Introduction

Periodontitis is a chronic disease that leads to tissue destruction¹. Periodontal treatment involves a first stage that halts progression by reducing pathogenic microorganisms and eliminating the inflammatory process¹. Conventional and resective therapies can slow disease progression but have not been shown to eliminate microorganisms located in soft tissues or hard-to-reach areas such as Furcation Involvements (FI)^2-4.

Guided tissue regeneration (GTR) has been proposed as an effective method for treating anatomical defects resulting from periodontitis, including Grade II FI⁵.

Nowadays, there is a consensus that Guided Tissue Regeneration (GTR) procedures in mandibular Grade II FI lead to significant gains in attachment levels, both horizontally and vertically^6,7. Although the combination of xenografts with collagen membranes has demonstrated positive clinical outcomes in furcation involvement, the concept of periodontal regeneration is intricate and demands complex coordination of cellular activities. Consequently, there are notable variations in its clinical predictability⁸.

Despite the potential clinical and biological benefits of regenerative therapies in the treatment of FI and intraosseous defects, combined modalities of treatment with GTR are being investigated for better and more accurate results. One of them is the combination of GTR with a low-level laser⁸.

It has been suggested that low-level laser can increase the amount of adenosine triphosphate (ATP) and simplify angiogenesis and collagen synthesis, as well as alter the behavior of cellular activity⁹. Laser biostimulation has also been reported to induce metabolic changes, resulting in faster cell division, increased proliferation, fibroblast migration and matrix production. It may also be effective in the repair and regeneration of bone metabolism^10-12.

Low-level laser is used in periodontics for bone surgery, intraosseous defects, gingivectomies, flaps, and scaling and root planing (SRP), but virtually no studies have been found on the clinical or biochemical effect of low-level laser on GTR-treated FI¹.

On the other hand, recent evidence-based scientific information identified potential applications of infrared laser tools for the treatment of periodontitis¹³.

Lasers have been shown to promote periodontal wound healing and regeneration. This is generally achieved by thorough debridement and decontamination of diseased tissues and by modulating or activating cellular metabolism in surrounding tissues¹⁴. During the last decade, photodynamic therapy (PDT) has also been used to reduce or eliminate periodontopathogenic bacteria as an adjunct to mechanical debridement in patients with periodontitis¹⁴.

PDT principles involve the use of a non-toxic light-sensitive dye called a photosensitizer (PS) combined with harmless (low-energy) visible light of an appropriate wavelength to match the absorption spectrum of the PS¹⁵. This procedure stimulates the dye to form singlet oxygen-free radicals that act as toxic agents to the bacteria/cell¹⁶. An increasing number of studies are examining the clinical efficacy of PDT when used as an adjunct to conventional surgical and non-surgical treatments for patients with periodontitis¹⁶. The objective of this review is to assess the scientific quality of evidence regarding laser treatment as an adjunct to mechanical instrumentation in Grade II furcation involvements, aiming to assist clinicians in decision-making.

Materials and Methods

In the preparation of this literature review, the databases PORTAL TIMBO FOCO, PUBMED, BVS, SciELO, and GOOGLE SCHOLAR were consulted. The following MeSH descriptors were employed in English: Photochemotherapy, Photodynamic Therapy, Furcation involvement, Periodontitis, Periodontal treatment, along with their corresponding Spanish terms for the search. Boolean operators were not utilized; instead, the search was conducted for each of the mentioned MeSH descriptors. The search was restricted to the past 15 years, with the exception of certain articles used for background information. A total of 105 articles addressing the topic were selected, and the search was supplemented by reviewing the bibliographies referenced in those articles. (Figure 1)

Laser Foundations in the Treatment of Grade II Furcations: Photobiomodulation

There is a consensus that, in mandibular Grade II FI, as well as in certain intraosseous defects, GTR procedures have resulted in significant clinical attachment gains, both horizontally and vertically⁶.

There are some limitations to clinical, histological, and radiographic evaluation after GTR treatment⁶. The response of periodontal tissues to this intervention is crucial and can be assessed through biochemical measurements, such as levels and composition of gingival crevicular fluid¹. Particularly in lower molars, the access to the furcation is often smaller than the diameter of the standard Gracey curette¹⁷.

