Affiliations
doi: 10.29271/jcpsppg.2025.01.74ABSTRACT
Objective: To compare the degree of dentinal tubular occlusion after the application of sodium fluoride (NaF) varnish, diode laser, and silver diamine fluoride (SDF) using a scanning electron microscope (SEM).
Study Design: In vitro experimental study.
Place and Duration of the Study: Department of Operative Dentistry and Endodontics, Ziauddin College of Dentistry, Karachi, Pakistan, from April to September 2024.
Methodology: A total of 120 dentine samples were obtained from extracted sound human premolars and molars using an osteotome. The samples were randomly divided into four groups, with 30 samples in each. Group I: Negative control group, Group II: Diode laser, Group III: Sodium fluoride (NaF) varnish, Group IV: Silver diamine fluoride (SDF). The samples were evaluated using SEM, and the rate of tubular occlusion for each sample was calculated and compared using the Kruskal-Wallis test.
Results: All intervention groups demonstrated significant tubular occlusion (p <0.001). The highest rate of occlusion was found in the laser group, followed by the varnish group, and the lowest in the SDF group. By pairwise comparison between the groups, there was a significant difference between all groups except the varnish and diode laser groups.
Conclusion: Despite the fact that SDF exhibits less dentinal occlusion than the diode laser and varnish, it can still be used as a material for dental hypersensitivity (DH) treatment due to other benefits, such as remineralisation, antibacterial effect, reduced pulpal damage, and affordability.
Key Words: Dentine hypersensitivity, Diode laser, Silver diamine fluoride, Sodium fluoride varnish, Scanning electron microscope.
INTRODUCTION
Dentine hypersensitivity (DH) is defined as sharp pain of short duration associated with osmotic, thermal, mechanical, chemical, or tactile stimuli that cannot be attributed to any other form of dental pathology.1 Tooth sensitivity is one of the most common dental problems, with a prevalence of 2.8-74%, as reported by a meta-analysis conducted in 2023.2 It can lead to physical and psychological problems, which can have negative effects on an individual’s quality of life, resulting in poor oral hygiene practice, unbalanced food selection, and poor aesthetics.3 DH is treated by either physical or chemical therapy. Various chemical agents function by occluding the tubules, restricting fluid passage, or altering the neurological response to painful stimuli.4
These agents work either through in-office or home-based methods to treat dentine sensitivity.5 The home-based treatment methods include toothpastes, gels, and mouthwashes. These materials exert their effects by two mechanisms: desensitisation of nerves and occlusion of the exposed dentinal tubules.6 Currently, different lasers are used for in-office desensitising treatment methods such as Er: YAG, Nd:YAG, diode laser, etc. Among all these, diode lasers have the advantage of versatility, lower cost, and smaller device size.6 However, some studies suggest the negative effect of lasers on dental pulp when irradiated on the dentinal surface, such as pulpal degeneration and necrosis, especially due to improper laser parameters used.7 Fluoride has been used for decades in the management of DH, as it precipitates and occludes the tubules, forming a protective layer on the dentinal surface.8 The drawbacks of varnish are that the topical application of high concentrations of fluoride exhibits a temporary effect for a short duration, and it may be toxic to odontoblasts.9 A study conducted in 2022 comparing tubular occlusion using 940 nm diode laser, sodium fluoride (NaF) varnish, GLUMA desensitiser, with negative control group proved laser group to be more effective with a mean tubular occlusion of 84.01 ± 12.08%, NaF varnish with 61.78 ± 15.25%, GLUMA with 74.4 ± 11.62%, and negative control group with the least occlusion of 15.03 ± 3.39%.10 Silver diamine fluoride (SDF) is a newer material and has recently been used in dentistry for various purposes, including remineralisation, non-invasive treatment of early childhood decay in children, and management of DH as it is a cost-effective treatment.11 SDF is a topical fluoride solution used to treat carious lesions. An in vitro study found that SDF increases mineral density in artificial carious lesions.12 Silver is also known for its antibacterial effect by exerting its inhibitory effect on the formation of cariogenic biofilm.13 The American Dental Association Council has recommended the use of 38% SDF as a non-invasive treatment for DH and as a dentinal tubular occluding agent, with a mean tubular occlusion of 62.6 ± 24.8% in gel form and 31.4 ± 7.9% in liquid form.14
The objective of this study was to compare the degree of dentinal tubule occlusion following the application of NaF varnish, diode laser, and SDF using scanning electron microscope (SEM).
METHODOLOGY
This in vitro experimental study was conducted at the Department of Operative Dentistry and Endodontics, Ziauddin College of Dentistry, Karachi, Pakistan, from April to September 2024 after obtaining permission from the Ethical Review Committee with reference code: 6780323HWOM.
Sound human premolars and molars were collected from the Department of Oral and Maxillofacial Surgery and Implantology, Ziauddin College of Dentistry, Clifton Campus, Karachi, Pakistan. The sample size was 120 teeth with 30 samples in each group, calculated through the power, analysis, and sample size (PASS) calculator.10,14 Power was set at 80% and the level of significance at 5%. Teeth extracted due to orthodontic reasons and sound wisdom teeth extracted due to impactions from patients aged 18-25 years, were included in the study. All the teeth with caries, fractures, previously root-treated, periodontal defects or extracted due to any cyst and tumour were excluded from the study.
