Dental electro-therapeutics

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DENTAL ELECTRO-THERAPEUTICS

Preface To The Second Edition

The kind reception accorded the first edition confirms the opinion expressed in the preface that there is urgent need for literature on dental electro-therapeutics.

This edition has been thoroughly revised and brought up to date with the addition of some new matter and illustrations. The work is specially intended to bring forward the value of electro-sterilization in treatment of root canals and periodontal diseases, and this part has been rewritten with the intention of explaining more fully the technical details of ionization treatment. Details are given in respect to ratio of time required to current strength available in the electro-sterilization of hard and soft oral tissues, and I hope that this will be of value to those who are inexperienced in electrical treatment. I would repeat a word of warning to all who undertake this method of treatment: Do not approach the subject lightly; study carefully sufficient electro-physics to understand the various phenomena of the current with which you are dealing; and obtain a knowledge of the electro-physiological effects; then the therapeutic effects will be most gratifying.

I gratefully acknowledge the assistance given by my friend Dr. C. H. Abbot who has revised the chapter on .T-ray technic and diagnosis, adding many useful hints to this part of the work. Best thanks are also accorded my daughter Miss Elsie Sturridge, L.D.S., R.C.S. (Eng.), for her valuable assistance in correcting proofs.

E. S.

London, 1918.

CHAPTER II. Galvanic Electricity

Volta's Contact Law — Electrolyte — Voltaic Cells — Electro-motive Force — Practical Electrical Units — Resistance — Heat Effect of the Current — Polarization — Poles — Testing the Poles — -Electrolysis — Ions — Electro-positive and Electro-negative 28-52

CHAPTER III. Cells

Leclanche Wet and Dry Cells — Smee Cell — Bichromate of Potash Cell — Persulphate of Mercury Cell — Bunsen Cell — Grove Cell — - Daniell Cell — Secondary Batteries or Accumulators — Edison Storage Battery — Arrangement of Cells — Cells in Series — Cells in Parallel — Cells in Multiple Arc — Density 53-73

CHAPTER IV. Magnetic Field, Dynamo Currents, and Batteries

Inducted Currents — Self-induction — Induction Coil — Secondary Coil — Continuous Current — Alternatin g Current — Transformers — Batteries — Home-made Battery — Cautery Battery — Accumulator Battery 74-97 vi CONTENTS

CHAPTER V. Batteey Accbssoeies

Current Collector — Milliamperemeter — Rheostats — Rheophores — Electrodes — Rheostat for Direct Current from the Main — -Resistance for Heavy Currents — Alternating Current Transformers — High-frequency Currents 98-122

CHAPTER VI. Dental, Electrical Appliances

Motors — Electric Engines — Electric Lathes — Switchboards — Accumulators — Direct Resistance — Motor Converter — Electric Hot-air Syringe — Electric Sterilizer and Hot-water Apparatus — Foot Warmer — Electric Furnaces — Pyrometer — -Electric Cold Annealer 123-136

CHAPTER IX. Physiological Effects of Currents

Cataphoric Effect — Electrolytic Effect — Path of the Current in the Body — Motor, Sensory and Special Nerve Effects — Effects of Current on Nutrition — Effects of Current on Salivary Glands — Resistance Effects of Current Passing through the Body . 213-230

CONTENTS vii

CHAPTER X. Electro-therapeutic Effects

Ionic Medication — From a Dental Aspect — The Zinc Ion — The Copper Ion — The Iodine Ion — The Silver Ion — The Cocaine Ion — The Adrenalin Ion — The Salicylic Ion — Advantages of Ionic Medication — Effects of Ions on Bacteria 231-249

CHAPTER XII. High-frequency and Static Currents

X-ray and High-frequency Currents 255-261

CHAPTER XIII. Electro-therapeutics in Dentistry

Treatment of Root Canals — Periodontitis from Septic Pulp — Acute Local Periodontitis — Alveolar Abscess — Trismus from Impacted Third Molar — Chronic Alveolar Abscess — Perforation of the Root — Necrosis of the Jaws — Marginal Gingivitis 262-276

