Proteolytic enzymes in dentin erosion: roles of matrix metalloproteinases and cathepsins and the effectiveness of synthetic and natural inhibitors—a systematic review

Abstract

Objectives

To evaluate the role of matrix metalloproteinases (MMPs) and cathepsins in dentin erosion and assess the efficacy of synthetic and natural inhibitors in preventing collagen matrix degradation and preserving dentin integrity.

Methods

A systematic literature search was conducted and updated in January 2025 across PubMed, Scopus, and Web of Science, targeting studies that investigated the role of matrix metalloproteinases (MMPs) and/or cysteine cathepsins in dentin erosion or erosion–abrasion models. In vitro, in situ, and in vivo experimental studies evaluating the effects of synthetic and natural protease inhibitors were included. Study selection, data extraction, and risk of bias assessment were performed following PRISMA 2020 guidelines.

Results

A total of 22 studies met the inclusion criteria, comprising predominantly in vitro designs, alongside in situ and combined experimental models. Across studies, MMP-2, MMP-8, and MMP-9, together with cathepsin K, were consistently identified as key enzymes involved in collagen degradation following acidic challenges. Erosive protocols varied in pH, exposure time, and cycling frequency, but uniformly promoted demineralization and enzymatic activation. Synthetic inhibitors (e.g., ferrous sulfate, stannous fluoride) and natural compounds (e.g., green tea catechins, theaflavins) demonstrated significant reductions in enzymatic activity and dentin loss. Importantly, studies assessing combined inhibition of MMPs and cathepsins reported the greatest protective effects, supporting a multimodal strategy to limit erosive dentin degradation.

Conclusions

Acidic challenges promote the activation of matrix metalloproteinases and cysteine cathepsins, thereby accelerating dentin erosion through progressive collagen degradation. Both synthetic and natural inhibitors were shown to attenuate proteolytic activity and reduce dentin loss under experimental conditions. Notably, strategies targeting multiple enzymatic pathways consistently demonstrated greater protective effects than single-agent approaches. Nevertheless, the predominance of in vitro and in situ evidence highlights the need for well-designed clinical studies to confirm the long-term efficacy and translational relevance of these interventions.

Clinical Significance

The incorporation of MMP and cathepsin inhibitors into preventive and therapeutic oral care strategies represents a promising adjunct for enhancing dentin resistance to erosive challenges. However, clinical implementation requires standardized experimental protocols, clearer dose–response characterization, and validation in long-term clinical settings. Advancing dual-targeted inhibitory approaches may contribute to more effective and durable dentin preservation in patients at risk of erosive tooth wear.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-026-08496-z.

Introduction

Dentin erosion is a progressive condition characterized by the loss of the tooth’s mineralized structure due to chemical processes unrelated to microbial activity [1]. Acidic challenges, whether extrinsic (e.g., dietary acids, acidic beverages) or intrinsic (e.g., gastric reflux), initiate demineralization of the hydroxyapatite matrix. This demineralization exposes the underlying organic matrix, primarily composed of type I collagen, to enzymatic degradation by endogenous proteolytic enzymes such as matrix metalloproteinases (MMPs) and cathepsins [2].

MMPs, including MMP-2, MMP-8, and MMP-9, are latent enzymes stored within dentin and activated under acidic conditions. Their activation perpetuates collagen breakdown, further compromising dentin integrity [3]. Similarly, cathepsin K, a lysosomal protease, plays a significant role in collagen degradation, particularly under acidic conditions. Evidence suggests a synergistic relationship between MMPs and cathepsins in accelerating the erosive process [4]. However, while the mechanisms of MMP activity are widely studied, the clinical implications of cathepsin activity remain underexplored, highlighting a critical gap in the literature. Furthermore, the role of MMPs in erosion has been underexplored, as erosion has traditionally been regarded as primarily a surface phenomenon [5]. This suggests that MMP activation may play a key role in tissue loss.

The clinical impact of dentin erosion is profound, leading to structural weakness, hypersensitivity, and aesthetic concerns [6]. Strategies to inhibit MMP and cathepsin activity have shown promise in mitigating these effects. Synthetic inhibitors, such as ferrous sulfate and stannous fluoride, as well as natural compounds like green tea catechins and theaflavins, have demonstrated significant efficacy in reducing enzymatic activity and preserving the collagen matrix [7–10]. Combination therapies, which integrate multiple inhibitory mechanisms, appear particularly effective in enhancing dentin resistance to erosive challenges.

Despite advances in understanding enzymatic activity in dentin erosion, inconsistencies in study designs and experimental protocols create challenges in synthesizing findings. Variations in erosive agents, pH levels, exposure durations, and methodologies for assessing enzymatic activity contribute to this heterogeneity. Furthermore, the predominance of in vitro studies limits the applicability of findings to clinical practice, underscoring the need for translational research.

Therefore, this systematic review aimed to critically synthesize the available evidence on the roles of matrix metalloproteinases (MMPs) and cathepsins in the progression of dentin erosion and to evaluate the effectiveness of synthetic and natural inhibitory strategies in mitigating enzymatic degradation and preserving dentin integrity.

Methods

A systematic review was conducted between December 2024 and January 2026, with the last search performed on January 23, 2026, in PubMed, Scopus, Embase, Cochrane and Web of Science (WOS) databases were used for the literature search. The review adhered to the Preferred Reporting Items for Systematic Reviews (PRISMA 2000) [11] and JBI Manual [12] guidelines (CRD42024626065).

Population-concept-context framework

Based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, the focused question was structured according to the Participants, Intervention, Control, and Outcomes (PICO) principle. The research question formulated is as follows:

What is the role of matrix metalloproteinases (MMPs) and cathepsins (I) when compared to untreated eroded dentin or placebo (C) in the progression of dentin erosion and the effectiveness of synthetic and natural inhibitors (O) in mitigating enzymatic degradation and preserving dentin integrity (P)?

This question aims to clarify the impact of MMPs and cathepsins in dentin erosion and assess the protective effects of different inhibitory strategies in maintaining dentin structure.

Inclusion criteria

• Articles written in any language.

• Studies involving focusing on erosion, abrasion, or combined erosion-abrasion.

• Studies investigating the collagenolytic activity or its inhibition mediated by MMPs and/or cathepsins.

Exclusion criteria

• Review articles (narrative, systematic, or meta-analyses), letters, case reports, books, theses, or preprints.

Search strategy

A comprehensive electronic search was conducted in PubMed/MEDLINE, Web of Science, Scopus, Embase, and the Cochrane Library to identify studies evaluating the role of dentin-derived proteolytic enzymes in erosive processes. The search strategy was designed to capture evidence related to matrix metalloproteinases (MMPs) and cysteine cathepsins, using a combination of free-text terms and controlled vocabulary (MeSH and Emtree terms, when applicable).

The following key concepts were combined using Boolean operators: (i) metalloproteinases and related enzymes (including matrix metalloproteinases, collagenases, gelatinases), (ii) cysteine cathepsins (including cathepsin K), (iii) dentin substrates, and (iv) erosive processes (dental erosion, erosive wear). Database-specific search algorithms are detailed in Supplementary Table S1.

No restrictions were applied regarding study design or publication year. Given the well-documented mechanistic overlap and functional interplay between matrix metalloproteinases and cysteine cathepsins in dentin matrix degradation, both enzyme families were considered a priori relevant to the research question and were therefore explicitly included in the search strategy.

Article selection methodology

Automated filters were applied in each database to exclude studies not meeting the inclusion criteria and to define the publication time range. The records extracted from each database were imported into Clarivate Analytics EndNote 21, where duplicates were removed. A preliminary review excluded articles that were clearly irrelevant based on eligibility criteria.

Calibration exercises were performed among the reviewers to ensure consistent evaluation of articles. Inter-reviewer agreement was assessed using Orwin’s method and Cohen’s kappa statistic. Kappa values were interpreted as follows:

• 0.40–0.59: Acceptable agreement,

• 0.60–0.74: Adequate agreement,

• ≥0.75: Excellent agreement.

The online tool Rayyan^® was used to facilitate collaboration among reviewers. In cases of disagreement, a third reviewer resolved disputes regarding inclusion or exclusion. Articles were screened based on titles and abstracts, and studies meeting inclusion criteria were read in full to extract relevant data.

Data extraction and variables

The following variables were extracted from each included study: Author(s) and year of publication, Article title, Journal name, Citation details (volume, issue, pages), and URL or DOI (preferably DOI).

Also, was included sample size (participants), sample size (teeth), erosion, abrasion or a combination, erosive solution used, pH, exposure time per cycle (minutes), total exposure time (minutes), number of cycles, MMP activity, type of MMP, type of assay, used of Cathepsin and Intensity of Variables Measured and Erosion Protocol Details.

