|Year : 2014 | Volume
| Issue : 2 | Page : 165-169
Measuring implant stability: A review of different methods
Gaurang Mistry1, Omkar Shetty1, Shreya Shetty1, Raghuwar D Singh2
1 Department of Prosthodontics, Dr. D. Y. Patil Dental College and Hospital, Navi Mumbai, Maharashtra, India
2 Department of Prosthodontics, King George's Medical University, Lucknow, Uttar Pradesh, India
|Date of Web Publication||16-Sep-2014|
Dr. D. Y. Patil Dental College and Hospital, Navi Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Achieving and maintaining implant stability are prerequisites for a dental implant to be successful. Implant stability can be defined as the absence of clinical mobility, which is also the suggested definition of osseointegration. Primary implant stability at placement is a mechanical phenomenon that is related to the local bone quality and quantity, the type of implant and placement technique used. Secondary implant stability is the increase instability attributable to bone formation and remodeling at the implant/tissue interface and in the surrounding bone. There are many ways in which the implant stability can be evaluated such as clinical measurement of cutting resistance during implant placement, reverse torque test, the periotest. This article aims to throw light on the various methods to determine implant stability.
Keywords: Implant stability, implant stability quotient, periotest, resonance frequency analysis
|How to cite this article:|
Mistry G, Shetty O, Shetty S, Singh RD. Measuring implant stability: A review of different methods. J Dent Implant 2014;4:165-9
| Introduction|| |
Successful osseointegration is a prerequisite for functional dental implants, and primary implant stability is a prerequisite for successful osseointegration. Implant stability is the absence of clinical mobility. Implant instability could result in fibrous encapsulation with resultant failure. Primary implant stability at placement is a mechanical phenomenon that is related to the local bone quality and quantity, the type of implant and placement technique used. Secondary implant stability is the increase in stability attributable to bone formation and remodeling at the implant/tissue interface and in the surrounding bone. ,
Under deﬁned circumstances, early and immediate loading protocols have now been recognized to be viable alternatives to the classical 1- or 2-stage delayed loading approaches. Subsequently, the clinician needs reliable and supportive objective guidelines to determine on an individual basis the prognosis of a given implant, if immediately loaded, early loaded within 6-8 weeks or left classically to heal for a 3-6 months period. 
Historically, the gold standard method used to evaluate the degree of osseointegration was microscopic or histologic analysis.  However, due to the invasiveness of this method and related ethical issues, various other methods of analysis have been proposed; clinically checking for mobility with the help of blunt ended instruments, radiographs, cutting torque resistance, reverse torque and resonance frequency analysis (RFA).
Measuring implant stability supports making good decisions about when to load, allows advantageous protocol choice on a patient-to-patient basis, indicates situations in which it is best to unload, supports good communication and increased trust and provides better case documentation. 
The methods to determine implant stability clinically are clinical perception, percussion test, reverse torque test, cutting torque resistance analysis, periotest RFA.
| Clinical perception|| |
The clinical perception of primary implant stability is frequently based on the mobility detected by blunt ended instruments. It's a very unreliable and nonobjective method. It can also be checked by the cutting resistance of the implant during its insertion. The feeling of "good" stability may be accentuated if there is the sense of an abrupt stop at the seating of the implant. Root forms of tapered implants often have a geometry that will provide a ﬁrm stop and perhaps a false perception of high stability. 
The percussion test may involve the tapping of a mirror handle against the implant carrier and is designed to elicit a ringing sound from the implant as an indication of good stability or osseointegration. Percussion tests probably provide more information about the tapping instrument, and will at best only yield poor qualitative information. 
Reverse torque test
Application of a reverse or unscrewing torque has also been proposed for the assessment of implant stability at the time of abutment connection.  Implants that rotate under the applied torque are considered failures and are then removed. However, the implant surface in the process of osseointegrating, albeit slowly, may fracture under the applied torque stress. Moreover, as animal experiments have demonstrated the re-integration of loosened and rotationally mobile implants, the reverse torque testing has fallen into disrepute  [Figure 1] and [Figure 2].
Cutting torque resistance analysis
The energy required for a current-fed electric motor in cutting off a unit volume of bone during implant surgery is measured. ,, The energy correlates to bone density, which is one of the factors determining implant stability. However, the lower limit value has not been established, which can denote potential failure of the implant. Moreover, it can only be used during the surgery and not as a diagnostic aid, and it cannot assess the secondary stability by new bone formation and remodeling around the implant. 
