Silicon-, Silica-, and Silicate-Toothpastes for Remineralization and Repair of Teeth: A Scoping Review

Abstract

Objective: The purpose of this scoping review was to identify gaps in the literature and summarize findings from studies examining the use of silicon-, silica-, and silicate-based toothpastes for the remineralization and repair of mineralized tooth tissues. Methods: A 10-year literature search was conducted using PubMed and Scopus, adhering to PRISMA 2020 guidelines. A total of 331 studies were initially identified, with 56 full-text review articles. After selecting the manuscripts, 27 studies were qualitatively analyzed by four reviewers, focusing on the results of both in vivo and in vitro methods. Results: The findings suggest that toothpastes containing silicon, silica, and silicate demonstrate promising results for remineralization and enamel repair, with evidence of mineral layer formation and/or deep enamel surface remineralization under various conditions. Additionally, the use of these toothpastes can lead to the obliteration of dentinal tubules within a few days. The results collectively support the efficacy of these toothpastes in enamel repair. Most of the clinical studies focused on dentine hypersensitivity, followed by white spot lesions. Conclusions: Silicon-, silica-, and silicate-based toothpastes (bioactive Si-toothpastes) can be considered effective based mostly on laboratory studies. There remains a need for more in vivo research studies on enamel and dentin mineral repair. Existing studies provide strong evidence that these technologies can reduce dentin hypersensitivity and promote enamel–dentin repair.

1. Introduction

The mechanisms underlying the remineralization of dental hard tissues are now increasingly well-understood. It is also important to recognize the importance of fluoride (F⁻) in this process, particularly when fluoride, in its ionic form, is available in toothpastes and other dental products [1,2]. Fluoride-containing toothpastes have been regarded as one of the most important strategies for dental caries prevention and for the caries decline in many countries. Therefore, fluoride-based strategies remain the standard for caries prevention [2].

However, dental caries persists as a major public health problem in many parts of the world, and new approaches for the remineralization of dental hard tissues have been proposed in the last decade [3,4,5,6,7,8]. These technologies can be divided into two major groups: (a) the non-fluoride remineralization technologies (biomimetic enamel regenerative formulations) that claim to achieve a deeper remineralization of lesions; and (b) the group of products that enhance fluoride efficacy, known as F-boosters [9].

A straightforward simple strategy to enhance fluoride efficacy and its bioavailability in the oral cavity would be to just add more fluoride into oral care products. However, this approach can raise concerns about the potential risk for dental fluorosis, as some children are exposed to multiple sources of fluoride. Moreover, a higher amount of fluoride in the mouth might not be efficacious for controlling erosive tooth wear and other oral complex conditions, such as MIH (molar incisor hypomineralization), associated with hypersensitivity [10,11,12]. In this manner, non-fluoride remineralization technologies and F-boosters can be interesting approaches for consumers that avoid F-toothpastes and for those who prefer low F⁻ in oral care products [2,9].

The incorporation of ions into the hydroxyapatite (HA) structure directly influences its physical, chemical, and physiological properties and, consequently, the tissue mineralization process. In general terms, demineralization is the removal of mineral ions from hydroxyapatite crystals of hard tissues (e.g.,: enamel, dentin, cementum, and bone). Remineralization is the opposite process and can be enhanced by substituting ionic species in the sites of the hydroxyapatite molecule [13]. The presence of substitute ions, either incorporated within the apatite lattice or only adsorbed on the surface, can modify the solubility of a dentin/enamel structure. These substitute ions could be anions such as fluoride and silicon.

The remineralization process can occur within the demineralized tooth structure as a natural repair event. Basically, remineralization is a net mineral gain since calcium (Ca²⁺) and phosphate (PO₄³⁻) ions are deposited into the crystal voids of the demineralized tooth structure [1,9].The incorporation of Ca²⁺ and PO₄³⁻ ions into the crystal lattice can be enhanced by the presence of free fluoride (F⁻) ions in the oral environment. This process can result in an apatite that is significantly more resistant to a subsequent acid challenge [14].

While studies on remineralization modulated by fluoride ions are already well studied, there are still gaps regarding the mechanisms of remineralization orchestrated by silicon. Each ionic grouping of apatite, namely calcium, phosphate, and hydroxyl, can be replaced by another ionic grouping of the same or different valence. In bones, the sites of hydroxyl (OH) and phosphate (PO₄) of hydroxyapatite (HA) are noted as A and B, respectively. Hence, fluoride ions (F⁻) can substitute hydroxyls in site A to form Ca₁₀(PO₄)₆(OH)_2−2xF_2x, whereas (SiO₄)⁴⁻ operates in site B. This substitution in site B will produce Ca₁₀(PO₄)_6−x(SiO₄)_x(OH)_2−x chemical structures [15,16].

Contrary to fluorine, silicon is a relatively inactive chemical element. However, these elements cannot be found in their isolated pure form in nature and both can form bioactive molecules. Silicon is a half-metallic element that reacts with oxygen to form silicon dioxide at high temperatures (SiO₂). In this form, the (SiO₄)⁴⁻ anions are versatile tetrahedral molecules that can be connected in different ways and may become bioactive. This natural form of silicon dioxide is also known as “silica” and can be found in different crystalline or amorphous forms. Silicates occur when silicon dioxide is bound to other elements (e.g., calcium, aluminum, iron, and magnesium) and can be defined as salts [17]. All forms (silicon ion, silica, and silicate) can be of great importance in dental products.

Toothpastes are regarded as one of the most complex healthcare products to produce [18]. It is a mixture of abrasives suspended in an aqueous humectant phase to form a hydrocolloid material that active ingredients will be incorporated into. Furthermore, this material will form a slurry in the oral cavity, a mixture of saliva and denser solids from toothpastes. On one hand, saliva will facilitate the dispersion of ingredients in the oral cavity. On the other hand, saliva will dilute all toothpaste ingredients, including the bioactive ones. Finally, the bioactive ingredients must be stable in different pH environments.

The current knowledge in this field is certainly mostly based on laboratory experimental studies. Probably, there is a lack of data on treatment outcomes since few randomized clinical trials (efficacy studies) were carried out for F-boosters. Moreover, no insights coming from longitudinal effectiveness studies (real life studies) is expected.

