Photobiomodulation in Periodontitis: Targeting Matrix Metalloproteinases, Tissue Inhibitors of Metalloproteinases, and Extracellular Matrix Remodeling

Abstract

Periodontitis is an inflammation-driven disease caused by dysbiosis, in which excessive host proteolytic activity contributes to connective tissue destruction and alveolar bone loss. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) are key regulators of extracellular matrix turnover and potential molecular targets of photobiomodulation (PBM). This review summarizes the biological basis of MMP/TIMP regulation and critically evaluates the available clinical evidence on the effects of adjunctive PBM on these biomarkers in periodontitis. Ten clinical studies published between 2005 and 2023 were identified, together with one systematic review. The included studies used PBM-compatible protocols or mixed laser studies with a PBM-related arm. Irradiation parameters, treatment schedules, comparator therapies, follow-up duration, and biomarker assessment varied considerably. MMP-8 was the most studied marker, and its levels tended to decrease following periodontal therapy regardless of PBM application. Some studies reported greater decrease with PBM while others reported clinical improvement with no further reductions in MMP-8. Evidence for MMP-1, MMP-9, TIMP-1, and MMP/TIMP ratios was limited and heterogeneous. Changes in biomarker levels did not always correlate with clinical improvements in probing depth, clinical attachment level, gingival inflammation, bleeding indices, and early wound healing. In conclusion, PBM may influence MMP-related responses during periodontal healing, but a definite consistent additional effect beyond conventional periodontal therapy has not been established. Future randomized trials should use well-defined non-thermal PBM protocols, identical background periodontal treatment in test and control groups, quantitative assessment of active MMPs and their corresponding TIMPs, and standardized long-term clinical and biochemical follow-up.

1. Introduction

Periodontitis is a chronic inflammatory disease of the supporting tissues of the tooth characterized by loss of connective tissue attachment and destruction of the alveolar bone. The disease is caused by the complex interaction between periodontal bacteria in a dysbiotic subgingival biofilm and a dysregulated host immune response that fails to adequately control either the infection or the associated inflammation [1,2]. Periodontitis is initiated by microorganisms, but the extent and progression of destruction of periodontal tissues is largely determined by the magnitude, persistence, and regulation of the host inflammatory response [1,2].

Matrix metalloproteinases (MMPs) have a central role in this destructive process. These proteolytic enzymes degrade collagen and other components of the extracellular matrix and regulate the activity of cytokines, chemokines, growth factors, and cell-surface receptors. MMP-8 and MMP-9 are particularly relevant to periodontitis because their excessive and prolonged activation contributes to degradation of the gingival connective tissue and periodontal ligament. Under physiological conditions, MMP activity is controlled by tissue inhibitors of metalloproteinases (TIMPs), whereas disruption of the MMP/TIMP balance in favor of active MMPs promotes progressive connective tissue attachment loss and periodontal tissue destruction [2,3].

The cornerstone of nonsurgical periodontal treatment is the mechanical disruption and removal of the supra- and subgingival biofilm and calculus through professional mechanical plaque removal and subgingival instrumentation, together with effective self-performed oral hygiene and control of relevant risk factors [4]. Depending on the clinical indication, several adjunctive approaches have also been investigated, including locally or systemically administered antimicrobials, antiseptics, anti-inflammatory agents, other host-modulating agents, and different laser- and light-based modalities [4,5]. These approaches are intended to complement rather than replace conventional mechanical periodontal therapy.

Photobiomodulation (PBM), formerly referred to primarily as low-level laser therapy (LLLT), is a noninvasive approach based on the application of low-intensity red or near-infrared light to modulate cellular and tissue responses. In periodontitis, PBM has been investigated mainly as an adjunct to nonsurgical periodontal therapy. Available evidence suggests that it may reduce excessive production of proinflammatory mediators and oxidative stress, modulate NF-κB-dependent signaling and macrophage polarization, and support angiogenesis, fibroblast activity, collagen synthesis, periodontal ligament cell function, and osteogenic repair [6,7,8]. Some clinical studies and meta-analyses have reported additional short-term improvements in inflammatory and periodontal parameters. However, considerable heterogeneity in wavelength, irradiance, fluence, treatment schedule, and study design currently prevents the definition of a universally accepted clinical protocol [6,7].

Because MMPs and TIMPs are expressed at the interface of inflammation, extracellular matrix degradation, and tissue repair, they may represent important molecular targets and biomarkers of PBM-mediated host modulation. By influencing inflammatory and redox signaling, immune–stromal cell interactions, and tissue-remodeling pathways, PBM could potentially restore a more favorable MMP/TIMP balance, thereby limiting pathological matrix degradation while supporting periodontal repair. Nevertheless, direct evidence demonstrating how specific PBM protocols regulate individual MMPs and TIMPs in periodontitis remains fragmented and insufficiently integrated.

The present narrative review aims to outline the roles of MMPs and TIMPs in periodontal pathogenesis and critically evaluate the available clinical evidence regarding their modulation by PBM as a potential host-directed adjunct to conventional periodontal therapy. Previous reviews have predominantly focused on clinical periodontal outcomes or more global inflammatory biomarker responses to a variety of laser-based interventions, including photodynamic and photothermal antimicrobial therapy [6,7], but the exact relationship between PBM and extracellular matrix remodeling associated with MMPs/TIMPs has been relatively under-explored.

2. Review Methodology and Scope

This narrative review was conducted using a structured literature search of PubMed/MEDLINE, Scopus, Web of Science, the Cochrane Central Register of Controlled Trials (CENTRAL), and Google Scholar. The preparation and reporting of this review were guided by the principles of the Scale for the Assessment of Narrative Review Articles (SANRA), particularly regarding literature search transparency, appropriate referencing, critical scientific reasoning, and presentation of relevant evidence [9].

The search strategy combined controlled vocabulary, where available, and free-text terms organized into three components: (1) “periodontitis” OR “periodontal disease” OR “chronic periodontitis”; (2) “photobiomodulation” OR “low-level laser therapy” OR “low-level light therapy” OR “laser therapy”; and (3) “matrix metalloproteinase” OR “MMP” OR “TIMP” OR “tissue inhibitor of metalloproteinase”. These components were combined using the Boolean operator AND, with syntax adapted to individual databases. Supplementary searches included clinical study-related terms. Google Scholar was searched using the keywords “periodontitis”, “photobiomodulation”, “MMP”, and “TIMP”.

Eligibility criteria for the primary clinical synthesis included: (1) original human clinical studies involving patients with periodontitis; (2) PBM or PBM-compatible interventions used as adjunctive periodontal treatment or compared with another relevant intervention; (3) measurement of at least one MMP or TIMP biomarker in GCF, periodontal tissues, saliva, serum, or plasma; and (4) sufficient information to evaluate the intervention and its outcomes. Only peer-reviewed articles published in English were included. Animal and in vitro studies were excluded, whereas selected experimental findings were considered only as background information on the general biological mechanisms of PBM, including their potential relevance to MMP/TIMP regulation.

Conference abstracts, editorials, case reports, non-peer-reviewed manuscripts, and studies without relevant MMP/TIMP outcomes were excluded.

PBM was operationally defined as light-based treatment primarily intended to modulate biological responses without deliberate tissue ablation, coagulation, or antimicrobial photodynamic action. PBM-related interventions were evaluated according to their reported therapeutic purpose and irradiation characteristics, including wavelength, output power, irradiance, fluence, exposure duration, emission mode, beam geometry, and application technique, consistent with the principles outlined in the WALT recommendations and established PBM dosimetry and reporting guidelines [10,11]. Interventions were considered PBM-compatible when their reported characteristics supported a predominantly non-ablative treatment intent, even if some dosimetric information was incomplete. Higher nominal laser power alone was not considered sufficient grounds for exclusion. Studies primarily involving intrapocket laser decontamination, tissue removal, or antimicrobial photodynamic therapy were excluded from the core PBM synthesis when a distinct PBM component could not be reliably identified. Incomplete or conflicting irradiation parameters were acknowledged as limitations in PBM classification rather than interpreted as evidence of an exclusively non-thermal mechanism.

