Abstract:
An ultrasonic orthodontal monitoring system and method of use is described herein, featuring an intraoral ultrasonic transducer and an ultrasonic monitoring apparatus configured to connect to the intraoral ultrasonic transducer, generate and send electrical pulse signals to the intraoral ultrasonic transducer, receive measured signals from the intraoral ultrasonic transducer, and generate time-of-flight and relative density based on the measured signals. This invention will permit routine measurements to be made of osseointegration by the patient&#39;s dentist during regular maintenance appointments, thereby reducing the risk of a failed implant, patient discomfort, and inconvenience. As a diagnostic tool, it can also aid in the diagnosis and treatment of progressive periodontal disease, peri-implantitis, and osteoporosis in edentulous patients.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to dental prosthetics. More particularly, the present invention relates to a system and method for monitoring an osseointegration stage of a bone graft used with dental implantation and prosthetics placement. 
       BACKGROUND 
       [0002]    The most commonly used dental implants are titanium alloy screws that date to Italian clinical use in 1959 by Dr S. M. Tremonte. In Gothenburg, Sweden, 1965, Dr. Per-Ingvar Br         nemark placed the first human titanium dental implant. Over the past 50 years, oral and maxillofacial surgeons around the world continue studies relating to failure mechanisms of implants relative to the timing of placement post extraction, physical state of the region requiring grafting, patient physiology and health, and mechanical loading capability of the implant and prosthesis over time. More recently, ceramic zirconium oxide implants have gained some popularity over the metal alloy counterparts as they may offer greater biocompatibility. 
         [0003]    The typical procedure involves extraction of the tooth to be replaced followed by a bone graft in the socket. It is critical to ensure sufficient maxillary or mandibular bone mass to accept drilling and secure placement of the implant. A variety of materials used for grafting include bovine bone, processed cadaver bone, autograft patient bone, and synthetic hydroxyapatite. The oral surgeon prepares the site, places the graft material, and sutures the site to permit healing and osseointegration. Normally a period of several months is required to ensure regeneration of live vascular bone with sufficient mass and density for the site to be drilled for placement of the implant. No common device technology is available to guide the oral surgeon on accurately choosing the incubation time necessary to ensure a high degree of implant stability. Incubation time is generally selected based on guesswork informed by experience. 
         [0004]    A Columbia University College of Dental Medicine review conducted in 2005 found that incubation times in a range of 6 to 12 months were generally selected for bone augmentation procedures. Not uncommonly, incubation times of as little as two months were selected. Too short incubation times can necessitate repetition of the bone graft in order to achieve implant stability. A repetition of the procedure can require as much as an additional 18 months at added cost and inconvenience for both surgeon and patient, as well as serious social and personal discomfort. 
         [0005]    The use of ultrasonic sensing systems became widely used in the early &#39;70s for quality control of high volume industrial products, especially in identifying internal defects that might lead to failure. Much more recently, use of ultrasonic sensing in medical diagnostics has increased. The absence of exposure to physically harmful ionizing radiation has been a driving factor, even as X-ray, CAT and MRI systems persist as widely employed tools. 
         [0006]    While ultrasonic sensing systems exist in the field of dentistry and dental implantology, with few exceptions, they are not well known or widely used. For wide practical analytical or diagnostic use, an ultrasonic sensing system should be no more complex to implement than routine production of x-rays by a dental technician or assistant. A discussion of the known art follows: 
         [0007]    U.S. Pat. No. 5,564,423 teaches the use of a caliper pair of ultrasonic transducers for the external measurement of bone density in a bone segment e.g. finger, arm, leg but does not disclose intraoral use for dental implantation, diagnosis or monitoring of maxilla and mandibular areas of interest. 
         [0008]    U.S. Pat. No. 6,702,746 teaches the use of a single ultrasonic probe placed in a cavity in the alveolar bone or on the surface of the posterior maxilla or mandible to measure the thickness of bone remaining between the cavity base and the alveolar canal to gauge its depth and to prevent drilling into the canal. The disclosed configuration is specific to measuring distances from an existing cavity socket or drill site and the alveolar canal. 
