Abstract:
Described are a handpiece, a coupling, and a device with a laser source and handpiece for emitting a laser beam for dental treatment. In order to avoid damage to the healthy tooth tissue, an improved determination of the tooth temperature by measurement of at least part of the heat radiation emitted from the treatment area using a temperature sensor, preferably an infra-red sensor, is carried out. Upon reaching or exceeding a temperature threshold, the emission of the laser beam to the treatment area is interrupted or the power output of the laser source reduced or the user made aware of the violation of the threshold value using an acoustic or visual signal. The temperature sensor can be located, e.g., on the handpiece or on the coupling, such as on the coupling tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from pending Austrian Patent Application No. A 730/2004, filed Apr. 28, 2004, which is incorporated herein by reference. 
     FIELD 
     The present invention relates to a handpiece, a coupling and a device with a laser source and handpiece for emitting a laser beam for dental treatment. 
     DESCRIPTION OF PRIOR ART 
     The aim of every therapeutic or diagnostic treatment is, beside the treatment of actual medical problems, to avoid side effects such as injuries to healthy tissue. In the case of dental treatment using laser beams the tooth is subject to heat caused by energy transfer, whereby healthy tooth material adjoining the carious regions, and the tooth pulp with its associated nerve endings in particular, is affected. If inflammatory processes occur, pain attacks can be initiated at pulp temperatures as low as 37° C. and irreversible damage be caused by long-term thermal stressing up to and including complete loss of vitality of the treated tooth. 
     Despite the use of cooling media, in particular cooling liquids or cooling air, sufficient cooling of the healthy tooth tissue surrounding the treatment area is not fully guaranteed. In order to avoid damage to the healthy tooth tissue a device and a method for monitoring the tooth temperature is disclosed in EP 941 707 A2, which allow use of the operating parameters of the laser, the treatment duration and information on the tooth to be treated to calculate the temperature prevalent in the tooth. The disadvantage of this device is that determination of the tooth temperature is performed solely by means of the calculations carried out by the control unit, based in part on the values entered before treatment commences, and therefore does not reflect the actual treatment situation at the tooth. The calculated values therefore provide the user only with an approximate estimate of the temperature conditions at the tooth. Moreover, the input of parameters before each treatment is time-consuming for the user. 
     The present invention therefore has the aim of providing a device for emitting a laser beam for dental treatment with an improved determination of the tooth temperature. 
     SUMMARY 
     Disclosed below are representative embodiments that are not intended to be limiting in any way. Instead, the present disclosure is directed toward novel and nonobvious features, aspects, and equivalents of the embodiments of the wire strapper dispenser for use with a press and methods described below. The disclosed features and aspects of the embodiments can be used alone or in various novel and nonobvious combinations and sub-combinations with one another. 
     The invented handpiece, which can be executed as a straight or contra-angle handpiece with an angled head, depending on the application, or the invented coupling, are equipped with a temperature sensor, e.g., an infra-red sensor, which measures the intensity of the heat radiation emitted by the tooth and in particular by the tissue around the treatment area (and thus the temperature of the tissue around the treatment area). The heat radiation emitted by the tooth is in the wavelength range greater than 5.0 μm and is thus sufficiently differentiated from the wavelength of the laser beam, which does not exceed 3.5 μm. Preferentially, therefore, a temperature sensor with a measuring range not below 5.0 μm is used, ensuring that the temperature sensor does not react to the laser beam. Alternatively, the temperature sensor can be fitted with a filter, preferably a spectral filter, which filters out wavelengths smaller than 5.0 μm. 
     In a first embodiment the temperature sensor is fitted to the outside of the handpiece, preferably on the outer perimeter of the distal end of the handpiece in the immediate vicinity of the orifice for emitting the laser beam. In accordance with a second preferred embodiment, the temperature sensor is located inside the handpiece, in particular in the optical path of the laser light or inside the coupling, allowing better protection from soiling and damage. 
     If the temperature sensor is located inside part of the handpiece/coupling in particular, which is held in the hand by the user for a prolonged period, there is a danger of the body heat of the user warming the hand grip sleeve and the radiation of the hand grip sleeve subsequently influencing and falsifying the measurement of the heat radiation. The handpiece and/or the coupling is therefore preferably equipped with an inner sleeve located inside the hand grip sleeve and connected to fixed components within the handpiece. A gap between the hand grip and the inner sleeve serves as an insulator. In addition, the gap between the two sleeves can be connected to a rotor wheel, preferably located in the control unit, which forces cooling air into the gap by means of a supply tube. The heat is convectively transported from the handpiece with the cooling air by means of an opening in the proximal area of the handpiece/coupling or via a return air line in the supply tube and the radiation of the hand grip sleeve thus reduced. 
