Patent Application
20210069756
The present invention generally relates to an apparatus for cleaning a cavity filled with a liquid (e.g., debridement, material removal, irrigation, disinfection, decontamination of surfaces of the cavity, and/or for fragmenting particles within such cavities) and corresponding methods.
When energy is locally deposited within a liquid, for example with intense focused electromagnetic radiation (e.g., laser light) or with an electrical discharge through a spark, locally induced boiling of the liquid leads to a creation of a cavitation bubble that rapidly expands due to the high pressure within the vapor. When the bubble reaches its maximum volume where the internal pressure is lower than in the surrounding liquid, the bubble starts to collapse. When the collapsing bubble reaches a given size, it may rebound, and the process repeats until there is insufficient energy for the bubble to rebound again. These violent cavitation oscillations lead to rapid streaming of liquid molecules around the cavitation bubble. It is also known that a cavitation bubble collapsing near a boundary forms a liquid jet directed at the boundary. Even more importantly, under appropriate conditions, an intense shock wave may be emitted during the bubble's collapse.
The strong mechanical forces associated with rapid bubble oscillations can break particles or remove particles from surfaces, thus locally cleaning them. This effect is of interest for industrial applications, and as well in medicine. Laser-induced cavitation bubbles have been used in ophthalmology, cardiology, urology and dentistry. For example, laser pulses produce plasma with subsequent bubble formation for ocular surgery by photo-disruption. Laser induced lithotripsy fragments kidney stones through cavitation erosion. Laser pulses have been used to remove thrombus in obstructed arteries. In endodontics, laser activated irrigation is used to debride dental root canals. Laser induced cavitation may be also used for cleaning (e.g., debriding and disinfection) of periodontal pockets, holes created during bone surgery, or surfaces of inserted implants.
The principle lying behind cavitation phenomena is the difference in compressibility between a gas and a liquid. The volume of liquid hardly changes in response to a variation in pressure, whereas the volume of the gaseous interior of a bubble can change dramatically. Any contraction or expansion of the bubble is inevitably accompanied by a displacement of an equal volume of the much denser surrounding liquid. As a result, a strong bubble response in combination with the compressible interior can provide not only localized fluid motion but also tremendous focusing of the liquid kinetic energy. Of particular interest for cleaning are the shock waves which may form during the bubble's collapse. These shock waves spread through the volume at supersonic speeds, and interact disruptively with the surrounding environment (e.g., cavity walls). These waves are not only very effective in removing any contamination from the cavity surfaces but can also kill bacteria, leading to a partial or complete disinfection of the cavity.
In an infinite liquid, a secondary shock wave is emitted during the accelerated contraction of the bubble cavity. This secondary shock wave is to be distinguished from the primary shock wave which is sometimes emitted during the initial bubble expansion phase when laser energy is locally deposited into a liquid within a very short time of nanoseconds or less. In what follows, the term “shock wave” will represent the secondary shock wave emission only.
The (secondary) shock wave emission occurs as follows. At the initial moment of the bubble's contraction, the pressure inside the bubble equals that of the saturated vapor which is much less than the liquid pressure. Because of this transition, the bubble starts to contract, and the bubble vapor pressure starts to grow. Initially, the bubble contraction is relatively slow. However, as the pressure rises, this leads to a vapor mass loss due to the condensation process on the bubble surface, accelerating the implosion even further. This ever-faster acceleration results in a violent collapse of the bubble, leading to heating up of the vapor and, most importantly, to emission of a supersonic shock wave emanating from the collapsed bubble. And finally, when the vapor temperature reaches its critical value the condensation process stops, which leads to an even faster rise of the vapor pressure until the contraction stops and the bubble begins to rebound.
Whether the shock wave is emitted and with what amplitude depends among other parameters on the properties of the liquid and on the dimensions of the reservoir that contains the liquid. For example, it is known that for liquids with higher viscosity, bubble's oscillations are slower and last longer. In viscous fluids, the dynamics of the collapse is slowed down, reducing the energy of the shock wave. In highly viscous fluids, shock waves are not observed at all.
Similar dependence applies also with regard to the dimensions of the reservoir. In a free liquid, bubble oscillations can be accommodated by displacing the liquid at long distances. However, in a confined environment, a free expansion of the bubble is not possible, and the expansion and contraction of the bubble is slowed down by the added resistance to flow due to the impermeability and the no-slip condition on the reservoir's surface. This process delays the dynamics of bubble's expansion and implosion compared to a free liquid situation. More importantly, because of the slowed down dynamics of the bubble's collapse, shock waves are weaker or do not occur at all.
For small reservoirs, shock waves are therefore weak or are not emitted at all. The cleaning effect of cavity oscillations is therefore limited to rapid liquid streaming and liquid jets, while the potential of much more violent shock waves is not utilized. For example, for dental endodontic cleaning, removing debris from root canal surfaces and eliminating infection consists of adding various chemical solvents into a root canal, and then using a laser irrigation method primarily to enhance the spreading of the chemical irrigant into hard to reach root canal areas. However, without creating shock waves, a sufficiently effective cleaning and disinfecting of small root canals remains elusive when using only water as the irrigating liquid. On the other hand, the use of potentially toxic irrigants is generally not desirable.
EP 3 127 502 A1 addresses this problem by delivering energy to a liquid in a set of a minimum of two individual laser pulses (a prior and a subsequent pulse) that follow temporally each other by an appropriate pulse repetition time (Tp), the pulse repetition time Tp being the time period from the beginning of one single pulse p to the beginning of the next, subsequent pulse p. This allows creation of a shock wave by the prior bubble, i.e., the bubble resulting from the prior laser pulse, even in situations when no shock wave is emitted by the bubble when only one laser pulse is delivered to the liquid. This observation is explained by the fact that the liquid pressure exerted on the prior bubble by the expanding subsequent bubble, i.e., the bubble resulting from the subsequent laser pulse, forces the prior bubble to collapse faster, thus facilitating the emission of a shock wave by the prior bubble. An important condition that needs to be fulfilled in order for the above described effect to be observed is that the subsequent bubble starts to develop when the prior bubble is already in its implosion phase.
EP 3 127 502 A1 discloses a feedback system that determines a bubble oscillation intensity and adjustment means to adjust the pulse repetition time TP as a function of the determined bubble oscillation intensity, such that an onset time of a second vapor bubble is within a first contraction phase of a first vapor bubble, when the later has contracted from its maximal volume to a size in the range from about 0.7 to about 0.1 of the maximal volume.
EP 3 127 502 A1 further discloses to use multiple pairs of pulses and to repeatedly vary the time difference between the onset time of the second vapor bubble and the onset time of the related first vapor bubble in a sweeping manner, such that within at least one pair of first and second bubbles, an onset time of a second vapor bubble is within the range indicated in the preceding paragraph.
However, the approaches disclosed in EP 3 127 502 A1 are still not perfect. Therefore, there is a need to improve the known methods, techniques and technologies that can improve the cleaning of small cavities.
In an aspect, the above object is at least partly solved by an apparatus for applying pulses of electromagnetic radiation to a cavity filled with a liquid. The apparatus comprises a source for generating a first pulse and a second pulse of electromagnetic radiation. Moreover, the apparatus comprises a control unit adapted to control a time between the first pulse and the second pulse as a function of a diameter D and/or a cross-sectional area of the cavity.
The inventors of the present invention have surprisingly found that it is typically a characteristic dimension of the cavity, e.g., as expressed in a diameter or a corresponding cross-sectional area of the cavity, that has the predominant effect on the required temporal pulse spacing. Hence, they found that the characteristic dimension of the cavity, e.g., as expressed in a diameter or a corresponding cross-sectional area of the cavity, provides a universal parameter that allows simple and effective control of the temporal pulse spacing to ensure generation of a shock wave even in small diameter (or corresponding small cross-sectional area) cavities. A complex feedback system that measures the actual bubble dynamics, i.e. its oscillation intensity, is not needed. Instead, static information about the cavity size is used to effectively control the temporal pulse spacing, which—through a variety of experiments described herein—was identified as a key parameter for pulse spacing control in order to effectively create shock waves also in small cavities. The control as a function of the diameter and/or cross-section also enables to reduce or even eliminate the need for sweeping, as an optimized pulse repetition frequency for the respective cavity diameter may be applied for all pulses.
Notably, the inventors have found out that the geometry of the cavity does not have to be known in a detailed way in order to enhance shock wave generation. Instead, it was found that the optimal time (e.g., pulse repetition time, being the time period from the beginning of one pulse p to the beginning of the next, subsequent pulse p) essentially only depends on an effective or average or mean diameter (or cross-sectional area) of the cavity. In other words, the variation in the bubble oscillation period arising from the variation in the size and shape of the lateral surface of the cavity may adequately be described by a cavity diameter, e.g. minor and/or major diameter, or the mean value thereof. The inventors have used this insight to pre-calibrate the optimum pulse repetition time as a function of the cavity diameter/cross-section and provided a control unit programmed accordingly, resulting in an apparatus that allows substantially improved cleaning of small cavities irrespective of their diameter by taking their diameter into account.
