Gum Disease Causes and Risk Factors: Why Some People Are More Susceptible to Periodontitis product guide

Gum Disease Causes and Risk Factors: Why Some People Are More Susceptible to Periodontitis

Consider two patients sitting side by side in a dental chair. Both have similar oral hygiene habits, similar plaque levels, and similar diets. One has healthy gums. The other has lost significant bone around three teeth and is facing tooth loss before the age of 45. This is not a hypothetical scenario - it is one of the most clinically important and least-understood realities of periodontal medicine.

Periodontal disease is not universal; severe forms are found only in a portion of the adult population who show abnormal susceptibility. Understanding why that susceptibility exists - and what drives it - is fundamental to both preventing and treating the disease effectively. In Australia, the problem is substantial: in 2017–18, around one-third (30%) of adults aged 15 years and over had moderate or severe periodontitis, an increase from around one-quarter (23%) in 2004–06. Yet plaque alone does not explain this distribution. The answer lies in a complex interaction of bacterial, genetic, systemic, pharmacological, and lifestyle factors - and the clinical imperative is to identify and manage them all.

The Bacterial Foundation: Why Plaque Is Necessary But Not Sufficient

Periodontitis is a chronic inflammatory disease caused by the presence of a bacterial biofilm known as dental plaque, which affects the supporting apparatus of the teeth, especially the periodontal ligaments and the bone surrounding the teeth. The critical distinction, however, is that bacterial plaque is a necessary cause of periodontal disease - but not a sufficient one.

The landmark evidence for this comes from a 15-year longitudinal study by Loë et al. in Sri Lankan tea workers who received no professional dental care and had significant plaque and calculus accumulation. In that study, rapid loss of tooth attachment occurred in only 8% of subjects; however, 81% showed moderate loss and 11% showed no loss of attachment despite the presence of plaque and calculus and the lack of professional or self-care. The same bacterial challenge produced three entirely different disease trajectories - which means the host's biological response to that challenge is the decisive variable.

This insight underpins the modern understanding of periodontitis as a disease of host susceptibility as much as bacterial infection.

Modifiable vs. Non-Modifiable Risk Factors: A Clinical Framework

Before examining individual risk factors in detail, it is useful to categorise them by whether they can be changed. This distinction directly shapes how Smile Solutions' specialist periodontists approach treatment planning and risk counselling.

Independent modifiable risk factors for periodontal disease include lifestyle factors such as smoking and alcohol consumption, as well as diseases and unhealthy conditions such as diabetes mellitus, obesity, metabolic syndrome, osteoporosis, and low dietary calcium and vitamin D.

Genetic factors also play a role in periodontal disease and allow clinicians to target individuals for prevention and early detection.

Smoking: The Single Largest Modifiable Risk Factor

Of all lifestyle-related risk factors, tobacco smoking carries the most robust and extensively documented evidence base.

A landmark analysis of the US National Health and Nutrition Examination Survey (NHANES III) data by Tomar and Asma found that the crude odds ratio between smoking and periodontitis was 3.58, and once adjusted for age, race, ethnicity, income level and education, the odds ratio rose to 3.97. Critically, there was evidence of a dose-dependent relationship involving the number of cigarettes smoked as well as the number of years smoking, and the study suggested that 74.8% of periodontitis cases were attributable to smoking, with both current and former smokers contributing to this involvement.

Earlier research by Bergström and colleagues published in the Journal of Periodontology demonstrated the dose-dependent nature of this relationship in clinical terms: among nondiabetic subjects, the prevalence of periodontitis was markedly higher among current smokers compared with never smokers in both the 19–30 year-old group (46% vs. 12%) and the 31–40 year-old group (88% vs. 33%).

