Success criteria for endosteal implants have been proposed previously by several authors1–6 The report by Albrektsson et al4 is widely used today. However, it does not consider the amount of crestal bone lost during the first year. In addition, success rates suggested in this guideline describe an ideal implant quality of health for a study or clinical report, but does not address individual implants that may have a stable condition in the mouth after a brief episode of bone loss.
The success criterion most commonly reported in clinical reports is the survival rate, meaning whether the implant is still physically in the mouth or has been removed.7 Proponents of this method say it provides the clearest presentation of the data. Critics argue that implants that should be removed because of pain or disease may be maintained and are wrongfully reported as being successful.
A natural tooth is not described in the literature as clinical success or failure. Instead, ideal conditions for a tooth are reported, and a quality of health scale is used to describe intraoral clinical conditions. In 1993, an implant quality of health scale was established by James and further developed by Misch.8,9 On 5th October, 2007, a Pisa, Italy Consensus Conference (sponsored by the International Congress of Oral Implantologists) modified the James–Misch Health Scale and approved 4 clinical category that contain conditions of implant success, survival, and failure. Survival conditions for implants may have 2 different categories: satisfactory survival describes an implant with less than ideal conditions, yet does not require clinical management; and compromised survival includes implants with less than ideal conditions, which require clinical treatment to reduce the risk of implant failure. Implant failure is the term used for implants that require removal or have already been lost.
The term implant success may be used to describe ideal clinical conditions. It should include a time period of at least 12 months for implants serving as prosthetic abutments. The term early implant success is suggested for a span of 1 to 3 years, intermediate implant success for 3 to 7 years, and long-term success for more than 7 years. The implant success rate should also include the associated prosthetic survival rate in a clinical report.
Periodontal indices are often used for the evaluation of dental implants.10,11 Periodontal indices, of themselves, do not define implant success or failure. These clinical indices must be related to other factors such as exudate or overloading of the prosthesis. However, understanding the basis of a few clinical indices for evaluation allows these criteria to establish a health-disease implant quality scale related to implant therapy.
Most clinical implant positions in the literature do not invade the structures of the infraorbital or inferior alveolar nerves. Therefore, in the success-to-failure criteria, it is assumed that the implant does not violate the major nerves of the jaws.12,13 Subjective findings of pain or tenderness associated with an implant body are more difficult to assess than these conditions with natural teeth.
Once the implant has achieved primary healing, absence of pain under vertical or horizontal forces is a primary subjective criterion. Pain should not be associated with the implant after healing. When present, it is more often an improper fitting prosthetic component, or pressure on the soft tissue from the prosthesis. Percussion and forces up to 500 g (1.2 psi) may be used clinically to evaluate implant pain or discomfort. Percussion is used for the impact force to the implant, not for the audible effect associated with integration. Usually, pain from the implant body does not occur unless the implant is mobile and surrounded by inflamed tissue or has rigid fixation but impinges on a nerve. Pain during function from an implant body is a subjective criterion that places the implant in the failure category. Sensitivity from an implant during function may place the implant in the survival criteria, and may warrant some clinical treatment.
Rigid fixation is a clinical term for implants, which describes the absence of observed clinical mobility with vertical or horizontal forces under 500 g, similar to evaluating teeth. Osseointegration is a histologic term defined as the surrounding bone in direct contact with an implant surface at the magnification of a light microscope.12 Over the years, rigid fixation and osseointegration have been used interchangeably. Today, the clinical term “lack of mobility” may be used to describe implant movement, and is a clinical condition most often used to determine as to whether the implant is integrated. A root-form implant supported prosthesis is most predictable with this type of support system.
Lack of clinical movement does not mean the true absence of mobility. A healthy implant may move less than 75 μm; yet, it appears as zero clinical mobility.14 Clinical lack of implant mobility does not always coincide with a direct bone–implant interface.3 However, when observed clinically, lack of mobility usually means that at least a portion of the implant is in direct contact with bone, although the percentage of bone contact cannot be specified.15 A clinically mobile implant indicates the presence of connective tissue between the implant and bone, and suggests clinical failure for an endosteal root-form implant. Implant “mobility” may be assessed by computer or various instruments,16,17 but at this point in time these instruments are not necessary to determine clinical movement in a horizontal or vertical direction as being implant failure.