The database searches yielded 479 records: 13 from PubMed/MEDLINE, 32 from Scopus, 95 from Web of Science, 26 from CENTRAL, and 313 from Google Scholar. The final search update was performed on 8 October 2026. Reference lists of relevant original studies and reviews were also screened manually.

Duplicate records were identified using EndNote 21 reference management software, with manual cross-checking of potentially eligible publications based on titles, authors, publication years, and DOI identifiers. After duplicate removal, 116 records underwent title and abstract screening, of which 58 publications were assessed in full text. Study selection and data extraction were performed by BI and BK, with further review by MČ. Uncertain eligibility decisions were discussed among the authors.

Following the application of the eligibility criteria and detailed examination of the original publications, ten primary clinical publications were included in the narrative synthesis. One systematic review addressing broader laser-based interventions and inflammatory biomarkers was considered separately as secondary evidence and was not counted among the primary clinical studies. Two potentially relevant registered clinical trials investigating laser-associated MMP-9 or MMP-13 responses were identified in CENTRAL (CTRI/2026/02/103082 and CTRI/2026/04/108535), but were not included in the clinical evidence synthesis because no results were available and the eligibility of the MMP-13 laser protocol could not be established.

The clinical studies were critically appraised with respect to randomization, allocation procedures, blinding, sample size, follow-up, irradiation parameters, biomarker assays, and statistical limitations, including possible non-independence of observations from multiple periodontal sites within individual patients. No formal risk-of-bias scoring was undertaken. We took care to distinguish PBM from other laser-based treatments that may involve photothermal, ablative, or antimicrobial effects. We discussed conflicting findings and study-specific limitations for each clinical study included in the review, and interpreted conclusions cautiously when mechanistic or clinical findings remained uncertain.

Given the limited number of available clinical studies and substantial heterogeneity in study design, laser protocols, biomarker measurements, and follow-up duration, the evidence was considered insufficient for a systematic review with quantitative synthesis. Therefore, a narrative approach was adopted.

3. Pathogenesis of Periodontitis

A healthy periodontal biofilm is part of the physiologic oral ecosystem and is in harmony with epithelial barrier function, the biochemical and humoral composition of GCF, and local immune mechanisms. However, dental plaque accumulation alters the local microenvironment, promotes anaerobic bacteria, increases GCF flow, and drives microbial dysbiosis [1,12,13]. Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia are of particular interest in the immunopathogenesis of periodontitis. Porphyromonas gingivalis can modulate the cross-talk between Toll-like receptor and complement signaling pathways. This results in poor microbial clearance, persistent inflammation, and a dysbiotic microbial community [13,14].

Periodontitis begins as gingivitis. There are many factors that have been related to the progression to periodontitis, including smoking, diabetes mellitus, aging, and systemic inflammatory diseases. Host genetic and epigenetic characteristics, particularly those related to proinflammatory and immunoregulatory cytokines, are also important [1,12]. The periodontal ligament and gingival epithelial cells form an active immune barrier. Innate immune cells express pattern recognition receptors (PRRs) that recognize bacterial lipopolysaccharides, lipoproteins, and other pathogen-associated molecular patterns (PAMPs) and activate nuclear factor (NF)-κB and related signaling pathways. This is followed by an increased production of IL-1β, tumor necrosis factor (TNF), IL-6, chemokines, prostaglandin E2, MMPs, and other bioactive molecules. These mediators increase vascular permeability, recruit circulating leukocytes to the site of inflammation, and promote the degradation of extracellular matrix. This response initially restricts microbial growth. However, when prolonged it is a major cause of collateral tissue damage [1,2,12].

Neutrophils are the most abundant immune cells in the inflamed periodontium and continuously migrate through the junctional epithelium toward the biofilm. Their protective role is dependent on phagocytosis, degranulation, generation of reactive oxygen species (ROS), and formation of neutrophil extracellular traps. However, disease development can be driven by both impaired neutrophil function and excessive neutrophil activation. When the immune system is stimulated for a long period, the activity of released proteases, myeloperoxidase, ROS, and other mediators exceeds local antioxidant and antiprotease defenses. This induces oxidative stress, leading to destruction of epithelium and connective tissue, activation of osteoclastogenic signaling, and increased microbial proliferation [15,16].

In addition, the NLRP3 inflammasome is of great importance in periodontal inflammation, leading to caspase-1-dependent maturation of IL-1β and IL-18 [17,18] and inflammatory cell death (pyroptosis) [19]. These responses may enhance local tissue destruction and osteoclastogenic signaling. Importantly, experimental inhibition of NLRP3 was associated with decreased inflammation and alveolar bone loss. Th1- and Th17-related responses cause persistent inflammation and neutrophil recruitment, whereas regulatory T cells, IL-10, and TGF-β are involved in the control of excess inflammation and osteoclastogenesis [2,12,18].

Moreover, repeated antigen stimulation leads to a chronic phase characterized by additional involvement of T and B cells. Advanced lesions are characterized by an increased number of B cells and plasma cells. Antibodies may help control bacteria, but activated B and T cells may also be an important source of receptor activator of nuclear factor κB ligand (RANKL). RANKL binds to the RANK receptor on osteoclast precursors, inducing their differentiation and activation. Osteoprotegerin (OPG) is a soluble decoy receptor that inhibits this process. Proinflammatory cytokines, including IL-1β, TNF-α, and IL-17, and prostaglandin E2, shift the balance between RANKL and OPG toward bone resorption. Consequently, alveolar bone loss reflects increased osteoclastogenesis and impaired bone formation [2,12].

As noted, the MMP/TIMP balance plays a key role in periodontal connective tissue degradation and in regulating extracellular matrix remodeling. In this context, MMP and TIMP expression levels, as well as their ratio, may serve as important biomarkers of active periodontal disease [1,3,12].

Resolution of inflammation is an active process involving the clearance of apoptotic cells, macrophage reprogramming, and restoration of tissue homeostasis. Experimental studies with pro-resolving mediators such as resolvin E1 support a putative role in limiting periodontal inflammation and bone loss. The available evidence indicates that both persistent microbial stimulation and impaired resolution of inflammation are associated with the chronicity of periodontitis [1,2,12].

Current knowledge on periodontal immunopathogenesis has revealed a number of potential targets for host-modulating therapies, such as pro-inflammatory cytokines, oxidative stress, excessive neutrophil activation, MMPs, and the RANKL/OPG axis. In particular, modulation of the MMP/TIMP balance may contribute to limiting excessive degradation of extracellular matrix, while supporting tissue repair. The therapeutic goal is therefore to attenuate destructive inflammation without compromising protective immunity and to promote restoration of periodontal homeostasis [12].

4. Matrix Metalloproteinases and Their Tissue Inhibitors: A General Overview and Significance in Dentistry

MMPs are a family of endogenous zinc- and calcium-dependent endopeptidases that participate in the precise remodeling of the extracellular matrix (ECM). They are among the principal proteolytic systems responsible for the turnover of major ECM components, including collagens, elastin, fibronectin, proteoglycans, and gelatin [3]. Although they were initially described primarily as enzymes that degrade collagen and other structural proteins, MMPs are now known to have much broader functions. They process cytokines, chemokines, growth factors, receptors, adhesion molecules, and antimicrobial peptides, thereby regulating cell migration, inflammation, angiogenesis, wound healing, and bone remodeling [3,20,21,22,23]. By modifying these non-matrix substrates, MMPs may either activate or inactivate signaling mediators and thereby exert regulatory effects that extend well beyond ECM degradation [21]. Their activity is therefore not exclusively destructive. Physiological MMP activity, which is spatially and temporally restricted, is required for tooth development, periodontal ligament turnover, alveolar bone remodeling, and tissue repair. More broadly, tightly regulated MMP activity contributes to embryogenesis, morphogenesis, angiogenesis, tissue remodeling, and wound repair [3,20,21,22,23]. In contrast, persistent or dysregulated MMP activity contributes to the development and progression of several oral diseases, including dental caries, pulpal and periapical inflammation, periodontitis, and peri-implant diseases, as well as the degradation of the dentin–resin adhesive interface [23].

