Dental Implant Rejection Does Not Exist. Here Is What Really Happens.

Let us start here: dental implant rejection does not exist.

True rejection is an immune mechanism that activates against living tissues transplanted into a patient — a kidney, a heart, a liver. The immune system recognises the other’s proteins and cells as different and attacks them as non-self.

A dental implant is titanium (or sometimes zirconia, equally biocompatible). It has no cells. No DNA. No proteins, no surface antigens. The body does not recognise it as foreign because it is not an organism. It is a biocompatible metal (more precisely, its oxide that coats the surface) on which bone simply grows. This process is called osseointegration.

When a patient searches “dental implant rejection” on Google — and many do — they are looking for the right answer to the wrong question. The right question is another one: why can an implant fail and not integrate with the bone?

The numbers: what the literature says

Dental implants work. Success rates are among the highest of any implantable medical device.

A study on 10,871 implants followed up to 22 years confirmed the robustness of implant therapy in the long term (French et al., Clin Implant Dent Relat Res, 2021). Another, on 3,448 implants with over 20 years of follow-up, recorded a survival rate of 94.5% (Guarnieri et al., Int J Oral Maxillofac Implants, 2025). And an analysis of 5,787 implants over 5 years showed a per-implant survival of 99.2% (Anitua et al., J Clin Periodontol, 2008).

These numbers say one thing clearly: failure is rare. But it is not zero. And when it happens, it has precise causes.

The real causes of failure

An implant can fail at two different moments. Early — in the first weeks, before bone integrates it. Or late — after years of function, when something around it deteriorates.

Early failure

Early failure concerns osseointegration that does not occur. Bone does not bond to the implant surface. A study on 6,113 implants found an early failure rate of 3.5%, concentrated in the first year (Wu et al., Clin Implant Dent Relat Res, 2021). An analysis of 9,080 implants identified bone quality, the posterior maxillary site and smoking among the main factors (Staedt et al., Int J Implant Dent, 2020).

In this context, the competition for the implant surface between myofibroblasts and osteoblasts also plays a role, leading to fibrointegration and failure.

In other words: the implant is not “rejected”. The biological environment does not allow healing.

There is also surgical site infection, which leads to almost immediate implant loss. But this is an extremely rare condition, attributable to absent antibiotic coverage or particular conditions of the patient’s immune system.

Late failure

Late failure is a different story. The implant has functioned for years, then begins to lose bone. The most frequent cause is peri-implantitis — a chronic inflammation of the tissues around the implant, very similar to the periodontitis that affects natural teeth.

A retrospective study on 871 implants followed for 10–18 years found that 56.5% of failures were late (European Review for Medical and Pharmacological Sciences, 2017). The determining factors: bruxism, unfavourable crown-to-implant ratio, and — always — the patient’s periodontal history.

Indeed, a clinical history of severe periodontitis increases the risk of failure. But this is probably related to insufficient correction of the same factors that caused the periodontal disease (see below).

The risk factors that matter

The literature is convergent. Certain factors increase failure risk consistently across different studies, different populations, different contexts. Let us look at them.

Smoking

Smoking impairs vascularisation, slows healing, depresses the immune response. In a dedicated study, smokers showed significantly higher failure rates on both smooth and rough-surfaced implants (Balshe et al., Int J Oral Maxillofac Implants, 2008). The study on 9,080 implants confirms it as a risk factor for both early and late failures (Staedt et al., 2020).

Periodontitis

Those with a history of periodontitis are more vulnerable. A multicentre study on 3,555 implants demonstrated that supportive periodontal therapy — a technical term for hygiene and home maintenance motivation — significantly improves implant survival in these patients (Lee et al., Clin Oral Implants Res, 2026). An analysis of 1,279 implants in Peru found that 69.6% of patients with implant failure had chronic or aggressive periodontitis (Mayta-Tovalino et al., Int J Dent, 2019).

The message is twofold: periodontitis increases the risk, but the risk is manageable with supportive therapy. Operating a patient with implants must always follow decontaminating treatment, and neglecting recalls is risky.

Diabetes

Poorly controlled diabetes alters healing and immune response. A case-control study confirmed periodontitis and type 2 diabetes as significant factors for implant failure (Sobhani et al., J Periodontol, 2025). In another analysis, patients without diabetes had nearly six times higher odds of success. But it is obvious that no sane dentist would treat a poorly controlled diabetic patient, for a thousand other reasons as well.

Bruxism

Bruxism (involuntary grinding or clenching, often nocturnal) is a silent enemy. In the long-term study (10–18 years), it was defined as “the most dangerous factor, even when isolated” — with success rates dropping to 69.23% in bruxist patients with unfavourable loading factors. Colleagues experienced in full-arch immediate loading know this well.

Hormonal factors

This section is very important and often overlooked.

Many people, especially women, are on chronic steroid therapy, including corticosteroids, hormone replacement therapy or oral contraceptives (“the pill”). Women on chronic steroid therapy showed a failure rate of 7.69% versus 1.54% in women without these therapies — a fivefold higher risk, independent of smoking and diabetes (Cohen et al., Dentistry Journal, 2023).

Site, bone and technique

Not all sites are equal. The posterior maxilla, with its softer bone, presents higher failure rates than the mandible (Staedt et al., 2020; Wu et al., 2021; Jemt, Clin Implant Dent Relat Res, 2017).

This is where approach matters. We prefer to expand the existing bone rather than graft new bone. The split crest works with what the patient already has. It is less invasive, faster, and the data — on 1,400 implants — speak clearly.

What you can do

Some risk factors cannot be chosen: bone density, genetics, the site of the lost tooth are patient characteristics we cannot directly act upon. But others can be addressed.

Quitting smoking before surgery improves success rates measurably. Carefully controlling blood glucose, if you are diabetic, makes a difference. Treating periodontitis before placing an implant — and not skipping recalls afterwards — is probably the single most important decision you can make.

Bruxism can be managed. Regular check-ups must be maintained to preserve results. Home oral hygiene must be a daily habit.

It is not the implant that fails. It is the context in which it is placed, and above all, the context in which it is maintained, that may negatively influence its success.

The point

The dental implant is not rejected. It is not biologically possible. What can happen is that bone does not integrate it (early failure) or that inflammation destabilises it over time (late failure).

Both scenarios have identifiable causes and, in most cases, preventable ones.

With good patient selection, appropriate technique and a serious maintenance programme, implants function for decades.

If you have concerns about an implant that is not doing well, or want to know if you are a good candidate for implant therapy, you can book an assessment at my practice in Frosinone.

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Frequently asked questions

Can the body reject a dental implant? No. Rejection is an immune reaction against transplanted biological tissues. A titanium implant has no cells and no proteins: the immune system does not recognise it as foreign. When an implant fails, the causes are different.

What are the most common causes of implant failure? The main causes are smoking, untreated periodontitis, poorly controlled diabetes, bruxism and certain chronic drug therapies (corticosteroids, hormone replacement therapy, oral contraceptives). Bone quality and anatomical site also play a role.

How long do dental implants last? Long-term studies on thousands of implants show survival rates between 94% and 99% at 20 years and beyond. With good patient selection, appropriate technique and regular check-ups, implants function for decades.

Does smoking affect dental implants? Yes. Smoking impairs vascularisation, slows healing and depresses the immune response. Smokers have significantly higher failure rates both during the osseointegration phase and in the long term.

Can someone with periodontitis get implants? Yes, but periodontitis must be treated before surgery. Patients with a history of periodontitis who regularly follow supportive therapy (hygiene recalls) have implant outcomes comparable to healthy patients.

Is diabetes a contraindication for implants? Poorly controlled diabetes increases the risk of failure. However, a diabetic patient with well-controlled blood glucose can receive implants with good chances of success.

Can medications cause an implant to fail? Yes. Chronic corticosteroids, hormone replacement therapy and oral contraceptives are associated with up to a 5-fold higher risk of failure. Proton pump inhibitors and SSRI antidepressants can also have an effect. It is essential to inform the dentist of all medications being taken.

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References

1. Hickin MP et al. Incidence and Determinants of Dental Implant Failure. J Dent Educ 2017. DOI
2. Anitua E et al. 5-year clinical experience with BTI® dental implants: risk factors for implant failure. J Clin Periodontol 2008. DOI
3. Balshe AA et al. Effects of smoking on the survival of smooth- and rough-surface dental implants. Int J Oral Maxillofac Implants 2008. https://pubmed.ncbi.nlm.nih.gov/19216282/
4. Jemt T. Retro-prospective effectiveness study on 3448 implant operations. Clin Implant Dent Relat Res 2017. DOI
5. Guarnieri R et al. Long-Term (>20 years) Evaluation of Laser-Lok® Dental Implants. Int J Oral Maxillofac Implants 2025. DOI
6. Lee CT et al. Supportive Periodontal Therapy Improves Implant Survival in Patients With a History of Periodontitis. Clin Oral Implants Res 2026. DOI
7. Mayta-Tovalino F et al. Predictive Factors of Peri-Implantitis and Implant Failure: 1279 Implants in Peru. Int J Dent 2019. DOI
8. Staedt H et al. Potential risk factors for early and late dental implant failure: 9080 implants. Int J Implant Dent 2020. DOI
9. Wu X et al. Risk factors of early implant failure: 6113 implants. Clin Implant Dent Relat Res 2021. DOI
10. French D et al. Long term clinical performance of 10,871 dental implants with up to 22 years of follow-up. Clin Implant Dent Relat Res 2021. DOI
11. Sobhani M et al. Periodontitis, type 2 diabetes, and other risk factors for implant failure. J Periodontol 2025. DOI
12. Cohen O et al. Systemic Steroids, HRT, or Oral Contraceptives and Implant Survival in Women. Dent J 2023. DOI
13. Jemt T. Implant Survival in the Edentulous Jaw: 30 Years of Experience. Int J Prosthodont 2018. DOI