AT511383A1 - METHOD FOR THE QUALITATIVE COMPARISON OF APPROXIMAL CONTACT POINT STICKERS OF ADJUSTABLE TEETH - Google Patents

Abstract

A device for estimating the contact forces of adjacent teeth, having a test body insertable into the interdental space, formed as a thread (1) and arranged between two prongs (2) of a fork (3), wherein between the fork and a handle (4) Force measuring cell (5) is arranged and the load cell (5) is connected to an evaluation device which is adapted to indicate the size of at least one force.

Description

PI2090

Method for the qualitative comparison of approximal contact point forces

BANACHBAR TEETH

The invention relates to a device for estimating the contact forces of adjacent teeth, with an insertable into the interdental space specimen and cooperating with this load cell, which is connected to an evaluation device.

Interdental contact forces are an important criterion for dentists and orthodontists, as they are essential parameters both for the subjective health of the patient and for his health. It is therefore attempted to estimate these forces by various methods, all of which use specimens inserted between the teeth, whereby a direct measurement of these forces is ruled out in practice.

From R. Fuhrmann, C. Grave, and P. Diedrich, "In Vitro Testing a Measurement Methodology for the Quantitative Assessment of Interdental Mesial Force", Advances in Orthodontics, vol.59, pp: 362-370 (No. 1998), a measuring method has become known in which a stainless steel plate is pushed between adjacent teeth of a human preparation and this plate is then pulled out with the interposition of a spring balance at a constant speed from the interdental space. From the force measured during extraction, in accordance with the frictional force occurring between the stainless steel plate and the tooth flanks, conclusions can be drawn on the mesial interdental forces. In contrast to the application to an extracorporeal preparation, the described device or the method can hardly be used in vivo, since the available space, especially distally and buccally, is insufficient.

Kim Hee-Sun, Na Hyun-Joon, Kim Hee-jung, Kang Dong-Wan and Oh Sang-Ho, "Evaluation of proximal contact by postural changes", Journal of Advanced * * * * * · · ** P12090 * · »· ** · ♦ ··» «« · · * · * «-2-

Prosthodontics 2009; 1 (3): 118-123 describe a similar method in which the end of a metal strip is brought into a tooth space, the strip is deflected and pulled out of the gap by means of a motor at a constant speed while measuring the force occurring by means of a Dehnmessstreifens. Although the intended deflection also makes it possible to measure at tooth pairs located further back, the expenditure for the motorized extraction and the deflection of the steel strip is considerable and not practical. Measuring errors due to incorrect posture on the part of the physician are very likely, and in particular must be thought of tilting or tilting of the steel strip.

An object of the invention is to provide a device which allows a simple and inexpensive construction a meaningful force measurement or estimation, with operating errors have little or no effect on the measurement results or should be immediately apparent.

This object is achieved with a device of the type mentioned, in which according to the invention the test piece is formed as a thread and is arranged between two prongs of a fork, the load cell between the fork and a handle arranged and is adapted to measure two forces in different directions , wherein the evaluation device is adapted to display the size of at least one force.

Thanks to the invention, the user, z. As a dentist, make no significant incorrect measurements, as indicated by the measurement of two forces and their evaluation, the correct adjustment of the device, in particular the thread and can be adhered to by the user. As will be shown below, the angular orientation of the thread can be determined from the ratio of the measured forces. Unlike the devices of the prior art, the device according to the invention can be manually operated by a user. can be used and a physical motion reference to the person to be examined can be omitted.

In order to simplify the signal processing, it is advantageous if the sensitivity vectors of the measuring cell span a plane which is substantially orthogonal to the thread axis.

In the sense of a simplified operator guidance and in order to avoid erroneous measurements, it can be provided that the evaluation device is set up to determine from the measured forces the relative angle of rotation of the thread or fork relative to the direction of insertion of the thread into the interdental space.

It is also expedient if the value-value device is set up to determine the press-in force in the direction of the interdental space from the measured forces, since this force is representative of the interdental contact force.

In an embodiment that is easy to implement in practice, it is provided that the force measuring cell is a cuboid made of elastically deformable material with strain sensors arranged on opposite surfaces, wherein the fork is inserted into one end of the cuboid and the end opposite to the handle is connected.

It can be provided that the opposite surfaces of the cuboid parallel to a plane containing the axis of the thread and that the strain sensors facing each other, in the cuboid in the region of each strain sensor each has a through hole is formed, wherein the axes of the holes in Run substantially parallel to the axis of the thread, and from each hole starting a slit passing through the rest of the cuboid obliquely. PI2090 • * • *

• · • »· 4 · · · · · 4 4»

If the strain sensors are strain gauges, a simple evaluation results in a cost-effective variant.

