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GB2339911A - Apparatus and method for measuring the resistance to rotation of a dental implant. - Google Patents

Apparatus and method for measuring the resistance to rotation of a dental implant. Download PDF

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Publication number
GB2339911A
GB2339911A GB9815776A GB9815776A GB2339911A GB 2339911 A GB2339911 A GB 2339911A GB 9815776 A GB9815776 A GB 9815776A GB 9815776 A GB9815776 A GB 9815776A GB 2339911 A GB2339911 A GB 2339911A
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United Kingdom
Prior art keywords
implant
dental implant
rotational resistance
torque
measuring apparatus
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9815776A
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GB9815776D0 (en
Inventor
Neil Meredith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Bristol
Original Assignee
University of Bristol
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University of Bristol filed Critical University of Bristol
Priority to GB9815776A priority Critical patent/GB2339911A/en
Publication of GB9815776D0 publication Critical patent/GB9815776D0/en
Publication of GB2339911A publication Critical patent/GB2339911A/en
Withdrawn legal-status Critical Current

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/24Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C19/00Dental auxiliary appliances
    • A61C19/04Measuring instruments specially adapted for dentistry
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C8/00Means to be fixed to the jaw-bone for consolidating natural teeth or for fixing dental prostheses thereon; Dental implants; Implanting tools
    • A61C8/0089Implanting tools or instruments
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C1/00Dental machines for boring or cutting ; General features of dental machines or apparatus, e.g. hand-piece design
    • A61C1/08Machine parts specially adapted for dentistry
    • A61C1/18Flexible shafts; Clutches or the like; Bearings or lubricating arrangements; Drives or transmissions
    • A61C1/185Drives or transmissions
    • A61C1/186Drives or transmissions with torque adjusting or limiting means

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Epidemiology (AREA)
  • Dentistry (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Orthopedic Medicine & Surgery (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Biophysics (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Dental Tools And Instruments Or Auxiliary Dental Instruments (AREA)

