Background
Tooth sensitivity is one of the adults’ most common dental problems, characterized by short, sharp, and transient pain. In a meta-analysis study, the prevalence of tooth sensitivity ranged from 2.8 to 74% [
1]. There is still no precise rationale for tooth sensitivity [
2,
3]. Among all mechanisms suggested by now, Brannstrom proposed the theory of hydrodynamics (Fluid Movement/Hydrodynamic) in 1964. The aforementioned theory is the most acceptable theory based on the dynamic flow of dentinal fluid [
4]. Usually, when dentin tubules are exposed to the external environment, different stimuli can make the fluid in dentin tubules to move, which leads to nerve fiber stimulation and pain [
5]. The cause of tubule exposure is multi-factorial. Generally, the gradual wearing of enamel or gingival recession (which causes dentin or root surface cementum exposure, respectively) is the most common cause [
6]. Usually, creating an outward flow caused by stimuli such as cold, dryness, and hyperosmotic solutions makes the tooth more sensitive than a flow toward the pulp (for example, by heat) [
3]. The most common stimulus in dentin hypersensitivity (DH) is cold air flow, such as breathing in cold winter air or applying a dental unit air syringe [
7].
Several active substances have been introduced for the treatment of DH. CPP-ACP (derived from cow’s milk protein, casein, calcium, and phosphate) [
8], TCP (tricalcium phosphate, a calcium phosphate system which is stable in aqueous environments [
9], Remin Pro (containing hydroxyapatite, fluoride, and xylitol) [
10], Pro-Argin (containing arginine/calcium carbonate) [
11], and NovaMin (containing calcium sodium phosphosilicate (CSPS)) [
12] have shown positive results. Different commercial products have been offered for each of the aforementioned mechanisms, some of which contain one or more active ingredients that use only one anti-sensitive mechanism for treatment. Nevertheless, some of these substances treat sensitivity using two or more active agents, employing the effects of both mechanisms (physical blockage and nerve stimulation).
Arginine is an essential amino acid with an alkaline pH, and its dentin-desensitizing effect in combination with calcium carbonate (as a rich source of calcium ions) has been proven in previous studies, both
in-vitro and in the clinic [
11,
13‐
19]. Arginine and calcium ions, which are positively charged at physiological pH (alkaline by bicarbonate buffer), bind to the negatively charged dentin surface and create a calcium-rich layer [
11].
By increasing the potassium concentration in nerve endings and preventing the generation of action potentials in interdental nerves, potassium salts have become the most popular desensitizer of dental nerves, whose dentin desensitizing effect has been proved in previous studies [
20‐
24]. By causing depolarization, potassium salts prevent repolarization and transmission of pain messages through nerves. Potassium nitrate (5%), potassium chloride (3.75%), and potassium citrate (5.5%), all of which contain 2% potassium ions, are used as active ingredients [
25]. Professional pastes, toothpastes, and gels containing potassium nitrate are specifically used to reduce the incidence of tooth sensitivity during the dental bleaching period. For this purpose, patient should start the treatment two weeks before the beginning of the bleaching period and continue treatment during the bleaching process.
To the best of the authors’ knowledge, no studies have evaluated the potential of the combination of Pro-Argin and KNO3 agents as a double-action anti-sensitive treatment. Few studies evaluating the combination of two mechanisms together have been published. Even those that utilized both mechanisms of action did not implement the Pro-Argin agent as an occluding mechanism [
26].
Pain, as one of the permanent and apparent characteristics of dentin hypersensitivity, affects quality of life [
27]. Recently, the Dentine Hypersensitivity Experience Questionnaire (DHEQ) was designed to evaluate the impact of DH on the quality of life. To prevent dentinal sensitivity recurrence, identifying etiological factors such as improper brushing technique, poor oral hygiene, premature occlusion contacts, gingival recession, and exogenous/endogenous acids is crucial [
28]. However, due to the difficulty, impossibility and time-consuming nature of removing all the primary causes, the most common action in the clinic is the use of anti-sensitive agents in-office and recommend to keep using at home. This work aimed to evaluate the effect of a new combination paste containing 8% L-Arginine and CaCO3 plus KNO3 in treating DH in non-carious lesions. The null hypotheses tested in this study are as follows:
-
There would be no difference between the two pastes with and without the desensitizing agents (8% L-Arginine and CaCO3 plus KNO3) in terms of dentinal tubule permeability.