Radiographic Crestal Bone Loss
The marginal bone around the implant crestal region is usually a significant indicator of implant health. The level of the crestal bone may be measured from the crestal position of the implant at the initial implant surgery. The most common method (in the literature) to asses bone loss after healing is by radiographic evaluation. Of course, conventional radiographics only monitor the mesial or distal aspect of bone loss around the implant body.
Several studies report yearly radiographic marginal bone loss after the first year of function in the range of 0 to 0.2 mm.18–20 The marginal bone loss for the quality of health scale should include the first year. Although there are many different aspects that contribute to early bone loss, regardless of the cause the overall amount of bone loss may affect clinical criteria of success to failure. Clinical studies often report statistical average bone loss—not the range of bone loss observed in the study. If 1 implant of 10 loses 5 mm of bone, the average bone loss in the study is 0.5 mm; yet, the range of bone loss was 0 to 5 mm. Each implant should be monitored as an independent unit when assessing bone loss for a clinical evaluation of success, survival, or failure.
Clinical observations obtained by probing or radiographic measurements of 0.1 mm for bone loss are operator sensitive and are not reliable. Therefore, the Pisa Consensus in this report suggests that the clinical assessment for each implant monitors marginal bone loss in increments of 1.0 mm. The bone loss measurement should be related to the original marginal bone level at implant insertion, rather than to a previous measurement (e.g., 1 year prior).
The most common method to assess the marginal bone loss is with a conventional periapical radiograph. Although this only determines the mesial and distal bone loss, it is a time-tested method. Computer-assisted image analysis and customized x-ray positioning devices may be superior methods of measuring bone loss,17 but are not required for the criteria established at this consensus.
Probing depths around teeth are an excellent proven means to assess the past and present health of natural teeth, but probing depths around implants may be of little diagnostic value, unless accompanied by signs (e.g., radiographic radiolucencies, purulent exudate, bleeding) and/or symptoms (e.g., discomfort, pain). The benefit of probing the implant sulcus has been challenged in the literature because sound scientific criteria are lacking. Increasing probing depths over time may indicate bone loss, but not necessarily indicate disease for an endosteal implant. Stable, rigid, fixated implants have been reported with pocket depths ranging from 2 to 6 mm. Lekholm et al20 found that the presence of deep pockets was not accompanied by accelerated marginal bone loss. Healthy, partially edentulous implant patients consistently exhibit greater probing depths around implants than around teeth.
Probing pressures are subjective, as is the angulation of the probe next to an implant crown. The “correct pressure” for probing has not been defined for implants, but may be less important than with teeth, because there is no connective tissue attachment zone next to an implant. The potential for damage to the fragile attachment or marring of the implant surface may exist during probing.3 On the other hand, there is no clinical or experimental evidence supporting this hypothesis.21 Future research in the area of probing is needed before including this as a primary criteria in a consensus for success, survival, and/or failure.
On the other hand, charting the attachment level in implant permucosal areas does aid the dentist in monitoring these regions. Probing to monitor implants has been suggested in several implant workshops and position articles.22–25 Sulcus depths greater than 5 to 6 mm around implants have a greater incidence of anaerobic bacteria26–28 and may require intervention in the presence of inflammation or exudate (e.g., surgery, antibiotic regimens). Probing not only measures pocket depth, but also reveals tissue consistency, bleeding, and the presence of exudate.29
It is of benefit to probe and establish a baseline measurement after the initial soft tissue healing around the permucosal aspect of the implant. Increases in this baseline measurement over time most often represents marginal bone loss. In the presence of other signs and/or symptoms, the probing depth compared with the baseline measurement may be diagnostic in a clinical evaluation.
Although routine probing healthy implants on a regular basis seems unwarranted, a baseline measurement and probing in the presence of other symptoms and/or signs is indicated. As such, in the ICOI Pisa Consensus Criteria, probing depths are not assessed in the success or satisfactory health conditions, but are included in the compromised survival condition.