CHAPTER XIV. Treatment of Pyorrhea Alveolaris

Periodontal Disease — Incipient Infection of the Gingival Trough — Septic Infection of Gingival Trough without Suppuration — Septic Infection of Periodontal Membrane — Acute Septic Infection of Gums and Periodontal Membrane — Chronic Septic Periodontal Disease 277-299

CHAPTER XV. Electricity for Anesthesia, for Bleaching, and for Neuralgia

Anesthesia of Sensitive Dentine — For Immediate Extirpation — Anesthesia of Gums and Alveolus — Electric Tooth Bleaching — Bleaching with Chlorinated Lime — Bleaching with Hydrogen Dioxide —Neuralgia 300-314

DENTAL ELECTRO-THERAPEUTICS.

PART I.

ELECTRO-PHYSICS

Chapter I. Frictional Or Static Electricity

Theories as to the Nature of Electricity— Electroscope — Ley den Jar — Conduction — Induction — Static Machine.

The study of electrical science embraces a wide and varied field. Many of the phenomena are well known and are placed on sure and scientific footing. Hypotheses have been suggested by eminent modern works in physics which connect electricity with "the ether" in a way comparable with light and heat.

The manifestations of electricity with which we have most to do from a dental aspect are those of energy, force, and power, and in order to understand how these are brought about, and how they can be utilized, the study of electricity should be undertaken from the very primitive forms of electrical phenomena which have been known for ages to the very latest discoveries of the effect of the current from a therapeutic stand -point.

A primitive electrical phenomenon was observed by

early workers in the science, who noted that when certain

substances are rubbed together a current of electricity is

generated which is possessed of certain definite properties.

18 FR1CT10NAL OR STATIC ELECTRICITY

The character of the current and the effect produced depend on the method of exciting it and the substance used.

From these early experiments in the production of electric current, methods have gradually developed into the present-day elaborate plans for the production of electricity.

It is said that Greek philosophers, many hundred years B.C., noted that when amber was rubbed with cloth it had the power of attracting other bodies, but it was Dr. Gilbert, of Colchester, an Englishman, who in the later part of the sixteenth century, made a study of this phenomenon, and who by experiments determined which bodies would and which would not acquire the property. He also gave the name of Electricity to the cause of this attraction. He tested substances by bringing them near a metal needle, lightly balanced on a pivot.

If we rub a glass rod with silk, or a piece of sealing wax with flannel, the friction will excite electricity in the rubbed end of glass or wax, and if we apply them to some light substances, such as scraps of paper or a suspended pith ball, we shall find that they will attract these bodies.

If we suspend a ball of elder-pith by a silk thread attached to the end of a ruler and apply the piece of silk, which has been used to rub the glass rod, we shall find that the pith ball will be repelled. It is clear that there are two forces excited, the one on the glass rod which attracts, and the other on the silk which repels the pith ball. The substances which have been rubbed have always contained electricity, and although the one attracts and the other repels the pith ball, it is not that there are two kinds of electricity, but only two degrees of the same current; in other words, there is a difference of power or potential. The approach of the glass rod to the pith ball alters the balance of electricity in the ball by inducing a current on the side nearest the rod of opposite sign to that on the rod, the farther side is charged with current of the same sign as that on the rod.

"Bodies charged with unlike electricities attract one another and bodies charged with like electricities repel," or

THEORIES AS TO NATURE OF ELECTRICITY 19

in the light of recent research, the current from the body which is more highly charged, tends to flow toward that in which there is a deficiency of charge, or away from that in which there is already a charge; in other words, there tends to be a levelling up.

The term positive (+) electricity is applied to current of greater power, and negative ( — ) electricity to the lesser, the differences are only potential, quantity, direction of flow, and rate of variation of these.

Metals do not become perceptibly electrified when rubbed with other substances in the same way as glass or sealing wax, because they possess the power of conducting electricity; friction fails to disturb the balance of electricity in a substance which so conveys electricity, a good conductor, as it is called, because any disturbance is promptly neutralized by the electricity flowing back to the point from which it was displaced.

Electricity may also pass from one substance in Avhich it has been excited to another which has affinity for it, without actually being brought in contact with it; that is, it may pass through an intervening air space and charge another body, or a currect of opposite sign may be excited in a body brought near a charged body, from which it is insulated. This effect is brought about by induction (see p. 24).