-
There would be no difference in reducing tooth sensitivity effectiveness between the two pastes.
Discussion
The
in-vitro and clinical investigation of the anti-sensitivity paste effectiveness containing L-arginine/calcium carbonate 8% and potassium nitrate demonstrated that the paste decreases the permeability, closes the dentinal tubules, and significantly reduces dentinal hypersensitivity (DH) regarding cold and tactile sensitivity in long term (3 months after treatment); therefore, the first null hypothesis was rejected. DH is linked to dentinal tubule permeability, resulting from factors like occlusal wear, deep caries, brushing abrasion, erosion, and parafunctional habits. Commonly, anti-sensitive toothpastes are used to alleviate DH and reduce patient discomfort [
34].
According to the in-vitro results of this study, the initial average permeability of the study groups did not display significant differences. However, a noteworthy reduction in dentin permeability was observed in the intervention group after one week of paste use, indicating the effectiveness of the formulated paste in closing dentinal tubules. Consequently, the second null hypothesis of the research is rejected. These findings were further supported by microscopic examination (at X5000 magnification), which revealed predominantly open dentinal tubules in the control group, whereas the intervention group exhibited almost complete closure of the tubules, thereby reinforcing the study’s results.
This finding aligns with Parmar et al.’s study [
18]. Their electron microscope analysis showed more closed tubules in the arginine group than in the control. Midha et al. [
35] found positive effects for all anti-sensitive agents, with NovaMin, followed by arginine and potassium nitrate, most effective in closing dentine tubules. In contrast to Midha et al., Rajguru et al. [
36] reported arginine paste as more efficient in closing tubules but found NovaMin to resist acid challenges better. Since the decrease in the permeability of dentinal tubules in laboratory conditions may be different from the changes that occur in the biological, complex, and dynamic environment of the mouth; further investigations under clinical conditions are necessary, that’s why this project was continued with a clinical investigation (phase 2).
Hydraulic conductivity refers to liquid transfer across a surface unit under pressure over time. Lab studies identify factors influencing dentin permeability, with various methods proposed for measurement [
37‐
40]. Dentin disc-based tubule closure assessment is the gold standard for hypersensitivity [
41,
42]. In this study, SEM analysis followed dentine permeability assessment, and clinical evaluation included touch, cold, and spontaneous sensitivity.
According to the hydrodynamic theory, there are two primary approaches to treating DH: (1) closing dentinal tubules to minimize fluid flow in response to stimulation, and (2) reducing excitability in interdental nerves to minimize their response to fluid movements [
43,
44]. Various commercial products are available for each mechanism, containing either single or multiple active substances, targeting only one anti-sensitive mechanism or employing a combination of methods (physical blockage and nerve stimulation).
In this study, the intervention group used a paste containing 8% L-arginine/calcium carbonate and potassium nitrate, while the control group used a base paste without the active anti-sensitive substance. Arginine, with an alkaline pH, has been proven effective in combination with calcium carbonate [
13,
14]. It binds strongly to negatively charged dentin surfaces due to its cationic nature, forming rapid hydrogen bonds and create a calcium-rich layer [
13,
14,
45]. The arginine-calcium carbonate method involves natural processes that block dentinal tubules with calcium-rich materials [
11]. In contrast, the potassium nitrate approach elevates potassium concentration in nerve terminals, preventing action potentials in interdental nerves and pain message transmission by causing depolarization and inhibiting repolarization. Potassium nitrate (5%), potassium chloride (3.75%), and potassium citrate (5.5%), all of which contain 2% potassium ions, are used as active ingredients [
25].
