EP0724413A1

EP0724413A1 - Method and apparatus for measuring tooth tightness

Info

Publication number: EP0724413A1
Application number: EP94931874A
Authority: EP
Inventors: A. D. Vardimon; Tamar Brosh; Mousa Labeeb
Original assignee: Ramot at Tel Aviv University Ltd
Current assignee: Ramot at Tel Aviv University Ltd
Priority date: 1993-10-19
Filing date: 1994-10-17
Publication date: 1996-08-07
Also published as: JPH09509336A; WO1995010988A1; IL107325A0; IL107325A; AU8079994A; EP0724413A4

Abstract

This invention is a method and instrument for measuring the tightness of two contiguous teeth. The method includes forcibly inserting an insertion strip (4) of predetermined thickness between the two teeth and measuring the insertion force, preferably including the peak insertion force.

Description

METHOD AND APPARATUS FOR MEASURING TOOTH TIGHTNESS

The present invention relates to a method and also to an apparatus

for measuring the tightness between two contiguous bodies. The invention

is particularly useful for measuring the tightness of contiguous dental

bodies, such as dental teeth, and are therefore described below with respect

to this application, it being understood that the method and instrument

according to the present invention is not limited to dental applications.

In the fields of orthodontics, periodontics and oral rehabilitation,

there are many instances where it is desirable to measure the tightness

(including looseness or spacing) between two contiguous teeth. For

example at the end of an orthodontic treatment, removable retentive

appliances are placed in the mouth to maintain the accomplished result.

The wearing time of the retentive appliances is successively reduced until

a steady state of the oral tissue is achieved. However, the extent of this

recovery process is individual, and therefore if the recovery process is not

monitored, there is a danger of a relapse to or towards the original

condition which was to be corrected. A similar situation arises when a

crown installed over a metal implant embedded in the alveolar bone, since

an excessively tight contact point between a crown linked to the implant

and an adjacent tooth can lead to a collapse of the bony bearing system. US Patents 4,571 ,181 , and 4,664,627 describe mechanical type dental thickness gauges for measuring the spacing between teeth, but such mechanical gauges are relatively inaccurate and generally unsuitable for use

in continuously monitoring a recovery process, such as described above.

A publication by Thomas E. Southard et al., entitled "Anterior Component

of Occlusal Force, Part 1 - Measurement and Distribution, Am. J. Orthod.

Dentofac. Orthop., December 1989, pp. 439-500, describes, for this

purpose, the use of a stainless steel strip slipped between the two teeth and

withdrawn by the use of a digital tension transducer to measure the

frictional force resisting the withdrawal of the strip.

An object of the present invention is to provide another method and

instrument for measuring the tightness of two contiguous bodies,

particularly dental teeth.

According to the present invention, there is provided a method of

measuring the tightness of two contiguous bodies by forcibly inserting an

insertion element of predetermined thickness between the two bodies; and

simultaneously measuring the insertion force, preferably including the peak

of the insertion force. As indicated earlier, the novel method is particularly

useful for measuring the tightness of dental teeth, e.g., to permit continuous

monitoring of the recovery process of an orthodontic treatment. The

invention thus provides a diagnostic tool to predict hazardous side effects

such as tissue relapse. According to further features in the described preferred embodiment,

the insertion element is forcibly inserted between the two teeth by attaching

the opposite ends of the insertion element to a holder, and manually forcing

the holder, with the insertion element attached thereto, inwardly between

the two teeth towards the gingiva. In addition, the insertion element is a

strip of predetermined thickness, preferably of stainless steel.

The peak of the insertion force is preferably measured by one or

more strain gauges. It is possible, however, to measure the peak insertion

force by measuring displacement by an optical system, a piezoelectric

device, capacitance, inductance, potentiometer, or by pneumatic device, a

manometer pressure device, or by the Hall effect.

It will thus be seen that the novel method of the present invention

distinguishes over that in the Southard et al. publication in a number of

important respects. Thus, the technique proposed by Southard et al.

