Periodontitis

Periodontitis is a chronic inflammatory disease of the tissues that hold teeth in place: the gingiva, the periodontal ligament, the cementum, and the alveolar bone. It begins with a bacterial biofilm on the tooth surface, but the damage is mainly done by the host's own immune system as it responds to that biofilm. The result is loss of connective-tissue attachment, deepening of gum pockets, and resorption of supporting bone. Because lost bone and attachment do not regenerate spontaneously, the disease is a leading cause of tooth loss in adults and a significant concern in public health and clinical medicine.

The condition matters beyond the mouth. Periodontitis is bidirectionally linked with diabetes, and it has been studied in relation to cardiovascular disease, rheumatoid arthritis, and cognitive decline. Its global prevalence, its effect on quality of life, and the modern shift toward a multidimensional staging and grading system have made it a central topic in dental and general health research. Current understanding of its causes has moved from a single-pathogen model toward models that emphasize microbial ecology and inflammatory dysregulation.

This entry first describes the anatomy of the periodontium and the microbial and immune mechanisms of tissue destruction. It then covers risk factors, clinical features, diagnosis, and the 2017 staging and grading classification, and it distinguishes periodontitis from peri-implant disease. The later sections address epidemiology, the history of research, and the prevention and treatment options from mechanical debridement through surgical regeneration and lifelong maintenance. The entry closes with associations with systemic health and the main unresolved questions in current research.

Definition and place among periodontal diseases

Periodontitis is an inflammatory disease of the tissues that hold teeth in place, the periodontium. Its defining feature is the loss of clinical attachment, which is the connection between the tooth root and the surrounding soft tissue, together with destruction of the alveolar bone that supports the tooth in its socket. Clinicians usually express attachment loss as the distance from the cementoenamel junction to the base of the pocket, so the measure captures both soft-tissue detachment and any recession of the gum margin.1 Because inflammation is the driving process, the disease is classed as an infection-triggered immune-mediated condition rather than simply a deposit or mechanical problem.

Periodontitis must be distinguished from gingivitis, the inflammatory condition confined to the gingiva. Gingival inflammation stays within the gingiva and does not cross the mucogingival junction, and it resolves once plaque at and below the gingival margin is reduced.2 Gingivitis involves no loss of connective tissue attachment and no radiographic bone loss. Longitudinal studies suggest that gingivitis is nonetheless a necessary precursor: sites that go on to lose attachment tend to show persistently greater gingival inflammation than sites that remain stable.3 The transition to periodontitis, by contrast, results in attachment loss that is, at present, regarded as irreversible.2

Pocket formation and the junctional epithelium

The key histological event is the change in the junctional epithelium, the thin band of epithelial cells that normally seals the gingival margin against the tooth. Under sustained bacterial challenge, these cells proliferate and extend apically along the root surface, moving the epithelial attachment away from the cementoenamel junction.4 The result is a periodontal pocket: a gingival sulcus that has deepened pathologically. Pockets can form in two ways. Coronal displacement of the gingival margin, as in gingival enlargement, produces a pseudo-pocket without tissue destruction, whereas apical migration of the junctional epithelium together with destruction of supporting tissue produces a true pocket.5 A probing depth of 4 mm or more is generally required before a true periodontal pocket is clinically recognized.6

Once the epithelium has migrated, the pocket lining changes from junctional epithelium to pocket epithelium, a shift regarded as a hallmark of periodontitis.7 The deeper, narrower environment also has lower oxygen tension, which favours the anaerobic, Gram-negative bacteria most strongly linked to the disease.4 Bacteria and their products can then penetrate the root surface, and bone loss follows the advancing base of the pocket.8

Why lost tissue is not restored

Gingivitis is generally reversible because its changes are limited to inflammation of soft tissue, with no structural loss underneath.9 Periodontitis differs in that the destroyed structures include collagen fibres anchoring the gingiva to the root, the periodontal ligament, and alveolar bone. Treatment can control the infection, reduce inflammation and prevent further loss, but lost bone and attachment are not typically restored without advanced procedures.10 Ordinary brushing or flossing therefore cannot rebuild bone that has already been resorbed.11

This irreversibility explains the clinical course. Without control, deep pockets lead to loosening of the teeth and, ultimately, tooth loss.12 The aim of therapy therefore shifts from reversing the disease to stabilising the remaining support, and patients whose attachment has been lost remain at lifelong risk of recurrence.2

Anatomy of the periodontium

The periodontium is the group of tissues that surrounds the tooth, anchors it in the jaw and maintains its function. It has four components: the gingiva, the periodontal ligament, the cementum and the alveolar bone. The gingiva is the part of the oral mucosa that covers the alveolar bone and surrounds the tooth neck. It has an attached, keratinized portion and a free gingival margin, and the interdental papillae fill the spaces between adjacent teeth. Cementum is a thin, mineralized layer covering the tooth root. It is largely acellular in its coronal and middle parts and has limited capacity for repair. The alveolar bone forms the socket (alveolus) that holds each root, and the bone lining the socket is the alveolar bone proper, which appears on radiographs as the lamina dura. Each of the four components depends on the others for stable attachment.

The gingival sulcus is the shallow crevice between the tooth surface and the free gingival margin. Its floor and wall are formed by the junctional epithelium, a non-keratinized epithelium that attaches to enamel or cementum through hemidesmosomes and a basal lamina rather than through a keratinized surface. The junctional epithelium is renewed rapidly, and it is the point where host tissue meets the subgingival biofilm. Gingival crevicular fluid seeps through the sulcular epithelium, and its volume rises with inflammation. Host defense cells, including neutrophils, migrate through the junctional epithelium into the sulcus. Because the sulcus lacks the protective keratinized barrier of the outer gingiva, it is the most exposed interface in the periodontium. Together with the underlying connective tissue, the junctional epithelium forms the biologic width, which is generally around 2 mm.

The periodontal ligament is a fibrous connective tissue that fills the narrow space between the root cementum and the alveolar bone. Its collagen fibers are arranged in named groups, including alveolar crest, horizontal, oblique, apical and interradicular fibers. The oblique group is the largest and carries most of the vertical load. The ends of the fibers are embedded in cementum and bone, which suspends the tooth within its socket. The ligament contains fibroblasts, cementoblasts, osteoblasts, epithelial rests of Malassez and progenitor cells. It is richly vascularized and innervated. Its hydrated matrix and fluid give it viscoelastic properties, so it cushions occlusal forces and allows a small physiological tooth movement. Its mechanoreceptors also signal the magnitude and direction of force, which helps regulate chewing.

Probing depth (PD) and clinical attachment level (CAL) are measured with a calibrated periodontal probe at several sites around each tooth. PD is the distance from the gingival margin to the base of the sulcus or pocket. CAL is the distance from a fixed reference point, the cemento-enamel junction (CEJ), to the base of the pocket. When the gingival margin lies apical to the CEJ, recession is added: CAL equals PD plus recession. For example, a site with 2 mm of recession and a 5 mm probing depth has a CAL of 7 mm. The two measurements reflect different tissue changes. PD is strongly influenced by gingival swelling, inflammation and the position of the margin, so gingival enlargement can increase PD without any loss of attachment. CAL reflects the cumulative history of attachment loss, which is largely irreversible unless tissue is regenerated. Recession can increase CAL without any change in PD. Probe force, probe angulation and inflamed tissue all affect readings, and restorations or caries can obscure the CEJ, so measurements from different examiners or visits can vary.

Dental biofilm and microbial dysbiosis

Periodontitis begins with the accumulation of a multispecies biofilm on tooth crowns and, below the gingival margin, on root surfaces. In health, this community is dominated by Gram-positive, facultative and aerobic species such as streptococci and actinomyces. Over time, the subgingival environment changes. As plaque matures and oxygen tension decreases, the environment shifts to favour anaerobes. Clinical samples from patients with periodontitis show the same direction of change. In juvenile periodontitis, for example, the subgingival biofilm typically carries more obligately anaerobic, asaccharolytic Gram-negative organisms and fewer beneficial Gram-positive species. Health-associated communities are thought to keep the local redox balance favourable, whereas the pathogens tend to be obligate anaerobes that ferment sugars or proteins.

Key pathogens and the red complex

Sigmund Socransky's group sorted subgingival species into colour-coded complexes in the late twentieth century. The best-known grouping is the red complex, which consists of Treponema denticola, Porphyromonas gingivalis and Tannerella forsythia. These species are often found together in deep pockets. Socransky's analyses also linked the red complex more closely to the orange complex, which includes Fusobacterium nucleatum and Prevotella intermedia, than to the other groups. Aggregatibacter actinomycetemcomitans, which is more strongly associated with aggressive forms of the disease, lies outside the red complex and is usually discussed separately.