Description

2339911 APPARATUS AND METHOD FOR MEASURING THE RESISTANCE TO ROTATION OF A
DENTAL IMPLANT This invention relates to an apparatus and method for non-destructively measuring the resistance to rotation of a dental implant.
When teeth have been lost, threaded or cylindrical metal implants may be placed in the underlying bone as a means of anchoring a prosthesis, whether it be a crown, bridge or denture. Following placement in the bone it is desirable to measure the implant's stability. Such a measurement provides an indication of the quality of fit and the degree of healing. At present the tissues surrounding implants are commonly allowed to heal for a period of between three and six months before loading with a prosthesis. Early overloading may lead to loss of bone or the formation of fibrous tissue and subsequent failure or loss of the implant. Conversely, it may be that an earlier loading is possible in implants that show a good level of stability at placement. Therefore an apparatus that is capable of non-invasive measurement of an implant stability at any stage following its placement could be used to predict the optimum healing period for an implant prior to loading; to determine the initial stability of an implant; to determine any increase in stability and anchorage due to bone formation; and to measure changes in stability due to bone loss and formation of fibrous tissue.
A device that measures the stiffness or tightness of an implant is disclosed in European Published Patent Application EP-A-0,777,439. This device comprises a probe with an accelerometer connected to the probe tip and an actuator comprising a hammer for impacting the probe tip against the implant. The accelerometer measures an acceleration time history of the implant. 'Me device can detect small changes in the condition of a dental implant over time so that the progress of the implant can be followed.
The above mentioned device has the disadvantage that the force is applied in a single impact and as such cannot be gradually increased while the implant is being monitored. Thus, the amount of information that can be gained is limited. Furthermore, as the force is all applied in one step, it cannot be controlled and stopped if the implant appears to be becoming unstable. The position of the load application is also unfavourable.
2 British Published Patent Application GB-A-2,296,127 discloses an apparatus for testing the fit of screw-retained structures, such as the fit of dental bridges to implants. The chang6 in motor torque of a motor is measured by monitoring the change in driving current drawn by the motor as it screws the bridge in place. A rapid increase in torque with minimal rotation of the retaining screw indicates a good fit with the bridge superstructure fitting the implant passively, whereas a relatively slow increase with prolonged rotation of the screw as the tension increases, indicates a poor fit. This apparatus is used to test the quality of fit between two metal components by measuring the torque required as they are screwed together. It does not measure the stability of a dental implant embedded in bone.
In accordance with one aspect of the present invention, there is provided a dental implant rotational resistance measuring apparatus comprising: an attachment coupling for attaching to a dental implant embedded in tissue; a handle connected to said attachment coupling for manually applying a torque via said attachment coupling to said implant; a sensor for sensing applied torque; and a sensor for sensing angular displacement of said implant.
Thus, the present invention alleviates the disadvantages of the prior art by providing an apparatus that measures implant stability by applying a rotational force to the dental implant. A low stiffiess with rotation of an implant may be an indication of poor stability at placement or the presence of fibrous tissue indicating possible failure, whereas a high stiffness withTninimal rotation is an indication of high stability and a high level of bone formation. The invention provides a device that is inexpensive and which can apply a rotational force to an implant in a simple manner. Furthermore, the angular displacement of the implant can be simply and accurately measured and provides a good indication of implant stability.
In accordance with another aspect of the present invention, there is provided a dental implant rotational resistance measuring apparatus comprising: an attachment coupling for attaching to a dental implant embedded in tissue; means for applying a predetermined torque to a dental implant embedded in tissue via said attachment coupling; and a sensor for measuring angular displacement of said implant.
Thus, this aspect of the present invention alleviates the disadvantages of the prior art by providing an apparatus that measures implant stability by applying a rotational torque to a dental
3 implant. The torque applied to the implant is set and the angular displacement occurring in response to this force measured. The applied torque can be varied with time and is produ6ed in a manner that is repeatable. Furthermore, the device provides for simple and accurate measurement of the angular displacement of the implant, thereby providing a good indication of implant stability.
Preferably, the means for applying the predetermined torque force is an electric motor. Alternatively a solenoid may be used. Electric motors and solenoids are both readily available and produce a rotational force that is easy to control by control of the driving current. Advantageously, the driving current is controlled to increase in a step-wise fashion or alternatively continuously with time. Such control of the driving current can produce a gradually increasing torque (a controlled application of load) which enables the stability of the implant to be carefiffly studied. Furthermore, the test can be stopped before a torque is reached that may damage the implant/tissue interface.
In one embodiment, the applied torque is measured using a strain gauge. A strain gauge is a readily available accurate means of measuring torque.
Preferably, when the torque is applied via a motor an encoder may be used to measure the angular displacement. Advantageously, the encoder is an integral part of the motor. A motor and encoder as an integral unit form a stable rigid part that is easy to mount on the apparatus.
In preferred embodiments the dental implant rotational resistance measuring apparatus comprises a force limiter to Emit the applied torque to less than a preset value. This helps prevent darnage to the implant by an excessive use of force.
Advantageously, the dental implant rotational resistance measuring apparatus comprises an angle limiter to limit the angular displacement of said implant to less than a preset angle. This helps prevent damage to the implant by excessive rotation of the implant.