To achieve periodontal regeneration, attachment to the cementum is necessary, requiring the prevention of epithelial cell migration, which is typically accomplished through the use of collagen membranes¹⁸.

Most studies involving GTR have indicated that the depth and width of the intraosseous components of the defect influence the extent of clinical and bone attachment increase¹⁹. Specifically, when GTR is applied to defects with 3, 2, and 1 intraosseous walls, it results in 95%, 82%, and 39% bone fill, respectively²⁰.

While some similar studies have demonstrated that the deeper the defect, the greater the attachment increase and bone repair¹⁹, others have shown that the wider the defect, the lower the clinical improvement^20,21.

This substantially lower increase in one-wall defects may be explained by the reduced number of progenitor cells available for repopulation in the wound area or the difficulty in placing membranes in the correct position, maintaining the required space between the membrane and the remnant bone¹⁹.

In the treatment of FI, the GTR predictability also improves if the defect presents a deep vertical component and maintains the interproximal bone level close to the cemento-enamel junction (CEJ), facilitating membrane retention in the correct position and allowing coronal repositioning of the flap with total membrane coverage¹⁹.

The horizontal depth of FI also influences clinical outcomes, and in most studies of Grade II FI, the preoperative probing depth (PD) correlates with the magnitude of clinical attachment gain and bone repair achieved after one year¹⁹.

Treatment predictability is enhanced when complete debridement of the exposed root surface in the FI area is achieved¹⁹. Factors affecting the operator's ability to debride in this area, such as root proximity or deformities, could influence the results of guided tissue regeneration (GTR)¹⁹. Additionally, lower molar roots often present deep concavities and the presence of enamel pearls that may hinder proper debridement ¹⁹. The anatomy of the upper molars is even less favorable, which may contribute to less predictable results in these teeth¹⁷.

It has been demonstrated that the dimension of the root trunk is correlated with the presence of FI¹⁷. This dimension may influence the selection of a better therapeutic approach; a longer root trunk facilitates the placement of the barrier membrane under the cementoenamel junction (CEJ) to achieve complete coverage of the FI and flap repositioning by fully covering the membrane¹⁹.

Gingival phenotype has also been linked to the amount of recession obtained after GTR in FI²². Anderegg et al. demonstrated that sites with a thicker phenotype exhibited less gingival recession compared to thinner phenotypes²². A thicker mucoperiosteal flap has more resistance to ischemia when placed on a non-vascularized surface, such as the membrane¹⁹.

Moreover, repositioning the flap with the aim of completely covering the membrane can apply excessive tension and induce ischemia. In the presence of thin gingiva, these factors can lead to increased recession, thus reducing attachment gain levels¹⁹.

Other factors that may influence the outcome of GTR are related to the surgical procedure, as it requires certain principles and care described for the treatment of intraosseous defects ²³. These include flap design, proper preparation of the root surface, correct membrane placement, good wound closure, and optimal postoperative care⁵.

The most common complications that worsen treatment outcomes are exposure of biomaterials and loss of the interdental papilla. These complications are associated with surgical techniques requiring a papillary incision²⁴.

To avoid such complications, various approaches have been proposed, including the use of enamel-derived proteins (EMDOGAIN®), alternative flap designs (papilla preservation techniques), and minimally-invasive techniques²⁴.

Tooth mobility has long been considered an important factor for periodontal regeneration²⁵. A multivariate analysis of a multicenter controlled clinical trial demonstrated that increased tooth mobility is negatively associated with clinical outcomes of regeneration²⁵.

A recent secondary analysis of three previously reported trials evaluated regenerative outcomes of mobile teeth and concluded that teeth with an initial mobility of < 1 mm horizontally could be successfully treated by periodontal regeneration, whereas severe and uncontrolled tooth mobility (Miller grade II) may affect regenerative outcomes and require splinting for regeneration²⁵.

Based on these results, it can be concluded that GTR treatment achieves the most significant and predictable results in deep and narrow intraosseous defects in vital or successfully endodontically treated teeth²⁵. The influence of defect anatomy seems to be reduced to some extent when a more stable flap design is applied²⁵.

