WO2016055883A1

WO2016055883A1 - Ultrasonic teeth cleaning apparatus with microbubble nucleation sites.

Info

Publication number: WO2016055883A1
Application number: PCT/IB2015/057114
Authority: WO
Inventors: Aaldert ZIJLSTRA; Paulus Cornelis Duineveld
Original assignee: Koninklijke Philips N.V.
Priority date: 2014-10-06
Filing date: 2015-09-16
Publication date: 2016-04-14

Abstract

An apparatus (10) for cleaning a dental surface, including a vibration generator (105) and at least one surface of the apparatus has a plurality of micro pits (120) formed in that surface. The plurality of micro pits are configured to generate microbubbles (110) in a liquid medium (180). The vibration generator is configured to generate vibrations of a first frequency, and transmits the vibrations to the plurality of micro pits, inducing the formation of microbubbles by cavitation.

Description

ULTRASONIC TEETH CLEANING APPARATUS

WITH MICROBUBBLE NUCLEATION SITES Field of the Invention

[0001] The present disclosure is directed generally to cleaning dental surfaces using ultrasonically driven microbubbles created with micro pit nucleation sites.

Background

[0002] Ultrasound-induced cavitation of air microbubbles is utilized for cleaning biofilm off of teeth surfaces, as well as below the gum line. The microbubbles can be generated either by spontaneous and uncontrolled nucleation or by insertion of externally created microbubbles.

[0003] The spatial, temporal, and dimensional distributions of existing dental cleaning devices are determined by the conditions of the liquid and the acoustic field, and can therefore be chaotic and unpredictable. Additionally, the acoustic pressure levels required to generate a sufficiently large bubble population are typically quite high, thereby exceeding the allowed mechanical index. As a result, ultrasonic cleaning devices based on spontaneous nucleation generally have low efficiencies and show strong variation in cleaning results.

[0004] Although controlling the location of microbubbles in the liquid medium as the dental cleaning device is used lowers the amount of energy needed for the creation of an active bubble population, there are still several drawbacks. For example, the generation and maintenance of the microbubbles requires special methods such as flow-focusing and the use of additives such as surfactants. Directing these cleaning agents to a particular location can be challenging and is mostly based on precise tuning of flow and acoustic parameters.

[0005] Accordingly, there is a need in the art for dental cleaning apparatus that control the location of microbubble formation using nucleation sites.

Summary of the Invention

[0006] The present disclosure is directed to inventive apparatuses and systems for cleaning dental surfaces using micro pit nucleation sites that facilitate microbubble formation. Various embodiments and implementations herein are directed to a dental cleaning device that generates ultrasonic signals or vibrations to promote microbubble formation in micro pit nucleation sites. The present invention may be used for the removal of biofilms or other debris within the oral cavity. Removal of biofilms or other debris as described herein is based on the exertion of stresses by ultrasonically-driven microbubble populations which are formed in micro pit nucleation sites, with such sites located at an interface of the cleaning device and the dental surface to be cleaned.

[0007] Generally in one aspect, a dental cleaning device is provided. The dental cleaning device includes a vibration generator and a surface of the dental cleaning device comprising a plurality of micro pits configured to generate microbubbles in a liquid medium. The vibration generator is located in close proximity to the liquid medium and plurality of micro pits , and is configured to generate vibrations of a first frequency and transmit the vibrations to the plurality of micro pits. According to embodiments herein, the dental cleaning device may be a mouthpiece, toothbrush, or any other dental apparatus.

[0008] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein.

[0009] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief Description of the Drawings

[0010] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

[0011] FIG. 1 is a schematic representation of an ultrasonic mouthpiece incorporating micro pits for microbubble formation in accordance with an embodiment.

[0012] FIG. 2 is a schematic representation of an ultrasonic mouthpiece incorporating micro pits for microbubble formation in accordance with an embodiment. [0013] FIG. 3 is a schematic representation of various micro pit structures in accordance with an embodiment.

[0014] FIG. 4 is a schematic representation of an ultrasonic toothbrush incorporating micro pits for microbubble formation in accordance with an embodiment.

Detailed Description of Embodiments

[0015] The present disclosure describes various embodiments of apparatus, systems, and devices that clean a dental surface using microbubbles. More generally, applicants have recognized and appreciated that it would be beneficial to clean a dental surface using microbubbles that are passively created at the location to be cleaned rather than actively generating microbubbles at another location and transporting them to the surface to be cleaned. For example, microbubbles can be generated from micro pit nucleation sites in response to ultrasonic signals or vibrations. The dental cleaning device can include a plurality of micro pits anywhere that the device interfaces with a dental surface.

