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Authors: Dr. Varun Singla, Dr. Neha Srivastava, Dr. Manesh Lahori

Abstract

Implant stability is considered to play a major role in the success of osseointegration. Implant stability is estimated at two different stages Primary and Secondary. Primay implant stability is a mechanical process related to the local bone quality and quantity,the type of implant and placement technique is used. Secondary implant stability is developed from regeneration remodelling of the bone and tissue around the implant after insertion and affected by primary stability. It is of utmost importance to be able to access implant stability at various times and to project a long term prognosis for successful therapy.

INTRODUCTION

Osseointegration is defined as a direct structural and functional connection between bone & the surface of a load bearing artificial implant.

Dental implant signifies one of the most beneficial & fruitful treatment methods and play a pivotal role in success of osseointegration.

Objective measurement of implant stability is an appreciate tool for attaining good decisions about when to load, allows advantageous protocol choice on a patient basis, indicates situations in which it is best to unload, supports good communication and increased trust and provides better case documentation.

Various methods to check implant stability as categorized as follows:-

nvasive or Destructive methods

  • Histologic/Histomorphologic Analysis
  • Tensional test
  • Push out/Pull out test
  • Removal torque analysis
Non Invasive Or Non Destructive Methods
  • Surgeon’s Perception
  • Radiographical Analysis / Imaging Techniques
  • Cutting Torque Resistance (for primary stability)
  • Insertion torque measurement
  • Reverse Torque
  • Seating Torque Test
  • Model Analysis And Implatest
  • Percussin Test
  • Pulsed Oscillation Waveform(POW)
  • Periotest
  • Resonance Frequency Analysis (RFA)
  • Electronic Technology
  • Magnetic Technology
INVASIVE OR DESTRUVTIVE METHODS

1.) HISTOLOGIC OR HISTOMORPHOLOGIC ANALYSIS

This method assess the bone contact and bone area from a dyed specimen of the implant and peri-implant bone. Due to invasive and destructive nature the technique is limited to non-clinical and experimental studies.

2.) TENSIONAL TEST

The strength of the implant was originally measured by detaching the implant plate from the supporting bone. It was later modified by applying the lateral load to the cylindrical implant fracture.

However there were difficulties in translating the test results to any area independent mechanical properties.

3.) PUSH OUT / PULL OUT TEST

This test assess the healing capabilities at the bone implant surface.

In a typical test, a cylinder type implant is placed transcortically or intramedullary in bone and then removed by applying a force parallel to the interface. The maximum load capability is defined as the maximum force displacement. However the push out pull out tests are only applicable for nonthreaded cylinder type implants, whereas most of clinically available fixtures are of threaded design and then interfacial failures are solely dependent an shear stress without any consideration for either tensile or compressive stresses.

4.) REMOVAL TORQUE ANALYSIS

In this technique, osseointegration is tested. This implant is considered stable if the reverse or unscrewing torque was > 20Ncm . However, the disadvantage is that at the time of abutment connection implant surface in the process of osseointegration may fracture under the applied torque stress.

NON – INVASIVE OR NON DESTRUCTIVE METHODS

The clinical perception of primary implant stability is frequently based on the cutting resistance and seating torque of the implant during insertion. The feeling of good stability may be accentuated if there is the sense of an abrupt

stop at the seating of implant. This type of measurement can only be made when the implant is inserted and not later for example ; before loading the implant.

1.) IMAGING TECHNIQUES

Various radiographic and imaging techniques are used to evaluate the quality and quantity of bone before placing the implant fixture.

LIMITATIONS
  1. Image is two dimensional.
  2. Image resolution is not good.
  3. Standardized x-rays are difficult to achieve.
  4. Neither bone quality nor density can be quantified with this method.
  5. It is difficult to perceive changes in the bone structure and morphology of the implant bone interface unless 40% of bone loss had occurred. This method can be performed at any stage.
2.) CUTTING – TORQUE RESISTANCE ANALYSIS

It was originally developed by Johansson and Strid and later improved by Friberg et al . The amount of unit volume of bone removed by current fed electric motor and is measured by controlling the hand pressure during drilling at lowest speed. It provides useful information in determining an optimal healing period in a given arch location with a certain bone quality.

LIMITATIONS
  1. Does not give any information on bone quality until the osteotomy site is prepared.
  2. CRA cannot estimate the value at which the implant would be at risk.
3.) INSERTION TORQUE MEASUREMENT

Measuring the insertion torque while installing the implant is an attempt to quantify the surgeon’s tactile perception. A disadvantage of this meathod is that the insertion torque varies depending on the cutting properties of the implant and the presence of fluid in the preparation.

However insertion torque measurements can only be used when the implant is inserted and are not possible at later stages of the treatment.

4.) REVERSE TORQUE TEST

It was proposed by Roberts et al and developed by Johannson and Alberktsson. It evaluates the secondary stability of the implant. It measure the torque threshold where bone implant contact was destroyed. Measurement of lateral mobility is more useful then measurement of rotational stability as in indicator of successful treatment result. It cannot quantify degree of osseointegration as threshold limits vary among patients implant material, bone quality and quantity. The studies showed the stress of applied torque may in itself be responsible for the failure.

5.) SEATING TORQUE TEST

Like insertion torque, the final seating torque gives some information about the primary stability of the implant when the implant reaches its final apicoocclusal position. It is done after implant placement.

6.) PERCUSSION TEST

A simple method used to measure the level of osseointegration.

This test is based upon vibrational acoustic science and impact response theory. The clinical judgement on osseointegration is based on the sound heard upon percussion with a metallic instrument. A clearly ringing ‘crystal’ sound indicates successful osseointegration whereas a ‘dull’ sound may indicate no osseointegration.

This method relies heavily on the doctor’s experience level and subjective belief. Therefore, it cannot be used experimentally as a standardized testing method.

7.) PERIOTEST

Quantifies the mobility of an implant by measuring the reaction of the periimplant tissues to a defined impact load. The periotest was introduced by Schulte to perform measurements of the damping characteristics of the periodontal ligaments, thus assessing the mobility of natural tooths.

It uses an electromagnetically driven and electronically controlled tapping metallic rod in a hand piece. Periotest value range from -8 (low mobility) to +50 (high mobility).

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.

The measurements are significantly affected by excitation conditions such as direction and position. It measures in plant stability and bone density at the time of implant placement and post surgical placement of the implant.

8.) PULSED OSCILLATION WAVE FORM

Kaneko described the use of a pulsed oscillation wave form (POWF) to evaluate the properties of mechanical vibrations of the bone-implant interface using forced excitation of a steady state wave .

POWF is based on estimation of frequency and amplitude of the vibration of the implant induced by a small pulsed force.

A multi frequency pulsed force of about 1 kHz is applied to an implant by lightly touching it with two fine needles connected with piezoelectric elements (contained in an accoustoelectric driver AED, and acoustoelectric receiver AER ).

It is used for in-vitro and experimental studies. The sensitivity of the POWF test depended on load directions and positions.

9.) RESONANCE FREQUENCY ANALYSIS

In 1998, Meredith suggested a non-invasive method of analyzing implant stability and bone density at various time points using vibration and a principle of structural analysis.

This method was L-shaped transducer that is tightened to the implant or abutment by a screw . The transducer provides a high frequency mechanical vibration and record the frequency and amplitude of the signal received.

The transducer comprises of two ceramic elements , one of which is vibrated by a sinusoidal angle (5 – 15 kHz ) while the other serves as a receptor. The transducer is screwed directly to the implant body and shakes the implant at a constant input and amplitude starting at a low frequency and increasing in pitch until the implant resonates. High frequency resonance indicates stronger bone-implant interface.

RFA has been widely used for clinically assessing osseointegration, as well as for prognostic evaluation. The most recent version of RFA is a wireless gadget. A metal rod is attached to the implant with a screw connection. The rod has a small magnet attached to its top that is stimulated by magnetic impulses from a handheld electronic device. The rod mounted on the implant has two fundamental resonance frequencies, it vibrates in two directions, perpendicular to each other. One of the vibrations is in the direction where

the implant is most stable and the other is in the direction where the implant is least stable.

10.) ELECTRONIC TECHNOLOGY RESONANCE FREQUENCY ANALYSIS (Osstell)

It was the first commercially available product for measuring implant stability. The electronic technology combines the transducer, computerized analysis and the excitation source into one machine.

Implant stability quotient (ISQ) is the measurement unit (ISQ of 0 to 100 ) used. When used at the time of implant placement it provides baseline reading for future comparison and post-surgical placement of the implant.

11.) MAGNETIC TECHNOLOGY RESONANCE FREQUENCY ANALYSIS (Osstell Mentor)

The transducer has a magnetic peg on the top and is fixed to implant or abutment. On activation by magnetic resonance frequency probe the activated, which vibrates and induces electric volt sample by magnetic resonance frequency analyzer. Values are expressed as ISQ of 0 – 100.

At the time of implant placement it provides base line reading for future comparison and post-surgical placement of the implant.

However this method is expensive and technique sensitive as it requires respective transducer and magnetic peg. It should maintain a distance of 1 – 3 mm , angle of 900 and should be 3 mm above the soft tissue otherwise the measured value will be affected.

12.) MODAL ANALYSIS

Modal analysis is also known as vibration analysis. It measures the natural frequency or displacement signal of a system in resonance, which is initiated by external steady – state waves or a transient impulse force.

It can be performed in two models Theoretical and experimental.

The theoretical modal analysis includes finite element analysis. It investigates vibrational characteristics of objects. It is done to calculate stress and strain in various anticipated bone levels. It is used in clinical studies and experiments.

The experimental modal analysis is a dynamic analysis. It measures natural characteristic frequency mode and attenuation via vibration testing. It is used in non-clinical studies in-vitro approach and provides reliable measurements.

CONCLUSION The description of various techniques in the above literature states that the advanced and tests and equipments may play a more prominent role in the assessment of implant stability as compared o conventional methods. The ability to monitor life expectancy of an implant and its osseointegration is a valuable diagnostic and a clinical tool. Although RFA has attracted considerable scientific interest in recent years , it can also be used to evaluate the effect of early and delayed loading assess stability over a period of time and early diagnosis of implant failure. However more research is needed to invent an accurate instrument which will help gauge the implant stability. REFERENCES
  1. Vasanthi Swami , Vasantha Vijayaraghavan , Vinit Swami : Current trends to measure implant stability : A review article. April-june 2016.
  2. Gaurang Mistry , Omkar Shetty , Shreya Shetty , Raghuwar D Singh :Measuring implant stability : A review article
  3. Dr. Ginnia Bhayana, Dr. Ferah Rehman , Dr. Vinnod khanna , Dr Sonia , Dr Taruna Arora : Assessment of implant stability- A critical review : April 2016 , vol 3 ,issue 4.
  4. Aman Sachdeva, Pankaj Dhawan and Suruch Sindwani : Assessment of implant stability : Methods and recent advances : 7th nov 20016.
  5. Mihoko Atsumi , Sang- Hoon Park,Hom-Lay Wang : Methods used to assess implant stability : Current status

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