         [0009]    U.S. Pat. No. 6,086,538 teaches transmission of an ultrasonic wave through the jawbone and measuring the reflected wave with the same transducer. The application requiring multiple placement positions of the transducer is used to locate cancaneus defects in the bone. The technique is virtually identical to that used for detection of internal porosity in metal castings. It has limited suitability for intraoral applications owing to size and complexity. 
         [0010]    U.S. Pat. No. 6,030,221 teaches a system similar to that of the &#39;538 patent discussed above, in that it also applies to location of jawbone bone defects. The &#39;221 patent teaches application of color coding based on relative pulse intensities, mapping a 4×4 color coded image representing the attenuation of sound through the region of interest. This too is limited in adaption to the needs of monitoring the course of osseointegration of a bone graft preceding placement of an implant. 
         [0011]    U.S. Pat. No. 7,285,093 introduces an improved 3D imaging system utilizing arrays of ultrasonic transducers with 6 degrees of freedom permitting virtually spherical data production for constructing a 3D image. The software used in producing and displaying the 3D image is analogous to that used in Dental CAT scanning now in common use. Its complexity and large capital investment will limit its use, particularly by smaller independent dental practices. 
         [0012]    U.S. Pat. No. 4,296,349 teaches a method for fabrication of a diagnostic ultrasonic transducer utilizing piezoelectric polymers e.g. polyvinylidene difluoride, PVDF. The &#39;349 patent lacks examples of uses or applications. 
         [0013]    US Patent Publication No.: 2004-40249285 teaches a method of fabrication of a composite transducer on a flexible base substrate. The flexible substrate enhances transmission and reception of acoustical waves from curved or modulated surfaces. Showing less signal attenuation, improved signal strength, and measurement. 
         [0014]    U.S. Pat. No. 6,720,709 teaches a method for manufacture of a miniature transducer with a flexible piezoelectric layer, e.g. PVDF, and switching circuitry to permit modulation of its mechanical impedance in use as an ultrasonic wave transmitter. 
         [0015]    U.S. Pat. No. 6,946,777 teaches a method for manufacture of a composite polymer film transducer and bandwidth control for use in determining the speed of sound in low density media. PVDF improves impedance matching for sound wave propagation in liquid and gaseous media. 
       SUMMARY AND ADVANTAGES 
       [0016]    Embodiments of ultrasonic orthodontal monitoring systems and methods are described herein. Such systems and methods are intended for use in the field of dentistry, particularly relating to practices of grafting natural or synthetic bone into a socket in the maxilla and/or mandibula of the jawbone following a dental extraction. In particular, these systems and methods are intended for use in measuring suitability of a graft for drilling and acceptance of an implant. The suitability of the graft for subsequent processing may be evaluated based on its relative density, which indicates degree of graft osseointegration. Relative density of the bone graft can be determined by transmitting an ultrasonic wave through the bone graft and measuring the transit time of the ultrasonic wave. Since it has been long known that the density of a solid is inversely proportional to the square of the velocity of sound in the solid, it follows that the density is directly proportional to the time of flight squared for an ultrasonic wave to transit a known thickness through a solid. Thus the relative density of a bone graft as a function of time can be monitored by comparing a series of time of flight (TOF) measurements performed over the entire course of the implantation process, beginning immediately prior to extraction, bone grafting the socket cavity, monitoring approach to mature endpoint density , and implant placement. 
         [0017]    This invention will permit routine measurements to be made during osseointegration by the patient&#39;s dentist during regular maintenance appointments reducing the risk of a failed implant, patient discomfort, and inconvenience. As a diagnostic tool, it can also aid in the diagnosis and treatment of progressive periodontal disease, peri-implantitis, and osteoporosis in edentulous patients. 