The red-complex species appear to function as an interdependent consortium. The red complex organisms are highly dependent on each other for proliferation and virulence. Physical attachment helps this cooperation: T. forsythia and P. gingivalis attach to T. denticola, the only motile member of the complex, and are carried along with it. Individual species also depend on the wider community. In experimental work, germ-free animals challenged with P. gingivalis did not develop gingival inflammation or alveolar bone loss, which suggests that the pathogen requires a resident microbiota to cause disease.

The keystone-pathogen concept

In ecology, a keystone species is one whose influence on a community is larger than its abundance would predict. A keystone species plays a critical role in maintaining the structure of an ecological community, and its impact on the community is greater than would be expected based on its relative abundance. P. gingivalis was proposed as a keystone pathogen on this basis. At abundances below 0.01% of the oral microbiota, it strongly altered the growth of other bacteria and promoted inflammation.

The proposed mechanism centres on the host complement system. P. gingivalis gingipains act as a C5 convertase-like enzyme that cleaves complement component C5, generating high levels of C5a locally. Signalling through the C5a receptor, which cross-talks with Toll-like receptor 2, impairs leukocyte killing. In the same line of work, blocking the C5a receptor promoted clearance of P. gingivalis and negated its dysbiotic effects, which indicated that the community effect was reversible. The keystone model remains debated. Newer frameworks have moved beyond pathogen-centred explanations, but this makes it harder to identify microbial signatures that predict progression.

Ecological and metabolic reprogramming

Philip Marsh's ecological plaque hypothesis, put forward in the late 1990s, proposed that health reflects a homeostatic balance between host and microbiota, and disease arises when an imbalance develops in the interaction between the two, driven by changes in their microenvironment. The later polymicrobial synergy and dysbiosis model, developed by George Hajishengallis and Richard Lamont, holds that different bacterial members, or combinations of them, fill distinct roles that together shape and stabilise a disease-provoking microbiota.

Recent reviews place more weight on function than on any single species. They argue that disease progression is critically associated with ecological disruption and functional reprogramming of the subgingival microbial community, rather than solely with enrichment of specific pathogens. Reprogramming changes the metabolic output of the community. It can alter the production of short-chain fatty acids, amino acid metabolites, polyamines, sulfur compounds, and other bioactive molecules that influence host immunity and tissue homeostasis. In one proposed framework, hydrogen sulphide and polyamines are regarded as toxic to host tissue, and impaired nitrate reduction is thought to sustain destruction. Metabolic exchange between species is also important. Experimental evidence suggests that inter-microbial exchange of metabolic products and gene expression is necessary to raise biomass virulence enough to induce disease, which weakly virulent species cannot achieve alone.

Finally, the model that links these processes to inflammation treats the host response as a driver rather than a bystander. The IMPEDE model identifies inflammation as the driving force behind periodontal dysbiosis. Because inflammation and dysbiosis reinforce each other, regardless of which came first, the initial trigger is difficult to isolate in clinical samples.

Host immune-inflammatory response and tissue destruction

Tissue loss in periodontitis is mainly produced by the host's own reaction to the subgingival microbiota. The pathogenic processes of destructive inflammatory periodontal diseases are instigated by subgingival plaque microflora and factors such as lipopolysaccharides derived from specific pathogens. Those bacterial products are recognized by resident and recruited cells, and the response they trigger is what damages the connective tissue and alveolar bone.

The innate arm begins with neutrophils and macrophages, which are attracted to the gingiva and release proinflammatory cytokines. The resultant influx of inflammatory cells produces a host of cytokines, for example, PGE2, IL-1, and RANK-L, that promote resorption through osteoclasts. TNF-α, IL-1 and IL-6 are the cytokines most often named in this context. Neutrophil accumulation is also functionally important: in a murine model, T_H17 cells and associated neutrophil accumulation were necessary for inflammatory tissue destruction in experimental periodontitis. Macrophage-lineage cells contribute further because osteoclasts themselves arise from monocyte/macrophage precursors under the regulation of the critical cytokines macrophage colony-stimulating factor, RANK ligand, and osteoprotegerin.

The adaptive immune response adds a more specific, and in many respects more damaging, layer. Th17 cells are a central effector population. In humans, an expansion of resident memory T helper 17 (T_H17) cells has been observed in periodontitis, and in mice this expansion depended on the dysbiotic microbiome and required both IL-6 and IL-23. Th17 cells produce IL-17, which recruits neutrophils and sustains inflammation. Opposing them, regulatory T cells normally restrain inflammation through IL-10 and TGF-β, but under chronic inflammation they can lose function. Tregs may become unstable and dysfunctional under inflammatory conditions, which can even accelerate tissue destruction. The resulting Th17/Treg imbalance is often described as a key driver of alveolar bone loss. B cells and plasma cells also infiltrate diseased tissue. They produce antibodies against periodontal pathogens, which can limit inflammation, but they also release cytokines such as IL-6 and RANKL, and so contribute to tissue degradation. The balance between these protective and destructive activities differs across individuals and lesions.

Bone resorption is largely governed by the RANK–RANKL–osteoprotegerin (OPG) axis. Osteoclast differentiation and activation depend on the interaction of RANK (receptor activator of nuclear factor-kB) with its ligand, RANKL. OPG acts as a decoy: it is a decoy receptor of RANKL that inhibits RANK-RANKL engagement. Under inflammatory stimulation the balance shifts, since the RANKL/OPG ratio increases in periodontal and periapical tissues and leads to stimulation of osteoclast activity and pathologic bone resorption. Structural cells also contribute. Osteocytes, osteoblasts, and periodontal ligament cells significantly contribute to osteoclastogenesis during periodontitis by translating inflammatory signals into RANKL overexpression, often paired with OPG downregulation. Cytokines add to this process: TNF-α can promote osteoclastogenesis independently of RANKL, and other cytokines act by raising RANKL expression.

Collagen and other extracellular matrix components are degraded largely by matrix metalloproteinases (MMPs). The 23 existing MMPs are zinc-dependent endopeptidases that belong to the metalloproteinase superfamily. Their activity is normally tightly controlled, including by endogenous inhibitors, such as tissue inhibitors of MMPs (TIMPs). In periodontitis, that control is lost: MMP activity is up-regulated to an extent far exceeding the regulatory control. Neutrophils are a major source of MMP-8 and related enzymes. The inflammation–MMP link also forms a self-reinforcing cycle: cytokines raise MMP expression, MMP-mediated matrix breakdown releases fragments and exposes tissue to further microbial and immune attack, and the ongoing inflammation keeps the cycle running. These proinflammatory cytokines are thought to generate an amplification loop that contributes to periodontal and periapical lesion progression.

Inflammation in a healthy periodontium is normally terminated by an active resolution program. This program is driven by specialized pro-resolving mediators (SPMs), which include resolvins and lipoxins, that are biosynthesized from omega-3 and omega-6 polyunsaturated fatty acids and serve as key molecular drivers of the resolution phase. Unlike conventional anti-inflammatory drugs, SPMs do not suppress host defense; they stop inflammation and support tissue repair. In periodontitis, the picture appears to be one of failed resolution rather than simply excessive initiation. Studies have found elevated SPM pathway markers in untreated periodontitis gingiva, while the receptors needed to respond to these mediators were deficient, which suggests that failure of resolution of inflammation contributes to excess, chronic inflammation in periodontitis. Resolvins and lipoxins also appear to act differently on the same cells: in localized aggressive periodontitis, neutrophils responded to resolvins but not to lipoxins, and a resolvin (RvE1) reversed several in vitro defects. Together these findings support the view that periodontitis can be more precisely described as a disorder of failed inflammatory resolution.

Risk factors and modifiers

Plaque accumulation and local retention

Bacterial biofilm on the tooth surface is the initiating condition in nearly every case, and the amount of plaque that persists at and below the gumline sets the microbial load the host must respond to. Inadequate self-performed plaque control is recognized as a risk factor for periodontitis, and it is linked to gingival bleeding and halitosis. Plaque control is therefore the most fundamental modifiable factor. Local features that make cleaning difficult also matter. Dental calculus, anatomical abnormalities, malocclusion, and poor restorations are among the general and local factors recognized in the literature, and each can shelter plaque and raise the chance that bacterial products reach the supporting tissues.

Smoking

Tobacco use is the environmental exposure most consistently linked to periodontitis. Smoking is considered the major environmental risk factor for periodontal diseases, and smokers show a higher risk of severe periodontitis, with more tissue destruction, more gingival recession, and greater susceptibility to tooth loss. A systematic review estimated that smoking increases the risk of periodontitis by 85% (risk ratio 1.85, 95% confidence interval 1.5–2.2), while the magnitude of relative risk across individual studies varies from 1.4 to 5.0.

The association is graded rather than all-or-nothing. Both the number of cigarettes smoked and the duration of smoking are positively associated with disease risk. A study of young people with aggressive disease reported that the effect appears to be dose related and is independent of levels of plaque accumulation, which suggests that smoking adds risk beyond what plaque alone explains. Proposed mechanisms include reduced gingival perfusion, suppression of the immune response, impaired regeneration of the periodontium, and dysbiosis that increases the infectivity of the oral microbiota. Smoking also alters the composition of subgingival plaque, which is one proposed route by which it shifts the microbial ecology toward disease.