Theories as to the Nature of Electricity. — A theory was propounded by Robert Symmer in 1789 which is generally known as the two-fluid theory, in which it is advocated that every body contains an unlimited store of electric fluid of two opposite kinds which neutralize one another, being of equal amounts, the positive and negative kinds. These two electric fluids, he assumed, are capable of being divided, when they are excited by friction or otherwise, and the body which contained the greater amount of fluid is positively electrified, and that which contains the lesser negatively electrified. This hypothesis, which, whether regarded as true or not, possesses an analogous bearing on facts which frequently must be referred to.

Another theory which was suggested by Sir William Watson in 1747, and further elaborated on by Benjamin Franklin, is that there is but one kind of electricity, that when the current is excited or set in motion by friction or otherwise, one body becomes possessed of more current than the other at the expense of the other, the former being positively and the latter negatively electrified. This theory is often referred to as the one-fluid theory. Other views on electricity may be obtained from such authors as Green, Stokes, Maxwell, and Oliver Lodge.

The latest theory is that propounded by Prof. J. J. Thomson, of Cambridge, at the beginning of the present century. "According to this, electricity is regarded not as a fluid, but yet as having real existence in the form of minute fragments called Electrons. Definite information has been obtained as to the size, etc., of only one kind of electron, that which conveys negative electricity. It is possible that positive electrons also exist. These negative electrons can exist alone : when in motion they form an electric current. They can become attached to the atoms of a solid body, and the body is then negatively charged. Each atom of an ordinary solid body is supposed to contain many such negative electrons, paired off with an equal number of positive electrons, and if any of these negative electrons are torn away the body is left positively charged.

"The process by which a metal conducts electricity probably consists in the passing of electrons from one immovable molecule in the solid body to the molecule next to it. The mass of each of these electrons is the same, and only about j^q of that of the lightest atom known (that of hydrogen)." This concise explanation of the electron theory is taken from C. E. Ashford's Electricity and Magnetism .

The Electroscope. — We have noted that electricity of unlike kinds generated by friction attracts, and that of like kinds repels each other. To tell when a body is electrified, and which kind of electricity it is charged with, the electroscope is an easy means.

THE LEY DEN JAR

Fig. 1.— Electroscope.

There are many forms and modifications of the electroscope. One of the simplest is the gold-leaf electroscope. This consists of a vessel in which is suspended by a metal wire two strips of gold-leaf placed slightly apart. The wire is connected to a brass rod, which passes through the center of the cork in the jar and terminates in a metal plate or knob. If we approach the knob of the electroscope with a glass rod, which has been charged with positive electricity the charge will pass to the gold-leaf, both strips become positively charged and repel each other. Similarly, if a negatively charged substance be applied to the uncharged electroscope, the gold-leaf will be repelled. If the electroscope be affected by a charged body whose sign we desire to determine by bringing in contact an electrified glass rod, if it be positively charged the gold-leaf will diverge still farther, but if negatively charged the gold-leaf will collapse. The glass rod used to test the electroscope will lose none of its electrification, and on removing it the gold-leaf will relapse into its former position.

This sensitive instrument will determine if a body is only slightly charged with electricity; if the gold-leaf diverge ever so little the body is charged.

The Leyden Jar. — This is a convenient form of condenser and collector of electricity. It is usually constructed of a glass jar lined with tin-foil on the inside to within a few inches of the top, and similarly coated on the outside. Through the cork is passed a brass rod which terminates externally in a knob, and after going more than half-way into the jar, terminates in a brass chain resting on the metallic lining of the bottom of the jar. The foil lining the inside and coating the outside constitutes the two conductors, the glass intervening, the dielectric of the condenser.

Fig. 2. — Ley den jar.

To charge the jar the knob is connected with the conductor of a working frictional machine, and the outer coat is connected with earth, the charge passing to the inner coating of the jar acts on the outer coating through the intervening dielectric by induction. This induced current is conveyed away to earth, leaving a charge of opposite sign held there by the charge on the inner coat. This increases the "capacity" of the inner coat.

