CA2158854C - An apparatus for testing the passive fit of screw retained structures - Google Patents
An apparatus for testing the passive fit of screw retained structures Download PDFInfo
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- CA2158854C CA2158854C CA002158854A CA2158854A CA2158854C CA 2158854 C CA2158854 C CA 2158854C CA 002158854 A CA002158854 A CA 002158854A CA 2158854 A CA2158854 A CA 2158854A CA 2158854 C CA2158854 C CA 2158854C
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- fit
- torque
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
- A61C8/00—Means to be fixed to the jaw-bone for consolidating natural teeth or for fixing dental prostheses thereon; Dental implants; Implanting tools
- A61C8/0089—Implanting tools or instruments
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
- A61C19/00—Dental auxiliary appliances
- A61C19/04—Measuring instruments specially adapted for dentistry
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/24—Apparatus 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
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
- A61C1/00—Dental machines for boring or cutting ; General features of dental machines or apparatus, e.g. hand-piece design
- A61C1/08—Machine parts specially adapted for dentistry
- A61C1/18—Flexible shafts; Clutches or the like; Bearings or lubricating arrangements; Drives or transmissions
- A61C1/185—Drives or transmissions
- A61C1/186—Drives or transmissions with torque adjusting or limiting means
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- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Veterinary Medicine (AREA)
- Oral & Maxillofacial Surgery (AREA)
- Public Health (AREA)
- Dentistry (AREA)
- Epidemiology (AREA)
- Animal Behavior & Ethology (AREA)
- Orthopedic Medicine & Surgery (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Biophysics (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
- Mutual Connection Of Rods And Tubes (AREA)
- Dental Tools And Instruments Or Auxiliary Dental Instruments (AREA)
Abstract
A passivity indicating apparatus for use where structures are to be joined by threaded components and a passive, precise, fit is sought, comprising means (9) for indicating the precision of fit of structures that are to be joined which means is responsive to a change in the resistance to rotation of the retention screw (4) or other threaded rotary component.
Description
An apparatus for testing the passive fit of screws retained structures There are many situations where a screw retained structure must fit against another structure to which it is to be connected with a high degree of accuracy and passivity -that is as the retaining screws are tightened. there should be no stress or strain induced in either structure.
This invention relates to an apparatus for checking that screw retained structures fit passivel~~. It is clear that there are numerous situations where structures must be precisely and passively joined by screws, bolts, or other threaded components, over a wide range of accuracy and torque; this invention has a particular application in dentistry, as described below, but it is understood that the governing principles could equally be applied in any other class of engineering application.
Where teeth have been lost, as a result of, for example, dental disease, it may become necessary to place dental implants. Dental implants are usually made of titanium or other bio-compatible materials, and form a strong inflexible union with bone.
This type of union has been termed "osseointegration". It is now understood that osseointegration will endure for many years in favorable circumstances. However this union may rapidly break down if the implant is overloaded by unfavorable forces.
It is common practice to use several implants to support a dental bridge. It is also common practice to use retaining screws to connect such bridges to the implants.
Bridges at present are fabricated by casting wax or plastic patterns in dental alloys. or by using computer aided design and computer aided milling technology. Most stages of construction are carried out on models prepared from impressions of the patient's mouth. There is thus a great potential for error in the fabrication of the bridge framework, and so it is not surprising that small discrepancies in the mechanical fit of the bridge superstructure to the dental implants may arise.
SUBSTITUTE S,~IEtT (RULE 26) When positioned in the mouth a small discrepancy may sometimes go unnoticed with the result that when the bridge is screwed into place in spite of a small error, flexure of the implant, surrounding bone, bridge superstructure, retaining screw, and any other prosthetic components may permit the bridge to be seated in spite of the imperfect fit. As a result of this flexure there may then be a considerable build up of stress or strain in the system. This later manifests itself as failure of one of the components, or failure of osseointegration and ultimately the loss of the implant.
When the implant supported bridge superstructure fits against the implants precisely it is commonly said to fit passively - that is when the screws are tightened no stress or strain is introduced. Under these circumstances, tightening the screws that retain the bridge superstructure merely compresses the framework against the head of the implant.