According to the clinical results of the present study, the study found that both groups experienced immediate cold sensitivity reduction after treatment, more pronounced in the intervention group, which also showed sustained long-term anti-sensitive effects compared to the base paste, over time. Unlike the control group, where sensitivity recurred over time, the sensitivity trend in the intervention group was downward steadily, maintaining lower levels until the third month. In terms of touch sensitivity, the intervention group consistently showed significant reductions over time, maintaining lower levels than before treatment. The same figure in the control group witnessed insignificant changes over-time, except immediately after the treatment. The two control and intervention groups showed no significant difference at each time point. For examining spontaneous sensitivity, there was no significant difference between the two groups at any time. In the intra-group comparison over time, as well as in the two-by-two before-after comparison, the level of spontaneous sensitivity did not show any significant changes.
Considering the noteworthy reduction in cold and touch sensitivity observed in the intervention group, this study aligns with previous research demonstrating the effectiveness of Pro-Argin-based pastes, both immediately after treatment and in subsequent evaluations at 3 days [
46] or 2 weeks later [
19,
47]. Hall et al. [
48] examined the long-term effects of NovaMin and Pro-Argin pastes over 11 weeks, revealing significant sustained sensitivity reduction in agreement with the present findings. Investigations into the impact of potassium on sensitivity reduction, both individually [
24] and in combinatio with fluoride ions [
22], consistently corroborate each other and the current study, confirming the positive influence of potassium ions. In a study, Tolentino et al. [
23] explored the effects of potassium nitrate and low-power laser, separately and concurrently, on dentin sensitivity reduction. They found that the combined treatment of these mechanisms proved more effective than individual approaches, suggesting a multi-session protocol with a minimum of three consecutive sessions to maintain prolonged desensitization. Mahesuti et al. [
49] compared UltraEZ, a 5% potassium nitrate-based paste, to MI Paste containing CPP-ACP. They concluded that while potassium nitrate offered short-term and rapid effects, MI Paste provided slower but longer-lasting effects through tubular blocking. Although few studies have addressed spontaneous sensitivity, likely due to its measurement method’s unreliability in evaluation sessions, there remains an unexplored avenue for investigating the combined effect of arginine and potassium, despite the established efficacy of each substance independently.
The Air Blast test measured cold sensitivity, and probe movement assessed touch sensitivity. The Air Blast test is a common, controllable and repeatable method for this purpose [
50]. The Visual Analog Scale (VAS) was utilized to recorded dental sensitivity at various times. VAS is an accurate scale for tooth sensitivity diagnosis based on previous studies [
51,
52]. An issue with VAS is its reliance on individual pain tolerance. To solve this, the Split-Mouth method was employed, making each individual both the intervention and control group simultaneously, which consequently reduces the negative impact of confounding factors. Several studies have previously used and proven the reliability of the split-mouth method to assess tooth sensitivity [
53,
54].
A clinical trial should have an appropriate duration to observe the maximum effect of the active substance while minimizing placebo effects and confounding factors. In this study, we measured sensitivities at six time points: before treatment (T0), immediately after treatment (T1), 24 h (T2), one week (T3), one month (T4), and three months after treatment (T5). This three-month follow-up aligns with recent studies, such as Bae et al.’s review [
50], where the long-term effects of anti-sensitive paste were evaluated over periods of four to twelve weeks.
Based on Wilcoxon test results showing significant sensitivity improvement over time, it’s evident that a single use of anti-sensitive substances reduces patient discomfort, and continued home use maintains treatment benefits. While previous studies recommend three days’ home use after in-office treatment [
55], some studies extend this period to two weeks for optimal results [
19,
22,
56,
57]. However, this extended home use presents challenges due to uncontrollable factors and variations in brushing methods. In this study, with participant consent for additional visits, in-office treatment was conducted in two 30-minute sessions on consecutive days.
In the current study, as many previous studies [
19,
24,
56,
58], the reduction in sensitivity in the control group was also significant, with the intervention group showing a more significant and sustained decrease over time. Reduced sensitivity in control groups is common, influenced by factors like placebo effects [
59,
60], participant awareness of the study [
61], and the Hawthorne effect [
56], where improved oral hygiene during the study period may contribute. The base paste’s components, such as silica, may contribute to dentin surface layer formation and permeability reduction [
22]. Despite these effects, the base paste formulation retained silica for its benefits, including thickening and sensitivity reduction, aligning with intended market release.
