the present invention is directed to a periodontal probe for measuring the sulfide concentration of sulcal fluid . the probe of the present invention is resistant to sulfide poisoning , and is stable in operation through repeated rinsings . fig1 depicts a typical probe 10 structured in accord with the principles of the present invention . the probe 10 includes a housing 12 having a length and a diameter configured to be easily handled by a practitioner and manipulated in the mouth of a patient . a portion of the housing 14 is configured to define a relatively small diameter tip configured to enter a patient &# 39 ; s sulcal pockets . as will be described in greater detail hereinbelow , the probe 10 includes a sulfide responsive measuring electrode , and a reference electrode . these electrodes each connected to a respective , electrically conductive lead 16 , 18 shown herein in phantom outline . the leads 16 , 18 are in electrical communication with an electro - chemical analyzer 20 which may optionally include a sound generator 24 in communication therewith . in operation , the probe is disposed so that the tip portion thereof is immersed in the patient &# 39 ; s sulcal fluid so that the measuring electrode contacts the fluid . the reference electrode is also in electrical communication with the sulcal fluid , via a salt bridge , as will be described in greater detail hereinbelow ; although , the reference electrode may not be actually immersed in the sulcal fluid . an electrical potential is developed between the measuring electrode and the reference electrode , and this potential is proportional to the sulfide concentration in the sulcal fluid . the electro - chemical analyzer 20 is operative to sense the potential between the electrodes and to provide a display which is directly indicative of , or correlatable with , sulfide concentration . since , in both instances , it is difficult for a practitioner to observe a visual display while properly positioning the probe in the sulcal pocket , a sound generator 24 may be utilized in combination with the electro - chemical analyzer 20 . the sound generator 24 produces an audible signal which is indicative of the potential generated between the electrodes . the sound generator may be operative to provide a signal having a pitch or volume which varies as a function of the measured potential ; or , the sound generator 24 may be operative in a threshold manner to provide a signal only if a preselected potential is achieved . it has been found that sulfide concentration in a sulcal pocket may have a spatial variation . generally , it is most desirable to measure the highest sulfide concentration . the use of an audible signal generator simplifies probing of the pocket by providing a direct , non - visual signal indicative of the magnitude of the potential . in a further refinement of this embodiment , the electro - chemical analyzer may be operative to store the highest potential measured so as to permit later reference thereto . referring now to fig2 there is shown an enlarged , cross - sectional view of a portion 14 of the probe 10 , including the tip portion at the first end 28 thereof which , in the operation of the probe , is placed in the periodontal pocket . as illustrated , the portion of the housing shown in fig2 is configured as a generally tapered member 42 fabricated from a body of an electrically insulating material , such as polymer . the housing may comprise a body of solid material onto which the various components of the tip are attached , or it may be made from a curable resin . a sulfide responsive measuring electrode 30 is disposed therein . this electrode 30 is most preferably fabricated from a material which undergoes an electro - chemical reaction with the sulfide ion . one particularly preferred material comprises silver , and accordingly , the electrode 30 may be simply comprised of a fine silver wire . in other instances , the electrode may comprise a wire , such as a stainless steel wire , coated with silver . other metals reactive with sulfide may be similarly employed , for example antimony . the measuring electrode 30 is disposed so that a surface portion thereof , for example portion 30 &# 39 ; as shown in fig4 is exposed at the tip 28 end of the probe for contact with sulcal fluid . as is known in the art , a reference electrode , disposed in an electro - chemical relationship with the measuring electrode 30 must be employed in order to provide a potential indicative of a sulfide ion concentration . in the illustrated embodiment , a reference electrode 32 is disposed in the probe . one particularly preferred reference electrode comprises a silver / silver chloride electrode , typically provided by disposing a chloride coating on a silver wire . in some instances , the chloride coating will be disposed to cover a substantial length of the wire , and in other instances , the wire will be insulated along substantially all of its length , and will have a body of silver chloride disposed so as to cover a free end of the wire . all such configurations may be employed in the practice of the present invention . it has been found that the operating voltage of the reference electrode is dependent upon the logarithm of the chloride ion concentration to which