations.

Brushing force has emerged as one of the most extensively studied mechanical factors associated with cervical abrasion. Evidence suggests that applying too much pressure while brushing can accelerate the wear of dental surfaces, especially when combined with abrasive toothpaste. Although the use of soft-bristled toothbrushes is generally recommended to reduce mechanical stress, debates persist regarding their efficacy in comparison to brushes with medium or hard bristles. Additionally, the choice between manual and electric toothbrushes introduces further complexity. Some studies advocate for electric brushes with built-in pressure sensors to help control brushing force, while others caution that high-speed oscillatory movements may also contribute to enamel and dentin loss under specific circumstances.

Brushing Techniques and Cervical Abrasion

Eccles suggested the term “tooth surface loss” when a single etiological factor was difficult to identify. However, Smith and Knight advocated the term “tooth-wear” to embrace all three processes of abrasion, attrition and erosion.

Smith and Knight presented the concept of measuring tooth wear fundamentally, irrespective of the etiology, which paved the way for other indices. The Tooth Wear Index is a comprehensive framework whereby every one of the four surfaces (buccal, cervical, lingual and occlusal-incisal) of all teeth present is scored for wear, independent of etiology. However, the drawback of this index was that it required computer assistance and was time-consuming [6].

Bardsley et al. pioneered a new simplified version of the Tooth Wear Index where the scoring was dichotomized into the presence or absence of dentine, with even cupping of dentine scoring one. Some debate still exists regarding the significance of dentinal cupping when exposed dentine does not relate to significant amounts of tissue loss [6].

Several studies have investigated the impact of brushing techniques on cervical abrasion. Horizontal brushing has been frequently associated with higher rates of abrasion due to the repetitive back-and-forth motion at the cervical region. A study by Addy et al. [8] demonstrated that horizontal brushing with excessive force significantly increased cervical wear compared to circular and vertical techniques.

A recent study by Grender et al. [9] explored the effect of modified Bass technique in preventing cervical abrasion. The findings indicated that the modified Bass technique, which involves gentle vibratory motion, resulted in minimal cervical wear over a six-month follow-up period.

A systematic review by Wiegand and Schlueter [10] reinforced that the horizontal brushing technique combined with abrasive toothpaste accelerates cervical wear. The study emphasized that brushing with low-abrasive toothpaste and gentle pressure reduced the risk of cervical abrasion.

A clinical trial by Joiner [11] evaluated the effect of brushing technique on cervical abrasion and found that vertical brushing with soft-bristle toothbrushes produced significantly lower cervical wear compared to horizontal techniques.

Factors Influencing the Severity of Cervical Abrasion

Toothbrush Type

The tubules in sensitive dentin are said to be open between the exposed dentinal surface and the pulp and are wider than those in no sensitive dentin. Furthermore, the number of tubules in the sensitive dentin is eightfold wider than the no sensitive dentin [7]. The factors associated with cervical abrasion include overzealous tooth brushing using hard bristles and the use of abrasive toothpaste [14-17]. It is stated that there is no ideal treatment for DH, even in the case of a combination of diverse protocols [18].

Manual and electric toothbrushes have been compared in various studies. While electric toothbrushes provide more consistent brushing pressure, some studies suggest they may reduce cervical abrasion when used with pressure control features.

Brushing Frequency, Duration, Force

Higher brushing frequency and prolonged brushing sessions increase mechanical stress on tooth surfaces. Several studies have reported a positive correlation between brushing frequency and cervical wear. Brushing force is a critical factor in cervical abrasion. Excessive force, particularly when combined with abrasive toothpaste, exacerbates cervical wear [11].

Selection of Teeth: It was mounted on a silicone mould with standard dimensions (Figure 1).

Medium bristle variety toothbrushes were fixed tightly with the help of screws in the automated brushing machines.

Figure 1: Forty Eight Molars were Selected

Roughness Evaluation

The baseline roughness was evaluated using a Stylus Profilometer (Figure 3). The Profilometer is a device that is used to measure the surface roughness changes. It produces a trace using the digital and analogue hardware and software. The Roughness average (Ra),The Roughness peak (Rz),The Root mean Square Roughness (Rq) were obtained for the mounted tooth specimens (Figure 2).

Figure 2: Toothbrushes

Figure 3: Stereomicroscopic View (30X)-Simulated Abrasion of Molar Teeth in Oscillatory Strokes

Duration and Frequency of Brushing

The tooth samples were mounted in the SD MECHATRONIK BRUSHING SIMULATOR (Figure 4) which consists of 20,000 cycles (Linear x5000, clockwise -5000 and anticlockwise-5000). After which the pre and post roughness mean were calculated and the change in the roughness was compared.