The extracted data were organized into a Microsoft^® Excel^® spreadsheet for analysis and to aid in creating tables and figures. When essential information was missing, corresponding authors were contacted via email. Studies with insufficient information and non-responding authors were excluded.

Methodology for risk of bias assessment

The risk of bias assessment for the included studies was conducted systematically using a modified version of established guidelines, such as the Cochrane Risk of Bias (RoB) tool for in vitro studies. The following steps detail how each domain of bias was evaluated and assigned a judgment of “low,” “high,” or “unclear” risk.

Selection bias was assessed by considering if the sample source (e.g., human or bovine dentin) was clearly described and appropriate for the study’s objectives. Random allocation of samples to experimental groups was a key factor; studies explicitly stating the use of randomization for assigning samples to groups were judged as “low risk.” If randomization was unclear or not mentioned, the study was rated as “unclear risk.” In cases where systematic or intentional allocation bias was evident, the study was rated as “high risk.”

Performance bias was assessed by evaluating whether experimental conditions were consistent across all groups, such as through identical erosion protocols, controlled pH, and consistent exposure times. The evaluation also considered whether researchers were blinded to group allocation during interventions. Studies that utilized standardized conditions and blinding were judged as “low risk.” If blinding was not mentioned or conditions varied between groups, an “unclear risk” was assigned. Finally, apparent inconsistencies or a lack of control over variables led to a “high risk” judgment.

Detection bias was assessed by determining whether outcome measurements, such as MMP activity and dentin loss, were performed using validated and reliable methods, and whether researchers measuring outcomes were blinded to group assignments. Studies that employed validated methodologies and blinded outcome assessment were rated as “low risk.” An “unclear risk” was assigned if the measurement process or blinding was unclear. Finally, the obvious influence of knowledge of group assignments on measurements resulted in a “high risk” rating.

Attrition bias was evaluated by assessing whether all initially included samples were accounted for in the final analysis and whether any exclusions or dropouts were explained and justified. Studies with complete data reporting and no exclusions were judged as “low risk.” An “unclear risk” was assigned if exclusions were not explained or accounted for. Finally, if significant dropouts or missing data were evident without justification, a “high risk” rating was given.

Reporting bias was evaluated by determining whether all pre-specified outcomes were reported and whether selective reporting was evident, such as focusing only on favorable results. Studies reporting all relevant outcomes were rated as “low risk.” An “unclear risk” was assigned if outcome reporting was incomplete or selectively focused. Finally, clear evidence of selective reporting resulted in a “high risk” judgment.

Each study was assessed independently by two reviewers for all domains of bias. Discrepancies in judgments were resolved through discussion or arbitration by a third reviewer. The final risk of bias for each study was determined as follows: Low Overall Risk when all domains rated as “low risk”, Moderate Overall Risk when One or two domains rated as “unclear risk” or “high risk” and High Overall Risk when three or more domains rated as “high risk”.

Data management

All extracted data were archived in the Mendeley Data repository (10.17632/6nt9t4bmyp.1), ensuring transparency, reproducibility, and adherence to Open Science principles.

Certainty of the evidence (conqual assessment)

The certainty of the evidence was appraised using the ConQual approach [12], which evaluates confidence in synthesized findings based on two core domains: dependability (methodological rigor) and credibility (coherence and consistency of findings). Given that most included studies were experimental in vitro or in situ investigations, initial certainty was rated as moderate and subsequently downgraded when methodological limitations were identified. Key factors influencing dependability included incomplete reporting of randomization procedures, limited blinding, and heterogeneity in erosion protocols and outcome assessment methods. Credibility was primarily affected by variability in experimental conditions and inhibitors tested, although consistency in the direction of effects across studies supported thematic convergence. Overall, ConQual assessment was applied at the level of each synthesized outcome to provide a transparent and structured evaluation of confidence in the review findings.

Results

This systematic review evaluated 22 studies [8, 10, 13–32]. that investigated the roles of matrix metalloproteinases (MMPs) and cathepsins in dentin erosion under diverse experimental conditions. The findings consistently highlighted the critical relationship between acidic environments and the activation or inhibition of endogenous proteolytic enzymes, which significantly influence the structural integrity of eroded dentin. Various protective strategies were also examined, emphasizing their potential to mitigate the detrimental effects of dentin erosion (Fig. 1).

Fig. 1.

Flow chart PRISMA

Characteristics of included studies

The included studies displayed substantial methodological heterogeneity, reflecting the multifaceted nature of dentin erosion research. Experimental designs were predominantly in vitro, complemented by in situ and hybrid in vitro/in situ approaches, allowing both mechanistic control and partial clinical extrapolation [8, 10, 13–32]. Sample sizes ranged from small, highly controlled experimental sets to larger designs incorporating multiple treatment arms, enhancing internal validity while maintaining feasibility across diverse protocols.

Most investigations employed human dentin substrates, primarily extracted permanent molars, whereas a smaller subset used bovine dentin as a standardized surrogate, supporting reproducibility and cross-study comparability. Across studies, the primary analytical emphasis was placed on quantifying proteolytic activity, characterizing collagen matrix degradation, and evaluating the inhibitory effects of synthetic and natural agents, either alone or in combination. Importantly, several studies explicitly explored the functional interplay between matrix metalloproteinases and cysteine cathepsins, reinforcing the biological plausibility of dual-enzyme modulation as a strategy to mitigate erosive dentin breakdown (Table 1).

Table 1.