         [0018]    Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. Further benefits and advantages of the embodiments of the invention will become apparent from consideration of the following detailed description given with reference to the accompanying drawings, which specify and show preferred embodiments of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present invention and, together with the detailed description, serve to explain the principles and implementations of the invention. 
           [0020]      FIG. 1(   a ) illustrates the left side view of a jawbone with a mandibular ridge having a tooth socket following an extraction and prior to placement of a bone graft. 
           [0021]      FIG. 1(   b ) illustrates a cross section of the tooth socket of  FIG. 1(   a ) showing retracted surrounding soft gum tissue prior to bone graft emplacement. 
           [0022]      FIG. 2(   a ) illustrates the tooth socket following placement of a bone graft and prior to drilling for implant placement. 
           [0023]      FIG. 2(   b ) illustrates a threaded biocompatible metal alloy or ceramic implant placed into a drilled and internally threaded hole in a mature bone graft. 
           [0024]      FIG. 3(   a ) illustrates an embodiment of an intraoral ultrasonic transducer. 
           [0025]      FIG. 3(   b ) illustrates an alternative embodiment of an intraoral ultrasonic transducer with matched piezoelectric elements forming transducer pairs of a 2×2 matrix array. 
           [0026]      FIG. 4(   a ) illustrates the placement of an intraoral ultrasonic transducer closely fitted over the mandibular ridge, including a tooth to be extracted and adjacent teeth. 
           [0027]      FIG. 4(   b ) illustrates ultrasonic paths from an element of a 2×2 matrix array transmitter to each element of a 2×2 matrix array receiver. 
           [0028]      FIG. 5  is a block diagram of an embodiment of an ultrasonic orthodontal monitoring system  52 . 
       
    
    
     REFERENCE NUMBERS USED IN DRAWINGS 
       [0029]    Turning now descriptively to the drawings, in which similar reference characters denote similar elements throughout the several views, the figures illustrate embodiments of the present invention. With regard to the reference numerals used, the following numbering is used throughout the various drawing figures: 
         [0030]      10  jaw bone 
         [0031]      12  mandibular ridge 
         [0032]      14  tooth socket 
         [0033]      16  soft tissue 
         [0034]      18  bone tissue 
         [0035]      20  bone graft 
         [0036]      22  apposition surface 
         [0037]      26  threaded implant 
         [0038]      30  intraoral ultrasonic transducer 
         [0039]      32  flexible substrate 
         [0040]      34  piezo element 
         [0041]      36  transducer connector 
         [0042]      38  16 pin transducer connector 
         [0043]      40  piezo array 
         [0044]      42  2×2 intraoral ultrasonic transducer 
         [0045]      44  encapsulating layer 
         [0046]      45  transmitting piezo array 
         [0047]      46  receiving piezo array 
         [0048]      48  extraction tooth 
         [0049]      50  adjacent teeth 
         [0050]      52  ultrasonic orthodontal monitoring system 
         [0051]      56  ultrasonic monitoring apparatus 
         [0052]      58  pulse generator 
         [0053]      60  apparatus connector 
         [0054]      62  piezo element acting as transmitter 
         [0055]      64  piezo leads 
         [0056]      66  piezo element acting as receiver 
         [0057]      68  signal processor 
         [0058]      70  data storage 
         [0059]      72  display 
         [0060]      74  control processor 
         [0061]      76  instruction memory 
         [0062]      78  control lines 
         [0063]      80  data switch 
       DETAILED DESCRIPTION 
       [0064]    Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference materials and characters are used to designate identical, corresponding, or similar components in differing figure drawings. The figure drawings associated with this disclosure typically are not drawn with dimensional accuracy to scale, i.e., such drawings have been drafted with a focus on clarity of viewing and understanding rather than dimensional accuracy. 