     Additional protection from the radiation of the hand grip sleeve is achieved by casing the temperature sensor, preferably in a metallic encapsulation, with a window of zinc selenide or germanium to allow passage of the heat radiation and a bore for the signal wire, sealed from the interior of the handpiece by a seal, preferably an O-ring. This also protects the temperature sensor from direct contact with vapours or chemicals during cleaning or disinfection. 
     Determination of the temperature at the treatment location is limited to a relatively small range between approximately 37° C. (body temperature of a healthy human) and approximately 43° C. (thermal stimulus threshold of the nerves in the pulp). The thermal wavelengths corresponding to this temperature range are thus situated approximately in the range of about 9.0 to about 9.4 μm. It follows that in a preferred embodiment the detection range of the temperature sensor may be limited to a range of about 9.0 to about 9.4 μm, in particular a range of about 9.10 to about 9.35 μm, or the temperature sensor be fitted with a filter which separates out the wavelengths outside of this range. 
     With the help of the procedure for controlling the power output of a laser source in a device for emitting a laser beam for dental treatment and the process steps:
         emission of a laser beam to a treatment area,   measurement of at least part of the heat radiation emitted from the treatment area by means of a temperature sensor, preferably with an infra-red sensor,   emission of a signal by the temperature sensor proportional to the intensity of the heat radiation,   guidance of the signal to and processing by the evaluation and control electronics,   interruption of emission of the laser beam to the treatment area or reduction of power output of the laser source
 
the chance overheating and damage of the healthy tooth tissue and the pulp neighbouring the treatment area is reduced during treatment.
       

     The process for warning a user about the reaching or exceeding a given temperature threshold during dental treatment with the process steps:
         emission of a laser beam to a treatment area,   measurement of at least part of the heat radiation emitted from the treatment area by means of a temperature sensor, preferably with an infra-red sensor,   emission of a signal by the temperature sensor proportional to the intensity of the heat radiation,   guidance of the signal to and processing by the evaluation and control electronics,   generation and emission of an acoustic or visual signal when reaching or exceeding the temperature threshold by an electrical acoustic or light element connected to the electronics, preferably a LED, provides immediate alarming of the user if critical temperature ranges are reached or exceeded. Preferably, when reaching or exceeding the temperature threshold, the emission of the laser beam to the treatment area is interrupted or the power output of the laser source reduced.       

     A procedure for intermittent emission of a laser beam and measurement of the heat radiation with the process steps:
         emission of a laser beam to a treatment area,   interruption of the laser beam emission   measurement of at least part of the heat radiation emitted from the treatment area by means of a temperature sensor, preferably with an infra-red sensor,   emission of a signal by the temperature sensor proportional to the intensity of the heat radiation,   guidance of the signal to and processing by the evaluation and control electronics,   renewed emission of the laser beam to a treatment area if the given temperature threshold is not reached or exceeded reduces the danger of influencing detection of heat radiation by the temperature sensor, in particular for laser sources that emit long wave radiation, e.g. CO 2  lasers. Preferably, when reaching or exceeding the temperature threshold, the emission of the laser beam to the treatment area is again interrupted or the power output of the laser source reduced or an acoustic or visual signal generated and emitted.       

     The invention is described below based on preferred embodiments and with reference to the drawings provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the invented device for emitting a laser beam for dental treatment. 
         FIG. 2  shows a first embodiment of the invented handpiece. 
         FIG. 3  shows an embodiment of the invented coupling with a handpiece. 
         FIG. 4  shows a second embodiment of the invented handpiece. 
         FIG. 5  shows a third embodiment of the invented handpiece. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invented device  100  for emitting a laser beam for dental treatment in accordance with  FIG. 1  consists of a casing  101 , containing the laser source and a control device with evaluation and control electronics, preferably as part of a microprocessor. The electronics serve as open and closed loop controls for the operating parameters, for example the power output of the laser source or volume control of the cooling media water and air, and for processing the signals from the sensors, which are connected to the handpiece  1  or the coupling  20 . On the display  102 , which is connected to the electronics, the user can read off operating data and select programmes or alter parameters with the help of a numbers of push buttons  103 . Via an interface  104  the evaluation and control electronics are connected to a printer for output of the operating settings and treatment parameters. Preset operating programs and editable settings and parameters are stored in one or more memories connected to the electronics or can be accessed from there. A supply tube  105  containing lines for cooling liquid, cooling air, a fibre optic cable for the laser beam and further lines for signal transmission and electricity supply to illumination elements connects the coupling and the handpiece  1  to the laser source and electronics within casing  101  and the connections for the external sources of electricity, compressed air and liquids. Of course, instead of the supply tube  105  an articulated mirror arm may be used to transmit the laser beam. The laser source can be any source emitting a laser beam in the wavelength range from about 400 nm to about 3.5 μm, in particular from about 700 nm to about 1.064 nm. 