General characteristics of the included studies

Study	Year	Country	Study type	Sample source	Sample size per group	Key focus	Primary outcome (mean ± SD)	Secondary outcome(s) (mean ± SD)
Kato et al.[14]	2010	Brazil	In vitro + in situ/ex vivo	Bovine coronal dentin blocks (palatal appliances)	In situ: 10 volunteers; 60 dentin blocks total (2 blocks per treatment per volunteer)	Effect of ferrous sulfate (FeSO₄) on MMP inhibition and prevention of dentin erosion	Dentin wear (µm): Placebo = 1.77 ± 0.33; NaF (1.23%) = 0.79 ± 0.08; FeSO₄ gel (1 mmol/L) = 0.05 ± 0.02 (Kruskal–Wallis + Dunn; p < 0.0001)	MMP inhibition (zymography): IC₅₀ MMP-2 = 0.75 mmol/L; IC₅₀ MMP-9 = 0.50 mmol/L; complete inhibition of both enzymes at 1.5 mmol/L FeSO₄. SEM: marked dentinal tubule occlusion in FeSO₄ group compared with NaF and placebo.
Kato et al. (2010a)[13]	2010	Brazil	In situ, randomized crossover	Bovine crown dentin blocks mounted in palatal appliances	n = 10 blocks per group; 10 volunteers	Effect of gels containing MMP inhibitors (EGCG and chlorhexidine) on dentin erosion prevention	Dentin wear (µm): EGCG 10 µM = 0.05 ± 0.02; EGCG 400 µM = 0.04 ± 0.02; Chlorhexidine 0.012% = 0.05 ± 0.02; NaF 1.23% = 0.79 ± 0.35; Placebo = 1.77 ± 0.35 (MMP inhibitors < NaF and placebo; p < 0.01)	SEM (qualitative): Absence of detectable wear and marked tubule occlusion in EGCG and CHX groups; clear erosion interface and exposed tubules in NaF and placebo groups
Silveira et al.[15]	2014	Brazil	In vitro	Bovine root dentin blocks (cervical dentin)	n = 12 per group (6 groups; total n = 72 specimens)	Effect of saturated anacardic acid (AA) on dentin erosion and MMP-2 inhibition	Dentin tissue loss (µm): Control = 6.03 ± 0.98; EGCG = 3.79 ± 0.83; NaF = 3.93 ± 1.54; Saturated AA = 1.97 ± 1.02; AA + EGCG = 1.89 ± 0.87; AA + EGCG + NaF = 2.08 ± 1.03 (all treatments < control, p < 0.0001; AA groups < EGCG and NaF)	MMP-2 activity (zymography): Saturated AA (100 µmol/L) inhibited ~ 20.0% of MMP-2 activity, comparable to phenanthroline (~ 21.2%). SEM analysis: Preservation of intertubular dentin and reduced tubule widening in AA-treated groups vs. control.
Zarella et al.[33]	2015	Brazil	In vitro	Human cervical dentin blocks from sound third molars	n = 17 per group (15 profilometry; 2 SEM)	Relative role of MMPs vs. cysteine cathepsins in dentin erosion progression	Loss of demineralized organic surface material (µm): CHX 8.4 ± 1.7; Galardin 8.6 ± 1.9; Cathepsin B inhibitor 9.6 ± 1.4; E-64 9.9 ± 1.3; NaF 9.9 ± 1.7; Placebo 10.9 ± 2.2; Untreated 11.0 ± 1.5 (MMP inhibitors < all other groups; p < 0.001)	Loss of mineralized tissue (µm): CHX 15.4 ± 2.2; Galardin 16.0 ± 1.8; Cathepsin B inhibitor 17.6 ± 2.4; E-64 17.6 ± 2.0; NaF 17.3 ± 2.8; Placebo 19.1 ± 2.1; Untreated 18.9 ± 2.4 (p < 0.001). Residual DOM thickness (µm): no significant differences among groups (≈ 7–8 μm; p = 0.845). SEM: better organized DOM in CHX and galardin groups.
do Amaral et al.[17]	2018	Brazil	In vitro	Pulverized human coronal and radicular dentin	NR (powder-based assays)	Effect of pH on MMP activation and collagen degradation	MMP-2 activity (AU): highest at pH 2.5, followed by pH 4.5–5.0; significantly lower at pH 6.0–7.0 (p < 0.05)	Hydroxyproline (µg/mg): undetectable at pH 2.5–4.5; highest at pH 7.0 (p < 0.05)
Cvikl et al.[8]	2018	Austria	In vitro	Human dentin discs + recombinant MMPs	n = 20 total	Stannous compounds as MMP inhibitors	MMP-2 / MMP-9 inhibition: SnCl₂ inhibited MMP-2 at 0.007% and MMP-9 at 0.12%; SnF₂ inhibited MMP-2 at 0.03% and MMP-9 at 0.5%	Cell viability: SnCl₂ ↑; NaF dose-dependent cytotoxicity
Ozan et al.[10]	2020	Turkey	In situ (randomized, crossover)	Human dentin slabs (5 × 3 × 2 mm) prepared from extracted third molars, mounted in palatal appliances	n = 30 specimens per group (3 specimens × 10 volunteers); 6 groups	Effect of MMP-inhibiting mouthrinses (0.2% chlorhexidine, NaF, CHX + NaF, green tea, black tea) on erosive dentin degradation under in situ conditions	Microhardness change (ΔKHN, %): NaF 13.05 ± 8.07; CHX + NaF 15.02 ± 7.48; Green tea 18.64 ± 9.97; Black tea 19.02 ± 7.82; CHX 21.01 ± 10.23; Water 33.80 ± 12.42 (NaF significantly lower vs. control, p < 0.05)	Maximum depth (R < sub> valley</sub>, µm): NaF 0.748 ± 0.303; CHX 0.852 ± 0.281; CHX + NaF 0.842 ± 0.163; Green tea 1.991 ± 0.904; Black tea 1.663 ± 0.464; Water 2.109 ± 0.881. Surface roughness change (ΔR < sub> rms</sub>, µm): NaF − 11.50; CHX − 9.41; CHX + NaF − 13.98; Green tea − 52.92; Black tea − 43.49 (NS)
de Moraes et al.[18]	2021	Brazil	In vitro / In situ	Human dentin blocks	3 blocks/volunteer (n = 10)	Green tea and EGCG as MMP inhibitors	Dentin wear (µm): Control 0.64 ± 0.10; NaF 0.65 ± 0.20; EGCG 0.66 ± 0.10; Green tea 0.58 ± 0.20 (p > 0.05)	Surface roughness (Ra, µm): Control 0.19 ± 0.40; NaF 0.17 ± 0.60; EGCG 0.17 ± 0.60; Green tea 0.16 ± 0.80
Kato et al.[20]	2021	Brazil	In situ (two crossover studies)	Bovine root dentin blocks mounted in palatal appliances	Study 1: 10 volunteers (n = 40 blocks/group); Study 2: 13 volunteers (n = 26 blocks/group)	Effect of dentifrices and gels containing MMP inhibitors on dentin erosion and erosion–abrasion	Dentin loss (µm): Study 1 (5 days) – Placebo: ERO 1.39 ± 0.32; ERO + ABR 1.67 ± 0.21. EGCG dentifrice: ERO 0.83 ± 0.17; ERO + ABR 0.99 ± 0.26. CHX dentifrice: ERO 0.92 ± 0.16; ERO + ABR 0.75 ± 0.18. NaF dentifrice: ERO 0.73 ± 0.27; ERO + ABR 0.93 ± 0.29 (all actives < placebo; p < 0.05). Study 2 (10 days) – Gels with EGCG, CHX or FeSO₄ showed significantly lower dentin loss than NaF gel, placebo, and untreated groups at both 5 and 10 days (p < 0.05).	Effect of abrasion: ERO + ABR > ERO in placebo and NaF groups after 10 days (p < 0.05); no significant increase with EGCG, CHX or FeSO₄ gels. Sustained protection: Single 1-min application of EGCG, CHX or FeSO₄ gels maintained protection up to 10 days.
Leal et al.[19]	2021	Brazil	In vitro randomized experimental study	Human root dentin blocks (4 × 4 × 2 mm) from extracted third molars	n = 10 per group (6 groups × 2 experiments: erosion; erosion + abrasion)	Effect of hesperidin (0.1%, 0.5%, 1%) on dentin erosive and erosive/abrasive wear, compared with EGCG and collagenase challenge	Dentin surface loss (µm, erosion): DW 29.42 ± 5.79; DW + Col 78.78 ± 4.28; EGCG 33.91 ± 9.08; HPN 0.1% 70.48 ± 11.00; HPN 0.5% 72.06 ± 9.08; HPN 1% 65.89 ± 9.45	Dentin surface loss (µm, erosion + abrasion): DW 27.28 ± 2.86; DW + Col 78.59 ± 3.67; EGCG 35.37 ± 3.08; HPN 0.1% 71.17 ± 7.02; HPN 0.5% 65.95 ± 7.22; HPN 1% 68.89 ± 5.90. SEM: tubule obliteration and DOM preservation in EGCG and HPN groups
Capalbo et al.[21]	2022	Brazil	In vitro	Bovine root dentin blocks	n = 12 / group	Combined fluoride–HMP–quercetin strategy	Dentin loss (µm): lowest in F + HMP+QC group (p < 0.001; mean ± SD)	Integrated hardness (KHN × µm): 724.3 ± 31.2 (5–30 μm depth); MMP inhibition: MMP-2 and MMP-9 fully inhibited in HMP-containing groups
Hanzen et al.[22]	2022	Brazil	In vitro	Human sound and eroded dentin from extracted molars	n = 5 teeth per condition (bond strength, nanoleakage, DC); n = 6 samples (MMP assays)	Effect of copper nanoparticles (0.1 wt%) incorporated into a universal adhesive on MMP inhibition and long-term hybrid layer stability in eroded dentin	Microtensile bond strength (µTBS, MPa): Eroded dentin, etch-and-rinse: Control 21.9 ± 2.4 (1 y) vs. Cu-adhesive 27.2 ± 2.1 (1 y); Self-etch: Control 20.9 ± 2.8 (1 y) vs. Cu-adhesive 27.6 ± 2.5 (1 y) (p < 0.002)	MMP activity (RFU): significant inhibition of MMP-2 and MMP-9 by 0.1% CuNp vs. positive control (p < 0.01). Nanoleakage (%): reduced in Cu-adhesive vs. control after 1 y (e.g., ER eroded dentin: 22.5 ± 1.6 vs. 32.9 ± 2.4). Degree of conversion (%): no significant difference vs. control (e.g., ER eroded dentin: 65.9 ± 3.0 vs. 69.4 ± 2.1).
