| Abstract|| |
The burning problem that all the implantologists are confronted today is the complications and failures occurring with the treatment of osseointegrated implants. To further optimize the treatment outcome, etiologies and factors associated with implant failures should be elucidated. Conceivably such knowledge is needed for developing adequate treatment and prevention strategies. Hence, this paper is intended to provide an insight regarding various aspects of failures that affect dental implants.
Keywords: Classification of failures, implant failures, peri-implantitis
|How to cite this article:|
Prashanti E, Sajjan S, Reddy JM. Failures in implants. Indian J Dent Res 2011;22:446-53
Dentistry has undergone many changes during the past quarter century; however, no changes have been more profound than those in the field of implant dentistry. Successful endosseous alloplastic implants can be found dating back to AD 600, but the surge in implants for tooth replacement did not flourish until the middle of 1900s.
Now that its scientific foundations have been laid, this branch of reconstructive dentistry has passed out of the phase of mere empiricism and sheer wishful thinking. As a result, implant dentistry is now taken much more seriously than was the case, 10 or 20 years ago.
As the patient population, able to benefit from implant therapy increases, the clinician is faced with increasingly complex options. Though the success rates reported with this form of therapy are relatively high, failures do occur. Hence, a thorough knowledge regarding the various aspects of failure is deemed necessary.
| Definitions|| |
- Implant failure is the first instance at which the performance of the implant, measured in some quantitative way falls below a specified and acceptable level. 
- Implant failure is defined as the total failure of the implant to fulfill its purpose (functional, esthetic or phonetic) because of mechanical or biological reasons. 
- Implant failure is the inadequacy of the host tissue to establish or to maintain ossiointegration. 
Iatrogenic failure and biologic failure
Iatrogenic failure is one characterized by a stable and osseointegrated implant, but due to malpositioning it is prevented from being used as part of the anchorage unit. 
Biological failure can be defined as the inadequacy of the host tissue to establish or to maintain osseointegration. 
- An implant that may demonstrate bone loss with deeper clinical probing depths but appears to be stable when evaluated at 3-4 months interval. 
- Ailing implants are those showing radiographic bone loss without inflammatory signs or mobility. 
- An implant that may demonstrate bone loss, increasing clinical probing depths, bleeding on probing, and suppuration. Bone loss may be progressive. 
- Failing implants are characterized by progressive bone loss, signs of inflammation and no mobility. 
- An implant that demonstrates clinical mobility, a peri-implant radiolucency, and a dull sound when percussed. A failed implant is non-functional and must be removed. 
- Failed implants are those with progressive bone loss, with clinical mobility and that which are not functioning in the intended sense. 
Surviving is a term described by Alberktson that applies to implants that are still in function but have not been tested against success criteria. 
| Success and Failure Statistics|| |
The longitudinal clinical studies have reported a success rate at 10 years ranging from 81% to 85%, for the maxilla and from 98% to 99% for the anterior mandible.  Despite high success rates, failures do occur. Esposito et al. reported the biologically related implant failures calculated on a sample of 2812 implants and found a failure rate of 7.7% over a 5 year period. 
Bain and Moy (1993), reviewed the outcome of 2194 Branemark implants placed in 540 patients over a 6 year period and reported a failure rate of 5.92%. Friberg et al. conducted a study comprising 4641 Branemark dental implants for a period of 3 years and reported a failure rate of 1.5%. 
| When to Say an Implant has Failed?|| |
The individual practitioner and certifying agencies are presented with a bewildering series of choices in determining which implant systems provide an adequate prognosis to warrant their acceptance for clinical use. To make these critical selections, a set of criteria for success based on scientific investigations is essential. 
Consideration must be given to evaluating the following criteria:
- Bone loss
- Gingival health
- Pocket depth
- Effect on adjacent teeth
- Presence of infection, discomfort, paraesthesia or anesthesia
- Intrusion on the mandibular canal
- Emotional and psychological attitude and satisfaction of the patient Smith and Zarb  have reviewed the success criteria given by different authors.
Schnitman and Schulman
- Mobility less than 1 mm in any direction.
- Radiologically observed radiolucency graded but no success criterion defined.
- Bone loss not greater than one third of the vertical height of the bone.
