Abstract:
This invention includes a method and a device for measuring a tooth. The method includes generating an ultrasonic impulse, which is echoed off of an area of the tooth. By analyzing the echo, the geometry of the tooth can be determined.

Description:
[0001]     This application claims priority to Provisional Application U.S. Ser. No. 60/703,239 filed Jul. 28, 2005, and to Provisional Application U.S. Ser. No. 60/754,166, filed Dec. 27, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to an ultrasonic measurement device, and specifically to an ultrasonic measurement device used in dental applications.  
         [0003]     A tooth is composed of multiple layers each having an associated thickness. During a dental treatment it is useful to estimate the thickness of the layers of the tooth and to determine the overall internal tooth structure. It is useful for a dentist to know the thickness of the enamel or dentin layer of the tooth to fully understand the extent of dental work required. As an example, information relating to the thickness of the enamel/dentin layer may aid in planning and/or controlling the depth of a drilling bore through the enamel layer. In addition, such information may dictate the necessary amount of surgical interference. Formerly, to obtain such information about the internal structure of the tooth, the dentist may have relied on an invasive procedure or radiographic analysis.  
         [0004]     In addition to evaluating the structure of the tooth, dentists often need to evaluate the quality of bonds between a dental prosthesis and the tooth. As an example, fixed permanent dental prostheses are typically adhered to the tooth utilizing a layer of adhesive. After securing the dental prosthesis to the tooth, it is difficult to detect and locate flaws in the layer of adhesive or the tooth without disturbing the adhesive bond. As a result, the dentist may have to remove the dental prosthesis before evaluating the quality of the bond.  
         [0005]     It would be desirable to determine the thickness of dental layers without requiring an invasive procedure.  
         [0006]     It would be further desirable to estimate adhesion quality and locate flaws in the adhesive layer or flaws in the tooth structure without removing a dental prosthesis.  
       SUMMARY OF THE INVENTION  
       [0007]     This invention includes a method and a device for measuring a tooth. The method includes generating an ultrasonic impulse, which is echoed off of an area of the tooth. By analyzing the echo, a user can determine the geometry of the tooth.  
         [0008]     Boundaries between layers of the tooth may produce distinguishable echoes. Because ultrasonic impulses travel with known speeds through different areas of the tooth, analysis of the echo may include comparing the time difference between receiving two echoes from differing portions of the tooth. Accordingly, a user can establish where those boundaries are based upon the timing differences between the echoes. In addition to evaluating structure within the tooth, the present invention may also be used to evaluate areas proximate to the tooth. A user may display the echoes graphically to aid in identifying distinct boundary layers.  
         [0009]     The device used to measure the tooth includes a transducer for generating an ultrasonic impulse and a receiver for accepting an echo from the tooth. The portion of the device including the transducer and receiver is ordinarily handheld. The device also includes a computer for converting the data relating to the echoes into data representative of the tooth geometry. The computer may produce a graphical representation of the echoes to aid in identifying areas of the tooth. Alternatively, the computer calculates the thickness of a layer of the tooth and generates measurement information. In addition to calculating the internal geometries of the tooth, the device also may calculate geometries based on echoes from areas other than the tooth. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a cross-sectional view of a tooth and a dental ultrasonic hand-piece in the case of enamel thickness measurement.  
         [0011]      FIG. 2  is a cross-sectional view of a tooth and the dental ultrasonic sensor in the case of measuring the distance from the surface to pulp.  
         [0012]      FIG. 3  is a cross-sectional view of a tooth with a crown prosthesis.  
         [0013]      FIG. 4  is a cross-sectional view of a tooth with a filling and a void.  
         [0014]      FIG. 5  schematically illustrates the components of a dental measurement system.  
         [0015]      FIG. 6  illustrates a dental measurement system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]      FIG. 1  illustrates a dental hand-piece  34  for examining the internal layers of a tooth  10 . As shown in the cross-sectional view, an enamel layer  14  partially covers a dentine layer  18  forming a dentine-enamel interface  22 . A pulp chamber and root canal  26  is embedded within the dentine layer  18  and supporting tissue (gingiva  29  and bone  30 ) anchors the tooth  10  in position.  
         [0017]     The dental hand-piece  34  incorporates a piezoelectric transducer  38 , which emits a brief ultrasonic impulse  42  toward the tooth  10  at a known frequency. The tooth  10  reflects the ultrasonic impulse  42  back to the dental hand-piece  34 . Different areas of the tooth  10 , e.g. the interfaces between layers of the tooth  10 , reflect varying echoes back to the dental hand-piece  34 , creating an ultrasonic echo. Accordingly, the thickness of a layer of the tooth  10  can be determined by measuring time delay between the ultrasonic echoes reflected from the appropriate portion of the tooth  10 , such as the dentine-enamel interface  22 . As a result, it is not necessary to remove the tooth  10  from the supporting tissue to evaluate the structure of the tooth  10 .  
         [0018]     In this example, the piezoelectric transducer  38  communicates with a computer  88  having pulse generating instrumentation, a receiver, and an analog to digital converter. The piezoelectric transducer  38  receives the ultrasonic echo, and after measuring the reflection time of the ultrasonic echo, an operator can determine the time of flight. For example, multiplying the time delay between the ultrasonic impulses  42  reflected from the borders of the layers of the tooth  10  by the known velocity of the ultrasonic impulse  42  produces the thickness of the layer of the tooth  10 .  
         [0019]     The ultrasonic impulse  42  echoes off of all portions of the tooth  10 , the interfaces between the main layers of tooth  10 , e.g., the enamel-dentine interface  22 , produce a substantial echo, which helps to identify the location of the interfaces between the main layers of the tooth  10 . For instance, a graphical representation of the echoes may illustrate the echoes from the enamel-dentine interface  22  as having greater amplitudes and shorter time delay than echoes from other portions of the tooth  10 . A person skilled in the art could identify the interfaces after observing the graphical representation. Preferably, the computer  88  interprets the amplitudes and delay times of the echoes and displays the thicknesses of the various layers.  
         [0020]     As an example, the thickness of the enamel layer  14  of the tooth  10  can be determined as follows. The piezoelectric transducer  38  first transmits the ultrasonic impulse  42  into the tooth  10 . The ultrasonic impulse  42  reflects two distinguishable echoes when the ultrasonic impulse  42  reaches the surface of the enamel  14  and the dentine-enamel interface  22  respectively. The velocity of the ultrasonic impulse  42  through enamel is known. Accordingly, measuring the time delay between the two echoes, multiplying the time delay by the sound velocity, and dividing the product by the factor of  2  produces the thickness of the enamel  14 .  
         [0021]      FIG. 2  illustrates the piezoelectric transducer  38  mounted into dental hand-piece  34  (different shape). In this example, the probe  38 , incorporates a nose-shaped cylindrical probe tip  62  having a cylindrical cross section. The piezoelectric transducer  38  produces the ultrasonic impulse  42  as the probe tip  62  is inserted into a bore  48  in the enamel layer  14  and the dentine layer  18  of the tooth  10 . Similar to determining the thickness of the enamel layer  14 , the thickness of the bored portion of the dentine layer  18  may be calculated using the echoes from the bottom of the drilled bore  48  and the dentine-pulp interface  44  as well a the sound velocity through dentin.  
         [0022]     As shown in  FIG. 3 , a crown  52 , a type of dental prosthesis, may be secured to the tooth  10  using an adhesive  56 . In so doing creating a crown-adhesive interface  64  and an adhesive-enamel interface  68  or if enamel is removed, then an adhesive/dentin interface would occur. The dental hand-piece  34  and the piezoelectric transducer  38 , with or without the tip attached, direct the ultrasonic impulse  42  to the tooth  10  and the crown  52 . Both the crown-adhesive interface  64  and the adhesive-enamel interface  68  produce distinguishable echoes. Flaws in the adhesive flaws or an adhesive void  54  can be located by interpreting amplitude increases and changes in the returning echoes of the ultrasonic impulse  42 . For example, a distortion in the return echo may identify the adhesive void  54 .  
         [0023]      FIG. 4  illustrates that the present invention may also be used to detect a cavity  84  between the tooth  10  and a filling  72 . Adding the filling  72  to the tooth  10  creates a filling-dentin interface  80 . As shown, the piezoelectric transducer  38  transmits the ultrasonic impulse  42  toward the filling  72  producing echoes. The ultrasonic impulse  42  travels from the piezoelectric transducer  38  and echoes off the filling-dentin interface  80 . Increases in the amplitude of the return signal may indicate the cavity  84  between the filling  72  and the tooth  10 .  
         [0024]      FIG. 5  is a schematic illustration of an exemplary dental measurement system  12  incorporating the dental hand-piece  34  communicating with a computer  88 . As shown, the piezoelectric transducer  38  with an attached ultrasonic guidance element  90  is located at one end of the dental hand-piece  34 . The example ultrasonic guidance element  90  is tapered to focus the ultrasonic impulses  42  from the piezoelectric transducer  38  to the tooth  10  or other desired area.  
         [0025]     To achieve maximum ultrasonic impulse  42  penetrations into the tooth  10 , axis X taken through the ultrasonic guidance element  90  should remain generally perpendicular to the surface of the tooth  10 . Irregularities in the surface of the tooth  10  may increase the difficulty of maintaining this position and elements of the ultrasonic guidance element  90  that do not maintain this position may produce distorted echoes of the ultrasonic impulse  42  that can be correspondingly interpreted. To counteract this result, a user may tilt the hand-piece  34  among varying angles while the ultrasonic impulse  42  is being operated. As is known in the art, the amplitudes of the signal at various angles can be stored, compared and analyzed to determine when the acoustical beam irradiated by the piezoelectric transducer  38  was perpendicular to the surface of the tooth  10 , such that the perpendicular measurement is used.  
         [0026]     Depending on the space constraints and handling desires, other varieties of dental hand pieces  34  may be used with differently shaped tips. A cylindrical probe tip  62  ( FIG. 2 ) may be used. The dental hand piece  34  also may incorporate protective measures, such as a sterile/aseptic sleeve, for bio-safety concerns.  
         [0027]     The size of the interchangeable ultrasonic guidance element  90  in the current invention aids in maintaining the position of the dental hand-piece  34  and better directs the ultrasonic impulse  42  into the tooth  10 . In addition, modifying the ultrasonic guidance element  90  enables access to many hard to reach areas, e.g., between the teeth  10 , at the lower edge of the crown  52 .  
         [0028]     In this example, the dental hand-piece  34  and piezoelectric transducer  38  communicate echoes of the ultrasonic impulse  42  to a pulser-receiver  92 . An analog-to-digital converter  96  coverts the echoes to the appropriate data format and moves the data through a controller  100  interfacing with a computer  88 . The computer  88  processes and analyzes the data using an algorithm, and then displays the data, typically in a numerical and graphical format, based upon time dependence of echoes.  
         [0029]     Although this example discloses that the computer  88  contains the relevant instrumentation, those skilled in the art, and having the benefit of this disclosure, may be able to identify other suitable instrumentation set-ups. For example, the dental hand-piece may separately connect to an ultrasonic generator and a graphical display.  
         [0030]      FIG. 6  shows the example dental measurement system  12  including the ultrasonic guidance element  90 , and incorporated piezoelectric transducer  38 , mounted to the dental hand-piece  34 . The computer  88  communicates with the pulser-receiver in the dental hand-piece  34 . When a user directs the dental hand-piece toward a tooth  10  ( FIG. 1 ), the computer may display, in real-time and in a graphical format, the measurements of the tooth  10  based on the echoes off of the tooth  10 . In addition, the display may include real-time visualization of the tooth  10  and any noted defects in the tooth  10 , enabling real time examination of the tooth  10 . The small portable size of the dental hand-piece  34  and the computer  88  aid in incorporating the dental measurement system  12  into clinical practice.  
         [0031]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention.