Patent Application
20110076638
This invention relates generally to devices for cleaning teeth using ultrasound, and more specifically concerns the combination of a bubble generator and an ultrasound source which vibrates the bubbles at or near their resonant frequency.
Gas bubbles in a liquid such as water results in a vigorous fluid flow when the bubbles are vibrated with ultrasound frequencies at or near the resonance frequency of the bubbles. Such a fluid flow directed toward teeth has the effect of disrupting and removing dental plaque from the teeth. Such a system is the subject of pending PCT patent application No. PCT/IB2006/054463, which is owned by the assignee of the present invention, the contents of which are hereby incorporated by reference. Such devices, however, use a single ultrasound frequency. The bubble generation for such systems must accordingly be quite precise, with the bubbles having a radius matched with the frequency of the ultrasound signal for maximum effect of the ultrasound signal.
In practice, such precise bubble generation is difficult to achieve, particularly in a mass-produced device, since the required precision requires additional expense. The lack of precision in bubble generation leads to bubbles having a range of sizes, which results in a decrease in efficiency of the device, because not all the bubbles can be effectively used for cleaning plaque with a single ultrasound frequency. In addition, the use of a single ultrasound frequency produces a stationary standing wave/interference pattern on the teeth, with the high intensity and the low intensity points of the ultrasound being always in the same position. This typically results in a particular biofilm removal pattern on the teeth, in which certain areas are not cleaned as well as other areas, leaving dental plaque on the teeth in those areas, which is undesirable.
Hence, it is desirable that a bubble generator/ultrasound system be able to effectively make use of a range of bubble sizes, while producing a more homogeneous cleaning of the teeth.
Accordingly, described and shown herein is an apparatus for cleaning biofilm from teeth, comprising: a source of gas bubbles in a liquid medium, the bubbles having a range of sizes associated with effective removal of bacteria in the biofilm, each gas bubble having a resonance frequency; and a source of ultrasound signals having a range of frequencies, the ultrasound frequency range including frequencies corresponding to the resonance frequencies of a majority of the air bubbles, wherein the ultrasound signals are applied to the flow of air bubbles/liquid, vibrating the bubbles so that upon reaching the biofilm, a cleansing action occurs.
Also described and shown herein is a toothbrush, comprising: a toothbrush handle portion; a toothbrush head portion extending from the body portion and having an extending cup-shaped portion; an ultrasound transducer mounted in the cup portion and operably connected to transmit ultrasound waves from the cup portion, focused on teeth surfaces; and a source of gas bubbles in a liquid medium, the bubbles having a size associated with effective removal of bacterial in the biofilm.
The apparatus of
Apparatus 10 includes a nozzle/standoff member 12 which is designed to be positioned against the teeth, particularly the interproximal area, to provide a desired spacing between the piezoelectric transducer 16, which produces a range of ultrasound frequencies, and the teeth, specifically to maintain the teeth at or near the focus of the transducer. For instance, at a 400 kHz center frequency of the ultrasound signal, the focus distance is 6.7 mm, for a flat, round transducer 10 mm in diameter. This size will provide good coverage for the teeth surfaces as well as the interproximal space. The range of transducer focus, for instance, for a frequency range of 300-500 kHz, will be 5.1-8.4 mm. The total height of the transducer 16 and standoff member should not be more than 20 mm, which is approximately the size of a regular toothbrush head. From the above, the standoff distance of member 12 will be in the range of 1-15 mm.
If the transducer 16, including the body/casing, has a thickness of 5 mm, the standoff distance is preferably equal to the focus distance of the transducer at the lowest efficient frequency, which in the example above is 5.1 mm. In another example, when the ultrasound frequency varies over a range of 0.75 to 1.25 MHz, with a center frequency of 1 MHz, the focal distance of a flat, round transducer 10 mm in diameter will range from 12.6 mm to 21 mm. The preferred standoff distance is 12.6 mm. This distance can be decreased if the transducer has a non-flat design.
Bubble generator 14 in operation produces a stream of air bubbles in a liquid jet to nozzle member 12. Bubble generator 14 produces bubbles of a range of sizes which are effective in removing dental plaque. In particular, the size of the bubbles will match the size of the bacteria, or colonies/clumps of bacteria, referred to as lumps, present in the biofilm on the teeth. Since the bacteria and/or the lumps have a range of sizes, the bubbles also will have a corresponding size range of bubbles, typically in the micron range. The piezoelectric transducer 16 is designed for broadband ultrasound generation, driven by the drive electronics 18, as mentioned above. The piezoelectric transducer producing a range of frequencies has the advantage of matching the resonant frequencies of a range of bubble sizes, thereby producing effective resonant vibration of a range of bubble sizes as opposed to just one bubble size. This results in effective cleaning for a range of bacteria/bacteria lump sizes, as well as producing homogeneous cleaning effect of the teeth, including the interproximal areas.