         [0065]    In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
         [0066]      FIG. 1(   a ) illustrates a left side of a jawbone  10 . The jawbone  10  has a mandibular ridge  12  including various teeth. The mandibular ridge  12  has a tooth socket  14  that previously held a tooth before the tooth was extracted.  FIG. 1(   b ) illustrates a cross section of the jawbone  10  through the center of the tooth socket  14 , showing soft tissue  16  and bone tissue  18  parts of the mandibular ridge  12 . 
         [0067]      FIG. 2(   a ) illustrates the insertion of a bone graft  20  into the tooth socket  14 , including an apposition surface  22  between the mandibular ridge  12  and the bone graft  20 . The bone graft  20  may be harvested bone material known in the art. Before bone graft  20  is ready to support an implant, the bone graft  20  and the adjacent bone tissue  18  have to sufficiently integrate with each other in a process known as osseointegration. Both the bone graft  20  and the adjacent bone tissue  18  should each achieve a sufficient bone density to support the implant. The time it takes for bone graft  20  to sufficiently integrate with adjacent bone tissue  18  can vary from as few as 2 months to greater than a year. Attempting an implant installation in the bone graft  20  when the bone density of the bone graft  20  and the adjacent bone tissue  18  is insufficient may cause the installation to fail and require that the unsuccessful bone graft  20  be removed, the tooth socket  14  be re-prepared, and another bone graft  20  be inserted into the tooth socket  14 . This repetition of the bone grafting process may be both expensive and time consuming. 
         [0068]      FIG. 2(   b ) shows bone graft  20  of  FIG. 2(   a ) following drilling and placement of a threaded implant  26 . The threaded implant  26  may be of biocompatible metallic alloy, such as titanium, ceramic, or some other suitable material. A dental prosthesis may be thereafter coupled to the threaded implant  26 . The threaded implant  26  will only be successful if the bone graft  20  supporting it is mature, i.e., the bone graft  20  has sufficient osseointegration with adjacent bone tissue  18  and sufficient bone mass and density. 
         [0069]    Traditionally, the determination of whether or not the bone graft  20  is properly integrated is largely subjective and based solely on the experience of the dental practitioner. Further, improper maturation and integration may only become apparent after the dental prosthesis coupled to the threaded implant  26  fails (e.g., by the threaded implant  26  at least partially detaching from the bone graft  20  and/or the bone graft  20  at least partially detaching from the bone tissue  18  in the tooth socket  14 ). The failure may be accompanied by discomfort and pain in addition to the time lost waiting for the initial bone graft  20  to mature and for a replacement bone graft  20  to do the same. One solution to the problem of determining when osseointegration is sufficient may be to simply wait a conservatively long period of time, one longer than most all bone grafts have been observed to require. This solution is inefficient it forces all patients to wait a long time, when some may be ready for implantation earlier. 
         [0070]      FIG. 3(A)  shows an embodiment of an intraoral ultrasonic transducer  30 . The intraoral ultrasonic transducer  30  has at least one pair of matched piezo elements  34 . The piezo elements  34  are held in place within the intraoral ultrasonic transducer  30  so that when the intraoral ultrasonic transducer  30  is placed in a desired location on the mandibular ridge  12  over a region of interest, then the piezo elements  34  of each matched pair are in desired positions on opposing sides of the region of interest. The region of interest in most cases includes the tooth socket  14  and a region of bone tissue  18  around the tooth socket  14 . However, the intraoral ultrasonic transducer  30  may be used to make measurements of regions of interest that do not include the tooth socket  14  or the region of bone tissue  18  around the tooth socket  14 . 
         [0071]    In this embodiment, the piezo elements  34  are coupled to a flexible substrate  32  configured to hold the piezo elements  34  in place within the ultrasonic transducer  30 . In other embodiments, described later herein, the intraoral ultrasonic transducer  30  does not have the flexible substrate  32  and the piezo elements  34  are held in place by other means. Each piezo element has a pair of electrical leads (not shown) that electrically connect that piezo element with a transducer connector  36 . Suitable dimensions for the intraoral ultrasonic transducer  30  and its components are determined by cataloguing measurements from dental impressions utilizing routine dental practice for crowns, implants, and the like. 
