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Clinical Science and Techniques

Dental Implant Success-Failure Analysis: A Concept of Implant Vulnerability

Tolstunov, Len DDS

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doi: 10.1097/
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The predictability of root-form implants with sustainable long-term function and esthetics has become a reality for oral implantologists and their patients. Patients who are facing a therapeutic procedure more often ask questions regarding the success rate of a particular medical, surgical, or dental intervention. In other words, they are concerned about the guarantee of the procedure and are interested in long-term results.

Criteria for implant success according to Roos et al1 and Albrektsson2 include: immobility of the individual implant when tested clinically; lack of radiographic evidence of peri-implant radiolucency; bone loss no greater than 0.2 mm annually; lack of gingival inflammation or peri-implant gingivitis amenable to treatment; absence of symptoms of infection and pain; absence of damage to adjacent teeth; absence of paresthesia, anesthesia, or violation of the inferior alveolar canal or maxillary sinus; and functional survival for 5 years in 90% of the cases and 10 years in 85%.

Implant success and failure are dynamic time-linked conditions, and require periodic reevaluation and, if needed, a salvation treatment. Implant failure is a static end-result condition that requires removal of a failed implant.

There are 2 commonly used periods to assess implant failures that relate to the time when failure occurs: (1) early failures or failures during the osseointegration period (usually within the first year after an implant insertion, during the healing period, and initial loading); and (2) late failures or failures after the osseointegration period (usually about a year after implant insertion, when an osseointegration process is complete and implant function is established).

The often-cited causes for early failures during the osseointegration process are:3–14

  1. Poor quality (type 4 bone, posterior maxillary bone, irradiated bone, etc.) and quantity of bone (severe alveolar bone resorption), which can often be improved by osseous compression, ridge expansion, and/or grafting. Poor quality of soft tissue (lack of keratinized gingiva), which can be enhanced by soft tissue augmentation (grafting).3,5–8,11,13
  2. Patient medical condition that affects normal bone healing: immunocompromised condition (uncontrolled diabetes, acquired immunodeficiency syndrome), advanced osteoporosis, steroid therapy, metastatic bone disease in the jaw, metabolic and endocrine conditions, malnutrition and malabsorption syndromes, drugs that affect bone metabolism (bisphosphonates, others), collagen disorders, psychotic syndromes, lack of compliance, and other conditions.3,4,8,13,14
  3. Unfavorable patient habits: bruxism, heavy long-term smoking, poor oral hygiene, plaque accumulation, and others.5,6,8,10,13
  4. Inadequate surgical analysis and technique: suboptimal insertion technique and lack of primary implant stability, poor 3-dimensional implant position, etc.4,5,10,11,13
  5. Inadequate prosthetic analysis and technique: improper choice of the prosthesis, suboptimal prosthetic design and an occlusal scheme of the prosthesis, excessive load, inadequate laboratory work, etc.5,9–13
  6. Suboptimal implant design and surface characteristics.4,8,12
  7. Unknown factor.

From the 7 aforementioned causes of implant failures during the osseointegration period, 3 are related to a patient’s condition (first, second and third), 2 are associated with a dental practitioner’s expertise (fourth and fifth), 1 is connected to an implant choice (sixth), and the last is an unknown factor (seventh) when an implant fails, despite prevention of the aforementioned factors.

The more often cited causes of late failures after the osseointegration period and delivery of prosthesis usually relate to loading issues or peri-implantitis.9,13,15,16 They are:

  1. Occlusal overload/excessive stress:9,13,16
    1. Excessive loading.
    2. Poor occlusal design.
    3. Bruxism that was not diagnosed, controlled, or treated.
  2. Peri-implantitis and poor oral hygiene:13,15,16
    1. Patient’s lack of desire for proper and adequate oral hygiene.
    2. Patient’s lack of dexterity because of handicap.
    3. Hygienically difficult and inaccessible prosthetic design.
    4. Inadequate doctor’s supervision of patient’s oral hygiene.
  3. Improper design, construction, and fit of the prosthesis:9,13
    1. Deficiency at any restorative and laboratory stage leading to dynamic failures and fractures of implant components.
    2. Defective implant components.
    3. Fatigue of implant components, resulting in loose screws, fractures, etc.
  4. Unknown factor

From the 4 causes of late implant failures, the first is related to a patient’s occlusal interferences and a chronic trauma associated with it. The second can be linked to an infection process around an implant accrued over a period of time.17 The third comes from the biomechanical problems with the design and construction of the implant prosthesis. The last is an unknown factor, when an implant fails, despite avoidance of the aforementioned factors.