It is noted that the cavity may be a canal (e.g., a root canal (system)), a vessel (e.g., a blood vessel), a urinary tract, a passage, a periodontal pocket, a surgical hole, an opening surface which is to be cleaned or disinfected, and it may generally be any liquid reservoir. In what follows the terms reservoir and/or cavity will be used interchangeably to describe any or all of the applicable liquid reservoirs. For example, the apparatus may particularly be used for application to elongate cavities, whose diameter is small compared to their axial dimension (e.g. having an opening whose diameters are smaller than a depth of the opening). The optical axis of first and second pulses may be approximately parallel to an elongate axis of an elongate cavity.
Particularly, the inventors have found out that for reservoirs whose smallest (lateral) dimension is less than 8 mm, assuming these are filled with water (or a fluid with similar viscosity), shock waves typically do not occur without proper setting of the temporal pulse spacing. The present invention is therefore particularly useful for such smaller reservoirs. It should be appreciated for most typical anatomic liquid reservoirs, such as blood vessels, ureter canals, ocular vitreous cavity, endodontic access openings or periodontal pockets, such small cavity diameters are typically at hand. Nevertheless, based on the present invention, these may be cleaned by shock waves as the temporal pulse spacing can be appropriately set according to the respective cavity diameter/cross-section.
In experiments, the inventors have found that there is an optimal repetition time (Tp-opt) between the pulses in order for the shock wave to occur, and that there should not be too much deviation therefrom. The optimal repetition time (Tp-opt) has been found to be such that the subsequent bubble starts to develop during the second half of the first bubble's oscillation period (TB), e.g., when Tp is in a range from about 1.2×(TB/2) to about 1.95×(TB/2), preferably in a range from about 1.5×(TB/2) to about 1.9×(TB/2), and particularly preferably in a range from about 1.6×(TB/2) to about 1.9×(TB/2).
The inventors have found that, in order to achieve the above relations, it is very effective to control the pulse repetition time as a function of a diameter or cross-section of the cavity. This is attributed to the experimental finding that, using the same liquid and the same laser parameters, for the optimal pulse repetition time, it is practically the only quantity that influences the optimal pulse repetition time. In fact, it is generally not necessary to determine the precise geometry of each individual cavity. Rather, it was found that, to significantly improve the setting of the optimal pulse repetition time, it is generally sufficient to determine a diameter and/or cross-sectional area. The temporal pulse spacing can thus be optimized such as to obtain strong secondary shock waves during bubble cavitation oscillations even in confined geometries without much added complexity.
The inventors have used this insight to pre-calibrate the optimum pulse repetition time, for a given liquid and a given set of pulse parameters, as a function of the cavity diameter (or cross-sectional area) and to adapt the control unit accordingly, resulting in an apparatus that allows substantially improved cleaning of small cavities irrespective of their diameter.
Notably, a diameter of a cavity as understood herein may refer to an effective or average diameter at an opening of the cavity or the approximate location of the bubble (e.g., as integrated, or simply defined by half of the sum of the maximum and minimum diameters Dmax and Dmin, respectively) that is approximately perpendicular to the optical axis of the first and second pulses. However, also a minor diameter Dmin or a major diameter Dmax of such opening can represent an appropriate characteristic dimension and may thus constitute a suitable diameter of a cavity according to the present invention. Their use may particularly be beneficial for procedures where there is a considerable correlation between Dmin and Dmax, such as for example exists in endodontic (e.g., root canal) cleaning (with minor and major diameters being the mesiodistal and buccolingual diameters, respectively.). Notably, a diameter may be understood as a diameter, e.g. as measured approximately perpendicular to the optical axis of the first and second pulses.
The cross-sectional area may be understood as effective cross-sectional area at an opening of the cavity or the approximate location of the bubble (e.g. as estimated from a maximum and/or minimum diameter, an integration, etc.), e.g. as the area circumscribed by the cavity walls approximately perpendicular to the optical axis of the first and second pulses.
However, representations of a characteristic dimension of the cavity, other than diameter or cross-sectional area, may also be appropriate when so required by the type of the procedure and of the cavity shape. For example, for procedures where there exists a considerable variation in the cavity's depth (Dz), an appropriate characteristic dimension may be represented by Dz either alone or in combination with the dimensions of the lateral surface (lateral cross section of the cavity at the location of the bubble and/or the cavity opening approximately perpendicular to the optical axis of the first and second pulse), e.g. diameter, cross-sectional area. In other words, in addition, or alternatively to the control unit being adapted to control the time as a function of a diameter and/or a cross sectional area of the cavity, it is contemplated that it may additionally or alternatively be adapted to control the time as a function of any other characteristic dimension of the cavity.
In case of cavities that have a depth that is large enough such that it does not significantly affect the bubble dynamics, the cavity depth is essentially irrelevant. However, if the cavity depth (at least in some portions) is smaller, the cavity depth may be an important characteristic dimension, just as the cavity diameter/cross-sectional area. In these cases, cavity depth may be a controlled parameter and the time between the first pulse and the second pulse may additionally be controlled also as a function of the depth of the cavity. However, the present disclosure may also be applicable to cavities whose depth is within a small expected range (e.g. such as in endodontics, since the depth of endodontic access openings typically do not vary significantly from patient to patient). Then a separate control of the time between the first pulse and the second pulse as a function of cavity depth may not be needed, even though the cavity depth is relatively short. Instead the control of the time (as a function of a diameter D and/or a cross-sectional area of the cavity and/or other parameters as described herein) may be pre-calibrated for an expected cavity depth. The “unconstrained” bubble oscillation period may then refer to an oscillation period for the expected cavity depth with “infinite” diameter and/or cross-sectional area, i.e., a diameter and/or cross-sectional area large enough such that the bubble dynamics are not affected anymore by the cavity sidewalls (e.g. increasing the diameter/cross-sectional area further does not significantly change the bubble oscillation period). Additionally or alternatively, the “unconstrained” bubble oscillation period may also relate to a predetermined insertion depth which may affect the effective depth of the cavity in which bubble oscillations may occur, and the control unit may be adapted accordingly (e.g. as outlined with reference to Table 2, further below).
It is noted that it is also within the scope of the present invention that the optical axis of the second pulse deviates from that of the first optical axis. It is merely decisive that the pulse repetition time is properly set. The terms “approximately perpendicular to the optical axis of the first and second pulses” and “approximately parallel to the optical axis of the first and second pulses” may thus include slight deviations from perfect perpendicularity and/or parallelism, e.g. up to ±40°, ±30°, ±20°, ±10°, or ±5°.
Herein, the terms “liquid” and “fluid” will be used interchangeably; furthermore, the term “cleaning” will be used to describe all or any of the potential mechanical, disinfecting or chemical effects of cavitation oscillations on surrounding environment (e.g., debridement, material removal, irrigation, disinfection, decontamination, e.g. of surfaces of the cavity, cleaning, and/or fragmentation of particles within such cavities). For example, removal of material may refer to removal of material, such as bacteria or debris (e.g., plaque, calculus, dirt, particulate matter, adhesives, biological matter, residue from another cleaning process, dust, stains, etc.) located on surfaces of the liquid reservoir, and/or suspended within the liquid filling the cavity.
Moreover, the terms electromagnetic radiation (e.g., light or laser light) will be used to describe any electromagnetic radiation, where the source of the electromagnetic radiation may be a laser, laser diode, diode, lamp or any other source configured to produce the electromagnetic radiation having the wavelength that is substantially absorbed in the liquid, either in a linear or non-linear regime. A substantial or significant absorption means in the context of the present invention any absorption of the electromagnetic radiation energy to such an extent, that bubbles are generated within the liquid (e.g. as further described below). Said substantial or significant absorption covers in particular the interaction of laser light having a wavelength in a range from above 0.4 μm to 11.0 μm inclusive, including both wavelength in the range from about 1.3 μm to about 11.0 μm being highly absorbed in OH containing liquids, and wavelength in the range from about 0.4 μm to about 1.3 μm being weakly absorbed in OH containing liquids. However, any other suitable radiation and wavelength is covered like IPL (Intense Pulse Light) from flashlamp sources, in particular with wavelength above 1.3 microns or in the UV region when focused, as well as green flashlamp or diode light in blood. A further option within the invention is the use of a radiofrequency (RF) radiation source and its RF radiation. Within the scope of the present invention further wavelengths may be contemplated in particular in combination with liquids having added absorption enhancing additives.
For the purposes of describing the present invention, the conditions under which a laser light is highly absorbed in a liquid is roughly divided into a linear, or thermal regime, and a non-linear regime. A linear absorption regime applies when laser pulse power density in a liquid is not high enough to result in the ionization or in other non-linear interactions with liquid molecules. Typically, lasers with pulse durations in a microsecond or millisecond range (from one microsecond to about 5000 μs), such as flash-lamp pumped free-generation Er:YAG lasers, operate in a linear regime. In this regime, the intensity I of laser light exponentially diminishes with distance x within a liquid according to I˜exp (−kx), where k (in cm−1) is a linear absorption coefficient of the liquid at the particular laser wavelength. The absorption coefficient k and the corresponding penetration depth, l=1/k, are strongly wavelength dependent. For example, the penetration depth of the Er:YAG laser wavelength of 2.94 μm in water is approximately 10−4 cm while the penetration depth of the Nd:YAG laser wavelength of 1.064 μm is 1 cm. According to this definition, laser wavelengths with 1>1000 μm in the linear regime may be defined as “weakly absorbed” wavelengths. For water, and other OH-containing liquids, the applicable range of highly absorbed wavelengths extends from about 1.3 μm, inclusive, to about 11 μm, and the applicable range of weakly absorbed wavelengths extends from about 0.4 μm to 1.3 μm. In another example, when the liquid is blood, the 532-nm wavelength of a frequency doubled Nd:YAG laser, the 585 nm wavelength of the pulsed-dye laser or the 568 nm wavelength of the Krypton laser, are of interest since they are strongly absorbed in blood's oxyhemoglobin, with their k being approximately within 300-500 cm−1 range.
At extremely high laser power densities, on the order of about of 1010-1011 W/cm2, an “optical breakdown” as a result of the ionization of liquid molecules may occur, leading to an abrupt increase in liquid's absorption. In this, non-linear regime, a high absorption of laser light is observed even for weakly absorbed wavelengths, i.e., for wavelengths which have a long penetration depth p in the linear regime. Non-linear conditions are typically achieved with high pulse power Q-switched laser beams, with pulse durations (tp) in a nanosecond range (from one nanosecond to about 100 ns), especially when these beams are focused into a sufficiently small volume of the liquid. But other high pulse power lasers with even shorter pulse durations, in the picosecond and femtosecond range, may be used to generate cavitation in liquids as well.
It is to be appreciated that when an optical path of a weakly absorbed high pulse power laser beam has a focal point located within a liquid, the beam will propagate within the liquid without being appreciably absorbed until it reaches the focal region where the laser power density becomes sufficiently high for non-linear effects to occur. It is only at this point that a bubble formation will occur.
The apparatus for applying pulses of electromagnetic radiation, e.g. including a laser system for generating laser pulses, can be configured to deliver pulses to a liquid in a contact or a non-contact manner. In a contact scenario, the pulses are delivered to the liquid through an exit surface of an optical exit component (e.g., fiber, fiber tip, optical window, lens) which is at least partially submersed into the liquid. The (laser) light's focus is located at the exit surface of the exit component, and the bubble develops in a contact with the exit surface of the submersed optical exit component.
In a non-contact scenario, the optical exit component is configured to be positioned above the surface of the liquid reservoir, with the (laser) pulse energy being directed through air and possibly other transparent materials (such as, for example an eye lens in case of ophthalmic applications) into the liquid reservoir. In a non-contact scenario, the beam is substantially focused to a point located bellow the liquid surface by means of an appropriate focusing device, and the resulting bubble does not develop in a contact with the optical exit component.
It is to be appreciated that the contact manner is more suitable for configurations when (laser) light is absorbed in a linear regime, and the non-contact manner is more suitable for configurations when (laser) light is absorbed in a non-linear regime. However, either of the delivery manners can be used in a linear or a non-linear regime.
Apart from the proper setting of the pulse repetition time, there is a further condition that needs to be fulfilled in order for a shock wave being created also in small cavities: The energy of the subsequent pulse must be delivered at a location nearby the prior bubble but not within the prior bubble. In the opposite case, the energy of the subsequent pulse will not be initially absorbed in the liquid but shall first pass through the prior vapor bubble and will be absorbed at the prior bubble's wall area generally opposite to the direction of the laser beam. This would result in extending the length of the prior bubble in the direction of pulse emission and would therefore shift the bubble's dynamics from the contraction to expansion phase, effectively preventing the formation of a shock wave.
When both pulses are focused to the same spot within the liquid, the second condition can be fulfilled only when the subsequent pulse is emitted when the prior bubble has already moved sufficiently away from its initial position, i.e., from the point in the liquid where energy is being locally absorbed within the liquid. Such movement occurs naturally in contact delivery scenarios where during its contraction phase the bubble separates and moves away from the exit surface of the optical exit component. In one of the embodiments, a highly absorbed wavelength may be delivered into a narrow, tube like reservoir, such as a root canal or a blood vessel, by a submerged fiber or fiber tip. In this configuration, the fluid dynamics has been observed to be such that during its contraction phase the bubble separates from the fiber end and moves away from the fiber. This allows the subsequent bubble to develop at the fiber end separately from the prior bubble, and by its expansion to cause the surrounding liquid to exert pressure on the prior bubble during its contraction.
The bubble may move away from the laser's focal point also in non-contact scenarios, providing that the confined reservoir wall's geometry is asymmetrical with regard to the bubble, and the resulting asymmetrical liquid flow shifts the bubble away from its original expansion position.
In another embodiment, the second condition may be fulfilled by physically moving the fiber to a different position within the liquid during the repetition time of the two laser pulses. In yet another embodiment, it is the laser focal point which may be moved in between the pulses, for example by a scanner.
It is to be appreciated that the invention is not limited to the emission of only two subsequent pulses within a pulse set. A third pulse following a second laser pulse, and fulfilling both conditions, may be delivered resulting in an emission of a shock wave by the previous (second) bubble. Similarly, an nth subsequent laser pulse will result in an emission of a shock wave by the (n−1)th bubble, and so on as further laser pulses are being added to the set of pulses. The more laser pulses are delivered in one pulse set, the higher is the laser-to-shock wave energy conversion, with the energy conversion efficiency being proportional to the ratio (n−1)/n where n is the total number of laser pulses delivered in a pulse set. Additionally, repetitive cavitations and shock wave emissions generate an ever-increasing number of longer persisting gas (e.g., air) micro-bubbles within a liquid. These micro-bubbles compress and expand under the influence of cavitation oscillations and shock waves, and thus improve the overall cleaning efficacy by contributing to the high-speed fluid motion.
In summary, when a pulsed laser beam which is highly absorbed in a liquid, either in a linear or non-linear regime, is delivered to such a liquid, a bubble oscillation sequence develops, typically with a temporal oscillation period (TB) in the range from about 50 μsec to about 1500 μsec. The oscillation is damped and lasts for only a few rebounds due to the bubble's energy being spent for heating, moving and displacing the liquid, and under appropriate conditions, also for emitting shock wave acoustic transients. For the purposes of cleaning it is desirable that as much as possible of the bubble's energy is spent in the emission of violent shock waves during the contraction phases of the bubble's oscillation, and preferably at least during the first bubble's contraction phase when the bubble's energy is still high. However, in spatially small reservoirs or in highly viscous liquids, more energy is wasted for overcoming the friction on the cavity walls and to fight against the resistance of the water which has to be displaced in the small reservoir, and/or for overcoming viscous damping. Consequently, the bubble's maximal volume is reduced, and the bubble's contraction is slowed down, resulting in a lower amplitude shock wave or no shock wave at all, as outlined above. By applying a first and a second pulse with the pulse repetition time controlled according to the present invention, shock waves may be generated in an effective and efficient way, such that also small cavities can be cleaned, irrespective of their diameter.
In an example, the apparatus may further comprise a user interface for receiving information on a diameter of the cavity. Hence, the respective user of the apparatus may input e.g. a value for a diameter of the cavity which he may know or estimate from his general practice for the type of cavity at hand or which he may (e.g. visually) estimate or measure for a specific cavity. Based thereon, the control unit controls the time between the first pulse and the second pulse accordingly. Hence, a very easy-to-operate but at the same time effective cleaning device is provided. It is to be appreciated that the expression “input” is to be understood broadly, describing any means of providing information to the user interface by the user, including but not limited to using typing in, e.g. by a keyboard, a touchpad, a touchscreen, a mouse, and/or a pointing device, also including visual and/or verbal commands.
For example, for dental applications, the user may input a tooth type, a cavity type and/or any other information on a characteristic dimension of the access cavity (for example a minor and/or major diameter, etc.). The control unit may determine, based on the user input (e.g. the tooth type, the cavity type, etc.), further information (e.g. a minor and/or major diameter for the tooth type). Exemplary values for tooth types and further information, e.g., suitable values for minor and/or major diameters associated with the tooth types are shown in Table 1. In some example, (only) two tooth types may be distinguished: a first minor and/or a first major diameter may, e.g., be associated with molar teeth (first type), and a second minor and/or a second major diameter may, e.g., be associated with all other teeth (second type). The further information may be stored in a storage device of the apparatus and/or a remote storage device, e.g. in the form as a look-up table or database. The control unit may, based on the user input and/or the further information automatically adjust the time between the pulses.
In an example, the apparatus may comprise a user interface for receiving information on the cross-sectional area of the cavity. As outlined above regarding a diameter of the cavity, similar benefits may be obtained by using information on the cross-sectional area of the cavity.
In addition or as an alternative to the mentioned user interface, in some examples, the apparatus may further comprise means for determining the diameter and/or cross-sectional area of the cavity. For example, the means for determining may provide, e.g., fully automatically, (information on) a diameter and/or cross-sectional area of the cavity. To this end, the means for determining may comprise a sensor unit. For example, a camera with corresponding image analysis software may be provided, or any other optical and/or acoustic sensor unit for measuring a diameter or cross-sectional area may be provided.
