Effect of Commercially Available Nano-Hydroxyapatite Containing Desensitizing Toothpaste and Mouthwash on Dentinal Tubular Occlusion: A SEM Analysis

ABSTRACT

The aim of this in vitro study was to evaluate and compare the dentinal tubule occlusion using nano-hydroxyapatite (n-HAP) containing toothpaste and mouthwash under a scanning electron microscope. The specimens were randomly divided into two groups with five specimens each: group 1—toothpaste group and group 2—mouthwash group. The percentage of the occluded dentinal tubules was assessed at the baseline, 7^th, 14^th, 21^st, and 28^th days under a scanning electron microscope. The toothpaste group showed a higher percentage of occluded dentinal tubules as compared to the mouthwash group at the 7^th, 14^th, 21^st, and 28^th days, respectively. It can be concluded that brushing twice daily with n-HAP containing toothpaste for duration of 28 days produced good dentinal tubule occlusion.

INTRODUCTION

Federation Dentaire Internationale defined dentine hypersensitivity (DH) as a “short sharp pain arising from exposed dentine most commonly at the tooth cervical area in response to thermal, tactile evaporative, osmotic or chemical stimuli but which cannot be ascribed to any other dental defects, diseases or restorative treatments” in 2009.[1] It may affect patients of any age and is common in the 20–50 years of age group.[2] The main etiologic factors for dentin hypersensitivity are wasting disease, recession of gingiva, and inappropriate brushing techniques.[3] To reduce dentinal hypersensitivity, numerous treatment approaches have been used that includes kinds of toothpaste, mouthwashes for home use and office application restorative material, varnishes, dentinal adhesives, liners, iontophoresis procedures, and laser.[4] Nano-hydroxyapatite (n-HAP) is a biocompatible and bioactive material that acts by blocking the dentinal tubules, which prevents the movement of the dentinal fluid.[5] The aim of this in vitro study was to evaluate and compare the efficacy of commercially available n-HAP containing toothpaste and mouthwash for dentinal tubule occlusion under a scanning electron microscope.

MATERIALS AND METHODS

This in vitro study was conducted in the Department of Periodontology, Rama Dental College, Hospital and Research Center, Kanpur, Uttar Pradesh, India, in collaboration with IIT, Kanpur (Department of Materials Science and Engineering), Uttar Pradesh, India.

The inclusion criteria were caries-free crown and root and teeth without any attrition, abrasion, and erosion. The exclusion criteria were teeth with developmental anomalies and endodontically treated teeth.

Specimen preparation

Premolars and canine were collected and stored in 10% formalin after extraction. Then, the teeth were sectioned mesiodistally in a horizontal manner using a diamond disk bur and straight micromotor handpiece.

Experimental design

Dentin blocks were prepared from the crown part adjacent to cemento-enamel junction (CEJ) measuring 8 mm × 5 mm × 2 mm. 17% ethylenediaminetetraacetic acid (EDTA) solution was used for 5 minutes to etch the dentinal disk.

Then, the specimens were randomly divided into two groups with five specimens in each group as follows:

Group 1—n-HAP containing toothpaste

Group 2—n-HAP containing mouthwash

In group 1, specimens were brushed with toothpaste for 2 minutes twice daily for 28 days.

In group 2, specimens were vigorously shaken in the mouthwash for 1 minute twice daily for 28 days.

Measurements of specimens of each group were taken at the baseline, 7^th, 14^th, 21^st, and 28^th days. The baseline recordings for each group acted as the control for that particular group.

Preparation of the specimens for scanning electron microscope (SEM) analysis

The sample disks were dried in a hot air oven for 8 hours. The sputter coating of samples was performed with a layer of gold measuring 1.5–3 nm. The extent of tubular occlusion was assessed using a Carl Zeiss EVO 50 SEM under 4000X magnification and a beam voltage of 15 Kv.