Hong et al.[23]	2022	China	In situ / in vivo	Human dentin blocks from third molars (palatal appliances)	n = 10 specimens per group (6 groups); 15 volunteers	Dual function of quercetin as MMP inhibitor and collagen crosslinker in dentin erosion and abrasion	Dentin loss (µm): Deionized water 1.83 ± 0.42; Ethanol 1.84 ± 0.53; CHX 1.24 ± 0.36; Q75 0.94 ± 0.38; Q150 0.85 ± 0.39; Q300 0.73 ± 0.37 (Q150 and Q300 < CHX; p < 0.05)	MMP inhibition (%): Q75 32.24 ± 5.22; Q150 41.37 ± 1.67; Q300 60.26 ± 5.35; CHX 59.68 ± 6.00. Collagen crosslinking (%): Q75 28.51 ± 2.64; Q150 43.54 ± 1.46; Q300 54.41 ± 3.30. µUTS (MPa): Q75 23.47 ± 8.62; Q150 24.29 ± 7.33; Q300 29.56 ± 8.55; controls ≈ 10 MPa. Penetration depth: ~25–30 μm (Raman mapping).
Salim et al.[24]	2022	Finland	In vitro	Demineralized human mid-coronal dentin beams	n = 10 per group (8 groups; total n = 80 beams)	Effect of ions released from S-PRG fillers on dentin protease activity (MMPs and cathepsin K)	Relative MMP activity (% of baseline): Control + 99.8 ± 13.0%; S-PRG eluate + 23.2 ± 4.6%; Fluoride − 3.5 ± 2.3% after treatment (all treatments < control, p < 0.05)	Dry mass loss (%): Fluoride 4.0 ± 1.5% (lowest; p < 0.05 vs. control and Sr); other ions ≈ control (p > 0.05). CTX (pg/mg dentin): S-PRG 122.6 ± 41.3; Control 165.5 ± 17.5; Sr 186.9 ± 50.1 (ns). ICTP (ng/mg dentin): Control 53.5 ± 14.1; Fluoride 15.4 ± 7.3 (lowest; p < 0.05); S-PRG, Na, Sr significantly lower than control (p < 0.05).
Guo et al.[25]	2023	China	In vitro	Human cervical dentin blocks from third molars	n = 5 per group	Effect of theaflavins (TFs) on dentin erosion and MMP inhibition	Erosive dentin wear (µm): Control (10% EtOH) = 11.23 ± 0.82; 1% TF = 7.56 ± 0.39; 2% TF = 5.29 ± 0.61; 4% TF = 3.28 ± 0.33; 8% TF = 2.62 ± 0.99 (4 cycles/day × 7 days; p < 0.05 vs. control)	µUTS (MPa): Control = 9.74 ± 2.03; 1% TF = 15.86 ± 3.19; 2% TF = 20.08 ± 5.29; 4% TF = 26.67 ± 6.31; 8% TF = 25.51 ± 4.97 (p < 0.05). MMP activity: significant reduction in relative fluorescence vs. control (in situ zymography, p < 0.05).
Lin et al.[36]	2023	China	In vitro	Human coronal dentin blocks (3 × 3 × 2 mm) from extracted sound third molars	n = 12 per subgroup (PRE/POST); 4 groups total (n = 24/group; N = 96)	Effect of MMP inhibition (1 mM 1,10-phenanthroline) and cathepsin K inhibition (1 µM odanacatib), alone or combined, and application timing on erosive dentin degradation	Erosive dentin loss (µm): DW PRE 6.64 ± 0.87; DW POST 7.36 ± 1.27. ODN PRE 4.20 ± 1.25; POST 4.15 ± 0.79. PHEN PRE 4.41 ± 1.38; POST 5.13 ± 1.80. COM PRE 4.31 ± 1.04; POST 4.16 ± 1.95 (all inhibitors < DW; p < 0.05)	Residual DOM thickness (µm): DW PRE 1.09 ± 0.87; POST 1.28 ± 0.74. ODN PRE 3.51 ± 1.61; POST 3.19 ± 1.65. PHEN PRE 2.62 ± 1.04; POST 1.12 ± 0.73. COM PRE 2.61 ± 1.02; POST 3.88 ± 2.14. Gelatinolytic inhibition (%): ODN ≈ 46.3; PHEN ≈ 58.6; COM ≈ 74.6
Yang et al.[27]	2023	China	In situ (in vivo erosion model)	Human coronal dentin blocks from third molars mounted in palatal appliances	n = 10 dentin specimens per group; 10 volunteers (4 groups)	Effect of MMP and cysteine cathepsin inhibition on dentin erosion and DOM preservation	Substance loss (µm): Control (deionized water) = 8.63 ± 1.82; MMP inhibitor (1,10-phenanthroline) = 4.79 ± 1.50; Cathepsin inhibitor (E-64) = 4.99 ± 1.67; Combined (phenanthroline + E-64) = 4.89 ± 2.62 (all inhibitors < control, p < 0.05; no differences among inhibitors)	DOM thickness (µm): Control = 4.29 ± 2.10; MMP inhibitor = 9.84 ± 3.44; Cathepsin inhibitor = 7.82 ± 2.56; Combined = 8.35 ± 2.88 (all inhibitors > control, p < 0.05). SEM: thicker and more organized DOM in all inhibitor groups
Chen et al.[28]	2023	China	In vitro	Human mid-coronal dentin beams from sound third molars	n = 16 per group (erosion model); n = 5 per group (collagen degradation assays)	Effect of cathepsin K inhibition (odanacatib and NaCl) on dentin erosion, preservation of the demineralized organic matrix (DOM), and collagen degradation	Erosive dentin loss (µm): Deionized water = 14.9 ± 1.1; 0.1 M NaCl = 13.8 ± 1.4; 0.3 M NaCl = 13.8 ± 0.9; 0.5 M NaCl = 15.0 ± 0.9; 1 µM odanacatib = 13.4 ± 1.1 (p < 0.05 vs. control). DOM thickness (µm): Control = 1.2 ± 0.6; 0.3 M NaCl = 3.4 ± 0.7; 0.5 M NaCl = 3.6 ± 1.2; 1 µM odanacatib = 4.1 ± 1.5	CTX (ng/mL): Control = 3.16 ± 0.33; 0.3 M NaCl = 1.20 ± 0.35; 0.5 M NaCl = 0.88 ± 0.21; 1 µM odanacatib = 0.16 ± 0.15. ICTP (ng/mL): Control = 5.90 ± 0.56; 0.3 M NaCl = 3.67 ± 0.61; 0.5 M NaCl = 4.50 ± 0.63; 1 µM odanacatib = 4.14 ± 0.77. HYP (µg/mL): Control = 17.04 ± 2.12; 0.3 M NaCl = 12.95 ± 1.83; 0.5 M NaCl = 11.35 ± 1.77; 1 µM odanacatib = 7.63 ± 1.68
Lin et al.[29]	2024	China	In vitro	Human cervical dentin blocks from extracted third molars	n = 6 per group	Combined inhibition of MMPs and cathepsin K to prevent erosive dentin degradation	Erosive dentin loss (µm): Control = 7.12 ± 0.68; MMP inhibitor (PHEN) = 5.02 ± 0.54; Cathepsin K inhibitor (ODN) = 4.71 ± 0.49; Combined (PHEN + ODN) = 3.86 ± 0.42 (p < 0.05 vs. control; combination < single inhibitors)	Residual demineralized organic matrix (DOM, µm): Control = 1.98 ± 0.31; PHEN = 2.54 ± 0.37; ODN = 2.88 ± 0.41; Combination = 3.42 ± 0.46 (p < 0.05). Proteolytic activity (% inhibition): PHEN ≈ 55%; ODN ≈ 48%; Combination ≈ 72% (in situ zymography). SEM: improved collagen network preservation in combined group.
Sek Lee et al.[30]	2024	South Korea	In vitro	Human mid-coronal dentin slices and beams from extracted premolars and third molars	Erosion test: n = 8 slices per group; µUTS: n = 30 beams per group; Zymography: 15 images per group	Effect of marine-derived compounds (fucosterol and fucoxanthin) as collagen cross-linkers and MMP inhibitors on dentin erosion resistance and mechanical stability	Tooth structure loss (TSL, nm): Deionized water 267.92 ± 51.27; Ethanol 263.38 ± 57.92; FS-200: 158.68 ± 54.79; FX-200: 196.43 ± 60.71 (FS-200 and FX-200 significantly lower vs. controls, p < 0.01)	µUTS (MPa): DW 9.99 ± 3.79; Ethanol 11.47 ± 2.28; FS-50 20.40 ± 4.66; FS-100 23.94 ± 4.17; FS-200: 25.63 ± 4.35; FX-50 20.59 ± 5.57; FX-100 21.41 ± 4.87; FX-200: 23.10 ± 3.96. MMP inhibition (%): FS-200 70.42 ± 5.72; FX-200 59.07 ± 11.73
Ozan et al.[34]	2025	Turkey	In vitro experimental study	Human enamel and dentin slabs from extracted third molars	n = 6 per group (6 experimental TF varnish groups + fluoride control)	Evaluation of theaflavin-based dental varnishes (TF-2a and TF-2b) on erosive demineralization and MMP inhibition	Mineral density (Micro-CT): baseline MD 1.72–1.92 → final MD 2.15–2.25 g/cm³; ΔMD = 14.81–38.07% depending on formulation	MMP-2 reduction: up to > 75% (TF-2a resin + polymer varnish); MMP-9 reduction: 43–75% vs. negative control (Western blot, % of NC)
Chen et al.[32]	2026	China	In vitro	Human coronal dentin blocks (2 × 2 × 2 mm) from sound third molars	n = 10 per group for EDL and ICTP (total specimens distributed across analyses)	Dual-action protection against dentin erosion using quercetin-loaded amine-functionalized mesoporous bioactive glass nanoparticles (Q@AF-MBGN): tubule occlusion + inhibition of organic matrix degradation	Erosive dentin loss (µm): DW = 16.88 ± 3.52; NaF = 12.25 ± 3.86; Quercetin = 8.45 ± 2.37; AF-MBGN = 9.01 ± 1.59; Q@AF-MBGN = 3.89 ± 1.24 (lowest EDL, p < 0.05)	Collagen degradation (ICTP, µg/L): DW = 42.76 ± 6.26; NaF = 38.13 ± 7.24; Quercetin = 20.63 ± 5.38; AF-MBGN = 35.35 ± 7.69; Q@AF-MBGN = 7.84 ± 2.52 (p < 0.05). Tubule occlusion (%): After second erosion cycle: Q@AF-MBGN 89.77 ± 3.36 vs. AF-MBGN 78.05 ± 6.21. In situ zymography: marked suppression of dentin-derived MMP activity in Q and Q@AF-MBGN groups

