CRP, leukocytes, and pro-inflammatory cytokines are among the most recognizable markers of inflammation. In the context of peri-implantitis, they may provide valuable information about the activity of the inflammatory response, but they also have important limitations. A single marker reflects only one fragment of a complex biological process and usually does not capture the full balance between inflammatory activation and immune regulation. This is why increasing attention is being paid to aggregated indices, such as NLR, PLR, MLR, SII, SIRI, and AISI/PIV, which attempt to describe the systemic immune-inflammatory response in a more synthetic and multidimensional way.
In the diagnostics of inflammatory diseases, clinicians have long relied on simple and well-known markers. CRP, leukocyte count, interleukin-6, TNF-α, and IL-1β are part of the medical language used to describe inflammatory activity, the intensity of immune response, and the potential inflammatory burden of the body. They are available, understandable, and used across many clinical fields. It is therefore natural that in research on peri-implantitis, the question arises whether they may also help in assessing patients with inflammation of peri-implant tissues.
This question is justified. Peri-implantitis is not limited to the mere presence of bacteria on the implant surface. Biofilm initiates the local inflammatory response, but the further course of the disease depends on how the patient’s organism responds to this stimulus. In some patients, inflammation may remain relatively limited and controllable. In others, it leads to rapid bone loss, recurrence, and difficult therapeutic decisions. If we want to better understand the course of peri-implantitis, it is natural to look not only at the area around the implant, but also at the systemic inflammatory response.
Single inflammatory markers have obvious value in this context. CRP may indicate that an inflammatory process is taking place in the body. Leukocyte count reflects the activity of basic immune response cells. Pro-inflammatory cytokines, such as IL-6, TNF-α, and IL-1β, are involved in biological cascades that may promote tissue destruction and bone resorption. In the PERI-EDU project materials, classical single inflammatory markers include CRP, IL-6, TNF-α, IL-1β, and WBC, while local markers in peri-implant crevicular fluid include IL-1β, IL-6, TNF-α, IL-8, and MMP-8.
The problem is that single markers are nonspecific. Elevated CRP does not indicate where the source of inflammation is located. An altered leukocyte count does not explain whether the cause is peri-implantitis, an infection elsewhere in the body, chronic disease, inflammatory stress, or pharmacotherapy. Cytokines may reflect immune activation, but they do not always allow us to determine its cause, clinical significance, or relationship with the local presentation of the disease.
This is why a single inflammatory marker is rarely sufficient to understand chronic, low-grade, and multifactorial inflammatory processes. It may be a signal, but not a complete description. It may show that the immune system is active, but it does not provide enough information about the relationships between different components of that response. Materials on non-aggregated inflammatory markers emphasize that they are easy to measure and sensitive in detecting inflammation, but they have limited specificity and do not reflect the complex immunological balance or interactions between immune cell populations.
In peri-implantitis, this is particularly important. The disease develops in an environment where biofilm, the implant surface, soft tissues, bone, host response, prosthetic factors, and the patient’s systemic condition intersect. Diabetes, metabolic syndrome, cardiovascular disease, history of periodontitis, smoking, obesity, impaired healing, and chronic inflammatory burden may all influence disease development and progression. In such a system, a single laboratory parameter may be too simplified to describe the full picture.
This does not mean that CRP, WBC, or cytokines lose their importance. On the contrary, they remain an important potential component of the biological assessment of the patient. Their role, however, may be to complement the overall picture rather than to provide an independent diagnostic conclusion. In clinical practice, the key is to combine data: examination of peri-implant tissues, probing, bleeding on probing, pocket depth, radiological assessment of bone loss, medical history, periodontal history, and, potentially, laboratory parameters.
For this reason, increasing interest is being directed toward aggregated indices, meaning indices created by mathematically combining at least two laboratory variables. Most commonly, these are indices derived from routine blood count parameters. Their aim is to provide a synthetic assessment of the systemic inflammatory and immune response by simultaneously considering different components of the immune system. In the PERI-EDU materials, this group includes NLR, PLR, MLR, SII, SIRI, and AISI/PIV.
The simplest of these are indices based on ratios between two types of cells. NLR, the neutrophil-to-lymphocyte ratio, combines a component associated with inflammatory and innate response with a regulatory and adaptive component. PLR, the platelet-to-lymphocyte ratio, may reflect the relationship between inflammation, platelet activation, and vascular processes. MLR, the monocyte-to-lymphocyte ratio, may indicate activity related to monocyte-macrophage response and chronic inflammation.