Additionally or alternatively, the means for determining may require operator intervention to determine the (information on) the diameter and/or cross-sectional area. The information may then e.g. be input by the user into the user interface. For example, a (microscope) objective and/or lens may be provided together with a scale (e.g., integrated with the apparatus), such that the operator may simply estimate or read the diameter/cross-section and subsequently enter it into the user interface. In other examples, e.g. a camera is provided such that the corresponding information is automatically determined by the means for determining. In both cases, the information on the diameter/cross-sectional area may be determined in-situ, such that separate measurements with different devices can be avoided.
In some examples, the control unit may be adapted to control the time between the first pulse and the second pulse such that it varies with the inverse root of the diameter of the cavity. As an alternative, also an implementation that lets the time vary as 1/(cross-section of the cavity)1/4 or any other mathematical relation that essentially leads to a dependence of the time on the inverse root of a diameter of the cavity is considered to fall within such an implementation. Such control has turned out to be particularly effective. This is attributed to the experimental finding that the bubble oscillation period, and hence the optimal pulse repetition time, approximately varies with the inverse root of the diameter of the respective cavity. This relation is particularly strong for cavity diameters of 8 mm and smaller.
Particularly for the case that the apparatus is to be used for different laser parameters (e.g. laser pulse energies, wavelength, duration, the characteristics of the employed (contact or non-contact) delivery, beam spot size, diameter of fiber tip, beam shape, beam angle, fiber tip shape, etc.) and/or different liquids (e.g. having different viscosity), the control unit may be further adapted to control the time between the first pulse and the second pulse as a function of one or more laser parameters and/or the liquid.
Generally, when the same apparatus is intended to be used for cleaning differently sized cavities, containing different liquids, and with different laser parameters, this poses a challenge since the bubble oscillation time (TB), and consequently the required pulse repetition time (Tp-opt) depends critically on a myriad of parameters, the bubble oscillation time being longer, for example, for higher laser pulse energies and smaller reservoirs, and/or for more viscous liquids.
However, typically all or at least most of these parameters are a-priori known or “controlled”. Notably, the inventors of the present invention have found that the set of “controlled” parameters can be reduced to a single parameter that, together with the diameter/cross-section of the cavity can be used to control the temporal pulse spacing.
This is based on the experimental finding that the influence of all controlled parameters (i.e., all parameters except for the cavity dimensions) can be approximately described by a single parameter, the “unconstrained” or free bubble oscillation period (To) representing the bubble dynamics under the conditions when the cavity dimensions are “infinitely” large, i.e., when the bubble dynamics is not affected by the spatial containment caused by the uncontrolled cavity dimensions. Further, it is our surprising finding that the optimal pulse repetition time (Tp-opt) is determined with sufficient accuracy solely by the known unconstrained bubble oscillation period (To) in combination with a characteristic cavity dimension (S), e.g. a diameter or a cross-sectional area of the cavity, characterizing the influence of the uncontrolled cavity dimensions on the damping of the bubble's oscillation.
In an example, the control unit may be adapted to control the time between the first pulse and the second pulse as a function of a predetermined parameter that is specific to at least an energy of the first pulse and/or to the liquid. Hence, the control unit may adapt the time in a particularly easy and efficient way, by simply using a single predetermined parameter (in addition to the information on the cavity diameter/cross-sectional area) corresponding to the respectively used pulse energy and/or liquid. In some examples the predetermined parameter may also be specific to other controlled parameters. Hence, the pulse repetition time may also be adapted to other controlled parameters in a simple manner, such that also for these, an efficient cleaning can be provided.
It is noted that the predetermined parameter may be independent of the geometry of the cavity. That is, it may be a universal parameter that only depends on the controlled parameters.
Moreover, in some examples the predetermined parameter corresponds to an unconstrained oscillation period To of a bubble that would be generated by the first pulse in an infinitely large cavity filled with the liquid.
In some examples, the control unit is adapted to determine the predetermined parameter by accessing a data storage device of the apparatus and/or a remote data storage device. For example, the predetermined parameter (e.g., unconstrained oscillation period) may be predetermined for each particular liquid and/or pulse energy (and/or further controlled parameters), for example. It may then be made available to the control unit either by storing it on a data storage device of the apparatus and/or a remote data storage device. When the user of the device wants to use different optical power and/or a different liquid (or changes any other controlled parameter), the new optimal pulse repetition time may simply be calculated based on the correspondingly altered predetermined parameter (e.g. the corresponding unconstrained oscillation period and the cavity diameter).
In some examples the predetermined parameter may be stored, as outlined above, in the form of a look up table. For the respectively used controlled parameters, the corresponding predetermined parameter may be read out by the control device, if needed. Based thereon, the temporal pules spacing may then be determined in a simple manner as also outlined above.
Similarly, as described with respect to the information on a diameter and/or cross-sectional area of the cavity, the user may also input the information on the unconstrained oscillation period (e.g. a specific unconstrained oscillation period) corresponding to the particular set of selected controlled parameters into the user interface. For example, the control unit may then control the pulse repetition time accordingly. In other words, the user interface may be adapted to receive information on the unconstrained oscillation period (e.g. a specific unconstrained oscillation period).
The user interface may, additionally or alternatively, be adapted to receive information on one or more controlled parameters and/or the diameter and/or cross-sectional area of the cavity. Additionally or alternatively, the apparatus may be adapted such that the information on one or more controlled parameters and/or the diameter and/or cross-sectional area of the cavity (e.g. as set by a (semi-)automatic mode of the apparatus for a certain mode selected by the user, etc.) are automatically provided to the control unit. The control unit may then determine the predetermined parameter based on the information received by the user interface and/or the information automatically provided.
It is particularly beneficial to unite the influence of all controlled parameters into the predetermined parameter (e.g. the unconstrained oscillation period). For example, if an operator wants to change, e.g. the size of a fiber tip with which the pulses are applied, the corresponding unconstrained oscillation period for the new tip size may be determined, and the corresponding new pulse repetition time may be easily calculated based on this single altered parameter. In some examples, the altered parameter and/or the new pulse repetition time may be displayed by the user interface (e.g., by means of a (touch-)screen, an LCD, TFT and/or LED display, etc.).
In some examples, the control unit may be adapted to control the time between the first pulse and the second pulse such that it is proportional to the predetermined parameter. This control has turned out to be particularly effective. It is attributed to the experimental finding that the bubble oscillation period of the pulses has been found to approximately vary linearly with the predetermined parameter (e.g., the unconstrained oscillation period).
The control unit may be adapted to control the pulse repetition time as a function of information on the diameter and/or cross-sectional area and the predetermined parameter, only.
In some examples, the control unit may be adapted to control the time according to the function KD×To×D−0.5, wherein KD is selected from the range 2 mm0.5 to 4.8 mm0.5, preferably from the range 2.5 mm0.5 to 3.8 mm0.5, and more preferably from the range 2.7 mm0.5 to 3.8 mm0.5 (and wherein D is a diameter of the cavity, and To is the predetermined “unconstrained oscillation period”).
In some examples, the control unit may be adapted to control the time according to the function KA×To×A−0.25, wherein KA is selected from the range 2 mm0.25 to 4.1 mm0.25, preferably from the range 2.5 mm0.25 to 3.3 mm0.25, and more preferably from the range 2.7 mm0.25 to 3.3 mm0.25 (and wherein A is an area of the lateral surface of the cavity, and To is the predetermined “unconstrained oscillation period”).
In some examples, the control unit is adapted to control the pulse repetition time Tp such that the subsequent bubble, i.e., the bubble generated by the subsequent laser pulse, starts to expand when the prior bubble has already started to contract, i.e., when Tp is in a range from about 1.2×(TB/2) to about 1.95×(TB/2), preferably in a range from about 1.5×(TB/2) to about 1.9×(TB/2), and expediently in a range from about 1.6×(TB/2) to about 1.9×(TB/2). This may be achieved, e.g., by using the aforementioned functional relationship between Tp, To, and D (or correspondingly any characteristic dimension other than D).
Note that in simple embodiments, the controlled parameters may be fixed such that also the unconstrained oscillation period To may be fixed. The control unit may thus be adapted to adjust the pulse repetition rate Tp, as a function of (only) the information on the characteristic dimension S of the cavity and the fixed To, to at least approximately correspond to the required optimal pulse repetition rate Tp-opt. To this end, the inventive relations, Tp-opt˜To×Dave−0.5, or Tp-opt˜To×Als−0.25 may be used, e.g. using constants KD and KA as outlined herein.
It is noted that, throughout the present disclosure, it is assumed that the first pulse is adapted to generate a first bubble within the liquid, and the second pulse is adapted to generate a second bubble within the liquid. By means of the control of the pulse repetition time by the control unit as described herein, it can be ensured that a shock wave is generated within the liquid, as explained above.
In some examples, the apparatus may further comprise means for providing the liquid to the cavity. This may make the cleaning of the cavity particularly quick and convenient, since all necessary steps may be carried out with a single apparatus.