Risk of bias assessment

The risk of bias assessment revealed a predominantly low to moderate overall risk of bias across the included studies, with heterogeneity concentrated in domains related to randomization, allocation concealment, and blinding (Fig. 2). Most in situ and in vitro experimental studies showed low risk for outcome assessment, incomplete outcome data, selective reporting, and other sources of bias (domains D4–D7), indicating generally robust analytical and reporting practices [4, 15, 16, 21, 22, 25, 26, 32].

Fig. 2.

Risk of bias assessment across studies included in the review. The table summarizes the risk of bias in six domains: D1 (bias due to participation), D2 (bias due to attrition), D3 (bias due to prognostic factor measurement), D4 (bias due to outcome measurement), D5 (bias due to confounding), and D6 (bias in statistical analysis and reporting). Each domain is assessed as low risk (green, “+”), moderate risk (yellow, “−“), or high risk (red, “X”). The overall risk of bias for each study is also provided

However, unclear or high risk was frequently observed in random sequence generation and allocation concealment (D1–D2), particularly in laboratory-based studies where formal randomization procedures were not explicitly reported [8, 17, 24, 27]. Blinding of participants and personnel (D3) was the most compromised domain overall, showing high risk in several studies [13, 23, 30], reflecting the inherent difficulty of implementing blinding in erosive and in situ dentin models.

Notably, Sek Lee et al. [30] presented a high overall risk of bias, driven by consistent high-risk judgments in randomization, allocation concealment, and blinding domains, whereas most other studies retained a low overall risk despite isolated domain-level concerns. In contrast, clinical crossover and well-controlled in situ studies, such as those by Ozan et al. [10, 33] and Kato et al. [14], demonstrated stronger methodological rigor with predominantly low-risk judgments across domains.

Overall, while the evidence base is methodologically sound in terms of outcome measurement and reporting, these findings highlight the need for clearer reporting of randomization procedures and blinding strategies, particularly in experimental dentin erosion research, to further strengthen internal validity and reproducibility.

Erosion protocols and enzymatic activity

Erosion protocols consistently demonstrated measurable impacts on dentin, with the severity of tissue loss modulated by pH, exposure duration, and cycling frequency. Across studies, highly acidic beverages and solutions (pH ≈ 2.3–2.6) applied in repeated daily cycles promoted demineralization of the inorganic phase, thereby exposing the collagenous matrix and facilitating enzymatic activation. Short but frequent erosive challenges, such as Coca-Cola exposure in 5-min cycles repeated four times daily over 5–7 days, resulted in pronounced dentin degradation and increased proteolytic activity, even in the absence of abrasion. In contrast, protocols involving prolonged or continuous acidic exposure, particularly citric or phosphoric acid models, intensified enzymatic effects and structural damage, highlighting that both cumulative acid contact time and cycling pattern critically influence dentin breakdown (Table 2).

Table 2.

Erosion and abrasion protocols of the included studies

Study	Erosion Protocol	Abrasion Protocol	Combined Protocol	Exposure Time	Cycles	pH	Solution
Kato et al. (2010)[14]	Extra-oral immersion of palatal appliances in soft drink	None (abrasion deliberately avoided)	No	5 min per cycle	4/day × 5 days	2.6	Coca-Cola®
Kato et al. (2010a)[13]	Extra-oral immersion of palatal appliances in soft drink	None	No	5 min per cycle	4/day × 5 days	2.6	Coca-Cola® (150 mL per challenge)
Silveira et al. (2014)[15]	Immersion in lemon-flavored soft drink	None	No	1.5 min per cycle	4/day × 5 days	2.91	Sprite Zero™
Zarella et al. (2015)[33]	In vitro immersion of dentin blocks in soft drink with pH-cycling and artificial saliva	None	No	90 s per cycle	4/day × 5 days	2.6	Coca-Cola® (30 mL per specimen per challenge)
Amaral et al. (2018)[17]	Enzymatic activation model using APMA	None	No	Not reported	Not reported	2.5–7.0	APMA
Cvikl et al. (2018)[8]	Single exposure to phosphoric acid	None	No	15 s	Once	Not reported	Phosphoric acid 37%
Ozan et al. (2020)[10]	Extra-oral immersion of palatal appliances in soft drink	None (abrasion deliberately avoided)	No	5 min per cycle	4/day × 5 days	≈ 2.6	Coca-Cola® (150 mL per challenge)
Leal et al. (2021)[19]	Immersion in 1% citric acid under agitation (100 rpm)	Automatic toothbrushing (150 strokes, 200 g load; erosion–abrasion arm only)	Yes (parallel erosion-only and erosion–abrasion models)	5 min per cycle	3/day × 5 days	2.3	Citric acid 1%
Moraes et al. (2021) [18]	In vitro: citric acid; In situ: soft drink	None	Yes (parallel models)	In vitro: 24 h; In situ: 1 min per cycle	In vitro: once; In situ: 4/day × 5 days	2.3 / 2.6	Citric acid / Coca-Cola®
Hanzen et al. (2021)[22]	Immersion in soft drink	None	No	1.5 min per cycle	4/day × 5 days	Not reported	Coca-Cola®
Salim et al. (2022)[24]	Continuous immersion in phosphoric acid	None	No	48 h	Once	Not reported	Phosphoric acid 10%
Capalbo et al. (2022)[21]	Immersion in citric acid	None	No	1.5 min per cycle	4/day × 5 days	3.2	Citric acid
Hong et al. (2022)[23]	Immersion in soft drink	Manual toothbrushing (30 s; fluoridated toothpaste)	Yes	5 min per cycle	4/day × 7 days	2.3	Coca-Cola®
Guo et al. (2023)[25]	Immersion in aqueous phosphoric acid	None	No	5 min per cycle	4/day × 7 days	2.3	Phosphoric acid
Lin et al. (2023)[36]	Immersion in soft drink	None	No	5 min per cycle	4/day × 5 days	2.3	Coca-Cola®
Yang et al. (2023)[27]	In situ intraoral erosion using palatal appliances with cola rinses	None	No	5 min per cycle	4/day × 7 days	≈ 2.3	Coca-Cola® (150 mL per challenge)
Chen et al. (2023)[28]	Immersion in soft drink under agitation	None	No	5 min per cycle	4/day × 5 days	2.3	Coca-Cola® (150 mL per challenge)
Lin et al. (2024)[29]	Immersion in citric acid	None	No	Not reported	7 days	2.3	Citric acid 5%
Sek Lee et al. (2024)[30]	In vitro immersion of dentin slices in phosphoric acid with artificial saliva remineralization	None	No	5 min per cycle	3/day × 5 days	1.0	Phosphoric acid 10% (5 mL per challenge)
Ozan et al. (2025)[34]	In vitro pH-cycling with citric acid and artificial saliva remineralization	None	No	5 min per cycle	4/day × 5 days	3.2	Citric acid 0.3%
Kato et al. (2021) – S1[20]	Extra-oral immersion of palatal appliances	Toothbrushing (15 s; dentifrice slurry; 2×/day)	Yes	5 min per cycle	4/day × 5 days	2.6	Coca-Cola® (150 mL per challenge)
Kato et al. (2021) – S2[20]	Extra-oral immersion of palatal appliances	Toothbrushing (15 s; dentifrice slurry; 2×/day)	Yes	5 min per cycle	4/day × 10 days	2.6	Coca-Cola® (150 mL per challenge)
Chen et al. (2026)[32]	Immersion in soft drink under agitation	None	No	5 min per cycle	4/day × 5 days	2.3	Coca-Cola® (150 mL per challenge)

Activation and inhibition of MMPs

MMP-2, MMP-8, and MMP-9 emerged as central players in collagen degradation. Acidic environments demineralized the dentin matrix, exposing collagen fibrils to enzymatic degradation. This enzymatic activity weakened the dentin structure and facilitated deeper acid penetration, accelerating erosion [34, 35].

