Abstract:
A surgical device for preparation of an implant site is disclosed. The device comprises a body capable of being held by a user and an insert that is capable of being coupled to an end of the body. An ultrasound transducer is disposed within the body and provides an ultrasound frequency vibration to the insert in response to an electrical signal. The insert includes a tip having a plurality of cutting elements disposed in a substantially circular configuration. The insert also includes a channel having an opening at the tip for the passage of fluid.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention refers to a surgical method of implant site preparation, in particular for endosseous dental implantology and to a piezoelectric surgical device used to implement said method. 
     2. Background of the Invention 
     Endosseous dental implantology uses cylindrical or conical implants which are inserted into a hole made in the bone called the implant site. The implant site is generally made with spiral-shaped rotating drills, driven by micromotors. The drills have variable diameters and are applied in ascending order until a hole of the size chosen to accommodate the implant is obtained. 
     These methods present severe limitations if they are to be used in difficult situations (such as, for example, restricted surgery access or anatomically delicate bone conditions, and in particular when it is necessary to operate in the vicinity of soft tissue. 
     The cutting characteristics of the techniques currently in use are unsatisfactory because the rotation of the drill and the consequent macrovibrations generated reduce the operator&#39;s tactile sensitivity with a consequent loss of control of the cutting depth. Furthermore, the high mechanical energy produced by the use of these instruments increases the risk of overheating of the tissues involved, compromising healing thereof. 
     Rotating drills act both on mineralized and non-mineralized tissue and consequently it is possible to damage involuntarily the soft tissue and the delicate structures (for example the vascular nerve bundles) near to the operating field. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to overcome the drawbacks of the prior art through the use of a surgical device combined with a method for preparation of the implant site which allow surgical procedures to be performed with extreme precision and control, maximum intra-operative visibility and selectivity of cutting, with an increase in safety and a reduction in the above described risks. 
     These objects are achieved in accordance with the invention with the characteristics listed in appended independent claims  1  and  3 . 
     Preferred embodiments of the invention will be apparent from the dependent claims. 
     The surgical device for implant site preparation according to the invention comprises:
         a body designed to be gripped by the user;   an insert mounted on the head of said body and having such a shape as to be able to operate on bone tissues, and   an ultrasonic transducer disposed inside the body and connected to said insert to make it vibrate at a frequency in the ultrasound range.       

     The insert comprises a tip consisting of a plurality of cutting elements disposed in a substantially circular configuration. In the body of the insert there is provided a channel which ends in an outlet channel opening in the tip of the insert for passage of an irrigating fluid, so as to cool efficiently the work area involved by the tip of the insert and at the same time to exploit the physical effect of cavitation which allows a greater cleaning of the operating field with a consequent increase in visibility with respect to the conventional method. 
     The object of this patent is the preparation of the implant site for cylindrical or conical implants using a suitable ultrasonic instrument for bone surgery, such as that described in U.S. Pat. No. 6,695,847, with specially designed inserts provided with internal irrigation means. 
     The combined use of the ultrasonic device and of the aforementioned inserts allows an implant site to be made with great surgical ease and with an excellent tissue response, with an acceleration of the mechanisms of healing and of new bone formation, as shown by tests and experimental research in animals (as reported below). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics of the invention will be made clearer by the detailed description that follows, referring to a purely exemplary and therefore non-limiting embodiment thereof, illustrated in the appended drawings, in which: 
         FIG. 1  is a perspective view illustrating an ultrasound handpiece according to the invention; 
         FIG. 2  is a perspective view of the insert mounted on the handpiece of  FIG. 1 ; 
         FIG. 3  is a sectional view of the insert of  FIG. 2 ; 
         FIG. 4  is a perspective view of a second type of insert; 
         FIG. 5  is a sectional view of the insert of  FIG. 4 ; 
         FIGS. 6-9  illustrate the successive steps of the surgical method carried out with the ultrasound handpiece according to the invention; 
         FIG. 10  illustrates an animal bone in which three holes have been made; one with the ultrasound method and the other two with the traditional method; 
         FIG. 11  illustrates the bone of  FIG. 10  in which three implants have been implanted in the three holes made previously; 
         FIG. 12  illustrates an autopsy specimen of the bone of  FIG. 11  after a sufficient time for mineralization of the bone around the implant; 
         FIGS. 13 and 14  are two histograms showing the results of biomolecular analyses, on the BMP4 and TGF-β2 molecules respectively, on autopsy specimens collected at successive times on implant sites made with the ultrasound method and with the traditional method. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A surgical device according to the invention, which is denoted as a whole with reference numeral  1 , is described with the aid of the figures. As shown in  FIG. 1 , the surgical device  1  is a handpiece that comprises a body  2 , substantially cylindrical in shape so that it can be easily gripped by a surgeon. At the head of the body  2  is mounted an insert  3  having a suitable shape for the creation of an implant site, as will be described hereunder. 