To discharge the jar it is only necessary to bring a conductor which is in contact with the outer coat near to the knob of the jar, when a spark will occur by the coming together of the two electricities, thus establishing equilibrium.

The quantity of electricity which the condenser will contain depends on the surface area of the metallic lining and the strength of the dielectric. If the Leyden jar is made of very thin glass, and a charge of very high potential passed into it, it is liable to be broken by the strain and a spark passes.

The phenomenon of the discharge of the Leyden jar, which takes place with sudden oscillations and a spark, enters into the principle of the construction of many appliances made for electrical treatment. The capacity of the jar varies with the area of the conducting surfaces and the thickness of the dielectric. If the area is large and the dielectric thin, the capacity will be greater than if the dielectric is thick with the same area — that is, the capacity of the jar is greatly increased if the area is increased and the dielectric remains the same thickness.

Conduction. — The conduction of electricity up to a point resembles that of heat, especially when we think of it as being conveyed along a metal. In whatever way an electric current moves it certainly is transferred from point to point by a certain class of substances, which when they permit of the free passing of electricity are known as

CONDUCTION 23

conductors, while other substances, which only allow of very little passing or apparently no passing of current are called non-conductors. If the gold-leaf of the electroscope be suspended by glass or vulcanite or some such substance known as a non-conductor, no current would pass, not that these substances do not contain electricity, because it has been shown that it may be excited on them. On the other hand, if a metal be rubbed and applied to the sensitive electroscope it will be found to have no effect on the gold-leaf, because, though current is generated, it is conducted away. A comparative list of substances which are good, poor, and non-conductors of electricity can be readily compiled. Metals and carbon come under the head of good conductors; silver, copper, platinum, iron, zinc, and mercury are the best. Poor conductors include water, saline solutions, acid solutions, the body, etc. Non-conductors include glass, vulcanite, paraffin, sealing-wax, dry skin, dry air, etc. Every conceivable thing might be included under one of these heads, those mentioned come most frequently under our notice. There is a certain amount of resistance offered to the passing of electricity even by the very best conductors, the comparison of the conductors depends entirely on this property of resistance, but even those substances known as insulators convey a certain amount of current. (The amount they allow to pass in some instances becomes dependent on the electrical force which repels the current.)

During conduction of electricity, heat is always generated. This property depends on the amount of current which is passing and the resistance which is present.

From the foregoing it may be concluded that there is no demarcation between conductors and insulators. All substances may be accounted conductors, but some conduct so badly that they are termed non-conductors. Even these are at times affected by their physical state. The skin, for example, when perfectly dry is a very poor conductor, but when moistened is a fairly good conductor. Inversely, good conductors are similarly affected by their physical state. Metals when heated become poorer conductors, whereas heat increases the conductivity of carbon. Pure water does not conduct, but acidulated water, or water to which is added a small quantity of salt becomes a good conductor. The reason for these effects of the physical state on the conductivity of current will be referred to later. The conduction of electricity through gases should not be lost sight of, for it has a bearing on the action of the current in passing through certain vacuum tubes like the .r-ray tube.

Induction. — It has been stated that all bodies more or less contain electricity, which if it is not manifest, one reason is that it is evenly distributed, and that it may be excited and made manifest in different ways. The glass rod, for example, contains electricity, which can be excited by rubbing with silk. If the electrified glass rod is brought near to a suspended insulated pith ball it will attract it. The explanation of this is that the positively electrified body brought in proximity of the body which contains a certain amount of electricity evenly distributed over its surface, causes an alteration in the distribution of electricity by inducing negative electricity to the surface nearest to the charged rod, and as unlike attracts, the light body is drawn toward the electrified rod. Induction takes place whenever an electrified body is brought near another body. If an insulated substance is touched by the electrified body it will become charged with electricity of the like sign, but if the electrified body be removed without touching, the distribution of electricity in the other becomes once more evenly dispersed over its surface. If the insulated body instead of being round be pointed at each end, and another insulated positively electrified body be brought near one end, it will induce current of a negative sign to the point, where the density will become so great, that if they are brought close enough a discharge across the intervening space in a spark will take place, neutralizing the electrified body and leaving itself charged with electricity of the opposite sign.

