GB1602496A - Ultrasonic dental scaler - Google Patents

Description

(54) ULTRASONIC DENTAL SCALER (71) We, LITTON INDUSTRIAL PRODUCTS, INC, a corporation of the State of Delaware, USA having an office at 360 North Crescent Drive, Beverly Hills, California 90210, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates generally to ultrasonic dental scalers.

Ultrasonic dental scalers usually comprise a dental handpiece having an ultrasonic transducer positioned with an energizing coil located within a sleeve. The transducer conventionally comprises a stack of laminar plates of magnetostrictive material that is excited by the coil to longitudinally expand and contract at a frequency of approximately 20,000 cycles per second.

The transducer stack is connected at one end to an acoustical impedance transformer which in turn is connected to a dental work tool, all of which comprises an electromechanical vibrator. The transformer provides an acoustic transmission line between the transducer and the work tool. The vibrator is typically mounted in the sleeve by means of an o-ring located at a node of longitudinal vibration of the assembly when compression waves of the operating frequency are generated by the transducer. For maximum amplitude of vibration of the tool end, and for maximum transmission of working energy, the overall length of the transducer, transformer and work tool is so correlated to the frequency of the electrical oscillation delivered to the transducer, that a loop of motion of the generated compressional waves will occur at or near the working end of the tool.In other words, the overall length of the vibrator is approximately equal to an integral number of one-half wavelengths of sound waves in the particular materials comprising these components at the working frequency. The length of the transducer is also an integral number of one-half wave-lengths, typically one owing to the desire to provide the least massive system possible. It may be appreciated that size and mass are important considerations in a field in which delicate work requires instruments having an ease of handling.

In conventional dental scalers, the entire length of the vibrator is approximately six to seven inches. Although it is desirable to shorten this length to make a smaller, more compact handpiece, the frequency of the system would then increase to over 40,000 cycles per second. This frequency range is considered unacceptable for dental practice.

According to the present invention, there is provided an ultrasonic scaler comprising an outer shell; an electromechanical vibrator assembly for producing vibrations for dental scaling, the assembly comprising an acoustic impedance transformer, an ultrasonic transducer and a dental work tool; and means for supporting the vibrator assembly within the shell, the transducer having a length of less than one-half wavelength at the vibrating frequency, and there being means for inducing in the assembly a forced nodal plane at a position other than a natural nodal plane of the assembly, the position being such that the transducer vibrates at a frequency below its natural resonant frequency. Such a scaler can be designed to obviate the above-mentioned shortcoming by providing a shortened handpiece that still operates at acceptable frequency ranges.

In essence, a forced nodal plane is induced at a location other than a natural nodal plane. The location is additionally one which forces a decrease in the vibratory frequency of the vibrator assembly from its natural resonant frequency. The transducer may accordingly be shortened, with the corresponding increase in vibratory frequency; the resulting shortened vibrator assembly produces a frequency within the acceptable range of ultrasonic scalers. In particular, means such as an O-ring for resiliently supporting the vibrator assembly at the balance point of the transformer are provided for inducing an unnatural node in the vibrator assembly at a position on the transformer which decreases the vibratory frequency of the transducer.It has been found that this forced shift of the nodal plane from the natural nodal plane to the balance point of the transformer causes the frequency of the system to be approximately 25,000 cycles per second, when the transducer has been so shortened as to have a much higher natural resonant frequency.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 is an elevational view of a dental scaler; and Figure 2 is a longitudinal, sectional view of the dental scaler of Figure 1.

Referring now to the drawings, Figures 1 and 2 illustrate a hand-supported dental scaler 10 comprising an outer cylindrical casing 11 and an interior casing 12. The casing 11 has an end section 13 which is of a relatively small diameter and is open-ended.

The other end section 15 of the casing 11 may be larger in diameter, and is apertured to receive a pair of conductors 17 and 19.

The terminal ends of the conductors 17 and 19 are encased in suitable insulation and lead through the apertures of the end section 15 to a suitable power source. The leads of the conductors 17 and 19 are connected to an energizing coil 21 superimposed about a section of the interior casing 12.

