Piezoelectric Polymeric Film Occlusal Force Indicator

The present invention relates to dental impression devices and more particularly to such a device which includes a transducing piezoelectric polymer film coated with conventional impression wax for providing bite impression data and bite force data.

Reference is hereby made to U.S. Pat. No. 3,604,116, the subject matter thereof being incorporated herein.

U.S. Pat. No. 3,604,116, issued to H. Shpuntoff, a co-inventor herein, discloses a dental impression wafer having a sheet carrier of strong pliable material sandwiched between deformable impression material such as bite wax. The wafer permits a precise visual indication of premature engagement of the teeth and bite deflection. The wafer however does not permit measurement of monitoring of the bite force and force exerted on the wafer by the patient during occlusal analysis, which analysis may suggest left/right muscular disbalance due possibly to premature contact or deflected contact between teeth of the maxilla and mandible. The force exerted during an occlusal analysis can now be monitored, and permanent records of the force exerted on either side of the mouth are readily obtainable. These records may be used to later compare the patient's muscle activity before and after correction and adaptation.

Briefly, the invention comprises a thin metallized film of polymer material having piezoelectric properties, the film being coated on all surfaces and edges with a conventional dental impression material, typically bite wax. The polymer film is preferably KYNAR.RTM. piezofilm, a polyvinylidene fluoride product of Pennwalt Corporation, Philadelphia, Pa., assignee of the present invention, although copolymers of vinylidene fluoride have been found to work satisfactorily.

The wax retains visible impressions of the relative positions and shapes of the tooth crowns, as well as bite deflection and premature teeth engagement indicia. The wax should deform plastically without affecting the spatial relationship of the teeth, and normally such condition obtains if the carrier sheet thickness is maintained below about 0.025 mm, although the abovementioned patent suggests a value no greater than about 0.020 mm. The piezoelectric film material, on the other hand, permits force measurements to be precisely continuously monitored, which measurements may be permanently recorded by conventional means. If the carrier film (piezoelectric film) thickness is greater than about 0.025 mm, an artificial prematurity may result.

FIG. 1 is a perspective view of a strip of metal coated polymer film having piezoelectric properties.

FIG. 2 is a sectional view of the strip of FIG. 1 folded to form the transducing element, the folded strip being substantially coated with dental impression material.

FIG. 3 is a sectional view of a modification of the folded strip of FIG. 2, the folded strip being completely coated with dental impression material.

FIG. 4 is a sectional view of FIG. 2 taken along line 4--4 thereof.

FIG. 5 is a schematic diagram of electronic means for converting voltages generated by the folded high impedance piezofilm strip to low impedance voltage outputs.

In FIG. 1, piezofilm assembly 10 comprises uniaxially or biaxially oriented polymer film 12, preferably KYNAR.RTM. piezofilm, having conventionally applied suitable metallized coatings 14 and 16, typically aluminum, secured to respective faces thereof. Coating 14 is preferably about 1000 .ANG. thick, or about 0.1.mu., to thereby provide about 0.60 ohms per square or sufficient electromagnetic interference shielding to the piezofilm 12. Coating 16 may be thinner, or only about 300 .ANG., or about 0.03.mu., to provide about 10 ohms per square. Piezofilm assembly 10 is preferably no greater than about 0.025 mm in thickness to avoid any interference with normal interengagement of the teeth, although thicknesses considerably greater may be used at the expense of accuracy and preciseness. We have found that piezofilm assembly 10 thicknesses ranging between about 0.016 to 0.020 mm work satisfactorily.

Thus, when coated piezofilm assembly 10 is folded, as shown exaggeratedly in FIG. 2, and piezofilm 12 measures 9.0.mu. thick, while coatings 14 and 16 are 0.1.mu. and 0.03.mu. thick respectively, the folded piezofilm assembly 10' will have a total thickness of 18.26.mu..

The folded piezofilm assembly 10' is provided with a layer of dental bite wax 20. The wax should be less than 0.5 mm thick, and preferably 0.35 mm. Wax 20 overlaps the folded piezofilm assembly 10' on each edge (except at front portion 23) by about 1/8" (FIG. 2) to form a dental strip or dental impression strip occlusal force indicator 22.

Wire leads from shielded coaxial cables 24 and 26 make contact to the metallized coatings 14 and 16 respectively; the high side 26, which may be + or -, is connected to the negative terminal of an IC operational amplifier 30 while the low side 24 is grounded with the positive terminal of op-amp 30 (FIG. 5).

In FIG. 3, folded piezofilm assembly 10' is provided with a layer of wax 20 completely therearound to form a dental impression strip occlusal force indicator 22'.

Op-amp 30 converts the high impedance output from the folded piezofilm assembly 10' to a low impedance voltage output which can be transmitted to a suitable display device (not shown) with no pickup of unwanted signals. The charge generated by folded piezofilm assembly 10' is collected by a feedback capacitor 32 whose voltage is measured as the output voltage of op-amp 30:

where

V.sub.o =voltage output of op-amp 30

.tau.=time

C=capacitance of capacitor 32

Q=closed circuit charge output of folded piezofilm assembly 10'

The numerals 2, 3, 4, 6 and 7 leading from op-amp 30 merely designate conventional pin connections.

Voltage output, V.sub.o, is proportional to the time integral of the current output of folded piezofilm assembly 10' and increases as the force of the bite increases.

Voltage output, V.sub.o, may be connected for display on a storage oscilloscope, or to a strip chart recorder if a permanent record of the bite force is desired, and to speaker means where amplitude or pitch may indicate the instantaneous value of the bite force.

Optionally, alternative electronic means for monitoring output voltages from the piezofilm assemblies may be utilized.

Separate strip occlusal force indicators 22 or 22' may be inserted in both sides of the mouth simultaneously to obtain data or information on first contact, high spots, disbalance, and the like. Also, one non-electrically active dental impression strip described in the aforementioned Shpuntoff patent may be used simultaneously with the occlusal force indicator of the present invention on opposite sides of the mouth in order to provide non-prejudiced bite monitoring.

The present occlusal force indicator may be used advantageously to monitor the occlusion of teeth other than natural.

For purposes of demonstration, the folded piezofilm assembly 10' may be coated with polytetrafluoroethylene, polyethylene, and the like, which is non-permanently deformable and reusable, and will not provide bite impressions, but will indicate to the dentist and patient that continuous monitoring and recording of forces exerted during occlusal analysis may readily be effected. The non-permanently deformable and reusable material may be up to several millimeters in thickness and may be coated over the piezofilm assembly 10' as is wax 20 (FIGS. 2 and 3) or in any other suitable manner.