- Gingival inflammation amenable to treatment.
- Functional service for 5 years in 75% of patients. 
Chainin, Silver Branch, Sher, and Salter
- In place for 60 months or more.
- Lack of significant evidence of cervical saucerization on radiographs.
- Freedom from hemorrhage according to Muhelman's index.
- Lack of mobility.
- Absence of pain and tenderness.
- No pericervical granulomatosis or gingival hyperplasia.
- No evidence of a widening peri-implant space on radiograph. 
Mckinney, Koth, and Steflik
- Adequate function.
- Absence of discomfort.
- Patient belief that esthetics, emotional, and psychological attitude are improved.
- Good occlusal balance and vertical dimension.
- Bone loss no greater than one third of the vertical height of the implant, absence of symptoms and functionally stable after 5 years.
- Gingival inflammation vulnerable to treatment.
- Mobility of less than 1 mm buccolingually, mesiodistally, and vertically.
- Absence of symptoms and infection associated with the dental implant.
- Absence of damage to adjacent tooth or teeth and their supporting structures.
- Absence of parasthesia or violation of mandibular canal, maxillary sinus, or floor of nasal passage.
- Healthy collagenous tissue without polymorphonuclear infiltration. 
Provides functional service for 5 years in 75% of implant patients.
| Revised Criteria for Implant Success|| |
Alberktson, Zarb, Washington, and Erickson
- Individual unattached implant that is immobile when tested clinically.
- Radiograph that does not demonstrate evidence of peri-implant radiolucency.
- Bone loss that is less than 0.2 mm annually after the implant's first year of service.
- Individual implant performance that is characterized by an absence of persistent and/or irreversible signs and symptoms of pain, infections, necropathies, paraesthesia, or violation of the mandibular canal.
- In content of criteria mentioned, a success rate of 85% at the end of a 5-year observation period and 80% at the end of 10-year observation as a minimum criterion for success. 
Further, in 1998 Esposito et al. have listed out the various criteria for success which were agreed upon at the 1 st European Workshop on Periodontology. 
According to them - absence of mobility and an average radiographic marginal bone loss of less than 1.5 mm during the first year of function and less than 0.2 mm annually thereafter, absence of pain/parasthesia were to be considered success criteria for osseointegrated implants. It was also suggested that probing depths related to a fixed reference point and bleeding on probing should be measured. 
Several authors have expressed many criteria to assess the success of a functional implant. The success criteria, which were initially targeted for evaluation as 5 years survival has changed. With the improved technology and understanding of the tissue behavior the criteria are set with a target of 10-year survival rate  .
| Failing V/S Failed Implants|| |
While it is possible to clearly differentiate between a successful and a failed implant, it still remains difficult to identify failing implants. The parameters, which have been employed clinically to evaluate implant conditions were discussed by Esposito et al.  with the attempt to identify the most reliable ones.
The most common diagnostic criteria employed for the evaluation of established implant failures (failed implants) are as follows:
Clinical signs of early infection
During the healing period (3-9 months) complications such as swelling, fistulas, suppuration, early/late mucosal dehiscences, and oseteomyelitis, can occasionally be present and may indicate implant failure. Signs of infection occurring during at an early stage of healing is more critical than if they occur at a later stage. This is because; the infection occurring at an early stage will lead to disturbance in the osseointegration of the implant to the surrounding bone.
Pain or sensitivity
Pain or discomfort is often associated with mobility and could be one of the first signs which indicate an implant failure.
Clinical discernible mobility
Mobility is always a clear sign of failure. Once the clinician has distinguished between the mobility of a poorly connected abutment and the mobility of the underlying implant, the implant must be suspected to be surrounded by a fibrous tissue capsule.
Several different types of mobility have been recognized as follows: 
- Rotation mobility
- Lateral or horizontal mobility
- Axial or vertical mobility.
Occasionally, clinically discernible mobility can be present without distinct radiographic bone changes. Therefore, mobility is the cardinal sign of implant failure. 
Radiographic signs of failure
There can be two well-distinct radiographic pictures: a thin peri-fixtural radiolucency surrounding the entire implant, suggesting the absence of a direct bone-implant contact and possibly a loss of stability, and an increased marginal bone loss.