Subsequently, teeth were disinfected with hydrogen peroxide and cleaned with pumice powder using a rubber cup mounted in a slow-speed handpiece for 10 seconds. After disinfecting, the teeth were washed with distilled water for 15 seconds, air dried, kept in normal saline, and then randomly divided into four groups using the envelope method. Group 1 Negative control: No treatment material was applied; Group 2 diode laser: Specimens were treated with a diode laser; Group 3 NaF varnish: Specimens were treated with 5% NaF varnish; Group 4 SDF: Specimens were treated with 38% SDF.
Crowns of the selected teeth in each group were separated from the roots at the cementoenamel junction using a diamond bur in a high-speed handpiece. Roots of multirooted teeth were also separated into single roots using a diamond bur in a high-speed handpiece. Each root was divided into two halves from the centre of the root using an osteotome. Then, dentinal disc was obtained from both halves using an osteotome into 3 × 3 mm width and 3 mm thickness, measuring with a vernier calliper, and then each dentinal disc was polished with carbide abrasive paper for smear layer removal. All disc samples were put in 17% ethylene diamine tetraacetic acid (EDTA) for one minute to expose dentinal tubules. Then the discs were stored in saline and divided into four groups: Group 1: The samples in this group were not treated with any intervention; Group 2: The samples were continuously irradiated by a 940 nm diode laser with a power of 0.5W for 15 seconds once a day for three consecutive days. During application, the laser was moved continuously in all directions; Group 3: NaF Varnish was applied using a microbrush onto the dentinal discs for three consecutive days; Group 4: One drop of SDF was applied on the specimens using a microbrush. SDF was allowed to remain on the exposed surface for one minute and then rinsed with normal saline for five seconds.
All the samples were stored in normal saline, dried with desiccator, and sputter-coated before evaluation under SEM.
All the procedures and evaluations were conducted by a single operator; therefore, blinding was not feasible.
All samples were examined under SEM at a magnification of ×1000. SEM images were analysed using ImageJ software. The percentage of occluded tubules (completely occluded and semi-occluded) was obtained by dividing the number of occluded and semi-occluded tubules by the total number of tubules seen in the image, multiplied by 100.15
Tubules completely sealed at the canal opening were considered fully occluded, whereas those with a reduced opening diameter but open in the centre were considered semi-occluded.
This study used SPSS version 27 for data entry and analysis. Quantitative variables such as dentinal tubule occlusion were represented as median with interquartile range (IQR) for each group. Dentinal tubule occlusions were compared among the four groups using the Kruskal-Wallis test, followed by post hoc analysis with the Mann-Whitney U test. A p-value of ≤0.05 was considered statistically significant.
RESULTS
Table I shows the mean tubular occlusion rate of different groups. The Shapiro-Wilk test indicated that negative control group, diode laser group, and SDF group were normally distributed (p >0.05), while the NaF varnish group was non- normally distributed (p <0.05). Accordingly, results for the negative control group, diode laser group, and SDF group are presented as mean ± SD, whereas results for the NaF varnish group are presented as median [IQR].
The diode laser group showed the highest mean tubular occlusion among all groups, with a mean ± SD of 70.57 ± 9.44. The NaF varnish group also produced almost similar results, though with greater variability and non-normally distributed data with a median tubular occlusion of 63.05 [37.33]. The SDF group gave moderate tubular occlusion with a mean of 34.54 ± 5.31. The negative control group showed the lowest tubular occlusion with a mean of 16.22 ± 6.71.
Table I: Normality test of the data distribution.
|
Groups |
p-values (Shapiro-Wilk test) |
Mean ± SD/ median [IQR] |
|
Negative control |
0.158 |
16.22 ± 6.71 |
|
Diode laser |
0.097 |
70.57 ± 9.44 |
|
NaF varnish |
0.007 |
63.05 [37.33] |
|
Silver diamine fluoride (SDF) |
0.148 |
34.54 ± 5.31 |
Table II: Comparison of tubular occlusion rates among the groups.
|
Groups |
Median [IQR] |
p-value |
|
Negative control |
14.71 [10.76] |
<0.001 |
|
Diode laser |
68.35 [15.19] |
|
|
Sodium fluoride (NaF) varnish |
63.05 [37.33] |
|
|
Silver diamine fluoride (SDF) |
33.49 [8.08] |
|
|
Kruskal-Wallis test applied. |
||
Figure 1: A boxplot graph showing the rate of tubular occlusion of all three interventions. There is a significant difference between all the groups with p <0.05, except NaF varnish and diode laser.
Figure 2: SEM image of dentinal sample treated with SDF, resulting in formation of protein precipitate and silver fluoride crystals with dentine tubules occlusion. Black portion represents open tubules.