The human MMP family comprises 23 members [21]. Most are synthesized as inactive proenzymes (pro-MMPs) containing a signal peptide, a propeptide with a conserved cysteine residue, a catalytic domain containing a Zn²⁺ ion, and, in most family members, a hemopexin domain that determines substrate binding and interactions with inhibitors. The catalytic and hemopexin domains are generally connected by a flexible linker or hinge region, although some smaller MMPs lack the hemopexin domain [20,21]. In the latent enzyme, the cysteine residue of the propeptide binds to the catalytic zinc ion and prevents substrate access, a mechanism known as the “cysteine switch.” Activation occurs through proteolytic removal of the propeptide or through its oxidative modification. According to their mode of localization, MMPs may also be broadly distinguished as enzymes secreted into the extracellular environment as latent proenzymes and membrane-associated MMPs positioned at the cell surface [3,21,22]. Within the inflammatory periodontal microenvironment, pro-MMPs may be activated by other host-derived proteases, ROS, hypochlorous acid generated by the neutrophil myeloperoxidase system, and certain bacterial proteases [20,21].

On the basis of substrate preference and structural organization, human MMPs are commonly classified as collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and several additional MMPs that are considered separately [3,21]. Collagenases include MMP-1, MMP-8, and MMP-13; gelatinases comprise MMP-2 and MMP-9; stromelysins include MMP-3, MMP-10, and MMP-11; and matrilysins comprise MMP-7 and MMP-26. The membrane-type group includes MMP-14, MMP-15, MMP-16, MMP-17, MMP-24, and MMP-25. The six membrane-type MMPs can be further divided into transmembrane proteins—MT1-, MT2-, MT3-, and MT5-MMP—and glycosylphosphatidylinositol-anchored proteins—MT4- and MT6-MMP [21]. MT1-MMP may additionally support osteoclast-associated degradation and remodeling of the bone matrix, which may be relevant to alveolar bone changes in periodontitis [20,21]. Other MMPs, such as MMP-12, MMP-19, MMP-20, MMP-21, MMP-23B, MMP-27, and MMP-28 are generally considered individually [21].

According to their structure and function, collagenases MMP-1, MMP-8, and MMP-13 cleave fibrillar collagens, whereas gelatinases MMP-2 and MMP-9 subsequently degrade denatured collagen, type IV collagen of basement membranes, and numerous non-collagenous proteins, thereby sustaining the proteolytic cascade. MMP-3 (stromelysin-1) degrades proteoglycans, laminin, and fibronectin and contributes to extracellular matrix remodeling through the activation of other pro-MMPs.

MMP-7 is a small secreted enzyme with a broad substrate spectrum, whereas MMP-12 is particularly associated with macrophages. Membrane-bound MMP-14, also known as membrane type 1 MMP (MT1-MMP), mediates pericellular proteolysis, cell migration through the ECM, and activation of pro-MMP-2 [20,21]. MMP-20, or enamelysin, has a specific role in enamel development [20,21]. MMP-25 and MMP-26 are among the most recent MMPs. MMP-25 is mainly expressed by neutrophils and is involved in the turnover of ECM. MMP-26 (endometase) can degrade ECM, degrade alpha-1 antitrypsin, and activate pro-MMP-9 [24].

MMP activity is regulated at several levels, including gene transcription, secretion of latent proenzymes, extracellular activation, localization at the cell membrane or within the ECM, and inhibition by endogenous inhibitors. The proinflammatory cytokines IL-1β and TNF, bacterial products, prostaglandin E2, oxidative stress, and mechanical loading can increase MMP expression through the mitogen-activated protein kinase (MAPK), NF-κB, and activator protein 1 (AP-1) signaling pathways. In contrast, anti-inflammatory and pro-resolving signals, restoration of redox homeostasis, and increased local activity of tissue inhibitors limit proteolysis. In circulation, active MMPs may be neutralized by α2-macroglobulin, whereas their primary direct regulators in tissues are the tissue inhibitors of metalloproteinases (TIMPs) [25,26,27].

The family of TIMPs includes TIMP-1, TIMP-2, TIMP-3, and TIMP-4. They are small proteins with an N-terminal domain that penetrates into the catalytic cleft of an MMP and coordinates the catalytic zinc ion, usually forming a reversible complex with the enzyme at a 1:1 molar ratio. The C-terminal domain mediates latent gelatinase binding as well as other protein–protein interactions [20,21,22]. TIMP-1, which is widely distributed, is a potent inhibitor of most secreted MMPs, including MMP-9. However, it is less effective against certain membrane-type MMPs. TIMP-2 inhibits active MMPs, but at the right concentration, it also participates in the formation of the MMP-14-TIMP-2-pro-MMP-2 complex, thereby allowing a controlled activation of MMP-2 at the cell surface. TIMP-3 is ECM-bound and, besides MMPs, can inhibit some ADAM and ADAMTS proteases. TIMP-4 is less abundant in oral tissues, and its local role is less well characterized [21,22,23]. TIMPs are more than passive “switches” of proteolysis. They can inhibit cell proliferation, apoptosis, angiogenesis, and differentiation, independently of MMP inhibition. Thus, the biological outcome cannot be predicted by measuring the levels of a single MMP or TIMP. The local ratio of active enzyme to available inhibitor, the presence of activators and substrates, the cellular source, and the duration of the response are more important. Increased TIMPs in inflamed tissue may be a compensatory response, but may not be sufficient to neutralize a much greater increase in active MMPs. Therefore, the MMP-8/TIMP-1 or MMP-9/TIMP-1 ratios may be a better indicator of the net proteolytic potential than individual levels of these molecules [3,22,26].

MMPs are implicated in the development and degradation of mineralized and soft tissues in dentistry. MMP-20 is required for amelogenesis to enable controlled proteolysis of enamel matrix proteins. Different types of MMPs have been identified in dentin, such as MMP-2, MMP-8, MMP-9, and MMP-13, which can be entrapped in a latent form in the mineralized matrix. They are released and activated by acid-mediated demineralization occurring during caries progression or adhesive procedures, and then participate in the degradation of exposed collagen. This mechanism is relevant to the progression of dentin caries and the gradual degradation of the hybrid layer at the dentin-composite interface [22,23]. MMP-1, MMP-2, MMP-8, and MMP-9 are up-regulated in pulpitis and apical periodontitis and are involved in tissue remodeling, leukocyte migration, and damage of the periapical ECM. However, their regulated activity may also be required during healing and the formation of reparative dentin, as well as for the physiological remodeling of the periodontal ligament and alveolar bone during orthodontic tooth movement (OTM) [28]. These facts further suggest that complete, nonselective inhibition of MMPs is undesirable.

5. Matrix Metalloproteinases and Their Tissue Inhibitors in Periodontitis

As mentioned above, MMPs and TIMPs are relevant to the pathogenesis of periodontal disease. Microbial antigens and inflammatory mediators produced during periodontitis increase MMP production and activation. Chronic inflammation disturbs the balance between MMPs and TIMPs. This causes uncontrolled collagen degradation in the gingiva and periodontal ligament, and loss of connective tissue attachment, thus creating a microenvironment that perpetuates dysbiosis and inflammation. Because type I collagen is the predominant structural component of the periodontal ligament ECM, collagenases and gelatinases are particularly important in periodontal tissue destruction [3,21,25,26,27].

MMP-1 mainly degrades type I and type III collagens and is involved in physiological extracellular matrix turnover and connective tissue remodeling. It is produced mainly by fibroblasts, macrophages, keratinocytes, endothelial cells, and osteoblasts in response to inflammatory stimuli. The increased MMP-1 expression is involved in collagen degradation in periodontitis, but the role of MMP-1 in periodontal tissue destruction seems to be less evident than that of MMP-8 and MMP-13 [24,26].

