Periodontitis

Background

The complex oral microbiota constitutes a diverse community of microorganisms that inhabit the oral cavity and plays a crucial role in maintaining the balance and overall health of the oral environment1. These microorganisms form a symbiotic relationship with the immune system, modulate immune responses, and prevent pathogenic invasion. Perturbation and dysbiosis of the oral microbiota can lead to the development of caries and periodontitis, which are two common oral diseases2. Periodontitis is a chronic inflammatory disease that affects the supporting structure of the teeth, including the gums, periodontal ligament, and alveolar bone3.

Periodontitis can be categorized based on its severity and extent. The American Academy of Periodontology has defined a classification system that divides periodontitis into several stages based on severity, including stages of mild, moderate, and severe periodontitis4, and based on the etiology and diagnosis of aggressive periodontitis, we find Chronic periodontitis, and Aggressive periodontitis. However, there are cases which set in neither category. Therefore, they classify in Necrotizing periodontal disease, where periodontal disease is more complex due to factors such as undiagnosed syndrome, or due to variation that could be genetic, or immunological, or systemic4. Aggressive periodontitis can be categorized into a localized periodontitis or a generalized periodontitis5. Periodontitis could also be plaque induced or non-plaque-induced6.

Risk factors associated with the development of periodontitis diseases include poor oral hygiene habits, smoking7, diet8, hormonal changes9, a significant reduction of polymorphonuclear leukocytes10, genetic polymorphisms of genes involved in the production of cytokines11, as well as systemic conditions such as diabetes12, cardiovascular disease13, and immunosuppressant drugs or immunocompromised conditions14.

Microorganisms associated with periodontal disease

The history of understanding the microorganisms associated with periodontal disease have come a long way. From believing that bacteria are simply secondary invaders rather than the primary cause of the disease15, to the identification of specific microorganisms that are commonly found in periodontal pockets and associated with the disease compared to health16,17,18,19. Following this, Loesche developed a ‘Specific plaque hypothesis’20,21. The key findings of this hypothesis are that periodontitis is a result of overgrowth of specific pathogens, characterized as the ‘red complex’ microorganisms, including Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola. These microorganisms have been strongly associated with the development and progression of periodontitis22. These microorganisms have been found to interact with the host immune system and manipulate inflammatory responses, leading to tissue destruction23. They produce a variety of virulence factors that contribute to their pathogenicity. These virulence factors include proteases, collagenases, lipases, and toxins, which facilitate tissue invasion, breakdown of connective tissues, and immune evasion24. Actinobacillus actinomycetemcomitans for instance, demonstrates its potent periodontopathogenicity by the ability to invade host cells and induce leukocytotoxicity25. For example, Porphyromonas gingivalis utilizes its fimbriae to adhere to oral surfaces and evade detection by the host immune cells26. Additionally, it produces lipopolysaccharides and outer membrane vesicles that can interfere with the host immune signaling pathways, promoting a chronic inflammatory state within the periodontal tissues27.

In addition to their direct effects on the host immune system and tissue destruction, the red complex microorganisms have also been implicated in the dysregulation of bone metabolism28, further contributing to the progression of periodontitis. These microorganisms have been shown to modulate osteoclast activity and interfere with the balance between bone resorption and formation, ultimately leading to alveolar bone loss and tooth mobility29, which are hallmark features of periodontitis. In addition to the red complex microorganisms, there are other microbial species that also contribute to the pathogenesis of the disease.

The orange complex microorganisms, classified as moderate pathogens including Fusobacterium nucleatum, Prevotella intermedia, and Campylobacter species have also been found to play a significant role in the progression of periodontitis by facilitating the colonization of other pathogens30, and creating an environment conducive to the growth and survival of pathogenic species31. In fact, these microorganisms appear to enhance the adherence of yellow, and purples complexes take place and facilitate the adhesion and survival of red complex microorganisms32.