[0016] In view of the foregoing, various embodiments and implementations are directed to a dental cleaning device that generates ultrasonic signals or vibrations to promote microbubble formation in micro pit nucleation sites.

[0017] According to an embodiment, FIG. 1 shows a dental cleaning device 100 for generating microbubbles 110 using micro pitsl20 formed on a mouthpiece 26. For example, micro pits 120 can be formed on any surface of a dental apparatus that is configured to engage or approach a dental surface for cleaning. Micro pits 120 basically consist of small holes of a certain depth made in the surface of a solid object. When immersed in a liquid 180, these micro pits 120 tend to entrap small pockets of air or gas. Ultrasonic waves are generated by the vibration generator element 105. An example of such a vibration generating element is a piezoelectric material. According to an embodiment, the vibrational generator 105 is mechanically coupled to the micro pits 120. This can be done for instance by a glue interconnection. When vibration is generated in the vicinity of the micro pits 120, the micro pits 120 act as nucleation sites for the generation of microbubbles 110 into the adjacent liquid 180. For the mouthpiece device 26 depicted in FIG. 1, for example, the micro pits 120 can be formed on any teeth -facing surfaces of the mouthpiece. According to one embodiment, micro pits 120 are formed in a temporary or replaceable surface that can be replaced if the micro pits become clogged and unable to produce microbubbles.

[0018] FIG. 2 shows a mouthpiece generally at 26, which may or may not have a set of bristles 28 for cleaning the upper and lower teeth by scrubbing. The bristles 28 may be mounted on the teeth-facing surfaces of mouthpiece 26. The mouthpiece may be manually operated by the user simply moving the teeth, or it can be power-operated by a power system shown generally at 30, although a power system may be located outside the mouthpiece. In the present invention, the mouthpiece 26 will also include a system 120 for producing microbubbles, as described herein, directed to the vicinity of the surface of the dental surface 10 to be cleaned, and an vibration generator system 105 for producing ultrasound signals to activate the microbubbles for cleaning. The vibrational element of the ultrasound system 105 (e.g. piezo-electric material) can be placed in mechanical contact with the micro pits 120, or can be placed in close proximity. Micro pits 120 are on the order of approximately 10 microns in size, although variations in this size are possible. At this size, the micro pits 120 act as nucleation sites for cavitation of microbubble clouds 110, as shown in FIG. 1. According to an embodiment, ultrasound system 105 produces ultrasound signals or vibrations that cause cavitation of microbubbles 110 i at an interface with a surface of the mouth to be cleaned. When immersed in a liquid medium 180 such as a cleaning fluid, water, or saliva, micro pits 120 entrap small pockets of air due to the balance of interfacial forces between the solid, liquid, and gas, generating microbubbles 110. The generated microbubbles 110 tend to remain in the close vicinity of the micro pits 120 and are very stable over time. Further, the vigorous liquid 180 motion induced by the microbubbles 110 promotes cleaning by placing the generated microbubble 110 cloud in contact with the dental surface 10.

[0019] Without ultrasonic signals or vibrations, a pocket of microbubbles 110 will tend to form in the micro pits 120. The microbubbles 110 will remain in the micro pits 120 when there is no pressure difference between the gas microbubbles 110 in the micro pits 120 and the liquid 180 outside the micro pits 120, and hence there is no diffusive flux of microbubbles 110 outward from the micro pits 120.

[0020] In contrast, when an ultrasound signal or vibration is generated from the vibration generator 105 in the vicinity of the micro pits 120, the gas-liquid interface deforms and microbubbles 110 are diffused into the liquid 180. Therefore, the micro pits 120 can be considered nucleation sites for clouds of microbubbles 110. According to an embodiment, as seen in FIG. 3, the response of the interface on the frequency is a function of the diameter a of the micro pit 120 For maximum efficiency, there should be a significant response of the gas interface to the vibration driving frequency in order to produce microbubbles 110. Accordingly, the dimensions of micro pits 120 and the frequency of the generated ultrasound signals 105 have to correspond as discussed below.

[0021] The height and depth dimensions of the pit have to match certain criteria in order for bubble formation to occur. According to an embodiment, therefore, the height h and diameter a of micro pits 120 are defined according to specific criteria to facilitate microbubble 110 formation. Preferrably, the height h to diameter d ratio of the micro pit 120 should be at least 20% and more preferably at least 50%. The diameter of micro pit 120 can be approximately 0.5- 500 μηι, and more preferably in the range of 2-50 μπι. It can be appreciated that different sizes of micro pits 120 can be used in a single arrangement.