The control unit may also be adapted to determine an optimal pulse repetition time Tp opt and to vary pulse repetition times between subsequent pairs of pulses within a range from Tp-opt-δ1 to Tp-opt+δ2, wherein δ1 and δ2 are selected from the range 10 μs to 300 μs, preferably from 20 μs to 75 μs and more preferably from 25 μs to 75 μs. This may be beneficial since it is ensured that the pulse repetition time is swept within an optimal range, such that the cleaning may be more efficient. This is attributed to the fact that the optimum pulse repetition time (e.g. determined from the “unconstrained bubble oscillation period” and a “diameter” of the cavity) provides an excellent estimation but may still not be 100% accurate. By sweeping the pulse repetition time within a small window around the estimated optimum pulse repetition time, it may be ensured that the true optimum pulse repetition time is achieved. This may be particularly useful for cavities with particularly irregular dimensions. The aspects of the present invention specifically allow to significantly reduce the interval within which the sweeping is to occur such that the efficiency of the cleaning is greatly improved.
In another aspect, a method is provided for applying pulses of electromagnetic radiation to a cavity filled with a liquid. A first pulse and a second pulse of electromagnetic radiation are generated. The time between the first pulse and the second pulse is controlled as a function of a diameter D and/or a cross-sectional area of the cavity.
It is noted that all aspects outlined herein with respect to the apparatus may also be part of the methods described herein, in the form of a corresponding method step, even if not explicitly mentioned.
For example, the method may include the step of controlling the time between the first pulse and the second pulse as a function of a controlled parameter (e.g. a pulse energy or the liquid), or a predetermined parameter that is specific to at least an energy of the first pulse and to the liquid.
For following the above mentioned inventive findings, the pulses as they are known in the prior art may be replaced by pulse sets according to the present invention whose temporal spacing or pulse repetition time (i.e., the time from the beginning of a pulse until the beginning of the subsequent pulse) is controlled accordingly. The individual pulses may be combined to pulse sets consisting of a minimum of two and maximally 20 individual pulses, with the intra-set pulse repetition times typically in the range from 50 μsec to 900 μsec, and the pulse sets being temporally separated from each other typically by at least 10 ms.
A further aspect is the use of the laser pulses as described herein for application to a cavity filled with a liquid, and in particular for cleaning the cavity.
The proposed laser system and method may be used for any kind of human or animal cavity (e.g. body or anatomical cavities), or any non-human or non-animal cavity, e.g. industrial or machinery cavities.
According to further examples, the apparatus may be provided as a cleaning system that is configured for cleaning of cavities filled with a liquid. The cavities may have lateral surface characterized by a minor inner diameter and/or major inner diameter (Dmin, Dmax), that vary from cavity to cavity. The cleaning system may comprise an electromagnetic radiation system, a control unit and, optionally, the liquid. The electromagnetic radiation system may comprise a radiation source for generating a radiation beam and an optical delivery system for the radiation beam. The delivery system may include a handpiece with an exit component, wherein the exit component may be configured to be inserted into the cavity with an insertion depth (h), wherein the handpiece and the exit component are configured to irradiate the liquid within the cavity with the radiation beam. The wavelength of the radiation beam may be chosen for significant absorption of the radiation beam in the liquid. The electromagnetic radiation system is adapted to be operated in pulsed operation with at least one pulse set containing at least two individual pulses (p) having each an individual pulse energy, wherein within the pulse set a first pulse (pa) of the pulses (p), having a pulse duration (tp) and pulse energy (EL), is followed by a second pulse (pb) of the pulses (p) with a pulse repetition time (Tp). The electromagnetic radiation system is adapted to generate a first vapor bubble within the liquid by means of the corresponding first pulse (pa) and to generate a second vapor bubble within the liquid by means of the corresponding second pulse (pb). The controlled parameters of the cleaning system and the cavity may be characterized by the unconstrained oscillation period To of the first vapor bubble for cavities with infinitely large minor and major diameter, wherein the control unit (22) is adapted to adjust for each cavity the pulse repetition time (Tp) to the optimal pulse repetition time (Tp-opt) depending on the unconstrained oscillation period To of the first vapor bubble and on the size of the lateral surface, such that the interaction between the first vapor bubble and the second vapor bubble generates a shock wave within the liquid.
The control unit may be adapted to adjust the pulse repetition time (Tp) to be varied or “swept” in discreet positive or negative steps Δ from an initial pulse period Tpo to a final pulse period Tpm, preferably +− across a range from Tpo=Tp-opt−δ1 to Tpm=Tp-opt+δ2 (or from Tpo=Tp-opt+δ2 to Tpm=Tp-opt−δ1 in the case of a negative Δ), where δ1 and δ2 are each preferably in a range from 10 to 300 μsec, even more preferably in a range from 20 to 75 μsec, and expediently in a range from 25 to 75 μsec.
The control unit may be adapted to calculate the optimal pulse period (Tp-opt) from the unconstrained bubble oscillation period (To) and an average diameter (Dave) of the lateral surface (Dave) using Tp-opt=FS×To×Cave×Dave−0.5 whereas the average diameter coefficient (Cave) is equal to Cave=3.74 mm0.5 and whereas the shock wave enhancing factor (FS) is in a range from about 0.6 to about 1.2, preferably in a range from about 0.75 to 0.95, and expediently in a range from about 0.8 to about 0.95.
Similarly, according to an aspect, a method is provided for cleaning a cavity, e.g. a dental root canal, filled with liquid, such as water or another irrigant. The method comprises the following steps:
Alternatively, a sweep configuration may be used instead of a fixed pulse repetition time (Tp), wherein Tp is being swept in a range from Tp-opt−50 μs to Tp-opt+50 μs.
More generally, various shortcomings of prior art medical and biomedical devices and methods (“medical” is understood as including “dental” techniques, for example, endodontic techniques, and other “medical” techniques) can be addressed by utilizing an apparatus or other exemplary system configured in accordance with principles of the present disclosure. Outside of the medical field, control of bacteria or other undesirable matter, such as dirt, particulate matter, adhesives, biological matter, residues, dust and stains, in various systems is also important. Further, cleaning and removal of various materials from surfaces and openings may be required for aesthetic or restoration reasons.
Embodiments of the invention will be explained in the following with the aid of the drawings in more detail. With reference to the following description, appended claims, and accompanying drawings:
With reference now to
In the shown preferred embodiment, the apparatus is implemented as electromagnetic radiation system, and more particularly, laser system 1. The source for generating pulses is implemented as laser source 4, generating a radiation beam, more particularly a laser beam 5, e.g. including laser pulses. Laser system 1 comprises at least one laser source 4 for generating at least one laser beam 5 (cf.
Laser system 1 further comprises a schematically indicated control unit 22 for controlling laser beam 5 parameters, wherein control unit 22 includes again schematically indicated adjusting means 10 for adjusting the laser beam 5 parameters as described herein, particularly for controlling the pulse repetition time.
The control unit may be implemented as a computer-related entity, either hardware, firmware, a combination of hardware and software and/or firmware, software, or software in execution, e.g. as a computer. The various functions of the control unit may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a data store. A data store can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, or digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, or DSL are included in the definition of medium.
Optical delivery system 6 preferably includes an articulated arm 14 and/or a handpiece 7, wherein the laser beam 5 is transmitted, relayed, delivered, and/or guided from the laser source 4 through the articulated arm 14 and the handpiece 7 to a target. The articulated arm 14 might preferably be an Optoflex® brand articulated arm available from Fotona, d.o.o. (Slovenia, EU). In the shown preferred embodiment, a second laser source 4′ and a second optical delivery system 6′ with a second handpiece 7′ is provided, wherein instead of the articulated arm a flexible elongated delivery fiber 19 for guiding the laser beam 5′ is incorporated. Despite both laser sources 4, 4′ and delivery systems 6, 6′ being shown in combination, one of both in the alternative may be provided and used within the scope of the present invention.
Moreover, laser system 1 may be configured with any appropriate components and/or elements configured to facilitate controlled application of laser energy, for example, in order to create vapor bubbles in a liquid 3 within a cavity 2 for cleaning (including debridement, material removal, irrigation, disinfection, and/or decontamination of said cavity 2 and/or fragmenting particles within such cavities), as shown and described herein.
With reference now to
The laser source 4 may be a pulsed laser. The laser source 1 may be solid state laser source and configured with a pulse duration of less than 500 μs. The laser pulse duration is defined as the time between the onset of the laser pulse, and the time when 50% of the total pulse energy has been delivered to the liquid. The pulse duration may be fixed; alternatively, the pulse duration may be variable and/or adjustable. The pulse energy may be fixed; alternatively, the pulse energy may be variable and/or adjustable. The wavelength of the laser beam 5 may be in a range from (above) 0.4 μm to 11.0 μm inclusive. As illustrated in
The laser source 4, 4′ may desirably be configured to generate coherent laser light having a wavelength such that the laser beam 5 is highly absorbed in the liquid 3, wherein the laser pulse duration is in the range of us and ≥500 μs, and preferably of ≥10 μs and <100 μs.
Preferably, the laser source 4, 4′ is one of an Er:YAG solid state laser source having a wavelength of 2940 nm, an Er:YSGG solid state laser source having a wavelength of 2790 nm, an Er:Cr:YSGG solid state laser source having a wavelength in a range of 2700 to 2800 nm, an Er:YAlO3 solid state laser having a wavelength of 2690 nm, a Ho:YAG solid state laser having a wavelength of 2100 nm, a CO2 or CO gas laser source having a wavelength of 9000 nm to 10600 nm, all of them providing a laser beam 5 highly absorbed in water and other OH-containing liquids.