According to one aspect the invention provides an apparatus for use with structures to be joined by a retaining screw for testing the passive fit of the structures to be joined, including a dental handpiece with an appropriate screw driving attachment for tightening said retaining screw to at least one of said structures and a micro-motor for driving said dental handpiece, characterised by appropriate circuitry for monitoring the rotation of the micro-motor from which the change in torque delivered to the retaining screw may be derived during tightening over a time period and display means in the form of (a) a numerical display for displaying data relating to the number of rotations used to tighten the screw, or the rate of tightening the screw, over a selected range of torques, or (b) a visual display which is adapted to display a graphical representation of the torque applied to the retaining screw as it is tightened, over a selected range of torques, or (c) indicating lights which illuminate at appropriate thresholds, adapted to receive an output from said monitoring means of said change in torque over said time period, the change in torque over said time period being indicative of the quality of fit of the structures to be joined, for indicating the precision of fit between said structures.
According to another aspect the invention provides a method for determining a precision of fit between dental structures to be joined by a threaded component, said method comprising the steps of: tightening said threaded component to said dental structures; measuring a torque applied to said threaded component during said tightening during a period of time; determining the precision of fit between said dental structures based on a variation in a rate of change in said torque during said period of time; and indicating the precision of fit between said dental structures in a visual display.
According to another aspect the invention provides a method of determining a precision of fit between dental structures to be joined by a threaded component, said method comprising the steps of: tightening said threaded component with a dental handpiece supplied with a constant voltage to join said dental structures; measuring a torque applied to said threaded component during a predetermined period of time during said tightening; determining a minimum threshold of torque which indicates a precise fit between said dental structures; visually indicating said precision of fit between said dental structures based on said measured torque and said minimum threshold.
2a Figure 1 illustrates the rapid increase in torque as the retaining screws are tightened when the screw head contacts the bridge superstructure, and the superstructure fits the implants passively.
where the implant retained bridge superstructure fits the implants poorly, tightening the retaining screws results in a relatively slower build up of tension in the screw as the various components of the system are flexed.
Figure 2 demonstrates how the tension in (or torque applied to) the retaining screw increases slowly as the various components of the system are flexed, and then rapidly increases as the superstructure is compressed against the implant when the superstructure finally contacts the implant.
The present invention is a device which monitors the build up of tension in the retaining screw as it is tightened. A rapid build up in tension, with minimal rotation of the retaining screw, indicates that a bridge superstructure fits the implants passively, whereas a relatively slow build up in tension with prolonged rotation of the screw as the tension increases, indicates that the superstructure is initially separated from the 2b implant.
A specific embodiment of this invention wiii now be described with reference to Figures 3 and 4.
With reference to Figure 3, a conventional, or dedicated, dental handpiece 1 is powered by a miniature electric motor (micro-motor) ~. An appropriate screw-driving attachment 3 is loaded in the handpiece to permit its use for tightening a retention screw 4.
With reference to Figure 4, power to the micro-motor 2 is regulated by the power supply 5 such that voltage is maintained at a constant level, and current may be monitored by appropriate circuitry. The handpiece and micro-motor are calibrated such that current in the power supply to the micro-motor is correlated with the torque delivered by the handpiece as it tightens the retaining screw.
In this embodiment of the invention an analogue to digital converter 7 samples the current to the micro-motor after current to voltage conversion and appropriate amplification 6. The digital output is then processed by a microcomputer 8 which then displays a graphic representation of a curve of current (torque) against time on a visual display 9; the shape of the curve may then be qualitatively assessed. Further processing will also return a numerical result, such as rate of change in torque.
Alternatively circuitry monitors the rate of change in current as the retaining screw is tightened. A rapidly increasing current, indicative of a passively fitting superstructure is indicated by an indicator Light, a g a green light emitting diode. Below a predetermined treshoid other indicators illuminate, thus demonstrating various ieveis of inadequacy of fit. Similarly, a numerical display may be provided.
The instrument may be calibrated by using the apparatus first upon standardised structures along with the desired retention screw and will also permit comparison SUBSTITUTE SHEET (RULE 26) WO 95/20146 ~r PCT/IB95100055 between the fit of the bridge when seated on the model or in the patient's mouth.
An alternative embodiment of this invention may employ components such as optical encoders or Hall effect sensors, or other types of transducers, in conjunction with appropriate circuitry, or may employ circuitry which monitors fluctuations induced in the supply to the micro-motor by the motor, which permits the rotation of the micro-motor to be monitored.
The number of rotations, or parts of rotations of the motor, which correlates with the rotation of the ecrew driving head, can thus be counted as the torque delivered to the retaining screw increases; as torque builds up over a specified range. the number of rotations of the micro-motor counted over the specified range is inversely related to the accuracy of the fit of the structures.