Smoking also affects the response to treatment. Smokers with periodontitis show less probing depth reduction and clinical attachment level gain than non-smokers after nonsurgical periodontal therapy. In a small retrospective case-control study with mean follow-up of about 3.4 years, smokers had pocket reductions that were significantly less pronounced, and smokers presented a higher risk for periodontitis progression. Reviews have described outcomes for smokers as 50–75% worse than for nonsmokers, although such figures depend heavily on the outcome measured. Smoking cessation can reduce probing depths and improve clinical attachment after nonsurgical periodontal therapy.

Diabetes and glycemic control

Diabetes and periodontitis are linked in both directions. Because periodontitis operates within the same chronic inflammatory framework seen in cardiovascular disease and diabetes, several studies have proposed a bidirectional relationship between periodontal health and these conditions. Within type 2 diabetes populations, the effect of smoking is pronounced. In a study of diabetic patients, pocket formation, calculus, increased tooth mobility and tooth loss occurred with greater frequency in smokers with diabetes than in non-smokers with diabetes. A Brazilian cross-sectional study of 102 patients reported that diabetes mellitus induced a general pro-inflammatory state, while smoking promoted immunosuppression in periodontal tissues, which suggests that the two factors act through different immunological routes. Poor glycemic control is generally associated with more severe periodontal breakdown and a weaker response to therapy, though the strength of this relationship varies between studies.

Genetic variation

Susceptibility has a heritable component, most clearly in the inflammatory genes that govern the host response. The identification of a specific IL-1 family genotype that correlates with the severity of periodontitis suggests that genetic mechanisms determine the intensity of the immunoinflammatory response in different individuals. In one cross-sectional study of 123 patients with generalized chronic periodontitis, 60 with generalized aggressive periodontitis, and 20 controls, the presence of a polymorphism in IL-1A and/or IL-1B was associated with a higher likelihood of periodontitis, although the likelihood was reduced when an IL-1RN polymorphism was also present. The evidence is inconsistent overall. Some variants that appear protective or harmful in one population show no association in another, and the IL-1β rs1143627 polymorphism is not related to periodontal disease susceptibility in the overall population based on the current evidence. Aggressive forms have been studied in family pedigrees, and several family-based studies demonstrated that aggressive periodontitis is an autosomal recessive disorder, although this interpretation is not universally accepted.

Age, obesity, psychological stress, and other systemic factors

Age is among the most consistently reported correlates of periodontitis. In a clinic-based study, periodontitis was significantly associated with smoking, diabetes, hypertension and age. Cumulative exposure to plaque and to smoking partly explains this pattern, and in a three-year follow-up study regression analysis did not demonstrate other influences of demographic and periodontal treatment characteristics on treatment outcomes, except patient age. Reviews also list age, poor oral hygiene, smoking, obesity, socioeconomic status, and chronic conditions such as cardiovascular disease, osteoporosis, and diabetes among factors associated with periodontal disease. Obesity is thought to add to the systemic inflammatory load, but its independent effect is difficult to separate from diet, glycemia, and smoking. Psychological stress has been studied as a modifier through stress-related hormonal and immune changes, but the evidence is less consistent than for smoking or diabetes. Most of these modifiers act on susceptibility and progression rather than initiation, and their effects are usually expressed through the inflammatory response to the same plaque-associated microbial challenge.

Clinical features and natural course

Early and visible signs

Early periodontitis is often painless and easy to miss. The most common finding is gingival inflammation, which appears as redness, swelling and a tendency to bleed. Bleeding on probing is a more sensitive marker than visible change, and in one examined cohort of patients with generalized chronic periodontitis, bleeding at one or more sites was recorded on 67% of the examined teeth.

Pocket formation is the apical extension of the sulcus or pocket beyond its normal depth. Gingival recession, in which the margin moves apically and exposes root surface, often occurs alongside attachment loss. For this reason, a pocket depth reading alone can misrepresent the amount of tissue lost. Recession must be added to the probing depth to obtain the attachment level, so the two measures capture different processes: pocket depth reflects inflammation and tissue swelling as well as loss, while attachment level reflects cumulative loss of support.

Attachment loss, furcation involvement and mobility

Clinical attachment loss is the distance from the cementoenamel junction to the base of the pocket. It is cumulative and does not spontaneously recover. Multirooted teeth are particularly vulnerable. Furcation defects develop when inflammatory alveolar bone resorption extends apically beyond the root trunk of multirooted teeth, exposing the complex interradicular space. Furcation involvement is graded from 0 to 3, with grade 3 denoting through-and-through destruction. Molars with furcation involvement are more likely to be lost, and the risk appears to increase with the severity of the furcation defect.

Furcation involvement is also dynamic. In a multicentre retrospective cohort of 3924 patients with periodontitis and at least 1 year of follow-up, over a mean follow-up of 4.7 years, 57.1% of patients experienced furcation progression, with a median time to the first event of 3.6 years. The strongest predictor of a tooth's future deterioration was its own initial furcation grade, while smoking, diabetes, and overall periodontal health were significant predictors of progression.

Tooth mobility develops as the alveolar bone supporting the root diminishes, and it is a critical clinical sign linked to a poorer prognosis. Mobility is graded by degree, and higher degrees are weighted heavily in staging because they signal secondary occlusal trauma. Tooth migration, including drifting and flaring of teeth into spaces left by lost neighbours, accompanies advanced disease and disrupts occlusal contacts and chewing.

Non-linear progression

Periodontitis does not advance at a constant pace. Most sites remain stable for long periods, while others undergo episodes of rapid attachment loss, and the same patient can show both patterns in different areas of the dentition. These bursts of activity are separated by remission, and the timing of activity is difficult to predict from a single examination. Individuals differ widely in overall rate because of differences in plaque control, smoking, glycaemic control, genetic variation in inflammatory pathways, and age. Within a single mouth, the local morphology of roots, furcations and restorations also affects which teeth are most at risk.

Late-stage symptoms and tooth loss

Pain is often a late event. In the same cohort of patients with generalized chronic periodontitis, the majority of the teeth were not associated with discomfort (92%), which indicates that many teeth with advanced destruction remain asymptomatic. When symptoms do appear, they may include spontaneous pain, tenderness on biting, and sensitivity from exposed roots. Periodontal abscesses form when purulent exudate becomes trapped in a deep pocket, and they can cause swelling and rapid bone loss. Infection can also spread through the furcation to the pulp, a complication that often has a poor prognosis and the affected tooth is generally extracted.

As support declines, chewing efficiency falls, food impaction between teeth becomes more frequent, and occlusal forces may be transmitted unevenly. Tooth loss is the usual terminal outcome. Its timing depends on the extent of furcation and mobility, the response to treatment, and the presence of modifiable risk factors.

Diagnosis and differential diagnosis

Clinical examination and probing

Diagnosis starts with a clinical examination in which the soft tissues are inspected and a periodontal probe is used. Probing parameters include bleeding on probing (BOP), probing pocket depth (PPD) and clinical attachment level (CAL). These probing methods are considered the standard of care for diagnosing periodontal disease. Clinical guidance generally calls for a full-mouth examination in adults, with six measurements per tooth: three on the facial surface and three on the lingual surface.

PPD and CAL measure different things. Clinical attachment level is measured in relation to the cemento-enamel junction (CEJ). Probing depth alone can mislead, because the sulcus depth usually ranges between 1 and 3 mm irrespective of the level of clinical attachment. So-called pseudopockets may be present in cases of increased probing depth without concomitant loss of clinical attachment and alveolar bone. PPD is indirectly a measure of the inflammatory burden of the patient, whereas CAL documents the extent and severity of the periodontal lesion. Where gingival recession is present, attachment level is the sum of probing depth and recession, so a site with a 2 mm pocket and 3 mm of recession has a CAL of 5 mm.

Gingival inflammation is useful but incomplete evidence. Periodontal pockets and other symptoms can be present without the telltale signs of gingival inflammation. Bleeding also carries prognostic information: in one long-term study, a BOP of 25% was the cutoff point between patients with maintained periodontal stability and those with recurrent disease after 4 years. Under the current case definitions, interdental clinical attachment loss detectable at two or more non-adjacent teeth, or buccal or oral attachment loss of 3 mm or more with pocketing of 3 mm or more at two or more teeth, establishes periodontitis.