Since the distinction between the two radiographic pictures is not always clear, when a suspected peri-fixtural radiolucency or excessive marginal bone loss is observed, it is recommended to remove the prosthetic construction and cheek the implants for stability. Clinically discernible mobility after bridge removal can confirm the presumptive radiographic diagnosis of implant failure.
Dull sound at percussion
It has been suggested that a subdued sound upon percussion is indicative of soft tissue encapsulation, whereas a clear crystallization sound indicates successful osseointegration. 
Although it is a rather subjective test without a solid scientific background, it can provide a useful indication to the examiner.
| Parameters used for Evaluating Failing Implants|| |
The clinical signs previously discussed emerge only when the failure process reaches an irreversible state. However, the ideal parameter for monitoring implant conditions should be sensitive enough to distinguish early signs of implant failure.
The following parameters have, therefore, been proposed.
Radiographically observed progressive marginal bone loss
There seems to be unanimous consensus that progressive marginal bone loss is a pathological sign, which can lead to implant failure. Alberktson et al. have suggested using less than 1.5 mm of marginal bone loss during the 1 st year of loading and thereafter less than 0.2 mm yearly as success criteria.
Adell et al. determined that the mean bone loss for Branemark osseointegrated implants is 1.5 mm for the first year, followed by a mean bone loss of 0.1 mm per year. This value was confirmed by Cox and Zarb with their 3-year report showing a mean bone loss of 1.6 mm for the first year and a mean of 0.13 mm in subsequent years. Because documentation demonstrates that a mean bone loss of not more than 0.2 mm per year after the first year is attainable, this figure should serve as a valid criterion for success. 
Clinical signs of late infection
A progressive marginal infection can lead to implant failure. However, clinical signs of infection such as hyperplastic soft tissues, suppuration (spontaneous, on probing or under pressure), swelling, fistulation, color changes of the marginal peri-implant tissues, etc., are signs, which call for intervention.
In the absence of mobility and radiographic changes, these signs indicate more a complication (amenable to treatment) than a failure.  Mobelli et al. compared clinical and microbiological finding related to healthy and failing dental implants. Unsuccessful implant sites were characterized by probing depths 6 mm or greater, suppuration, bone loss, and micro biota consisting primarily of gram negative anaerobic rods. 
William Becker et al. reported that failing implants showed evidence of increased mobility and a high incidence of peri-implant radiolucencies. 
Bleeding on probing
Bleeding on probing has been employed to measure peri-implant tissue conditions. However, recent findings suggest that it cannot be used to discriminate between a healthy or diseased peri-implant state and it does not have a scientific support. 
Absence of keratinized mucosa
A relationship and correlation between implant failure and absence of an adequate band of keratinized mucosa surrounding the abutment has been suggested. Esposito et al.  state that nowadays, there seems to be consensus that clinical data, acquired via an evidence based format have failed to show any correlation between the width of keratinized mucosa and implant failures. However, there might be some situations where the patient can benefit form the presence of attached keratinized tissue specifically to facilitate plaque removal. 
| Classifications|| |
Many factors are attributed to failure of the dental implant, either directly or indirectly.  Various authors have classified implant failures depending on several criteria.
Rosenberg et al.  classified implant failures as
An implant was determined to have failed from infection if one or more of the following criteria were seen.
- Clinical signs of infection with classic symptoms of inflammation.
- High plaque and gingival indices.
- Attachment loss.
- Radiographic peri-implant radiolucency.
- Presence of glaucomatous tissue upon removal.
Implant was suspected to fail from traumatic conditions if the following conditions existed.
- Radiographic peri-implant radiolucency.
- Lack of glaucomatous tissue upon removal.
- Lack of increased probing depths.
- Low plaque and gingival indices.
Hobo et al.  listed out the various complications occurring in implants as follows: [Table 1]
Esposito et al. have classified oral implant failures according to the osseointegration concept. 
Early or primary (before loading): failure to establish osseointegration.
Late and secondary (after loading): failure to maintain the achieved osseointegration.
Fracture of implants, connecting screws, bridge frameworks, coating etc.
Nerve damages, wrong alignment of implants, etc.