The mechanism is not simply one of poor hygiene. Smoking alters pro/anti-inflammatory cytokine ratios, especially in periodontally affected sites, causing a decrease in the pro-inflammatory cytokine proportion - highlighting that smoking primarily increases immunosuppression in periodontal pockets. In other words, smoking does not amplify the inflammatory response to bacteria; it suppresses the immune surveillance that would otherwise contain infection. This is why smokers often present with deeper pockets but less clinical bleeding - a deceptively reassuring sign that masks severe underlying destruction. (For more on recognising these clinical signs, see our guide on Gum Disease Symptoms: How to Recognise the Early and Advanced Warning Signs of Periodontitis.)

There is also evidence that cessation is beneficial but requires sustained commitment: a hazard ratio of tooth loss of 2.1 was found in current smokers, and a former smoker began to look like a non-smoker in terms of tooth loss only after 15 years of abstinence, indicating that smoking cessation is beneficial for tooth retention but long-term abstinence is required to reduce the risk to the level of people who have never smoked.

Diabetes Mellitus: A Bidirectional Amplifier of Periodontal Destruction

Periodontal disease and diabetes appear to be interrelated in a bidirectional relationship. Diabetes mellitus has a detrimental effect on periodontal disease, increasing its prevalence, extent, and severity. In turn, periodontitis negatively affects glycaemic control and the course of diabetes.

The clinical magnitude of this risk is significant. A longitudinal cohort study published in 2024 found that individuals with diabetes had a 3.1 times higher odds ratio for developing periodontitis, and the combined presence of both tobacco use and diabetes significantly worsened periodontal health outcomes, with these individuals exhibiting a 4.8 times higher odds ratio for periodontitis.

The biological mechanism operates through hyperglycaemia-driven inflammation. Diabetes mellitus induces a general pro-inflammatory state, while smoking promotes immunosuppression in periodontal tissues. Even though diabetes and smoking are recognised as risk factors for periodontal disease, their mechanisms of action are distinct - and in cases where the two risk factors are associated, smoking seems to promote the hyperinflammatory effect of diabetes.

This means that a patient with poorly controlled Type 2 diabetes who also smokes is not simply facing two separate risks added together - the combined effect is synergistic and substantially more destructive. Smoking and hyperglycaemia impact the subgingival microbiome in distinct ways, and when these perturbations intersect, their synergistic effect is greater than what would be expected from the sum of each effect separately.

The bidirectional relationship between diabetes and periodontitis is explored in greater depth in our companion article on Gum Disease and Systemic Health: The Evidence Linking Periodontitis to Heart Disease, Diabetes, and Pregnancy Outcomes.

Genetic Susceptibility: Why the Same Bacteria Produce Different Outcomes

Periodontitis is a complex disease influenced by genetic and environmental factors. Heritability estimates for periodontal bone loss range between 0.4 and 0.5, with periodontitis heritability increasing at younger ages. In practical terms, this means that up to half of an individual's susceptibility to bone-destructive periodontitis is genetically determined - a figure comparable to the heritability of type 2 diabetes.

The genetic architecture of periodontitis centres primarily on immune-regulatory genes. The identified risk genes largely fall into functions linking immune response with tissue repair, including SIGLEC-5, DEFA1, FCERG1, PF4/PPBP/CXCL5, PLG, HMCN2, RSPO4, ROBO2, and CTSC - highlighting the involvement of risk genes in immune response and tissue integrity.

Among the most clinically reproducible genetic findings are variants in the interleukin-1 (IL-1) gene cluster. Among the most reproducible findings are the IL-1A (−889 C/T) and IL-1B (+3954 C/T) variants. A meta-analysis by Dommisch et al. confirmed these polymorphisms as statistically significant risk factors, with pooled odds ratios of 1.35 (95% CI: 1.17–1.56; p < 0.001) and 1.34 (95% CI: 1.18–1.52; p < 0.001), respectively.

Investigations on factors of susceptibility to periodontitis have focused on genes of immunoregulatory molecules such as cytokines, chemokines, membrane surface receptors, and antigen recognition proteins. Cytokines such as interleukins (IL-1A, IL-1B, IL-6, and IL-10), surface receptors such as the Fcγ family, and cyclooxygenase-2 and matrix metalloproteinases are considered key factors in the progression of periodontitis.