A clinical trial, published in 2016, assessed 33 grade II FIs in patients with chronic periodontitis. Among them, 17 received GTR along with low-level laser, while 16 underwent GTR alone¹. Long-term results revealed that both GTR alone and GTR plus low-level laser led to significant improvements in the treatment of grade II FIs, with reductions in PD and horizontal PD (p=0.0001) and attachment gain (p=0.0001) compared to baseline¹. The study evaluated clinical and biochemical parameters to observe the effect of low-level laser as an adjunct for periodontal regeneration of grade II FIs (maxillary and mandibular) and demonstrated significant differences between GTR and GTR plus low-level laser application¹. The recorded parameters included PD, clinical attachment level (CAL), horizontal PD, alkaline phosphatase (ALP), and Osteocalcin (OC) levels in the gingival crevicular fluid (GCF) at baseline, 3, and 6 months after the procedure¹.

Photodynamic Therapy

Photodynamic therapy (PDT) has emerged in recent years as a novel non-invasive treatment modality for bacterial, fungal, and viral infections. It is defined as a photochemical, oxygen-dependent reaction that occurs following light-mediated activation of a PS, leading to the generation of cytotoxic reactive species, predominantly singlet oxygen²⁶.

This therapy can be topically applied to a periodontal pocket or intraosseous defect, thereby avoiding overdose. Additional advantages of PDT include a reduced likelihood of adverse effects associated with systemic administration of antimicrobial agents and the minimization of microbial resistance^27,28. PDT also diminishes the activities of virulence factors in Gram-negative bacilli ²⁹. Among the PS, cationic phenothiazinium dyes such as toluidine blue (TB) and methylene blue (MB) have demonstrated phototoxicity against Gram-negative bacilli when exposed to red light^30,31.

Several in vitro^30,31 and in vivo^32,33 experimental studies have demonstrated satisfactory results using PDT to eliminate periodontopathic bacteria. The mechanism by which PDT eliminates certain microorganisms, such as Porphyromonas gingivalis (Pg), Prevotella intermedia (Pi), Aggregatibacter actinomycetemcomitans (Aa), and Fusobacterium nucleatum (Fn), has been established^34,35. The lethal PS of these microorganisms involves changes in membrane or membrane plastid proteins and singlet oxygen-mediated DNA damage^34-37.

Previous experimental studies in animals^38-40 and humans^4,41 evaluated PDT in periodontal treatment and the progression of inflammatory periodontal disease. However, there is a shortage of in vivo studies evaluating the effect of PDT on the progression of bone loss in the furcal area⁴.

To assess the impact of this therapy during the treatment of FI, one study investigated the role of PDT combined with non-surgical mechanical debridement in the treatment of grade II furcations⁴². Previous research has shown that PDT, when associated with non-surgical debridement, achieved greater reductions in PD and attachment gain in non-furcation sites⁴¹. However, these clinical advantages promoted by PDT in non-furcation sites were not observed in the study conducted by Luchessi in grade II FI⁴². This study showed a significant reduction in PD of 1.59 mm and an average clinical attachment level (CAL) gain of 0.78 mm in the test group, while in the control group, the respective numbers were 1.50 mm and 1.00 mm (p > 0.05)⁴². The absence of significant differences between the therapies may be related to the fact that PS was applied to the control sites (without laser application), which may have optimized the clinical results in the control group, contrary to previous studies^4,41,43,44, which compared the performance of PDT plus SRP with mechanical debridement alone⁴². There is evidence showing that subgingival application of PS as monotherapy can exhibit bactericidal action, and even in sites with chronic periodontitis, it achieved superior microbiological benefits compared to controls⁴².