(Southard, T.E., Behrents, R.G., Tolley, E.A., The Anterior Component of

Occlusal Force, Part 2, Relationship with Dental Malalignment, Am. J.

Orthod. Dentofac. Orthop. 97; 41-4, 1990), is based on the insertion of a

stainless steel strip between two teeth and the subsequent drawing of the

strip laterally between the two teeth. It is during this lateral drawing that

tension measurements are made. The measurements are thus primarily a

combination of the tightness of adjacent teeth and the frictional forces

resisting the lateral withdrawal of the steel strip. Therefore, the friction between the teeth, which is often influenced by extraneous factors, such as

the presence of food particles, plaque, calculus and saliva, largely

influences the tension reading and tends to mask the true tightness, thus

making it impossible to distinguish between the true effect (pure tightness)

and the hiss (friction).

By contrast, the present invention, involves the forcible insertion of

the insertion elements between two teeth and the simultaneous measuring

of the insertion force. The measurements are thus related more directly to

the prying or wedging apart of the two teeth and are thus more closely

related solely to the tightness of the two teeth.

Furthermore, in the Southard method, the teeth are first moved apart

and then try to approach each other and thereby applying force on the

insertion element. However, the very act of inserting an insertion element

between a pair of teeth tends to temporarily loosen the periodontal fibers

which connect the teeth to the supporting bone. Because the periodontal

fibers have viscoelastic properties they will resort to their original shape

after an undetermined time. Thus, during the lateral drawing of the strip

in the Southard method the teeth are already considerably looser than they

were prior to the insertion of the strip, rendering the measurements less

accurate. By contrast, under the present invention, the measurements are

conducted during the initial insertion of the insertion element

simultaneously with the displacement of the teeth. The invention also provides an instrument for measuring the

tightness of two contiguous bodies, particularly dental teeth, in accordance

with the above method.

Further feature and advantages of the invention will be apparent

from the description below.

The invention is herein described, by way of example only, with

reference to the accompanying drawings, wherein:

Fig. 1 illustrates one form of measuring instrument constructed in

accordance with the present invention;

Fig. 2 illustrates a set of the insertion elements or strips of different

thicknesses which may be used in the instrument of Fig. 1 ;

Fig. 3 illustrates typical results obtained when using three of the four

different insertion strips illustrated in Fig. 2 between the same contiguous

teeth;

Fig. 4 illustrates results produced when using a strip of single

thickness for measuring teeth tightness with respect to several pairs of teeth

during different phases of orthodontic treatment;

Fig. 5 is a typical strain curve; and

Fig. 6 shows an embodiment of a device according to the present

invention. With reference first to Fig. 1 , there is illustrated one form of

instrument for measuring the tightness of two contiguous bodies,

particularly dental teeth, in accordance with the present invention.

The instrument illustrated in Fig. 1 includes a holder, generally

designated 2, for holding an insertion strip 4 of predetermined thickness,

such as to permit the strip to be forcibly inserted between the two dental

teeth while a measurement is made of the force during the insertion or

penetration between the two teeth. Preferably, the measurement includes

a determination of the peak force during the insertion. An analysis of the

force function, preferably including the peak of the insertion force, together

with the thickness of the insertion strip 4, provide an objective indication

of the tightness of the two teeth such that the tightness can be accurately

measured, not only before and during the orthodontic treatment, but also

after the treatment to monitor the recovery process in order to determine

the stability of the results and to predict any relapse tendency in order to

take whatever corrective action may be necessary to preserve the treatment

results. A typical insertion force function is represented in Figure 5. Here,

the insertion force increases as the insertion element is pushed downward

or upward between two adjoining teeth (or other bodies). The force peaks

and then drops off again. A slight increase is typically observed when the

insertion member impacts the gums. Negative tightness units are recorded

when the strip is pulled out of the contact point of adjacent teeth. Holder 2 includes a manually-graspable handle 10 mounting a U-

shaped frame member 12 to which the opposite ends of the insertion strip

4 are attached. The juncture 14 between the handle 10 and the U-shaped

frame 12 includes one or more strain gauges 16 which measures the strain,

which is related to the insertion force, at the time strip 4 is forcibly

inserted between the two teeth in order to measure the tightness thereof.