The term peri-implantitis describes the bone loss from bacteria around an implant.30 Peri-implantitis is defined as an inflammatory process affecting the tissue around an implant in function that has resulted in loss of supporting bone.28 Bacteria, on occasion, may be the primary factor for bone loss around an implant. Anaerobic bacteria have been observed in the sulcus of implants, especially when probing depths are greater than 5 mm.27
Stress-induced bone loss (e.g., overloading the bone implant interface) occurs without bacteria as the primary causative agent.31–34 However, once the bone loss from stress or bacteria deepens the sulcular crevice and decreases the oxygen tension, anaerobic bacteria may become the primary promoters of the continued bone loss. In other words, the bacteria involved in peri-implatitis may oftentimes be secondary to one of the prime causative factors, such as overloading the bone–implant interface.
Exudate or an abscess around an implant indicates exacerbation of the peri-implant disease and possible accelerated bone loss. An exudate persisting for more than 1 to 2 weeks usually warrants surgical revision of the peri-implant area to eliminate causative elements. The reduced bone height, after the exudate episode, makes the implant more prone to secondary occlusal trauma. Therefore, the dentist must reevaluate stress factors for the new bony condition and often must reduce them to improve long-term performance.
The ICOI Pisa Implant Quality of Health Scale
The ICOI Pisa Implant Quality of Health is based on clinical evaluation. This scale allows the dentist to evaluate an implant using the listed criteria, place it in the appropriate category of health or disease, and then treat the implant accordingly. Three primary categories were established by the Consensus: success, survival, and failure. The success category describes optimum conditions, the survival category describes implants still in function but not with ideal conditions, and the failure of an implant represents an implant that should be or already has been removed. There are 4 implant groups to describe the clinical conditions of success, survival, or failure (Table 1).
Group I represents success and is considered optimum health conditions. No pain is observed with palpation, percussion, or function. No clinical implant mobility is noted in any direction with loads less than 500 g. Less than 2.0 mm of radiographically crestal bone loss is observed compared with the implant insertion surgery. The implant has no history of exudate. The prognosis of Group I implants is very good to excellent.
Group II implants are categorized as “survival” and have satisfactory health. They are stable, but show a history of, or potential for, clinical problems. No pain or tenderness is observed on palpation, percussion, or function. No observable mobility exists with loads less than 500 g. Radiographic crestal bone loss is between 2.0 and 4.0 mm from the implant insertion. The prognosis is good to very good, depending on the stable condition of the crestal bone.
Group III implants are also in the “survival” category, but exhibit a slight to moderate peri-implantitis and compromised health status. Group III implants are characterized by no pain in function. No vertical or initial horizontal mobility is evident. Greater than 4 mm radiographic crestal bone loss has occurred since implant placement, but bone loss is less than 50% from around the implant. Probing depths have increased from baseline up to one-half the length of the implant, often accompanied with bleeding on probing. Exudate episodes (if present) may have lasted more than 2 weeks. The prognosis is good to guarded, depending on the ability to reduce and control stress once the surgical corrections have improved the soft and hard tissue health.
The Group IV of the Pisa Implant Health Scale is clinical or absolute failure. The implant should be removed under any of these conditions: (1) pain on palpation, percussion or function, (2) horizontal and/or vertical mobility, (3) uncontrolled progressive bone loss, (4) uncontrolled exudate, or (5) more than 50% bone loss around the implant. Implants surgically placed but unable to be restored (sleepers) are also included in Group IV failure. Regardless of whether the implant is still in the mouth or removed, the implant is recorded in this category as a failure in all statistical data. Implants that have exfoliated or have been surgically removed are also in this failure category.
Implant success is as difficult to describe as the success criteria required for a tooth. A range from health to disease exists in both conditions. The primary criteria for assessing implant, quality, or health are pain and mobility. The presence of either one greatly compromises the implant and removal usually is indicated. Routine probing depths are not suggested in the absence of other sings or symptoms and may be related to the presence of local disease or preexisting tissue thickness before the implant was inserted. Bone loss is most often evaluated with radiographs, which only monitor the mesial and distal marginal bone next to the implant.
Implant failure is easier to describe than implant success or survival and may consist of a variety of factors. Any pain, vertical mobility, and uncontrolled progressive bone loss warrant implant removal.
The ICOI Pisa Consensus Conference has simplified and updated a Health Scale specific for endosteal implants and included categories of success, survival, and failure. In addition, these categories of health may be related to the prognosis of the existing conditions.
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