The aims of this scoping revision were to identify gaps in the literature and summarize findings from several studies related to silicon-, silica-, and silicate- toothpastes that can be used for tooth remineralization and the repair of mineralized tissues, such as dental caries, molar incisor hypomineralization (MIH), and erosive tooth wear. It is also relevant to update information on this topic because there are many technologies claiming enamel–dentin repair. However, it appears that few clinical trials were carried out to provide robust evidence about the magnitude of the efficacy of these bioactive ingredients.

1.1. Enamel Regeneration or Repair: Background and Definitions

The term “regenerative dentistry” has several definitions that can overlap concepts and goals and raise some confusion. Regenerative dentistry and tissue engineering have been exploring at least three domains that aim to act as scaffolds to promote cell growth and differentiation for tissue regeneration/healing: stem cells, bioactive molecules, and biomaterials [19]. However, a direct approach to hard tissues brings into question whether this concept is suitable. Certainly, it is appropriate for bones and dentin, but for dental enamel, some additional thoughts are worth the effort.

Dental enamel is the only cell-free tissue in the human body, organized in a complex multilevel structure [20]. As a result, dental enamel cannot be biologically repaired or regenerated, and simply recovering the lost minerals may not be sufficient. The challenge lies in recreating the hierarchical structure on the surface of the damaged enamel, mimicking its original structure [21]. As for dentin, the concept of “healing” of the damaged tissue must include the organic portion. This challenging scenario is an open opportunity for a biomimetic approach within a broad perspective of the regenerative dentistry field.

Biomimetics in Dentistry was first proposed by Professor Stephen Mann in 1997: “…biomimetics concepts can be useful for the fabrication of biomaterial implants with controlled porosity and microstructure” [22]. The original idea was related to dental materials and was later expanded to other oral care products. Nevertheless, for both dental materials and toothpastes, the challenges continue: mature enamel, conversely, to dentin and bone, is acellular and does not resorb or remodel. Therefore, a true enamel regeneration cannot occur in vivo [23]; and considering how many toothpastes claim a full regeneration of enamel, the appropriate terminology for their beneficial effect is probably “enamel repair”. To justify the choice of the term “repair” instead of “regeneration”, one must bear in mind that these concepts are commonly used in soft tissue healing processes. A healing repair event takes place with a restored tissue with some failures or even scars from a previously damaged skin/mucosa. Whereas a regenerative healing process brings the idea of a complete restoration of the whole tissue architecture, function, and esthetics [24]. Transposing these definitions to hard tissue is of utmost importance to avoid some conflicting concepts.

It is relevant to point out that the concept of enamel regeneration is preserved when cell-based strategies, tissue engineering laboratory techniques, and similar methods are proposed. However, the focus of this review is the ion-based remineralization and repair of the enamel and dentin by the regular use of toothpastes.

There are more definitions that can raise confusion and need to be clarified, particularly for remineralization (e.g.,: functional remineralization, biomineralization, and biomimetic remineralization). Therefore, to clarify these terminologies and facilitate the rationale for using them, it is important to present a few definitions commonly used in these articles related to enamel/dentin mineral turnover.

Functional remineralization (FR) stands for remineralization that leads to improved tissue mechanics and functionality [25]. This is a close concept to enamel repair.

Biomineralization of hard tissues (enamel, dentin, and bone) involves the deposition of apatite mineral crystals within an organic matrix. Bone and teeth are regarded as biomaterials with unique biomechanical properties that are crucial to their function [26]. Hence, biomineralization is a complex series of events regulated by cells expressing matrix proteins that act as crystallization promoters or inhibitors [27,28]. As a result, the use of a bioactive agent for dental remineralization is not necessarily a biomineralization process.

Biomimetic mineralization (BIMIN) is another technique developed to stimulate the guided formation of a layer of fluorapatite that resembles enamel. This is conducted on a mineral substrate and has the potential to enhance the remineralization of superficial enamel and exposed demineralized dentin [29].

Bioactive remineralization is a general term related to the net mineral gain of a demineralized dentin surface and the following clinical benefits promoted by bioactive agents: acid resistance (carious and erosive challenges), abrasion resistance (mechanical/masticatory wear), and surface impermeability (microleakage and hypersensitivity) [30].

1.2. Silicon, Silica, and Silicate Toothpastes

In dentistry, silicon and silica are best known as hydrated silica SiO₂·nH₂O (silicon dioxide with a variable amount of water), which is used as the abrasive component of many brands of toothpastes. It is the abrasive of choice in clear gel formulations [18]. However, silicon, silica, and silicate can push forward and act as bioactive agents or compose a bioactive material for enamel/dentin remineralization or repair. Since the 1980s, a bioactive material has been explained as one that “elicits a specific biological response at the interface of the material that results in the formation of a bond between tissues and the material” [30,31,32].

Bioactive glasses (BGs or BAG), also known as bioglasses, are a quaternary oxide system of SiO₂–CaO–Na₂O–P₂O₅. It is regarded as the first inorganic material with the ability to bond with living bone tissue and form a stable and tightly bound interface. In addition to bone regeneration, this material is highly versatile. It can deliver pharmaceutical compounds and be useful in many hard tissues engineering challenging conditions. Bioactive glass can mineralize dentine tubules to relieve tooth sensitivity. [32,33].

In the oral cavity, once interacting with saliva, bioglass particles trigger a complex phenomenon termed bioactivity. As a result, this ionic-rich bioglass environment fosters the creation of hydroxyapatite layers and calcium phosphate compounds (Ca₃(PO4)₂) within the tooth structure [34]. The formation of a crystalline hydroxyl carbonate apatite (HCA) layer is regarded as strong evidence of bioactivity in bones and other hard tissues [35]. Basically, a proposed mechanism of action of bioglass for remineralizing dental enamel relies on the following steps, as described by Dai et al. [36]: (a) the aqueous oral environment stimulates the exchange of sodium bioglass ions with hydrogen ions (H⁺); (b) calcium ions (Ca²⁺) in the particles as well as phosphate ions (PO₄³⁻) are released from the biomaterial; (c) a localized pH rise will allow the precipitates of calcium and phosphate ions, together with the ions from saliva, to form a calcium phosphate (Ca–P) layer on the hard tissue (lesion surface); (d) the silica network from the bioactive glass can react with the hydroxyl ions (OH⁻) from the aqueous solution and form soluble silanol compounds; (e) experimental observations indicate that the increase in Ca and P content would induce a decrease in the silicon content. Finally, the newly formed layer displays good resistance to abrasion and transforms into a hydroxyapatite layer, which is structurally like those of the original enamel and dentine [36,37,38,39]. It is important to keep in mind that this cycle has a continuum. Hence, it further increases calcium and phosphate ion concentrations and leads to the precipitation of calcium phosphate on the silica-rich layer [38].

