Implant Stability Quotient (ISQ): A Reliable Guide for Implant Treatment

Abstract

Implant stability is a prerequisite for successful dental implants and osseointegration. To determine the status of implant stability, continuous monitoring in an objective and qualitative manner is important. To measure implant stability two different stages are there: Primary and secondary. 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. Primary stability is checked from mechanical engagement with cortical bone. Secondary stability is developed from regeneration and remodeling of the bone and tissue around the implant after insertion and affected by the primary stability, bone formation and remodeling. Implant stability is essential for the time of functional loading. Classical benchmark methods to measure implant stability were radiographs or microscopic analysis, removal torque, push-through and pull-through but due to lack of feasibility, time consumption and ethical reasons other methods have been propounded over period of time like measurement of implant torque, model analysis and most important ISQ which has the ability to monitor osseointegration and the life expectancy of an implant. ISQ is a valuable diagnostic and clinical tool that has far-reaching consequences on implant dentistry and this article throws light on advanced and reliable methods of assessing ISQ.

1. Introduction

Implant treatment has become the first choice of treatment for replacement of missing teeth and oral rehabilitation over last few years. Osseointegration is the most important requirement for long term success of dental implant procedure. Many techniques have been experimented to reduce the failure rate of dental implants in long term. So far, insertion torque value and implant stability quotient (ISQ) obtained by the Osstell instrument are common clinical methods to assess the initial stability of an implant for a predictable loading procedure. The ISQ-values are used as an indicator for mechanical implant stability, and are believed to have predictive power for clinical outcome. Nowadays in clinical practice ISQ readings are used as gauging factor to decide the time interval for practical implant loading and to decide the prognosis of implant procedure [1]. Quantitative measurement of implant stability is of high clinical significance so various principles have been used to estimate this parameter accurately like, the periotest assay and resonance frequency analysis (RFA). A device called Osstell was formulated which works on the principle of RFA. The instrument measures the resonance frequency through the transducer attached to a implant fixture and display the result ISQ value on a scale of 1 to 100. It is an objective method of measuring implant stability. Higher ISQ value denotes higher primary stability. Usually ISQ value of 55–80 is considered optimal for implant success. In our clinical practice we have observed higher ISQ values in mandible cases than maxilla. The ISQ scale has a non-linear correlation to micro mobility [2]. Finite element analysis also has been recently used to analyze the mechanical and vibration behavior of the three dimensionally designed structure [3, 4, 5, 6].

In our cases we found out that if ISQ value is on higher side of the scale initially, a small dip in values normally compensated with time and should be considered as a normal event which does necessitate alteration of routine treatment plan [2]. All implants with ISQ values higher than 54 considered for immediate loading.

But on the contrary, if values fall drastically then it should be taken as warning sign for unsuccessful implant in future and appropriate actions should be considered in terms of more follow-up schedule and to take additional precautionary measurements to wait before loading, to check for signs of infection and mechanical trauma. Lower values are expected to increase after the healing period in some cases.

2. Discussion

2.1 Principle: resonance frequency analysis

This diagnostic method computes implant stability and bone density by vibrational and structural analysis in noninvasive manner [7]. Two devices have been developed commercially to measure implant stability, one is electrical and other is based on magnetic principle. First method uses direct wire connection between transducer and resonance frequency analyzer. The second method based upon measurement of magnetic frequencies between transducer and resonance frequency analyzer by a wireless probe (Figures 1 and 2). Both methods are competent for measuring similar changes; however the magnetic device results in higher ISQ value when measuring the stability of non submerged dental implant (Figures 3–6) [8].

Figure 1.

Osstell devices: Electrical and magnetic RFA based devices.

Figure 2.

Osstell Beacon cordless device: Electrical and magnetic RFA based devices.

Figure 3.

Outstanding ISQ readings by Osstell device encouraging for immediate loading in lower front region.

Figure 4.

Measurement of ISQ by advanced RFA bases magnetic Osstell device immediately after implant placement.

Figure 5.

Measurement of ISQ by Osstell device 3 months after implant placement depicting good biologic stability.

Figure 6.

Implant stability on the abutment and platform level Resonance Frequency Analysis by Osstell (a) Implant platform (b) 1 mm microvunit (c) 5 mm microvunit.

These methods can reveal considerable increase or decrease in implant stability which could not be appraised clinically. Various factors can affect the readings like effective implant length (length of the exposed threads and abutment height), implant shape and diameter and bone quality and quantity [9].

Measuring implant stability by implant oscillation frequency of bone can be assessed by RFA. Meredith et al. 1998 described the noninvasive method of assessing implant stability by OSSTELL devices. In 1999, OSSTELL devices was designed by the Integration Diagnostics Ltd., Sweden. Over last few years, various types of Osstell devices have developed to extemporize the implant stability measurements, namely, OSSTELL™, OSSTELL Mentor, and OSSTELL ISQ.

In 2009 the last and latest generation of this device was developed, OSSTELL ISQ, which includes a new control unit with a probe connected to it by means of a cable. These devices are gaining popularity due to reliability and ease of assessing implant stability. These measurements are independent of intra and inter observer variability and reproduce accurate results.

Nedir et al. [2] estimated the implant primary stability as an indicator of osseointegration. As per his study, ISQ value of more than 49 will osseointegrate over period of three months and those with values higher than 54 can be loaded immediately.

Primary stability of implants which was assessed through RFA using OSSTELL Mentor devices was underestimated to analyze the comparability and reproducibility [10]. Clinical trials concluded the almost perfect replicability and high reliability of ISQ measurements with Osstell devices [11]. ISQ measurement by OSSTELL Mentor device during immediate and delayed loading implant cases concluded that it offers an objective method to determine the implant stability and for immediate loading [12].

Comparison of OSSTELL Mentor and OSSTELL ISQ in measuring implant stability was evaluated and the mean values of ISQ for OSSTELL ISQ and OSSTELL Mentor were 72.87 and 72.04 respectively, suggesting perfect compliance, consistency and recreatability between these devices [13].

There are various factors which affect the ISQ readings like anatomical direction of measurement in patient’s mouth, gender of the patient, intraoral location of the implant [14], sex of the patient, immediate versus delayed implantation, diameter and length of implant, designing of implant, insertion torque [15, 16], bone type at the site of implant, contact surface area of implant. Various research studies indicated the possible interplay of insertiuon torque and ISQ values. Insertion torque was introduced to assess the primary stability of the implant and accordingly plant the surgical procedure on solid backgrounds. Good cortical bone thickness results in increased ISQ values due to better osseointegration, whereas less trhickness results in reduced stability and lesser ISQ. In last few decades immediate implant protocol has become more popular due to less clinical treatment time. If the favorable preclinical condition exist, immediate implant results in almost similar ISQ values when compared to delayed implant procedures. After 3 months when loading begins in delayed implant cases, secondary stability equalize to the level of ISQ values of similar magnitude as those achieved in primary stability phases.

In our practice we compared the ISQ values of successful implants at the time of loading and post operatively with the ISQ values of implant failure cases, which manifested significant difference in values. However, ISQ distributions at implant insertion denoted overlapping which indicated that there was no correlation among the data that could be used to predict successful osseointegration. The predictiveness of ISQ values were enigmatic [17].

3. Conclusion

Though the connection between bone density/quality and resonance frequency analysis is still enigmatic but our clinical practice suggested a significant interrelation between RFA measurement by Osstell device and implant success. Further studies are needed to evaluate a correlation of RFA with bone quality analysis and implant stability, which can ascertain success, failure or long-term prognosis of an implant.