MMP-8 is considered an important proteolytic enzyme in the destruction of periodontal tissue. It is stored in specific neutrophil granules as pro-MMP-8 and is rapidly released upon cell activation. MMP-8 is mainly produced by neutrophils in active periodontal lesions, but macrophages, plasma cells, fibroblasts, keratinocytes, endothelial cells, and osteoblasts may also produce it under inflammatory conditions [29]. Its release may be promoted by inflammatory mediators such as IL-1β, IL-8, TNF-α, complement components, fibrin-degradation products, and granulocyte colony-stimulating factor [21,29]. MMP-8 is the major collagenolytic enzyme measured in GCF in periodontitis [25,26,27] and efficiently degrades type I and type III collagens. In addition to fibrillar collagen, MMP-8 can process fibronectin, aggrecan, fibrinogen, serpins, bradykinin, angiotensin I, and substance P, suggesting that its activity may also modulate inflammatory and vascular signaling [21].

The active form of MMP-8 (aMMP-8) is particularly relevant to periodontal tissue destruction, as total MMP-8 also includes the inactive proenzyme. It can be activated by other MMPs, bacterial and serine proteases, and neutrophil-derived ROS [26]. Although MMP-8 may also regulate inflammatory mediators, its excessive and prolonged activity contributes to periodontal tissue damage [3,26,29,30].

Active MMP-8 can also be detected in saliva, mouth-rinse samples, and peri-implant sulcular fluid. Its levels generally increase with periodontal disease severity, correlate with probing pocket depth, clinical attachment loss, and bleeding on probing, and decrease following successful periodontal therapy. Elevated MMP-8 concentrations have also been associated with a higher plaque index and with the presence of periodontal pathogens such as Fusobacterium nucleatum, Tannerella forsythia, and Treponema denticola [21]. Because aMMP-8 reflects ongoing collagen degradation rather than only previously accumulated tissue damage, it is considered a potentially useful biomarker for early detection, assessment of disease activity, and monitoring of the therapeutic response [30,31]. Importantly, elevated aMMP-8 appears to distinguish gingivitis from periodontitis more effectively than measurements of total or latent MMP-8 and may identify individuals at increased risk of attachment loss and disease progression [21,30,31]. A recent review supports the diagnostic potential of both MMP-8 and aMMP-8, although greater methodological standardization across different oral samples is still required before their routine clinical implementation [21]. In addition to its role in periodontal destruction, controlled MMP-8 activity may participate in physiological tissue remodeling and wound healing [32].

MMP-9 participates in periodontal inflammation through the degradation and remodeling of extracellular matrix components, particularly denatured collagens and basement membrane proteins. As a major source of MMP-9, neutrophils release this enzyme during their migration into inflamed periodontal tissues [26,33]. Its activity may facilitate leukocyte movement and local matrix degradation, but it may also influence inflammatory responses and tissue remodeling. MMP-9 has also been involved in bone remodeling, although its contribution to osteoclast-mediated bone resorption remains less clearly established than that of cathepsin K [33]. Interestingly, experimental evidence also suggests a protective role for MMP-9, since its deficiency has been associated with accelerated periodontal destruction [34].

The clinical significance of MMP-9 appears to be more complex than previously assumed. Elevated salivary MMP-9 levels have been reported in patients with periodontitis, with reductions following non-surgical treatment [35]. However, a recent longitudinal study found higher MMP-9 levels in stable than in progressing periodontal sites and an increase after treatment [36]. These observations suggest that MMP-9 is involved in several stages of periodontal inflammation and healing, and that its concentration alone may not reliably reflect ongoing tissue destruction.

MMP-2 is more constitutively expressed by fibroblasts and other resident cells and is involved in basal extracellular matrix turnover. However, its activity can be increased during periodontal inflammation treatment [21,26]. MMP-13 has potent activity against fibrillar collagen and participates in the interface between connective tissue and bone remodeling. It can also activate pro-MMP-9. MMP-3 degrades non-collagenous matrix components during periodontitis and activates other pro-MMPs. MMP-7 is associated with epithelial tissues and the processing of several signaling molecules. MMP-12 is associated with activated macrophages, whereas MMP-14 is involved in pericellular invasion, cell migration, and MMP-2 activation, all functions relevant to periodontal inflammation [23,25,26,27]. Periodontal bacterial proteases may further intensify this network. Proteases produced by T. denticola can activate MMP-2, promote fibronectin fragmentation, induce apoptosis, and suppress osteoblast differentiation, whereas P. gingivalis may enhance MMP-2 activity, monocyte migration, and MMP-9 expression [21,23].

MMP-13, MMP-2, and MMP-14 also cooperate in a proteolytic cascade to amplify extracellular matrix degradation. Pericellular proteolysis is controlled by the membrane-bound MMP-14 that activates latent MMPs, notably pro-MMP-2 and MMP-13. MMP-2 then degrades gelatin, type IV collagen, basement membrane components, and collagen fragments initially generated by collagenases [3,26]. Together, these enzymes contribute to connective tissue destruction and the remodeling of alveolar bone that occurs during periodontitis.

Destruction of the periodontal tissues does not occur solely through direct cleavage of matrix components. Proteolytic processing of cytokines, chemokines, receptors, and adhesion molecules can enhance, redirect, or inhibit inflammatory signaling. MMPs liberate entrapped growth factors from the extracellular matrix, alter chemokine gradients, and affect the recruitment and survival of leukocytes. Proteolytic fragments of collagen, fibronectin, and laminin can act as matrikines, i.e., biologically active signals that further modulate inflammation and angiogenesis [20,26]. MMPs are not directly responsible for the removal of the mineral component of bone; instead, they facilitate the removal of osteoid and organic matrix, osteoclast migration, and remodeling of the bone surface. Thus, their activity is functionally associated with the RANKL/OPG axis and cytokine-mediated stimulation of osteoclastogenesis [3,20,26].

Expression and activity of TIMPs play an important role in the maintenance of periodontal tissue homeostasis and regulation of extracellular matrix degradation. The TIMP family consists of four members (TIMP-1, TIMP-2, TIMP-3 and TIMP-4) that are produced by fibroblasts, macrophages, endothelial cells and other resident or infiltrating cells. TIMPs bind to active MMPs and inhibit their proteolytic activity, thereby preventing excessive degradation of the extracellular matrix and facilitating controlled remodeling of periodontal tissues [3,25,27].

In healthy periodontium, TIMP-1 and TIMP-2 are implicated in the modulation of basal MMP activity and physiological collagen turnover. MMPs and TIMPs may be up-regulated in periodontitis, but an increase in inhibitor production does not necessarily compensate for excessive protease activity. Thus, an imbalance favoring active MMPs results in destruction of the extracellular matrix [3,25,27].

Among this family, TIMP-1 has been the most widely studied in GCF and saliva. TIMP-2 regulates pericellular proteolysis and MMP-2. Its involvement in periodontal disease is supported by increased expression of both TIMP-2 and membrane-type MMP-1 (MT1-MMP/MMP-14) in diseased gingival tissues, accompanied by an altered balance between these molecules [37]. TIMP-3 may also exert local protective effects because of its broad inhibitory activity and association with the extracellular matrix, although clinical evidence in periodontitis remains limited [3,20,27].

Elevated TIMP levels should therefore not necessarily be regarded as evidence of effective protection against tissue destruction. The balance between active MMPs and their inhibitors is more informative than their individual concentrations, although measured MMP/TIMP ratios do not directly establish net proteolytic activity. Changes in these ratios, however, may provide useful information on periodontal disease activity and treatment response [3,27].

Besides endogenous TIMPs, various synthetic, pharmacological, and naturally derived MMP inhibitors have been developed or explored as adjunctive therapies in periodontal therapy. These include hydroxamate-based inhibitors; non-hydroxamate compounds such as carboxylates, sulfonamides, and phosphates; antibody-based inhibitors; bisphosphonates; chlorhexidine; and naturally occurring polyphenols such as proanthocyanidins [21]. However, the mechanisms, selectivity, clinical efficacy, and limitations of these exogenous MMP inhibitors are beyond the scope of the present review.