STATIC MACHINES 25

Static Machines. — The current produced by frictional machines is the most ancient form of procuring a continuous current of electricity for therapeutic purposes. One older type of machine was constructed on the principle of generating a current by friction of a revolving glass cylinder with an amalgamated leather rubber. The negative electricity generated on the rubber is conducted to earth with the aid of the amalgam, and the positive electricity on the glass attracts a negative charge from a stationary metallic prime conductor placed in close proximity. A negative charge from the prime conductor neutralizes the positive charged glass cylinder, and retains a charge of positive electricity, which can be conducted from the prime conductor. This form of machine has been superseded by improved induction or influence machines. One type, long known and used, is the Holtz machine, which, with the many modern improvements, is still very popular. In this country the Wimshurst machine seems to be preferred. It has the advantages of being self-exciting, and does not reverse the current generated under climatic influences while in action. "It consists of two circular glass disks (or any even number), mounted in pairs upon a fixed horizontal spindle in such a way that they rotate in opposite directions at a distance apart of not more than a fraction of an inch. Each disk is attached to the end of a hollow boss of wood, or of metal, upon which is turned a small pulley. The pulleys are driven by a cord or belt from larger pulleys attached to a spindle below the machine, and rotated by a winch handle or by a motor, the differences in the direction of rotation of the disks being obtained by crossing the alternating belts. Both disks are well varnished, and attached to the outer surface of each of these are radial sector-shaped plates of tin-foil or thin brass disposed around the disks at equal angles. These sectors are not essential to the action of the machine but they make it more easily self-exciting.

"Twice in each revolution the two sectors situated on the same diameter of each disk are momentarily placed in metallic connection with one another by a pair of fixed wire brushes attached to the ends of a curved rod, called the neutralizing rod, supported at the middle of its length by one of the projecting ends of the fixed spindle upon which the disks rotate, the sector-shaped plates just grazing the tips of the brushes as they pass them.

Fig. 3. — Wimshurst machine.

" The position of the two pairs of brushes with respect to the fixed collecting combs and to one another is variable, as each pair is capable of being rotated on the spindle through a certain angle, and there is one position of maximum efficiency. This position in the machine appears to

STATIC MACHINES 2?

be when the brushes touch the disks on diameters situated about 75° from the collecting combs, and 30° from one another.

"The fixed conductors consist of two forks furnished with collecting combs directed toward one another, and toward the two disks which rotate between them, the position of the two forks, which are supported on ebonite pillars, being along the horizontal diameter of the disks. To these fixed conductors are attached the terminal electrodes, whose distance apart can be varied. Leyden jars are usually fitted to the machine by the makers, but these must admit of their outer coating being disconnected, if the machine is to be used for treating patients." 1 There are many modifications of the Wimshurst machine, some having ebonite plates, others mica disks. These substances permit of driving the machine at a high speed without fear of breaking the plates. All, however, are made on the principle of the above description of a frictional machine here quoted.

1 Lewis Jones: Medical electricity.

Chapter II. Galvanic Electricity

Volta's Contact Law — Electrolyte — Voltaic Cells — Electro-motive Force — Practical Electrical Units — Resistance — Heat Effect of the Current — Polarization — Poles — - Testing the Poles — Electrolysis — Ions — Electro-positive and Electro-negative.

Galvanic electricity is generated by galvanic or voltaic cells and by dynamos. It is the form of current which is most used in electro-therapeutics. Its force and current-strength can be graduated and controlled at will. This form of current is universally in use in the world's commerce, for which purpose it is generated by dynamos. Thus it is often termed Dynamic Electricity.

Discovered by Galvani in 1780 and improved in method of production by Volta in 1800, it often bears the names of these eminent students.

Galvanic electricity is produced when two dissimilar conductors are immersed in a liquid medium, called an electrolyte, which has the power of acting chemically on one of them more than the other — the metals being joined outside the liquid; that is, a circuit is formed, and the current will flow between the two metals within the fluid and be conducted along the plates and connecting wire.

It is necessary to dwell upon and study the foregoing statement that two dissimilar substances are required to form a current-producing cell.