An electromechanical vibrator assembly is located within the casing 11 and comprises a magnetostrictive transducer 23, an acoustical impedance transformer 25 and a work tool 31. The magnetostrictive transducer 23 is positioned within the casing 12 at the section housing the coil 21. The transducer 23 comprises a laminated stack composed of a series of relatively thin and compactively stacked plates formed of nickel or other magnetostrictive material. One end of the transducer stack 23 is welded or soldered to end of the tool holder 25 shaped to serve as an acoustical impedance transformer. The transformer 25 extends through the intermediate section of the outer casing 11 and comprises a main body section 27 of cylindrical construction and a tapered body section 29.The end of the tapered body section 29 contains an internally-threaded bore 30 for receiving the threaded end of the work tool 31. The work tool 31 can be of any conventional construction and usually includes an angled distal end 33. An axial bore 35 is provided within the transformer 25 and is adapted to communicate with a radial bore 37 at one end, and at the other end with an axial bore 39 formed in the work tool 31. These bores 35, 37 and 39 are provided to allow cooling fluid from the interior of the casing 11 to pass therethrough and be directed to impinge on the distal end 33 of the work tool 31 for cooling and cleansing purposes. Water is provided to the interior of the outer casing via a conduit 41 extending through an aperture of the end section 15.

An o-ring support chamber 50 is formed by a shoulder 51 on the main body section 27 of the transformer 25 and the inner end of a bushing 52 located near the open end 13 of the casing 11. The bushing 52 is forcefitted within the open end of the casing 12.

The bushing 52 also functions to retain a wrench element 53 which is freely rotatable to enable its keyed aperture 54 to engage a pair of lugs 55 of the work tool 31 for detachment purposes. The o-ring support chamber 50 is positioned at the balance point of the transformer, i.e. in the plane containing the centre of gravity of the transformer. It should be noted that this balance point is spaced from the natural nodal plane of the combination. The chamber 50 is adapted to receive an o-ring 60 which is supported within the interior of the inner casing 12. The o-ring 60 functions not only as the sole support for the vibrator assembly, but it also functions as a seal to prevent water from within the casing 12 to leak from the aperture 54. Secondary seals can also be utilized to function as auxiliary water seals.

In the preferred embodiment, the length of the transducer stack 23 is 2.620 inches, while the length of the transformer 25 is .975 inches. Although the length of the various work tools can vary, the illustrated work tool 31 is 1.232 inches. The o-ring chamber 50 is formed .400 inches from the forward end of the transformer 25 facing the work tip 31 and .565 inches from the opposite end facing the transducer 23.

The overall length of the vibrator is 4.827 inches, which is much shorter than previous vibrators utilizing the same materials and vibrating at the same frequencies. This forced shift of the node enables the vibrator to vibrate within the acceptable frequency range for dental scalers.

It should be noted that various modifications can be made to the assembly while still remaining within the purview of the follow

Claims (12)

ing claims. WHAT WE CLAIM IS:

1. An ultrasonic scaler comprising an outer shell; an electromechanical vibrator assembly for producing vibrations for dental scaling, the assembly comprising an acoustic impedance transformer, an ultrasonic transducer and a dental work tool; and means for supporting the vibrator assembly within the shell, the transducer having a length of less than one-half wavelength at the vibrating frequency, and there being means for inducing in the assembly a forced nodal plane at a position other than a natural nodal plane of the assembly, the position being such that the transducer vibrates at a frequency below its natural resonant frequency.

2. A scaler according to claim 1, wherein the supporting means provides the sole, and resilient support for the vibrator assembly and provides the inducing means.

3. A scaler according to claim 2, wherein the supporting means comprises an Oring.

4. A scaler according to claim 3, wherein said acoustic impedance transformer includes a shoulder for retaining said o-ring at the desired location.

5. A scaler according to claim 2, 3 or 4, wherein the assembly is supported by the supporting means at a plane containing the centre of gravity of the transformer.

6. A scaler according to any one of the preceding claims, wherein said ultrasonic transducer comprises a laminated stack of a series of relatively thin and compactly stacked plates formed of a magnetostrictive material.

7. A scaler according to claim 6, wherein the length of said laminated stack is about 2.620 inches.

8. A scaler according to any one of the preceding claims, wherein said transducer is bonded to one end of said transformer.

9. A scaler according to any one of the preceding claims, wherein the length of said acoustical impedance transformer is about .975 inches.

10. A scaler according to any one of the preceding claims, wherein said forced nodal plane is located about .400 inches from that end of said transformer connected to said work tool.

11. A scaler according to any one of the preceding claims, wherein the length of said work tool is about 1.232 inches.

12. An ultrasonic scaler substantially as hereinbefore described with reference to the accompanying drawing.