In practice, it is useful not least for hygienic reasons, when the fork is releasably secured to one end of the load cell.

The invention together with further advantages is explained in more detail below with reference to an exemplary embodiment, which is illustrated in the drawing. In this show

1 is a perspective view of the application of a test body of a device according to the invention on a denture model,

2 is a schematic side view of a fork with test body and load cell of a device according to the invention and the coordinate systems used,

2 a fork with test specimen and the relationship between the coordinate systems of the device and the interdental space of two teeth,

4 shows a possible flow chart of the force measurement during the pressing in and out of the test specimen in a device according to the invention,

Fig. 5 is a block diagram of an evaluation device of the device according to the invention, and

Fig. 6 shows an example of force during the pressing or pulling out of the thread-like test specimen.

1, a test specimen is formed as a thread 1 and arranged between two prongs 2 of a fork 3. The fork 3 can with the help of a handle 4 to a -5- -5-

• * «·« ·· »» «· ·» * · * «·

Interdental space (interdental space) out and pressed into this or introduced. In principle, this process is similar to the use of so-called dental floss sticks in dental care.

In order to measure the forces exerted on the thread 1, as shown in Fig. 2, between the fork 3 and the handle 4, a load cell 5 is arranged at the front end of this measuring cell 5 is a blind bore 6 for receiving the pin-shaped rear end of Fork 3 is provided, wherein a fixing screw, not shown, can be screwed into a threaded hole 7 to fix the rear end of the fork 3. The handle 4 can for example be attached to the rear end of the measuring cell 5 with an indicated fixation 8, for example with two screws. The handle 4 is here tubular and surrounds the measuring cell 5 and a portion of the fork. 3

The load cell 5 is in this embodiment, a cuboid of elastically deformable material, eg. As steel, arranged on opposite surfaces

Force measuring sensors, in the present case strain sensors 9o, 9u.

The opposing surfaces of the cuboid load cell 5 extend parallel to a plane containing the axis of the thread 1, wherein the strain sensors 9o, 9u opposite each other and in the cuboid force cell in the region of each strain sensor each have a through hole 10o, lou formed, wherein the axes of these bores are substantially parallel to the axis of the thread 1, and starting from each bore, a slit llo, Hu passing through the rest of the cuboid is present. The bores 10o, 10u and the slots llo, lu out of these give the required mobility of the load cell 5 in the region of the strain sensors 9o, 9u.

If, as in the exemplary embodiment shown, the strain sensors 9o, 9u lie directly opposite one another and on an axis with the holes 10o, 10 '' · ··················································································································································

In the exemplary embodiment, the strain sensors 9o, 9u are commercially available strain gauges, which are inexpensive in size and only need to be glued, but the skilled person many known ways to measure force available, such as capacitive, inductive, interference optical or piezoelectric encoder.

The principle of the force measurement is based on the fact that the force required to press in the test body used is first detected in a sensor coordinate system, given a geometry of the arrangement clearly results in a force in a measuring cell coordinate system, the time course using two strain gauges in electrical Signals is converted.

In the following, a possible evaluation of the signals determined by means of the measuring cell 5 or the strain sensors 9o, 9u will be explained with reference to FIGS. Vectorial quantities are indicated by an arrow (eg F, ex). In a given coordinate system CS, the vector can be expressed by magnitude and direction or its coordinates, i. H.

Fcs = F-e ^

0)

If there is no likelihood of confusion, the designation of the coordinate system is omitted.

A coordinate system in 2D is defined by the origin O, as well as by an orthonormal pair of basis vectors ex and e.

In the modeling used here, three coordinate systems are used, namely a measuring cell coordinate system, a sensor coordinate system and an interdental coordinate system.

Cells coordinate system:

Referring to Fig. 2, the origin OM of the coordinate system is at the intersection of the measuring cell axis a with the end face of the measuring cell. The system is oriented so that the x-axis (unit-direction vector x M) points rightward from the origin in the direction of the measuring cell axis and orthogonal to the y-axis (unit-direction vector e u).