The U-shaped frame 12 is constituted of a rod bent into a U-shape

and terminating in end extensions 18, 20 which are received within

openings 22, 24 formed in the opposite ends of the insertion strip 4. Thus,

end extensions 18, 20 of the U-shaped frame serve as attaching elements

receivable within openings 22, 24 of the strip 4 for firmly attaching the

strip to the U-shaped frame 12. To facilitate attaching strip 4, the frame

is formed with a loop 26 providing flexibility to the end 24 of the frame,

enabling that end to be engaged in the hole 24 of the strip 4.

Strain gauge 16, which senses the insertion force when inserting

strip 4 between two teeth, is connected to a measuring circuit 30 for

measuring the force function, preferably including at least the peak

insertion force, and also to a data acquisition system 32 for processing,

recording and/or displaying the measured insertion force. Preferably, the

measuring circuit 30 (which may be a Wheatstone Bridge) and the data

acquisition system 32 are housed within the handle 10 for ease of use of

the device. The handle 10 (Figure 6) preferably also includes a power supply 31 and preferably also a suitable display 33 for displaying the

results to the user.

The one or more strain gauges 16 may be located outside of the

handle 10 (as in Figure 1) or may alternatively be located within the

housing 10 (as in Figure 6), the latter configuration offering added

protection and reliability to the strain gauges 16 but requiring that the U-

shaped frame member 12 and the insertion strip 4 be handled as a single

item, i.e., that the combination of the U-shaped frame 12 and the insertion

strip 4 be changed when desired, rather than changing merely the insertion

strip 4 as in the embodiment of Figure 1.

As indicated earlier, the insertion force depends to a great extent on

the thickness of the insertion strip 4. For this reason, the instrument would

be provided with a plurality of such insertion strips of different

thicknesses. This is illustrated in Fig. 2, wherein, for purposes of example,

strip 4a is of 0.05 mm, strip 4b is of 0.10 mm, strip 4c is of 0.15 mm and

strip 4d is of 0.20 mm.

The manner of using the instrument illustrated in Figs. 1 and 2 will

be apparent from the above description.

Thus, when instrument is to be used for measuring teeth tightness,

a strip 4 of suitable thickness is selected according to the particular case

and is attached to the ends 18, 20 of the U-shaped frame 12. Handle 10

of the instrument is manually grasped with the strip 4 aligned in the space or contact point between the two teeth, and is pressed firmly towards the

subject's gingiva to cause the strip 4 to be inserted or penetrate between

the two teeth. The force required to do this is sensed by the strain gauge

16, which outputs an electrical signal to the measuring circuit 30. Circuit

30 measures the insertion force, preferably including the peak insertion

force, and feeds this information to the data acquisition circuit 32, which

records, displays and/or otherwise processes this information.

Fig. 3 illustrates the results of using the instrument illustrated in

Figs. 1 and 2 during a typical orthodontic treatment involving an active

phase Pa during which a fixed orthodontic appliance was applied to the

subject's teeth, a deboning phase Pd when the fixed orthodontic appliance

was removed, and a retention phase Pr during which a removable retention

appliance was applied. In the example illustrated in Fig. 3, the insertion

strip 4 was applied between the same two teeth, i.e., at the same single

contact point indicated by the arrow 40 in the upper right hand corner of

Fig. 3. Curve A in Fig. 3 indicates the microstrain (in arbitrary tightness

units) over the indicated period of time when the insertion strip 4 was strip

4a in Fig.22, of 0.05 mm; curve B indicates the results when the insertion

strip was 4b in Fig. 2, namely 0.10 mm; and curve C illustrates the results

when the strip 4c, namely 0.15 mm was used.