Following the specific plaque hypothesis, an ‘Ecological catastrophe hypothesis’ was suggested by Marsh P.D.33, where he emphasizes the relationship between plaque bacteria and the host in health and disease, and implicated the concept of environmental factors influencing the selection and enrichment of pathogenic bacteria. A noteworthy remark that Marsh has pointed is that clinicians only treat symptoms of the disease rather than identifying the factor(s) driving the dysbiosis or so-called ‘ecological catastrophe’. Thus, modulating the shift in the oral microbiota back to sustainable homeostasis is the direction scientists in preventive dentistry should focus on. However, the polymicrobial synergy and dysbiosis of oral microbiota in periodontitis puts into question the red complex to something beyond and more complex30.

Clinical changes associated with periodontal disease

Periodontitis is a result of untreated gingivitis associated to bacterial plaque accumulation, and alteration of the marginal gum, bleeding on probing, and an irreversible periodontal attachment loss with formation of pockets and recessions, and bone resorption with tooth mobility and exfoliation. Currently, there are no reliable clinical parameters to indicate existing periodontitis activity or to predict its occurrence, and existing clinical parameters vary in their degrees of accuracy and reliability34. However, the European Federation of Periodontology defined the clinical characteristics of periodontitis as the manifestation of three factors: Clinical Attachment Loss CAL, the presence of periodontal pockets, and bleeding on probing BOP, and gingival bleeding.

Pocket probing depths (PPD)

PPD refers to the depth measured in millimeters between the gingival margin and the base of the periodontal pocket, the progression of periodontal disease is related to an increase of PPD, which translates to deepening of the pockets due to inflammation and tissue destruction. PPD is monitored overtime to assess disease severity and response to treatment using a periodontal probe at various sites around each tooth. The value of mild to moderate pocket is >3 and <5 mm, moderate pockets have values between 5 mm and 7, and deep pockets have values of ≥7 mm35.

Bleeding on probing (BOP) percentage

BOP is the presence of bleeding from the gingival sulcus or periodontal pocket upon probing, an increase in BOP indicates the presence of periodontal disease, reflecting an active inflammation. BOP is assessed by gently probing the gingival sulcus or periodontal pockets, and the percentage of bleeding sites is recorded, this parameter helps to evaluate the oral hygiene practices and periodontal treatment. Presence or absence of BOP is used to determine the presence or absence of periodontitis. Studies have validated that non-bleeding gingival units may serve as an indication of periodontal stability36,37. Another study assessing BOP as a periodontal monitor revealed a very low predictive value for disease progression (6%), while the negative predictive value for absence was high (98%)38.

Clinical Attachment Level (CAL) loss

CAL loss is the amount of attachment loss between the tooth and surrounding tissues. CAL loss reflect the progression of the disease while a CAL gain reflects the regression of the disease. Thus, it is another crucial clinical parameter in the periodontal examination using a periodontal probe. The CAL value that indicates a progression of periodontal disease has varied in literature from a CAL loss of ≥2 mm39 to a loss of ≥3 mm40.

An analysis of periodontal disease progression vis-à-vis to CAL between healthy and diseased patients showed that subjects classified as “periodontally healthy” had an average of CAL of 1.1 mm, while “mild periodontitis” had a mean of 2.1 mm, and “severe periodontitis” had a mean of 2.5 mm41.

Plaque Index (PI)

Plaque Index is the amount of dental plaque present on tooth surfaces, an increased plaque accumulation reflects the initiation and progression of periodontal diseases, while a decrease of PI reflects the regression of the disease. Thus, it is also used to assess the response to treatment by visually assessing the presence and thickness of plaque on tooth surfaces. Currently, there are different methods to assess the plaque formation on the surface42. However, the development of several different types of index system is needed43.