Chondros et al (2009) demonstrated that the combination of PDT with non-surgical therapy leads to a significant reduction in BOP compared to debridement alone during maintenance therapy⁴⁵. In fact, research has emphasized the effect of low-level laser on cells and tissues (photobiomodulation). Light has a positive influence on supporting tissues and cells during healing, positively affecting tissue repair and decreasing inflammation due to potential biomodulatory effects^45,46. These positive effects associated with laser use may have contributed to the reduction in BOP in PDT-treated FI in Luchesi's study⁴². Furthermore, these biomodulatory effects of PDT may also be related to the positive results observed in the study regarding the levels of markers regulating immune response and bone metabolism⁴². Most notably, PDT has been shown to achieve improvements in the modulation of local levels of inflammatory mediators during 6 months of follow-up⁴².

Laser Parameters that Influence Treatment Outcomes

In recent years, the beneficial impact of laser irradiation on bone regeneration has been documented^11,12,46. It is known that low-level laser application involves specific variations such as dose, wavelength, energy density, application time, and intervals between applications¹.

Among these parameters, the applied dose emerges as one of the most crucial factors to consider ¹. At low doses (2-4 J/cm²), low-level laser stimulates cell proliferation and the production of basic growth factors by fibroblasts. However, both activities are deactivated at higher doses exceeding 16 J/cm^{2 (47}.

Regarding wavelength, Almeida-Lópes investigated the effects of different diode laser wavelengths (670nm, 692nm, 780nm, and 786nm) at a fixed dose of 2 J/cm² on fibroblasts⁴⁸. Regardless of the wavelength used, cell proliferation increased in all groups by the end of the study ⁽⁴⁸.

The laser application period constitutes another pivotal factor ¹. A sole application at the wound and defect site may prove insufficient to stimulate cells and reach the edges of the surgical bed. Consequently, multiple irradiations are more efficient than a singular irradiation¹.

The irradiation frequency plays a crucial role in both bone formation and fibroblast growth¹. Furthermore, employing laser light during the initial stages of healing demonstrated greater effectiveness in achieving complete defect filling compared to later stages, which primarily contribute to maintaining bone volume¹.

Discussion

The use of PDT in periodontal therapy has demonstrated promising results in previous studies^{(49, 50)}. Consequently, it is crucial to assess the impact of this therapy during the treatment of FI⁴².

PDT, when combined with non-surgical debridement, has proven to achieve a more substantial reduction in PD and CAL gain in teeth without furcations⁵¹. However, these clinical benefits of PDT in teeth without furcations were not observed in a study evaluating its effects in sites with grade II FI⁴². In this study, there was a significant reduction in PD of 1.59 mm and CAL of 0.78 mm in the test group, while in the control group, the respective numbers were 1.50 mm and 1.00 mm (p>0.05)⁴².

Respectively, conservative therapy for FI, involving debridement combined with the local application of antimicrobial agents, has not provided any evidence of promising results during either initial or maintenance periodontal therapy⁴².

In a 2013 study by Luchesi⁴², investigating the effect of PDT on grade II FI as an adjunct to mechanical therapy (with a test group and a control group receiving only mechanical therapy), the absence of clinical differences between the two therapies could be related to the photosensitizer in the control sites. This factor could have optimized clinical outcomes in these groups, contrary to other studies that compared the development of PDT plus SRP with SRP alone^{(42, 51)}.

It is worth noting that the PS alone can also exhibit bactericidal action, and that subgingival application of methylene blue as monotherapy in periodontitis sites achieved greater benefits in microbiological parameters compared to control sites that received sterile water⁴².

Another investigation also showed that the application of toluidine blue O (TBO) alone resulted in a significant reduction of periodontopathogens on contaminated surfaces of dental implants⁴². However, it may be hypothesized that the maintenance of reduced levels of periodontopathogens throughout the re-evaluation period depends on the PDT approach⁴².

In terms of Porphyromonas gingivalis (Pg) and Tannerella forsythia (Tf) reduction, advantages were observed for the PDT group⁴². It was shown that the decrease in Tf from baseline was achieved only in the PDT group, 6 months after therapy⁴². Furthermore, although a decrease in Pg levels was observed from baseline and after 3 months for both treatments, this reduction was maintained until 6 months after therapy only in the PDT group⁴².

These microbiological profile changes are in line with the reduction in BOP at these sites⁴².

In this study, the significant reduction in BOP-positive sites detected for both therapies at 3 months was only maintained with lower levels at 6 months in the PDT group⁴².

In line with the results obtained, it was also shown that the combination of PDT with non-surgical therapy promoted a greater reduction in BOP scores compared to non-surgical debridement used alone during maintenance therapy⁴².

In fact, researchers have noted the effect of low-level lasers on cells and tissues, an effect known as "photobiomodulation"⁴².

Light has a positive influence on surrounding tissues and cells during tissue healing, successfully influencing tissue repair and decreasing periodontal inflammation as a result of possible biomodulatory effects⁴². These positive effects associated with laser use may have contributed to a reduction in BOP in PDT-treated FI sites throughout this investigation⁴².

These PDT biomodulatory effects may be related to the positive results observed in this study in terms of the levels of key markers regulating immune response and bone metabolism⁴². Scarce and conflicting data are available on the role of PDT in the inflammatory mediator profile during periodontal therapy⁴².

Recently, Giannopoulou et al.⁵², comparing the effects of PDT, diode low-level laser, or SRP on local levels of various cytokines and acute-phase proteins in residual pockets therapy, revealed that significant changes were achieved regardless of the treatment modality over 6 months. However, no differences were observed between the three treatment modalities at any time point⁴².

Additionally, in an experimental rat model of periodontitis, it was demonstrated that animals treated with PDT exhibited decreased bone resorption, reduced neutrophil migration, and decreased TNF-α expression compared to animals treated with photosensitizer alone, aligning with the results presented here⁴².

An important aspect to discuss in the Luchesi 2013 trial is the number of PDT episodes ⁴². In this study, a single application of PDT was used as an adjunct to mechanical therapy, and this approach did not yield clinical benefits for the treated sites in terms of Probing Pocket Depth (PPD) reduction or CAL gain⁴².

Conversely, it has also been revealed that additional PDT sessions following non-surgical therapy provided benefits in clinical outcomes in residual pockets during maintenance periodontal treatment, supporting the use of repeated PDT applications⁴².

It may be speculated that the effects of PDT as a single-episode adjunct, as conducted in this study, might not suffice to contribute to clinical improvements in FI⁴². Further investigations are needed to elucidate whether multiple courses of PDT could enhance treatment outcomes⁴²⁾ .

No data from controlled clinical studies evaluating the performance of PDT in combination with SRP for the treatment of grade II FI are available in the literature⁴². Thus, considering the limitations of the therapeutic approaches studied so far to manage FI, additional studies with more longitudinal follow-up periods are required⁴².

Moreover, it is crucial to note that topical therapeutic strategies offer several advantages compared to the use of systemic antibiotics as adjunctive therapy⁴².

Negative aspects related to the use of systemic antimicrobials in treating sites with periodontal disease should be acknowledged, particularly, side-effects for individual patients such as gastrointestinal disorders, and the development of bacterial resistance—a significant global public health concern. For these reasons, patient compliance may also be compromised⁴².

Conclusions

Although low-level laser is widely recommended for biostimulation and as an anti-inflammatory agent, to date, it has only demonstrated positive short-term outcomes as an adjunct to regenerative periodontal treatment in grade II FI. It is evident that GTR yields favorable results in FI, showcasing both clinical and biochemical improvements. The integration of low-level laser can enhance GTR effects, exhibiting attachment gain and reductions in both vertical and horizontal probing depths. However, the long-term efficacy remains unclear due to methodological weaknesses, a scarcity of comprehensive studies, and the absence of standardized parameters.

PDT could be an alternative for controlling bone loss in FI caused by periodontitis. Nevertheless, further studies are imperative to elucidate the mechanisms of action for PDT, low-level laser, and the effects of different photosensitizers as adjuncts in FI treatment. Clinical trials featuring better study designs, adequate sample sizes, extended follow-up periods, and standardized parameters are necessary to assess the effectiveness of laser therapy as an adjunct in the quest to enhance the treatment strategy for grade II FI, ultimately improving the prognosis of these lesions.

These locally applied therapies, in combination with SRP, could emerge as a significant and safe strategy in treating FI, offering an alternative to conventional chemotherapies, even those tested in this type of periodontal defect.