Fig. 4 illustrates further typical results when a strip thickness of 0.15

mm was used at three contact points: teeth 2, 3; 3, 5; and 5, 6 of the fourth quadrant (right mandibular dentition). Thus, curve A shows the results

when the measurement was made between teeth 2 and 3; curve B shows

the results when the measurement was made between teeth 3 and 5 (teeth

4 having been removed); and curve C shows the results when the

measurement was made with respect to teeth 5 and 6. The drop in the

measurement indicated by the arrow (Figure 4, contact point 45-46) is due

to the removal of a band which was wrapped around the tooth 46. Due to

the thickness of the band a gap was produced between the adjacent teeth

which caused the sharp drop in the tightness.

While the invention has been described with respect to one preferred

embodiment, it will be appreciated that this is set forth merely for purposes

of example. Thus, other force measuring system could be used, for

example by an optical system for measuring displacement, a piezoelectric

system for measuring pressure changes, a capacitance, inductance or

resistor-potentiometer system for measuring displacement. The

measurement could also be pneumatically, by a manometric pressure

device, or by the magnetic Hall effect.

In addition, other means can be provided for attaching the insertion

strips 4 to the instrument, e.g., arrangements for attaching blades to

hacksaws or jigsaws. Also, a single holder can hold a plurality of such

insertion strips each made selectively operable. Further, the invention could be advantageously used for measuring tightness between other

bodies.

Many other variations, modifications and applications of the

invention will be apparent.

Claims

WHAT IS CLAIMED IS:

1. A method of measuring the tightness of two contiguous

bodies, comprising the steps of:

(a) forcibly inserting an insertion element of predetermined

thickness between the two bodies; and

(b) simultaneously measuring the insertion force.

2. A method according to Claim 1, wherein said measuring the

insertion force includes measuring the peak of the insertion force.

3. The method according to Claim 1, wherein said contiguous

bodies are dental teeth.

4. The method according to Claim 3, wherein said insertion

element is forcibly inserted between the two teeth by attaching the opposite

ends of the insertion element to a holder, and manually forcing the holder,

with the insertion element attached thereto, inwardly between the two teeth

towards the gingiva.

5. The method according to Claim 1, wherein said insertion

element is a strip of predetermined thickness.

6. The method according to Claim 5, wherein said strip is of

stainless steel.

7. The method according to Claims 1 , wherein insertion force

is measured by at least one strain gauge.

8. An instrument for measuring the tightness between two

contiguous bodies, comprising:

(a) an insertion element of predetermined thickness;

(b) a holder for holding said insertion element to enable the

element to be forcibly inserted between the two bodies; and

(c) a sensor for sensing the insertion force applied when

inserting said element between the two bodies.

9. An instrument according to Claim 8, wherein said sensor

senses at least the peak of the force applied when inserting said element

between the two bodies.

10. The instrument according to Claim 8, wherein said holder

comprises a manually graspable handle, and a U-shaped frame carrying a

pair of attaching elements at opposite ends thereof for attaching thereto the

opposite ends of said insertion element.

1 1. The instrument according to Claim 10, wherein said insertion

element is a strip of predetermined thickness.

12. The instrument according to Claim 11, wherein said strip is

formed with openings at its opposite ends for attaching the strip to said

attaching elements of the U-shaped frame.

13. The instrument according to Claim 12, wherein one of said

attaching elements is movable with respect to the other parallel to the

longitudinal axis of the insertion strip to facilitate attachment of the

opposite ends of the insertion strip.

14. The instrument according to Claim 13, wherein said frame

includes a rod bent into a U-shape and formed with a loop to permit

movement of the attaching element at one end of the frame with respect to

the attaching element at the opposite end of the frame to facilitate attaching

said insertion strip thereto.

15. The instrument according to Claims 1 1 , wherein there are a

plurality of said insertion strips of different predetermined thicknesses

selectively attachable to the opposite ends of said U-shaped frame.

16. The instrument according to Claim 1 1 , wherein said sensor

s carried at the juncture of said handle and said U-shaped frame.

17. The instrument according to Claim 1 1 , wherein said sensor

s a strain gauge.

18. The instrument according to Claim 10, further including a

measuring circuit for measuring the force sensed by said sensor and a data

processor for processing and/or recording and/or displaying said

measurement.

19. The instrument according to Claim 18, wherein said

measuring and said data processor are located in said handle.