[0022] It can be appreciated that the overall shape of micro pit 120 can vary, including but not limited to cylindrical or conical, and that multiple sizes or shapes of micro pits 120 can be used in a single device. . Further, the contact angle of the micro pit surface with the liquid can be a variety of angles. Preferrably, for a micro pit with a non-cylindrical shape, the advancing contact angle is larger than 90°. According to an embodiment, the receding contact angle is equal to or smaller than the advancing contact angle.

[0023] When a plurality of micro pits 120 are formed on a surface, the distance between the micro pits can similarly be configured to maximize microbubble formation and cleaning efficiency. For example, the distance between micro pits in an array can be in the range of 1 to 1000 μηι, with a suitably dense array having a range between 10 to 200 μπι. The plurality of micro pits 120 can also be ordered in a two-dimensional array. Although all the micro pits 120 in an array can have the same or approximately the same dimensions, including diameter, height, spacing, and shape, in some arrays the plurality of micro pits in a single array can adopt a wide variety of these and other dimensions.

[0024] Micro pits 120 can be formed in or on any surface of a mouthpiece, toothbrush, or other dental cleaning device, and thus can be manufactured from a variety of materials. For example, micro pits can be formed in a surface made of silicon, photoresist, plastic or metals. To preserve the structural integrity of micro pits 120, and/or to enhance microbubble formation, a coating can be applied to the formed micro pits. As another embodiment, a non -wetting coating containing fluoride may be applied to the surface of the micro pits.

[0025] According to an embodiment, the driving frequency of the transducer elements of the dental cleaning device, which may be part of vibration generator 105, is in the ultrasonic range, such as in the range of 30 kHz to 30 Mhz and more preferably in the range of 50 to 500 kHz, although other ranges are possible.

[0026] According to an embodiment, the Eigen frequency from the pit can be shown to be equal to the scaled Minnaert frequency of a microbubble:

(Equation 1) where P is the pressure (Pa), γ is the polytropic gas constant («1 for the size of the utilized microbubbles 110), p the liquid density and a is the diameter of the micro pit 120, such as seen in FIG. 3.

Similarly:

₌ αγλΡ

σ (Equation 2) with Z a non-dimensional parameter, where λ is the aspect ratio =na³/V, where V is the volume of the pit and σ is the surface tension of the liquid. This frequency, f_pU, is optimal for microbubble formation. According to an embodiment, the system is driven in a range between 0.1 and 10.0 times this optimal frequency, with embodiments driving the system between 0.5 and 1.5 times this optimal frequency. The pit design is such that Z is in the range of 1 to 1000 and more preferably Z is in the range of 10 to 200.

[0027] According to an embodiment, the bubble sizes that are generated have a size that is smaller than the micro pit 120 in which they are formed. The Eigen frequency of these bubbles is given by the same Equation 1 , above, but now the pit diameter a is replaced by the bubble radius r. In this case, the frequency of the bubbles may not match with the frequency of the pit. Accordingly, the system can therefore be driven with two or more driving frequencies, with one driving frequency given by Equation 1 (and the provided ranges) and the other driving frequency calculated by Equation 1 but with a microbubble 110 radius in the range of 0.2-0.5 times the micro pit 120 size. Hence the frequency of a second driving frequency can be 1.5 to 8 times larger than the base frequency, and more preferably in the range of 2 to 5 times larger than the base frequency. According to an embodiment, the driving frequency or frequencies may be generated in continuous mode or may also be generated in bursts. The duty cycle of the bursts can be in the range between 0.01% to 90%. In another embodiment of the invention, the vibrating element is used in a burst mode where in the time slot where the vibrating element is not emitting ultrasonic waves the vibrating element is sensing the response of the wave that it has emitted. As the acoustical impedance of a mixture of water and bubbles is significantly different from a pure liquid it will be possible to detect whether bubbles are being formed in the liquid 180. In this way it will be possible to provide a signal to a user for replacement of the micropits 120. In yet another embodiment the recorded signal gives information to adapt the frequency of the ultrasonic waves generated by the vibrating element 105.

[0028] The amplitude of the driving frequency or frequencies must be in a safe range to apply to humans. For example, the amplitude can be in the range of a mechanical index in the range of a time averaged value of 0.1 to 1.9, where the mechanical index has been defined as:

_{(Equation 3)}

[0029] The distance of the micro pits 120 to the dental surface 10 is in the range of 0.1 to 10 mm and more preferably in the range between 0.3 and 5 mm. In one of the embodiments it is possible that the driving frequency and distance are matched such that a standing wave occurs.