it is exposed . and in the use of electrode systems of the prior art , it has been found that the chloride ion concentration in the vicinity of the reference electrode can vary over a wide range of values and such variation is further increased when the electrode is rinsed between uses . variations of chloride concentration lead to fluctuations in the reference voltage , and hence a variation in the final reading of sulfide ion concentration . in accord with the present invention , it has been found that the output of the reference electrode can be stabilized , if the electrode is disposed in a saturated chloride solution . toward that end , the reference electrode 32 is disposed within a pellet of a salt , such as potassium chloride 34 . as will be better seen in fig5 the pellet of potassium chloride 34 is partially covered by the material of the housing 42 , and preferably has a major portion of its free surface covered by a moisture impervious material 36 , such as a layer of epoxy resin . the moisture impervious layer 36 covers most , but not all , of the pellet 34 . when the probe is first prepared for use , it is immersed in a rinse / hydration solution . this solution enters the opening in the impervious layer 36 and moistens the salt comprising the pellet 34 so as to produce a saturated solution therein in the region of the reference electrode 32 . the fact that the opening in the impervious layer 36 is relatively small limits entry of water and dissolution of the pellet 34 when the probe is subsequently rinsed . it is necessary that the measuring electrode and reference electrode be in electrical communication if an accurate reading is to be obtained . as noted above , problems arise in prior art systems in which the reference electrode is disposed in the sulcal fluid during use , because of sulfide poisoning of the electrode . in accord with the present invention , the reference electrode is removed from contact with the sulcal fluid , and ionic conductivity between the reference electrode and the measuring electrode is established through a salt bridge . as illustrated in the figures , a salt bridge 38 extends from the salt pellet 34 to the tip 28 of the probe . as is known in the art , a salt bridge material comprises a body having mobile ions contained therein for providing ionic conductivity therethrough . one particularly preferred salt bridge material for the practice of the present invention comprises an organic matrix defining an open lattice having a plurality of interconnected channels therethrough with an aqueous salt solution contained in the channels . one specific and preferred salt bridge material comprises an epoxy polymer matrix with potassium chloride contained therein . it has been found , in accord with the present invention , that a salt bridge may be readily provided within the probe by disposing a layer 38 of an epoxy polymer having a salt dispersed therein , between the salt pellet 34 surrounding the reference electrode 32 , and the region of the tip proximate the measuring electrode 30 . preferably , the salt bridge is prepared by coating a thin layer of curable epoxy resin and sprinkling potassium chloride salt onto the unhardened epoxy layer . the salt penetrates the layer , and the layer subsequently hardens . when the salt bridge layer is hydrated during the initial wash of the electrode , salt exposed on the surface of the bridge hydrates forming an electrically conductive surface layer . the salt embedded within the underlying matrix is leached from the matrix during successive washings so as to regenerate the conductive surface . while a variety of salts may be employed in the practice of the present invention , potassium chloride is particularly preferred because the mobility of the potassium ions and the chloride ions in solution is comparable , thereby avoiding space charge effects and the like . while epoxy resin is described as one preferred material for the fabrication of the salt bridge , it is to be understood that within the context of the present invention , the salt bridge may be fabricated from any matrix material , including organic as well as inorganic materials , which can contain salt crystals , which crystals are subsequently leached during hydration and operation of the bridge . in accord with another feature of the present invention , there is provided a hydration layer 40 on the probe , in the region of the reference electrode , measuring electrode and salt bridge . the hydration layer comprises a smooth , open structured , over coated layer which assures the maintenance of hydrated conditions between the electrodes and salt bridge and allows for wider tolerances in the fabrication of the salt bridge . as illustrated in fig2 - 5 , the hydration layer 40 comprises a layer overcoating the tip portion of the probe , and as such covers the salt bridge layer 38 . one particular hydration layer is comprised of a porous cellulose acetate layer containing a salt residue lining the pores . the layer may be prepared by coating an emulsion comprising an organic phase , which is an organic cellulose acetate solution , and an aqueous phase which comprises an aqueous salt solution . upon evaporation of the organic solvent , the water based phase is trapped within the