Sensor coordinate system:

The origin Os of this coordinate system is located at the piercing point of the test piece or thread 1 through the plane of the drawing (FIG. 2). The system is oriented so that the x-axis (unit-direction vector xS) points to the right parallel to the measuring cell axis and the y-axis (unit-direction vector evS) points orthogonal to it, using the 1-coordinate system:

In Fig. 3, two adjacent teeth Dl, Dr can be seen, which is between the crown of the interdental space Z, which is closed down through the gums G. The origin O, this coordinate system is located at the piercing point of the thread 1 through the plane of the drawing. The system is oriented so that the λ-axis (unit-direction vectors,.,) To the left and the y-

Axis (unit direction vector e}) in the direction of the interdental space shows. -8- P12090 • «· · · · · ··· # * a * · ** ·· • * I t *» »· ···

Reference is made to FIG. The desired measured variable is the amount of the press-in force FT (i) in the direction of the interdental space Z determined at the moment of press-fitting t = t0. This force is estimated from the time profiles of the sensor signals of the two strain gauges 9o, 9u in the following steps. The further modeling is based on the assumption that the orientation of the thread 1 by the doctor is such that the thread is oriented orthogonally to the plane of the drawing (see FIG. 3). The orientation of the sensor coordinate system (rotation around the thread) is arbitrary within the limits of anatomy. The forces in the measuring cell coordinate system are evaluated by evaluating the changes in resistance Δ / Ϊ and ΔR2 of the two strain gauges ΔRi + M2 r. = --- Λ / ?. - Mt. (2)

Given the geometry of the measuring arrangement according to FIG. 2, there is the connection between the forces in the measuring cell coordinate system and those in the sensor coordinate system

f 1 j, M '1 h 0' h Xs " F 1 > 'M. h L F, S_ = M-FS, (3) respectively

Fs = M '! F,

M (4)

The primary measure of the device is the force Fl measured during the pressing in of the thread 1 in the direction of the interdental space Z (FIG. 3). This force is determined from the force vector Fs taking into account the following systematic deviations: The orientation of the fork 3 and the thread 1 to the interdental space varies with different users and applications. In addition, a fluctuation is observed during a measurement. • During the pressing process, lateral forces may deviate from f \ if the thread 1 follows the geometric course of the contact surface or the user exerts a lateral force.

The starting point for the correction of these deviations is the estimate of the current orientation of the thread 1 from the time courses of Fs. This is done by

< p {t) = arctane V

(5)

Systematic deviations are minimized by the mean orientation φ of the thread 1 before being pressed in (t = i0) by means of

(6) is estimated. This orientation is used to determine the position of the thread 1 and thus to determine the direction of the interdental space Z, since it is assumed that without systematic deviation 5, s = ä (~ pKs (7)), where R (-φ) is a rotation of the measuring cell Coordinate system by the angle -φ ". The time course of the measured variable / ^ (/) results - in particular with P12090 * * »·

-10-

Occurrence of the described systematic deviations <p (t) ψ φ - from the projection of the force Fs onto the interdental axis e, by F, (l) = (e? J-Fs (,). (8)

The required press-in force corresponds to the instantaneous value of this size at the time of insertion, ie. H. o) · P)

FIG. 4 shows an example flow chart for measuring the press-in force. After an initialization of the device (step Al, "initialization"), the detection and estimation of the force vector F & (t) in the measuring cell coordinate system is performed continuously (step A2, "estimation Fs (t)"). This force vector is used to detect the injection event (step A3, "detection of a measurement"). The result of this processing step is the press-in time t0. If there is no press-in event, the detection in step A2 is continued.

If a press-in event has been detected, the orientation of the thread 1 and thus the fork 3 or the measuring cell 5 is estimated in the next step (step A4, "estimation of the sensor angle"). Based on this estimate and given limits of orientation, the validity of the measurement is checked (step A5, "validity check"). Measurements outside permitted orientations, or measurements with a high noise component are thereby rejected to the operator while the cause is reported (step A6, "Feedback to operator"). In these cases, the process continues with the capture of additional data. For valid measurements, in the next step A7 ("estimation of approximal contact force projected into the interdental space"), the insertion force becomes PI2090 PI2090

-11 t ----- tly estimated and communicated to the operator (step A8, "contact force display").

If from the "contact force &quot; it is to be made clear that this force, which is exerted on the thread 1 by the adjacent teeth D1, Dr, is not directly measured, but is estimated from the press-in force, for example, based on experience or on hand a table.

Of course, methods for improving the robustness of the method (statistics, outlier treatment, etc.) can also be used within the scope of the invention, but in this context, methods known to those skilled in the art are not discussed.

Below, with reference to FIG. 5, a possible block diagram of an evaluation device 12, which forms part of the device according to the invention, is explained.