Limitations of conventional methods in periodontal therapy

Conventional periodontal treatment involves scaling and root planning, antibiotic treatment, and surgical procedures. The pathogenesis of periodontitis involves the colonization of pathogenic species, such as those in the orange complex, which produce virulence factors that contribute to tissue invasion and immune impairment. Additionally, the plaque hypothesis (discussed previously) has led to the exploration of targeted interventions, such as antibiotic treatment or non-surgical procedures, to eliminate the specific pathogen causing periodontal disease and promote healing. Scaling and root planning (SRP) is considered the gold standard in periodontitis therapy; it is a non-surgical therapy used to remove dental plaque and calculus by scaling and to smooth the infected root surfaces by root planning44. However, bacterial recolonization occurs shortly after treatment, and pathogenic microbiota is re-established within months after treatment45. Antibiotic treatment, in the other hand, is also used in treating periodontitis. However, it has become more complex due to the emergence of antibiotic-resistance bacteria46.

Probiotics

Background

Recently, there has been growing interest in the use of probiotics as a novel approach to prevent and treat periodontal disease. Probiotics are live microorganisms that, when administered in adequate amounts, confer health benefits to the host by modulating the composition and activity of the microbiota47 Probiotics have been studied as potential mechanisms for promoting oral health in periodontal disease, and caries48. Probiotic microorganisms, such as Lactobacillus reuteri, Streptococcus salivarius, and Bifidobacterium dentium, show promise in maintaining periodontal health by inhibiting the growth and virulence of pathogenic species in the oral microbiome, modulating the immune response, and promoting tissue healing processes49. The mechanisms in which probiotics act in the prevention and treatment of periodontal disease involve inhibiting the growth and virulence of pathogenic species by competing for resources50 and producing antimicrobial compounds51, modulating the immune response to control inflammation and promote healing52, and restoring microbial balance in the oral microbiome53. Inhibition of cariogenic microbial biofilm can also be achieved using probiotic microorganisms by competing with cariogenic bacteria for nutrients and adhesion sites54, producing antagonistic substances like lactic acid, hydrogen peroxide, and bacteriocins55.

During inflammation response, there is an overproduction of reactive oxygen species (ROS) causing an increase of oxidative stress and leading to tissue damage and disease progression56. Targeting oxidative stress and restoring its balanced level could lead to better management of apical periodontitis and enhance patients’ quality of life. Probiotics have been shown to activate antioxidant pathways and enhance the expression of various antioxidant enzymes and downregulate the inflammatory processes that lead to excessive ROS generation, thereby reducing oxidative damage, and decreasing inflammation in periodontal tissues57. Although there is not enough evidence in the use of probiotics in apical periodontitis, probiotics could offer an adjunctive benefit to apical periodontitis.

Recent research has highlighted the involvement of the NLRP3 inflammasome and NT-PRO-BNP in the progression of periodontitis. The NLRP3 inflammasome plays a central role in the activation of inflammatory responses, leading to the release of cytokines such as IL-1β, which exacerbates tissue destruction in periodontal disease58,59. Additionally, NT-PRO-BNP, commonly associated with cardiovascular health, has been linked to increased inflammation in periodontitis patients60.

Probiotics can promote anti-inflammatory pathways and antioxidant defenses, by inhibiting the damaging effects of NLRP3 inflammasome overactivation which can positively influence the host’s immune response by enhancing the production of anti-inflammatory cytokines and decreasing the production of pro-inflammatory cytokines such as IL-1β and TNF-α61, by inhibiting NLRP3 inflammasome activation.

Although the current review does not focus on the specific interactions between probiotics and these mediators, understanding their role in periodontitis pathophysiology provides a broader context for future studies. We suggest that ongoing research should further investigate how probiotic interventions may interact with these inflammatory pathways, as this could be a promising area for enhancing periodontitis treatment strategies62.

In oral health, probiotics have been found to improve clinical parameters such as pocket depth reduction, bleeding on probing reduction, and clinical attachment level gain63. Additionally, probiotics have been shown to improve the overall ecological balance of the oral microbiome, leading to a reduction in disease-associated dysbiosis64. One of the key strategies in the use of probiotics for periodontal disease is the modulation of the oral microbiome. This can be achieved by introducing beneficial probiotic microorganisms that could compete with pathogenic species for resources and adhesion sites, produce antimicrobial compounds, and promote a balanced microbial community. The available forms of probiotics for dental diseases include oral probiotic lozenges, gums, toothpaste, mouthwashes, and supplements65. Recent studies have shown promising results regarding the use of probiotics for the prevention and treatment of dental diseases66,67,68,69,70,71,72.