Radiographic assessment

Radiographs add information on bone, which probing cannot directly show. Periapical and bitewing radiographs are considered the gold standard for assessing periodontal bone level and destruction pattern. Their limitations are substantial. Two-dimensional intraoral radiography is difficult to standardize geometrically, and superimposition and distortion of relevant structures can lead to underestimation of the size and presence of bony defects. Lingually located and funnel-shaped defects are difficult to detect in 2D radiographs. Panoramic films cover a wider field but have lower resolution for individual teeth, making them more prone to distortion, overlapping structures, and blurred dental edges. Intraoral views also tend to underestimate bone loss, while radiographic assessment of severe osseous destruction was shown to overestimate actual bone loss. In comparative studies, cone-beam computed tomography (CBCT) has a sensitivity of 80% to 100% in the detection and classification of bone defects, while intraoral radiographs present a sensitivity of 63% to 67%. Automated detection of bone loss on 2D images is being explored, but a 2024-era systematic review found that many works use different imaging protocols and X-ray equipment, introducing variability into the data and limiting reproducibility. For this reason, a complete diagnosis requires reviewing the clinical and radiographic data together, including the patient's history, probing depth, clinical attachment loss, bleeding on probing, and tooth mobility.

Differential diagnosis

Several conditions can mimic periodontitis, and the most difficult is the endodontic-periodontal lesion. Because the root canal system and periodontium are interconnected, determining the precise etiology of an endodontic-periodontal lesion can be challenging, as these lesions can present with similar signs and symptoms. Pulp vitality is the first step: if the tooth has not been previously endodontically treated, the clinician should perform pulp sensibility testing.

Vertical root fracture (VRF) is a key mimic. Classic features include a previously endodontically treated tooth, a J-shaped or "halo" radiolucency, a deep isolated periodontal pocket, and a coronally located sinus tract. However, there are no typical hallmark signs or symptoms associated with VRFs, and the clinical signs, symptoms and radiographic appearance of VRFs frequently resemble endodontic failure or periodontal disease. Because primary endodontic lesions may mimic the appearance of vertical root fractures, a fracture is harder to exclude when a root-filled tooth has persistent disease. Some studies have reported that CBCT, which allows the lesion shape to be examined in three dimensions, can separate VRF from non-VRF lesions with good accuracy, although cone beam computed tomography has a low specificity for visualization of such fractures, and in some cases the diagnosis is confirmed only at surgery, as in a case report in which vertical root fracture of the mesial root was diagnosed with the help of an exploratory flap and microscopic observation.

Other differentials are managed on general clinical grounds. Subgingival caries or overhanging restorations at the margin can create localized deep defects that resemble a periodontal pocket; these are identified by probing around the margin, inspecting the tooth crown, and checking the radiograph for a lesion that does not follow the expected bone-loss pattern. Necrotizing periodontal disease is distinguished by its acute, painful course with necrosis of the interdental papillae and ulceration, and is classified separately from chronic periodontitis.

Establishing progression

A single examination shows the present extent of disease but says little about its rate. Serial records are therefore essential. In one definition used in longitudinal studies, progression of periodontal disease is defined by a clinical attachment loss (CAL) of 2mm or more. Historical diagnosis also depends on attachment loss that can be attributed to periodontal rather than non-periodontal causes; in one 2017-based case definition, presence of periodontitis was detected as clinical attachment loss (CAL) with reference to the cemento-enamel junction (CEJ) not ascribed to non-periodontal causes. Prior charts and radiographs therefore allow clinicians to compare attachment levels and bone heights over time, and tooth-loss history helps separate periodontal from non-periodontal causes; tooth loss due to periodontitis is one of the variables used in staging.

Classification: 2017 staging and grading

From chronic and aggressive categories to a single framework

The 2017 World Workshop replaced the 1999 division into chronic and aggressive periodontitis with one category. Forms of the disease previously recognized as "chronic" or "aggressive" are now grouped under a single category ("periodontitis") and are further characterized by a multidimensional staging and grading system. The term "aggressive periodontitis" was dropped, and the system relies mainly on attachment and bone loss. It classifies the disease into four stages based on severity (I, II, III or IV) and three grades based on disease susceptibility (A, B or C). A complete diagnosis has three components: extent, stage, and grade.

Stage: severity and complexity

Staging is driven by how severe the disease is at presentation and how complex its management will be. The main criteria are interdental clinical attachment loss (CAL), radiographic bone loss (RBL), and tooth loss. In outline:

• Stage I (early/mild): CAL of 1–2 mm, with radiographic bone loss under 15% or under 2 mm, mostly in the coronal third of the root.
• Stage II (moderate): CAL of 3–4 mm, with bone loss extending into the middle third of the root, and probing depths generally of 5 mm or less.
• Stage III (severe): CAL of 5 mm or more, with bone loss reaching the apical third, and complicating features such as probing depths of 6 mm or more, vertical defects, or furcation involvement. Tooth loss of up to four teeth is typical of this stage.
• Stage IV (very severe): All Stage III features, plus needs for complex rehabilitation such as masticatory dysfunction, secondary occlusal trauma, bite collapse, or pathological tooth migration. Tooth loss of five or more teeth is one marker, and fewer than 20 remaining teeth is another.

Complexity is weighted heavily. It takes only one complexity factor to shift the diagnosis to a higher stage. A stage-raising factor that is later removed by treatment does not move the diagnosis back down, so the stage records the disease's history as well as its current state.

Grade: rate of progression and risk

Grading gives supplemental biological information. Grading provides supplemental information about biological features of the disease including a history-based analysis of the rate of periodontitis progression; assessment of the risk for further progression, and the likelihood of poor treatment outcomes or harm to general health. The primary criteria are either direct or indirect evidence of progression.

Direct evidence is documented loss of attachment or bone over time, usually compared with earlier charts and radiographs. Where that history is missing, indirect evidence is used, mainly the ratio of percentage radiographic bone loss to the patient's age. In the 2017 framework, a ratio below 0.25 corresponds to Grade A, 0.25 to 1.0 to Grade B, and above 1.0 to Grade C. The British Society of Periodontology's simplified implementation uses different cut-offs, with Grade A below 0.5, Grade B from 0.5 to 1.5, and Grade C above 1.5. Risk factors, such as cigarette or vape smoking and diabetes, have been described and are considered as grade modifiers. In practice, the presence of smoking or poorly controlled diabetes can move a case toward a higher grade. A Grade A patient, for example, is someone with no measurable loss over several years, no smoking, and no diabetes.

Extent and the default grade

Extent describes how much of the dentition is affected. Localized periodontitis is defined as fewer than 30% of teeth showing the characteristics of periodontitis, and generalized as 30% or more. A molar/incisor pattern is recorded separately, and it is used in particular for early-onset disease that mainly affects first molars and incisors.

Clinicians are advised to assume Grade B disease until evidence supports moving the case to Grade A or Grade C. Once a grade is set, it can be changed as current risk factors are reassessed.

Use in practice and validation

The framework was designed for routine clinical use, because most periodontal disease is diagnosed and managed in general practice rather than in specialist settings. Its uptake has been uneven. In one review of dental records at a periodontics clinic, 100% of patients previously diagnosed with aggressive periodontitis were reclassified as grade C, while chronic cases spread across grades A, B, and C. Prognostic validation has been encouraging. In a cohort of 270 treated patients, the overall prognostic performance of the two systems was excellent, with both systems having a Harrell C index score of >0.92. The same study found that the 2017 extent category was less predictive than the simplified British version, and that the "localized" class carried a better prognosis than "generalized."

Peri-implantitis and related conditions

Peri-implant mucositis and peri-implantitis

Peri-implant diseases are inflammatory conditions affecting the tissues around dental implants. In the 2017 World Workshop classification, peri-implant mucositis is inflammation of the peri-implant mucosa, with bleeding on gentle probing as its main clinical sign and no progressive loss of supporting bone. Erythema, swelling, or suppuration may also be present. Peri-implantitis is defined as a plaque-associated pathological condition in which inflammation of the peri-implant mucosa is followed by progressive loss of supporting bone. Diagnosis rests on signs of inflammation, bleeding or suppuration, increased probing depth or mucosal recession, and radiographic bone loss.

The two conditions parallel gingivitis and periodontitis. Mucositis is assumed to precede peri-implantitis, but not every mucositis site progresses. Data indicate that progression is more likely when regular maintenance care is absent. Peri-implantitis is reported to advance faster than periodontitis, and its lesions extend apically beyond the junctional or pocket epithelium and are larger than those seen at mucositis and periodontitis sites. The 2017 consensus described peri-implantitis as an inflammatory process of microbial origin that causes bone loss, with poor plaque control and a history of periodontitis proposed as co-drivers. Not all lesions that resemble peri-implantitis are plaque-induced at onset; some may initially arise from other causes and become colonized by oral microflora later. A 2025 systematic review and meta-analysis that applied the 2017 criteria estimated that about two in three adults with implants had peri-implant mucositis and about one in four had peri-implantitis.

Anatomical and host-response differences from natural teeth

A natural tooth is surrounded by a collagen-rich periodontal ligament and anchored to cementum, whereas an implant is held directly by bone in contact with its surface. The implant therefore lacks a periodontal ligament, cementum, and the ligament's shock-absorbing and proprioceptive functions, so occlusal loads are transmitted directly to the bone. The peri-implant soft tissue forms a barrier with fewer blood vessels and collagen fibers that run roughly parallel to the implant surface rather than perpendicular to it, which is commonly cited as a reason why the seal is less resistant to bacterial invasion than the junctional epithelium of a tooth. Implant designs, surface characteristics, and loading protocols vary widely, and the 2017 case definitions were written with this in mind.