Bioglass^® 45S5 was the first commercial bioglass. Later, other formulations were developed: Class A and Class B, with and without sodium. NovaMin^® is a calcium–sodium–phosphatesilicate glass also described as amorphous sodium calcium phosphosilicate (SCPS) that has the ability of a consistently release calcium ions. To increase remineralization performance, a bioglass combined with fluoride and high phosphate content was developed: BiominF^® [39]. This product seems to form a more stable and resistant layer. Fluoride is particularly relevant in improving the bioactivity for enamel protection by the formation of the more acid-resistant fluorapatite, rather than hydroxyapatite [39]. In addition, fluoride-bioglass may enhance the remineralization of dentin and decrease the risk of dentin-matrix degradation. A further beneficial effect of bioglass is the antimicrobial activity of this material.

Conversely to other technologies that operate in an alkaline milieu, REFIX dental regeneration technology is an acidified bioactive complex produced mainly from compounds containing silica and phosphates [7,12]. Upon contact with the oral environment, they ionize, and these particles bind to the tooth structure, capturing calcium particles available in the oral environment. The interaction of these elements forms layers of hydroxyapatite enriched with silicon. REFIX technology has proven to be effective in tooth remineralization/regeneration, depositing minerals in areas deficient in mineral structures. This action reduces tooth sensitivity and prevents dental caries and erosion from tooth wear [40].

The evidence supporting the efficacy of these technologies for enamel repair and reducing dentin hypersensitivity is increasing. For instance, a recent clinical study comparing NovaMin (Sensodyne Repair & Protect, GlaxoSmithKline, Philadelphia, PA, USA) and REFIX Technology (Regenerador Sensitive, Dentalclean, Londrina, PR, Brazil) showed that both products reduced the tooth hypersensitivity reported by the volunteers [41]. Similar results were also observed in a pilot study performed with participants that report dentin hypersensitivity (DH) caused by root surface exposure or periodontal treatment [42].

NR5™ technology is known for its combination of two compounds—sodium phosphate and calcium silicate. When they encounter the tooth surface during brushing, the combination of these compounds fosters the formation of a new mineral layer of hydroxyapatite, depositing minerals in areas lacking mineral structures. This action reduces tooth sensitivity and prevents tooth decay and erosion [43]. The producers of the NR5™ technology claim that, when the REGENERATE Advanced Toothpaste is used in combination with the serum, it boosts the toothpaste’s effectiveness, enhancing the power of enamel regeneration [4,44].

Table 1. Characteristics of toothpastes in the market that use bioactive Si-compounds.

Technology	Dentifrice	pH	Bioactive Si-Compounds	Fluoride Compound and Concentration
NovaMin	Sensodyne Repair & Protect—Haleon	8.63	Bioglass	1.420 ppm F- (MFP *)
NR5	Regenerate—UNILEVER	8.92	Calcium Silicate/Sodium Phosphate	1.450 ppm F- (NaF and MFP)
REFIX	Regenerator Sensitive—Dentalclean	4.72	Silica/Sodium Phosphate and Phosphoric Acid	1.450 ppm F- (NaF)

* MFP: Sodium monofluorphosphate.

presents the main commercial brands in the market. Note that pH can differ from these technologies suggesting that bioactive silicon, silica, or silicates do not operate in the same manner.

1.3. Rationale for the Review—Guiding Question

Silica is an impressive, versatile compound that can be modified for many purposes in toothpastes. Recently, a modified silica surface produced a promising mucoadhesive compound that may increase the retention of toothpaste particles in the oral cavity [4].

Until now, there have been few publications concerning the effect of bioactive silicon on tooth enamel. Silicon and silica, along with calcium, phosphates, and fluoride induce the remineralization of demineralized tooth enamel and dentine in vitro [4,39,40,41,42,43].

Therefore, this issue needs updated information regarding the positive points and potential limitations regarding the silicon-, silica-, and silicate-toothpastes aiming for dental remineralization and other therapeutic uses. Thus, the guiding question of the review can be summarized as: “Is there supporting evidence about silicon-, silica-, and silicate-toothpastes efficacy for remineralization and/or enamel repair of teeth and relieving dentin hypersensitivity (DH)?”

2. Material and Methods

This scoping review was performed following the 2020 PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for the Scoping Reviews Checklist [45]. This review was registered with the OSF Registries (registration DOI: https://doi.org/10.17605/OSF.IO/U2B8D, accessed on 12 August 2024).

A literature research of papers published in the last 10 years was carried out on PubMed and Scopus (21 July 2024), using the following search strategy:

“silicon” OR “silica” OR “silicate”

AND

“toothpaste” OR “dental gel”

AND

“bioactive” OR “biomimetics”

AND

“teeth”.

It is important to point out that only articles shedding light on bioactive toothpastes/dentifrices/gels were included [30,31,34,40,41,42,46,47,48]. Articles presenting results about hydroxyapatites in these products were excluded unless a combination with silicon, silica, and/or silicate was present. The primary target was enamel–dentin repair. Additionally, the relevant literature was hand-searched and included if the criteria for testing these silicon/silica/silicate technologies for enamel/dentin repair were tested for: “dental caries”; “molar incisor hypomineralization”; “dentine hypersensitivity”; “dental erosion”.

All types of studies were selected (including reviews, systematic reviews, and meta-analyses) but not included for the scoping review. The final reading focused on the therapeutic potential of these technologies in two major categories: A: “in vitro” or “laboratory studies” and B: “in vivo” studies, or general clinical studies, or clinical trials.

Table 2. Inclusion and exclusion criteria used in this scoping review.

Inclusion	Exclusion
All geographical areas but published in English language	Language other than English
Experimental studies (in vitro and in vivo)	Literature reviews, opinions, dissertations, conference presentations, discussion papers
Peer reviewed articles	Not peer reviewed
Published in the last 10 years	More than 10-year publication
Bioactive Si-toothpastes	Silica as abrasive component or incorporated in dental materials or other oral health products

presents the inclusion and exclusion criteria.