In particular, the laser source 4 and/or laser source 4′ may be an Er:YAG laser having a wavelength of 2940 nm, wherein the laser pulse energy is in a range from 1 mJ to 100 mJ, preferably from 1 mJ to 40 mJ, and more preferably within a range from 5.0 mJ to 20.0 mJ. This type of laser source may be combined with an exit component 8 that is cylindrical, having a diameter between 200 μm and 1000 μm, wherein the conical output surface 13 has a conical half angle α being in the range from 16° to 38°, preferably from 34° to 38°, wherein the temporal separation Ts between pulse sets 21 is <0.5 s, and wherein the cumulative delivered energy during a cleaning session is below iso J.
Additionally or alternatively, laser source 4 and/or laser source 4′ is configured to generate coherent light having a wavelength highly absorbed in OH-containing liquids, e.g., by means of one of an Er:YAG laser source having a wavelength of 2940 nm, an Er:YSGG laser source having a wavelength of 2790 nm, an Er:Cr:YSGG laser source having a wavelength of 2780 nm or 2790 nm, or a CO2 laser source having a wavelength of about 9300 to about 10600 nm. The laser pulse energy may be in a range from 1 mJ to 500 mJ.
Other examples of laser sources 4,4′ with a laser wavelength highly absorbed in water and other liquids include quadrupled Nd:YAG laser which generates light having a wavelength of 266 nm; an ArF excimer laser which generates light having a wavelength of 193 nm, an XeCl excimer laser which generates light having a wavelength of 308 nm, and a KrF excimer laser which generates light having a wavelength of 248 nm.
In another embodiment, laser source 4 and/or laser source 4′ may be one of a frequency doubled Nd:YAG laser source having a wavelength of 532 nm, a dye laser source having a wavelength of 585 nm, or a Krypton laser source having a wavelength of 568 nm, all of them providing a laser beam 5 highly absorbed in oxyhemoglobin within blood vessels.
Alternatively, the laser source 4, 4′ may be configured to generate coherent laser light having a wavelength such that the laser beam 5 is weakly absorbed in the liquid 3, wherein the laser pulse duration is in the range of 1 fs and <100 ns, and preferably of ≤1 ns and <25 ns. To this end, the laser source 4 and/or the laser source 4′ may be one of a Q-switched Nd:YAG laser source having a wavelength of 1064 nm, a Q-switched ruby laser source having a wavelength of 690 nm, or an alexandrite laser source having a wavelength of 755 nm, including laser sources 4, 4′ with frequency doubled wavelengths of these laser sources 4, 4′, all of them providing a laser beam 5 weakly absorbed in water and other OH-containing liquids. For such weakly absorbed wavelength the pulse energy of one individual laser pulse p is in the range from 0.05 mJ to 1000 mJ, preferably in the range from 0.5 to 200 mJ, and in particular from 1 mJ to 20 mJ.
Moreover, any other suitable laser source 4, 4′ may be utilized, as desired. In certain embodiments, the laser source may be installed directly into the handpiece 7, 7′, and no further laser light delivery system 6, 6′ such as the articulated arm 14 or elongated delivery fiber 19 is required. Additionally, such handpiece may not be intended to be held in hand but may be built into a table-top or similar device as is the case with laser photo-disruptors for ocular surgery.
Laser system 1 comprises a user interface 3o. User interface 3o comprises a screen and a plurality of keys and/or buttons.
The handpiece 7, 7′ includes an exit component 8, through which the laser beam 5 exits the delivery system 6, 6′ for entering the liquid 3, as shown in
For the “contact” scenario as shown in
In one of the embodiments of our invention, the laser system 1 comprises a sensor system 9 to determine a characterizing dimension of the cavity, e.g. of its lateral surface 27. For example, the sensor may determine information on a diameter and/or a cross-sectional area of the cavity and provide it to the control unit. The sensor system 9 preferably comprises an optical and/or an acoustical measurement sensor for sensing the lateral surface size.
Furthermore, the laser system 1 comprises control unit 22 for controlling the pulse repetition time Tp to achieve at least approximately that the subsequent bubble 18′, i.e., the bubble 18′ generated by the subsequent laser pulse pb, starts to expand when the volume of the prior bubble 18 has already contracted to the desired size as described above. This control may be implemented by control unit 22, e.g. via its adjusting means 10 adapted to adjust the repetition time of pulses emitted by laser source 4 and/or 4′. For example, the control unit may determine a specific repetition time, and trigger the adjusting means 10 to control the laser source accordingly. For example, the adjusting means may be an actuator of the laser source or it may simply an electronic control input of the laser source that alters the pulse repetition time according to steps as known in the art. The control unit may thus automatically ensure that pulses are delivered at the appropriate Tp-opt depending on the cavity dimension (e.g. diameter, cross-sectional area) and/or one or more controlled parameters. However, the laser pulse repetition time Tp might also be manually adjusted by the user, e.g. to be approximately equal to Tp opt, e.g., corresponding to the cavity dimension and/or one or more controlled parameters.
When the handpiece 7, 7′, and its exit component 8 are configured for a non-contact delivery (
Moreover, handpiece 7 may comprise any suitable components or elements configured for targeted and/or controllable delivery of laser energy to a liquid 3. Preferably, the laser system 1 comprises a scanner 15 as schematically indicated in
Turning now to
In one preferred embodiment the exit tip 24 of the exit component 8 has a flat output surface 11 (
In another embodiment as shown in
Typically, when fiber tips with output surface 13 are used, the laser beam 5 extends substantially across the whole output surface 13. This will result in a circumferentially spread exiting beam portion 12. In certain embodiments, however, as shown in
With reference now to
It is also to be appreciated that with shock waves generated according to present invention, conically shaped tips may get more quickly damaged during the violent shock wave emission, and therefore it may be advantageous to use flat surface fiber tips with the present invention.
Moreover, it is to be appreciated, that when in certain embodiments a weakly absorbed laser beam is delivered to a liquid 3 in a non-contact manner, and the beam's focus is located within the liquid 3, and away from the liquid surface, no bubble gets formed at or near the liquid's surface. Instead, the beam gets transmitted deeper into the liquid, and providing that the pulse duration is sufficiently short (×100 ns), and the power density at the focal point within the liquid is sufficiently high, a bubble 18 is generated only when the laser beam 5 reaches its focal point deeper within the liquid 3.
Turning now to
In the 2nd phase (from time tmax1 to time tmin1), the internal pressure is lower than the pressure in the surrounding liquid 3, and this difference in pressures forces the vapor bubble 18 to collapse.
When the vapor bubble 18 collapse completes at time Limn, a rebound occurs thereafter, and the vapor bubble 18 starts to grow again up until time tmax2. This 3rd phase (from time tmin1 to time tmax2) is followed again by a collapse in the 4th phase (from time tmax2 to time tmin2). This oscillation process of the vapor bubble 18 continues, decreasing in amplitude and temporal period each time as illustrated in
In various embodiments, a temporal bubble oscillation period TB may be defined as the time between t01 and tmin1. Temporal bubble oscillation period TB varies based at least in part on the thermo-mechanical properties of the liquid 3, the shape and volume of the liquid 3 reservoir, the laser beam 5 emission profile, pulse duration, pulse energy, and so forth. Specifically, when the liquid 3 medium is contained in an endodontic access opening, e.g. in a body cavity 2 as shown in
The exemplary dependence of the bubble's oscillation period TB on the cavity dimensions is shown in
Referring again to
T
B
=K×D
−0.5 (1)
with best fits obtained with K=475, 671, 1145 and 1320 μs·mm0.5, for pulse energies EL=5, 7.5, 19 and 26 mJ, correspondingly.
The dependence of TB on the square root of D resembles the dependence of the oscillating period Tlin of a standard damped linear oscillator on a damping factor β, as
T
lin
=T
lino×(1−(β×Tlino/2π)2)−0.5 (2)
where Tlino is the oscillating period of the linear oscillator in the absence of damping (β=0). Even though the oscillation dynamics of a three-dimensional bubble in a fluid within a constrained environment is much more complex than that of an ideal linear oscillator, we have thus found that the square root dependence applies to the bubble dynamics as well, providing that the oscillation period of an unconstrained bubble in a large reservoir (To) is assigned to a relatively large but not infinite cavity diameter of about D=14 mm. Above this diameter, the square root approximation breaks down, and the imaginary damping factor β becomes negative. We attribute this observation to the bubble characteristics according to which the bubble oscillation period starts to increase appreciably and with the square root dependence only after the cavity diameter becomes smaller than about D=14 mm.