         [0072]    In some embodiments, the piezo elements  34  are flexible piezopolymers such as polyvinylidene difluoride (PVDF). The flexibility of the piezo elements  34  enhances the overall flexibility of the intraoral ultrasonic transducer  30 . In other embodiments, the piezo elements  34  may be ceramic piezoelectric elements such as PZT, Lead-Zirconate-Titanate. 
         [0073]    In some embodiments, the piezo elements  34  are discrete, made separately from the flexible substrate  32  and later coupled thereto by adhesive bonding, lamination, or other means. In other embodiments, the piezo elements  34  and flexible substrate  32  are fabricated together using thin film deposition techniques. The layered film deposition technique includes starting with a base substrate, followed by lamination or deposition of a lower electrode, then deposition of a piezoelectric film, then deposition of an insulating layer to prevent electrode shorting, and then deposition of an upper electrode. 
         [0074]    The flexible substrate  32  is configured to wrap over teeth in the mandibular ridge  12  in the mouth of a patient. Preferably, the piezo elements  34  are coupled to flexible substrate  32  on a side that is not adjacent to the mandibular ridge  12  to allow a snug and smooth contact and precise placement of the intraoral ultrasonic transducer  30 . 
         [0075]    To allow the flexible substrate  32  to be sufficiently flexible to wrap over the teeth of the mandibular ridge  12 , a suitable material must be selected. One suitable material is DuPont&#39;s Kapton polyimide film developed specifically for micro-circuitry and amenable to bending or shaping over a toothy ridge. Other suitable materials include photopolymerizable Thiolene monomer liquid adhesive film, Nippon Mektron 3D formable liquid crystal polymer flexible substrate, or the like. 
         [0076]      FIG. 3(B)  shows an alternative embodiment of the intraoral ultrasonic transducer  30 , specifically a 2×2 intraoral ultrasonic transducer  42 . The 2×2 intraoral ultrasonic transducer  42  is similar to the intraoral ultrasonic transducer  30  shown in  FIG. 3(A) , having a flexible substrate  32 , but instead of the single pair of piezo elements  34 , it has 4 matched pairs of piezo elements  34  in 2×2 piezo arrays  40  and instead of a four pin transducer connector  36 , it has a 16 pin transducer connector  38 . A larger or differently dimensioned array of piezo elements  34  will allow monitoring of a larger or differently shaped region of interest. A person of skill in the art would realize that other embodiments of the intraoral ultrasonic transducer  30  can have other numbers of piezo elements  34  and piezo arrays  40  with other dimensions, such as 1×2 or 3×3. 
         [0077]      FIG. 4(   a ) illustrates how the intraoral ultrasonic transducer  30  is capable of being closely fitted over the mandibular ridge  12 , including a tooth to be extracted (extraction tooth  48 ) and adjacent teeth  50 . The intraoral ultrasonic transducer  30  can be placed over the mandibular ridge  12  such that the piezo elements  34  of each matched pair are in the desired positions on opposing sides of the region of interest. So positioned, the intraoral ultrasonic transducer  30  can be used to determine relative bone density. 
         [0078]    To determine relative bone density, the intraoral ultrasonic transducer  30  sends ultrasonic waves though the region of interest in the mandibular ridge  12 . One of the matched pair of piezo elements  34  acts as an ultrasonic transmitter and the other as a receiver. A time-of-flight (TOF) through the region of interest is measured for each of the ultrasonic waves. A time of flight principle is then used to calculate relative bone density. 