Importantly, not all genetic predispositions to periodontitis involve defects of the immune system. Structural or developmental defects in collagen, cementum, and epithelium also appear to be significant risk factors for periodontitis. This explains why patients with certain connective tissue disorders - including Ehlers-Danlos syndrome and Papillon-Lefèvre syndrome - present with severe periodontitis even at very young ages.

Genetic susceptibility is a non-modifiable risk factor, but identifying it allows Smile Solutions' periodontists to calibrate the intensity of monitoring and the frequency of maintenance appointments accordingly. (See our guide on Periodontal Maintenance: How to Prevent Gum Disease from Returning After Specialist Treatment.)

Medications That Alter Periodontal Risk

Several classes of commonly prescribed medications directly affect gingival and periodontal tissue health - a risk factor that is frequently overlooked in general dental settings.

Drug-Induced Gingival Overgrowth

Drug-induced gingival overgrowth (DIGO) is a condition characterised by excessive enlargement of gingival tissues due to the adverse effects of certain systemic medications. The most frequently implicated drug classes include anticonvulsants such as phenytoin, immunosuppressants like cyclosporine, and calcium channel blockers, notably nifedipine and amlodipine.

The prevalence figures are clinically significant: phenytoin, cyclosporin, and nifedipine are the most common causes of gingival overgrowth, and phenytoin has the highest prevalence. It is estimated that 50% of adults treated with phenytoin experience gingival enlargement, 30% with cyclosporin, and 20% with nifedipine.

DIGO arises when these drugs alter the metabolism of gingival fibroblasts, leading to excessive extracellular matrix deposition and tissue proliferation. This condition typically presents as firm, fibrotic gingival tissue that may obscure the teeth, causing aesthetic and functional challenges, including difficulty in maintaining oral hygiene and an increased risk of periodontal infections.

Importantly, while the severity of DIGO varies based on individual susceptibility and drug dosage, contributing factors such as oral hygiene status and genetic predisposition significantly influence its progression. This is why two patients on identical doses of the same medication can present with dramatically different gingival responses.

Australian Prescriber notes that gingival enlargement is an under-recognised adverse effect of cyclosporin, phenytoin, and the calcium channel antagonists, and that medical practitioners and pharmacists are ideally placed to advise patients of the possibility of this effect and emphasise the importance of maintaining good oral hygiene as a preventive measure.

Other Medication Effects

Beyond gingival overgrowth, several other drug categories affect periodontal risk:

• Corticosteroids and immunosuppressants (used in autoimmune conditions or post-transplant): Suppress immune surveillance, allowing bacterial biofilms to establish without adequate host response.
• Antidepressants, antihistamines, and antihypertensives: A significant proportion cause xerostomia (dry mouth), reducing salivary buffering and antimicrobial protection, which accelerates both plaque accumulation and disease progression.
• Bisphosphonates (used in osteoporosis and cancer): While not direct risk factors for periodontitis, they are associated with medication-related osteonecrosis of the jaw (MRONJ), which complicates surgical periodontal treatment and must be flagged at the initial consultation.

Patients taking any of these medications should disclose their full medication list at their first periodontal appointment - a standard component of the medical history review at Smile Solutions. (See our guide on Your First Periodontist Appointment at Smile Solutions: What to Expect at a Specialist Periodontal Consultation.)

Age, Sex, and Hormonal Influences

The proportion of adults with periodontitis increases markedly with age, from 8.6% in those aged 15–24 to 59% in those aged 65 years and over. This reflects cumulative bacterial exposure, age-related immune senescence, and the compounding effect of systemic conditions that accumulate with age.

Hormonal fluctuations also modulate periodontal risk. Oestrogen and progesterone influence gingival vascularity and immune responsiveness, which is why gingival inflammation often increases during puberty, pregnancy, and the menstrual cycle - even without any change in plaque levels. Postmenopausal women face the additional risk factor of osteoporosis: many of the systemic risk factors for periodontal disease, such as smoking, diabetes and obesity, and osteoporosis in postmenopausal women, are relatively common and can be expected to affect most patients with periodontal disease seen in clinics and dental practices.