6. Photobiomodulation and Its Application in Dentistry

PBM is based on the biological effects of low-intensity light, which can modify cellular and tissue responses without producing significant thermal effects, tissue ablation, or coagulation. The previously used term LLLT refers primarily to laser sources, whereas PBM is a broader term that also includes light-emitting diodes (LEDs) and other sources of non-coherent light. Red and near-infrared light, typically within the approximate range of 600–1100 nm, is most commonly used because it penetrates soft tissues relatively well and can initiate photophysical and photochemical reactions within cells [38,39,40,41]. The biological effects of PBM depend not only on wavelength but also on a combination of power, irradiance, energy density (fluence), exposure time, irradiated area, continuous or pulsed mode, the number and frequency of treatment sessions, and the optical properties of the target tissue. Consequently, the same nominal dose may not produce the same effect when device power, applicator diameter, distance from the tissue, or irradiation time differ. Importantly, nominal output power alone does not establish whether an intervention produces predominantly PBM or photothermal effects. The actual tissue exposure also depends on beam geometry, contact or non-contact application, and irradiation technique [40,41].

Red light primarily affects more superficial structures, whereas near-infrared light penetrates more deeply. However, the actual amount of energy reaching the target cells depends on absorption and scattering within the epithelium, connective tissue, blood, and mineralized structures [40,42,43]. Precise reporting of all dosimetric parameters is therefore essential for study reproducibility and for the safe translation of experimental findings into clinical practice.

Cytochrome c oxidase, complex IV of the respiratory chain located in the inner mitochondrial membrane, is widely considered the primary photoreceptor for red and near-infrared light. Photon absorption may facilitate the dissociation of inhibitory nitric oxide from the enzyme, improve electron transport, and transiently increase mitochondrial membrane potential, ATP synthesis, and the production of low signaling levels of ROS. Besides mitochondria, early cellular responses that promote Ca²⁺ influx may involve photosensitive and thermosensitive ion channels, especially members of the transient receptor potential (TRP) family [38,40,41]. ATP, ROS, nitric oxide, and Ca²⁺ then act as second messengers, linking the energy of the absorbed light to changes in metabolism, gene expression, and downstream physiological processes within the cell.

Early redox and calcium signaling induce a plethora of interconnected pathways like MAPK/extracellular signal-regulated kinase (ERK), phosphoinositide 3-kinase/protein kinase B/mechanistic target of rapamycin (PI3K/Akt/mTOR), NF-κB, AP-1, cAMP response element-binding protein (CREB), hypoxia-inducible factor 1 alpha (HIF-1α), nuclear factor erythroid 2-related factor 2 (Nrf2), transforming growth factor beta/Smad signaling pathway (TGF-β/Smad), and wingless-related integration site/beta-catenin (Wnt/β-catenin) signaling pathway [8,38,39]. The relative importance of these pathways depends on cell type, metabolic state, presence of inflammation, and dose applied. Effects include increased ATP synthesis, activation of antioxidant enzymes, altered expression of cytokines and growth factors, stimulation of cell proliferation and migration, and modulation of stem and progenitor cell differentiation [8,38,41]. PBM has a biphasic (hormetic) dose–response curve. Low and optimal doses can stimulate cellular functions, whereas very high doses may be ineffective or even inhibitory to the desired response. This principle explains why increasing the power or total energy delivered does not necessarily lead to better clinical outcomes. The therapeutic window may be narrow and variable between healthy and inflamed, hypoxic, or metabolically compromised tissues, and between superficial and deeper target structures [39,42,43,44]. Results from one protocol cannot be blindly transferred to another device, anatomic region, or disease.

PBM exerts significant immunomodulatory and anti-inflammatory activities. This therapeutic modality is not a diffuse, universal inhibitor of inflammation but rather a modulator of its intensity and duration. Experimental models and clinical studies showed decreased excessive activation of NF-kB, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2, with reduced production of TNF-α, IL-1β, IL-6, prostaglandin E2, and reactive nitrogen and oxygen species. At the same time, PBM may also increase Nrf2-mediated antioxidant responses, IL-10 production, and mechanisms relevant to the resolution of inflammation [39,41]. However, these effects are time- and dose-dependent. Mild stimulation of inflammatory and phagocytic functions during the early phase of tissue repair may be beneficial, whereas PBM may facilitate the transition toward an anti-inflammatory and reparative phenotype at later stages. Of particular interest are macrophage modulation and functional plasticity. Under appropriate conditions, PBM may inhibit prolonged M1 polarization and promote M2-directed reparative programs, thereby contributing to the clearance of cellular debris, angiogenesis, the MMP/TIMP axis, extracellular matrix remodeling, and tissue restoration. In periodontal and bone models, these processes are closely associated with signaling interactions among immune cells, fibroblasts, endothelial cells, osteoblasts, osteoclasts, and mesenchymal stromal cells [8,45].

In tissue repair, PBM can improve fibroblast survival, proliferation, and migration, increase synthesis of collagen and other extracellular matrix components, and stimulate VEGF expression and neovascularization. Changes in the expression of RUNX2, BMP-2, alkaline phosphatase, osteopontin, and osteocalcin, along with possible increases in matrix maturation and mineralization, have been reported in osteogenic cells and mesenchymal stromal cells. The systematic analysis of studies involving periodontal ligament stem cells (PDLSCs) shows, in most cases, positive effects on proliferation and osteogenic differentiation, but also confirms significant heterogeneity among studies and the lack of a single optimal treatment protocol [41,45]. The analgesic effects of PBM likely result from reduced local inflammation and edema, modulation of peripheral nerve fiber excitability, alterations in axonal transport, and transient effects on mitochondrial activity in nociceptors. The clinical effect seems to be most prominent in acute or subacute pain and depends on direct light delivery to the target tissue at an appropriate dose. PBM is generally well tolerated, and serious adverse effects are rarely reported. Eye protection, the choice of an appropriate applicator, and strict adherence to standardized safety procedures are mandatory [41,42,46,47].

In dentistry, LLLT/PBM is used as an adjunctive modality in periodontology, oral and maxillofacial surgery, implantology, and the management of oral mucositis, temporomandibular disorders, and dentin hypersensitivity, as well as to reduce postoperative pain and promote wound healing [46,47,48,49,50,51]. In orthodontics, it has been investigated for reducing early treatment-related pain, potentially accelerating tooth movement, and supporting periodontal and bone remodeling. However, its effects on the rate of tooth movement are generally moderate and highly dependent on the protocol used [8].

7. Clinical Evidence on the Effects of Photobiomodulation on Matrix Metalloproteinases and Their Tissue Inhibitors in Periodontitis

Ten clinical publications and one review were identified as relevant to the effects of PBM or PBM-related irradiation on MMP/TIMP biomarkers in periodontitis. Based on the characteristics of the interventions, they can be divided into two groups: PBM-compatible studies and mixed laser studies containing a distinct or potentially PBM treatment arm. The main methodological characteristics, patient populations, irradiation parameters, treatment schedules, and analytical methods are presented in Table 1, whereas the narrative part focuses on the relationships between MMP/TIMP-related findings, other GCF biomarkers, and clinical periodontal outcomes.

Table 1. Clinical publications evaluating PBM or PBM-related irradiation effects on MMP/TIMP biomarkers in periodontitis.

