Dental implants are a predictable and effective modality for replacing missing teeth, with high long-term survival rates. However, implant failure can occur due to biologic, mechanical, or patient-related factors. Risk factors, such as smoking, uncontrolled-systemic diseases (e.g. diabetes), certain medications, and a history of periodontitis, must be screened and identified during the treatment planning phase. Although absolute contraindications are rare, thorough patient evaluation and coordination with the patient’s physician are critical for optimal outcomes.
Key points
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Patient risks factors for dental implants should be carefully assessed during the treatment planning phase, and not later in the course.
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Smoking is a significant factor causing implant failure.
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Systemic factors including diabetes, drugs/medications, radiation, and autoimmune conditions may pose a risk for dental implants.
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Existing and previous history of periodontitis may adversely affect implant survival.
Abbreviations
| BMD | bone mineral density |
| IL | Interleukin |
Introduction
In modern dentistry, dental implants have become a widely accepted method for restoring edentulous areas. Dental implants are now considered a viable alternative to conventional therapies, for replacing partially or fully edentulous arches. In implantology, the emphasis is predominantly on the technical precision of implant placement and strict adherence to established protocols. However, relatively little focus is placed on identifying and managing risk factors associated with implant failure. Many a time, the diagnostic process in implant dentistry often dedicates insufficient time to the comprehensive evaluation and mitigation of these risk factors. Therefore, it is crucial for dental implant clinicians to develop an in-depth understanding of the various factors that contribute to implant failure, in order to enhance treatment outcomes, and ensure prognosis and long-term success. Implant failure factors relating to the restorative and surgical components are addressed elsewhere in this special edition. In this article, we discuss definition, prevalence, classification, and the systemic factors that influence implant success and failure.
Definition of implant failure
There is no definitive universally acceptable definition for implant failure. This is primarily by the virtue of the fact that numerous variables may define the failure differently. For example, the criteria for labeling an implant as “failed” may vary considerably across the dental literature. It must be noted, that although the clinician may consider the implant as “successful”, a patient believing it has failed due to whatever the patient factors are, may essentially end up as a “case failure”. In this article, we have looked primarily at the biologic basis for implant failures. Another philosophic question is the potential difference between implant “failure” as opposed to the “sub-optimal success” of the implant. Another factor to consider is the level of residual healthy bone that supports the implant, as a factor of “success” or “failure”. For example, if 50% of the supporting bone is eroded off, but the implant is otherwise stable, can this be labeled as “success” or “failure” or “sub-optimal implant survival”.
The definition of implant failure appears to be widely varied in literature, with no apparent consensus between and amongst various professional organizations and academies. Implant failure is loosely defined as the instance where a decision for removal of a dental implant has been made, due to clinical signs or symptoms that indicate the inability to maintain its function and stability. In this definition, “failure” specifically refers to the loss of the implant fixture, rather than subjective outcomes, such as aesthetics and other factors. An implant is considered failed when biologic or mechanical complications necessitate its removal, irrespective of the underlying cause. ,,,
Implant success
An implant is considered successful when it remains in place with healthy surrounding hard and soft tissues, demonstrating proper osseointegration and functional stability without any signs of pathology. However, the question in a clinician’s mind becomes this: The implant appears well-integrated and “stable” but has gone through 50% bone loss: Is this a successful implant? How about if we extrapolate this to a case with 75% bone loss, but still satisfies the criteria for “stability”? When considering the actual failure of implants, it appears that there is a spectrum starting with the initial implant “success” to implant “survival” through implant “failure”. For a dental clinician, success is determined by achieving the patient’s desired outcome without any associated complications. Any need for additional treatment post-procedure, such as patient dissatisfaction with prosthetic aesthetics despite clinical success, qualifies as a complication due to the necessity of further intervention. Under this definition, success rates would be significantly lower than those based solely on implant integration. An implant is considered to have survived when it remains in place, but exhibits compromised surrounding hard or soft tissues, such as bone loss, peri-implantitis, or other complications, while still maintaining functionality without requiring removal.
Prevalence of implant failure
Dental implants have a reported 10 y survival rate of approximately 95%. The reported prevalence of early and late implant failure (at the implant level) varies between 0.5% to 5% and 0.5% to 8%, respectively. Variations in prevalence may be influenced by implant design, surgical protocol, and sample characteristics. Additionally, the length of the follow-up period may contribute to differences in late failure rates.
Basis of classification of implant failure
Type of Failure Based on Time Elapsed from Implant Placement
Early implant failure is defined as the failure/lack of osseointegration prior to functional loading of dental implant. It is typically observed within the initial weeks to months following implant placement. Early failures represent a failure of the initial healing phase and are considered a biologically driven phenomenon rather than a mechanical or functional complication. , Late implant failure refers to the loss of an Osseo-integrated implant, typically occurring during or after the restorative phase following the application of occlusal loading. Unlike early failures, which are solely biologic, late failures can result from either biologic or mechanical complications. , The time interval between the initial diagnosis of implant failure and its eventual removal is generally longer in late failures compared to early failures, and they are often associated with significant peri-implant bone loss. Since late failures occur after the final prosthetic restoration has been placed, they pose greater challenges in terms of retreatment, cost implications, and patient dissatisfaction. , A summary of classification of implant failure based on time factor is given in Table 1 .
Table 1
Classification of implant failures based on time elapsed from placement
| Type of Failure | Timing |
|---|---|
| Early failure (before functional loading) | Weeks to months after placement |
| Late failure (after functional loading) | Months to years’ post-placement |
| Very late failure (few years after functional loading) | Years after successful osseointegration |
Classification of Implant Failure Based on Phases of Implant Treatment
Dental implant failure can be classified according to the different phases of treatment, ranging from pre-operative planning to long-term prosthetic function. Each phase presents unique challenges and risk factors that can contribute to implant failure. A summary of this classification is given in Table 2 .
