Different Methods to Evaluate Osseointegration

The criteria of success in implant dentistry remains complex. The vast majority of clinical reports noting success and failure do not qualify the success achieved.Earlier implant failure only meant that the implant was no longer present. The concept of success should be eliminated and replaced with the concept of quality of health.The criteria for endosteal implants have been previously proposed by many authors including Schnitman and Shulman, Cranin et al, McKinney et al and Albrektsson et al and those included in this discussion are as follows:

1. Pain

2. Rigid fixation

3. Percussion

4. Bone loss

5. Radiographic evaluation

6. Periimplant diseases

7. Probing depth

8. Bleeding index

Criteria for Implant Success as given by Albrektsson are:

1. An individual unattached implant is immobile when tested clinically

2. A radiograph does not demonstrate any evidence of peri implant radiolucency

3. Vertical bone loss is less than 0.2 mm annually following the implant's first year of service

4. Individual implant performance is characterized by an absence of persistent and/or irreversible signs and symptoms such as pain, infection, neuropathies,paresthesia or violation of mandibular canal

5. In the context of above, a success rate of 85% at the end of a 5 year observation period and 80% at the end of a 10 year period are the minimum criteria for success

It is important to understand that these criteria are for the overall success of the implant and the prosthesis over a longer period of time and will be discussed in the unit of success criteria and maintenance of implants. However at this stage of evaluating the implants prior to Stage II the following criteria apply.

Pain

Pain and tenderness are subjective criteria and depend on patient's interpretation of the degree of discomfort. Pain is defined as unpleasant sensation from mild discomfort to excruciating agony. Tenderness is more of an unpleasant awareness of the region. Once the implant has achieved primary healing, absence of pain under vertical or horizontal forces is the primary subjective criteria. Percussion and forces upto 500g (1.2lb) are clinically used to evaluate implant pain or discomfort. Pain does not occur unless the implant is mobile and surrounded by inflamed tissue or has rigid fixation but impinges on the nerve. The presence ofpain requires removal of the implant, even in the absence of mobility. Pain from rigid fixated implants is expressed as an early problem, whereas pain from mobile implant may occur early or late in the treatment. In either case the condition rarely improves.

Implant sensitivity or mild tenderness rather than pain in a rigid implant is most unusual and signals more a complication for an implant than for a tooth. Tenderness during function or percussion usually implies healing in the proximity of a nerve or on rare occasion bone stress beyond physiologic limit. If implant tenderness immediately postsurgery occurs in the proximity of the mandibular canal the implant may be unthreaded 1 mm and re evaluated for a decrease in symptoms after 3 or more weeks. If the tenderness is after stage 1 healing and is not due to surgical encroachment on an anatomical landmark stress may be the causative factor. Treatment then consists of elimination of as much stress on implant and or prosthesis (If immediate loading) as is possible for 3 or more weeks.

Rigid Fixation

Is a clinical term that means absence of observed mobility. Rigid fixation indicates the absence of clinical mobility of an implant that was tested with vertical or horizontal forces under 500g similar to evaluating teeth. Lack of clinically observable movement does not mean the true absence of any movement. A healthy implant moves less than 75 micro meter hence it has zero clinical mobility. The rigid fixation usually means that at least a portion of the implant is in direct contact cannot be specified. A mobile implant indicates the presence of connective tissue between the implant and the bone. Unlike a tooth where mobility is not a primary factor for longevity mobility is a major determinant factor for implant health. Rigid fixation is also an excellent indicator for health status because it is an easy objective test. The technique to assess rigid fixation involves use of two rigid instruments which apply a labiolingual force of approximately 500g. the amplitude of mobility may be measured from 0 to 4.

Clinical Implant Mobility Scale

Implants with slight detectable mobility of approximately 0.1mm horizontal movement may on occasion return to rigid fixation and zero mobility. An implant with horizontal movement greater than 0.5mm is at much greater risk than a tooth.The clinician should not restore an implant with any clinical mobility because the risk of failure is great.Once the prosthesis is completed and the mobility develops, there is little risk to decrease most of all stress. An implant with > 0.5 mm horizontal mobility or any vertical mobility should be removed to avoid continued bone loss and a compromised implant site for the future.

Periotest being used to evaluate implant rigid fixation

The Periotest is a computerised mechanical device developed by Schulte that measures the dampening effect or attenuation degree against objects by developing a force of 12 to 18 Newton. A soft surface or mobile object will give a higher recordings than a hard or rigid object. The recording ranges from -8 to +50. Teeth with 0 clinical mobility have typical ranges from +5 to +9. The degree of absence of clinical movement, therefore, can be evaluated from -8 to +9, or 17 degrees.This greatly aides the clinician's tactile senses. The bone density around the implant can be correlated to these numbers. This device may be used as a clinical tool to evaluate slight changes in implant rigid fixation.Resonance Frequency Analysis is another contemporary noninvasive diagnostic method that measures implant stability and bone density at various points of time using vibration and a principle of structural analysis. It utilizes a small transducer that is tightened to the implant and a hand unit that gives a sinusoidal wave which generates a resonance peaks which have been converted to form a implant stability quotient. (ISQ) which ranges from 0-100. A successful implant has an ISQ greater than 65 while ISQ < 50 may indicate a potential failure or increased risk of failure.