Figure 4: Stereomicroscopic View (30X) -Simulated Abrasion of Molar Teeth in To and Fro Strokes

Procedure The profilometric analysis was done for the mounted tooth samples before tooth brushing and the mean surface roughness was calculated.

Brushing Simulation

• Brushing was conducted using an automated brushing machine to ensure consistency in stroke application
• Each toothbrush was replaced every three months to simulate real-world conditions of wear and effectiveness loss
• Brushing was performed under a controlled pressure of 100 g, with a stroke frequency of 180 strokes/min
• The toothbrushes used were standard commercially available medium-bristled brushes
• The brushing simulation was conducted for a total period of one year, with toothbrushes changed every three months
• Over the course of the study, each sample underwent a total of 131,400 brushing strokes, corresponding to the estimated number of strokes a person would perform in a year of daily brushing at a rate of 3 strokes per second

Outcome Measure

• Tooth surface roughness was measured using a non-contact profilometer at baseline and at the end of the one-year period
• Measurements were taken at three points and the mean value was recorded for statistical analysis

Ra value (Roughness Average) is a common measure of surface roughness, which quantifies the average height deviation of a surface profile from a mean line over a specified length. The Ra value is used in various fields, including materials science and engineering, to assess the smoothness or roughness of a surface.

Here’s a general idea of how different Ra values translate into surface roughness:

• Ra = 0.01-0.05 µm: Extremely smooth, often seen in precision engineering, like polished metal surfaces in aerospace or semiconductor manufacturing.
• Ra = 0.1-0.3 µm: Smooth, used in high-precision machinery, fine polishing of metals, or polished glass surfaces.
• Ra = 0.5-1.0 µm: Lightly rough, typical of ground steel or lightly machined surfaces.
• Ra = 1.0-3.2 µm: Moderate roughness, commonly found in machined parts, industrial steel, or castings.
• Ra = 5.0 - 10.0 µm: Rough surfaces, such as those found in typical castings, welds and some structural components.
• Ra = 10.0-25.0 µm: Very rough, seen in heavily casted parts, or surfaces where a significant amount of machining is done.
• Ra>25.0 µm: Extremely rough, often a result of processes like sandblasting or large- scale casting operations.

Brushing Simulation with Oscillatory Strokes (Table 1 and 2)

Brushing Simulation with To and Fro Strokes (Table 3 and 4)

• The oscillatory brushing shows a small increase in Ra with slightly higher variability
• The to and fro brushing causes a much larger mean increase in Ra with lower variability, suggesting a more uniform but aggressive effect

This shows that to and fro brushing causes a much greater increase in surface roughness than oscillatory brushing.

Independent Samples t-test: To and Fro vs. Oscillatory Brushing on Molar tooth Surface Roughness (Ra Difference)

An independent samples t-test was conducted to compare the effect of vertical and horizontal brushing techniques on surface roughness (Ra difference) (Figure 5-6).

Figure 5: Pre and Post Brushing Simulation with Oscillatory Strokes

Figure 6: Pre and Post Brushing Simulation with To and Fro Strokes

Table 1: Surface Roughness (Ra, µm) – Group A (Oscillatory Brushing: Pre vs Post)

Table 2: Mean Surface Roughness Difference – Group A (Oscillatory Brushing)

Table 3: Surface Roughness (Ra, µm) – Group B (To and Fro Brushing: Pre vs Post)

Table 4: Mean Surface Roughness Difference – Group B (To and Fro Brushing)

Table 5: Final Results

To and Fro Brushing:

• Mean Ra difference: 5.300
• SD: 0.025
• n = 24

Oscillatory Brushing:

• Mean Ra difference: 0.055
• SD: 0.024
• n = 24

Independent t-test Results:

• t-statistic: 741.45
• p-value: 1.09 × 10⁻⁹²

Interpretation

There is a highly significant difference between the mean surface roughness change from to and fro brushing and oscillatory brushing (Figure 7-9).

Since the p-value is far below 0.05, you can conclude that the increase in surface roughness is significantly greater in the to and fro brushing group.

The analysis revealed a statistically significant difference between the two groups.

Figure 7: Sample Picture Made using Stereomicroscope at 30X Magnification

Figure 8: Sd Mechatronik Brushing Simulator Used For Brushing the tooth Samples