Study	Population/Design	PBM-Related Protocol	Biomarker(s)	MMP/TIMP Findings	Clinical/Other Findings/Limit.
Qadri et al., 2005 [52]	Moderate CP; n = 17; split-mouth, double-blind RCT; short FU	Bilateral SRP; PBM 635 nm/10 mW/90 s + 830 nm/70 mW/25 s, weekly ×6; slight contact contralateral placebo	GCF MMP-8 (immunoassay, total amount, pg), IL-1β; elastase, microbial assessment	MMP-8 ↓ PBM, ↑ placebo; between-side p = 0.052 (NS); active MMP-8 not specifically quantified	PBM: greater ↓ PD/GI/PI/GCF volume; IL-1β, elastase and microbiology; ↔; n = 17, short FU
Qadri et al., 2007 [53]	Moderate CP; n = 20; randomized split-mouth pilot study; two active PBM protocols;	HeNe 632.8 nm vs. InGaAlP diode 650 nm; 3 mW each; 0.54 J/point; 180 s/point; slight contact; weekly ×6	GCF MMP-8 (ELISA, ng/site), IL-8; subgingival microbiology	Greater numerical MMP-8 ↓ with HeNe (−44.9%) than diode (−8.6%); between-treatment p = 0.066 (NS)	Greater ↓ PD, PI, GI and GCF volume with HeNe; no placebo/SRP-only arm; n = 20, short FU; MMP-8 activity NR;
Aykol et al., 2011 [54]	Moderate–advanced CP; n = 36 (18/group); randomized parallel-group trial; smokers/non-smokers	SRP ± 808 nm GaAlAs PBM (0.25 W; 4 J/cm2; non-contact), 0.5–1 cm; d1, d2, d7; FU 1, 3, 6 mo	GCF MMP-1, TIMP-1, MMP-1/TIMP-1 ratio, TGF-β1, bFGF; ELISA; total amounts	Both: ↓MMP-1 and ↓MMP-1/TIMP-1; TIMP-1 ↔; between-group ↔ enzyme activity not measured	PBM: greater ↓ SBI/PD and ↑ CAL, strongest in smokers; TGF-β1 ↓; bFGF early ↓ then ↑; between-group ↔
Ismaili & Bokonjić, 2014 [55]	RCT CP; n = 36 (18/group); randomized parallel-group study; 10-day FU	Scaling ± 635 nm LLLT; 25 mW; reported ~100 mW/cm2; 4 min/site; daily ×9; incomplete dosimetry	GCF MMP-9; IL-1α; IL-1β; ELISA; concentrations (pg/µL); baseline/d10	PBM: ↑ MMP-9 (within-group p < 0.01); +corr with IL-1α; −corr with PI/PBI; MMP-9 activity not measured	PBM: ↓ PI/PBI/PPD and ↓ IL-1α/IL-1β; short follow-up; between-group effect estimates insufficiently characterized
Chen et al., 2020 [56]	Severe CP; n = 19; randomized split-mouth study with sequential LED phases; 2 dropouts	NSPT + 660 nm LED (10 J/cm2; 3 min/d); LED01 during SRP, LED02 after SRP; home-use appliance	GCF MMP-8 and IL-1β; ELISA; GCF concentrations; T0, T1, T2	All groups: ↓MMP-8 and ↓ IL-1β; between-group ↔; greatest numerical ↓MMP-8 with post-SRP LED	Greater ↓PD/CAL measurements at sites with greatest initial disease severity; overall clinical differences ↔; short follow-up
Misra et al., 2023 [57]	Stage II, grade B periodontitis; n = 40; randomized split-mouth; 120 sites/arm; FU 6 mo	OFD ± 890 nm diode laser; 1.5 W; non-contact, 30 s × 2/session; days 0, 3, 7; fluence not reported	GCF MMP-8, TNF-α, IL-6, OPG; ELISA; baseline, 3/6 mo	MMP-8 ↓ at 6 mo (p = 0.005 between arms); TNF-α ↓, OPG ↑; IL-6 NS; MMP-8 activity NR	Early wound healing improved (p < 0.001); PD/CAL NS between arms; uncertain PBM dosimetry and site-level analysis
Sopi et al., 2020 [58]	CP; n = 80; three-arm comparative clinical study; FU 3/6 mo	Basic therapy + 980 nm diode laser, 10 mW, 60 s/tooth, intrapocket; vs. SRP alone or SRP + MWF; incomplete dosimetry	GCF MMP-8; qualitative dipstick immunoassay (+/−); baseline/6 mo	MMP-8-negative at 6 mo: laser 96.3%; MWF 86.3%; assay threshold/form not reported	Several favorable clinical outcomes vs. SRP; laser vs. surgery: CAL difference at 6 mo, but PD/GI ↔; no isolated PBM effect
Sopi et al., 2023 [59]	Generalized Stage III periodontitis; n = 100 (50/group); randomized single-blind study; FU 3/6 mo	Basic therapy + 980 nm intrapocket diode laser, 10 mW, 60 s; vs. basic therapy + MWF; incomplete dosimetry	GCF MMP-8; qualitative dipstick immunoassay (+/−); baseline/6 mo	MMP-8-positive samples: laser 80%→4%; MWF 82%→20%; between-group p = 0.0138 at 6 mo	Both groups improved; laser: lower PPD (p < 0.0001), GI (p = 0.004), and CAL (p = 0.036) at 6 mo; different treatment strategies, not isolated PBM efficacy.
Yang et al., 2022 [60]	Severe periodontitis; n = 50; randomized split-mouth, 4 arms	SRP alone, +Er:YAG debridement, +Nd:YAG PBM, or combined; FU 1 and 3 mo	GCF MMP-8; melatonin	1 mo: combined ↔, other arms ↓; 3 mo: ↓ in all arms; between-group ↔	Laser arms improved; combined: greatest ↓ PD/PLI/BI and ↑ CAL; melatonin ↑ in all laser arms (max combined); pain ↓ at d7
Ezber et al., 2022 [61]	Stage III, grade C periodontitis; 80 smokers (20/group); randomized four-arm trial; FU 1/3 mo	SRP + Nd:YAG LLLT (1064 nm, 0.5 W, 10 Hz, long-pulse, non-contact, 1 cm, 120 s); separate debridement/combined arms	GCF MMP-8; ELISA; total amount (ng/30 s); baseline, 1/3 mo	MMP-8 ↓ in all groups (p < 0.001 within-group); no between-group difference (p = 0.149 at 1 mo; p = 0.390 at 3 mo)	Greater PD/CAL reductions in moderate/deep pocket subgroups; full-mouth intergroup differences NS;
Akram et al., 2016 [62]	Systematic review; 8 aPDT + 10 LT studies; search through Jul 2016	LT = laser without photosensitizer + SRP; heterogeneous protocols; LT ≠ PBM	GCF inflammatory proteins incl. MMP-8 and TIMP-1	LT: significant ↓MMP-8 in 3 studies and ↓ TIMP-1 in 1; overall evidence inconclusive; findings not PBM-specific	Clear PBM among LT MMP/TIMP studies: [52,54]; other LT protocols not unequivocal PBM; mixed modalities and heterogeneous parameters

Symbols: ↓, decrease/reduction; ↑, increase/improvement; ↔, no significant change/difference; +/−, positive/negative; NS, not statistically significant; +corr/−corr, positive/negative correlation. Abbreviations: aPDT, antimicrobial photodynamic therapy; bFGF, basic fibroblast growth factor; BI, bleeding index; CAL, clinical attachment level; CP, chronic periodontitis; d, day; ELISA, enzyme-linked immunosorbent assay; Er:YAG, erbium-doped yttrium aluminum garnet laser; FU, follow-up; GaAlAs, gallium aluminum arsenide; GCF, gingival crevicular fluid; GI, gingival index; HeNe, helium–neon laser; IL, interleukin; InGaAlP, indium gallium aluminum phosphide; LED, light-emitting diode; LLLT, low-level laser therapy; LT, laser therapy without a photosensitizer; MMP, matrix metalloproteinase; mo, month; MWF, modified Widman flap; Nd:YAG, neodymium-doped yttrium aluminum garnet laser; NR, not reported; NSPT, nonsurgical periodontal therapy; OFD, open flap debridement; OPG, osteoprotegerin; PBI, papillary bleeding index; PBM, photobiomodulation; PD/PPD, probing depth/probing pocket depth; PI/PLI, plaque index; RCT, randomized controlled trial; SBI, sulcus bleeding index; SRP, scaling and root planing; T0/T1/T2, successive study assessment time points; TGF-β1, transforming growth factor-β1; TIMP, tissue inhibitor of metalloproteinases; TNF-α, tumor necrosis factor-α.

Eight publications evaluated PBM-compatible protocols. Qadri et al. [52] provided the first clinical evidence that adjunctive LLLT could modulate MMP-8-associated responses in non-surgical periodontal therapy. In a randomized, double-blind, placebo-controlled split-mouth study involving 17 patients, low-power lasers (635 and 830 nm; 10 and 70 mW) were applied weekly for six weeks. PBM was associated with greater reductions in probing depth, plaque index, gingival index, and GCF volume than the placebo-treated side. MMP-8 levels increased in the placebo-treated arm but decreased slightly after PBM treatment. However, the difference between groups was not statistically significant (p = 0.052). No significant differences between the two sides were observed in elastase activity, IL-1β levels, or microbiological findings. Therefore, the clinical response and reduced GCF flow were not accompanied by widespread suppression of inflammatory or collagenolytic mediators. The small sample size, short follow-up, incompletely reported allocation concealment, and measurement of MMP-8 protein amounts rather than enzymatic activity limit the biochemical conclusions.