Interventions to inhibit MMP activity included both synthetic and natural compounds. Ferrous sulfate (FeSO₄) achieved complete inhibition of MMP-2 and MMP-9 activity [7], while stannous-based compounds, such as stannous chloride (SnCl₂) and stannous fluoride (SnF₂), significantly reduced enzymatic activity and preserved dentin structure [8]. Natural inhibitors, including green tea catechins and theaflavins, reduced MMP activity by up to 74%, as reported by Moraes et al. [36] and Guo et al. [25]. These polyphenol-based compounds also offered antioxidant protection, enhancing their dual functionality (Table 3).

Table 3.

Cathepsin activity

Study	Cathepsin Type	Activity Increase	Intervention	Reduction (%)	Synergy with MMPs
Zarella et al., 2015[33]	Cysteine cathepsins (primarily cathepsin B; non-specific CC activity).	Increased activity after erosive demineralization, but markedly lower than MMP activity; CC activity estimated ~ 10× lower than MMPs in demineralized dentin.	Specific cathepsin B inhibitor (0.2 mM), non-specific CC inhibitor E-64 (0.5 mM); compared with MMP inhibitors (chlorhexidine, galardin), fluoride, placebo, and untreated controls.	No statistically significant reduction in dentin erosion compared with controls; only minor, non-significant trends versus placebo/untreated.	Indirect synergy suggested—CCs may contribute to MMP activation (e.g., via TIMP degradation), but MMPs identified as the dominant enzymes driving dentin erosion.
Yang et al., 2023[27]	Cysteine cathepsins (mainly cathepsins B/L; non-selective inhibition).	Increased activity under acidic erosive conditions; secondary to MMPs but biologically relevant in DOM degradation.	E-64 (50 µM, cysteine cathepsin inhibitor), 1,10-phenanthroline (1 mM, MMP inhibitor), and combined E-64 + 1,10-phenanthroline (in situ model).	Qualitative reduction of dentin substance loss (~ 40–45% vs. control); no additional reduction with combined inhibition compared to single inhibitors.	Yes—functional synergy suggested; cathepsin inhibition may indirectly reduce MMP activation, but no additive effect observed when both pathways were inhibited simultaneously.
Chen et al., 2023[28]	Cathepsin K (catK).	Markedly increased under acidic erosive conditions; high collagenolytic activity on demineralized dentin.	Cathepsin K inhibition using 1 µM odanacatib and NaCl solutions (0.1–0.5 M) in an in vitro erosion model.	≈ 15% reduction in erosive dentin loss with 0.3 M NaCl and 1 µM odanacatib; significant reductions in CTX, ICTP, and HYP release	Yes—indirect synergy suggested; catK inhibition reduced collagen telopeptide release associated with MMP-mediated degradation pathways.
Lin et al., 2023[36]	Cathepsin K (catK).	Increased activity in eroded dentin under acidic conditions; active alongside MMPs in DOM degradation.	CatK inhibitor (1 µM odanacatib), MMP inhibitor (1 mM 1,10-phenanthroline), and combined inhibition (in vitro erosive cycling model).	Erosive dentin loss reduced by ~ 35–40% vs. control; gelatinolytic activity reduced by ~ 46% (catK inhibitor), ~ 59% (MMP inhibitor), and ~ 75% (combined).	No clear additive/synergistic effect on dentin loss; combined inhibition did not significantly outperform single inhibitors, despite greater enzymatic activity suppression.
Lin et al., 2024[29]	Cathepsin K (catK).	Significantly increased activity in eroded dentin compared with intact dentin; concomitant marked increase in MMP activity.	No inhibitory intervention; experimental in vitro erosion model (5% citric acid) assessing endogenous enzyme activity, distribution, and colocalization.	Not applicable (mechanistic observational study; no erosion-reduction intervention tested).	Yes—strong spatial and functional synergy; colocalization of catK with MMP-2 and MMP-9 increased 13- to 26-fold in eroded dentin, supporting cooperative roles in collagen degradation during dentin erosion.

Role of cathepsins in erosion

While MMPs were the primary focus, several studies explored the role of cathepsins, particularly cathepsin K. Lin et al. [35] demonstrated that cathepsin K activity in eroded dentin was 13–26 times higher than in intact dentin, with significant colocalization observed with MMP-2 and MMP-9. This synergistic interaction exacerbates the proteolytic degradation of collagen fibrils, highlighting the complexity of enzymatic activity during erosion. Moraes et al. [36] reported an 8-fold increase in cathepsin K activity, which was reduced by 60% through green tea catechins, emphasizing the potential for targeted interventions to modulate enzymatic activity (Table 3).

Protective strategies

Protective interventions were categorized into synthetic inhibitors, natural compounds, and combination therapies. Synthetic inhibitors, such as ferrous sulfate and stannous fluoride, demonstrated robust efficacy in reducing enzymatic activity and preserving dentin integrity. For example, Capalbo et al. [21] found that a fluoride-polyphenol formulation achieved 100% inhibition of MMP activity, significantly reducing dentin erosion severity. Additionally, Mendes Soares et al. [24] showed that S-PRG fillers offered similar protection by reducing collagen degradation .

Natural compounds, including catechins, theaflavins, and anacardic acid, were effective in mitigating collagen degradation and enhancing dentin resistance. Guo et al. [25] reported that theaflavins provided significant MMP inhibition, reducing enzymatic activity by up to 74% (Table 3).

Combination therapies showed the greatest promise, leveraging the strengths of multiple agents. For instance, fluoride-polyphenol formulations combining fluoride, hexametaphosphate, and quercetin achieved 100% inhibition of enzymatic activity [21], while the combination of quercetin and chlorhexidine significantly reduced MMP activity and improved dentin resistance to erosion and abrasion [37].

Certainty and confidence in the synthesized findings

Overall, the certainty of evidence for the role of MMPs and cathepsins in dentin erosion progression was judged as moderate, supported by consistent experimental evidence demonstrating enzyme activation following acidic challenges and subsequent collagen degradation. Findings related to the effectiveness of synthetic inhibitors (e.g., ferrous sulfate, chlorhexidine, stannous compounds) showed moderate-to-high confidence, as results were reproducible across multiple studies with similar outcome patterns. In contrast, evidence supporting natural inhibitors and dual-inhibition strategies was rated as low-to-moderate certainty, reflecting smaller sample sizes, greater protocol heterogeneity, and reliance on surrogate outcomes. The predominance of laboratory-based designs and the scarcity of long-term in situ or clinical data further limited certainty, underscoring that conclusions should be interpreted as mechanistic and proof-of-concept, rather than definitive clinical recommendations.

Discussion

This systematic review comprehensively evaluated the roles of matrix metalloproteinases (MMPs) and cathepsins in dentin erosion, synthesizing data from the included studies. The findings highlight the mechanisms of enzymatic activity under acidic conditions, the efficacy of various interventions, and the clinical implications of protecting dentin integrity against erosive damage. The review successfully achieved its objective and addressed the research question by demonstrating the critical role of MMPs and cathepsins in the progression of dentin erosion and evaluating the effectiveness of synthetic and natural inhibitors in mitigating enzymatic degradation and preserving dentin structure.

Dental erosion is increasingly recognized as a multifactorial condition in which the chemical dissolution of mineralized tissues is compounded by endogenous proteolytic activity. Acidic challenges from intrinsic sources such as gastroesophageal reflux, chronic vomiting, and eating disorders and extrinsic sources such as frequent consumption of carbonated beverages, citrus juices, and occupational acid exposure initiate the demineralization process and soften the dentin substrate [22, 38]. This demineralization exposes collagen fibrils, creating an optimal substrate for the activation of matrix metalloproteinases (MMPs) and cysteine cathepsins. Evidence synthesized in this review confirms that MMP-2, MMP-8, MMP-9, and cathepsin K are consistently implicated in erosive lesions, with their activity persisting even after the acidic pH returns to near-neutral values, thereby prolonging collagen degradation.

Traditional management strategies have largely focused on mitigating etiological factors—dietary counseling, acid exposure reduction, treatment of reflux, and enhancement of salivary defense mechanisms. However, recent literature underscores the importance of integrating enzymatic inhibition into these preventive frameworks [39, 40]. This dual approach aims to not only reduce the frequency and intensity of erosive episodes but also to preserve the structural integrity of the demineralized collagen matrix, thereby addressing both the cause and the progression of the condition.