This article attempts to investigate late implant failures by comparing bone connection of dental implants, healthy natural teeth, and ankylosed teeth. Based on this comparison, a concept of implant vulnerability is proposed.

Similarities and Differences Among Dental Implants, Healthy Natural Teeth, and Ankylosed Teeth

Implants and Healthy Natural Teeth: Similarities

Under optimal local and systemic conditions, both natural teeth (with a healthy periodontal ligament) and implants (without Sharpey fibers and with a direct connection to bone) maintain a healthy periodontal and peri-implant environment. Unfavorable local factors, like poor oral hygiene, advanced and uncontrolled periodontal disease, chronic occlusal trauma, etc., or systemic conditions (uncontrolled diabetes, etc.) can often initiate clinically significant gingival inflammation around both natural teeth (gingivitis) and implants (peri-implant mucositis). It is well understood that if this soft tissue disease is not corrected in time, the gingival inflammatory condition in many cases can progress to the underlying bone and cause marginal bone loss (marginal periodontitis around teeth or peri-implantitis around implants). This local body response to a chronic bacterial or traumatic insult appears to be similar for healthy teeth, as well as implants, and often results in the compromised bone integrity around them.

Implants and Ankylosed Teeth: Differences

An ankylosed tooth (endodontically treated or vital) by definition forms a very strong bond to the surrounding bone without periodontal ligament interface. In the case of tooth ankylosis, analogous or similar tissues (i.e., root cementum and surrounding bone) directly contact each other and create a strong union. In fact, histologically, the root cementum and surrounding bone are so similar that oral pathologists often cannot distinguish between them under the microscope. They frequently recommend clinical correlation and rely on a doctor’s judgment to determine the nature of a tissue that resembles either bone or root cementum.

In the literature and clinical practice, dental practitioners often compare osseointegrated implants with ankylosed teeth, trying to illustrate similarities in bone fusion and rigidity. If under healthy conditions, this comparison seems to make sense, then under pathologic conditions (local and/or systemic disease), their behavior appears to be very different.

It appears that ankylosed teeth consistently maintain their bone union and resist periodontal bone loss even in the presence of unfavorable conditions, like traumatic occlusion, advanced local periodontal disease, poor oral hygiene, etc. This ankylosed root-to-bone connection is exceedingly strong. Ankylosed teeth often remain in the mouth indefinitely or until surgical removal by a doctor. On the contrary, implants, like healthy teeth, appear to be quite susceptible to the influence of detrimental systemic or local factors of the bacterial or traumatic nature and can develop a peri-implant bone resorption as a reaction to these factors.

A Concept of Implant Vulnerability

In this article, an attempt is made to investigate why a fully integrated implant can develop bone loss and possibly fail many years after completion of the osseointegration process. This attempt is based on the aforementioned comparison of dental implants and natural teeth, and their bone contacting surfaces: TiO of implants, root cementum and periodontal ligament of teeth.

It appears that under unfavorable local and/or systemic conditions, one of the reasons for a fully osseointegrated implant in some cases to develop a progressive marginal bone loss (peri-implantitis) is the relative weakness or a vulnerability of the implant-to-bone connection. The implant and bone contacting surfaces consists of histologically different tissues: metal (titanium oxide) and the jaw bone. Under normal conditions, this metal-to-bone contact is stable and balanced, and resists bone resorption. Under adverse or pathologic chronic conditions, often of a bacterial or traumatic nature, as well as deterioration in the systemic health, the tissue balance can become disturbed (stressed), leading to initiation of a bone loss, compromised bone integrity, and, eventually, an implant failure.