In a subsequent randomized split-mouth pilot study, Qadri et al. [53] compared two low-power PBM protocols using HeNe (632.8 nm) and diode (650 nm) lasers, both operating at 3 mW, in 20 patients with periodontitis. After six weekly treatments, HeNe irradiation produced significantly greater improvements in probing depth, gingival and plaque indices, and GCF volume. Although GCF MMP-8 decreased more markedly with HeNe (−44.9%) than with diode irradiation (−8.6%), the between-treatment difference was not statistically significant (p = 0.066). The authors did not observe significant differences in IL-8 or microbiological outcomes. The small sample size, short follow-up, absence of a scaling and root planing (SRP)-only or placebo control, and differences in wavelength and optical characteristics limit interpretation. Moreover, MMP-8 protein measurements did not establish changes in enzymatic activity.

Aykol et al. [54] assessed the effect of PBM (808 nm, 250 mW; reported fluence 4 J/cm²; three sessions) as an adjunct to nonsurgical periodontal therapy in smokers and nonsmokers. They showed that PBM was associated with greater improvements in selected clinical parameters, including probing depth, clinical attachment level, and sulcus bleeding index, than conventional treatment alone. Clinical benefits were particularly apparent in smokers, although these subgroup observations should be regarded as exploratory. Despite these clinical differences, MMP-1, TIMP-1, and the MMP-1/TIMP-1 ratio did not differ significantly between groups. In both groups, MMP-1 and the MMP-1/TIMP-1 ratio decreased during follow-up. These changes were mainly attributable to inflammation resolution after mechanical biofilm removal. TGF-β1 also decreased in both groups, whereas basic fibroblast growth factor (bFGF) initially declined and subsequently increased during the later follow-up period. This temporal pattern may reflect an early reduction in the inflammatory response, followed by increased reparative activity. However, because none of the GCF biomarker changes differed significantly between the groups, the enhanced clinical response to PBM could not be directly attributed to modulation of MMP-1, TIMP-1, TGF-β1, or bFGF. A small number of participants in subgroups, site-level clinical analysis without clearly accounting for multiple periodontal sites per patient, inconsistencies in reported irradiation dosimetry, and measurement of MMP/TIMP protein amounts rather than enzymatic activity further limit interpretation.

Ismaili and Bokonjić [55] reported a distinctly different biochemical response following short-term LLLT (635 nm, 25 mW; nine daily sessions; n = 36). The treatment was associated with significant decreases in GCF concentrations of IL-1α and IL-1β and improvements in clinical indices of periodontal inflammation. Conversely, MMP-9 increased (within-group p < 0.01) after PBM. Following treatment, IL-1α correlated positively with MMP-9, whereas MMP-9 correlated negatively with the plaque index and papillary bleeding index. The negative association between MMP-9 and clinical inflammation suggests that its short-term increase may not reflect ongoing periodontal destruction. Instead, increased MMP-9 could hypothetically reflect processes associated with leukocyte migration, basement membrane remodeling, angiogenesis, or other processes involved in early tissue repair. Nevertheless, these mechanisms were not directly investigated, and the absence of measurements distinguishing latent from active MMP-9, incomplete dosimetric reporting, limited statistical characterization of between-group effects, and the short follow-up period prevent a definitive interpretation of whether this increase in MMP-9 levels represented reparative remodeling or sustained proteolytic activity.

Chen et al. [56] assessed LED-delivered PBM (660 nm, 10 J/cm², 3 min daily) applied during either the active phase of SRP or the subsequent healing phase in a randomized split-mouth study involving 19 patients. All treatment protocols significantly improved probing depth, clinical attachment level, gingival bleeding, plaque score, and treatment-associated discomfort. At sites with the greatest initial probing depth and attachment loss, both LED protocols provided greater probing-depth reduction and attachment gain than conventional treatment alone, suggesting that PBM may be particularly beneficial in initially severe periodontal defects. IL-1β and MMP-8 decreased after treatment in all groups, without significant intergroup differences for either biomarker. The protocol applied after completion of mechanical treatment resulted in a numerically greater reduction in MMP-8, although the difference was not statistically significant. Therefore, the clinical benefit observed at the deepest sites was not consistently accompanied by an additional reduction in IL-1β or MMP-8. These findings suggest that PBM timing may influence clinical healing, but they do not establish a corresponding timing-dependent effect on the measured GCF biomarkers. The small sample size, missing biomarker data from the control site, sequential treatment periods, and incompletely reported optical dosimetry limit interpretation. Changes in MMP-8 concentration do not establish altered enzymatic activity. At sites with the greatest initial probing depth and attachment loss, both LED protocols provided greater probing-depth reduction and attachment gain than conventional treatment alone (p < 0.05). The authors also reported modest additional improvements in PD (approximately 0.17–0.24 mm) and CAL (0.21–0.25 mm). However, these site-specific findings should be interpreted cautiously as exploratory, particularly given the small sample size and the lack of significant overall between-group differences.

The most complete combined clinical and biochemical assessment among the included studies, described as PBM by the authors, was that of Misra et al. [57]. The authors used an 890 nm diode laser at 1.5 W following open flap debridement (OFD), but incomplete irradiance and fluence reporting prevented reliable confirmation of a non-thermal PBM protocol. After open flap debridement, both PBM-treated and control sites showed significant improvements in plaque index, gingival index, probing depth, and clinical attachment level, with no significant intergroup differences in the conventional periodontal parameters at follow-up. In contrast, early wound healing assessed using the Landry index was significantly better at PBM-treated sites during the first and second postoperative weeks. The biochemical findings also indicated differences in selected GCF biomarkers following adjunctive laser treatment. MMP-8 and TNF-α decreased in both groups but were significantly lower at PBM-treated sites after six months, whereas OPG increased in both groups and reached significantly higher levels in the PBM group. IL-6 also declined, but neither its intragroup nor intergroup changes were statistically significant. The concomitant reduction in MMP-8 and TNF-α, together with increased OPG, is consistent with possible modulation of inflammatory responses. However, increased OPG levels alone do not establish a change in the RANKL/OPG ratio or demonstrate reduced osteoclast activity, particularly because RANKL was not measured. In addition, the study does not establish reduced MMP-8 enzymatic activity or osteoclastogenesis. These biochemical changes, accompanied by improved early wound healing, were not reflected in additional long-term gains in probing depth or clinical attachment level. Interpretation is further limited by the relatively high laser power, incomplete dosimetry, and analyses that did not clearly account for correlated periodontal sites within patients.

The two studies by Sopi et al. [58,59] used very low-power intrapocket diode-laser irradiation (980 nm, 10 mW, 60 s) potentially compatible with PBM, although they incompletely reported essential dosimetric parameters. Rather than comparing the laser with an identical nonirradiated protocol, they assessed its clinical effectiveness against SRP or modified Widman flap surgery. The possibility of participant overlap between the two publications could not be excluded, as the available reports did not establish whether the study cohorts were entirely independent.

Although this design does not isolate a PBM-specific effect, it provides clinically relevant comparative evidence on outcomes across different periodontal treatment strategies. Consequently, these publications were considered separately from direct comparisons of adjunctive PBM with otherwise identical periodontal treatment.

The earlier study [58] compared three treatment strategies: SRP alone, SRP followed by intrapocket low-power diode-laser irradiation (980 nm, 10 mW), and SRP followed by modified Widman flap surgery. All three approaches improved periodontal status, but the laser group showed greater improvements in several clinical parameters and radiographic bone outcomes compared with SRP alone. Compared with flap surgery, CAL measurements were significantly lower in the laser group at six months, whereas probing depth and gingival index did not differ significantly.

MMP-8 was assessed qualitatively using a dipstick immunoassay. After six months, 96.3% of samples in the laser group were MMP-8-negative, compared with 86.3% in the surgical group and 75.0% in the SRP group. The clinical, radiographic, and biomarker findings are consistent with a favorable treatment response, although no other GCF mediators or direct correlations between MMP-8 positivity and clinical outcomes were reported. The qualitative assay, incomplete laser dosimetry, and comparison of different treatment strategies limit PBM-specific conclusions.