It is a device which is an electrically driven and electronically monitored tapping head that percusses the implant a total of 16 times. The entire measuring procedure takes about 4 s [Figure 3]. The instrument includes a tapping rod that impacts the abutment/implant assembly. The rod is drawn by a propulsion coil toward the impacting surface and essentially moves at a constant velocity from the moment it leaves the hand piece until it impacts the surface. This means that over a certain distance (approximately 4 mm), the tapping rod is moving at the same velocity and is designed to impact the surface at any time during this constant velocity travel. The end of the rod inside the hand piece is rigidly connected to an accelerometer, which produces an output proportional to its acceleration. The readings are from −8 to +50 and are interpreted as in [Table 1].
The factors that influence the periotest value are the quality of the hard tissue in the region of the implant, so that no specific values can be deemed as appropriate for higher or lower degrees of integration.  It is a function of the distance from the implant flange to the point at which the rod impacts the abutment. These variations suggest that for implants, there is no absolute value that can be regarded as acceptable; rather, variations that occur over time may be more meaningful.
In vitro evaluations revealed that no statistically signiﬁcant difference existed in measuring periotest values from the operator to operator, as well as high level of repeatability between different periotest units. Successfully integrated dental implants have yielded a wide range of stability readings with the periotest. This range in values is believed to reﬂect bone density at the implant interface, which is related to implant location.
The measurements are significantly affected by excitation conditions such as direction and position. The measurements must be made in the mid buccal region and be perpendicular to the implant axes [Figure 4]. Considering the intra oral environment, it is considerably easy to make measurements on anterior implants whereas it is not possible for molars owing to the buccal mucosa. The periotest cannot diagnose a "borderline" case or "an implant in the process of osseointegration."  It does not reﬂect the level of peri-implant bone and therefore cannot be substituted for radiography.
| Resonance frequency analysis|| |
It is a noninvasive diagnostic method that measures implant stability and bone density at various time points using vibration and structural principle analysis.  Two commercially devices have been developed to assess implant stability. The original (electrical) method uses a direct connection (wire) between the transducer and the resonance frequency analyzer [Figure 5] and [Figure 6]. The second method uses magnetic frequencies between transducer and resonance frequency analyzer. In the electronic device, the transducer is L shaped cantilever beam which connects to the implant via a screw attachment. A piezoelectrical crystal on the vertical portion of the L beam is used to stimulate the implant/transducer complex; second piezoelectric crystal on the opposite side of the beam is used as a receiving element to detect the response of the beam.
The new magnetic RFA device has a transducer, a metallic rod with a magnet on top, which is screwed onto an implant or abutment. The magnet is excited by a magnetic pulse from a wireless probe. The pulse duration is about 1 ms. After excitation, the peg vibrates freely, and the magnet induces an electric voltage in the probe coil. That voltage is the measurement signal sampled by the resonance frequency analyzer. The electronic device and the magnetic device are capable of measuring similar changes; however the magnetic device results in higher implant stability quotient (ISQ) value when measuring the stability of nonsubmerged dental implant.
With this method, implant stability is measured either by determining the resonance frequency of the implant-bone complex or by reading an ISQ value given by the Osstell apparatus (Integration Diagnostics AB, Gothenburg, Sweden). Classically, the ISQ has been found to vary between 40 and 80, the higher the ISQ, the higher the implant stability.  A substantial increase or decrease in implant stability could be detected with this method that otherwise could not be clinically perceived. The factors affecting the readings are effective implant length, bone quality and quantity, implant length, diameter and shape. Effective implant length is the length of the exposed threads and abutment height. It is inversely proportional to the resonance frequency. 
Implant stability can be determined for implants with an ISQ of 47. All implants with an ISQ more than 49 osseointegrated when left to heal for 3 months. All implants with an ISQ more than 54 osseointegrated when immediately loaded. For implants with low ISQ values, a decrease in implant stability should alert the practitioner to submit these implants to a tighter follow-up schedule and to take additional precautionary measurements in terms of unloading until implant stability is regained or if nonloaded to check for mechanical trauma and/or infection. For implants with high ISQ values, reduction of implant stability during the ﬁrst 12 weeks of healing should be considered as a common event that should not require alteration of routine follow-up. 
The drawbacks with this technology are that the transducer is limited to a set of 60 measurements, thus making the method rather expensive. In order to perform the RFA, a transducer is ﬁxed to the implant. This excludes monitoring all implants that support a cemented restoration.
| Conclusion|| |
Although there are various methods which help to determine implant stability, the number variables affecting the results makes it difficult to come to a critical value which can determine the success, failure or long-term prognosis of an implant. Hence, more research is required to devise an accurate instrument which will help gauge the implant stability.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]