These differences change diagnosis. Health cannot be defined by a probing-depth range, because peri-implant health can exist around implants with reduced bone support and deep probing readings. Clinicians therefore depend more on bleeding on probing, serial radiographs, and the trajectory of bone loss. Anatomical differences also affect treatment, since implant surfaces are harder to debride and decontaminate than root surfaces, and the choice between non-surgical and surgical management depends on the extent of bone loss and the implant's accessibility.

Classification framework and related conditions

Before 2017, consensus on parameters for classifying peri-implant diseases did not exist, and diagnosis was marked by uncertainty. The 2017 classification was the first to include peri-implant conditions within the same framework as periodontal diseases. Its peri-implant category recognizes four states: peri-implant health, peri-implant mucositis, peri-implantitis, and peri-implant soft and hard tissue deficiencies. The case definitions were designed for use both in routine clinical practice and in epidemiological and disease-surveillance studies.

Within the same classification, periodontitis is recognized as a manifestation of systemic disease, which places it within the broader disease context and reflects the link between periodontal and systemic health. Necrotizing periodontal disease is listed as a separate category, because its clinical course, tissue involvement, and management differ from those of plaque-associated periodontitis. Its place in the framework allows clinicians to distinguish it from both natural-tooth and implant-associated inflammatory disease. This unified approach enables a single diagnostic language across natural teeth and implants, although the authors of the consensus stressed that case definitions should be applied with awareness of implant design variability.

Epidemiology and global burden

Severe periodontitis is among the most widespread chronic conditions in the world. In 2021, over 1 billion people worldwide had severe periodontitis, with a global age-standardized prevalence of 12.50%, and there were nearly 90 million new cases. Earlier estimates from a 2010 systematic review were lower but of the same order: SP was then the sixth-most prevalent condition, affecting 10.8% of people, or 743 million. The difference reflects changes in population size and methods as much as in disease occurrence. The GBD 2021 analysis itself notes that its case definition, based mainly on the CPITN index, is considered unreliable, which may lead to underestimation. The GBD study uses a diverse case definition for severe periodontitis, primarily based on the CPITN assessment, which is considered unreliable (non-confident definition). This raises concerns about the accuracy of the prevalence data, potentially leading to underestimation.

Prevalence rises with age, but the peak is not at the oldest ages. In 2021, the prevalence of severe periodontitis peaked among people between 50 and 64. Survey-based data show a broader pattern: nearly half of adults and over 60% of those aged 65 years or older exhibited periodontitis, although these figures cover periodontitis in any form rather than only the severe stage. Because the disease accumulates over decades, older cohorts carry the cumulative consequences of earlier attachment loss.

Geographic and socioeconomic gradients are pronounced. South Asia demonstrated the highest number and age-standardized rates of incidence, prevalence, and DALYs. At the level of development indices, the low-middle SDI region reported the highest ASPR, at 15,252.3 per 100,000. The GBD 2021 data also show that the age-standardized prevalence exceeded 20% in 12 countries, most of which were from Sub-Saharan Africa. Among high-income countries, the pattern is less uniform, with Denmark standing out in the same analysis. Within countries, the gradient follows income and education. The prevalence of periodontitis is notably higher in low- and middle-income countries, attributed to factors like inadequate oral hygiene, limited access to dental care, and lifestyle influences. Several analyses report that inequality has widened over time: the slope index of inequality for severe periodontitis prevalence rose from about 2,130 in 1990 to about 7,198 in 2021 in one cross-country analysis.

Tooth loss is the principal population-level outcome. Severe periodontal disease is the primary cause of multiple tooth loss and missing teeth in adults. Because the disease is concentrated in later adulthood, its population impact grows in aging societies. In the United States, approximately 40% of adults aged 65 and older experience significant tooth loss, with about 13% who have lost all of their teeth, according to National Health and Nutrition Examination Survey data. Projections based on GBD 2021 estimate that by 2050, more than 1.5 billion people are projected to have severe periodontitis, and over 660 million to be edentulous. The projected rise is driven mainly by demographic change, since age-standardized rates are expected to remain relatively stable.

Global Burden of Disease studies quantify health loss through years lived with disability and disability-adjusted life years, allowing comparison with other conditions. Globally, there were 6.90 million YLDs attributable to severe periodontitis in 2021, with an age-standardized YLD rate of 80.89 per 100,000. Results also show that the burden is not confined to periodontitis. In the broader GBD 2019 oral disorders analysis, oral disorders, including dental caries, periodontitis, and tooth loss, affected more than 44.5% of the global population. At the national level, the GBD 2019 estimates for Brazil indicated that all oral diseases combined ranked eighth among all causes of disability. Because these estimates depend on modelled inputs and case definitions that differ across countries and periods, they are most informative for comparing trends and relative burden rather than for estimating exact counts.

Historical understanding and research milestones

For much of recorded history, explanations of gum disease rested on bodily humours and general constitutional causes. In the nineteenth century, the causes proposed for gingivitis and periodontitis included ageing, circulatory problems, gout, nutritional deficiency, endocrine disturbance, occlusal trauma, and local calculus. Most of these theories were supported by little or no scientific evidence.

From germ theory to the plaque hypothesis

Once bacteria were accepted as agents of infection, the idea took hold that oral microbes were responsible for periodontal disease. After experimental proof of the germ theory of disease was provided in 1876, some investigators, including Willoughby D. Miller, believed that bacteria played an important etiologic role in periodontal diseases. Miller worked in Robert Koch's laboratory in Berlin and proposed a "chemo-parasitic" account in which the mouth's own bacteria could attack dental and gingival tissues. G.V. Black described pyorrhea alveolaris as an infection, caused by an invasion of the peridental membrane by certain infectious organisms. Under this framework, periodontal disease came to be treated as an infection. Germ theory thus shaped both the diagnosis and the treatment of the disease.

The first comprehensive microbial model was the nonspecific plaque hypothesis. Because cultivation methods could not yet separate disease-causing organisms from harmless ones, the accumulation of dental plaque was held responsible for oral disease without discriminating between the levels of virulence of bacteria. This view placed the emphasis on the quantity of bacterial biomass rather than on the identity of individual species. Later, the dental plaque hypothesis became the working explanation, and prevention was built around removing plaque mechanically.

Experimental gingivitis and the proof of causation

Direct human evidence came from the experimental gingivitis studies. In 1965, Löe, Theilade and Jensen asked dentally healthy volunteers to stop oral hygiene for a period of about three weeks. Not brushing for 3 weeks caused gingivitis and a dramatic increase in the number of bacteria colonizing teeth, with changes in the bacterial ecology. When the volunteers resumed cleaning, the inflammation subsided. This reversibility was as important as the onset itself, because it showed that a clear, direct relationship between plaque accumulation and the onset of gingivitis, as well as between plaque removal and the resolution of inflammation existed in the same individuals. Earlier work on beagle dogs at the University of Kentucky had already linked plaque to periodontal breakdown, but the human model provided more direct evidence. The results are often summarised as establishing plaque as the cause of gingival inflammation, although the 1965 model applied to gingivitis rather than to periodontitis itself.

Specific pathogens and the shift toward the host

From the 1970s onward, improved anaerobic culture methods allowed investigators to separate plaque species. The first common hypothesis was the "Specific Plaque Hypothesis" (1976) proposing that only a few species of the total microflora are actively involved in disease. This approach dominated periodontal microbiology for several decades and led to the identification of specific pathogens and complexes, including the red complex. The nonspecific idea was then revised rather than abandoned. The "Non-Specific Plaque Hypothesis" was updated (1986) and the idea that the overall activity of the total microflora could lead to disease, was enriched by taking into account difference in virulence among bacteria.

Later work moved the focus from which microbes are present to how the community and the host respond. The "ecological plaque hypothesis" was introduced, together with an expanded list of potential periodontopathogens, suggesting that the key factor in the disease process was the ecological shift to a dysbiosis. In parallel, researchers noted that the development of periodontitis requires more than a mere increase in the biomass of dental plaque. Some authors went further and proposed that destructive disease reflects the host's response to long-term plaque exposure rather than properties of the biofilm alone. These developments set the stage for the host-response models discussed in later sections.

Prevention and non-surgical mechanical therapy

Daily plaque control at home

Prevention rests on removing dental plaque every day, because bacterial deposits re-accumulate quickly after cleaning. Toothbrushing alone reaches the proximal surfaces poorly, so interproximal cleaning is usually added. A Cochrane review found that floss or interdental brushes used with a toothbrush may reduce gingivitis or plaque more than brushing alone, and that brushes may outperform floss Using floss or interdental brushes in addition to toothbrushing may reduce gingivitis or plaque, or both, more than toothbrushing alone. Interdental brushes may be more effective than floss. An umbrella review of systematic reviews reached a similar ranking, identifying interdental brushes as the most effective device for removing interdental plaque, while most trials found that string floss did little to remove plaque A meta‐review (an umbrella or systematic review) of systematic reviews regarding interdental cleaning concluded that IDBs are the most effective devices for removing interdental plaque and are most appreciated by patients. In the meta‐review, most of the available studies found that flossing was generally ineffective for plaque removal.