The result of the test may be displayed numerically, or may be indicated by indicating lights which illuminate at appropriate tresholds. The instrument may be calibrated by using the apparatus first upon standardised bridge frameworks and models with the appropriate retention screws, and will also permit comparison between the bridge when seated on the model or in the patient's mouth.
In both these embodiments, signal processing and other processing functions may be carried out with the aid of a micro computer and associated software. This facilitates the calibration process and permits comparison of the digital data derived from the analogue to digital converter from measurements carried out on a patient, with measurements carried out on a standardised bridge framework, or the patient's bridge framework when seated on the model upon which it was fabricated. This will also facilitate compensation for play or friction in the system which may result in increasing current in the motor, or rotation of an element of the apparatus, prior to actual rotation of the retaining screw.
This invention relates to an apparatus for checking that screw retained structures fit passivel~~. It is clear that there are numerous situations where structures must be precisely and passively joined by screws, bolts, or other threaded components, over a wide range of accuracy and torque; this invention has a particular application in dentistry, as described below, but it is understood that the governing principles could equally be applied in any other class of engineering application.
Where teeth have been lost, as a result of, for example, dental disease, it may become necessary to place dental implants. Dental implants are usually made of titanium or other bio-compatible materials, and form a strong inflexible union with bone.
This type of union has been termed "osseointegration". It is now understood that osseointegration will endure for many years in favorable circumstances. However this union may rapidly break down if the implant is overloaded by unfavorable forces.
It is common practice to use several implants to support a dental bridge. It is also common practice to use retaining screws to connect such bridges to the implants.
Bridges at present are fabricated by casting wax or plastic patterns in dental alloys. or by using computer aided design and computer aided milling technology. Most stages of construction are carried out on models prepared from impressions of the patient's mouth. There is thus a great potential for error in the fabrication of the bridge framework, and so it is not surprising that small discrepancies in the mechanical fit of the bridge superstructure to the dental implants may arise.
SUBSTITUTE S,~IEtT (RULE 26) When positioned in the mouth a small discrepancy may sometimes go unnoticed with the result that when the bridge is screwed into place in spite of a small error, flexure of the implant, surrounding bone, bridge superstructure, retaining screw, and any other prosthetic components may permit the bridge to be seated in spite of the imperfect fit. As a result of this flexure there may then be a considerable build up of stress or strain in the system. This later manifests itself as failure of one of the components, or failure of osseointegration and ultimately the loss of the implant.
When the implant supported bridge superstructure fits against the implants precisely it is commonly said to fit passively - that is when the screws are tightened no stress or strain is introduced. Under these circumstances, tightening the screws that retain the bridge superstructure merely compresses the framework against the head of the implant.
According to one aspect the invention provides an apparatus for use with structures to be joined by a retaining screw for testing the passive fit of the structures to be joined, including a dental handpiece with an appropriate screw driving attachment for tightening said retaining screw to at least one of said structures and a micro-motor for driving said dental handpiece, characterised by appropriate circuitry for monitoring the rotation of the micro-motor from which the change in torque delivered to the retaining screw may be derived during tightening over a time period and display means in the form of (a) a numerical display for displaying data relating to the number of rotations used to tighten the screw, or the rate of tightening the screw, over a selected range of torques, or (b) a visual display which is adapted to display a graphical representation of the torque applied to the retaining screw as it is tightened, over a selected range of torques, or (c) indicating lights which illuminate at appropriate thresholds, adapted to receive an output from said monitoring means of said change in torque over said time period, the change in torque over said time period being indicative of the quality of fit of the structures to be joined, for indicating the precision of fit between said structures.
According to another aspect the invention provides a method for determining a precision of fit between dental structures to be joined by a threaded component, said method comprising the steps of: tightening said threaded component to said dental structures; measuring a torque applied to said threaded component during said tightening during a period of time; determining the precision of fit between said dental structures based on a variation in a rate of change in said torque during said period of time; and indicating the precision of fit between said dental structures in a visual display.
According to another aspect the invention provides a method of determining a precision of fit between dental structures to be joined by a threaded component, said method comprising the steps of: tightening said threaded component with a dental handpiece supplied with a constant voltage to join said dental structures; measuring a torque applied to said threaded component during a predetermined period of time during said tightening; determining a minimum threshold of torque which indicates a precise fit between said dental structures; visually indicating said precision of fit between said dental structures based on said measured torque and said minimum threshold.
2a Figure 1 illustrates the rapid increase in torque as the retaining screws are tightened when the screw head contacts the bridge superstructure, and the superstructure fits the implants passively.
where the implant retained bridge superstructure fits the implants poorly, tightening the retaining screws results in a relatively slower build up of tension in the screw as the various components of the system are flexed.
Figure 2 demonstrates how the tension in (or torque applied to) the retaining screw increases slowly as the various components of the system are flexed, and then rapidly increases as the superstructure is compressed against the implant when the superstructure finally contacts the implant.
The present invention is a device which monitors the build up of tension in the retaining screw as it is tightened. A rapid build up in tension, with minimal rotation of the retaining screw, indicates that a bridge superstructure fits the implants passively, whereas a relatively slow build up in tension with prolonged rotation of the screw as the tension increases, indicates that the superstructure is initially separated from the 2b implant.
A specific embodiment of this invention wiii now be described with reference to Figures 3 and 4.
With reference to Figure 3, a conventional, or dedicated, dental handpiece 1 is powered by a miniature electric motor (micro-motor) ~. An appropriate screw-driving attachment 3 is loaded in the handpiece to permit its use for tightening a retention screw 4.
With reference to Figure 4, power to the micro-motor 2 is regulated by the power supply 5 such that voltage is maintained at a constant level, and current may be monitored by appropriate circuitry. The handpiece and micro-motor are calibrated such that current in the power supply to the micro-motor is correlated with the torque delivered by the handpiece as it tightens the retaining screw.
In this embodiment of the invention an analogue to digital converter 7 samples the current to the micro-motor after current to voltage conversion and appropriate amplification 6. The digital output is then processed by a microcomputer 8 which then displays a graphic representation of a curve of current (torque) against time on a visual display 9; the shape of the curve may then be qualitatively assessed. Further processing will also return a numerical result, such as rate of change in torque.
Alternatively circuitry monitors the rate of change in current as the retaining screw is tightened. A rapidly increasing current, indicative of a passively fitting superstructure is indicated by an indicator Light, a g a green light emitting diode. Below a predetermined treshoid other indicators illuminate, thus demonstrating various ieveis of inadequacy of fit. Similarly, a numerical display may be provided.
The instrument may be calibrated by using the apparatus first upon standardised structures along with the desired retention screw and will also permit comparison SUBSTITUTE SHEET (RULE 26) WO 95/20146 ~r PCT/IB95100055 between the fit of the bridge when seated on the model or in the patient's mouth.
An alternative embodiment of this invention may employ components such as optical encoders or Hall effect sensors, or other types of transducers, in conjunction with appropriate circuitry, or may employ circuitry which monitors fluctuations induced in the supply to the micro-motor by the motor, which permits the rotation of the micro-motor to be monitored.
The number of rotations, or parts of rotations of the motor, which correlates with the rotation of the ecrew driving head, can thus be counted as the torque delivered to the retaining screw increases; as torque builds up over a specified range. the number of rotations of the micro-motor counted over the specified range is inversely related to the accuracy of the fit of the structures.
The result of the test may be displayed numerically, or may be indicated by indicating lights which illuminate at appropriate tresholds. The instrument may be calibrated by using the apparatus first upon standardised bridge frameworks and models with the appropriate retention screws, and will also permit comparison between the bridge when seated on the model or in the patient's mouth.
In both these embodiments, signal processing and other processing functions may be carried out with the aid of a micro computer and associated software. This facilitates the calibration process and permits comparison of the digital data derived from the analogue to digital converter from measurements carried out on a patient, with measurements carried out on a standardised bridge framework, or the patient's bridge framework when seated on the model upon which it was fabricated. This will also facilitate compensation for play or friction in the system which may result in increasing current in the motor, or rotation of an element of the apparatus, prior to actual rotation of the retaining screw.
SUBSTITUTE SHEET (RULE 28)
Claims (14)
1. An apparatus for use with structures to be joined by a retaining screw for testing the passive fit of the structures to be joined, including a dental handpiece with an appropriate screw driving attachment for tightening said retaining screw to at least one of said structures and a micro-motor for driving said dental handpiece, characterised by appropriate circuitry for monitoring the rotation of the micro-motor from which the change in torque delivered to the retaining screw may be derived during tightening over a time period and display means in the form of (a) a numerical display for displaying data relating to the number of rotations used to tighten the screw, or the rate of tightening the screw, over a selected range of torques, or (b) a visual display which is adapted to display a graphical representation of the torque applied to the retaining screw as it is tightened, over a selected range of torques, or (c) indicating lights which illuminate at appropriate thresholds, adapted to receive an output from said monitoring means of said change in torque over said time period, the change in torque over said time period being indicative of the quality of fit of the structures to be joined, for indicating the precision of fit between said structures.