     The body  2  of the handpiece is connected to an external connector element  4 . The external connector  4  bears electrical supply and hydraulic supply cables designed to be connected respectively to an electrical supply, to a hydraulic supply and to a peristaltic pump provided on a console. The console provides a control panel for operation of the surgical device  1 . 
     Inside the surgical device  1  there is provided a transducer connected to the insert  3 . The transducer can be piezoceramic resonator, designed to transform the electrical input signal into a vibration in the ultrasound frequency, so as to make the insert  3  vibrate. For this purpose the transducer is supplied with alternating voltage and current, preferably with sinusoidal voltage of about 160 Volt r.m.s. at a frequency ranging between 25 kHz and 30 kHz, so as to act as a sound wave concentrator and to set the insert  3  in vibration at an ultrasonic working frequency. An ultrasonic work carrier frequency of 27 KHz is preferably chosen. 
     According to requirements, the supply signal of the transducer having a carrier ultrasound frequency can be modulated or overmodulated with a low-frequency signal (6-40 Hz); or can be modulated or overmodulated with a series of low-frequency bursts. 
     The power of the vibrations of the insert  3  is regulated by varying the duty cycle of the signal with the carrier ultrasound frequency and by maintaining constant the duty cycle of the signal at the modulation or overmodulation frequency. 
     This method, which adopts modulation of the vibration of the insert  3 , makes it possible to minimize the heat that develops in the soft tissue because of the energy dissipation due to vibration of the insert. 
     The method, which provides for use of a carrier signal at ultrasound frequency modulated with low frequency bursts, varying the duty cycle of the carrier signal at ultrasound frequency, makes it possible to have a hammering effect of the insert  3 , combined with the efficacy of the ultrasound vibration which causes a clean, precise cut in the mineralized tissues. 
     As shown in  FIGS. 2 and 3 , the insert  3  comprises a cylindrical tang  30  designed to be connected to the ultrasonic transducer inside the surgical device  1 . The tang  30  comprises a groove  31  designed to be engaged by a mounting key of the handpiece and an inner thread  39  for connection to an attachment of the transducer of the handpiece. 
     The tang  30  is connected to a shank  32  with a smaller diameter than the tang  30 , by means of a tapered transitional portion  33  having a decreasing diameter from the tang  30  to the shank  32 . 
     The shank  32  has at its end a tip  35  which is the working part of the insert  3 . The shank  32  has centrally a curved portion  34  so as to be able to direct the tip  35  more easily towards the work area. The curved portion  34  defines an obtuse angle which can range from 90° to 170°. 
     As shown in  FIG. 3 , a duct  36  is formed axially in the body of the insert for passage of a cooling fluid, such as a physiological solution for example. The duct  36  is open in the rear part of the tang  30  to be connected to a hydraulic supply tube provided in the handpiece and ends with an outlet duct  37  disposed in the tip  35  of the insert. 
     From the outlet duct  37  there protrude radially outward a plurality of radial tongues  138 , preferably six in number, disposed equidistant from each other by an angle of about 60°. The peripheral edges of the tongues  138  define a circumference having a diameter of about 2-2.5 mm, preferably 2.2 mm. 
     Each radial tongue  138  comprises a cutting end profile  50  and a cutting lateral profile  51  so as to be able to make an incision in the bone, when the tip  35  of the insert vibrates at ultrasound frequency. 
       FIGS. 4 and 5  show a second type of insert  103 , in which like or corresponding elements to those already described are denoted with the same reference numerals and are not described in detail. 
     The insert  103  differs from the insert  3  only in the shape of its tip  135 . The tip  135  of the insert  103  has a circular plate  139  at the centre of which the outlet duct  37  opens. 
     A plurality of segments  138  preferably eight in number, disposed radially with respect to the outlet duct  37  and equidistant from each other by an angle of about 45° are provided on the circular plate  139 . Each segment  138  is shaped as a pyramid with an upturned triangular base, with the vertex pointing towards the outlet duct  37 . Each segment  138  has a cutting profile  150  which converges radially from the periphery of the segment towards the outlet duct  37 . 
     Corridors  140  which start from the outlet duct  37  and extend radially outward are left between the segments  138 . 
     In this manner the irrigating liquid flows out radially from the outlet duct  37  and spreads radially through the radial corridors  140 , so as to maximise the cooling of the cutting area. 
     The peripheral edges of the segments  138  and of the corridors  140  define a circumference having a diameter of about 2.5-4 mm, preferably 3.3 mm. 