     The invented handpiece  1  shown in  FIG. 2  is designed as a contra angle handpiece with a hand grip  3  and an angled head  2 . By means of the fibre optic cable  8 , which protrudes into the handgrip sleeve  4  of the handpiece  1 , the laser beam  10  is transmitted into the distal area of handgrip section  3 , where it exits the fibre optic cable  8 . After passing through an optical element, for example a convex lens  7 , the laser beam  10  is deflected towards the exit aperture  6  in the head  2  of the handpiece  1  by a mirror  5  in the head, exits the handpiece  1  through the exit aperture  6  and is projected onto the treatment area  51  of the tooth  50 . In order to avoid ingress of particles (ablated tissue, cooling liquid, etc.) into the handpiece  1  thus causing soiling of the mirror  5  in particular and other optical elements  7 , a protective glass can be fitted to the exit aperture  6 . The protective glass is preferably designed as a lens or with a refraction index which is variable across the cross-section for conditioning the passing beam  10 ,  12 . 
     The energy transferred by the laser beam  10  leads to warming of the tooth  50  and the tissue surrounding the treatment area  51  in particular. Part of this energy is emitted by the tooth  50  as heat radiation  12  (infra-red radiation in particular at a wavelength greater than 5.0 μm) to a half-space. At least part of this heat radiation  12  enters the handpiece  1  through the exit aperture  6  and can here be detected by a temperature sensor  11 , in particular an infra-red sensor for wavelengths greater than 5.0 μm, preferably an infra-red sensor for wavelengths in the range of about 9.0 μm to about 9.4 μm, most preferably in the range of about 9.10 μm to about 9.35 μm. The temperature sensor  11  generates a signal corresponding to the intensity of the heat radiation  12  (and thus the temperature of the tissue surrounding the treatment area  51 ), which is transmitted to the evaluation and control electronics  15 , which are formed as part of the handpiece  1  (see  FIG. 4 ), the coupling  20  or the device  100 , via a signal wire  9 . The evaluation and control electronics, preferably forming an integral part of the microprocessor in the device  100 , receive, process and compare the signals to a preset temperature threshold and interrupts the laser beam  10  to the treatment area if the temperature threshold is reached or exceeded, preferably by closing a shutter in the path of the laser beam  10 . Alternatively, the power output of the laser source can be reduced or the user be made aware of exceeding the threshold value by an acoustic or visual signal, for example by illumination of a warning light. 
     The temperature threshold (or a temperature range) is stored in a memory connected to the electronics. It is entered by the handpiece  1  or device  100  manufacturer. However, the user can preferably edit the temperature threshold via the push buttons  103  ( FIG. 1 ) and thus take special treatment requirements into consideration, e.g. for an already inflamed tooth, by reducing the threshold value. 
     In accordance with  FIG. 2 , the temperature sensor  11  is located in the head  2  of the handpiece  1 , allowing favourable proximity of the temperature sensor  11  to the treatment area  51  and thus to the source of the heat radiation  12 . The temperature sensor  11  is preferably located behind the mirror  5  and thus outside of the optical path of the laser beam  10 . The mirror  5  is designed as a semi-transparent mirror which reflects wavelengths below 3.5 μm, preferably below 1.1 μm, i.e. the laser beam  10  or plasma radiation occurring as a result of the treatment of the tooth and which is transmitted for evaluation to an evaluation device forming part of the laser treatment device, and which is transparent to wavelengths above 5.0 μm, preferably between about 9.0 to about 9.4 μm, most preferably between about 9.10 to about 9.35 μm, i.e. heat radiation  12 . 
     If it is not possible, for example due to space considerations, to locate the temperature sensor  11  in the head  2  of the handpiece  1 , the temperature sensor  11  may be located in the grip  3 . The temperature sensor  11  is preferably arranged between the distal opening  6  and the nearest optical element for the laser beam, for example a lens  7  or a scanner, in order to ensure that the properties of the optical element (and any following optical elements), for example transmission or reflection properties, only need be optimised for the laser beam  10 . 
       FIG. 4  shows an embodiment in which the temperature sensor  11  is located in the optical path of the laser beam  10  in the grip  3 . For the term optical path we understand the cavity for passage of the fibre optic cable  8  or the free laser beam  10  in the handpiece  1 . In contrast to  FIG. 2 , the laser source  17  here is located in the handpiece  1 , making a fibre optic cable  8  for transmitting the laser beam  10  redundant. A two-part protective glass cover  6 A,  6 B is fitted to the exit aperture  6 , whereby the two protective glasses  6 A,  6 B possess different properties for preparing the different types of radiation, preferably different focal lengths or different refraction indices, or the glasses  6 A,  6 B are manufactured from different materials. Of course, instead of a two- or more part protective glass a one-piece glass can also be used, divided into two or more areas of differing properties. The properties of protective glass  6 A are optimised for the laser beam  10 , which preferably passes through protective glass  6 A. It is preferably manufactured from quartz glass and in designed as a convex lens, which bundles the laser beam  10  passing out through the handpiece  1 . Protective glass  6 B is preferably manufactured from zinc selenide or germanium and also designed as a convex lens, but intended to bundle the heat radiation  12  for transfer into the handpiece  1 . 