2. An apparatus according to claim 1 characterised in that said monitoring means is adapted to measure change in resistance to rotation during tightening of said retaining screw.
3. An apparatus according to claim 1 characterised in that said monitoring means includes electronic circuitry.
4. An apparatus according to claim 1 characterised in that said monitoring means is adapted to measure change in powder supply voltage or current for said micro-motor over time.
5. An apparatus according to claim 1 characterised in that it is adapted to operate over a torque range which is commonly used for dental applications in which retaining screws are used to connect crowns or bridges to teeth or dental implants.
6. An apparatus according to claim 1 characterised in that said dental handpiece for tightening said retaining screw is a compressed air driven handpiece and said monitoring means is adapted to measure a change over said time period in air flow to said compressed air driven handpiece.
7. An apparatus according to claim 1 characterised in that said monitoring means are adapted to count a number of rotations of the screw driving attachment over a specified range of torque as the retaining screw is tightened to indicate precision of fit between said structures.
8. An apparatus according to claim 1 characterised in that said monitoring means are adapted to count a number of rotations of the screw driving attachment over a specified range of time as the retaining screw is tightened over a specified range of torque to indicate precision of fit between said structure and said retaining screw.
9. A method for determining a precision of fit between dental structures to be joined by a threaded component, said method comprising the steps of:
tightening said threaded component to said dental structures;
measuring a torque applied to said threaded component during said tightening during a period of time;
determining the precision of fit between said dental structures based on a variation in a rate of change in said torque during said period of time; and indicating the precision of fit between said dental structures in a visual display.
tightening said threaded component to said dental structures;
measuring a torque applied to said threaded component during said tightening during a period of time;
determining the precision of fit between said dental structures based on a variation in a rate of change in said torque during said period of time; and indicating the precision of fit between said dental structures in a visual display.
10. The method according to claim 9, wherein said measuring and determining are performed with electronic circuitry.
11. The method according to claim 9, further comprising the step of:
counting a number of rotations of said threaded component over a specified range of torque.
counting a number of rotations of said threaded component over a specified range of torque.
12. The method according to claim 9 wherein said determining step comprises:
detecting a passive fit between said dental structures when said rate of change in said torque is substantially constant during said predetermined period of time; and detecting an imprecise fit between said dental structures when said rate of change of said torque varies during said predetermined period of time.
detecting a passive fit between said dental structures when said rate of change in said torque is substantially constant during said predetermined period of time; and detecting an imprecise fit between said dental structures when said rate of change of said torque varies during said predetermined period of time.
13. A method of determining a precision of fit between dental structures to be joined by a threaded component, said method comprising the steps of:
tightening said threaded component with a dental handpiece supplied with a constant voltage to join said dental structures;
measuring a torque applied to said threaded component during a predetermined period of time during said tightening;
determining a minimum threshold of torque which indicates a precise fit between said dental structures;
visually indicating said precision of fit between said dental structures based on said measured torque and said minimum threshold.
tightening said threaded component with a dental handpiece supplied with a constant voltage to join said dental structures;
measuring a torque applied to said threaded component during a predetermined period of time during said tightening;
determining a minimum threshold of torque which indicates a precise fit between said dental structures;
visually indicating said precision of fit between said dental structures based on said measured torque and said minimum threshold.
14. The method of claim 13 wherein the step of visually indicating further comprises indicating various levels of an imprecise fit based on a difference between said measured torque and said minimum threshold.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9401332.3 | 1994-01-25 | ||
| GB9401332A GB9401332D0 (en) | 1994-01-25 | 1994-01-25 | An apparatus for testing the passive fit of screw retained structures |
| PCT/IB1995/000055 WO1995020146A1 (en) | 1994-01-25 | 1995-01-25 | An apparatus for testing the passive fit of screw retained structures |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2158854A1 CA2158854A1 (en) | 1995-07-27 |
| CA2158854C true CA2158854C (en) | 2007-04-10 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002158854A Expired - Fee Related CA2158854C (en) | 1994-01-25 | 1995-01-25 | An apparatus for testing the passive fit of screw retained structures |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2158854C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2758093T5 (en) * | 2015-07-20 | 2023-04-17 | W & H Dentalwerk Buermoos Gmbh | Medical device, particularly dental, to determine the quality of a bone |
-
1995
- 1995-01-25 CA CA002158854A patent/CA2158854C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2158854A1 (en) | 1995-07-27 |
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