According to the above, the data points for D=14 mm in
It is to be appreciated that the bubble implosion begins near the fiber tip where the expansion started, resulting in a separation of the bubble 18 from the fiber, as can be seen from the insert in
The foregoing oscillation dynamics of vapor bubbles 18 and 18′ and associated relation to shock wave emission, facilitate the improved inventive system for and methods of cleaning utilizing delivery of laser pulses p, for example cleaning of root canals, drilled bone, and/or the like anatomical cavities 2 preferably with Dave less than 8 mm and even more preferably with Dave≤6 mm. Moreover, and referring now to
It is to be appreciated that the invention is not limited to the emission of only two subsequent pulses within a pulse set. A third pulse following a second laser pulse, and fulfilling both conditions, may be delivered resulting in an emission of a shock wave by the previous (second) bubble. Similarly, an nth subsequent laser pulse will result in an emission of a shock wave by the (n−1)th bubble, and so on as further laser pulses are being added to the set of pulses. The more laser pulses are delivered in one pulse set, the higher is the laser-to-shock wave energy conversion, with the energy conversion efficiency being proportional to the ratio (n−1)/n where n is the total number of laser pulses delivered in one pulse set 21 (
Our experiments show that the optimal repetition time (Tp-opt) is the pulse repetition time where the subsequent bubble starts to develop during the second half of the bubble's period (TB), i.e., when Tp=Tp-opt=FS×TB where the shock wave enhancing factor (FS) is in a range from about 0.6 to about 1.2, preferably in a range from about 0.75 to 0.95, and expediently in a range from about 0.8 to about 0.95. When the same device is intended to be used for cleaning differently sized cavities, containing different liquids, and with different device parameters (laser pulse energy, for example), as mentioned, this poses a challenge since as shown in FIG. 7 the bubble oscillation time (TB), and consequently the optimal pulse repetition time (Tp-opt) depend critically on these conditions, being longer, for example, for smaller reservoirs and larger laser pulse energies.
However, for most procedures there is typically only a limited set of cavity dimensions which vary from one cleaning session to another and are not under the control of the operator or the device, as opposed to “controlled” parameters, i.e., the parameters which are under the control, at least to a sufficient degree, by the device and/or the operator. Examples of controlled parameters are the wavelength of the electromagnetic source, its pulse energy and duration, or the characteristics of the employed (contact or non-contact) delivery. Therefore when keeping all the “controlled” parameters the same, the optimal repetition time (Tp-opt) varies from cleaning session to cleaning session only as a function of the “uncontrolled” cavity dimensions. The present invention is based on the finding that particularly the lateral diameter or cross-section be advantageously used to adapt the pulse repetition time accordingly. Moreover, an aspect is also the finding that the influence of the controlled parameters, i.e., of the parameters which are at least in principle under the control of the device and the operator, can be approximately characterized by a single parameter, the “unconstrained” or “free” bubble oscillation period (To) representing the bubble dynamics under the conditions when the uncontrolled cavity dimensions are “infinitely” large, i.e., when the bubble dynamics is not affected by the uncontrolled spatially limited cavity dimensions. Further, it is our discovery that the optimal pulse repetition time (Tp-opt) can be determined with sufficient accuracy solely from the known unconstrained (“free”) bubble oscillation period (To) in combination with a characteristic cavity dimension (S), the characteristic cavity dimension S characterizing the damping influence of the constraining cavity environment (e.g. the diameter and or cross-section).
This is demonstrated in
T
B
/T
o=Cave×Dave−0.5 (3)
With the best fit obtained for the average diameter coefficient Cave=3.74 mm0.5, with the statistical coefficient of determination of R2=0.99. Typically a fit is considered good when R2≥0.7.
Similarly, and as shown in
T
B
/T
o
=C
ls
×A
ls
−0.25 (4)
with the lateral area coefficient Cls=3.50 mm0.5, with R2=0.98.
Therefore, for an “ideal” cylindrically shaped cavity, the characteristic dimension is represented either by S=D=Dave or S=Als=π×D2/4, and the optimal pulse separation (Tp) can be calculated for any value of the characteristic dimension using the predetermined unconstrained bubble oscillation period To characterizing the influence of the controlled parameters (such as the laser pulse energy in
T
p-opt
=F
S
×T
o
×C
ave
×D
ave
−0.5 (5)
or
T
p-opt
=F
S
×T
o
×C
ls
×A
ls
−0.25 (6)
where To can be predetermined by a measurement and/or calculation for any combination of controlled parameters under free reservoir conditions.
It should be appreciated that in real situations the cavities may not be cylindrical but can be of any shape, an exemplary shape being illustrated in
For an arbitrarily shaped lateral surface 27, it will be assumed that in most situations the characteristic cavity dimension S can be sufficiently well represented by either the average of the minor and major axes of the lateral surface, S=Dave=(Dmin+Dmax)/2, Also the cross-section area according to the present invention may be represented by the area of the lateral surface S=Als=π×Dmin×Dmax/4. It is to be noted that for a case of an elliptically shaped lateral, the minor and major diameters may correspond to the major and minor axes of such ellipse. For circularly shaped surface, the characteristic dimension may be represented by the diameter of the circle, and the cross-sectional area may be represented by Als=π×D2/4. However, other definitions of the characteristic cavity dimension may be appropriate when so required by the type of the procedure and of the cavity shape, including potential influence of the cavity dimension in the vertical direction.
As an example, in endodontic root canal cleaning, and as shown in
Very roughly, the clinically encountered range from small to large minor diameters, and from small to large major diameters for different tooth types and patients is depicted in in Table 1.
The exemplary measured dependence of the bubble's oscillation period TB on the average diameter of the lateral surface, Dave=(Dmin+Dmax)/2 of the endodontic access opening is shown in
Referring again to
When analogously to
Similarly, when the bubble oscillation period data TB according to
Therefore, for the embodiments of our invention where the size and shape of the lateral surface 27 represent the most significant uncontrolled varying cavity size influencing the bubble dynamics, the pulse separation times which are about optimal for most of the cavities can be taken to be the same as for an ideal cylindrical cavity, and are thus determined according to Eq. 3 using Dave=(Dmin+Dmax)/2, and Cave=3.74 mm0.5 or according to Eq. 4 using Als=π×Dmin×Dmax/4, and Cls=3.50 mm0.5.
However, for some procedures where there exists a sufficiently strong correlation between sizes of Dmin and Dmax, the minor or major diameter alone can represent a statistically significant characteristic dimension. For example, for the endodontic data according to
T
B
/T
o
=C
min
×D
min
−0.5 (7)
where Cmin=3.45 mm0.5 with R2=0.75; and
T
B
/T
o
=C
max
×D
max
−0.5 (8)
where Cmax=3.95 mm0.5 with R2=0.70, resulting in
T
p-opt
=F
S
×T
o
×C
min
×D
min
−0.5 (9)
and
T
p-opt
=F
S
×T
o
×C
max
×D
max
−0.5 (10)
It is noted that the ranges indicated above for parameters KD and KA approximately correspond to the ranges of the products FS×Cave, FS×Cmin, FS×Cmax, and of the product FS×Cls respectively.
Further, it is also within the present scope that more specific ranges of KD relate to ranges of each of FS×Cave, FS×Cmin, and/or FS×Cmax individually, wherein Fs varies within the preferred ranges as outlined herein and Dave, Dmin, Dmax would be used as D (in the formula KD×To×D−0.5). Similarly, the ranges specified for KD may also be used instead of those for KA (in KA×To×A−0.25), providing that the units for KD (in mm0.5) are replaced by units for KA (in mm0.25).
It is to be appreciated that the function as given by Eq. 1 represents only one of possible fitting functions to the oscillation data. For example, our analysis shows that a very good fit to the oscillation data can be obtained also by using the following function:
T
B
=T
o(1+Ki/Di), (11)
leading to
T
p-opt
=F
s
×T
o(1+Ki/Di), (12)
wherein Di represents one of the main lateral dimensions of a treated cavity, Dmin, Dmax or Dave, and Kmin, Kmax and Kave are the corresponding fitting parameters. As above, the time To represents the bubble oscillation time for the infinitely wide cavity (Di≈∞).
For the oscillation times in endodontic access cavities, as shown for example for Dave in
In one of the exemplary embodiments an Er:YAG laser was used to perform enhanced irrigation of the access opening and root canals, where the set of relevant controlled parameters includes laser pulse energy (EL), laser pulse duration (tp), the fiber tip geometry: a flat fiber with output shape 11 or a pointed fiber with output shape 13, the fiber tip's diameter D, and the depth of insertion h. The corresponding values of the bubble oscillation period for an infinitely large lateral surface 27 of the endodontic access cavity 28, as obtained using the same fitting technique as presented in
It is to be appreciated that the values of To for EL, tp, h, and D which are not presented in Table 2, can be approximately obtained by constructing new data points within and as well below and above the range of the discrete set of values depicted in Table 2, using a linear or a suitable higher order interpolation or fitting method. In some examples, the control unit may be adapted to interpolate such values for To based on two or more known values of To. For example, a table including one or more values of Table 2 may be stored in a storage device as outlined above, and, depending on the controlled parameters, the control unit may select a value of To from the table and/or interpolate a suitable value based on two or more values stored in the table. Additionally or alternatively, the operator of the apparatus may be provided with the table, and he/she may then enter a suitable value for To via the user interface.
The control unit may be adapted to control the pulse repetition as a function of the unconstrained oscillation period To of the first vapor bubble, which may depend on the wavelength of the radiation beam, and/or the energy of the first laser pulse (pa), and/or the pulse duration of the first pulse (tp), and/or the exit component 8 and/or the insertion depth, e.g. according to Table 2 or interpolations thereof, e.g. using one or more of the Eqs. 5, 6, 9 or 10, such that the interaction between the first vapor bubble 18 and the second vapor bubble 18′ generates a shock wave within the liquid 3.