         [0079]    Time of flight is proportional to the velocity of sound in a particular solid. For example, the velocity of sound in a solid C=(E/ρ) 1/2  where C is the velocity of sound in the medium, E is the modulus of elasticity, and ρ is the density. For a given distance L in the solid, C may also be obtained by measuring the transit time or time of flight (TOF) for a sound wave to propagate through the solid, then dividing the distance L by time of flight TOF, or: C=L/TOF. Substituting for C, one can see that: L/TOF=(E/ρ) 1/2 . Squaring both sides of the equation yields: (L/TOF) 2 =E/ρ. Assuming that L and E remain substantially constant for a particular measurement, then it is clear that the density ρ is directly proportional to (TOF) 2 . Thus for a given solid and dimension L, relative density is defined as the square of density ρ 1  (density at time t 1 ) divided by the square of density ρ 0  (density at initial time t 0 ), or: Relative density=ρ 1 /ρ 0 =(TOF(t 1 )/TOF(t 0 )) 2 , where TOF(t 0 ) is the time of flight at the initial time and TOF(t 1 ) is the time of flight at time t 1 . Typically, initial time t 0  is a time before extraction, time t 1  is some time after extraction and bone graft placement. 
         [0080]    Relative density is a metric that a dental practitioner can use to judge bone graft maturity. Relative density above a relative density threshold indicates the bone graft is sufficiently mature to hold an implant. A relative density threshold of 95% or more indicates mature endpoint density. Some dental practitioners may decide to use different values for the relative density threshold, depending on their experience. Periodic measurements taken every 2 weeks or so over a minimum of 3 to 4 months will permit determination of bone graft  20  rate of growth, which in turn will permit a prediction of a time required to reach mature endpoint density. 
         [0081]    The intraoral ultrasonic transducer  30  can be used for periodic measurements of relative bone density throughout the process of extraction, bone grafting, and implant placement. To aid reproducibility and accuracy of relative bone density measurements, some embodiments of the intraoral ultrasonic transducer  30  have an encapsulating layer  44  coupled to the flexible substrate  32  and piezo elements  34 . The encapsulating layer  44  is configured to hold the piezo elements  34  in the desired positions on the mandibular ridge  12 . This will allow the intraoral ultrasonic transducer  30  to be removed and placed back in the exact same position multiple times following extraction for monitoring of re-growth of live vascular bone in the region of interest and the osseointegration of the bone graft  20 . 
         [0082]    In some embodiments, the intraoral ultrasonic transducer  30  is made by placing unsolidified dental impression material over the flexible substrate  32  and mandibular ridge  12  while the flexible substrate  32  and piezo elements  34  are in the desired positions on the mandibular ridge  12 . The dental impression material extends onto and over the extraction tooth  48  as well as at least a portion of the adjacent teeth  50 , conforming to the surfaces thereof, and forming the encapsulating layer  44 . As the dental impression material of the encapsulating layer  44  solidifies, it bonds to the flexible substrate  32  and piezo elements  34 . The dental impression material may be any material commonly used for dental impressions, such as sodium alginate, polyether and silicones. 
         [0083]    In some embodiments, the intraoral ultrasonic transducer  30  is made from a cast of the region of interest. Dental impression material is placed over the mandibular ridge  12  to form an impression mold. Preferably, the impression mold should include an impression of the entire mandibular ridge  12 , including all teeth therein. At least, the impression mold should include an impression of the extraction tooth  48  as well as at least a portion of the adjacent teeth  50 . The cast is then made using the impression mold and plaster of Paris or some similar material. The cast is thus a replica of the mandibular ridge  12 . The piezo elements  34  are then placed in positions on the cast that match the desired positions on the mandibular ridge  12 . Dental impression material is pressed onto the cast of the mandibular ridge  12 , forming the encapsulating layer  44 . A preferred dental impression material for this purpose is polymerized siloxane (silicone), but other dental impression material may be used. In some embodiments, the piezo elements  34  are held in place with a weak adhesive while the encapsulating layer  44  is formed. In some embodiments, the flexible substrate  32  holds the piezo elements  34  in place. As the dental impression material solidifies, it bonds to the flexible substrate  32 , if present, and to the piezo elements  34 . The intraoral ultrasonic transducer  30  can then be removed from the cast and placed on the mandibular ridge  12 . So constructed, the intraoral ultrasonic transducer  30  can be removed and replaced repeatedly for periodic monitoring relative bone density. 