The application vehicle

The choice of the delivery vehicle of probiotics in the oral cavity may influence the oral colonization and the cariogenic potential of probiotics48. The daily dose of probiotic intake may also influence the outcome of the intervention73. A range of vehicles was used in delivering probiotics as an adjunct to periodontal treatment, including lozenges, tablets, sachets, capsules, toothpaste, mouthwashes as well as local delivery using gel or drops based probiotics (table). Table 1 mentions the basic characteristics of the studies like number of patients in both genders, age range, and inclusion criteria and exclusion or not of smokers and diabetics if reported.

Table 1 Basic characteristics of the studies
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Aim of the review

This review evaluates the role of probiotics as an adjunctive therapy for periodontitis from a clinical perspective. We analyzed the baseline clinical parameters of each study, assessing how these metrics changed following intervention. Additionally, we outlined the inclusion and exclusion criteria for each study, detailing the selected probiotic strains, their administration methods, and frequency. This comprehensive overview aims to clarify the effects of probiotics in periodontal treatment.

The findings of this review hold significant clinical relevance by providing valuable insights into selecting appropriate probiotic strains, dosing, and intervention periods for future studies. Moreover, it emphasizes the importance for researchers working with periodontitis patients to ensure that the baseline clinical parameters of recruited individuals align with international periodontal guidelines. This alignment can enhance the validity and applicability of research outcomes, ultimately improving patient care.

Clinical efficiency of adjunctive treatment probiotics in patients with chronic periodontitis, a controversy

Different variables influence the outcome of the intervention

Table 2 mentions the probiotic strain, form and dosage used per day, the intervention period and the follow-up of the studies (Table 2), while Table 3 shows in the clinical parameters at baseline, after intervention, and -if exist- after follow-up (Table 3). These studies using probiotics as an adjunctive to periodontitis treatment showed a direct correlation between the period of intervention, the administrated dose with the gain of CAL and the reduction of PD. The follow up of treated patients also varies between studies, longer follow up shows regression with time in monitored clinical parameters and need of retreatment.

Table 2 Treatment type, frequency and duration
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Table 3 Probiotic efficacy on the clinical parameters, its clinical significance vs conclusions by the authors
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Thus, studies showing improvement of post probiotic intervention without evaluating the necessity of retreatment after an extended period, lack sufficient evidence to support the recommendation of probiotics as an adjunctive therapy in periodontitis. A study conducted by Vohra and colleagues utilized a probiotic-based lozenge containing Lactobacillus reuteri strains (ATCC-PTA 5289 and DSM 17938) as an adjunct to scaling and root planing (SRP). The findings revealed significant improvement in clinical parameters at the 3 month follow-up in comparison to the control group. However, by the 6 month follow-up, the probiotic test group demonstrated values closer to the placebo group, with differences of 0.9% in bleeding on probing (BOP), 0.1 mm in probing depth (PD), 0.3 mm in clinical attachment level (CAL), and plaque index (PI) values showing a significant difference at the 3 month mark but converging to the same difference value at the 6 month follow-up74. An additional noteworthy aspect, as detailed in the clinical parameters section, is that the evaluation of most of these parameters relies on visual assessment using a probe with a 1 mm margin of error. Consequently, and from a clinical perspective, relevance of significances related to <1 mm does not conclusively demonstrate the added benefits.

It is noteworthy that while probiotic therapy may demonstrate initial benefits post-intervention and sustained improvement for a few months thereafter, subsequent regression and the absence of additional benefits compared to control groups during long-term follow-up periods raise questions regarding the efficacy of this therapy.

Furthermore, it may be suggested that achieving a permanent shift in the oral microbiome towards a healthier state might necessitate long-term or even lifelong administration of probiotics. These observations highlight the importance of further research to elucidate the optimal duration and efficacy of probiotic therapy in promoting lasting oral health benefits.