A total of 331 studies were imported from screening (148 from PubMed and 183 from Scopus) by F.C.S. After this was the removal of articles related to dental materials and implants or other issues (169) and duplicates (106 studies). F.C.S. and F.V. screened 56 articles (title and abstract). The final number of studies retrieved from the query was 27 (Figure 1). Twelve articles had their full text read by N.L.S.F. and A.F.B.O. in group A (in vitro studies). A.C.C.G. and G.B.M. read 15 full-text articles in group B (in vivo, clinical trials).

3. Results

Qualitative and quantitative analyses were carried out considering the therapeutic potential of silicon, silica, and silicates in toothpastes. Technical and methodological strengths and weaknesses were also explored. However, there are significant methodological differences that need to be considered. From 12 in vitro experiments, half of them used human enamel or dentin specimens, while the other half used bovine blocks for pH cycling and subsequently characterization by different techniques (e.g., scanning electron microscopy (SEM) imaging, EDX elemental analysis, surface microhardness and roughness). The technologies investigated also included non-silicon- and non-silica-toothpastes, such as arginine sodium monofluorophosphate and casein phosphopeptide-amorphous calcium phosphate (CCP-ACP).

Among the in vivo clinical studies (n = 15), 11 were randomized clinical trials (RCTs). Only two of these RCTs were testing the effect on white spot lesions, whereas the others aimed at the reduction of pain due to dentin hypersensitivity.

In general, we observed a substantial heterogeneity of pH cycling methods and techniques for measuring mineral loss/gain in laboratorial in vitro studies. Conversely, the randomized clinical trials were quite homogenous with short studies mainly carried out to evaluate the same outcome: pain relief.

This work retrieved in vitro studies from Brazil (n = 5), the United Arab Emirates (n = 2) and many other nationalities of Europe, Asia, and North America. For in vivo studies, more than half of the studies were concentrated in India, UK, China, and Egypt.

Table 3. Characteristics of the included articles (in vitro studies).