         [0084]    In another embodiment of this invention, the intraoral ultrasonic transducer  30  is made by placing the piezo elements  34  inside a dental impression tray, filling the tray with the dental impression material, then placing the tray over the patient&#39;s mandibular ridge  12  so that the piezo elements  34  are in the desired positions on the mandibular ridge  12 . The dental impression material solidifies, forming the encapsulating layer  44 . After the dental impression material solidifies, the intraoral ultrasonic transducer  30  can be removed and placed back in the exact same position multiple times following extraction for monitoring relative bone density. 
         [0085]    In another embodiment of this invention, the intraoral ultrasonic transducer  30  is made with materials that are curable utilizing ultraviolet (UV) light. Specifically, the flexible substrate  32  is made of materials that are moldable and curable. The flexible substrate  32  is moldable in the sense that it can readily be bent into a certain shape and will maintain that shape until bent again. Following placement of the flexible substrate  32  over the mandibular ridge  12 , including the extraction tooth  48  and adjacent teeth  50 , the flexible substrate  32  is subjected to UV light. The UV light cures the flexible substrate  32  and creates a negative replica of the mandibular ridge  12  over the region of interest. The flexible substrate  32  after curing is no longer moldable and will retain its cured shape, but will still have some flexibility. That is, the cured flexible substrate  32  can be bent, but will return to its cured shape when bending forces are released. This embodiment will also permit the intraoral ultrasonic transducer  30  to removed and placed back in the exact same position multiple times following extraction for monitoring of the region of interest. To be moldable and curable, the flexible substrate  32  is made of partially photopolymerized adhesive Thiolene film or some other similar material. Use of flexible substrates  32  that are moldable and curable reduces the need for the encapsulating layer  44 . In some embodiments, the encapsulating layer  44  is still used in conjunction with flexible substrates  32  that are moldable and curable. In other embodiments, the encapsulating layer  44  is dispensed with when using flexible substrates  32  that are moldable and curable. 
         [0086]      FIG. 4(   b ) shows the 2×2 intraoral ultrasonic transducer  42  of  FIG. 3(   b ) in the process of taking a measurement. The 2×2 intraoral ultrasonic transducer  42  has a transmitting piezo array  45  configured to be electrically pulsed, consequently transmitting ultrasonic waves. On the other side, the 2×2 intraoral ultrasonic transducer  42  has a receiving piezo array  46  configured to receive the ultrasonic waves and convert them into electrical signals. Typically each of the piezo elements  34  in the transmitting piezo array  45  are pulsed sequentially. After one of the piezo elements  34  pulses, the four piezo elements  34  in the receiving array receive the ultrasonic wave, each typically receiving at slightly different times due to differences in the length of the path between the transmitting and receiving piezo elements  34  and the density of the material inbetween them. Using two 2×2 arrays pulsed in a single direction results in 16 discrete measurements, four measurements for each pulse duration of the four transmitter elements in one direction. The transmitting and receiving functions of opposite sides of the 2×2 intraoral ultrasonic transducer  42  can be switched to enable signals to be transmitted though the region of interest in opposite directions to double the number of measurements from each ultrasonic pulse transmission. This allows for an option of a total of 32 discrete measurements and helps to reduce transducer positioning error. Larger arrays capable of further reducing measurement scatter are possible. Larger arrays extending laterally to regions adjacent to the bone graft  20  can serve as a calibration index for comparison to the grafted area itself. 
         [0087]      FIG. 5  is a block diagram of an embodiment of an ultrasonic orthodontal monitoring system  52 . The ultrasonic orthodontal monitoring system  52  comprises an ultrasonic monitoring apparatus  56  and the intraoral ultrasonic transducer  30  described above. 
