TECHNICAL FIELD The present invention relates to a method and apparatus for testing an object, such as an implant attached to a bone.

BACKGROUND Measurement and analysis of the oscillation frequency in dental implants are used to obtain information on how well an implant is anchored to the jawbone. There is a need for an arrangement for clinically observing the quality of the union between the bone and an implant surface. Implant failures can be caused by errors in placement, and premature or inappropriate loading. Non-destructive tests, which are used before loading the implant helps to reduce failures of this type and also enable periodic tests to be carried out on implants which are in use to ensure that they are still satisfactory.

EP 1641394, by the same Applicant, relates to an arrangement for non-destructive testing an implant attached to a bone. According to this invention a peg is brought into contact with the implant and excited, then at least one resonance frequency of the peg is detected contactless and the detected frequency is interpreted as the detected resonance frequency in terms of the degree of attachment of the implant with respect to the bone.

A peg is attached to the implant or abutment when a measurement is made. It is easy to mount and requires minimal space thanks to its small size.

Implant Stability Quotient (ISQ) is objective world standards for measuring implant stability. The clinical range of ISQ is normally 55-80. Higher values are generally observed in the mandible than in the maxilla. The overall average value of all implants over time is approximately 70 ISQ. If the initial ISQ value is high, a small drop in stability normally levels out with time. A big drop in stability or decrease should be taken as a warning sign. Lower values are expected to be higher after the healing period. The opposite could be a sign of an unsuccessful implant and actions should be considered. SUMMARY

The present invention provides additional enhancements to above apparatus by allowing measurement of both (resonance) frequencies and oscillation direction. The invention substantially improves measurement methods to provide unique information on the status of an implant. By using a new type of sensing technique and data processing the measurements provides additional information in shorter time to the user. The present invention makes it possible to measure stability of the implant in a precise and objective manner (and monitor osseo-integration). The main advantages may include reduced treatment time and manage patients at risk in more accurate way and simple way. With the conventional probes, the probe must be directed in several directions to achieve satisfactory results. The probe of the present invention, according to one example, produces a substantially circular movement of the peg, which eliminates or reduces number of measurements in several directions. This increases the security for the patient as the risk for follow-up measurements in wrong directions is reduced. Currently, the dentist or a person carrying out the measurement must register the measurement direction.

The invention may also allow for identifying weaknesses in the bone surrounding the implant.

When measuring the stability (ISQ) repeated times, e.g. within weeks or some months, it is important that the position of the probe in the measuring position is at least the same each time. For a correct clinical measurement, presently the measurement is conducted in both mesiodistal and buccoligual directions. It is also possible to measure in four directions. The probe of the present invention allows measurement in all directions during one measurement.

The result of the measurements can be provided in simple way, allowing filtering unnecessary results, while visualizing, e.g. defects, in a simple and apprehensive way. For these and additional reasons described below a method of testing an implant, attached to a bone is provided. The method comprises the steps of: magnetically bringing a member attached to the implant into excitation, detecting by a detecting unit, spaced apart from the member and contactlessly, at least one resonance frequency and/or oscillation direction of the member; and interpreting the detected resonance frequency and oscillation direction in terms stability of implant. The method may include the step of detachably attaching the member to the implant. In one embodiment the member comprises an at least partly magnetic cantilever beam. The method may comprise using a detector comprising two coils arranged in substantially 90 degrees with respect to their center line. In one embodiment the detector comprises at least two 3-axis magnet sensors for instance based on the magneto resistive sensor technique. The method may further comprise calculation of a position of the detector with respect to the member. The method may comprise the step of comparing the detected resonance frequency with one or more values for the resonance frequencies of the same or similar members in contact with the same or other attachments. The method may further comprise: after an excitation of the member sampling the movements of the member; averaging the sampled signal; applying FFT over each channel; for each channel extracting signals; for each channel calculating a position (x(t), y(t)); generating a result. The invention also relates to a detector for testing an implant, attached to a bone comprising: a support structure comprising first and second support portions; and first and second force generators arranged perpendicular with respect to each generator central line. In one embodiment the detector further comprises a set/reset-circuit, low-pass filter, amplifiers for each channel and 3-axis magnet sensor. In one embodiment the detector further comprises a holding portion comprising holders, each holder being shaped to receive the generator and comprising a bottom portion, so formed that a prolonging line parallel to each bottom surface cross each other in a perpendicular angle providing a substantially 90 degree angle of incidence between the center lines of each generator. The generators may comprise coils for generating a magnetic force. Function of generating the force may alternate between the coils. The 3-axis magnetic sensor may be an Anisotropic Magneto-Resistive sensor (AMR), Giant Magneto-Resistive sensor (GMR), or any other suitable magnetic field sensors.

The invention also relates to a controller for testing an implant, attached to a bone comprising: a processing unit, an interface unit, a memory; and a communication portion. The processing unit is configured to receive signals from the interface unit and process signal for computing and providing the results detection, the interface unite is arranged to receive signals from the detector and according to above and converts the signal to data for the processing unit. The processing unit may further be configured to: generate an excitation instruction; after an excitation of a member connected to the implant, sampling the field caused by the movements of the member; average the sampled signal; apply FFT over each channel; for each channel extract signals; for each channel calculate a position (x(t), y(t)); generating a result. The calculation of positions may comprise:

computing the position relationship of the sensors and the member, assuming that the member moves in the xy-plane and the distance between the sensor and the member is r. Magnetic moment of the member is in the z-direction that is:

jUj = μ(0,0, μ _ζ )

and the magnetic field at the m he member is:

dBz dBz

B _z (t) = x(t) + y(t)

dx dy

wherein:

The invention also relates to a method of testing an implant attached to a bone. The method may comprise the steps of: exciting a member attached to the implant by application of a magnetic force, the excitation bringing one free end of the member into a substantially circular movement, spaced apart from the member and contactlessly detecting by a detecting unit, at least one resonance frequency and oscillation direction of the member; interpreting the detected resonance frequency and oscillation direction in terms of the degree of stability of the implant. The method may comprise the step of illustrating a direction relating to attachment degree.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the attached drawings, wherein elements having the same reference number designation may represent like elements throughout. Fig. 1 is a diagram of an exemplary system in which methods and systems described herein may be implemented; Fig. 2 illustrates a schematic view of a probe according to one embodiment of the invention,

Fig. 3 is a schematic view of probe and peg according to one embodiment of the invention,

Fig. 4 illustrates a schematic outline of the setup showing the position and orientation relationship of the sensor and peg,

Fig. 5 is a flow diagram illustrating exemplary processing by the system of Fig. 1.

DETAILED DESCRIPTION

In principle, the invention relates to measuring a magnetic measurable device's (peg) position (and direction), which corresponds to five unknown parameters: three for the position in space and two angles of the peg's direction, i.e. x, y, z, theta and phi, as will be described in following examples. In order to solve this, at least five independent measurement points may be needed (however, one measurement with one sensor and one coil is possible). One way to technically obtain this is using two 3-axis sensors that are separated by a known distance. Thus according to the present invention, the frequency and amplitudes in measurement points (e.g. 2x2) are measured and calculated based on the peg's position and movement and no ratio of the response voltage to the excitation, as in previous technics is used.

The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements.

Fig. 1 is a diagram of an exemplary system 100 in which methods and systems described herein may be implemented. System 100 may include a controller and analyzer unit 110, a probe 120 and a detection part 130. The controller and analyzer unit 1 10 may comprise processing unit 11 1 , an interface unit 1 12, a memory 113 and a communication portion 114. The processing unit 1 11 is arranged to receive signals from interface unit 1 12 and signal processing for computing and providing the results of the invention. The interface unite 1 12 receives signals from the probe and converts it to data for processing unit. The memory unit 113 is arranged to store data and may also store instructions to be executed by the processing unit. The interface unit may further comprise an amplifier, a D/A converter and a signal generator. The communication portion 114 is arranged to communicate with peripheral devices, such as a computer. The probe 120 comprises a magnetic exciter and detector which will be explained below.

System 100 may also include one or more power supplies (not shown). One skilled in the art would recognize that system 100 may be configured in a number of other ways and may include other or different elements.

Fig. 2 illustrates a schematic probe 120 layout according to the present invention. The probe comprises a carrier (PCB) 121 having a holding portion 122. The carrier 121 may also carry electronics, such as Set/reset-circuit 123, low-pass filter 124, amplifiers 125 for each channel and 3-axis magnet sensors 126 and 128, and corresponding connections. The holding portion 122 is arranged with two "legs" 1221 and 1222 each having a holder 12211 and 12221. Each holder is shaped to receive a coil 127a and 127b. Each holder is shaped with a bottom portion, so formed that a prolonging line parallel to each bottom surface cross each other in a perpendicular angle; this provides a 90 degree angle of incidence between the center lines of each coil.

The coils 127a and 127b are used for generating a magnetic force to the magnetic member. They may also alternate functionality between excitation, which sets the peg in a substantially rotational movement. Signals detected by the sensors 126 and 128 may be amplified by the amplifiers 125 and applied as an input to the analyzer unit 1 10. The output from the analyzer is fed to the processor 1 11 , which may be used to vary the frequency output of the oscillator of the analyzer, and store the results in the data store 133. The results can be printed out, and/or displayed on a display or the like (output through communication portion 114). Fig. 3, in a top view, illustrates the principals of the invention. A probe 120, schematically illustrated from above is positioned adjacent to a magnetic peg or a cantilever beam 350. The peg may be attached by means of a threaded section to an implanted fixture (not shown). The implant fixture can be a dental implant attached by a threaded section in a section of a bone, typically a human jawbone or any other type of an implant for humans or animals. The implant may be any one of a number of known types, formed from a metal, such as titanium, from a ceramic material, or any other appropriate material. The peg 350 may be entirely magnetic or provided with a magnetic portion 351. The magnetic portion 351 can be provided at one end of the peg 350, e. g. the free end or integrated inside the peg.

To be able to measure both frequencies (ISQ) and oscillation direction the position of the probe with respect to the peg must be calculated. This is achieved by using at least two 3-axis magnetic sensors, which in an embodiment may comprise for instance two Anisotropic Magneto-Resistive (AMR) or similar sensors 126 (fig. 2) which may use magnetic field to conduct measurement information between the sensor and the physical value, i.e. angle or linear position. This allows computing the probe's position and angle (e.g. 5 degree of freedom) in relation to the magnetic peg.

Fig. 4 illustrates schematically an outline of the setup showing the position and orientation relationship of the sensor and peg. The used theoretical model for computing the position of the peg relative to the probe, is given below. It is assumed that the peg moves in the xy-plane and the distance between the sensor and the peg is r.

Magnetic moment of the peg is oriented in the z-direction according to:

jUj = μ(0,0, μ _ζ )

The magnetic field in the x, y and z directions at the sensor due to the motion of the peg is described according to:

dBz dBz

B _z (t) = x(t) + y(t)

dx dy Wherein:

Fig. 5 illustrates exemplary computation steps for computing peg movements:

(1) After an excitation of the peg, peg movement is sampled by the probe sensor as mentioned above. The excitation and detection is alternated;

(2) The signal is averaged. The graph shows the raw signal (B(t) over time t in seconds) for x, y and z axes;

(3) FFT is applied over each channel. The graph shows the FFT of sampled

signals for x, y and z axes;

(4) (4') signals are extracted for each channel f1 and f2

(5) (5') the position x(t) and y(t) is calculated using above equation (2)

(6) The result may be visualized or presented on a computer screen by computing movement, direction and total. The result may be presented in such a way that it is easily understandable by a user.

To be able to measure the movement of the peg, the position of the peg relative the sensor must be known. The position of the sensors may be computed by:

Measuring the DC magnetic field in three orthogonal axis x, y and z , using both 3- axis magnetic sensors on the probe

- Assuming that the peg is realized as a magnetic dipole,

Solving the non-linear equation system with respect to the position of peg relative the probe using equation (2):

Fig. 6 illustrates an exemplary result output according to one embodiment of the present invention: a monitor 60 is used for visualizing the results. In this case the peg 130 is illustrated in a center portion of the monitor 60. The ISQ values are reproduced in a field 62. The system of the invention simplifies the visualization by just showing the most important values; lowest 621 and highest 622 ISQ values are provided. The lowest ISQ value also reviles in which direction the osseo-integration is weakest (poor stability), which is detected due to the rotation of the peg. An indicator 63, for example in form of an arrow, may illustrate the direction of weakness. The position of the probe 120 may be indicated by illustrating a presentation of it on the image.

Although we have exemplified the invention with reference to tooth/jawbone implants, it should be evident that the invention may be used for all types of implants where stability of implant needs to be measured. The implants may include endosteal, subperiosteal, prostheses implant, etc.

In previous exemplary embodiments, we have discussed using at least two 3-axis sensors to measure the peg's oscillation directions. However, generally at least five independent measurements of the field from the peg may be needed to determine the peg's position relative to the probe, which may be the key input to calculate the peg's movements. To measure the magnetic field in five independent directions and/or positions it is possible to, e.g. use two 3-axis magnetic field sensors, but it is also possible to accomplish the same measurement with one 2-axis and one 3-axis sensor, or two 2-axis and one 1-axis sensor, and so on.

If the position of the probe relative peg is known, instead at least two independent measuring points (direction/position) may be needed to measure the peg's oscillation directions, which may be achieved with a 3-axis sensor, as mentioned earlier.

In the forgoing examples, at least two excitation coils arranged at 90 degrees to each other are described. However, it is possible to use an excitation coil to trigger the oscillations, although two coils can be used to increases the start of rotation movement.

The mentioned, substantially 90 degrees between the coils is preferred, but not an absolute requirement, for example, between 45 to 90 degrees or the like may also be used. Thus, to measure the oscillation directions, it is required at least one coil which excites the peg and measuring the magnetic field of the peg in five independent directions/positions (e.g. with two 3-axis sensors). Thus, in its simplest configuration, the probe may comprise at least one coil and one 1-axis magnetic field sensor. In this case, a first measurement is carried out by exciting the peg, which normally may rotate on excitation and the ISQ value is determined and one direction is determined. The second direction is substantially 90 degrees from the first measurement point value and a second ISQ value is determined. At a substantially optimal position of the probe two values are obtained, i.e. a maximal rotation can be obtained using only one excitation coil. Consequently, two ISQ values are obtained at one measurement. If one direction relative the probe is obtained, then the other direction is displaced substantially 90 degrees.

It should be noted that the word "comprising" does not exclude the presence of other elements or steps than those listed and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the invention may be

implemented at least in part by means of both hardware and software, and that several "means", "units" or "devices" may be represented by the same item of hardware. The above mentioned and described embodiments are only given as examples and should not be limiting to the present invention. Other solutions, uses, objectives, and functions within the scope of the invention as claimed in the below described patent claims should be apparent for the person skilled in the art. The various embodiments of the present invention described herein is described in the general context of method steps or processes, which may be implemented in one embodiment by a computer program product, embodied in a computer-readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A computer-readable medium may include removable and non-removable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), compact discs (CDs), digital versatile discs (DVD), etc. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes. Software and web implementations of various embodiments of the present invention can be accomplished with standard programming techniques with rule-based logic and other logic to accomplish various database searching steps or processes, correlation steps or processes, comparison steps or processes and decision steps or processes. It should be noted that the words "component" and "module," as used herein and in the following claims, is intended to encompass implementations using one or more lines of software code, and/or hardware implementations, and/or equipment for receiving manual inputs.

The foregoing description of embodiments of the present invention, have been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit embodiments of the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments of the present invention. The

embodiments discussed herein were chosen and described in order to explain the principles and the nature of various embodiments of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments and with various modifications as are suited to the particular use

contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products.