Author (Year)	Study Aim	Outcome Measurement	Sample Size (SS), Follow-Up (FU)	Material(s) or Technology (ies) Used	Active Agent(s)	Primary Results
[49] Poggio et al. (2017) Italy	Evaluate effects of protective agents on dentin erosion by soft drinks.	Percent weight loss, SEM imaging	SS: 70 human dentin specimens FU: 32 min total immersion in Coca-Cola	Remin Pro	Hydroxyapatite	Biorepair and regenerate significantly reduced dentin weight loss, showing greater resistance to acid erosion compared to other agents. Remin Pro and MI Paste Plus showed results similar to the control group, while Tooth Mousse and Biorepair Plus increased dentin demineralization.
				MI Paste Plus	CPP-ACPF and fluoride
				Tooth Mousse	CPP-ACP and fluoride
				Biorepair	Zinc hydroxyapatite, silica and tetrapotassiumpyrophospate
				Biorepair Plus	Zinc hydroxyapatite, silica and tetrapotassiumpyrophospate
				Regenerate	Calcium silicate, sodium phosphate, sodium monofluorophosphate (1450 ppm fluoride)
[50] Altan et al. (2019) Turkey	Evaluate inhibition of demineralization in enamel lesions.	SEM imaging, EDX with weight percentage of mineral changes (Ca, P, Na, Si)	SS: 50 human enamel blocks FU: 5 days pH cycling	Arginine	Arginine	All toothpaste groups showed a statistically significant increase in Ca and P compared to the control group (p < 0.05). CPP-ACP showed the highest increase in Ca and P. NovaMin increased Na and Si significantly.
				Fluoride	Sodium monofluorophosphate (fluoride)
				CPP-ACP	CPP-ACP
				Novamin	NaF, calcium sodium phosphosilicate 5% (NovaMin)
[12] Vilhena et al. (2021) Brazil	Assess mineral content and surface and cross-sectional morphology of enamel and dentin tissues treated with REFIX technology.	SEM imaging, with an energy-dispersive X-ray spectroscopy (EDS).	SS: Bovine enamel blocks (n = 5) FU: 7 days of pH cycling	REFIX technology	NaF, tetrasodium pyrophosphate, silica	REFIX created a silicon-enriched layer on enamel and occluded dentin tubules after 7 days.
[47] Tomaz et al. (2020) Brazil	Investigate remineralization of enamel with fluoride-containing toothpastes with different active remineralization agents.	Surface hardness recovery (% SHR), surface enamel roughness (Ra), pH, %weight of particles, zeta potential, and polydispersity index of toothpaste	SS: Bovine enamel blocks (n = 8/per group) FU: 7 days of pH cycling	REFIX	1450 ppm F− (as sodium fluoride), tetrasodium pyrophosphate, silica	Elmex Sensitive and REFIXshowed more effective remineralization; higher surface roughness when treatedwith REFIX, and NR-5 after a cariogenic challenge.
				NR-5	1450 ppm F− (as sodium fluoride and sodium monofluorophosphate), calcium silicate and sodium phosphate
				Colgate Total 12 Daily Repair	1450 ppm F− (as sodium fluoride), tetrasodium pyrophosphate, arginine
				Bianco Pro Clinical	1450 ppm F− (as sodium fluoride) 3% tricalcium phosphate (β-TCP)
				Elmex Sensitive	1450 ppm F− (as sodium monofluorophosphate), β-TCP and tetrasodium pyrophosphate
[51] El-Damanhoury et al. (2021) United Arab Emirates	Evaluate the effect of in-office bleaching on enamel surface and compare the efficacy of calcium silicate–sodium phosphate–fluoride (CS) and NovaMin bioactive glass (NM) in remineralizing bleached enamel.	Surface microhardness, surface roughness, SEM/EDX elemental analysis	SS: 40 human premolars (n = 10) FU: 7 days pH cycling	NovaMin	NaF, calcium sodium phosphosilicate 5%	CS and CS + NR-5 were more effective in remineralization and reducing roughness compared to NovaMin. CS and CS + NR-5 were more effective in restoring hardness and smoothness.
				NR-5 (CS)	1450 ppm F− (as sodium fluoride and sodium monofluorophosphate), calcium silicate and sodium phosphate
				Additional treatment with NR-5 boosting serum (CS + NR-5)	Calcium silicate, sodium phosphate, and sodium monoflourophosphate
[48] Fernandes et al. (2021) Brazil	Assess enamel superficial and subsurface morphology treated with fluoridated gels containing different biomimetic compounds after erosive challenge.	SEM imaging, with an energy-dispersive X-ray spectros- copy (EDS).	SS: Bovine enamel blocks (n = 5/per group) FU: 6 days of pH cycling	NR-5	1450 ppm F− (as sodium fluoride and sodium monofluorophosphate), calcium silicate and sodium phosphate	REFIX provided smoother enamel surface and higher resistance to erosion.
				REFIX	1450 ppm F− (as sodium fluoride), tetrasodium pyrophosphate, silica
				NovaMin	NaF, calcium sodium phosphosilicate 5%
[44] Rahman et al. (2021) United Arab Emirates	Compare dentinal tubule occlusion and permeability of a calcium silicate-, sodium phosphate-, and fluoride-based (CSSPF) toothpaste.	SEM imaging, with an energy-dispersive X-ray spectros- copy (EDS).	SS: 78 human dentin discs FU: 7 days	NR-5	Sodium monofluorophosphate (1450 ppm fluoride), calcium silicate, trisodium phosphate	Regenerate showed highest occlusion and calcium deposition, followed by NovaMin. Signal Sensitive Expert showed a less effective tubule occlusion and permeability reduction.
				NovaMin	NaF, calcium sodium phosphosilicate 5%
				Potassium Nitrate (Signal Sensitive Expert)	Hydrated silica, potassium nitrate and NaF
[40] Vilhena et al. (2021) Brazil	Characterize mineral content and morphology of enamel treated with REFIX toothpaste.	SEM imaging, with an energy-dispersive X-ray spectros- copy (EDS).	SS: Bovine enamel blocks (n = 5) FU: 7 days of pH cycling	REFIX	1450 ppm F− (as sodium fluoride), tetrasodium pyrophosphate, silica	EDS demonstrated the presence of Si (silicon), Na (sodium), P (phosphorus), andF (fluorine), among others. REFIX formed a 14 μm thick mineral layer enriched with silicon on enamel surface.
[4] Fernandes et al. (2022) Brazil	Evaluate fluoride-containing toothpastes with different technologies in remineralizing artificial enamel caries.	Surface microhardness recovery (%SMHR), fluorescence recovery (ΔFRE) with quantitative light-induced fluorescence, SEM imaging, with an energy-dispersive X-ray spectros- copy (EDS).	SS: Bovine enamel blocks (n = 12/per group) FU: 6 days of pH cycling	REFIX	1450 ppm F− (as sodium fluoride), tetrasodium pyrophosphate, silica	REFIX promoted enamel surface microhardness enamel recovery and the formation of a silicon-enriched mineral layer.
				NR-5	1450 ppm F− (as sodium fluoride and sodium monofluorophosphate), calcium silicate and sodium phosphate
				NovaMin	NaF, calcium sodium phosphosilicate 5%
[43] Moras et al. (2023) India	Compare the surface remineralization potential of SAP P11-4 (self-assembling peptide) and CSSP (calcium silicate plus sodium phosphate) on sound and demineralized enamel.	Laser-induced breakdown spectroscopy (LIBS)	SS:32 human enamel samples (16 intact, 16 demineralized) FU: 30 days pH cycling	SAP P11-4 (CURODONT™ PROTECT)	SAP P11-4, sodium monoflourophosphate and silica	Both agents significantly increased Ca and P levels; no significant difference between intact and demineralized enamel.
				CSSP (REGENERATE™ Enamel Science™ Advanced Toothpaste and Serum)	Calcium silicate, sodium phosphate, and sodium monoflourophosphate
[7] Vilhena et al. (2023) Brazil	Assess regenerative and protective effects of a fluoride–silicon-rich toothpaste combined with a calcium booster on dental tissues.	SEM imaging, with an energy-dispersive X-ray spectroscopy (EDS)	SS: 5 bovine enamel and 5 bovine dentin blocks FU: Immediate and after 5 days	Fluoride–silicon-rich toothpaste with calcium booster—REFIX technology	NaF, tetrasodiumpyrophosphate, silica, calcium carbonate, and tricalcium phosphate	Mineralized layer formed on enamel and dentin, significant remineralization after treatment with increasing calcium and silicon signals after immediate treatment, and occlusion of dentin tubules.
[46] Athanasiadou et al. (2024) Canada	Investigate chemical and ultrastructural changes in dentin with remineralizing toothpastes.	Atomic force microscopy (AFM), SEM imaging, with an energy-dispersive X-ray spectroscopy (EDS), transmissionelectron microscopy (TEM), and selected area electron diffraction (SAED).	SS: 12 human dentin blocks (n = 3 per group) FU: 14 days of toothbrushing	REFIX	1450 ppm F− (as sodium fluoride), tetrasodium pyrophosphate, silica	All evaluated dentifrices led to successful formation of hydroxyapatite andincreased dentin stiffness.
				REFIX + Booster	NaF, tetrasodiumpyrophosphate, silica, calcium carbonate, and tricalcium phosphate
				NovaMin	NaF, calcium sodium phosphosilicate 5%

and

Table 4. Characteristics of included articles (in vivo studies).

