CATEGORY 72 AUSTRALASIAN DENTIST Dental implant stability has historically been defined as Primary and Secondary Stability. Primary stability is the level of stiffness and the resistance of an implant to an applied load in bone at the time of its placement. Secondary stability is the change in stiffness and load capacity between a dental implant and the surrounding bone following osseointegration1. Over many years and numerous clinical studies Brånemark and Albrektsson2 deduced that dental implants of the appropriate geometry and surface placed with a gentle surgical technique and in bone of adequate quality and quantity achieved clinical success in excess of 85% when buried for three months in the mandible and six months in the maxilla. These findings were pivotal in making what has become successful dental implant treatment today3. However, the clinical techniques used to assess bone quality, implant stability and osseointegration remained relatively crude until recently. Tapping an implant with a mirror handle4 using a percussion hammer or applying a reverse torque of 32Ncm5 to assess its osseointegration yield very little useful information. Radiographic assessment of bone prior to implant placement can give an indication of bone quality and quantity. Although changes in radiodensity attributable to bone formation or resorption may take several months to become visible. Hounsfield units are often quoted (and maybe misquoted) as a measurement of bone density and indirectly quality. It is important to remember that Hu are a linear transformation based on the arbitrarilyassigned radio densities of air and pure water and were originally conceived to measure soft tissue parameters such as fatty liver and tumour staging6. Brånemark‘s original protocol7 created little need for a quantitative measurement of implant stability as in itself it achieved a high level of clinical success. Soon, clinicians wanted to explore reduced healing periods and eliminate two stage implant placement procedures. Some even suggested extraction and placement with immediate loading. Studies demonstrated that the success rate was not as high under such conditions8. developed commercially as Osstell and Rf was converted into an Implant Stability Quotient scaled from 0-100 according to bone-implant stiffness and height (Osstell AB, Goteborg, Sweden). ISQ is an easily interpreted clinical scale. Typically, at placement ISQ <50 is a high risk implant of poor stability, >50<60 is satisfactory, >60<70 is good primary stability and >70 is very good stability12. The physical components comprising the Osstell system are a ‘Smartpeg‘ transducer that is attached by screwing onto an implant fixture or abutment (Figure 3). A handheld measuring unit measures the excitement and response of the ‘smartpeg’, displaying it as the Implant Stability Quotient (ISQ) (Figure 4). Bluetooth communications can enable data storage on a PC or in the ‘Cloud’. The test itself is completely non-destructive and applies no load to the implant. A question often asked is if ISQ can Understanding the importance of stability in successful dental implant treatment By Professor Neil Meredith, BDS., MSc., FDS RCS., PhD (U.Got), PhD (U.Lond) Dean, Post Graduate Institute of Dental Surgery Figure 1. A small electronic transducer attached to a dental implant excited to its resonance frequency. Figure 2. The resonance frequency of a tuning fork is dependent on its length and the stiffness with which it is held Figure 3. A smartpeg transducer attached to a dental implant in a molar extraction socket. Figure 4. Osstell unit displaying two ISQ measurements. The desire to better measure and understand clinical implant stability led to significant research. Meredith and Cawley investigated many non-invasive test methods to study implant stiffness and bone to implant contact9. These included; percussion methods, dynamic modal analysis, damping and resonance frequency analysis10.The small sizeof dental implants and the heterogenous nature of bone made this very challenging but it became clear that Resonance Frequency Analysis was most suited. This entails the measurement of the resonance frequency of a small electronically excited transducer attached to a dental implant (Figure 1). The Rf is a function of the stiffness of an implant in the surrounding bone and the marginal bone level11 (Figure 2). This was LINICAL Professor Neil Meredith
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