By comparison, an ankylosed tooth connection to the bone has similar or matching connecting surfaces (cementum and bone) with an exceptionally strong union that can last indefinitely, undisturbed by changes in the local or systemic environment. In other words, the jaw bone reacts to an implant insertion, like an invasion of privacy. Although the bone can establish a balance with certain metals and maintain a rigid connection for a long period of time, in a state of detrimental repetitive local or systemic factors, an implant-bone connection can become compromised and may lead to implant failure.

Summarizing the functional comparison of implants, natural healthy teeth, and ankylosed teeth, it seems that periodontally healthy teeth, under unfavorable conditions, react in a similar manner as implants by developing marginal bone loss or resorption. It appears to be nature’s protective mechanism to reestablish the crestal bone to the lower level as a reaction to a prolonged bacterial or traumatic impact (a “pathologic width”, in comparison with a naturally occurring biologic width). Ankylosed teeth under the same circumstances respond in a different way than implants and can retain the crestal bone level because of the intrinsic superiority of their connection relative to osseointegration. The comparison in behavior of natural healthy teeth, ankylosed teeth, and osseointegrated implants is summarized in Table 1. The other causes of marginal bone loss around implants, like implant-abutment interface (micro-gap theory), anatomic discrepancies of the thin alveolar ridge and implant diameter, too close implant placement, an implant body and platform design (platform switching theory), etc., are outside the scope of this article.

Table 1
Table 1:
Comparison Between Implants, Healthy Natural Teeth and Ankylosed Teeth


Although overwhelming research beginning with Dr. P.I. Brånemark confirms successful integration of root-form implants, we are still far from understanding the causes of implant failure years after successful initial integration. The proposed implant vulnerability theory attempts to explain why it can happen, as well as emphasizes an importance for prevention of detrimental local conditions, like poor oral hygiene, advanced periodontal disease, occlusal interferences, and others at any stage of implant function. Logically, clinical supervision of a patient’s implant situation with a good recall program should continue indefinitely.

It is important that surgical and restorative dental implant practitioners accumulate clinical data in a standardized manner to analyze implant successes and failures over an extended period of time. This accumulated knowledge should help to explain stillunknown factors of implant failures. The following chart is used in the author’s practice to monitor and analyze implant failures (Table 2). At this time, caution needs to be exercised in giving guarantees of long-term implant success to our patients.

Table 2
Table 2:
Dental Implant Failure Analysis


The author claims to have no financial interest in any company or product mentioned in this article.


The author thanks Drs. Dennis Flanagan and Gregory Kurtzmann for their assistance in preparation of this article.


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Abstract Translations


AUTOR: Len Tolstunov, DDS*. *Privat praktizierender Arzt, San Francisco, CA; Klinischer Assistenzprofessor, Pazifik-Universität, zahnmedizinische Fakultät, San Francisco, CA. Schriftverkehr: Len Tolstunov, DDS, 1 Daniel Burnham Court, Suite 366C, San Francisco, CA 94109; Telefon: 415-346-5966, Fax: 415-346-5969.

Erfolgs-Versagens-Analyse bei Zahnimplantaten: Eine Konzeption der Verletzlichkeit von Implantaten

ZUSAMMENFASSUNG: Der vorliegende Artikel stellt die für einen langfristigen Erfolg oder ein dauerhaftes Versagen von Zahnimplantaten wichtigen Faktoren anhand einer Prüfung der vorhandenen Fachliteratur heraus. Viele Faktoren werden mit dem Versagen von Zahnimplantaten in Verbindung gebracht. Die für ein frühzeitiges wie spätes Fehlschlagen der Zahnimplantierung kritischen Komponenten werden bewertet. Das Verhalten von gesunden Zähnen und Implantaten wird bei sowohl stabilen wie auch ungünstigen lokalen und systemischen Bedingungen verglichen. Es erfolgt eine Gegenüberstellung der Áhnlichkeiten und Unterschiede zwischen Zahnimplantaten, gesunden natürlichen Zähnen und versteiftem Zahnapparat. Von diesem Vergleich ausgehend, versucht der Autor eine Schlussfolgerung bezüglich der Verletzlichkeit von Zahnimplantaten und ihren Aussichten auf langfristigen Erfolg zu ziehen. Es wird betont, wie wichtig eine fortdauernde klinische Nachverfolgung des Implantatzustands eines Patienten über ein überzeugendes Rückrufprogramm ist. Außerdem wird der Notwendigkeit, die klinischen Daten bezüglich Implantatversagen über einen langen Zeitraum in standardisierter Form zu sammeln, besonderer Nachdruck verliehen. Zusätzlich erfolgt die Empfehlung an die implantierenden Zahnärzte, ihren Patienten keine Garantie für Langzeit-Implantate auszustellen.