The evidence base is strongest for gingival bleeding and gingivitis, and weaker for established periodontitis. A network meta-analysis reported that unsupervised flossing produced no substantial reduction in gingival inflammation, whereas brushes and water-jets ranked near the top for reducing bleeding unsupervised flossing does not yield substantial reduction in gingival inflammation. Among 10 IOH aids, interdental brushes and water-jets ranked high among other aids for reducing gingival bleeding. Cochrane's analysis of periodontitis outcomes, measured by probing depth, did not show a clear difference between interdental brushes and floss though there was no clear difference in bleeding sites. The choice of device therefore depends on the patient's dexterity, the interdental anatomy and the periodontal status, rather than on a single preferred tool.

Professional supragingival cleaning and subgingival debridement

Professional cleaning removes calculus and plaque that the patient cannot clear at home. Its supragingival component targets the crown surfaces and the gum margin, and its subgingival component is most often delivered as scaling and root planing. Scaling removes plaque and calculus from the crown and root, while root planing removes the cementum or dentine that is rough, calculus-laden or contaminated with toxins and microorganisms ScRP is the instrumentation of the crown and root surfaces of teeth to remove plaque, tartar, and stains, as well as, the removal of cementum or surface dentin that is rough, impregnated with calculus or contaminated with toxins and/or microorganisms.

Systematic reviews and randomized trials have repeatedly documented clinical gains within about three months of treatment, although these gains were not seen in every group, notably in patients with milder disease at baseline Evidence from two systematic reviews, 12 randomized-controlled trials, and one non-randomized controlled clinical trial showed that scaling with or without root planing, provided with or without oral hygiene instructions, were associated with improvements in periodontal outcomes across a variety of adult patient populations within three months of treatment. Exceptions to this trend were noted in patients with less severe periodontal disease at baseline and in one study of pregnant women. Long-term data are limited. Microbiological studies show that the subgingival community shifts after debridement but tends to drift back, and that pathogens can reappear within weeks the effects of SRP are short lived, as evidenced by the recolonization of subgingival sites with potential periodontal pathogens 3 weeks after tx. A small split-mouth study of seven patients also found that intensive supragingival plaque control did not change the pattern of subgingival recolonization compared with control sites 7 patients with moderate to severe inflammatory periodontal disease received a full-mouth scaling and subgingival curettage. No difference in the pattern of bacterial recolonization of the subgingival area could be detected between the sites under strict supragingival plaque control and the control sites.

Incomplete debridement is a recognized failure mode. Superficial scaling can allow the gingiva to heal and regain a normal contour, which may give the impression that the disease is controlled while deeper pockets remain active Superficial scaling may allow the gingiva to heal and return to a normal contour and texture, giving patient and clinician the false sense that the periodontal disease is under control and no additional periodontal therapy is required. In reality, the disease continues unabated at the depth of the pocket.

Behaviour change and patient motivation

Mechanical therapy produces lasting benefit only when the patient keeps up daily biofilm control, so motivation is treated as part of the treatment itself. The European Federation of Periodontology treats compliance with oral hygiene routines and healthy lifestyle habits as an integral part of supportive care "In addition," the EFP adds, "compliance with the recommended oral hygiene regimens and healthy lifestyles are part of supportive periodontal care". Reinforcing patient understanding before definitive surgery is also recommended, because adherence to maintenance schedules is often incomplete in published cohorts Motivational techniques and reinforcement of the importance of the maintenance phase of treatment should be considered before performing definitive periodontal surgery. Practitioners often find that simply telling patients to return is insufficient; the purpose of each visit and the tasks expected between visits must be explained clearly. Limits on capacity also matter: older adults with advanced dementia or severe arthritis may be unable to clean effectively, which makes caregiver involvement part of the plan.

Recall visits and prevention of recurrence

After active treatment, patients enter a recall phase in which the periodontium is monitored, reinstruction is given and new plaque or pocket formation is detected early. The European Federation of Periodontology suggests intervals of three to a maximum of twelve months, tailored to each patient's risk profile supportive periodontal care visits should be scheduled at intervals of 3 to a maximum of 12 months and ought to be tailored according to patient's risk profile and periodontal conditions after active therapy. A guideline on chronic periodontitis specifically recommends visits every three to six months supportive periodontal therapy every three to six months for patients with chronic periodontitis. Risk-stratified data point in the same direction: frequent recall at three to six months for moderate- to high-risk patients, and up to twelve months for low-risk patients, is associated with better results Frequent recalls—every 3–6 months for moderate- to high-risk patients and up to 12 months for low-risk—result in significantly better outcomes.

Non-attendance is a major reason for tooth loss in treated patients. One study found that treated patients who did not return for regular recall had about 5.6 times the risk of tooth loss One study found that treated patients who do not return for regular recall are at 5.6 times greater risk for tooth loss. Recurrence is closely tied to residual disease, and non-compliance and residual pockets of 5–6 mm or more are major predictors of recurrence Non-compliance and residual pockets (≥5–6 mm) are major predictors of recurrence.. The optimal interval is still debated: one trial found no significant difference in recurrence between a three-month schedule and an average interval of about 19 months No significant difference in disease recurrence was noted between the two schedules (q3 months or avg q19.4 months)., and systematic reviews describe wide heterogeneity in recommended frequencies. When recurrent disease is found at a recall visit, a new diagnosis and treatment plan are required any patient may need re‐treatment if recurrent disease is detected, and in these situations, a proper diagnosis and treatment plan should be reinstituted.

Antimicrobial and adjunctive pharmacological therapy

Pharmacological measures are added to mechanical debridement, either to reduce the subgingival bacterial load or to dampen the tissue-destroying host response. Their value is usually judged as an increment over scaling and root planing (SRP) alone, so most trials compare an added agent with SRP by itself.

Local antiseptics

Chlorhexidine (CHX) is the most widely used local antiseptic. It is applied as a rinse, as a 1.5% gel in a xanthan gum matrix, or as a bioabsorbable chip that carries 2.5 mg of chlorhexidine gluconate incorporated in the matrix. Its appeal rests on a wide antibacterial range and limited systemic toxicity, and the reviews that support it also note that oral microorganisms have not developed resistance to it. Local agents are generally advised for deeper sites, and one meta-analysis notes that additional local antimicrobials are recommended in patients with a probing depth of ≥ 5 mm.

The early evidence was mixed. A 2006 review of randomized trials found that some studies showed significantly higher pocket reductions and clinical attachment gains with CHX chip placement, but some recent studies failed to confirm the additional value of the chlorhexidine chip. Later meta-analyses of gels and chips report more consistent gains: adding CHX is more effective than scaling and root planing alone, although long-term use can cause extrinsic tooth staining and calculus formation.

Systemic antibiotics

Systemic antibiotics are generally reserved for more severe or refractory disease. The most studied regimen is the combination of amoxicillin and metronidazole. A 2015 systematic review found moderate to strong evidence that adding this combination to SRP improves probing depth and attachment levels, especially in initially deep (≥6 mm) pockets. Its rationale is partly microbiological: the combination suppresses A. actinomycetemcomitans and black pigmented bacteria, which is why it is often preferred for advanced A. actinomycetemcomitans-associated periodontitis. Clinically, the benefit is largest in severe disease. A 2026 retrospective cohort reported that the greatest benefits were seen in severe disease, and that the combination was superior to several monotherapies in head-to-head comparisons, although it is a non-randomized design.

The evidence is less consistent in special populations. A systematic review of trials in patients with type 2 diabetes concluded that the evidence for prescribing this drug combination to patients with diabetes remains insufficient. Network meta-analyses have also ranked agents differently: one reported that minimally important clinical differences were observed following the adjunctive use of satranidazole, metronidazole, and clindamycin for attachment gain, while the network estimates were supported by evidence with certainty ranging from very low to high. Side effects also limit use: vomiting, nausea, and metallic taste associated with metronidazole are cited as reasons for prescribing it only under clear guidance.

Host-modulating agents

Host modulation aims to limit tissue breakdown rather than microbial growth. Sub-antimicrobial dose doxycycline (SDD) is the most extensively studied agent of this type. At a dose of 20 mg twice daily, doxycycline exerts negligible antimicrobial action but significantly inhibits MMP activity, thereby reducing collagen breakdown and connective tissue loss. The rationale came from the observation that tetracyclines inhibit MMP activity at levels considerably lower than those required for antimicrobial activity. Serum concentrations of the 20 mg formulation are low: peak serum levels of 0.3–0.7 μg/mL, and levels below 1 μg/mL are considered too low to have an antibacterial effect. Beyond MMP inhibition, SDD reduces inflammatory cytokine production, decreases osteoclast activity, and limits oxidative stress within periodontal tissues.