The following processing blocks (see Figure 4) are used to determine the press-in force:

Bl represents a converter, which decodes the conversion of the resistance signals Δ /,, (t), AR2 (t) into corresponding forces FM (t) or force signals taking into account the geometry of the measuring cell 5.

In block B2 there is a transformation M S of the forces in the measuring cell coordinate system into the sensor coordinate system and in block B3 a projection S - &gt; /, d. H. a transformation of forces in the measuring cell coordinate system in the interdental coordinate system with projection of the main component of the force on the interdental axis.

In block B4, the sensor orientation φ &quot; determined from the time course of the force vector Fs (t) and in block B5, the detection of the measurement time t0 from the time course of the force vector Fs (/).

In block B6, the determination of the pressing force F from the time course of and the block B7 is used to assess the signal quality and the feedback, z. Eg "good", "bad" to the operator.

The understanding of the invention is also facilitated by the illustrations of FIG. In Fig. 6a, the time course of the force signal / ^ (/) is shown, which occurs during the pressing or pulling out of the thread 1 in an interdental space. During the insertion of the thread 1, the force increases approximately linearly to 2.52 N, when leaving the interdental space it falls off for a short time (peak of the upward course in the diagram) and a further brief increase in force in this case shows the impact of the thread on the gum. When pulling out the thread, the force increases again - in the opposite direction - up to 2.86 N in this example, to naturally fall to zero at the final leaving the interdental space.

The evaluation can be the sudden drop of the force in the sense of a

The course of the orientation (angle φ) in Fig. 6b shows the press-fitting shortly after the time ls and there an angle φ of about 50 °. The curves at the beginning of the measurement (up to about 0.5 s) and after the end of the measurement (from about 1.9 s) represent due to the low forces acting in principle noise and can on hand of the size of the force signal F , (/) reliably detected and excluded from further processing.

In the device according to the invention it has also proved to be particularly advantageous that it is applicable even in the confined space in the mouth of a patient and that the fork together with the thread as a sterile and extremely PI 2090 -13- &quot; · * · «« * »· ·« ··

cheaper disposable items and can be easily replaced before each new application. The display of the force and the correct orientation (angular position) can be easily readable, z. For example, in order to display the correct orientation, a binary representation such as &quot; good &quot; - &quot; bad &quot; or a corresponding display with a green and a red LED directly on the handle 4 is possible.

Vienna, May 9, 2011

Claims (10)

Claims 1. Apparatus for estimating the contact forces of adjacent teeth, with a test body (1) insertable into the interdental space and a with this cooperating load cell (5), which is connected to an evaluation device (12), characterized in that the test piece is formed as a thread (1) and arranged between two prongs (2) of a fork (3), the load cell (5) arranged between the fork and a handle (4) and adapted to measure two forces in different directions, wherein the evaluation device (12) is adapted to display the size of at least one force. 2. Apparatus according to claim 1, characterized in that the Sensitivi-tätsvektoren the measuring cell (5) span a plane which is substantially orthogonal to the thread axis. 3. Apparatus according to claim 1 or 2, characterized in that the evaluation device (12) is adapted to, from the measured forces, the relative angle of rotation of the thread (1) or the fork (3) with respect to the insertion direction of the thread in the Interdental space (Z) to determine. 4. Device according to one of claims 1 to 3, characterized in that the evaluation device (12) is adapted to determine from the measured forces, the press-in force (F,) in the direction of the interdental space (Z). 5. Device according to one of claims 1 to 3, characterized in that the fork (3) with the thread (1) is a disposable design and with the measuring cell (5) is interchangeable connected. PI 2090 PI 2090 -15 6. Device according to one of claims 1 to 5, characterized in that the load cell (5) is a cuboid of elastically deformable material with arranged on opposite surfaces of strain sensors (9o, 9u), wherein in one end of the cuboid, the fork (3) used and the opposite end of this with the handle (4) is connected. Device according to claim 6, characterized in that the opposite surfaces of the cuboid are parallel to a plane containing the axis of the filament (1). 8. Apparatus according to claim 6 or 7, characterized in that the strain sensors are opposed to each other in the cuboid in the region of each strain sensor (9o, 9u) is formed a continuous bore (10O, loOu), wherein the axes of the bores substantially parallel extend to the axis of the thread (1), and starting from each hole, a the rest of the cuboid obliquely penetrating slot is present. 9. Device according to one of claims 6 to 8, characterized in that the strain sensors (9o, 9u) are strain gauges. 10. Device according to one of claims 1 to 9, characterized in that the fork (3) at one end of the load cell (5) is releasably attached. Vienna, May 9, 2011