More complex indices go a step further. SII, the Systemic Immune-Inflammation Index, combines platelet count, neutrophils, and lymphocytes. SIRI includes neutrophils, monocytes, and lymphocytes. AISI or PIV use an even broader combination of cellular parameters, usually including neutrophils, monocytes, platelets, and lymphocytes. In simplified terms, all these indices attempt to capture not a single inflammatory signal, but a network of relationships between pro-inflammatory, effector, vascular, and regulatory cells.
This approach is attractive for several reasons. First, it is based on routine blood count, a test that is inexpensive, widely available, and reproducible. Second, it allows inflammation to be viewed more dynamically than through a single parameter. Third, it may be useful in monitoring patients over time, especially if the assessment is combined with clinical and radiological data. Fourth, it may help identify patients with a more pronounced or unfavorable immune-inflammatory profile.
In the context of peri-implantitis, aggregated indices are interesting because the disease may be associated with chronic, low-grade inflammatory burden. If inflammation of peri-implant tissues is not merely a local episode, but part of a broader biological response of the patient, blood count-derived indices may in the future help improve risk assessment. They may also support the question of why patients with a similar local clinical picture may experience different disease courses.
However, research potential should not be confused with a ready clinical tool. Aggregated indices are not currently standalone diagnostic tests for peri-implantitis. They do not replace clinical examination, radiological assessment, or analysis of local factors. Their value depends on context: comorbidities, infections, medications, age, smoking, stress, obesity, autoimmune diseases, and many other variables.
This limitation is particularly important because hematological indices may change for reasons unrelated to the implant. A patient with systemic infection, active autoimmune disease, cancer, trauma, or intense inflammatory stress may show altered index values regardless of the condition of peri-implant tissues. Conversely, a patient with locally active peri-implantitis may not show a clear deviation in blood tests. Project materials emphasize that the advantages of CBC-derived indices include availability, low cost, and the possibility of assessing the systemic dimension of inflammation, but their limitations include lack of specificity, lack of standardized peri-implantitis-specific cut-off values, and the need for further validation.
Therefore, the most important question is not whether NLR, SII, or SIRI diagnose peri-implantitis. The more appropriate question is whether they can provide additional information about the patient that is not visible in local examination alone. Can they help capture a systemic inflammatory profile that influences the course of the disease? Can they improve risk stratification when combined with clinical and radiological assessment?
This is where the relevance of the PERI-EDU project becomes clear. The project does not treat inflammatory indices as a simple diagnostic shortcut. It analyzes them as part of a larger puzzle in which the clinical picture of peri-implantitis, the patient’s systemic condition, immune response, laboratory results, and potential new educational tools come together. This direction is particularly important for implantologists, who often see patients with a similar local presentation but a completely different clinical course.
From an educational perspective, the transition from CRP to SII means more than a change in laboratory parameter. It represents a change in thinking: from a single inflammatory signal to an attempt to describe the entire immune-inflammatory balance. For students and young clinicians, this is an important lesson that peri-implant tissue diseases are not one-dimensional. For practitioners, it may be an impulse to combine local diagnostics more consciously with assessment of the patient’s overall biological profile.
In the future, this approach may support more personalized implant dentistry. The aim is not for every implant patient to undergo an extensive panel of laboratory tests. Rather, the point is that in selected clinical situations, the clinician may be able to better understand whether they are dealing with a patient at increased risk of progression, with a more pronounced inflammatory response, or with poorer healing potential. In such cases, blood tests and aggregated indices could become part of a rational complementary assessment.
CRP and other single inflammatory markers remain important, but they may not be sufficient to describe a disease as complex as peri-implantitis. Aggregated indices such as NLR, PLR, MLR, SII, SIRI, and AISI/PIV offer a more multidimensional view of the immune-inflammatory response, although they require further research, standardization, and validation. Their greatest value may lie not in replacing classical diagnostics, but in complementing it with the biological context of the patient.
This is the direction developed by PERI-EDU: from simple markers to integrated assessment, from the local picture of disease to a broader understanding of the body’s response, from individual data points to more responsible clinical interpretation. In peri-implantitis, the mere presence of inflammation is only the beginning of the question. What becomes crucial is understanding how the patient’s organism responds to that inflammation — and whether this response can be measured in a way that genuinely supports education, diagnostics, and implant practice.