Percussion

It is neither an indicator of clinical health nor of rigid fixation. Ringing sound that occurs on percussion corresponds to the presence of some bone at the interface because 2 mm of bone and 16 mm bone implant interface sounds almost identical. It is misleading if used to determine the status of rigid fixation.

Bone Loss

Crestal bone loss after intial healing is a primary indicator of the need for initial preventive therapy. Early loss of crestal bone is usually a result of excess stress at the permucosal site. It is suggested that an implant be inserted at or above the bone crest to avoid an increase in the Sulcus Depth subsequent to abutment placement. The initial bone loss after the abutment is connected and during the 1st 2 years of function is usually a result of excessive stress at the crestal implant bone interface. Secondly, bone loss around an implant is usually a compound condition created by bacteria and increased stress (a result of parafunction and / increasing crown height from crestal bone loss and anaerobic bacteria forming once the sulcus is > 4 to 5 mm). Clinical observations obtained by probing or radiographic measurements of 0.1 mm per year for bone loss are operator sensitive and not reliable. Instead the threaded implant pitch (distance between the threads) is usually 0.6 mm and can be used as a radiographic marker. Probing changes of 0.5mm or more are also more realistic to monitor. In general, if more than 1 half of the implant height has lost crestal bony contact, the implant is at significant risk and considered a failure regardless of the intial amount of implant bone contact.

Radiographic Evaluation

Surgical and interventional imaging involves imaging the patient during and immediately after surgery and during the placement of the prosthesis.The purpose of surgical imaging is to evaluate the depth of implant placement, the position and orientation of implants/osteotomies, and to evaluate donor or graft sites.The patient can be generally imaged at chair side with periapical radiography to determine implant/osteotomy depth, position, and orientation and subsequently, after 6-8 weeks to evaluate radiographic changes for levels of osseointegration .Digital periapical image receptors enable virtually instantaneous image acquisition, produce image quality similar to that of dental film, and enable the surgical procedure to proceed without undue delay.Additional features of digital imaging include image enhancement and the use of digital measuring techniques, which help the surgeon in establishing the optimum depth and orientation of the implants.

Implant Imaging Modalities:

•  Periapical radiography
•  Digital periapical radiography
•  Bite-wing radiographs
•  Temporal digital subtraction radiography

Periapical radiography

Periapical radiographs are images of a limited region of the mandibular or maxillary alveolus. Periapical radiographs are produced by placing the film intraorally parallel to the body of the alveolus with the central ray of the X-ray device perpendicular to the alveolus at the region of interest, producing a lateral view of the alveolus. Periapical radiographs provide a lateral view of the jaws and no cross sectional information.

In terms of the objectives of pre-prosthetic imaging, periapical radiography is

1. A useful high yield modality for ruling out local bone or dental disease.

2. Of limited value in determining quantity because the image is magnified, may be distorted, and does not depict the third dimension of bone width.

3. Of limited value in determining bone density or mineralization (the lateral cortical plates prevent accurate interpretation and cannot differentiate subtle trabecular bone changes.

4. Of value in identifying critical structures, but of little use in depicting the spatial relationship between the structures and the implant site.

5. The implant bone interface is depicted only at the mesial, or distal, inferior, and crestal aspects or, where the central ray the X-ray source is tangent to the implant surface. Other regions of the implant interface are simply not depicted well by this modality.IOPA radiograph depicting implant bone interface at the mesial, distal, inferior and crestal aspects IOPA radiograph depicting implant bone interface at the mesial, distal, inferior and crestal aspects

IOPA radiograph depicting implant bone interface at the mesial, distal, inferior and crestal aspects

Digital radiographs can be subjected to image processing with which the images can be altered to achieve task specific image characteristics. For example, density and contrast can be lowered for evaluations of the marginal bone and increased for evaluations of the implant components.

The possibilities of pseudo-coloring, that is, to assign different colors to different gray-level values, have been suggested to be of value in evaluating the bone surrounding the implant. So has the possibility to graphically display the variations in gray-level values over a distance, e.g. one that covers the implant-bone interface

Digital radiograph showing contrast enhancement

Digital radiograph showing edge enhancement

Bite-wing radiographs

The short and long-term evaluation of crestal bone loss around implants is best evaluated with intraoral radiographs.Threaded implants make quantification of marginal bone loss easier to read. Most threaded implants have a smooth crestal region that measures 0.8 to 2 mm,depending on the manufacturer, before the threads begin. Once the threads begin, there is a consistent pitch (distance between the threads). As a result, the amount of crestal bone loss can be determined when compared to the original implant insertion and initial radiograph of the prosthesis.