If the metals or plates of a cell are exactly alike or even very similar and are immersed into a fluid electrolyte, which is capable of acting chemically upon them, no electric current will be produced; for example, if two zinc plates or two copper plates are placed in a solution of weak sulphuric

VOLTA'S CONTACT LAW 29

acid and the plates connected without by wires, on testing the wires connecting these similar plates no current will be found to pass, but if a zinc plate and a copper plate are immersed in a similar acid solution and connected by copper wire a strong electric current will immediately flow from the zinc to the copper within the solution and then along the copper plate and copper wire connection without in a continuous circuit.

Electrolytic conduction only occurs by chemical action, as will subsequently be explained, and it is necessary that the metals or conductors employed must have different affinities for oxygen. This law is observed in the construction of all galvanic cells.

The potential or electro-motive force depends on the amount of chemical action of the electrolyte on the substances employed, and this potential difference is governed by the dissimilarity in the chemical affinities of the plates employed. If, for instance, platinum and copper be brought together in a cell, the copper would become positively electrified and the platinum negatively, and the current produced by such a cell would be feeble compared to one composed of zinc and copper, both of which are oxidizable, the zinc in this case being more highly so becomes positively electrified and the copper negatively; the potential of the current from this cell is much greater than the other.

Zinc is one of the most oxidizable metals and most easily acted upon by electrolytes. It is therefore much used in the formation of voltaic cells. Copper, carbon, and silver are very dissimilar to zinc and are often used as negative elements in the construction of cells where zinc is the positive element.

Volta's Contact Law. — To Volta is due the discovery of the manifestation of difference in potential by contact of dissimilar metals in air, and also, as is known in the construction of cells, that the size or form of the metals does not affect the potential, but only their dissimilarity and the nature of the metals employed. The electro-motive force which can be obtained by bringing together two metals in an electrolyte varies as the degree to which one becomes electro-positive and the other electro-negative when in contact.

Lists have been arranged according to Volta's contact list, in which each substance or metal in the list will be positively electrified when in contact with any metal succeeding it, and vice versa, negatively electrified in contact with any metal preceding it on the list. In the list the farther removed from one another in the series the greater will be the electro-faction of the metals if brought together in contact; thus zinc and carbon will have a potential difference far greater than zinc and iron.

Such a contact series is as follows:

Sodium. Copper.

Zinc. Silver.

Iron. Gold.

Lead. Platinum.

Tin. Carbon.

According to Volta's contact law, "The difference of potential between any two metals is equal to the sum of the difference of the potential between the intervening metals in the contact series."

In the construction of galvanic or voltaic cells the metal plates are usually chosen with due respect to their difference of potential, but other properties have also to be taken into account, e. g., sodium is never used, although between it and carbon there is one of the highest potential differences, because it would not be manageable for a battery.

The Electrolyte. — The electrolyte of a cell is the excitant and conductor of current. It acts chemically on the two elements and conveys electrically charged atoms from one to the other when the circuit is closed.

Among the commoner fluids used as electrolytes in galvanic cells are dilute sulphuric acid, ammonium chloride, persulphate of mercury, etc.

Voltaic Cells. — To construct a voltaic or galvanic cell, select any two of the dissimilar metals from the foregoing

>n e^s

Fig. 4. — Voltaic cell.

contact series, the one farthest removed from one another will be the most highly electrified when placed in an electrolyte, which has a greater chemical action on one than the other. Take zinc and copper for the elements, and sulphuric acid; immerse the two metals in the acid, connect the ends outside the vessel with wires (see Fig. 4). As soon as the contact is made a continuous current will flow from the zinc through the liquid to the copper; this is the stronger current set up by establishing a potential difference between the two elements — that is, electrifying one element positively and the other negatively. The positive ( + ) electricity on reaching the opposite element is conducted by it to the wire connection without the cell, and conveyed back to the zinc again through the electrolyte, making a complete circuit, which will go on until the electrolytic strain on the higher potential is reduced to equilibrium by the ceasing of chemical action of the electrolyte on the elements, either by their destruction or by the conversion of the oxidizable surface through the deposit of some chemical product of a less electrostatic nature.