Figure 3: SEM image of dentine treated with the diode laser. The occluded tubules appear white, while black areas represent open tubules.
Table II shows the comparison of tubular occlusion rates among the groups, showing a statistically significant difference (p <0.001). The diode laser group showed the highest tubular occlusion in median [IQR], followed by NaF varnish and SDF (Figure 1). SEM images of the tubular occlusions are shown in Figure 2 and 3.
DISCUSSION
The aetiology of DH includes dental caries, gingival recession, ageing, improper brushing habits, and damage to the gingival tissues after periodontal treatment.15
The application of a diode laser has been explored as a treatment modality in DH management by inducing morphological changes in dentine. This study shows that the laser group had the highest dentinal tubular occlusion rate. This aligns with a previous study conducted by Vazirizadeh et al., which compared the effectiveness of tubular occlusion using a 940 nm diode laser, NaF varnish, and GLUMA desensitiser with a negative control. The study showed that the mean tubular occlusion for the 940 nm diode laser was maximum at 84.01 ± 12.08%, followed by GLUMA with 74.4% ± 11.62%, and NaF varnish with 61.78 ± 15.25%.10
According to this study, the diode laser was the most effective agent for promoting tubular occlusion, followed by varnish and SDF. Similar findings were reported in a study by Corneli et al.16
A review conducted by Behniafer et al. in 2024 concluded that laser therapy alone can demonstrate an instant pain-relieving effect upon application. It can also provide long-lasting advantages, and when combined with other desensitisers such as GLUMA, it provides a practical approach for treating DH with a low-power laser.17
NaF varnish is widely used in clinical practice due to its ability to precipitate calcium fluoride crystals within dentinal tubules, reducing their permeability. In this study, the NaF varnish group showed a high median occlusion rate, though with considerable variability. This variability may be attributed to differences in individual responses or application techniques.
The study conducted by Sahoo et al. concluded that the varnish group also showed a significant tubular occlusion; however, the result would be enhanced when combined with laser. These results are in correspondence with this study.18
A study conducted by Nair et al. concluded that both diode laser and NaF varnish are effective separately in causing tubular occlusion, while the combined effect of both produces the most tubular occlusion.19
SDF has gained attention for its dual action in arresting caries progression and reducing DH. The SDF group in this study demonstrated a moderate median occlusion rate, which was significantly higher than the negative control but lower than both the diode laser and NaF varnish groups. The lower variability observed in the SDF group suggests consistent performance in tubule occlusion. The mechanism involved is the formation of silver protein conjugates and calcium fluoride crystals that occlude the tubules.
A study conducted by Kiesow et al. compared tubular occlusion using liquid and gel forms of SDF. The liquid form of SDF produced results similar to the present study, with a mean tubular occlusion of 31.4 ± 7.9%. The gel form of SDF, which was experimentally prepared to enhance its tubular occlusion efficiency, showed improved results with a mean tubular occlusion of 62.6 ± 24.8%.14 However, the current study did not utilise the gel form due to its unavailability.
According to this study, SDF is not as effective in producing tubular occlusion as varnish and laser. Despite this, it maintained a higher degree of tubular occlusion after brushing. As proved by the study by Narra et al., who treated dentine specimens with either GLUMA desensitiser or SDF and simulated oral conditions by regularly brushing the treated specimens for one month, concluded that SDF is not effective in tubular occlusion, while maintaining a higher degree of tubular occlusion after being stimulated with brushing.20
The negative control group exhibited the lowest median occlusion rate, reflecting the natural state of exposed dentinal tubules without intervention. These baseline measurements show that some kind of intervention is necessary for the occlusion of dentine tubules in the treatment of hypersensitivity.
Limitations of the study include that this is an in vitro study, which cannot completely simulate the oral environmental conditions. This study used the liquid form of SDF due to the unavailability of the gel form. Evaluation of the combined effect of SDF with laser was not performed in this study, which would otherwise have provided better outcomes, as in previous studies.
Future recommendations should include the use of a gel form of SDF and a comparison of the combined effect of SDF with laser and NaF varnish with laser to provide even better results.
CONCLUSION
All three materials (NaF varnish, diode laser, and SDF) are effective in dentinal tubular occlusion. Laser was most effective, NaF varnish moderately effective, while SDF was least effective in occluding dentinal tubules among the three groups. However, SDF has other additional benefits such as remineralisation, prevention of caries, and less pulpal damage as compared to NaF varnish and laser, so it can be considered as one of the treatment options to treat DH.
ETHICAL APPROVAL:
Ethical approval was obtained from the Ethical Review Committee of Ziauddin College of Dentistry, Karachi, Pakistan (Reference Code: 6780323HWOM).
PATIENTS’ CONSENT:
Since this is an in vitro study, patients’ consent was not required.
COMPETING INTEREST:
The authors declared no conflict of interest.
AUTHORS’ CONTRIBUTION:
HW: Conceptualisation and design, data acquisition, analysis, interpretation, drafting, and critical revision of the manuscript.
AJ, PB: Accountability for content integrity.
All authors approved the final version of the manuscript to be published.
REFERENCES