The clinical effect is modest. One review estimates approximately 0.3–0.4 mm greater clinical attachment gain beyond scaling and root planning (SRP) alone, along with reduced inflammation. The drug has regulatory approval: low-dose doxycycline is currently the only FDA-approved host-modulating drug specifically indicated as an adjunct to periodontal therapy. Other candidates, including non-steroidal anti-inflammatory drugs and omega-3-derived pro-resolving mediators, remain at the research stage.

Antimicrobial stewardship and resistance

Each systemic antibiotic course carries the general risk of selecting resistant organisms in the oral and systemic microbiota, a concern discussed more fully under antibiotic resistance. The reviews reflect this caution. The network meta-analysis explicitly argued that the use of these antibiotics adjunct to subgingival debridement should be weighed against possible harm to avoid overuse and inappropriate use of these antibiotics in patients with periodontitis. Methodological concerns also arise, since some trials combined antibiotics with other active adjuncts such as chlorhexidine, which may confound the true effect of the adjunctive use of these antibiotics. By contrast, one review states that SDD does not alter oral microbiota and does not lead to antibiotic resistance, which is one reason it is positioned as a non-antibiotic-dose option. Stewardship therefore favors selecting agents by indication, pathogen profile, and disease severity rather than applying systemic antibiotics routinely.

Surgical and regenerative treatment

Surgery is considered when residual periodontal pockets persist after non-surgical debridement, or when deep sites and root morphology cannot be cleaned adequately through the sulcus. The basic procedure is an access flap: the gingiva is reflected, calculus and diseased cementum are removed from the root surface under direct vision, and the flap is repositioned, usually with sutures. This allows debridement of areas that instruments cannot reach otherwise, but the flap by itself does not regrow lost bone or attachment.

Access flaps and regenerative materials for intrabony defects

Intrabony defects, in which bone loss forms a trough that is deeper than the adjacent bone, are the main target of regenerative surgery. Three approaches are common:

• Guided tissue regeneration (GTR) places a biocompatible membrane over the defect. The barrier excludes epithelial cells and allows cells from the periodontal ligament to repopulate the root surface, which is the rationale for membrane use.
• Enamel matrix derivative (EMD) is a gel prepared from the enamel matrix of young pigs. It is placed into the debrided defect and is thought to support the formation of new cementum and ligament.
• Bone grafts, which may be autogenous, allograft, xenograft or synthetic, fill the defect and provide a scaffold for new bone.

A Cochrane review found that EMD improved clinical attachment level by a mean of 1.3 mm and reduced probing depth by 1 mm compared with flap surgery alone, but it found no evidence that more teeth were saved. It found no important difference between EMD and GTR. A later meta-analysis of trials comparing EMD and resorbable membranes with open flap debridement alone reported gains in clinical attachment of roughly 1.3 to 1.4 mm for both regenerative approaches, with no significant difference between them. Results were heterogeneous across studies.

Because EMD is a gel with limited ability to create space, it may be less suitable for non-contained defects, where the surrounding bone walls are incomplete. In these cases, combining it with a bone graft is intended to prevent flap collapse and maintain a space for regeneration. A 2015 meta-analysis of twelve studies (434 patients) found mean attachment gain of about 3.76 mm with EMD plus graft versus about 3.32 mm with EMD alone, although the authors judged that the influence of graft material and flap design remained unclear.

Furcation involvement

Furcation involvement occurs where periodontal breakdown exposes the bifurcation or trifurcation of multirooted teeth, most often molars. Class II furcations, in which the defect does not pass completely through the furcation, respond better to treatment than class III furcations. A Bayesian network meta-analysis of 19 randomized trials (575 patients, 787 defects) found that regenerative surgery produced better furcation closure or conversion to class I than open flap debridement for class II defects, with bone-replacement grafts ranked highest for horizontal bone gain. Complete furcation closure, however, is not a predictable outcome. For class III furcations, histological evidence is very limited; in humans it rests on only two case reports, so regenerative surgery is not considered a reliable option there.

Limits of regeneration and extraction

Regenerative procedures generally produce partial rather than complete restoration. Gains in attachment are modest, long-term evidence on tooth survival is limited, and outcomes depend heavily on patient factors such as smoking and plaque control. When a tooth has severe mobility, extensive bone loss or a poor prognosis, extraction followed by replacement with a dental implant or a fixed prosthesis is the conventional alternative. Implants osseointegrate directly with bone rather than being attached through a periodontal ligament, and so lack its cushioning function, which is one reason tooth preservation is still favored where feasible. Intentional replantation, in which a tooth is extracted, treated endodontically or with root-surface work, and reinserted, has been reported in case series and a cohort of 60 patients followed for 18 months, though ankylosis is frequently the predominant healing outcome. A randomized trial comparing periodontal regeneration with extraction and replacement in teeth with a hopeless prognosis has been registered, but its results are not yet established.

Maintenance, outcomes, and tooth retention

Active periodontal treatment is followed by a long maintenance phase. Supportive periodontal therapy (SPT, also called supportive periodontal care) aims to stabilize tissues after basic or surgical treatment and to lower the risk of re-infection and progression. A typical session includes the components of a routine dental recall visit, along with periodontal re-evaluation, risk assessment, removal of supragingival and subgingival plaque and calculus, and re-treatment of sites where disease has returned. Evidence for SPT rests largely on long-term retrospective studies. The Cochrane review of randomized trials rated the certainty of the evidence as very low in its key comparisons, so the efficacy of specific schedules remains debated.

Recall intervals are generally set by residual risk rather than by a fixed calendar. In a retrospective cohort of 160 patients, reassessed after active therapy and after an average of about 9.5 years of SPT, periodontitis recurred in roughly 18% of low-risk, 42% of moderate-risk and 49% of high-risk patients. Patients with erratic attendance lost significantly more teeth than those who attended consistently, and SPT lasting more than ten years was itself associated with recurrence. A 2021 study of patients at PerioRisk levels 3 and 4 concluded that recall intervals of three to six months could limit long-term tooth loss. For PerioRisk level 5 patients, the authors found that even fully adherent three-month recall did not appear to be effective. A 2022 systematic review of stage III and IV patients reported that only a small proportion lost teeth during long-term SPT, although the prevalence tended to rise over time, and that no single method of managing recurrence was clearly superior.

Outcome measures in maintenance research include probing depth (PD), clinical attachment level (CAL), bleeding on probing (BoP) and tooth survival. Probing depth reflects the depth of a pocket, whereas CAL reflects cumulative attachment loss, so attachment gain and loss over time capture changes that a single PD reading cannot. A 2025 systematic review of randomized trials described active therapy as aimed at reducing probing depth and improving attachment, while strict supportive care is needed to maintain those gains. In a retrospective study of 108 patients re-examined about ten years after active therapy, 135 teeth were lost during SPT, and only 1.8% of sites still measured 6 mm or more in probing depth. Tooth loss is the most patient-relevant endpoint, but it is also the least frequently reported in trials.

Smoking and diabetes are the factors most consistently linked to poor response. A cross-sectional study of 91 patients found that smokers had a higher proportion of severe, generalized periodontitis with rapid progression than non-smokers and former smokers. Among dental implant patients, smoking and regular attendance at a supportive program were both strongly associated with implant survival. Results are not uniform, however. In a secondary analysis of a trial in adults with type 2 diabetes, former smokers showed higher odds of CAL progression than never-smokers, whereas current smokers showed no similar association. In a large database analysis of more than 415,000 patients, the four-year extraction-free survival was lower in patients with type 1 diabetes (51.7%) and type 2 diabetes (54.0% to 57.7%) than in non-diabetic controls (65.9%), and both diabetes types were associated with further tooth loss after treatment. Other studies have found that short-term pocket reduction and attachment gain were largely independent of glycemic control, and that long-term effects remain poorly quantified. A randomized trial in smokers with type 2 diabetes reported improved glycemic control and inflammatory markers at six months after nonsurgical therapy.

Patient-reported outcomes have become a more prominent part of evaluation. Periodontitis is associated with poorer oral health-related quality of life, and the Oral Health Impact Profile (OHIP) is widely used to measure it, although OHIP is not a preference-based instrument and cannot directly support cost-utility analysis. Patients with untreated disease report lower satisfaction than periodontally healthy individuals, and treated patients often report reduced impacts, although some measurable chewing and aesthetic concerns can persist after years of maintenance. Economic evaluations divide the cost of periodontitis into direct treatment expenditure, indirect productivity losses, and intangible burdens such as pain and self-esteem. A 2019 global estimate placed direct treatment costs and productivity losses at US$186 billion and US$142 billion, respectively, although the published versions of the same analysis report different breakdowns, so these figures should be read as approximate.