cellulose acetate matrix . subsequent evaporation of the water droplets opens small pores in the coating matrix and leaves a salt residue that assists in hydration of the coating during the initial wash / hydration step . a number of different materials may be utilized for the hydration layer . as noted , one preferred material involves cellulose acetate , and it has been found that a hydration layer may be prepared from a 30 % solution of cellulose acetate in acetone formed into an emulsion with up to 1 % of an aqueous solution of 4m potassium chloride . other embodiments of hydration layer may similarly be prepared from a variety of polymers such as cellulose acetate - butyrate , vinyls , and the like . in general , the polymer and solvent system should be chosen so as to allow for initial evaporation of the organic phase with the aqueous phase remaining , so as to provide the porous , salt containing matrix . in use , the probe of the present invention is first rinsed with a wash / hydration solution so as to wet the hydration layer , salt bridge , and salt pellet . the wash / hydration solution may simply comprise water , or may comprise a dilute salt solution and may further include disinfectants , surfactants and the like . either before , or after hydration , the probe is placed in electrical connection with a standard electrochemical analyzer such as a d . g . electro - chem analyzer ( model 1200 ) by means of a standard connector such as a mini coaxial connector cable , which is attached to the first and second leads of the probe . the mode switch of the analyzer is set down to a reference position and the selector control to the lower volt position ( inactivating most other controls ). the power supply switch of the analyzer is turned on and the probe tip may be placed in a sterile 0 . 5 molar nacl solution . a base line reading may be taken which will usually vary between 30 - 100 mv +, reflecting the potential difference between the first and second electrodes in the probe , that is , the silver versus silver / silver chloride potential in the saline solution . if desired , the probe may then be dipped into a calibration solution including a known concentration of sulfide ion to verify operation thereof . once hydrated , the probe is ready for insertion into a periodontal pocket of a patient . the probe is inserted so that it comes into contact with the periodontal sulcal fluid contained therein . as noted above , the probe is configured so that the reference electrode does not directly contact the sulcal fluid in normal use . the electrolytes within the sulcal fluid will cause an electrical potential to develop between the electrodes , the magnitude of which corresponds to the concentration of sulfide in the fluid . typically , a clearly , clinically - observable diseased or inflamed pocket should produce a readout on the analyzer in the 500 - 700 mv + range . responses in the range of 250 - 500 mv + may indicate subclinical disease activity not readily diagnosable by conventional means . readings below this level may be borderline . readings below the borderline ( i . e . 250 mv +) down to the base line ( typically 30 - 100 mv +) generally indicate an absence of active disease . after measurement of each pocket , the probe tip is immersed in a sterile rinse solution . as noted above , the particular configuration of the reference electrode prevents disintegration and depletion of the salt during the rinse steps . while one particular configuration of probe has been illustrated , it will be appreciated that in accord with the principles disclosed herein , other configurations may be implemented . for example , the probe may be fabricated in an inverted embodiment wherein the housing may comprise a hollow , tapered cylindrical body which encloses the measuring electrode as well as the reference electrode , salt pellet , salt bridge and hydration layer . in another embodiment , the measuring electrode will comprise a cylindrical body which forms the tip itself as well as the electrode . in this particular embodiment , the reference electrode may be disposed upon an electrically insulating coating covering a portion of the body forming the reference electrode , and may be connected thereto by the salt bridge as previously noted . the reference electrode may be disposed in yet other configurations , provided that it is separated from the sulcal fluid by salt bridge material and provided that ionic conductivity between the reference electrode and measuring electrode is established . in view of the foregoing , it will be appreciated that numerous other modifications and variations of the present invention may be implemented . the foregoing drawings , discussion and description are meant to be illustrative of particular embodiments of the invention and not meant to be limitations upon the practice thereof . it is the following claims , including all equivalents , which define the scope of the invention .
a probe for diagnosing periodontal disease includes a sulfide responsive measuring electrode and a reference electrode joined by a salt bridge . the reference electrode is maintained in a saturated salt environment . the probe may include a sound generation for providing an auditory indication of sulfide concentration .