     By means of a mirror  13  the heat radiation  12  advances further to one or more filters  14 , whereby the filter  14  is either a resonator (Etalon), transmission filter, refraction filter (prism) or diffraction filter (grid). The filter  14  filters wavelengths smaller than 5.0 μm, preferably outside of the range of about 9.0 to about 9.4 μm, in particular of about 9.10 to about 9.35 μm. The filtered heat radiation  12  finally arrives at the temperature sensor  11 , which sends a signal corresponding to the intensity of the heat radiation  12  along the signal wire  9  to an amplifier  18  located in the grip  3  and further to the evaluation and control electronics  15  located on a circuit board. The electronics  15  are connected to the laser source  17  by a further signal wire  16  which affects an interruption of the laser beam  10 , or a reduction in the power output of the laser source  17 , if a temperature threshold is reached or exceeded. Of course, further optical elements for preparing the heat radiation  12  may be located between the mirror  13  and the temperature sensor  11 , for example lenses. An additional digitisation unit (analogue-digital converter) can be connected to the temperature sensor  11  to convert the analogue signal of the temperature sensor  11  to a digital signal, making the signal transmission independent of the current strength. 
       FIG. 3  shows the invented coupling  20  connected to the handpiece  1 , which serves as a connector between the handpiece  1  and the supply tube  105  ( FIG. 1 ). The coupling  20  is preferably implemented as a rotary coupling, enabling the user to rotate the handpiece  1  against the coupling  20  and the neighbouring components during treatment. The laser beam  10  is transferred to the mirror  5  via the optical path in the coupling  20 , by means of optical elements, for example a lens  7 , through the optical path in the coupling tube  21  and the distal end of the grip  3 . The heat radiation  12  emitted by the treatment area  51  is also deflected by the mirror  5  into the optical path of the laser beam  10 . The wide reflection range (about 400 nm to about 10.60 μm) of the mirror  5  is preferably achieved by providing multiple coatings of the mirror surface to facilitate selective reflection of certain wavelength ranges. Alternatively, a purely metal mirror can be employed. 
     The temperature sensor  11  for measuring the heat radiation  12  is fitted to the coupling tube  21 , preferably in the optical path of the laser beam  10 . Favourable for this arrangement is that by freeing the handpiece  1  from the coupling  20 , the temperature sensor  11  can be removed from the handpiece  1  and the handpiece  1  thus be sterilised without further problems. This is particularly important for applications involving the removal of tissue and simultaneous use of cooling media, in particular cooling liquids, as the danger of particles and pathogens entering the handpiece  1  on droplets of liquid is particularly great and can lead to cross-contamination between patients. Also, with the temperature sensor  11  located on the coupling  20 , no contacts, for example sliding contacts and sliprings, are required to transfer the signals across the handpiece  1 /coupling  20  interface. The transmission and evaluation of the signal from the temperature sensor  11  corresponds to the description to  FIGS. 2 and 4 . To avoid repetition, this will not be dealt with further here. 
     The length of the coupling tube  21  is preferably dimensioned such that the distal end of the coupling tube  21  reaches close to the head  2  of the handpiece  1  and the temperature sensor  11  is located in the distal area of the coupling tube  21 . This, in turn, allows close proximity of the temperature sensor  11  to the treatment area  51  and thus to the source of the heat radiation  12 , which results in a reduction in attenuation and scattering of the heat radiation  12  with increasing distance. 
     In place of the two mirrors  5 ,  13 , only one mirror  5  is used in the handpiece  1  shown in  FIG. 5 . The mirror  5  has a front surface  5 B (i.e. a side close to the laser source) and a rear surface  5 A (i.e. a side further away from the laser source). Both sides  5 A,  5 B are coated with different materials, such that only one of the two types of radiation  10 ,  12  is selectively reflected respectively by one of the two sides  5 A,  5 B. In  FIG. 5 , for example, the front surface  5 B reflects radiation below about 3.5 μm (laser beam  10 ) and allows radiation above about 5.0 μm (heat radiation  12 ) to pass, which is then reflected by the rear surface  5 A. In this way it is possible to achieve beam separation and heat radiation  12  is deflected to temperature sensor  11  located in the side of the optical path of the laser beam  10 . To amplify the deflection the two reflecting sides  5 A,  5 B are arranged approximately antiparallel. 
     The invention is not restricted to the described embodiments, but encompasses all possible embodiments that do not alter the basic design principle of the invention and analogous functions.