Inadequate patient adaptation
Phonetical, esthetical, psychological problems, etc.
Truhlar  classified failures as
- That occur with in weeks to few months after placement.
- Caused by factors that can interfere with normal healing processes or by an altered healing response.
El Askary et al.  have divided the failures into seven categories.
- Failure that arise from pathologic processes that involve a previously osseointegrated implant.
According to etiology
Failures because of host factors
- Medical status - Osteoporosis and other bone diseases; uncontrolled diabetes.
- Habits - smoking, para-functional habits.
- Oral status - poor home care [Figure 1], juvenile, and rapidly progressive periodontitis, irradiation therapy.
Excessive cantilever, pier abutments, no passive fit, improper fit of the abutment, improper prosthetic design, improper occlusal scheme, bending moments, connecting implants to natural dentition, premature loading, excessive torquing.
- Off axis placement (severe angulation) [Figure 2]
- Lack of initial stabilization
- Impaired healing and infection because of improper flap design or others.
- Overheating the bone and exerting too much pressure.
- Minimal space between implants
- Placing the implant in immature bone grafted sites.
- Placement of the implant in an infected socket or a pathologic lesion.
- Contamination of the implant body before insertion.
According to origin of infection
- Improper implant type in improper bone type.
- Length of the implant (too short, crown-implant ratio unfavorable)
- Diameter of the implant.
- Peri-implantitis (infective process, bacterial origin) [Figure 3]
- Retrograde peri-implantitis (traumatic occlusion origin, non-infective, forces off the long axis, premature, or excessive loading).
According to timing of failure
- Before stage II (after surgery)
- At stage II (With healing head and or abutment insertion)
- After restoration.
According to condition of failure: (clinical and radiographic status)
According to responsible personnel
- Ailing implants
- Failing implants
- Failed implants
- Surviving implants.
- Dentist (oral surgeon, prosthodontist, periodontist)
- Dental hygienist
- Laboratory technician
According to failure mode
According to supporting tissue type
- Lack of osseointegration (usually mobility)
- Unacceptable esthetics [Figure 4]
- Functional problems
- Psychological problems.
Heydenrijik et al.  The authors classified implant failures referring to occurrence in time as
- Soft tissue problems (lack of keratinized tissues, inflammation, etc.) [Figure 5]
- Bone loss (Radiographic changes, etc.)
- Both soft tissue and bone loss.
Osseointegration has never been established, thus representing an interference with healing process.
Osseointegration not maintained implying processes involving loss of osseointegration.
Soon late failures
Implants failing during the first year of loading.
Delayed late failures
Implants failing in subsequent years.
The authors suggest that early failures occur prior to prosthetic rehabilitation.
Late failures, which occur following prosthetic rehabilitation have been divided into:
Overloading in relation to poor bone quality and insufficient bone volume.
Progressive changes of the loading conditions in relation to bone quality and volume and peri-implantitis.
Esposito et al. , reviewed the various factors associated with increased failure rates, based on the present literature review [Table 2].
| Conclusion|| |
With any biomechanical entity, difficulties can arise in the area of biologic function as well as mechanical or engineering stability. 
Implant prosthodontics has been fraught with compromises and complications, which are frustrating to the patients and prosthodontists alike.
Predicting the adverse implant events and knowledge of treating the failing implants becomes mandatory for every clinician.
Avoiding those conditions that contribute to poor results, choosing cases that offer ideal surgical and prosthetic circumstances and scrupulously evading complex clinical challenges can improve favorable outcome data substantially.
Anticipating and diligently observing for implant fixture and restoration failure are the first step in managing and interdicting a declining clinical circumstance. Vigilance should be heightened when predictors of treatment compromise are present independent of the stage of treatment or the life of the prosthesis. As someone well said, it is not how much success we obtain, but how best we tackle complex situations and failures that determine the skill of a clinician. No doubt, failures are stepping-stones to success but not until their etiologies are established and their occurrence is prevented. Hence, it is mandatory for every clinician to know, how and why the failures occur and how best we can prevent them in order to give the upcoming branch of dentistry a new horizon.
After all, difficulties mastered are opportunities won.
| References|| |
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Department of Prosthodontics, Manipal College of Dental Sciences, Mangalore
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]