Author (Year)	Study Design	Study Aim	Outcome Measurement	Sample Size (SS), Follow-Up (FU)	Material(s) or Technology(ies) Used	Active Agent(s)	Primary Results
[52] Chalas (2015) Poland	Longitudinal study	Effectiveness of single application for dentin hypersensitivity.	Pain assessed using VAS after air and tactile stimuli.	SS: 92 teeth with hypersensitivity FU: Baseline, and after 1 week	NUPRO® Sensodyne® Prophylaxis Paste	Calcium sodium	NovaMin reduced dentin sensitivity in 1 week.
					Dentsply (NovaMin Formula)	Phosphosilicate (CSPS)
[53] Zang (2016) China	Randomized clinical trial	To compare the efficacy in dentin hypersensitivity relief.	Hypersensitivity measured using Yeaple probe and Schiff scale.	SS: 133 subjects FU: Baseline, and after 1, 2, 4, and 8 weeks	Vitryxx® (NaF and <5% CSPS)	NaF and CSPS	No significant CSPS (calcium sodium phosphosilicate) treatment benefit found.
					NovaMin® (NaF or SMFP and 5% CSPS)	Sodium monofluorophosphate (SMFP) and CSPS
					Regular fluoride toothpaste	Fluoride
[54] Sufi (2016) UK	Randomized clinical trial	To compare the efficacy in relieving dentin hypersensitivity.	Dentin hypersensitivity assessed using tactile and evaporative stimuli, and OHIP-14.	SS: 137 subjects FU: Baseline, and after 4 and 8 weeks	Experimental toothpaste w/5% CSPS	Calcium sodium phosphosilicate (CSPS)	5% CSPS (calcium sodium phosphosilicate) significantly reduced sensitivity at 4 and 8 weeks.
					Placebo abrasivity matched 0% CSPS with additional abrasive silica	No active ingrident
					Two control fluoride toothpastes	Fluoride
[55] Hall (2017) UK	Randomized clinical trial	To compare the efficacyin relieving dentine hypersensitivity.	Sensitivity assessed using Schiff scale/VAS and tactile threshold.	SS: 135 subjects FU: Baseline, and after 1, 2, 4, 6, and 11 weeks	Sensodyne Repair & Protect (5% CSPS)	Calcium sodium phosphosilicate (CSPS)	5% CSPS and 8% ACP equally reduced DH over 11 weeks.
					Colgate Sensitive Pro-Relief (8% arginine and calcium carbonate)	Arginine and calcium carbonate
					Colgate Triple Protection (1450 ppm fluoride)	Fluoride
[56] Fu (2019) China	Randomized clinical trial	To compare the efficacyin relieving dentine hypersensitivity.	Hypersensitivity assessed using Schiff scale/VAS and tactile threshold.	SS: 147 subjects FU: Baseline, and after 1, 2, 4, and 8 weeks	2.5% calcium sodium phosphosilicate toothpaste	Calcium sodium phosphosilicate (CSPS)	No significant difference between CSPS and arginine dentifrices.
					8% arginine toothpaste	Arginine
					Negative control toothpaste	Fluoride
[16] Patel (2019) India	Randomized clinical trial	To compare the efficacyin relieving dentine hypersensitivity.	Hypersensitivity assessed using tactile and evaporative stimuli (VAS).	SS: 75 subjects FU: Baseline, 15 days, and 1 month	BioMin-F (5% FCPS)	FCPS	5% FCPS (fluorocalciumphosphosilicate) toothpaste is most effective for reducing DH symptoms.
					Pro-Argin (8% arginine and calcium carbonate)	Arginine and calcium carbonate
					Placebo	Fluoride
[57] Bhowmik (2020) India	Randomized clinical trial	Comparison of fluorinol and sodium calcium phosphosilicate for dentin hypersensitivity.	Sensitivity assessed using VAS for tactile, evaporative, and cold stimuli. Gingival and plaque indices recorded. OHIP-14 used for quality of life.	SS: 30 subjects FU: Baseline, 2nd week, 3rd week, 4th week	Fluorinol-containing Elgydium Sensitive toothpaste	Fluorinol	Both groups reduced DH, but no significant differences were found.
					7.5% calcium sodium phosphosilicate-containing Shy-NM toothpaste	Sodium calciumphosphosilicate
[58] Arshad (2021) Pakistan	Randomized clinical trial	Compared Pro-Argin™, strontium acetate, and FCPS dentifrices for immediate DH pain relief.	Sensitivity assessed using SCASS and VAS for airblast, mechanical, and waterjet stimuli.	SS: 128 participants FU: 1 min, 3 days, 2, 4, and 6 weeks	BioMinF®	Fluoro-calcium-phospho-silicates (FCPS)	All groups reduced DH, with Pro-Argin™ and FCPS showing superior efficacy.
					Colgate® Sensitive Pro-Relief™	Pro-Argin™ with 8.0% arginine and 1450 ppm fuorides as sodium monofluoro-phosphate in calcium carbonate base
					Sensodyne Rapid Action™	8% strontium acetate, 1040 ppm fluorides as sodium fuoride
					Colgate® Total (Placebo)	NaF, sodium monofluorophosphate, dicalcium phosphate with 1150 ppm F
[59] Majji (2016) India	Randomized clinical trial	To compare the efficacyin reduction of dentinal hypersensitivity.	Dentin hypersensitivity measured using VAS for tactile, thermal, and evaporative stimuli.	SS: 160 subjects FU: Baseline, after 2 weeks, and after 12 months	Toothpaste with 5% potassium nitrate	Potassium nitrate	CSPS (calcium sodium phosphosilicate) toothpaste most effective for dentin sensitivity.
					NovaMin toothpaste (CSPS)	CSPS, strontium chloride
					10% strontium chloride, herbal formulation	Hekla lava, calendula, kresote, andplantago
[60] Gallob (2017) USA	Randomized clinical trial	To compare the efficacyin relieving dentine hypersensitivity.	Dentin hypersensitivity assessed using tactile and evaporative stimuli, and VRS.	SS: 249 subjects FU: After 4 and 8 weeks	US Sensodyne® Freshmint Maximum Strength	5% potassium nitrate and fluoride in silica base	Negative controls essential for DH dentifrice evaluation.
					US Crest® Pro-Health™ Healthy Fresh	Stannous fluoride in silica base
					US Colgate® Cavity Protection	Sodium mono fluorophosphate in dicalcium phosphate base
					US Colgate® Triple Action	NaF (different concentrations) in silica base and different ppm fluoride concentrations
					US Crest® Cavity Protection	Sodium fluoride in silica base and Fluoride
					Three toothpastes with non-marketed formulation	Sodium mono fluorophosphate in a silica base and different concentrations of abrasive silica
[41] Alonso et al. (2024) Brazil	Open clinical treatment trial	Evaluated efficacy of new toothpaste for dentin hypersensitivity.	Hypersensitivity assessed using tactile and evaporative stimuli (VAS).	SS: 62 subjects FU: Baseline, immediately after treatment, 1-week treatment	Dentifrice-containing REFIX technology (Regenerador + Sensitive DentalClean, Rabbit Corp, Londrina, PR, Brazil).	Fluoride Tetrasodiumpyrophosphate Silica	Immediate and sustained pain reduction after first use.
[10] Seong (2020) UK	Double-blind parallel study	Compared CSSP and fluoride toothpaste for DH pain reduction.	Sensitivity assessed using Schiff/VAS, Yeaple probe, and OHQoL.	SS: 247 subjects FU: Baseline, 14, and 28 days, and at 29 days, 12 h after last productapplication.	Calcium silicate and sodium phosphate toothpaste (CSSP)	Calcium silicate and sodium phosphate (CSSP)	CSSP significantly reduced DH symptoms compared to control.
					Negative control toothpaste	1450 ppm fluoride as sodiummonofluorophosphate
[61] Salah (2022) Egypt	Randomized controlled trial	Compared bioactive glass and CPP-ACP for orthodontically-induced WSLs.	WSL dimensions assessed using digital intraoral photos and DIAGNOdent.	SS: 60 subjects FU: Assessment before treatment (T0) and at 1 week (T1), 1 month (T2), 3 months (T3), and 6 months (T4), follow up	BioMinF® (Bio-BAG, Glaxo SmithKline, UK)	Bioactive glass 45S5, Calcium fluoride (3 mol%)	Bio-BAG significantly reduced WSL compared to control.
					NovaMin (N-BAG, BioMin Technologies Ltd., UK)	Bioactive glass 45S5
					Recaldent (CPP-ACP, GC Corporation, Japan)	Casein phospho-peptide-amorphous calciumphosphate
[62] Hamdi (2022) Egypt	Randomized clinical trial	To compare remineralization potential of TCS, SDF-KI, and CPP-ACP.	Lesions were evaluated clinically using DIAGNOdent.	SS: 45 patients and 92 teeth FU: Immediately, and after 3, 6, 12, and 24 months of treatment	Riva star silver fluoride + potassium iodide	SDF-KI	SDF-KI is more effective than CPP-ACP or TCS for remineralization.
					Tooth Mousse (CPP-ACP)	Casein phosphopeptide-amorphous calcium phosphate
					Tri-calcium silicate paste	TCS
[63] Mollabashi (2022) Iran	Randomized clinical trial	Evaluated NovaMin’s effect on WSL remineralization in orthodontic patients	DIAGNOdent pen was used to score the WSLs	SS: 38 subjects FU: Baseline, and then after usage for 1 and 3 months	Fluoride toothpaste (Sensodyne® Rapid Relief, England)	Fluoride-hydrated silica	DIAGNOdent readings reduced significantly in both groups.
					NovaMin (Sensodyne® Repair & Protect, England).	Sodium monofluorophosphate (SMFP)