Synthetic inhibitors such as stannous salts, ferrous sulfate, and chlorhexidine have demonstrated efficacy in reducing MMP activity, while natural compounds including polyphenols from green tea and grape seed extract—offer similar inhibition alongside antioxidant benefits [41]. In vitro evidence suggests that combination therapies (e.g., fluoride with polyphenols) may synergistically enhance remineralization while simultaneously reducing enzymatic degradation, a particularly relevant strategy in patients with unavoidable intrinsic acid exposure.

Nonetheless, the extrapolation of these findings to clinical practice remains challenged by methodological heterogeneity. Differences in erosive protocols, pH cycling regimens, exposure times, and types of acids used across in vitro models limit direct comparability. Moreover, in vitro designs fail to fully account for protective biological factors such as the acquired pellicle, salivary buffering, and the complex mechanical–chemical interactions present in vivo. Consequently, well-designed in situ and clinical studies are necessary to validate the real-world efficacy of MMP inhibitors as adjuncts to conventional preventive measures.

From a precision dentistry perspective, integrating MMP and cathepsin inhibition into tailored preventive regimens delivered via dentifrices, rinses, or professional applications has the potential to enhance long-term outcomes. For high-risk individuals, such as those with chronic reflux or high dietary acid intake, this combined strategy could provide more sustainable protection, slowing the subclinical progression of collagen degradation and preserving both function and aesthetics over time. This approach aligns with a mechanistic understanding of erosion that recognizes the synergistic roles of chemical dissolution and proteolytic degradation in the pathogenesis of dentin loss.

Dentin erosion is a multifaceted process involving the chemical demineralization of hydroxyapatite, which exposes the organic collagen matrix to enzymatic degradation. MMPs, particularly MMP-2, MMP-8, and MMP-9, and cathepsins, notably cathepsin K [29], play pivotal roles in this breakdown. Acidic environments disrupt the mineralized dentin matrix, creating optimal conditions for enzymatic activation. Kato et al. [7] demonstrated that repeated exposure to Coca-Cola (pH 2.4–2.6) significantly increased MMP-2 and MMP-9 activity, degrading exposed collagen fibrils. Similarly, Lin et al. [35] found that citric acid exposure (pH 2.3) amplified enzymatic activity by 13–26 times compared to intact dentin. These findings underscore the critical role of acidic challenges in activating proteolytic enzymes and perpetuating dentin tissue degradation.

Host-derived cysteine cathepsins have emerged as relevant contributors to dentin matrix degradation following acid-induced demineralization. Together with matrix metalloproteinases (MMPs), these proteases participate in the breakdown of the exposed organic matrix predominantly type I collagen during dentin caries and erosive challenges. Seminal conceptual frameworks in dentin degradomics have established that both enzyme families are embedded within the dentin matrix and become activated after mineral loss, with cathepsins, particularly cathepsin K, retaining activity at lower pH levels than MMPs and therefore potentially initiating or sustaining collagen degradation during acidic episodes [42, 43]. In vitro and in situ experimental studies have demonstrated that selective inhibition of cysteine cathepsins reduces dentin erosion progression and preserves the demineralized organic matrix, albeit generally to a lesser extent than MMP inhibition alone [16, 27]. Targeted investigations focusing on cathepsin K further confirmed that pharmacological catK inhibition significantly decreases erosive dentin loss and collagen degradation markers, supporting its functional role in erosion-associated matrix breakdown [28]. Mechanistic evidence indicates that cathepsin K can regulate MMP activity in a pH-dependent manner and interact with dentin matrix components such as glycosaminoglycans, thereby influencing the overall proteolytic balance within eroded dentin [44]. In parallel, proteomic analyses of the acquired enamel and dentin pellicle in erosive conditions, including gastroesophageal reflux disease, have revealed qualitative and quantitative alterations in protein profiles associated with protease-rich environments, further supporting the biological plausibility of host-derived protease involvement in erosive tooth wear [45, 46]. Collectively, this body of evidence underscores that cysteine cathepsins are integral components of the dentin proteolytic network and sets the stage for exploring their functional interplay with MMPs under erosive conditions [47].

The synergistic interaction between matrix metalloproteinases (MMPs) and cysteine cathepsins plays a critical role in exacerbating dentin erosion. Mechanistic evidence indicates that while MMPs remain the dominant drivers of collagen degradation, cathepsins act as complementary amplifiers of proteolytic activity. Early in vitro data by Zarella et al. [16] demonstrated that cysteine cathepsins exhibit lower absolute activity than MMPs but may contribute indirectly to erosion progression, potentially through modulation of tissue inhibitors of metalloproteinases (TIMPs). Subsequent in situ and in vitro studies confirmed that erosive acidic conditions significantly increase cathepsin activity, particularly cathepsin K, alongside MMP activation [4, 27]. Notably, Lin et al. [35] reported marked spatial colocalization of cathepsin K with MMP-2 and MMP-9 in eroded dentin, with a 13- to 26-fold increase compared with intact substrates, supporting a strong functional synergy between these protease systems. Although combined inhibition of MMPs and cathepsins did not consistently yield additive reductions in dentin loss, dual-target strategies achieved the greatest suppression of overall proteolytic activity, reinforcing the concept that coordinated enzymatic interplay, rather than isolated protease action, underlies collagen matrix degradation during dentin erosion [16, 26–28].

Matrix metalloproteinases (MMPs) are zinc- and calcium-dependent endopeptidases that are sequestered within the mineralized dentin matrix in a latent form. During erosive episodes, acidic challenges dissolve the inorganic phase, exposing these enzymes and creating conditions that favor their subsequent activation when the pH returns to near-neutral values [3, 17]. In dentin, MMP-2, MMP-8, and MMP-9 are the most relevant isoforms and are capable of cleaving collagen fibrils within the demineralized organic matrix, thereby accelerating structural breakdown [16]. This proteolytic process is further amplified by the activity of cysteine cathepsins, particularly cathepsin K, which not only degrades collagen directly but also modulates MMP activity in a pH-dependent manner [16, 44]. Experimental evidence has demonstrated that MMP activity is suppressed under strongly acidic conditions but increases markedly at mildly acidic to neutral pH, explaining why dentin degradation continues even after the erosive acid is cleared [17, 48]. This biphasic mechanism—acid-mediated mineral dissolution followed by enzyme-driven organic matrix degradation—underpins the progressive nature of dentin erosion and contributes to the loss of mechanical integrity observed in advanced lesions [16, 49].

The enzymatic degradation patterns in erosion parallel those observed in dental caries and in the deterioration of the adhesive hybrid layer. Evidence from adhesive dentistry shows that MMP inhibition via agents such as chlorhexidine, benzalkonium chloride, or quaternary ammonium methacrylates—prolongs bond strength retention [50], highlighting the clinical relevance of controlling these enzymes. In erosion, incorporating MMP inhibitors alongside remineralizing agents could stabilize exposed collagen fibrils, enhance remineralization efficacy, and protect restorative margins, particularly in high-risk patients with chronic acid exposure [38, 39, 41].

Despite robust mechanistic evidence, most data derive from in vitro studies lacking the modulating effects of saliva and the acquired pellicle. Future in situ and clinical trials should quantify MMP activity under realistic erosive conditions and evaluate sustained-delivery systems for inhibitors [40]. Integrating MMP control with etiological management aligns with precision dentistry, offering a dual biological and preventive strategy to preserve dentin function and aesthetics over time.

Synthetic inhibitors showed robust results across multiple studies. Ferrous sulfate (FeSO₄) was reported by Kato et al. [7] to achieve complete inhibition of MMP-2 and MMP-9 activity, effectively preserving the collagen matrix by chelating zinc ions essential for enzymatic activity. Similarly, stannous compounds, such as stannous fluoride (SnF₂) and stannous chloride (SnCl₂), reduced enzymatic activity by up to 85% [8]. These compounds also promoted remineralization by depositing protective layers on dentin surfaces.

Natural polyphenols, such as green tea catechins and theaflavins, offer dual benefits of enzymatic inhibition and antioxidative protection. Moraes et al. [36] observed that green tea catechins reduced MMP activity by 74% and decreased surface loss by 40% during erosion-abrasion cycles. Similarly, Guo et al. [25] reported a concentration-dependent inhibition of MMP-2 and MMP-9 by theaflavins, achieving up to 74% reduction in enzymatic activity. These findings suggest the potential for incorporating natural compounds into oral care products.

Combination therapies have shown the highest efficacy by targeting multiple pathways of erosion progression. Capalbo et al. [21] demonstrated that a fluoride-polyphenol formulation combining fluoride, hexametaphosphate, and quercetin (F + HMP+QC) achieved 100% inhibition of MMP activity, while simultaneously strengthening the dentin matrix through remineralization. Additionally, Hong et al. [37] showed that combining quercetin with chlorhexidine reduced MMP activity by 80%, providing significant protection against erosion and abrasion.