In preferred embodiments, the dental implant rotational resistance measuring apparatus, comprises a microprocessor for calculating the implant rotational resistance of the implant. Thus, the device can quickly produce implant rotational resistance results from the measured values. In 4 one embodiment this is done by recording the angular displacement of said implant as a fimetion of applied torque and generating a torque/displacement curve therefrom, the implant rotati6nal resistance being calculated from the slope or area under the torque/displacement curve.
Advantageously, the microprocessor comprises calibration data storage means having calibration data for calibrating angular displacement with rotational resistance of a dental implant. Thus, the accuracy of the device can be maintained by repeated calibrations.
According to another aspect of the present invention, there is provided a method for measuring the rotational resistance of a dental implant embedded in tissue, comprising attaching a torque applying mechanism to said dental implant; applying a torque to said dental implant with said torque applying mechanism; measuring the angular diVlacement of said dental implant resulting from said applied torque; and calculating from said applied torque and said angular displacement the rotational resistance of said dental implant embedded in said tissue.
Thus, the present invention alleviates the disadvantages of the prior art by providing a method of measuring implant stability by applying a rotational torque to a dental implant. A rotational torque is an easy force to administer and control, and thus the stability of the implant can be accurately measured in a reproducible manner.
In one embodiment the torque applied is a predetermined torque and the angular displacement produced by this torque is measured. Alternatively the implant is rotated to a predetermined angle and the torque required for this rotation is measured. Both of these methods provide simple repeatable stability tests that can be applied to implants. The type of test and implant determines which method is most appropriate.
Preferably the method includes the steps of increasing the torque with time; and measuring the angular displacement of the implant as a fimetion of applied torque; generating a torque/angular displacement curve; deriving the rotational resistance of said implant from the area under said curve. This method provides an accurate way of determining the stability of an implant.
According to a fin-ther aspect of the present invention there is provided a method of fi)dng C a crown for cosmetic purposesa's defined in claim 19. When affixing a crown for cosmetic purposes to an implant it is important to know that the implant is firmly embedded in the tissue. The method of the present invention provides a simple and accurate way of determining if this is the case or not.
Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:
Figure 1 illustrates a first embodiment of the invention; Figure 2 illustrates a block diagram of a second embodiment of the invention; Figure 3 illustrates the rate of change of torque with steadily increasing displacement angle for a stable osseointegrated dental implant; and Figure 4 illustrates the rate of change of torque with steadily increasing displacement angle of an unstable/failing dental implant.
With reference to Figure 1, the device according to a first embodiment comprises an attachment coupling 10 for attaching to a dental implant 20 embedded in tissue. The dental implant may be threaded or smooth and of a cylindrical or irregular cross-section. The device fin-ther comprises a handle 30 connected to said attachment coupling for manually applying a rotational force or torque (measured by a strain guage 35 coupled to the handle) to the dental implant via the attachment coupling 10 and a sensor 40 for measuring angular displacement of the dental implant, such as a Hall effect angular displacement sensor. An angle limiter 50 is associated with the gauge and acts to decouple the handle from the attachment coupling by means of a ratchet device when a preset angular displacement is reached. In other embodiments, not illustrated, a force limiter may be attached between the handle and attachment coupling 10 to decouple them when a preset torque is exceeded.
With reference to Figure 2, the device according to a second embodiment comprises a constant current motor 300 which, in conjunction with an appropriate gearing system, supplies the rotational torque in place of the manual handle 30 of the first embodiment. The motor 300 and gearing system may be handheld. Ihe angular displacement is measured using a rotary encoder 400 (Hall effect, optical or by detection of commutator pulses) which is an integral part 6 of the motor 300. Alternatively, the encoder could be separately provided between the motor and the implant. The applied torque is a function of the drive current of the motor 300 and is controlled by a control system. Ile motor 300 comprises a current limiter 500 that acts to limit the current and thus the torque of the motor 300; this may be in addition to or instead of an angular displacement limiter that acts in conjunction with the encoder to limit the angular displacement of the motor 300. These limiters act to avoid damaging the implant/tissue interface.
A graphical display 600 shows the stiffness/elasticity of the implanttissue interface as a fimction of the variation in torque with angular displacement. The device further comprises a processor 700 with memory in which preset trip levels are stored that set alarms or deactivate the motor 300 at certain levels. The motor 300 has a control system that acts to control the driving current to produce a certain desired torque. This control system can be programmed to increase the driving current, and thus the applied torque, with time. This can be done as a continuous increase or in steps.
The device is calibrated by comparing measured torque and displacement to the result when the instrument is attached to a known torque stffhess, Le. calibration of stiffiess may be performed by measuring the stiffness of test implants placed in materials of known stiffiess. The microprocessor is used to analyse the stiffness data and compare it with known experimental data.
In use the attachment coupling 100 of Fig 2 is attached to the dental implant 200 and a gradually increasing torque is applied to the dental implant via the motor 300. The angular displacement produced and torque applied are continually measured, and a graph of one versus the other is plotted. The implant rotational resistance is calculated from the slope of the curve.
Figures 3 and 4 illustrate such curves produced by the apparatus of Figure 2. The steep slope of the line in Figure 3 indicates an implant that is osseointegrated and therefore stable, whereas the flatter line of Figure 4 indicates that the implant is unstable and failing.
It is clear that in other embodiments other types of motor can be used, with either voltage or cur-rent or both being measured to determine torque. Alternatively a solenoid could be used instead of the motor.