In previous literature, physical blockage of tubules has proven more effective than reducing nerve excitability [
35,
56,
62]. Studies show mixed results for desensitizers with potassium ions, with some expressing doubt [
63] and others confirming their effectiveness [
49,
64‐
69]. No clear superiority has been established between these methods, suggesting that combining both approaches may yield better outcomes. Although dentinal tubule closure is a common approach in anti-sensitive toothpaste, no product permanently achieves this. Potassium ions also require prolonged use (2 weeks, up to 8 weeks for significant relief) [
70], and there is debate about their effectiveness because they have to move inward to reach the pulpal nerves against the direction of the flow of dentin fluid to reach their point of action [
71]. Thus, neither method alone is ideal.
The ideal goal for reducing sensitivity involve immediate pain relief while maintaining long-term effects. Most studies focus on the short-term impact of substances using the physical blockade desensitization method. For instance, clinical trials demonstrated that an 8% arginine and calcium carbonate combination (Pro-Argin Technology) provided “immediate” relief after just one application [
72]. Another study by Minkoff et al. [
73] examined strontium chloride’s desensitization effects, which were noticeable immediately and lasted for two more weeks. Conversely, the potassium ion mechanism often targets long-term relief. Bartold et al.’s study on potassium nitrate noted its cumulative effects taking weeks for a significant reduction in sensitivity [
74]. The paste in this study achieved both goals, reducing short-term sensitivity (immediately and 24 h post-treatment) and maintaining effects in the long term (the downward trend until the final three-month evaluation), aligning with prior research on this topic.
This study combined two desensitizing methods using two substances to make it more effective. Although, chemically, no adverse reaction occurs between these two substances, but the immediate sealing of arginine/calcium carbonate may disturb the penetration of potassium ions and this possible interference must be considered. Limited research has simultaneously combined desensitizers to address dentin sensitivity. For example, Sowinski et al. [
22] used a two-chamber syringe to administer potassium nitrate with stannous fluoride, ensuring separate paths with different pHs mixed only during application to avoid chemical interference. Parmar et al. [
18] showed that initial sensitivity reduction with Pro-Argin paste is related to fully closed tubules, while semi-open or open tubules gradually close with repeated paste use, facilitating potassium ion penetration to reduce sensitivity. Our electron microscope images, aligned with prior research, revealed not all tubules closed with the Pro-Argin mechanism, leaving some open for potassium ion penetration. Sowinski et al. [
22] indicated that these methods not only avoid interference but also enhance potassium’s effect, creating a layer that reduces fluid stimulation in tubules and allowing faster potassium ion travel to nerve terminals, especially in response to stimuli like cold, drying, and hyperosmotic solutions, causing tubular fluid outflow [
75]. Another recent study also assessed the efficacy of a biomimetic nano-hydroxyapatite remineralizing solution on a hypomineralized enamel surface and its effect on enamel microhardness. The application of nano-hydroxyapatite solution induced a significant
in-vitro decline of demineralized areas after the first week of application. Conversely, no significant differences were seen between untreated enamel surfaces and remineralized surfaces after 2 months of remineralizing treatment. Remineralized enamel showed significantly higher microhardness figures than demineralized enamel, but lower figures than intact enamel [
76].
Limitations and future suggestions
The study had limitations due to a small number of patients and a limited treatment schedule. Economic and time constraints hindered conducting multi-session treatments, and the Fluid Filtration device lacked full standardization for research purposes, affecting the results. To standardize in-vitro specimens after abrasive papers use on the buccal height of contour, we had to assess the mid-buccal dentine. On the other hand, cervical dentine was assessed in clinical phase because most of the samples had tooth sensitivity due to gingival recession.
Future studies should investigate the efficacy of low-power laser therapy as a complementary approach to manage dentinal hypersensitivity, especially in cases of severe sensitivity. Additionally, thorough evaluations of sensitivity-reducing agents are advised to ensure their effectiveness in resisting acidic conditions. To enhance the credibility of sensitivity research, innovative study designs should be adopted to minimize the impact of the placebo effect.