SCHLÜSSELWÖRTER: Knochengewebsintegration, Verletzlichkeit der Implantate, Knochengewebsverbindung, echte Zähne, versteifte Zähne


AUTOR: Len Tolstunov, DDS*. *Práctica Privada, San Francisco, CA; Profesor Clínico Asistente, Facultad de Odontología de la Universidad of the Pacific, San Francisco, CA. Correspondencia a: Len Tolstunov, DDS, 1 Daniel Burnham Court, Suite 366C, San Francisco, CA 94109. Teléfono: 415-346-5966, Fax: 415-346-5969, Correo electrónico:

Análisis del éxito o fracaso de implantes dentales: Concepto de vulnerabilidad del implante

ABSTRACTO: Este artículo demuestra los factores de importancia en el éxito o falla a largo plazo de implantes orales basados en un análisis de la literatura. Se atribuyen muchos factores a la falla de los implantes dentales. Se evalúan los componentes críticos que llevan a una falla temprana y tardía del implante. El comportamiento de los dientes naturales y los implantes se compara con condiciones locales y sistémicas saludables y desfavorables. Se examinan las diferencias y similitudes entre implantes dentales, dientes naturales y dientes anquilosados. Basado en esta comparación, el autor trata de llegar a una conclusión sobre la vulnerabilidad de los implantes dentales y su pronóstico. Se enfatiza la importancia de una supervisión clínica continua de la condición del implante del paciente con un buen programa de recuperación y la necesidad de acumular datos clínicos sobre las fallas del implante durante un largo período de tiempo de manera estándar. También se sugiere que los profesionales de los implantes deberían evitar dar garantías a sus pacientes de éxito de los implantes a largo plazo.

PALABRAS CLAVES: oseointegración, vulnerabilidad del implante, conexión con el hueso, dientes naturales, dientes anquilosados


AUTOR: Len Tolstunov, DDS*. *Clínica particular, San Francisco, CA; Professor Clínico Assistente, Universidade do Pacífico, Faculdade de Odontologia, San Francisco, CA. Correspondência para: Len Tolstunov, DDS, 1 Daniel Burnham Court, Suite 366C, San Francisco, CA 94109. Telefone: 415-346-5966, Fax: 415-346-5969, E-Mail:

Análise de Sucesso-Falha de Implantes Dentários: Conceito de Vulnerabilidade do Implante

RESUMO: Este artigo demonstra os fatores de importância no sucesso e falha de longo prazo de implantes orais baseados em resenha de literatura. Muitos fatores são atribuídos a falha de implantes dentários. O componentes críticos que lavam a falhas de implantes precoces e tardias são avaliadas. O comportamento de dentes naturais e implantes é comparado em condições locais e sistêmicas saudáveis e desfavoráveis. As semelhanças e diferenças entre implantes dentários, dentes naturais saudáveis e dentes ancilosados são examinadas. Com base nessa comparação, o autor tenta tirar uma conclusão sobre a vulnerabilidade de implantes dentários e seus prognósticos. A importância de supervisão clínica em curso da condição do implante de um paciente com bom programa de retorno periódico e a necessidade de acumular dados clínicos com relação a falhas de implantes por um período prolongado de tempo de maneira padronizada é enfatizada. Também é sugerido que os profissionais de implantes devem evitar dar garantias de sucesso de implante de longo prazo a seus pacientes.

PALAVRAS-CHAVE: osseointegração, vulnerabilidade dos implantes, conexão do osso, dentes naturais, dentes ancilosados





osseointegration; implant vulnerability; bone connection; natural teeth; ankylosed teeth

© 2006 Lippincott Williams & Wilkins, Inc.