The studies in this review employed diverse protocols to simulate real-world conditions of erosion and abrasion, contributing to a comprehensive understanding of intervention efficacy. Citric acid (pH 2.3) and Coca-Cola (pH 2.4–2.6) were commonly used agents to replicate dietary acid exposure. For instance, Lin et al. [35] exposed dentin samples to citric acid for 60 min per cycle over seven days, observing significant enzymatic activity and collagen breakdown. Abrasion protocols, such as toothbrush abrasion with 200 strokes per cycle [36], further illustrated the additive effects of mechanical wear on dentin loss. Combined protocols, such as those used by Hong et al. [37], provided insights into the synergistic effects of chemical and mechanical challenges, revealing that Coca-Cola erosion combined with toothbrush abrasion significantly increased MMP activity and collagen degradation.

Recent advances in MMP inhibition and relevance to dentin erosion

While our findings confirm the significant role of matrix metalloproteinases in dentin collagen degradation, recent research offers novel perspectives that deepen this understanding. For instance, Wang [51] describes how selective MMP-13 inhibitors—developed using structure-based, ligand-based, and fragment-based drug discovery, as well as machine learning—have shown high specificity and potency in targeting collagenase-3 activity1-s2.0-S0960894 × 2,400,411, Although these developments are primarily directed toward osteoarthritis, the underlying mechanisms selective blockade of active-site subsites (e.g., S1′, S1′*) and precise delivery systems—are directly relevant to dentin preservation, where unwanted inhibition of other MMPs can cause off-target effects. Incorporating such targeted strategies into oral biomaterials could improve the durability of erosion-preventive treatments.

Similarly, biomimetic approaches, such as those reviewed by Singer et al. [52], aim to restore or reinforce the mineralized–collagen interface rather than merely inhibiting enzymatic activity. These methods may complement MMP inhibition by providing a substrate less susceptible to enzymatic hydrolysis. The integration of selective inhibitors with biomimetic remineralization agents could represent a synergistic therapeutic pathway for erosion management.

The mention of SnF₂ in dentin erosion prevention, as studied by West et al. [53], should be framed in terms of its distinct protective mechanism—forming a protective Sn-rich layer and occluding dentinal tubules—rather than as a direct modulator of MMP or cysteine cathepsin activity. Its inclusion in comparative models is justified when evaluating multi-modal strategies for erosion protection, but its biochemical independence from MMP inhibition must be clearly stated to avoid conceptual drift. Clarifying these mechanistic differences will strengthen the coherence between our study focus and broader advancements in the field.

While MMPs have been extensively studied, the role of cathepsins, particularly cathepsin K, in dentin erosion is increasingly recognized. Lin et al. [26] found that cathepsin K activity was 13–26 times higher in eroded dentin, acting synergistically with MMPs to degrade collagen fibrils. Inhibiting both MMPs and cathepsins, as explored by Lin et al. [35], demonstrated enhanced preservation of dentin integrity, presenting a promising therapeutic approach.

Despite overall consistency in findings, significant heterogeneity was observed among the included studies, stemming from variations in sample sources, erosion protocols, and assessment methods. For instance, some studies used human molars, while others relied on bovine dentin due to its availability. Differences in erosion protocols, such as exposure times ranging from 30s [36] to 60 min per cycle [35], further complicate direct comparisons. Additionally, the methods used to measure enzymatic activity—such as zymography, spectrophotometry, and Scanning electron microscope—have distinct strengths and limitations, highlighting the need for standardized protocols.

Several limitations must be acknowledged when interpreting the findings of this systematic review. First, the predominance of in vitro and in situ studies limits the direct extrapolation of results to clinical settings, as these models cannot fully replicate the complexity of the oral environment, including salivary dynamics, biofilm interactions, and patient-related behavioral factors. Second, substantial methodological heterogeneity was observed across studies with respect to erosion protocols, acidic challenges, exposure durations, outcome measures, and enzymatic assays, precluding quantitative synthesis and contributing to reduced certainty of evidence. Third, incomplete reporting of randomization, blinding, and sample size justification in several studies increased the risk of bias in specific domains. Additionally, variability in the type, concentration, and application mode of inhibitors complicates direct comparison between interventions. Finally, publication bias cannot be excluded, as negative or null findings are less likely to be reported. These limitations highlight the need for standardized experimental protocols and well-designed in situ and clinical trials to validate the long-term effectiveness and clinical relevance of MMP- and cathepsin-targeted strategies in dentin erosion prevention.

The findings of this review have important implications for clinical practice, particularly in the development of preventive strategies against dentin erosion. Incorporating MMP and cathepsin inhibitors into oral care products, such as toothpaste and mouth rinses, could provide daily protection against erosion. Combination therapies, such as fluoride-polyphenol formulations, offer enhanced protection and could be tailored for individuals with high exposure to dietary acids or gastroesophageal reflux. Educating patients about the risks of acidic diets and the benefits of protective interventions can further reduce erosion risk.

Although the present review consolidates extensive evidence on the proteolytic roles of MMPs and cysteine cathepsins in dentin erosion, it is important to acknowledge that much of this enzymatic behavior has been described previously in the contexts of caries and adhesive degradation. The novelty of future work in this domain should lie in bridging the translational gap between in vitro mechanistic insights and in vivo or clinical application [39]. Promising directions include the evaluation of novel inhibitors such as highly selective MMP-13 blockers [51] in combination with established agents like chlorhexidine or polyphenols, to assess synergistic effects on collagen stability. Equally critical is the long-term assessment of these strategies under cyclic erosive challenges in situ or in vivo, where salivary modulation, pellicle dynamics, and patient-specific risk profiles can influence both enzymatic activity and treatment durability. By targeting these gaps, subsequent research could move beyond confirming established mechanisms to generating clinically actionable protocols for the prevention and management of dentin erosion.

Conclusion

This systematic review underscores the central involvement of matrix metalloproteinases (MMPs) and cysteine cathepsins in the progression of dentin erosion, which is initiated by acidic challenges that expose and degrade the collagenous matrix, ultimately compromising dentin structure. Both synthetic inhibitors, such as ferrous sulfate and stannous fluoride, and natural compounds, including catechins and theaflavins, demonstrated the ability to attenuate proteolytic activity and limit dentin degradation under experimental conditions. Approaches combining different inhibitory mechanisms, particularly those integrating fluoride and polyphenolic agents, consistently showed enhanced protective effects by targeting multiple pathways involved in erosive breakdown.

From a certainty-of-evidence perspective, the findings of this systematic review should be interpreted with moderate confidence, primarily reflecting the predominance of in vitro and in situ experimental designs. Although a high degree of biological plausibility and directional consistency was observed across studies particularly regarding the activation of MMPs and cathepsins under acidic conditions and their inhibition by synthetic and natural agents—methodological heterogeneity limited overall dependability. Variations in erosion protocols, exposure times, outcome measures, and reporting of randomization or blinding procedures contributed to downgrading certainty for several synthesized outcomes. Nevertheless, the convergence of results across independent models supports the robustness of the mechanistic pathways identified. According to the ConQual assessment, evidence supporting synthetic inhibitors showed higher confidence than that for natural or dual-inhibition strategies, which were constrained by smaller sample sizes and exploratory designs. These limitations underscore that current conclusions are best regarded as mechanistic and translational, highlighting promising preventive strategies while reinforcing the need for standardized protocols and well-designed in situ and clinical studies to strengthen the certainty and clinical applicability of future evidence.

Despite these promising findings, the current evidence base is largely derived from in vitro and in situ models, emphasizing the need for well-designed in vivo and clinical studies to confirm long-term effectiveness and clinical relevance. Moreover, the synergistic interaction between MMPs and cathepsins during erosion progression warrants further investigation to refine dual-targeted strategies. Addressing these gaps will be essential for the development of effective, safe, and sustainable interventions aimed at preserving dentin integrity in patients at risk of erosive tooth wear.

Authors' contributions

V.G. and E.F. conceived and designed the study. V.G., M.D., and R.C. collected and organized the data. V.G. and A.C. performed the data analysis. V.G., A.C., and E.F. interpreted the results. V.G. and A.C. drafted the main manuscript. E.F. and M.D. critically revised the manuscript for important intellectual content. All authors reviewed and approved the final version of the manuscript and agreed to be accountable for all aspects of the work.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Data availability

10.17632/6nt9t4bmyp.1

Declarations

Ethics approval and consent to participate

Not applicable.

Competing interests

The authors declare no competing interests.