present the overall characteristics and details about the in vitro and in vivo studies with these technologies, respectively.

4. Discussion

The lack of consensus on terminologies related to these Si-based technologies for remineralizing dental hard tissues was a survey problem, since hydrated silica is a common component of many toothpastes. As a result, the search query used for this scoping review eventually selected studies testing abrasives. In addition, remineralization is a frequently surveyed issue of research related to bioactive materials for repairing or regenerating bones and teeth.

A similar commercial and academic terminology may be useful to encompass technologies using silicon (Si), silica (SiO₂), and silicate (Si₂O₅)_2n−n in toothpastes. This could facilitate communication and differentiate these products from regular hydrated silica. This approach is very important since the borderline between biomimetic products and F-boosters is increasingly blurred [9]. Accordingly, a parallel outcome of this scoping review is the proposal for using the term “bioactive Si-toothpaste” for biomimetic or F-boosters technologies for enamel repair that use silicon (Si), silica (SiO₂), and silicate (Si₂O₅)_2n−n in toothpastes.

As a result of this terminology issue, it was quite challenging to summarize the main findings and to identify a major pattern among the in vitro and in vivo studies (Table 3 and Table 4). Another limitation of this scoping review is the difficulty inaccessing the quality of the laboratory studies due to the high heterogeneity of pH cycling methods and techniques for measuring loss/gain mineral in laboratory studies.

The major technologies investigated in the 27 articles selected for this review were: NovaMin^®, BiominF^®, REFIX Technology, and NR5™technology (with and without serum booster).

In vitro study articles evaluating the NovaMin and REFIX technologies followed similar methodologies, involving the preparation of bovine enamel blocks, demineralization to create caries-like lesions, pH cycling with treatment based on different toothpastes, and subsequent analysis with surface microhardness, scanning electron microscopy, and EDS [4].

However, if we take a closer look at the methodological aspects, some differences are worth highlighting. While some researchers [46,47] used human teeth, others [4,12,40,48] used bovine teeth. This may influence the comparability of the results due to differences in the composition and structure of human and bovine teeth. However, the polishing and sample preparation procedures are similar between the articles using bovine teeth, ensuring a uniform surface for the tests.

Most of the articles used demineralization methods with acetate solutions to simulate caries lesions and pH cycling, ensuring controlled conditions for evaluating the effects of the dentifrices tested. However, some studies used brushing methods associated with pH cycling, which varied between manual brushing [46] and electric brushing [12,40], which may impact the effectiveness of the remineralization and protection effects observed.

For sample analysis and characterization, scanning electron microscopy (SEM) and EDS are the most common methods, allowing a detailed comparison of the morphology and chemical composition of the samples after treatment. However, quantitative methods such as surface microhardness and enamel surface roughness [4,47] are important and deserve to be highlighted, as they provide more robust evidence on the clinical applicability of these composites.

Methodological differences are crucial for interpreting the results of each study, as they directly influence conclusions about the effectiveness of the technologies evaluated and the comparison of data [47]. When it comes to methodological rigor, we must consider certain aspects, such as clarity and the detail of the methodology, control of variables, reproducibility, data analysis and interpretation, validity, and reliability of the methods used. Thus, the studies [4,12,40,48], demonstrate greater methodological rigor due to the following points: preparation and polishing of detailed samples, which ensures uniformity of the specimens; standardized procedures for demineralization and pH cycling, ensuring controlled conditions for the creation of caries lesions; use of electric brushing [12,40], as it reduces variability and improves the reproducibility of results; SEM and EDS analyses, offering a detailed characterization of the morphology and chemical composition of dental tissues after treatments [48].

The main differences found in the results of the studies evaluated are related to the effectiveness of the different toothpastes in remineralizing enamel and forming new “layers” of minerals. Each study observed variations, depending on the compounds tested, in the presence of elements such as silicon and fluoride, as well as in the hardness and roughness properties of the enamel and dentin surfaces after treatment.

REFIX technology induces the formation of a mineralized layer on both enamel and dentin. On enamel, this layer is approximately 6 µm thick and forms on the surface after pH cycling. In dentin, after brushing with the same toothpaste, a mineralized layer is formed, only less thick, up to 3 µm. After 7 days of treatment, partial obliteration of the dentinal tubules is observed [40].