In one of the preferred embodiments, the apparatus, e.g. implemented as a cleaning system configured for cleaning of cavities, e.g., endodontic access opening cavities, filled with liquid. A cavity may have a lateral surface characterized by a minor and/or major inner diameter (Dmin, Dmax), that may vary from cavity to cavity. The cleaning system may comprise an electromagnetic radiation system, e.g. a laser system, wherein the electromagnetic radiation system is adapted to be operated in pulsed operation with at least one pulse set (21) containing at least two individual pulses (p) having each an individual pulse energy, wherein within the pulse set (21) a first pulse (pa) of the pulses (p), having a pulse duration (tp) and pulse energy (EL), is followed by a second pulse (pb) of the pulses (p) with a pulse repetition time (Tp), wherein the pulses are adapted to generate a first vapor bubble (18) within the liquid (3) by means of the corresponding first pulse (pa) and to generate a second vapor bubble (18′) within the liquid (3) by means of the
corresponding second pulse (pb). The pulse repetition time is controlled, e.g. by a control unit, based on the unconstrained oscillation period To of the first vapor bubble as a function of the wavelength of the radiation beam, and/or the energy of the first laser pulse (pa), and/or the pulse duration of the first pulse (tp), and/or the exit component 8 and/or the insertion depth (h) according to Table 2 or by some other data characterizing the influence of the above said parameters. Preferably, the control unit 22 is adapted to adjust the pulse repetition time (Tp) as a function of the unconstrained oscillation period To of the first vapor bubble and of the cavity minor inner diameter (Dmin) and/or major inner diameter (Dmax), using at least one of the Eqs. 5, 6, 9 or 10, such that the interaction between the first vapor bubble (18) and the second vapor bubble (18′) generates a shock wave within the liquid (3).
It is to be appreciated that, the bubble oscillation periods TB as defined by Eqs. 3, 4, 7, 8 represent only average oscillation periods, and that in practice the oscillation periods may be spread around those average values of the oscillation periods TB, as demonstrated in exemplary embodiments depicted in
This may be solved in yet another embodiment, where, in order to facilitate automatic adjustability of the pulse repetition time Tp to an expected spread of the bubble oscillation period around the expected average oscillation period (e.g. corresponding to minor deviations due to the specifics of the cavity geometries), the apparatus (e.g. laser system 1) is configured with a laser source 4 having a (automatically) variable, “sweeping” pulse generation. In this manner, the shock wave emission may be automatically optimized for particular cavity dimensions and shapes and or for particular controlled parameters. The general idea of the inventive sweeping technique is to generate multiple pairs of first and second bubbles 18, 18′ such, that the time difference between the onset time tob of the second vapor bubble 18′ and the onset time toa of the first vapor bubble 18 (
The pulse duration tp is for weakly absorbed wavelengths in the range of ≥1 ns and <85 ns, and preferably ≥1 ns and ≤25 ns. The lower temporal limit of the pulse duration tp for weakly absorbed wavelengths ensures that there are no shock waves created in the liquid 3 during the vapor bubble 18 expansion. And the upper pulse duration tp limit for weakly absorbed wavelengths ensures that the laser pulse power is sufficiently high to generate optical breakdown in the liquid.
For highly absorbed wavelengths, the pulse duration tp is in the range of ≥1 us and <500 μs, and preferably of ≥10 μs and <100 μs. The lower temporal limit for highly absorbed wavelengths ensures that there is sufficient pulse energy available from a free-running laser. And the upper pulse duration limit for highly absorbed wavelengths ensures that the generated heat does not spread via diffusion too far away from the vapor bubble, thus reducing the laser-to-bubble energy conversion efficiency. Even more importantly, the upper pulse duration limit ensures that laser pulses are shorter than the vapor bubble rise time, tmax1−t01, in order not to interfere with the bubble temporal oscillation dynamics. In
Referring now to
The pulse repetition time TP may be “swept” within each pulse set 21 as exemplarily shown in
Alternatively, as a second preferred sweeping pattern, a number of m pulse sets 21 may be applied, wherein the pulse repetition time TP may be varied or “swept” from pulse set 21 to pulse set 21 as exemplarily shown in
A further preferred, third sweeping pattern is schematically depicted in
A combined SWEEP method may be used as well, where the pulse repetition time TP is “swept” within pulse sets 21 from one pulse p to another, and/or from pulse set 21 to pulse set 21. Furthermore, the sweeping pulse energy of
In order to facilitate improved adjustability and/or control, in various embodiments, the laser system 1 may be configured with a laser source 4 having variable pulse parameters, e.g. a variable pulse rate or repetition time, a variable pulse energy, a variable pulse set rate, and/or a variable temporal pulse set length is of the pulse set 21. In this manner, the shock wave emission may be optimized for particular cavity dimensions and shape, and also for a particular placement of the fiber tip or positioning of the laser focus in the different locations relative to the cavity. Namely, the placement of the fiber tip or positioning of the laser focus relative to the cavity may affect the properties of the bubble oscillations and shock wave emission. In one of the embodiments, a centering system may be used to center the fiber tip relative to the walls of the cavity, and/or to center the fiber tip near the entrance, or bottom of the cavity, or near an occlusion within the cavity.
The bubble oscillation period TB may for example vary from about 10 μs to about 3000 is, based at least in part on the thermo-mechanical properties of the liquid3, the shape and volume of the liquid reservoir, the laser wavelength, beam emission profile, configuration of the head, and so forth. Accordingly, when the pulse repetition time TP will be adjusted to approximately match Tp-opt (e.g. adjusted to a range between approximately 60% TB and approximately 95% TB), the pulse repetition rate FP, will be in the range from about 0.35 kHz to about 167 kHz, such that the laser source 1 may be adapted accordingly.
The laser pulse energy EL, according to the invention, may be fixed for all pulses within a pulse set 21. In certain embodiments, however, the energy of the subsequent pulse may be adjustable to automatically gradually decrease, for example linearly or exponentially, from pulse to pulse within each set 21. This approach may be especially advantageous for pulse sets with a pulse number of n=2, where the energy EL of the second pulse pb may be lower than that of the first pulse pa, since the function of the second bubble 18′ is only to create an additional pressure on the collapsing bubble 18 during the initial expansion phase of the bubble 18′.
Alternatively, the laser pulse energy EL may be adjustable to gradually increase from pulse to pulse within a pulse set 21, in order to increase even further the pressure of the subsequent bubbles on the prior bubbles.
Additionally or alternatively, in one of the embodiments of our invention, the laser system may comprise a feedback system to determine the bubble dynamics and feed it back to the control unit such as to control deviations of the pulse repetition time around the estimated optimum frequency to optimize shock wave generation.
For example, the amount of shock waves generated may be measured by sweeping, and the feedback system may be adapted to control the pulse repetition frequency such as to maximize the shock wave generation. In other words, a closed control loop control for automatically delivering a subsequent laser pulse at the appropriate Tp-opt is formed. In other examples, as a result of the measured amount of shock waves, the laser pulse repetition time Tp might be manually adjusted by the user to be approximately equal to Tp-opt.
Several irrigants for the endodontic cleaning are available, and include sodium hypochlorite (NaOCl), chlorhexidine gluconate, alcohol, hydrogen peroxide and ethylenediaminetetraacetic acid (EDTA). However, in one of the preferred embodiments only water may be used instead of a potentially toxic irrigant since the generation of shock waves according to our invention reduces or eliminates the need for the use of chemicals.
It will be appreciated that, while the foregoing example methods are directed to cleaning of root canals and/or bone cavities, in accordance with principles of the present disclosure, similar methods and/or systems may be utilized to clean other body tissues, for example periodontal pockets, and/or the like. The method may be also used to clean selected small surfaces of electronic and precision mechanical components during manufacturing, maintenance and servicing, especially when it is not desirable or possible to expose the whole electronic or other component to a standard cleaning or irrigation procedure.
While the principles of this disclosure have been shown in various embodiments, many modifications of structure, arrangements, proportions, the elements, materials and components, used in practice, which are particularly adapted for a specific environment and operating requirements may be used without departing from the principles and scope of this disclosure. These and other changes or modifications are intended to be included within the scope of the present disclosure and may be expressed in the following claims.
The present disclosure has been described with reference to various embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure. Likewise, benefits, other advantages, and solutions to problems have been described above with regard to various embodiments. However, benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims.
Systems, methods and computer program products are provided. In the detailed description herein, references to “various embodiments”, “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments.
As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, as used herein, the terms “coupled,” “coupling,” or any other variation thereof, are intended to cover a physical connection, an electrical connection, a magnetic connection, an optical connection, a communicative connection, a functional connection, and/or any other connection. When language similar to “at least one of A, B, or C” is used in the claims, the phrase is intended to mean any of the following: (1) at least one of A; (2) at least one of B; (3) at least one of C; (4) at least one of A and at least one of B; (5) at least one of B and at least one of C; (6) at least one of A and at least one of C; or (7) at least one of A, at least one of B, and at least one of C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19196370.1 | Sep 2019 | EP | regional |