         [0088]    The ultrasonic monitoring apparatus  56  has an apparatus connector  60  that is configured to electrically connect to the transducer connector  36 . Piezo element leads  64  within the intraoral ultrasonic transducer  30  are routed from the piezo elements  34  through the transducer connector  36  and apparatus connector  60 . Each piezo element  34  has its own pair of piezo element leads  64 , including a signal lead and a return lead. In the embodiment shown in  FIG. 5 , the flexible transducer has a single pair of piezo elements  34 . Thus, it has 2 pairs of piezo element leads  64  and the transducer connector  36  and apparatus connector are at least four pin connectors. In other embodiments, the intraoral ultrasonic transducer  30  has two or more pairs of piezo elements  34 , and will thus have proportionally more pairs of piezo element leads  64  and a transducer connector with a higher pin count. For example, the 2×2 intraoral ultrasonic transducer  42  shown in  FIG. 3(   b ) has 8 pairs of piezo element leads  64  and the transducer connector  36  and the apparatus connector  60  in such an embodiment has at least 16 pin connectors. 
         [0089]    The ultrasonic monitoring apparatus  56  has a pulse generator  58 , a apparatus connector  60 , a signal processor  68 , a data switch  80 , data storage  70 , a control processor  74 , instruction memory and control lines  78 . The pulse generator  58  is configured to generate electrical pulse signals. The pulse signals are carried on internal leads to the data switch  80 . Suitable pulse generators are well known in the art, such as Maxim&#39;s MAX4644. 
         [0090]    The data switch  80  routes the pulse signals over piezo element leads  64  to one of the piezo elements  34 , which converts the electrical pulse signals to ultrasonic waves. The ultrasonic waves pass through the region of interest in the mandibular ridge  12  (see  FIGS. 4(   a ) and  4 ( b )). Another of the piezo elements  34  receives the ultrasonic waves and converts them into a measured signal, which is once again electrical. Other piezo element leads  64  carry the measured signal back through the data switch  80  which carries it to the signal processor  68 . 
         [0091]    The signal processor  68  calculates time-of-flight and relative density according to the formulas discussed above based on a time difference between when the pulse signal was generated and when the measured signal was received. The signal processor  68  determines a time when the pulse signal was generated by receiving a copy of the pulse signal split off on its way to the intraoral ultrasonic transducer  30 . In other embodiments, the signal processor  68  determines the time when the pulse signal was generated based on a copy of a command signal from the control processor  74  to the pulse generator  58  that orders a pulse be generated. Once the signal processor  68  has calculated time-of-flight information and relative density, it sends this information to data storage  70 . In some embodiments the signal processor  68  is a National Instruments NI system based on a SCM single chip microcomputer programmed with Labview Software to provide a capability to produce real time and archival records for full use of the ultrasonic measurements. In other embodiment, other components may be used for the signal processor  68 . 
         [0092]    Some embodiments of the ultrasonic orthodontal monitoring system  52  include a display  72  configured to connect with the ultrasonic monitoring apparatus  56 . The display  72  in some embodiments is a Liquid Crystal Display (LCD). In other embodiments, the display  72  is a printer or some other device that can be used to present information. 
         [0093]    The control processor  74  is configured to send control signals to other components of the ultrasonic monitoring apparatus  56  over control lines  78 . The instruction memory is configured to hold instructions for the control processor  74  regarding operation of the ultrasonic monitoring apparatus  56 . 
         [0094]    In embodiments where the intraoral ultrasonic transducer  30  has more than a single pair of piezo elements, the control processor  74  coordinates when sequential pulse signals are generated, and prior to each pulse signal, instructs the data switch  80  to which piezo element  34  that pulse signal is to be routed and which piezo elements  34  are to be connected to the signal processor  68 . 
         [0095]    Those skilled in the art will recognize that numerous modifications and changes may be made to the preferred embodiment without departing from the scope of the claimed invention. It will, of course, be understood that modifications of the invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the preferred embodiment is essential. Other embodiments are possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof.