Evaluation of the Bone Implant Interface

The bone-implant interface is the most critical area which affects the success. The following ways are used to assess it:

1) Implant Mobility and Discomfort: Implant mobility is an indication of the lack of osseointegration. Even if periimplant disease has progressed relatively far,implants may still appear immobile because of some residual direct bone-implant contact. The recording of the implant mobility may be a very specific but not at all-sensitive clinical parameter in detecting the loss of osseointegration. The parameter more likely detects the final stage of loss of integration and therefore, represents a late implant loss.

Once the implant has achieved primary healing, absence of pain under vertical or horizontal forces is the primary subjective criterion. Percussion and forces upto 500 g are used clinically to evaluate tooth or implant pain or discomfort.Usually (but not always) pain does not occur unless the implant is mobile and surrounded by inflamed tissue or has rigid fixation but impinges on a nerve.Persistent discomfort may be evident long before any radiographic change is detectable. Technique to assess the rigid fixation is similar to that used for teeth. Two rigid instruments apply a labio-lingual force of 500 g. The implant mobility scale (Table ) is then used to assess the implant.

Clinical Implant Mobility Scale

2) Periotest: An electronic device originally developed by Schulte designed to measure the dampening effect or attenuation degree characteristics of the periodontium around natural teeth has been recommended to monitor the initial degrees of implant. It develops a force of 12 to 18 N. A soft surface or a mobile object will give higher recordings than a hard or rigid object. The recordings range from negative (-8) to positive (+50) numbers. Teeth with zero clinical mobility have typical ranges +5 to +9. The degree of absence of movement can thus be valuated from -8 to + 9. (17 degrees) However, differences in Periotest Values (PTV) have been reported for implants in the mandible and in the maxilla with implants in the maxilla showing higher PTVs.Despite some positive claims for this method, the prognostic accuracy of PTVs for the diagnosis of perimplantitis and early signs of implant failure has been criticized for the lack of resolution, poor sensitivity and susceptibility to operator variables.

3) Resonance Frequency Analysis: A non invasive device based on the principles of resonance frequency analysis (RFA) has been developed to measure primary implant stability and to monitor implant stability over time. This method evaluates the stiffness of the bone implant interface by means of a signal transducer connected to a frequency response organizer. The resonance frequency of the transducer implant unit is calculated from the peak amplitude of the signal and is graphically  illustrated on the display of the unit as peak of the frequency-amplitude plot. In addition, an implant stability quotient (ISQ) is displayed as a number between 1 and 100. This ISQ is to quantify the frequency measurements of implants within a range between 3500 and 8500 HZ. ISQ values of a stable osseointegrated implant increases with time, indicating the increase in bone implant contact area.On the other hand, crestal bone loss is correlated with loss of implant stability.

4) Radiographic Assessment: Radiographic examination is very different with implants than with teeth. Radiographs are frequently used in implant treatment to evaluate:

• Initial osseointegration.
• Seating of abutments.
• Fit of prosthesis.
• Baseline bone level evaluation following completion of prosthetic treatment.
• Longitudinal evaluation of bone levels.

In general, the long cone paralleling technique, supported by positioning devices is used.

Annual radiographs following treatment are recommended in the maintenance protocol to assess crestal bone levels. When examining the radiograph, make sure to pay attention to both crestal bone levels and implant integrity.

Crestal Bone Levels: Bone levels should be assessed on the mesial and distal surfaces of implants. Any changes between visits should be documented and evaluated along with clinical evidence to determine if any treatment is required.Due to routine bone remodeling, normal peri-implant bone level is expected to be at the first thread when using two-stage screw-type implants. For other types, the bone level should be approximately 2 mm from the implant platform. The distance from a landmark on the implant to the alveolar bone crest represents a reliable parameter for long-term monitoring in clinical practice.

Implant Integrity: A horizontal dark line at the abutment level is most probably due to screw-loosening and separation of elements. This may happen between the abutment and the implant or between the prosthesis and the abutment. If screw-loosening with separation has occurred, in addition to the radiographic evidence,clinical evidence should also be present.

It should be noted that conventional radiography yields a high proportion of false negative findings, i.e. It has a low sensitivity in the detection of early pathologic and/ or bone remodeling changes. Therefore, radiographic methods are confirmatory rather than exploratory and should only be considered in conjunction with assessment of the clinical parameters.