The subsequent study [59] reported significantly lower probing depth (p < 0.0001), CAL measurements (p = 0.036), and gingival index (p = 0.004) in the low-power laser group compared with the flap-surgery group at six months. MMP-8-positive GCF samples decreased from 80% to 4% in the laser group and from 82% to 20% in the surgical group over six months (between-group p = 0.0138 at six months). Such results indicate favorable outcomes for the laser-based treatment strategy, but do not establish an independent PBM-specific effect or demonstrate equivalence to surgery. However, the qualitative assay does not provide information on MMP-8 concentration or molecular activity. A negative dipstick result indicates a value below the assay’s positivity threshold, rather than complete absence of MMP-8 or a quantifiable reduction in its concentration. Incomplete irradiation dosimetry and insufficient detail on randomization and blinding also limit the conclusions.

Two publications involved mixed laser protocols containing a PBM-related treatment arm. Yang et al. [60] compared SRP alone with SRP combined with Er laser debridement, Nd irradiation described as PBM, or both modalities. The Nd protocol (1064 nm, 50 mJ, 10 Hz, 30 s) was incompletely characterized, with a discrepancy between the calculated average power of 0.5 W and the additionally reported 1.5 W. Since Er irradiation was used for calculus and granulation tissue removal, only the SRP plus Nd irradiation arm can be considered PBM-related without an additional debridement modality. All laser treatments improved clinical parameters, with the greatest probing-depth reduction and attachment gain observed in the combined-treatment group. Melatonin levels increased in all laser-treated groups, whereas MMP-8 showed a different response. At one month, MMP-8 decreased in the Er:YAG- and PBM-only groups but remained unchanged in the combined group, resulting in significantly higher levels than in the other laser-treated groups (p = 0.0012). By three months, MMP-8 had decreased in all groups, without significant between-group differences. Thus, the superior clinical outcomes of combined treatment were not accompanied by greater MMP-8 suppression, while the individual contribution of PBM could not be determined. Incomplete irradiation dosimetry, the short follow-up, and statistical analyses that did not clearly account for the paired four-quadrant design further warrant caution when interpreting PBM-specific effects.

Ezber et al. [61] investigated different adjunctive Nd laser applications in 80 smokers with stage III, grade C periodontitis. The study compared four treatment approaches: SRP alone, LLLT, laser debridement, and combined therapy. Including an LLLT group (1064 nm, 0.5 W, non-contact mode) allowed evaluation of the additional effects of PBM relative to conventional SRP. Although MMP-8 levels decreased significantly across all treatment groups, no significant differences were observed between groups at either one month (p = 0.149) or three months (p = 0.390). Although the LLLT group showed greater probing-depth reduction and attachment gain at moderately deep and deep periodontal sites, full-mouth clinical parameters did not differ significantly between groups. The incomplete reporting of irradiance and fluence, short follow-up, and site-level subgroup analyses limit interpretation. These findings suggest that adjunctive LLLT may provide certain site-specific clinical benefits, although it did not demonstrate additional reductions in MMP-8 levels.

In addition to the ten primary clinical studies, the systematic review by Akram et al. [62] is considered separately as secondary evidence. This review included 18 clinical studies, of which 8 evaluated antimicrobial photodynamic therapy (aPDT), and 10 analyzed laser therapy (LT) without photosensitizers. The study analyzed inflammatory biomarkers in GCF, including MMP-8 and TIMP-1. Importantly, LT encompassed different laser modalities and was not synonymous with PBM. Among the LT studies addressing MMP/TIMP-related outcomes, only two, Qadri et al. [52] and Aykol et al. [54], used low-power laser protocols applicable to PBM, and we already included them in our analysis. Other studies included laser procedures with possible thermal, antimicrobial, or debridement effects that we could not unequivocally classify as PBM. The authors highlighted that differences in irradiation parameters, inconsistent biomarker findings, and short follow-up periods made it difficult to draw firm conclusions. In contrast, our review focuses specifically on PBM-associated MMP/TIMP responses, their relationship with extracellular matrix remodeling, biomarker measurement characteristics, and corresponding clinical periodontal outcomes.

Other clinical studies have examined MMP/TIMP-related responses following intrapocket laser irradiation, either primarily aimed at periodontal decontamination or involving potential photothermal and tissue-ablative effects [63,64,65]. Although some irradiation characteristics overlap with those used in PBM, these protocols involved relatively high power, high local energy densities, or treatment mechanisms that did not permit reliable attribution of the observed biochemical responses to PBM. Therefore, these studies were excluded from the primary PBM synthesis, despite reporting potentially relevant changes in MMP/TIMP biomarkers.

A later systematic review by Pawelczyk-Madalińska et al. [66] looked at high-intensity diode laser-assisted periodontal debridement and specifically excluded PBM protocols. This review related to MMP/TIMP findings, but focused more on the clinical, microbiological, and immunological effects of laser-assisted debridement than on PBM-specific effects on extracellular matrix remodeling. Other systematic reviews and meta-analyses, e.g., Ren et al. [6], Dalvi et al. [7], da Silva et al. [46], Corbella et al. [67], mainly evaluated the clinical efficacy of adjunctive PBM or laser therapy in the treatment of periodontitis without specifically synthesizing MMP/TIMP-related outcomes.

8. Limitations of the Review

This narrative review is limited by the small number of eligible studies and the substantial heterogeneity in PBM protocols, comparator treatments, follow-up periods, and biomarker assessment methods. In addition, several studies used PBM-compatible or mixed laser protocols rather than unequivocally defined PBM, thereby limiting direct comparisons and the attribution of observed effects specifically to PBM. These methodological differences precluded a meaningful quantitative synthesis and formal meta-analysis; therefore, the available evidence was better suited to a structured narrative evaluation.

Differences in GCF sampling and biomarker assessment add another methodological limitation. Changes in GCF volume following periodontal treatment may affect measured biomarker concentrations and total amounts, which are not directly interchangeable. Moreover, immunoassays measuring MMP protein levels do not necessarily distinguish active from latent enzyme forms. Therefore, changes in MMP concentrations or amounts should not be interpreted as direct evidence of altered enzymatic activity. In this context, MMP/TIMP ratios should be interpreted with caution, as this parameter, derived from measured protein concentrations, does not necessarily represent net proteolytic activity without information on enzyme activation and inhibition.

Additional limitations were related to the analysis of only peer-reviewed publications in English, as well as potential selection and publication bias. The original studies also had methodological limitations, such as small sample sizes, poor reporting of randomization and blinding, and potential errors in statistical analyses of split-mouth or site-level data. Reporting of between-group effect estimates and confidence intervals limited assessment of statistical precision. The possibility of overlapping patient cohorts in some studies could not be excluded. Although individual studies were critically appraised, no formal risk-of-bias assessment was undertaken, which further limits the certainty of the overall conclusions.

9. Conclusions

Current clinical evidence suggests that PBM may modulate MMP-related responses during periodontal healing, but the available comparative studies do not consistently demonstrate additional biomarker effect beyond that achieved with conventional periodontal treatment. MMP-8 appears to be the most frequently investigated and treatment-responsive marker, although its reduction is not specific to PBM and depends on treatment context, sampling time, molecular form, and analytical method. Evidence for MMP-1, MMP-9, and TIMP-1 remains limited and heterogeneous.

Clinical improvements were frequently observed without consistent additional PBM-associated changes in MMP or TIMP levels, whereas certain biochemical effects occurred without superior long-term clinical outcomes. These findings indicate that MMP/TIMP responses represent only one component of the complex periodontal healing process and should be interpreted together with inflammatory cytokines, regulators of bone remodeling, wound-healing parameters, and conventional clinical indices. Importantly, the current lack of consistent evidence for an additional PBM effect should not be interpreted as evidence that such an effect does not exist. Future randomized trials should use clearly defined non-thermal PBM parameters, identical background periodontal treatment in test and control groups, quantitative assessment of active MMPs and their corresponding TIMPs, and standardized long-term clinical and biochemical follow-up.