[0030] According to an embodiment, FIG. 4 shows a toothbrush 30 with a handle 32 and a brushhead portion 34. Handle 32 includes a power system 38. Brushhead portion 34 includes a bristle field 36 although a bristle field is not essential to the device. Toothbrush 30 can be either a manual toothbrush, i.e. where the bristles are moved by manual means, or an electric toothbrush where the bristles are moved by electro-mechanical means. The brushhead 34 also includes a dental cleaning device 100 for generating microbubbles 110 in a liquid 180 using micro pits 120 adjacent to a vibrational generator 105 for producing microbubbles 110 as discussed herein, the microbubbles 110 typically on the order of 1 μιη to 150 μηι in size, although the size can vary beyond this range. The vibration generator 105 produces an ultrasound field to generate microbubbles 110 adjacent the dental surfaces 10 to be cleaned. The vibration generator 105 generates vibrations of a first frequency and transmits the vibrations to the micro pit 120 array.

[0031] Toothbrush 30 may also contain a distance holder 150 to prevent the micro pits 120 from touching the dental surface 10, although the bristles 36 can also serve the purpose of being a distance holder.

[0032] According to a further embodiment, the invention includes one or more liquid jets that transport or force or otherwise drive the generated microbubbles 110 to the dental surface 10. The jets in the mouthpiece or the toothbrush can be generated by standard means, such as a pump.

[0033] According to one embodiment, the liquid medium 180 can be water, saliva, mouthwash, toothpaste, or other liquids. For example, the liquid medium 180 can be super saturated liquids, e.g. with dissolved C0₂. Further the liquid 180 can contain fluorides, surfactants, particles, and/or anti-bacterial agents such as essential oils or chlorhexidine. Preferably, the viscosity of the liquid is low, not exceeding 1 Pa at small shear rates (less than 1 s^"1) and at room temperature. More preferably, the viscosity can be the range of 0.5-10 mPa s at room temperature.

[0034] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

[0035] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[0036] The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified.

[0037] As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of."

[0038] As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified.

[0039] While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

Claims

Claims What is claimed is:

1. A dental cleaning device (100) comprising:

A plurality of micro pits (120) on at least a surface of the dental cleaning device; and a vibration generator (105);

wherein the vibration generator is located in close proximity to the plurality of micro pits, and wherein the vibration generator is configured to generate vibrations of a first frequency and transmit the vibrations to the plurality of micro pits so that the micro pits (120) generate microbubbles (110) in a liquid medium (180) adjacent to the micro pits for cleaning a dental surface (10).

2. The dental cleaning device of claim 1 , wherein the dental cleaning device is a mouthpiece (26).

3. The dental cleaning device of claim 1 , wherein the dental cleaning device is a toothbrush (30) comprising a handle (32) and brushhead portion (34) having at least one bristle field portion (36), and wherein the plurality of micro pits (120) are located within the bristle field portion (36). .

4. The dental cleaning device of claim 1 , wherein the generated microbubbles comprise a diameter of approximately 1 μπι to 150 μπι.

5. The dental cleaning device of claim 1, wherein each of the plurality of micro pits comprises a diameter of approximately 0.5-500 μπι.

6. The dental cleaning device of claim 1, wherein a ratio of a height of each of the plurality of micro pits to a diameter of each of the plurality of micro pits is greater than 20%.

7. The dental cleaning device of claim 1, wherein each of the plurality of micro pits are approximately identically shaped and sized.

8 A method of cleaning a dental surface (10), the method comprising:

Providing a liquid medium (180) adjacent to the dental surface (10);

Placing dental cleaning device (100) having a vibration generator (105) and a plurality of micro pits (120) on at least one surface with the at least one surface of the dental device having the micro pits in close proximity to the liquid medium;

Applying power to the vibration generator by means of a power system (30, 38) that produces vibration at a first frequency that is transferred to the micro pits to create microbubbles (110) in the micro pits that are vibrated outward from the micro pits into the liquid medium to clean the dental surface.

9. The method of claim 8 wherein the vibration generator is adjacent to the at least one surface having a plurality of micro pits.

10. The method of claim 8 wherein the vibration generator is in close proximity to the at least one surface having a plurality of micro pits.

11. The method of claim 8 wherein the generated microbubbles have a diameter of approximately 1 μιη to 150 μπι.

12. The method of claim 8 wherein the microbubbles are formed in the micro pits by means of cavitation.