More specifically, drive electronics 18 and piezoelectric transducer 16 will produce an ultrasound signal having a selected center frequency, with a particular bandwidth about that frequency. The center frequency can vary over a considerable range. At the low end, the center frequency could be 200 kHz, while at the high end, the center frequency could be 2 or even 4 MHz. A more preferred range is between 200 kHz and 2 MHz, while a preferred center frequency is approximately 1.0 MHz, although a 400 kHz center frequency has also produced good results. In the case of a 1 MHz center frequency, with a bandwidth of 50%, the range of ultrasound frequencies produced will be 750-1250 kHz, while a 50% bandwidth for a 400 kHz center frequency is 300 kHz-500 kHz.
Besides the range of ultrasound frequencies produced by the piezoelectric transducer/drive electronics combination about a selected center frequency, the drive signal produces bursts of ultrasound, instead of a continuous ultrasound signal.
Time T2 contains one or more ultrasound bursts. The frequency of the bursts, indicated at 24-24, can be varied. In one example, the frequency of the bursts ranges between 25 and 600 Hz. This is referred to as the burst repetition frequency (BRF), controlled by a second trigger signal (trigger 2). The lowest possible BRF depends on the value of T1+T2, where BRF=1/T1+T2, where there is only one burst during T2. Preferably, the burst repetition frequency is within the range of 100-500 Hz. Most preferably the frequency is approximately 200 Hz. Within each burst, there are a number of individual ultrasound cycles 25 at one ultrasound frequency within the range of frequencies produced by the ultrasound device. In one example, the ultrasound signal frequency in one burst is 1 MHz. The number of cycles within each burst can vary, typically within the range of 50-5000, with a preferred value of approximately 1000. This results in an ultrasound signal pattern indicated at 26 in
It should be understood, however, that the above-noted preferred values of T1, T2, BRF and the number of cycles per burst are merely illustrative, as the optimal settings are determined by the parameters of the actual flow, including the bubble concentration, bubble size distribution, bubble flow velocity, bubble liquid flow rate and bubble liquid velocity.
The frequency of the ultrasound signal within each time period T2 can be the same, with the frequency changing for each successive time T2, or the frequency of the ultrasound signal can change within each time T2, i.e. in accordance with a pre-selected pattern, as the ultrasound frequency changes over the bandwidth of the ultrasound device.
The optimal frequency range of the ultrasound signal depends on several parameters, including several safety parameters. The lower end of the frequency range is limited by one such safety concern, determined as follows. The amplitude of the ultrasound signal needed for effective removal of biofilm is within the range 0.3-0.5 MPa, referred to peak rarefractional pressure. The peak rarefractional pressure is related to the mechanical index (MI) value associated with the ultrasound signal, which in turn is a good predictor of the likelihood of possible damage to the tissues, including teeth, gum and bones. The mechanical index is defined as follows:
In the use of diagnostic ultrasound, the FDA permits a maximum MI of 1.9. Using a pressure P of 0.5 MPa, which is at the upper end of effective pressure, the resulting lower limit of ultrasound frequency is 69 kHz in order to meet the FDA MI standard.
The intensity of the ultrasound signal is also limited by safety issues. For example, a 1.9 MI would limit the maximum peak rarefractional pressure at a 300 kHz ultrasound signal to 1.0 MPa. This value will change, depending on the actual ultrasound frequency. Further, the FDA maximum time averaged intensity, which takes into account duty cycle, is set at 0.72 W/cm2. The intensity I can be calculated from a value of P as follows:
With a continuous wave of ultrasound, and a pressure of 1 MPa, the intensity is 34 W/cm2. Accordingly, the maximum duty cycle with those values would be 2.1%. Using 0.5 MPa, the intensity decreases to 8.4 W/cm2, which increases the maximum duty cycle value to 8.5%. Hence, duty cycle is important to accommodate safety concerns of pressure and intensity while still producing effective ultrasound action.
The duty cycle can be calculated from the ultrasound driving signal parameters shown in
As indicated above, an important aspect of the present system is that the ultrasound generates a range of ultrasound frequencies, in the form of signal bursts of ultrasound, with the range of frequencies being associated with/corresponding to the range of bubble sizes produced by the bubble generator, which in turn is associated with the range of bacterial and/or bacterial lump sizes in the dental plaque biofilm on the teeth.