In terms of erosion prevention, enamel samples treated with REFIX exhibit a smoother surface and resistance to subsequent erosive challenges. Elemental mapping analyses with EDS indicate that there are no significant changes in the chemical elements present on the surface after the erosive challenge, confirming the robustness of the layer formed [48].

NovaMin technology, in turn, induces the formation of a mineralized layer both on the dentin surface and inside the dentin tubules. The mechanism of action suggested for this dentifrice is through the release of calcium and phosphate when in contact with saliva, promoting remineralization and obliteration of the dentinal tubules [46].

However, the results presented in the studies show that NovaMin technology was less effective in forming a new mineral layer on the surface enamel compared to REFIX. In addition, there was a significant reduction in the percentage weight of calcium in NovaMin-treated samples after erosive challenges, indicating a lower resistance and stability of the mineral content.

In short, depending on what the study sets out to analyze, REFIX stands out in terms of enamel surface remineralization and erosion prevention. However, when applied to dentin, both technologies promote the obliteration of the dentinal tubules, which can help control tooth sensitivity. However, the mineral deposition provided by REFIX forms a thicker and more resistant layer over time.

All in vitro studies support that a net mineral gain is achieved and an enamel repair is also observed depending on the technique used. These in vitro investigations support the beneficial effect of these bioactive Si-toothpastes which are related to the potential control of dental caries lesions, erosive tooth wear [4,7,12,40,43,46,47,48,49,50,51].

The clinical efficacy of various bioactive Si-toothpastes has been extensively studied, with a particular emphasis on formulations containing sodium calcium phosphosilicate (SCPS) and related technologies. Clinical studies have consistently demonstrated the ability of SCPS to occlude dentinal tubules, thereby alleviating pain associated with dentin hypersensitivity (DH). For instance, Chałas et al. (2015) [52] and Zang et al. (2016) [53] observed significant pain reduction with smaller SCPS particles, which exhibited greater efficiency in tubule occlusion. Similarly, Sufi et al. (2016) [54] reported a marked reduction in DH with the use of toothpastes containing 5% SCPS. Hall et al. (2017) [55] further confirmed the superiority of SCPS over arginine/calcium carbonate in long-term treatments, although a work performed later found no significant differences when comparing smaller SCPS particles (2.5%) to arginine/carbonate formulations [56].

Studies by Patel et al. (2019) [16] and Bhowmik et al. (2021) [57] have also highlighted the efficacy of bioglass-containing toothpastes in reducing DH, particularly the remineralizing effect of BioMin-F compared to popular brands like Colgate Sensitive Pro-Relief and Sensodyne Rapid Action [58]. In a clinical comparison of four different interventions for DH reduction, Majjiand Murthy (2016) [59] concluded that SCPS-based pastes were the most effective, a finding consistent with other investigation that demonstrated significant DH reduction using a toothpaste containing REFIX technology [12].

Additionally, Seong et al. (2020) [10] conducted a randomized controlled trial evaluating a toothpaste with calcium silicate and sodium phosphate, finding a significant pain reduction compared to a control group using only fluoridated toothpaste. Gallob et al. (2017) [59] also supported the efficacy of experimental toothpastes containing silica, silicate, and silicon in reducing DH.

In the treatment of white spot lesions, few clinical studies explored bioglass-based technologies, showing that these formulations not only alleviate DH but also promote the remineralization of enamel, particularly in orthodontic patients [61,62]. A further study demonstrated that combining NovaMin^® with a fluoridated toothpaste significantly improved the remineralization of white lesions, highlighting the potential of sodium monofluorophosphate (SMFP) to enhance fluoride therapy’s efficacy [63].

Surprisingly, this review retrieved no clinical studies about these bioactive Si-toothpastes for DH associated with molar incisor hypomineralization (MIH). MIH is a developmental enamel defect primarily diagnosed in childhood and adolescence, which can lead to compromised function of the affected teeth [64]. Characterized by increased porosity and dentin tubule exposure [65], this defect can result in post-eruptive fractures, dentin hypersensitivity, and pain. These conditions can significantly impact patients’ oral health-related quality of life (OHRQoL) [66,67], including difficulties with mastication, particularly when consuming hot or cold foods and beverages [68]. Moreover, MIH can lead to psychosocial challenges, such as decreased self-esteem, embarrassment when smiling, and difficulties with socialization [69].

Given these challenges, silica-, silicate-, and silicon-based technologies have shown promise in dental remineralization and the reduction of dentin hypersensitivity through dentin tubule obliteration. Therefore, these materials can alleviate pain, reduce dentin hypersensitivity, and, in turn, reduce the negative impact on OHRQoL.

In vitro and in vivo studies are currently underway to evaluate the efficacy of these remineralizing agents in teeth with MIH, particularly in children. These studies aim to assess the potential of toothpastes containing these technologies as adjuncts in the treatment and management of dentin hypersensitivity and their impact on the oral health-related quality of life of these patients.

The authors acknowledge some strengths and limitations of the included studies. For instance, enamel/dentin repair and remineralization was surveyed by many different techniques. However, the heterogeneity of the laboratory studies in this field might not be interpreted as a limitation since all studies provided consistent evidence in terms of in vitro mineral gain when testing bioactive Si-toothpastes. The in vivo studies were of short duration (4 weeks) testing pain relief. Despite the homogeneity of these clinical trials, there still is a need for building up efficacy from longer randomized clinical trials and effectiveness evidence from “real life studies”. Future in vitro and in vivo researchers must also consider testing these products for other therapeutic purposes such as white spot lesions, MIH, dental fluorosis.

Finally, it must also be pointed out that the mechanisms of action of bioactive Si-toothpastes in the market may differ since there are products with different technologies and with acidic or alkaline formulations (Table 1). The combination of silicon and derivates with other strategies will probably be the next frontier for new bioactive Si-toothpastes on the market.

5. Conclusions

This scoping review retrieved in vitro (laboratory) and in vivo studies that support the evidence about the beneficial effects of using silicon-, silica-, and silicate-toothpastes for enamel repair and remineralization.

The clinical studies were mostly of short duration, but support the efficacy of SCPS, bioglass, and innovative technologies like REFIX in occluding dentinal tubules and remineralizing enamel, offering long-lasting relief from DH. The choice of treatment should be tailored to the patient’s specific needs and the properties of the desensitizing agent used.