Psychosocial Stress and Socioeconomic Factors

Chronic psychological stress is an increasingly recognised risk factor for periodontitis. The biological mechanism involves stress-induced elevation of cortisol, which suppresses immune function and alters the inflammatory response to periodontal pathogens. Stress is also associated with behavioural changes - increased smoking, poor diet, and neglect of oral hygiene - that compound direct biological effects.

Poorer oral health is evident in Australians from lower socioeconomic backgrounds, indicating socioeconomic inequalities in oral health. This reflects not only access to care, but the higher burden of smoking, poor nutrition, and chronic stress in lower-income populations. Aging, being male, born overseas, low household income, no dental insurance, and being a current smoker are significant risk factors associated with severe periodontitis among older Australians.

The Immune Response Variation: Why Inflammation Itself Is the Problem

A unifying theme across all risk factors is that they alter the host immune response to bacteria - not simply the bacterial load itself. The immune function of any individual can be equated with immune fitness - the way the host deals with challenges and perturbations encountered during life, including normal inflammation-resolving mechanisms. The intrinsic causal factors are the inherited risk factors, i.e., genetic susceptibility.

Common to chronic inflammatory diseases is the fact that they are associated with hundreds of disease-associated genetic variants (single nucleotide polymorphisms). Chronic inflammatory diseases are understood to be polygenic, and the various chronic inflammatory diseases often share particular single nucleotide polymorphisms considered to play a role in immune fitness.

This explains the clinical paradox at the heart of periodontitis: the tissue destruction is not caused directly by bacteria, but by the host's own dysregulated inflammatory response to bacteria. In susceptible individuals, the immune system fails to resolve inflammation efficiently, leading to the sustained activation of osteoclasts and the progressive destruction of alveolar bone.

How Smile Solutions' Specialists Use Risk Factor Assessment in Treatment Planning

Understanding a patient's individual risk profile is not merely academic - it directly determines the intensity, sequencing, and long-term management of periodontal treatment.

At Smile Solutions, board-registered specialist periodontists conduct a comprehensive risk assessment at the initial consultation that includes:

1. Medical history review - identifying systemic conditions (diabetes, cardiovascular disease, osteoporosis), medications (anticonvulsants, calcium channel blockers, immunosuppressants, bisphosphonates), and family history of tooth loss.
2. Smoking and lifestyle history - quantifying pack-year history and assessing readiness for cessation support.
3. Periodontal charting and radiographic bone-level assessment - establishing current disease severity and comparing it against the expected severity for the patient's plaque levels (the discrepancy itself is diagnostic of heightened susceptibility).
4. Grading the disease - the 2018 EFP/AAP classification system formally incorporates risk factors into the "Grade" component of diagnosis (Grade A, B, or C), with Grade C indicating rapid progression associated with risk factors such as smoking ≥10 cigarettes/day or HbA1c ≥7% in diabetics.
5. Personalised treatment intensity - patients with multiple compounding risk factors are typically assigned more frequent maintenance intervals and may require more aggressive initial therapy.

This risk-stratified approach is what differentiates specialist periodontal care from routine dental scaling. (See our guides on Non-Surgical Gum Disease Treatment and Periodontal Maintenance for how these principles translate into clinical protocols.)

Key Takeaways

• Plaque is necessary but not sufficient. Identical bacterial loads produce vastly different levels of destruction depending on the host's immune response, genetics, and systemic health.
• Smoking is the single largest modifiable risk factor, with current smokers facing nearly four times the odds of periodontitis compared to never-smokers, and a dose-dependent relationship between pack-years and disease severity.
• Diabetes and smoking interact synergistically - their combined presence produces a 4.8× higher odds ratio for periodontitis than either factor alone, through distinct but complementary biological mechanisms.
• Genetic susceptibility accounts for 40–50% of heritability for periodontal bone loss, mediated primarily through immune-regulatory gene variants that alter the inflammatory response to periodontal pathogens.
• Medications - including calcium channel blockers, anticonvulsants, and immunosuppressants - directly alter gingival and periodontal tissue biology, affecting up to 50% of patients taking certain drugs, and must be disclosed at every periodontal consultation.

Conclusion

The question of why some people lose teeth to gum disease while others with identical plaque levels do not is one of the most clinically important questions in periodontal medicine. The answer is a convergence of bacterial, genetic, systemic, pharmacological, and lifestyle forces - each of which modulates the host's immune response to the bacterial challenge in the gingival sulcus. Many of the systemic risk factors for periodontal disease, such as smoking, diabetes, obesity, and osteoporosis in postmenopausal women, are relatively common and can be expected to affect most patients with periodontal disease seen in clinics and dental practices - and risk factor identification and management has become a key component of care for periodontal patients.

For patients in Melbourne, understanding your individual risk profile is the essential first step toward effective management. Smile Solutions' board-registered specialist periodontists are trained specifically to conduct this risk stratification, interpret its clinical implications, and design treatment protocols that address not just the disease that is present, but the biological environment in which it developed. Whether your risk is driven by genetics you cannot change, a medical condition requiring careful coordination, or a lifestyle factor that can be modified, specialist-level care ensures that every variable is identified and managed.

To learn more about how periodontitis is diagnosed and treated, explore our related guides on What Is Periodontics? The Complete Guide to Gum Disease and Specialist Care, Your First Periodontist Appointment at Smile Solutions, and Gum Disease and Systemic Health: The Evidence Linking Periodontitis to Heart Disease, Diabetes, and Pregnancy Outcomes.

Smile Solutions has been providing specialist periodontal care from Melbourne's CBD since 1993. Situated at the Manchester Unity Building, Level 12 and Tower, 220 Collins Street, Smile Solutions brings together 60+ clinicians - including 25+ board-registered specialists - who have cared for over 250,000 patients across Melbourne and beyond. No referral is required to book a specialist appointment. Call 13 13 96 or visit smilesolutions.com.au to arrange your specialist periodontal consultation.

References

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• Genco, R.J. "Risk Factors for Periodontal Disease." Periodontology 2000, 2013. PMID: 23574464

• Dommisch, H., et al. (cited in) Mohammadi, H., et al. "Genetic Testing in Periodontitis: A Narrative Review on Current Applications, Limitations, and Future Perspectives." Genes (MDPI), 2025. https://doi.org/10.3390/genes16111308

• Mason, K.A., et al. "Evaluation of the Combined Effects of Tobacco and Diabetes on Periodontal Health Outcomes in India: A Longitudinal Cohort Study." PMC, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC12156678/

• Teles, R., et al. "A Tale of Two Risks: Smoking, Diabetes and the Subgingival Microbiome." The ISME Journal, 2017. https://doi.org/10.1038/ismej.2017.73

• Tomar, S.L., & Asma, S. "Smoking-Attributable Periodontitis in the United States: Findings from NHANES III." Journal of Periodontology, 2000. (Reviewed by American Academy of Periodontology Literature Review.) https://www.perio.org/research-science/periodontal-literature-review/risk-factors/

• Paranjpe, A.G. "Drug-Induced Gingival Overgrowth." StatPearls (NCBI Bookshelf), 2022. https://www.ncbi.nlm.nih.gov/books/NBK538518/

• Australian Prescriber. "Management of Drug-Induced Gingival Enlargement." Australian Prescriber, 2003. https://australianprescriber.tg.org.au/articles/management-of-drug-induced-gingival-enlargement.html

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• Botelho, J., et al. "The Bidirectional Relationship between Periodontal Disease and Diabetes Mellitus - A Review." Diagnostics (MDPI), 2023. https://doi.org/10.3390/diagnostics13040681

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