The bubble generator 14 is shown in more detail in
The velocity of the bubble mixture is produced by a pump. A continuous flow centrifugal pump is generally preferred, as shown at 40 in
The formation of the gas (preferably air) bubble/liquid mixture which moves to the impeller is shown in
The bubble/liquid mixture coming from through outlet 62 is sucked into the impeller, which thoroughly mixes the liquid and air. The resulting flow of bubbles/liquid is then directed into a connecting line 70 to the nozzle/standoff element 12. A soap or a surface active substance (surfactant) can be added to the liquid from a container 72. This reduces the surface tension of the fluid, increasing the number of small bubbles and the uniformity of the bubbles. One example of a suitable surfactant is sodium laurylsulphate, which may be added in an amount of 0.25 m %. This results in optimal surface tension and viscosity. Increasing the viscosity of the liquid increases the shear forces and may have a greater effect against the bacteria on the teeth. It should be understood that
Typical bacteria in dental plaque biofilm are somewhat spherical in shape, with a radius of approximately 4 μm. Since the bacteria are typically very rigid, they may not break under the applied shear stress, particularly if the bubbles are smaller than the bacteria. Hence, the bubbles should typically be greater than the size of the bacteria. It has been found that the bacteria are usually organized in colonies. These colonies or lumps are typically easier to dislodge than the bacteria within the lumps. The colonies can vary between 5 μm and 25 μm in radius. Bubbles in this size range are thus most efficient in effectively and quickly removing bacteria from the teeth.
In operation, bubbles of a desired size are produced by the bubble generator in a continuing stream. The size of the bubbles may vary over a range of +/−30%, which permits the use of a relatively inexpensive bubble generator. A range of bubble size is important and the various bubble sizes, when energized by the ultrasound at their resonant frequencies, operate on a variety of bacteria colony sizes normally encountered in dental plaque. The bubbles are resonated by periodic bursts of ultrasound signals, with the ultrasound having a selected on/off pattern, which tends to prevent aggregation of the bubbles, thus increasing the effectiveness of the plaque removal. Using a range of ultrasound frequencies, besides the advantages of operating effectively on a range of bubble sizes, produces a varying interference pattern on the plaque, which produces a more homogeneous cleaning effect.
As discussed above, the apparatus of
Another embodiment of an oral cleaning device in the form of a toothbrush using gas bubbles and/or vibration of the toothbrush with an ultrasound signal is shown in
Handle portion 81 includes an elongated section 90 which extends to head portion 82. A wire 91 or similar element carrying the piezoelectric drive signals from piezoelectronics 84 extends through elongated section 90, as does a line 92 for the gas bubble/liquid mixture, from bubble generator 86. Head portion 82 includes a curved surface 98 in which is disposed a cup member 100. Cup member 100 is curved, for instance a prophy cup, which is shaped to focus, i.e. direct, ultrasound waves produced by piezoelectric transducers 102 and 104 positioned on or in the cup member 100 toward the teeth. Cup member 100 is preferably fabricated from a flexible, pliable material, such as rubber or other polymer elastomers. Additional ultrasound transducers can be provided so as to provide a ring of ultrasound transducers around the cup member. The ultrasound transducers are typically located near the middle of cup member 100, as shown.
An opening 106 in the center of cup member 100 provides an exit for the gas bubble/liquid moving through line 92. During operation, opening 106 serves as an outlet for the gas bubbles in the liquid medium, directed toward the target surface, e.g. teeth. The ultrasound waves produced by transducers 102 and 104 are focused toward the target surface by the shape of cup member 100. The ultrasound waves vibrate the bubbles in the liquid medium, as discussed in detail above, producing the desired cleansing bubble action described above. The characteristics of the ultrasound signal discussed above with respect to the embodiments of
Bristles 83 are provided on the head portion 82 to provide a brushing action if desired, with a brushhead motion produced by driver circuit 88. The vibrating action can be used with just the ultrasound or with the ultrasound and the gas bubbles.
In addition to the effect of the ultrasound waves acting on the bubbles, which in turn act on the dental plaque for cleaning plaque from the teeth, as discussed above, the gas bubble/liquid can be used to transport the ultrasound waves from the transducer to the teeth for direct action on the dental plaque. The gas bubble/liquid thus acts as a guide for the ultrasound waves. When the successive bursts of ultrasound energy in this arrangement are sufficiently long, a portion of each ultrasound burst will reach the surface of the teeth without much energy loss, producing a desired cleaning effect.
In this arrangement, when water, for instance, is used as a fluid for guiding the ultrasound waves, the fluid needs to be refreshed (replenished) as it escapes from the cup or other openings in the hollow member during operation. In another embodiment, two separate pumps 107, 108 can be used, as shown in
With the two-liquid embodiment of
Although a preferred embodiment of the invention has been disclosed here for the purposes of illustration, it should be understood that various changes, modifications and substitutions may be incorporated in the embodiment without departing from the spirit of the invention, which is defined by the claims which follow.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2008/054001 | 10/1/2008 | WO | 00 | 12/3/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60978196 | Oct 2007 | US |