Associations with systemic health

Diabetes

The best-documented systemic link is with diabetes, and it runs in both directions. One meta-analysis of 53 studies estimated that type 2 diabetes increases the risk of developing periodontitis by 34% and is linked to greater disease severity. In the other direction, higher glycated hemoglobin (HbA1c) is associated with more severe periodontal breakdown and tooth loss, and this pattern appears in both diabetic and non-diabetic people, although some findings remain conflicting. Proposed explanations include shifts in the oral microbiota and a systemic inflammatory state that interferes with insulin action. Intervention studies show that non-surgical periodontal therapy lowers HbA1c, but the effect is modest. In one review of 30 studies, HbA1c fell by about 0.43% 3 to 4 months after periodontal treatment, compared to those receiving routine care or no intervention. Other trials report smaller reductions at six months and a larger one at twelve months. Patients with higher starting HbA1c values appear to gain more, which suggests that the effect depends on baseline glycemic control. Systematic reviews of randomized trials still describe the overall evidence as inconsistent, so it is unclear whether periodontal therapy reliably improves diabetes outcomes.

Cardiovascular disease

The periodontitis–cardiovascular association is the most extensively studied after diabetes. A meta-analysis of 29 studies with more than 57,000 participants found that periodontitis carried a 1.14 to 2.2-fold increased risk for coronary heart disease development. Longitudinal cohorts have reported similar, though smaller, hazard ratios for cardiovascular events after adjustment for conventional risk factors. Two broad mechanisms have been proposed: periodontal pathogens directly invade the bloodstream or indirectly raise the systemic level of inflammatory mediators. Interventional evidence is mixed. In a randomized trial in people with metabolic syndrome, periodontal treatment led to a significant fall in C-reactive protein after nine months. However, trials using hard cardiovascular endpoints remain inconclusive regarding their direct effects on cardiovascular events. Current reviews therefore describe the benefit of periodontal therapy as seen in surrogate markers, not in clinical outcomes such as myocardial infarction or stroke.

Pregnancy and other associations

Adverse pregnancy outcomes, including preterm birth, low birth weight, and preeclampsia, have also been examined. Estimates vary considerably by outcome. One meta-analysis reported an odds ratio of 3.18 for preeclampsia in women with periodontitis. For preterm birth, pooled estimates have ranged from weak (odds ratio about 1.9) to roughly double the risk, and the studies differ in how they define periodontitis. An overview of systematic reviews judged that the evidence was consistent for preterm birth and low birth weight in the reviews with the lowest risk of bias. Biologically, systemic inflammation with raised pro-inflammatory cytokines and matrix metalloproteinase activity, along with the spread of periodontal bacteria to the fetoplacental unit, has been suggested as a pathway. Links to rheumatoid arthritis and cognitive decline have also been explored. It has been proposed that enzymes produced by Porphyromonas gingivalis could contribute to autoantigen formation in rheumatoid arthritis, and some studies of dementia have detected oral bacteria or their products in brain tissue. Evidence for both remains largely observational.

Mechanisms and the problem of causation

The main proposed routes from the mouth to distant sites are bacterial and inflammatory. In the first, gingival ulceration within the periodontal pocket allows bacteria to enter systemic circulation, leading to bacteremia, which may provide an atherogenic stimulus. In the second, locally produced cytokines and other mediators reach the circulation and affect the endothelium and metabolism. A third route involves antibodies raised against periodontal antigens, which may trigger immune cells to release inflammatory molecules within blood vessels. Animal models support a causal role, but these studies, however, are limited in their ability to definitively prove causality. Most human data come from cohort and cross-sectional studies, where positive associations ... may also be influenced by various biases, such as confounding and collider stratification. Smoking, diabetes, and socioeconomic status all affect both periodontitis and systemic disease, and they are only partially captured by statistical adjustment. Periodontitis and cardiovascular disease also share several genetic and environmental risk factors, such as smoking, which makes it difficult to separate shared causes from a direct effect. For these reasons, the associations are generally regarded as biologically plausible but not yet proven to be causal.

Current research and unresolved questions

Ecosystem restoration versus pathogen elimination

Most established therapy aims to remove biofilm mechanically and to lower the load of specific pathogens. Repeated recolonization of treated sites by periodontal bacteria is one reason that approach sometimes fails, and it has prompted interest in new strategies (The frequent recolonization of treated sites by periodontopathogens, as well as microbial resistance emergency calls for new therapeutic approaches for managing periodontitis.). The ecosystem view changes the goal. Dysbiosis is now understood as functional as well as compositional, with shifts toward proteolytic and iron-acquiring pathways that can precede clinical deterioration (longitudinal sequencing and multi-omics approaches indicate that dysbiosis is not only compositional but also functional). Under this framing, a successful intervention would aim to restore a stable, health-associated community rather than simply eradicate a named pathogen. Clinical translation is still limited. Few trials measure community-level outcomes over long periods, and there is no agreed definition of a healthy target community.

Probiotics and bacteriophage therapy

Probiotic adjuncts have been tested mainly in small, short trials. In one pilot randomized trial with a six-week follow-up, the control group showed a PD improvement rate of 17.0% and a CAL improvement of 12.7%, while in the probiotic group both parameters improved by approximately 30%. Another trial reported larger gains when probiotic use was combined with dietary support (PD improved by 41.5% and CAL by 42.7%). Trials comparing a probiotic with azithromycin as an adjunct to scaling and root planing have also been published (the clinical effects of Lactobacillus rhamnosus SP1 or azithromycin as an adjunct to scaling and root planing in patients with stage III periodontitis). Systematic reviews, however, still describe the central question as open, namely whether such adjunct therapy truly improves periodontal disease over the long term (the question of whether the use of this adjunct therapy could improve the periodontal disease remains). Open issues include strain specificity, whether benefits persist after the supplement is stopped, and safety in immunocompromised patients.

Bacteriophage therapy is at an earlier stage. A narrative review argues that for phages to act as adjuncts, they would need to cause the collapse of the dysbiotic bacterial community, thereby resolving inflammation and enabling the reestablishment of a health-associated mutualistic community. The clinical phage evidence cited there comes largely from other infections, such as chronic otitis caused by antibiotic-resistant Pseudomonas aeruginosa (The efficacy and safety of a bacteriophage cocktail treatment for antibiotic resistant Pseudomonas aeruginosa-associated chronic otitis was determined in a controlled double-blind Phase I/II clinical trial). Questions about host-range specificity, emergence of phage resistance, and durability in the subgingival niche remain unresolved.

Artificial intelligence for staging and grading

Automated staging from radiographs is being developed with artificial intelligence and deep learning. One validation study trained three YOLOv8-based models on five hundred panoramic radiographs from patients diagnosed with periodontitis, and the bone level and CEJ detection models achieved high precision (0.95–0.97) and recall (0.94–0.96), while the tooth detection model achieved a precision of approximately 0.82 and a recall of 0.81. These systems rely on the radiographic component of the 2017 scheme. The 2017 system also uses tooth loss, furcation involvement, probing depth, and vertical bone loss, and other factors, including tooth loss and complexity aspects (such as furcation involvement, probing depth, vertical bone loss, and ridge defects), were not evaluated in that study. Performance also varies by image type. A validation study using periapical radiographs reported an overall accuracy of 61.3%, weighted F1-score of 61.3%, and a macro-ROC-AUC of 75.4%, with lower recall for Stages I and II. A meta-analysis found substantial heterogeneity across studies (I²≈96–97%). The authors of the original YOLOv8 study call for larger datasets and validate the system in clinical settings to support large-scale periodontal screening. Integration into practice also requires clinicians to check outputs, as the interface was designed to let them review and adjust outputs if necessary.

Biomarkers for progression and individualized treatment

Biomarker research aims to identify people who will progress before attachment loss is visible. In a longitudinal study of 114 patients with generalized moderate to severe disease, disease progression occurred in 24.6% of subjects (28/114), and the concerted role of salivary matrix metalloproteinase-8, serum biomarkers ... along with levels of Porphryomonas gingivalis and Tannerella forsythia in plaque in predicting progressors was emphasized. Individual markers have performed less well. A salivary study found that the combination of ALT level and the P. gingivalis ratio showed the highest likelihood (p < 0.001, sensitivity 0.40, specificity 0.96, likelihood 11.30). Combining clinical, microbial, and cytokine measures has reached higher sensitivity in some analyses (up to 74% sensitivity for predicting periodontitis progression). Many candidates remain unvalidated. Longitudinal data on salivary bacterial counts are still lacking, and no single biomarker has been shown to combine high sensitivity and specificity. Proposed point-of-care panels based on MMP-8, calprotectin, and cytokines are at an early stage. Using such markers to select individual treatment intensity is an aim rather than an established practice.

Causal links with systemic disease

Biomarker studies are often conducted in the same populations in which periodontitis has been linked to systemic conditions. Whether shared inflammatory or microbial signals reflect a causal pathway, or confounding by smoking, diabetes, and socioeconomic status, is still unresolved. Interventional trials that test whether periodontal treatment changes the course of systemic disease are needed to address this question.

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