Assessment of dentinal tubular occlusion

By observing the SEM images, dentinal tubule occlusion was evaluated and expressed in percentages. The dentinal tubules were segregated into three categories depending on the percentage of occlusion:[6]

1. Unoccluded (when the occlusion was 0%)

2. Partially occluded (when the occlusion was <75%)

3. Completely occluded (when the occlusion was >75%)

Statistical analysis

The data were recorded in Microsoft (MS) Excel sheet and were further subjected to statistical analysis using the Statistical Package for the Social Sciences (SPSS) software 24. A statistical significance was recorded at P < 0.05.

RESULTS

Table 1 shows that the percentage of occluded tubules was higher in the toothpaste group than in the mouthwash group at the 7^th, 14^th, 21^st, and 28^th days, respectively.

Table 1.

Intergroup comparison of the percentage of unoccluded, partially occluded, and completely occluded tubules at different time intervals

Interval		Toothpaste (%)		Mouthwash (%)		P
		Mean	SD	Mean	SD
Baseline	Unoccluded	100	0.00	100	0.00	----
	Partially occluded	0	0.00	0	0.00	----
	Completely occluded	0	0.00	0	0.00	----
7th day	Unoccluded	36.52	5.68	53.11	8.41	<0.001*
	Partially occluded	39.43	7.46	32.70	9.62	0.392
	Completely occluded	25.87	5.73	14.16	6.20	<0.001*
14th day	Unoccluded	23.00	4.66	33.16	5.70	<0.001*
	Partially occluded	31.58	4.64	33.20	4.23	0.534
	Completely occluded	44.84	6.45	34.47	8.28	0.002*
21st day	Unoccluded	13.27	3.62	22.56	3.61	<0.001*
	Partially Occluded	28.22	2.63	27.00	6.38	0.579
	Completely occluded	58.45	5.46	52.24	7.63	<0.001*
28th day	Unoccluded	3.34	2.50	9.70	2.86	<0.001*
	Partially occluded	15.82	9.08	19.86	3.80	<0.001*
	Completely occluded	80.84	8.06	71.03	4.68	<0.001*

One-way analysis of variance (ANOVA) test; *indicates statistically significant difference at P≤0.05

DISCUSSION

Dentin is a vital tissue mainly consisting of dentinal tubules.[7] In the current study, extracted canine and premolars were used because these teeth are most affected by dentinal hypersensitivity.[8]

Cervical dentine blocks were used because dentin hypersensitivity mainly occurs in cervical areas.[9]

17% EDTA solution was used to remove the smear layer from the dentinal disk and to stimulate the open dentinal tubules of the sensitive teeth.[10]

In the mouthwash group, the dentinal disks were vigorously shaken to copy the clinical circumstances, which occur during oral rising.[10]

Since the tooth is nonconductive, before SEM analysis, the sputter coating of dentinal disks with a thin layer (1.4–2.5 nm) of gold was performed to make them conductive.[11]

Here, the percentage of occluded dentinal tubules increased in both groups at the 7^th, 14^th, 21^st, and 28^th days, respectively. The percentage of occluded dentinal tubules predicts the efficacy of n-HAP as a desensitizing agent.

There is no study in the literature that compared n-HAP containing toothpaste and mouthwash for the occlusion of dentinal tubules. However, there is a single similar kind of study performed by James et al.[12] who compared potassium nitrate in toothpaste and mouthwash form and found similar results; that is, the toothpaste form was better at showing 100% of occluded dentinal tubules as compared to the mouthwash group with only 60% of occluded dentinal tubules.

The toothpaste group showed better performance than the mouthwash group because of the presence of hydrated silica in abrasive form and the formation of smear layer during brushing, which is further pushed into dentinal tubules.

The limitations of the study are the limited sample size, and the estimation of the toothpaste and mouthwash action was made in the absence of any acid challenge, which normally occurs in the mouth.

CONCLUSION

It can be concluded that brushing twice daily with n-HAP containing toothpaste for duration of 28 days produced good dentinal tubule occlusion and may be useful in the treatment of dentinal hypersensitivity.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.