     In this manner the first insert  3  can be made to form a small diameter hole in the bone and the second insert  103  can be used to enlarge the hole made by the first insert  3 . 
     Performance of the surgical procedure according to the invention is described with reference to  FIGS. 6-9 . 
     As shown in  FIG. 6 , using suitable tools  7 ,  8  the muco-periosteal flaps  9  and  10  of the surgical area are lifted so as to expose the bone  11  in which the procedure is to be performed. The smaller diameter tip  35  of the insert  3  of the ultrasound surgical device  1  is applied to the portion of bone concerned  11 . 
     The tip of the insert is made to vibrate at ultrasound frequency and at the same time the cooling fluid passes through the duct  36  inside the insert and reaches the outlet duct  37  in the tip  35  of the insert, from which it flows out, cooling the area on which the tip  35  is working. 
     A light pressure is exerted with the hand on the surgical device  1 , combined with an angular oscillating movement, so that the tip  35  of the insert presses on the bone cortex  11 , at the area chosen for the implant site. 
     This procedure continues until a suitable depth for the length of the implant is reached. Then the insert  3  is removed from the bone  11  and, as shown in  FIG. 7 , a hole  12  having a slightly greater diameter than the tip  35  of the insert  3  is left. 
     As shown in  FIG. 8 , at the end of this operation the insert  103  having a tip  135  with a larger diameter is used in a similar fashion so as to enlarge the hole  12 , until an enlarged hole  13  ( FIG. 9 ) is obtained, having a diameter substantially equal to the diameter of the selected implant. 
     At this point the selected implant can be implanted in the hole  13 . 
     This system for the preparation of implant sites holds various advantages. 
     Extreme ease of execution of the procedure is achieved, thanks to the precision and to the control afforded by ultrasound piezoelectric surgery. The action of traditional devices (micromotors combined with drills) is associated with macrovibrations so that performance of the procedure lacks precision, whereas the action of the ultrasound handpiece is characterized by microvibrations of the insert  3 ,  103  which allow a greater tactile sensitivity of the operator with a better intraoperative precision. 
     Reliability is achieved in cutting of the bone which, thanks to the particular ultrasonic frequency vibrations of the insert  3 ,  103 , allows a selective cutting, that is a cutting which is effective in removing biological material in mineralized structures (bone) with minimal trauma for the soft tissues and for the delicate structures. Accidental contact of the cutting tip  35 ,  135  of the insert with a nerve does not cause injury, thus it is possible to operate in safety, even in areas that are anatomically difficult or high risk with traditional instruments. 
     The duct  36  carries the irrigation fluid to the outlet duct  37  in the tip of the insert, allowing the surgical field to be irrigated precisely, avoiding critical overheating of the bone during the operation. 
     Use of the surgical device  1  combined with the method described for preparation of the implant site, allows better regeneration of biological tissue compared with traditional methods, as shown by comparative tests on animals reported below with reference to  FIGS. 10-14 . 
     Comparative Tests 
     Sixteen implants (Nobel Biocare porous implants MK III Ti unite) were placed in the tibia of eight minipigs. The experimental animals were divided into two groups of four animals. 
     In a first group of four animals a single implant per animal was placed and the implant site was prepared using a piezoelectric surgical technique. 
     In a second group of four animals three implants per animal were placed. In each animal of the second group one implant site was prepared by the piezoelectric surgical method and two implant sites were prepared by a traditional surgical method using Brånemark system drills (control test). 
       FIG. 10  shows the bone  20  of the animal in which the hole A was prepared with the piezoelectric method and the holes B and C with the traditional method. 
       FIG. 11  shows the bone  20  of the animal, in which the implants  9 A,  9 B and  9 C have been implanted in the respective holes A, B and C. 
     In the second group comprising four animals, each with three implants, the animals were sacrificed at successive intervals of time, namely exactly 7, 14, 28 and 56 days after placement of the implants, to collect the relative autopsy specimens (bone block with implant). 
       FIG. 12  shows an autopsy specimen  21  in which the implant  9 A is healed into the bone  20 . 
     The relative autopsy specimens were then subjected to histological (decalification) and biomolecular tests (cDNA evaluated with PCR Real-Time for gene expression of BMP-4, TGF-β). 
     The two surgical methods (traditional and with ultrasound surgical device  1 ) showed no qualitative histological differences in the times observed. As shown in the graphs of  FIGS. 13 and 14 , respectively, the biological analysis showed that expression of the two molecules (BMP-4, TGF-β2) was increased in the piezoelectric surgical method (Piezo) in the first experimental times compared with the traditional method (Control).