Claims (1)

  1. 7 Claims
    1. Dental implant rotational resistance measuring apparatus comprising:
    an attachment coupling for attaching to a dental implant embedded in tissue; a handle connected to said attachment coupling for manually applying a torque via said attachment coupling to said implant; a sensor for sensing applied torque; and a sensor for sensing angular displacement of said implant.
    2. Dental implant rotational resistance measuring apparatus comprising:
    an attachment coupling for attaching to a dental implant embedded in tissue; means for applying a predetermined torque to a dental implant embedded in tissue via said attachment coupling; and a sensor for measuring angular displacement of said implant.
    3. Dental implant rotational resistance measuring apparatus according to claim 2, wherein the means for applying the predetermined torque comprises an electrical motor and a control system, wherein said control system is adapted to supply an appropriate driving current to said motor to produce said predetermined torque.
    4. Dental implant rotational resistance measuring apparatus according to claim 2, wherein the means for applying the predetermined torque comprises a solenoid and a control system, wherein said control system is adapted to supply an appropriate driving current to said solenoid to produce said predetermined torque.
    5. Dental implant rotational resistance measuring apparatus according to claim 3 or 4, wherein said control system is adapted to supply a first driving current for a first time period, and a second driving current for a second time period, wherein said second driving current is greater than said first driving current.
    6. Dental implant rotational resistance measuring apparatus according to claim 4 or 5, wherein said control system is adapted to increase said driving current with time.
    8 7. Dental implant rotational resistance measuring apparatus according to any of the preceding claims, fiu-ther comprising a strain gauge for measuring said applied torque.
    8. Dental implant rotational resistance measuring apparatus according to claim 3 or claim 3 and any one of claims 5 or 6, wherein said angular displacement sensor comprises an encoder.
    9. Dental implant rotational resistance measuring apparatus according to claim 8, wherein said encoder is an integral part of said motor.
    10. Dental implant rotational resistance measuring apparatus according to any of the preceding claims, wherein said means for apphying the torque comprises a force limiter to limit said applied torque to less than a preset value.
    11. Dental implant rotational resistance measuring apparatus according to any of the preceding claims, wherein said device fin-ther comprises an angle limiter to limit said angular displacement to less than a preset angle.
    12. Dental implant rotational resistance measuring apparatus according to any of the preceding claims, further comprising a microprocessor programmed to calculate the implant rotational resistance of said implant.
    13. Dental implant rotational resistance measuring apparatus according to claitu 12, wherein said microprocessor is programmed to record the angular displacement of said implant as a fimction of applied force and to generate a torque/angular displacement curve therefrom, said implant rotational resistance being calculated from the slope or area under said torque/displacement curve.
    14. Dental inaplant rotational resistance measuring apparatus according to claim 12, wherein said microprocessor further comprises calibration data storage means, having calibration data for calibrating angular displacement with rotational resistance of a dental implant.
    9 15. A method for measuring the rotational resistance of a dental implant embedded in tiisue, said method comprising the steps of attaching a torque applying mechanism to said dental implant; applying a torque to said dental implant with said torque applying mechanism; measuring the angular displacement of said dental implant resulting from said applied torque;and calculating from said applied torque and said angular displacement the rotational resistance of said dental implant embedded in said tissue.
    16. A method for measuring the rotational resistance of a dental implant embedded in tissue according to claim 15, wherein the torque applied is a predetermined torque and the angular displacement produced by this torque is measured.
    17. A method for measuring the rotational resistance of a dental implant embedded in tissue according to claim 15, wherein the implant is rotated to a predetermined angle and the torque required for this rotation is measured.
    18. A method for measuring the rotational resistance of a dental implant embedded in tissue according to claim 15, further comprising the steps of. increasing said torque with time; and recording the angular displacement of said implant as a fimction of applied torquing force; generating a torque/angular displacement curve; deriving the rotational resistance of said implant from the area under said curve.
    19. A method of fi)Cmg a crown for cosmetic purposes comprising:
    embedding a dental implant in a dental tissue; measurinc, the rotational resistance of said implant accordin to any of claims 15 to 17; C 9 attaching said crown to said implant if the rotational resistance of said implant is greater 0 than a preset value.
    20. A dental implant rotational resistance measuring apparatus substantially as hereinbefore described with reference to the accompanying drawings.
    21. A method for measuring the rotational resistance of a dental implant embedded in tissue substantially as hereinbefore described with reference to the accompanying drawings. 22. A method of fl)Cmg a crown for cosmetic purposes substantially as hereinbefore described with reference to the accompanying drawings.
GB9815776A 1998-07-20 1998-07-20 Apparatus and method for measuring the resistance to rotation of a dental implant. Withdrawn GB2339911A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9815776A GB2339911A (en) 1998-07-20 1998-07-20 Apparatus and method for measuring the resistance to rotation of a dental implant.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9815776A GB2339911A (en) 1998-07-20 1998-07-20 Apparatus and method for measuring the resistance to rotation of a dental implant.

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GB9815776D0 GB9815776D0 (en) 1998-09-16
GB2339911A true GB2339911A (en) 2000-02-09

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4259869A (en) * 1977-10-07 1981-04-07 Atlas Copco Aktiebolag Method and apparatus for inspection and fail-safe control of threaded joint tightening processes
US4265109A (en) * 1975-10-25 1981-05-05 C. Plath Kg Wrench with angular rotation readout
GB2286127A (en) * 1994-01-25 1995-08-09 Andrew Joseph Stanley Dawood Apparatus for testing the passive fit of screw-retained structures

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4265109A (en) * 1975-10-25 1981-05-05 C. Plath Kg Wrench with angular rotation readout
US4259869A (en) * 1977-10-07 1981-04-07 Atlas Copco Aktiebolag Method and apparatus for inspection and fail-safe control of threaded joint tightening processes
GB2286127A (en) * 1994-01-25 1995-08-09 Andrew Joseph Stanley Dawood Apparatus for testing the passive fit of screw-retained structures

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Publication number Publication date
GB9815776D0 (en) 1998-09-16

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