In a study conducted by Yılmaz and colleagues, follow-up assessments were carried out on days 21, 90, 180, and 360. The findings demonstrated a notable improvement in clinical parameters until day 180. However, by day 360, all clinical parameter values experienced a slight increase, resulting in a difference of 1.18 mm in probing depth (PD), 0.65 in plaque index (PI), and 0.86 in clinical attachment level (CAL) gain66. A different work from the same group lead to the same observation75. In another study, a noteworthy improvement was noted, particularly in deep pockets, after a 3 month period. Importantly, no regression was observed in the test group throughout the entire follow-up period67. In a different study employing a lozenge based on Lactobacillus reuteri DSM 17938 and ATCC PTA 5389, improvements were observed for probing pocket depths (PPD) >4 mm. However, an intriguing increase was noted at the 9-month mark, similarly observed in the placebo group at the 12 month interval 68.

Baseline parameters hold significant importance in every study, particularly in research on periodontitis treatment. Emphasizing the probing depth (PD) baseline values are essential, as they serve as a key indicator of disease severity and are instrumental in evaluating the treatment response, as elucidated in the PD section. Assigning individuals without pre-existing periodontitis to categories such as chronic or aggressive periodontitis, and obtaining positive results, may raise questions about the appropriateness of the categorization. The American Academy of Periodontology35 and the European Federation of Periodontology76 share a value of >3 mm for a patient to be a periodontitis case.

Morales and colleagues assessed the effect of Lactobacillus rhamnosus in Non-Surgical Treatment of Chronic Periodontitis, using a baseline of 2.7 mm in test group and 2.5 in control group77. A separate work assessed the clinical effect of Lactobacillus salivarius NK02-based mouthwash, they have used a linear model to describe the baseline of clinical parameters, which gives a better visualization of the distribution of statistical values of clinical parameters, and the PD mean was around 2.6 and 2.778. Same could be observed in other studies79,80,81,82,83. Providing a baseline value of each group rather than just the inter and intra group values, would give a better idea on the effect of probiotics in periodontitis treatment. Other studies have categorized Probing Depths into PD, and PD ≥ 5 mm70, or to moderate pockets and deep pockets PD ≥ 7 mm71,72,73,84. A recurrent observation in these studies is that probiotic interventions result in notable improvements, particularly in deep pockets, implying a potential role for probiotics as adjunctive therapy in individuals with aggressive periodontitis.

Clinical studies assessing the clinical and microbiological effects of probiotic based treatment differ not only in the baseline parameters, probiotic formulation, intervention period and frequency, and follow up, but also in their approach, most studies use an oral administration, meanwhile others took a different direction where they administrate probiotics locally72,79,85,86,87; one study assessed the effect of probiotics on different routes (locally and/or orally) as well as antibiotic treatment alone or with probiotics, better results were observed in combining both administrating routes. Interestingly, adjunctive probiotics increased the number of persisting diseased sites with PD > 4 mm and BOP%71. In a distinct study, a comparative analysis between probiotics alone and probiotics combined with scaling and root planing (SRP) was conducted, treating only two quadrants.

The probiotics+SRP group exhibited superior outcomes. However, after 42 days of leaving one quadrant untreated, the results mirrored those observed at day 21 in the SRP-treated quadrant. The coexistence of an untreated quadrant with a treated quadrant within the same oral cavity might have impacted the overall microbiome, potentially exerting a negative influence on the SRP-treated quadrant and providing a plausible explanation for the observed regression of results after 42 days86. Boyeena and colleagues conducted a study evaluating the effectiveness of probiotics compared to tetracycline fibers as adjunctive therapy to scaling and root planning (SRP). The combination of probiotics and antibiotics yielded the most favorable outcomes, with probiotics alone producing the second-best results. However, it is noteworthy that the local delivery of probiotics and antibiotic fibers necessitates refraining from brushing around the designated area, and the comfort of the patient does not appear to have been taken into consideration71. Recently, research directions are leaning toward symbiotic supplementation84,85, heat killed probiotics88, and photodynamic therapy in combination with probiotics83.

Table 4 summarize the clinical relevance related to adjunct periodontitis therapy, using a score scale of 0/+/++ of pre-mentioned work but excluding all papers with missing clinical parameters (PPD, BOP, and CAL) or provided in mean of total patients, in figures, as well as papers with a PPD value <3 mm at baseline. From a total of 26 research paper, 18 of them resulted a difference of <1 mm between probiotic groups and the other groups, 1 with no additional effect, and 7 with a positive effect (Table 4).

Table 4 Scoring of probiotic effect as an adjunctive therapy to periodontitis treatment from published studies
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Conclusion and future perspectives

Previously published systematic reviews provided conflicting results when examining the clinical efficacy of probiotics on periodontitis. In another hand, a systematic review and meta-analysis by Gheisary et al.89 have suggested that probiotic supplementation improves clinical parameters and reduces the periodontopathogens and pro-inflammatory markers in patients with periodontitis. Another systematic review by Ausenda et al.90 has presented the adjunctive probiotic effect over time and delivery method used which was more insightful compared to other systematic studies. A recent meta-analysis by Li et al.91 suggested that probiotic as an adjunctive therapy to scaling and root planning can improve the clinical outcome of chronic periodontitis patients and reduce periodontitis pathogens level. Interestingly, the European Association of Periodontology do not recommend the use of probiotics as an adjunct to subgingival instrumentation92.

The strength of this review relies on presenting all 40 clinical and experimental studies using probiotics as an adjunctive therapy to non-surgical periodontal therapy, and presenting clinical parameter changes over time, follow-up period and dose of probiotic were calculated in each study and presented by Colony-forming unit per day (CFU/ day) which provides important information on which strain, form, dose, duration might be most clinically useful. Based on the clinical outcome of studies that included a baseline of probing depth >3 mm, we can suggest that probiotics can somewhat improve the clinical outcome in few different cases, as single strain like L. reuteri like done by Tekce et al.66 with a dosage of 2 * 10^8 per day for a period of 3 weeks or in the form of sachet (Morales et al. 2021 and Jebin et al. 2021) with a lower dosage (2 * 10^7) but prolonged intervention (12 weeks)93,94. Probiotics also showed a positive outcome when used as a combination of strains such as the study of Boyeena et al.71. and and Bayzaar et al.84. Local delivery by the dentists could also be an option like the study of Chandra et al. where they used a combination of probiotic and prebiotics as an adjunctive therapy for periodontitis85.

The limitation of this review is the high heterogeneity in the studies. The different strains, forms, intervention period and administration route, in addition to the baseline parameters represent a limit. Another limitation of this study is that it focused only on the clinical parameters of the studies in details and have not included microbiological and immunological effects of probiotics as an adjunctive therapy in periodontitis as not all the studies have assessed these aspects.

Probiotic strain alone or combinations of strains, their form, dose, the intervention time, follow-up period, and inclusion criteria especially the baseline of the PPD in the clinical parameters are all factors that influence the results of the probiotic therapy.

Studies in probiotics as an adjunctive therapy showed a promise outcome in both clinical and microbiological parameters. However, addressing the challenges associated with probiotic interventions in periodontitis necessitates a multidimensional approach. In addition to evaluating clinical parameters, future research should emphasize the assessment of the potential side effects or safety concerns associated with probiotic administration. Long-term follow-up studies are crucial for elucidating the sustained effects of probiotics on periodontal health and the prevention of disease recurrence.

Moving forward, comprehensive clinical trials that consider the diverse characteristics of patients with chronic periodontitis, standardize probiotic interventions, and incorporate advanced microbiome analysis techniques will be instrumental in establishing the potential of probiotics as a viable adjunctive therapy in periodontal treatment. Thus, developing a personalized probiotic-based treatment is critical direction for future research to achieve a safer, more effective, and long-lasting results in preventive dentistry in general and periodontitis treatment specifically.