Table 2
Classification of implant failure based on phases of implant treatment
| Treatment Phase | Timing of Failure |
|---|---|
| Planning | Early failure (prior to surgery) |
| Surgical | Early failure (during or shortly after surgery) |
| Healing and osseointegration | Early failure (before functional loading—weeks to months after surgery) |
| Restorative | Late failure |
| Functional | Late failure |
Etiology of Implant Failures: Patient Factors
Numerous factors affect the success and survival of implants, and many of these are patient-related. These include systemic, anatomic, parafunctional, and other factors. A summary of this is included in Table 3 .
Table 3
Patient factors in implant failure
| Patient Factor | Entities | |
|---|---|---|
| Systemic factors |
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| Local factors |
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| Parafunction | Bruxism | |
| Other factors |
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Age
The relationship between age and early implant failure remains controversial. Earlier implant literature reported that older age was significantly associated with higher implant failure rate. PMID: 16161741 More recent studies reported no significant correlation between the age and early implant failure, except older adults in their 80s and beyond may have a subtle propensity for a higher early implant failure. ,, A recent retrospective study demonstrated that younger patients exhibited a higher incidence of early dental implant failure, with the risk of failure decreasing by approximately 13% to 15% for every additional decade of age. Age alone is not a determinant of early implant failure—rather, patient-specific factors, such as local and systemic factors, and peri-implant care, play a more critical role. Patients ≥80 y may have a slightly higher risk of failure, necessitating careful treatment/surgical planning, prosthetic considerations, and long-term maintenance strategies.
Smoking
The detrimental impact of smoking on systemic and oral health is well-documented. It adversely affects oral tissues, compromising both soft and hard tissue integrity. ,, Smoking is recognized as a key risk factor for impaired wound healing, dry socket, implant failure, and marginal bone loss around both natural teeth and dental implants. In the context of dental implants, a significant association has been established between smoking and an increased risk of implant failure, , particularly in the maxilla. This site-specific susceptibility may be attributed to several anatomic and physiologic factors, including reduced cortical bone thickness, compromised bone quality, greater direct exposure of the palatal tissues to tobacco smoke, and the absence of protective mechanisms, such as tongue coverage, which may exacerbate the deleterious effects of smoking. Evidence suggests that smokers exhibit altered-bone structure and composition compared to non-smokers. , Cigarette smoking has been linked to a reduction in bone mineral density (BMD) in a dose-dependent and duration-dependent manner. Existing literature supports evidence that smoking adversely affects the prognosis of dental implants in a dose-dependent manner. A recent meta-analysis indicates that smoking significantly increases the risk of early implant failure by 1.5-fold to 2.5-fold. However, tobacco use alone may not be a definitive risk factor for early implant failure. Smoking cessation for at least 8 d before and continuing through 60 d after implant placement has been shown to enhance implant survival rates in smokers. , Comprehensive pre-operative assessment should include evaluation of smoking history, and dental professionals must integrate structured-counseling and cessation strategies into the treatment plan. Such proactive interventions can significantly enhance implant outcomes, particularly in high-risk individuals, and should be considered standard practice in implantology.
E-cigarette and cannabis
Emerging evidence indicates that e-cigarette use has an adverse effect on the clinical, radiographic, and immunologic outcomes associated with dental implants. Similar to conventional cigarette smoking, e-cigarettes may compromise the healing process and overall outcomes of implant therapy. ,, Cannabis use has been linked to impaired-gingival healing due to the presence of nicotine and the inhibitory effects of cannabidiol on cell proliferation, as well as reduced levels of interleukin-8 (IL-8)—a cytokine essential for wound repair. Additionally, heavy cannabis users exhibit decreased BMD, lower body mass index, higher fracture rates, and reduced-serum vitamin D levels. Together, these effects suggest that chronic cannabis consumption may negatively impact both soft tissue healing and overall bone health, potentially compromising implant treatment outcomes.
Systemic factors affecting implant failure: possible mechanism and management
A number of systemic factors have been proposed and shown to robustly influence the success and survival of dental implants. It must be noted that some of the corresponding literature in this regard is still emerging. A summary of these factors is included in Table 4 . A few of these factors are exemplified in Fig. 1 A–C .
Table 4
Systemic factors affecting implant failure: possible mechanism and management
| Systemic Factor | Potential/Shown Effect on Dental Implant | Clinical Pearls in Management |
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| DM |
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| Osteoporosis |
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Anti-resorptive medications.
Bis- phosphonate (BP) |
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| \Glucocorticoids |
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| Anti-depressants (SSRI) |
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| Proton-pump inhibitors (PPI) |
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| Radiation therapy |
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| Prophylactic Antibiotic |
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| Immuno-Suppressants (CsA) |
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| Nonsteroidal Anti-inflammatory Drugs (NSAIDS) |
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| Vitamin- D |
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| Thyroid Hormones |
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| Cardiovascular Diseases (CVDs) |
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| Movement disorder |
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| Genetic disorder |
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| Penicillin allergy |
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| Inflammatory bowel diseases |
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| Anti-hypertensive medications |
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| Fibrous Dysplasia (FD) |
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| Cemento- osseous dysplasia (COD) |
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| Osteogenesis imperfecta (OI) |
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| Epidermolysis bullosa |
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| Oral lichen planus |
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| Sjogren syndrome (SS) |
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| Systemic sclerosis (SSc) |
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| Rheumatoid arthritis (RA) |
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| Papillon-Lefevre syndrome |
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| Psychiatric disorders |
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