Dentistry – Apparatus – Having motor or means to transmit motion from motor to tool
Reexamination Certificate
2002-01-30
2004-06-22
Manahan, Todd E. (Department: 3732)
Dentistry
Apparatus
Having motor or means to transmit motion from motor to tool
Reexamination Certificate
active
06752629
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in a hand-held air-driven dental vibratory instrument such as an air-driven dental scaler.
2. Description of the Prior Art
It has been customary to use powered dental vibratory instruments to carry out certain dental treatments such as scaling of teeth and reaming of root canals of teeth.
Typically, a powered dental vibratory instrument includes an elongated outer casing adapted to be held by a hand, a vibrator unit arranged within the casing to serve as a source of vibration, and a dental vibratory tool such as a scaling tip and a root canal reamer detachably connected to the vibrator unit, the dental tool being subjected to vibratory movement in response to vibration generated in the vibrator unit to thereby perform desired dental treatment such as scaling and root canal reaming.
The vibrators which are used in the powered dental vibratory instruments may be grouped into two classes according to the principle of operation; electrical vibrators wherein the vibration is generated by making use of an electric power and air-driven vibrators wherein a compressed air is used as a power source.
The electrical vibrators of the first class are disclosed, for example, in JP-A-59-25738 and JP-A-60-55941. An electrical vibrator includes an electrostrictive or piezoelectric transducer which generates vibration in response to application of an alternating voltage. The advantage of the electrical vibrators is that they are substantially free from emission of audible noise because they are operable at a supersonic frequency exceeding 20,000 Hz.
However, the problem involved in the electrical vibrators is that there is a danger that electromagnetic waves emitted from the electrostrictive or piezoelectric transducer would inadvertently cause malfunction of medical electronic and electrical devices and instruments such as a cardiac pacemaker.
In contrast, the air-driven vibrators of the other class are designed to generate vibration in response to oscillatory movement of a rotor or a vibratory element caused by a jet of compressed air supplied from a dental unit. Accordingly, dental instruments incorporating the air-driven vibrators have an advantage that they are free from the problem associated with the emission of the electromagnetic waves.
However, two fundamental problems must be overcome in designing dental instruments equipped with the air-driven vibrators.
The first problem is that a movable part such as a rotor and a vibratory element inevitably undergoes a wear as it is operated. This necessitates replacement of the rotor or vibratory element at the end of its service life. To this end, maintenance must be carried out either by dentists at individual dental clinics or by specialized mechanicians at predetermined repair centers.
The second problem is that, as normally the rotor or vibratory element of the air-driven vibrator could be oscillated only at a frequency in the subsonic or audible range, a very annoying audible sound or noise is generated which often cause a patient uneasy.
To discuss the prior art, U.S. Re. 29,687 (Sertich) discloses 30 a dental scaler incorporating an air-driven vibrator. The vibrator includes a tubular shaft resiliently supported within an outer casing and a sleeve-like rotor loosely and rotatably mounted over the shaft. Upon injecting compressed air in the tangential direction toward the inner periphery of the rotor through air nozzles formed across the wall of the shaft, the rotor is rotated about the shaft and imparts a vibration thereto. through air nozzles formed across the wall of the shaft, the rotor is rotated about the shaft and imparts a vibration thereto.
The dental scaler of Sertich enjoys the aforementioned advantage of the air-driven vibrator that it is free from the problem caused by the emission of electromagnetic waves.
Furthermore, as the rotor is mounted freely over the shaft and is axially confined by a pair of spaced O-rings fitted over the shaft, the rotor may be readily replaced whenever the rotor is worn out or damaged, by simply removing the shaft out of the outer casing and by removing the positioning O-rings. As in this manner the replacement of the rotor can be readily carried out even by the user, there is no problem of maintenance.
However, the problem of this scaler is that the air-driven vibrator incorporated therein is only able to produce a vibration having a frequency in the range of as low as 3,000-6,000 Hz. This is because vibration takes place in the so-called bending or flexural vibration mode wherein the elongated shaft is excited by the rotating rotor to oscillate by bending or flexural movement of the shaft. Consequently, this scaler cannot solve the afore-mentioned problem inherent in the air-driven vibrators that an annoying audible noise that would make patients uneasy is generated.
U.S. Pat. No. 4,453,919 (Takeshita) describes an arrangement and principle of operation of different type of air-driven vibrator which may be incorporated in a dental scaler as a source of vibration. This vibrator includes a casing provided with a disc-shaped working chamber (or rotor chamber), a disc-shaped vibratory element (or rotor) movably received in the chamber, and injection nozzles for injecting compressed air tangentially into the working chamber.
As compressed air is injected through the nozzles into the working chamber, the vibratory element is oscillated as it is rotated to strike the side walls of the chamber thereby generating a vibration. The vibration generated in the vibrator is transmitted through a shaft to a scaling tip. It is considered that the vibration transmitted through the shaft to the scaling tip is a combination of a flexural mode of vibration and an acoustic or elastic-wave mode of vibration.
U.S. Pat. No. 5,190,456 (Hasegawa) is directed to improve the dental scaler described in U.S. Pat. No. 4,453,919 (Takeshita) and proposes to increase the frequency of vibration of the vibrator as close as possible to the supersonic range in order to reduce the annoying noise inherent in the conventional air-driven vibrators.
To this end, the shaft is shorted in order to transmit to the scaling tip the acoustic or elastic mode of vibration proportionally more than the flexural mode of vibration and the shaft is supported in such a manner as to avoid the presence of a node of vibration which would give rise to the flexural mode of vibration.
According to the concept of U.S. Pat. No. 5,190,456 (Hasegawa), by reducing the size of the vibratory element (or rotor) as far as possible, the frequency of vibration can be increased to approach to the supersonic range in a manner to avoid emission of annoying noise. For example, with a vibratory element having a diameter of as small as 5 mm, the frequency of vibration will be increased up to about 15,000 Hz so that audible noise is considerably subdued.
However, increasing the frequency of vibration will, in turn, accelerate wear of the vibratory element and side walls. In addition, the more the size of the vibratory element is reduced in an attempt to increase the frequency of vibration to the degree to approach the supersonic range, the effect of wear produced on the vibratory element will be more dominant and serious and this will also shorten the service life of the element. As a result, it will be necessary to replace the vibratory element and side walls more frequently.
However, in contrast to the scaler described in U.S. RE 29,687 (Sertich) wherein the vibrator rotor may readily be replaced by anyone concerned as mentioned hereinabove, in the case of the scaler described in U.S. Pat. No. 5,190,456 (Hasegawa), it is considerably difficult for an ordinary user (e.g., a dentist) to successfully replace the vibratory element and associated wearable parts.
This is firstly because it is difficult to withdraw the vibrator unit as a whole out of the outer casing because the vibrator unit is installed deeply within the elongated outer casing. A special jig is required to drive t
Kadota Yutaka
Suzuki Eiji
Lorusso, Loud & Kelly
Manahan Todd #E.
Micron Co., Ltd.
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