Temporal digital subtraction radiography

Temporal digital subtraction radiography (SR) is a radiographic technique that enable two radiographs made at different points of time of the same anatomic region to be subtracted resulting in an image of the difference between the two original radiographs.The resulting substraction image depicts changes in the patient's anatomy such as alveolar mineralization or volume changes during the time between which the two radiographs were made.SR has had limited utilization in clinical practice because of the difficulty in obtaining reproducible periapical radiographs.

Use of temporal digital subtraction radiography (SR) in assessing changes in the patient's interdental bone anatomy.

Implant Failure

Signs and symptoms of implant failure are :

1. Horizontal mobility beyond 0.5 mm or any clinically observed vertical movement under less than 500 g force

2. Rapid progressive bone loss regardless of the stress reduction and peri implant therapy

3. Pain during percussion or function

4. Continued uncontrolled exudate in spite of surgical attempts at correction

5. Generalized radiolucency around an implant

6. More than one half of the surrounding bone is lost around an implant

7. Implants inserted in poor position making them useless for prosthetic supportThe ultimate decision of implant success lies with the practicing dentist rendering continued dental therapy for the patient.

Peri-Implant Disease

The term peri-implantitis is used to describe the boneloss around an implant.This may be induced by stress or bacteria or a combination of both. Stress induced boneloss occurs without bacteria as the primary causative agent. Boneloss from stress or bacteria deepens, the sulcular crevice and decreases the oxygen tension.Anaerobic bacteria may become the primary promotor of the continued boneloss.An exudate or abscess indicates exacerbation of peri-implant disease and possible accelerated boneloss. Short term antibiotic treatment and aggressive topical application of chlorhexidine along with extensive professional and patient care is indicated and exudate persisting for more than 1 to 2 weeks usually warrants surgical revision of peri-implant area to eliminate the causative elements. Once the exudate is eliminated the bacterial smear layer remaining on the implant surface must be eliminated before bone can grow in close contact with the implant. These will be described in detail in the unit of Failure of implant and the treatment of Periimplantitis .

Probing Depth

This parameter is applicable to one stage implants when they are evaluated priorto prosthetic phase and used to evaluate the health of the implant after the prosthesis has been fabricated.The periodontal depth indices are often used to evaluate the dental implants. The increase in sulcus depth around natural teeth is related to disease and bone loss.However, relating implant sulcus depth is controversial. Stable rigid fixated implants have been reported with pocket depths ranging from 2 to 6 mm. Partially edentulous patients consistently exhibit greater probing depths around implantsthan around teeth. Primary reason for increased probing depth around implants is that, the implant does not have a connective tissue attachment zone that extends approximately 1 mm above the bone as does a tooth. With an implant the probe goes beyond the sulcus through the type 3 collagen connective tissues and reaches closer to the bone. As a result, the probing depth next to an implant is greater than that of natural tooth. The location of the probe tip sub-gingivally for a tooth depends on the pressure used, the presence of information and the angle at which the probe is introduced in the sulcus depth. The benefit of probing the implant sulcus has been challenged in the literature. There is a potential damage to then fragile attachment or marring of the implant surface when the probing is performed.

The correct pressure recommended for probing is 20 grams, Yet conventional probing often exerts a force more than 5 times of this level and is extremely variable. Pressure sensitive probes are now available to address these issues.\ Probing using fixed reference points on the abutment or crown margin allows the evaluation of the crestal bone loss versus tissue hypertrophy. As the sulcus depth increases, the oxygen tension reduces. Sulcus depth > 5 to 6 mm have greater incidence of anaerobic bacteria and require gingivectomy or revision surgery.Therefore to allow the patient to perform effective oral hygiene, the implant sulcus should be maintained at less than 4 mm.

Bleeding Index

This factor is applicable at this stage to evaluate the health of one stage implants in which the transmucosal component allows the formation of a mature gingival collar around the implant prior to the prosthetic phase. Gingival bleeding, when probing is co-related through inflammation and the plaque index. Bleeding index is indicator of sulcus health. The most common bleeding gingival index used for implants is the Loe and Silness gingival index (GI). When used on teeth this index scores gingival information from 0 to 3 on the facial,lingual and mesial surfaces of all teeth. The symptoms of bleeding comprises of score of atleast 2. The GI score may also be used to record the gingival information on the facial, lingual and mesial surfaces of all implants. When the sulcus depth is less than 5 mm but the bleeding index increases, chlorhexidine is often indicating along with other professional and home care methods. Sulcus Depth in excess of 5-6 mm has a greater incidence of bleeding and usually requires gingivectomy or revision surgery.During the 1st year of clinical examinations for the peri-implant tissues, colour, form and consistency should be recorded along with bleeding on probing and probing depths of all sites.