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The Ideal Amalgam Restoration*
T in g le y — I d e a l A m a lg a m R estoration
the effect of prophylactic vitamin D ther apy on dental structure. W e have such a group of about 450 children who have received viosterol in infancy, many of whom are now getting their permanent teeth. Unlike the rachitic group, which is composed mostly of colored children, the prophylactic group contains about an equal number of w hite children; hence, it will be possible to ascertain the correct ness of the supposed predisposition of the white race to dental decay. T h e plan, for next year, therefore, is to study the
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group in the same manner that the rachitic group was investigated this year, namely, a physical examination, dental roentgenographic examination and a study of malocclusion, hypoplasia and caries. As in the rachitic group, each child in the prophylactic group has had a series of roentgenograms during infancy and the absence of rickets in each one is therefore definitely known. Respectfully submitted, H a r r y E. K e l s e y , Advisor.
TH E IDEAL AMALGAM RESTORATION* By H A R O L D E. TIN G LEY , D .M .D ., B oston, Mass.
E B S T E R defines the adjective “ideal” as m eaning “conforming to a standard of perfection.” W hile it is difficult to qualify perfection in anything, we should do so, I believe, when we allude to perfection in amalgam work. It is doubtful th a t any authority believes a state of perfection to exist in amalgam restorations. T his lack of ac complishment is due mainly to the com plexity of the m ultiple physical and chemical factors involved and to an in different technic. Since its adoption in the field of den tistry, amalgam has been the subject of many empiricisms; which is one of the reasons that the scientific study of amalgam has progressed so slowly until comparatively recent years. A t the present time, the laboratory
W
*R ead at the S ev en ty -F ifth A n n u al Session o f the A m erican D en ta l A ssociation in con junction w ith the C h ica g o C entennial D ental Congress, A u g. 11, 1933.
Jour. A .D .A ., October, 1934
study of the physical and chemical prop erties of amalgam is, I believe, ahead of our study of the development of an accu rate and a scientific technic. Pond states that 75 per cent of restora tions are today made with amalgam. If this is true, amalgam is a material which deserves all the study th at can be given it. It has been said many times, and I hesi tate to repeat it, that “amalgam is the most widely used and abused of filling materials.” If this statement is true, and it undoubtedly is, the time has come when empiricism should be cast aside and amalgam restorations made according to the latest scientific knowledge on the sub ject. Paffenbarger and Sweeney sta te: The Research Commission has directed its research associates to purchase in the open market materials that are guaranteed by their makers to meet the various American Dental Association specifications and to test these materials for compliance with these specifica tions. Thus, by these check tests, the profes sion will be further protected against inferior
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T he Journal of the American D en ta l Association
products. Likewise, the manufacturer who is actually producing specification materials and has adequate testing facilities will also be pro tected against unfair trade practice.
I believe that every practitioner is in sympathy w ith the above-mentioned re port. Such precautions are bound to be re flected in an improved product, and no stone should be left unturned to improve our dental materials. T h e last sentence of the last paragraph of this report seems to me the most pertinent: “ It is felt that these safeguards will protect the dentist in the purchase of satisfactory materials. It is then his duty to employ them cor rectly.” A
Fig. 1.—Above, A , frail enamel, which is likely to fracture under stress. The enamel margin at B is much stronger. Below, shaded areas indicating probable enamel fractures resulting from placing margins in critical location ; i.e., near tips of cusps.
T h e implication from the foregoing sentence is, I believe, a challenge to the dentist to exert his best efforts in the use of dental materials. In the last analysis, this means th at the use of the materials should be based on scientific findings. One has only to refer to W a rd and Scott’s recent report to learn th at even the use of a differently surfaced m ortar and pestle will make a measurable difference in volumetric behavior of amalgam.
Knowledge of physics and chemistry is sufficiently complete at this time to as sure us safe materials and safe technic. By safe, I mean materials and a technic which w ill give us more accurate clinical results than were ever before obtained. C redit and recognition should be given to all the investigators of amalgam, but especial appreciation should be accorded the m en at the Bureau of Standards. T he efforts of Souder, Taylor, Sweeney and Paffenbarger were unquestionably of out standing m erit; for their contributions definitely improved the quality of dental alloys on the market today. T h e recent work of W ard and Scott
Fig. 2.—Above, A , B and C, points making adaptation and finishing a difficult task. Below, sharp, irregular angles in outline form, which make adaptation and finishing difficult.
deserves mention and recognition. T he report recently made by them was an other milestone in our progress toward ideal amalgam restorations. H arper should receive great credit for his contri butions and untiring efforts in the field of amalgam. H e has undoubtedly done more than any other investigator to im prove the amalgam technic of dentists. I t is unquestionable that the higher grade alloys must be available for the dental profession. H igh silver alloys of favorable proportional contents are the
Tingley— Ideal Amalgam Restoration only safe materials to use, since the best clinical results can be obtained only from high grade alloys of a known and favor able physical behavior. Volume changes alone vary sufficiently in alloys selected at random to make it necessary to choose a high-grade alloy in order to insure good results. An accurate and painstaking technic is of little help if the basis of the technic is the employment of a poor alloy; yet, con versely, the use of a high-grade alloy com bined w ith an inferior technic w ill not give satisfactory results either. T h e ques tion at once arises as to w hether the use of a good alloy or good technic is the more
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far more interested in the selection of a proper alloy than in the utilization of an improved technic, and such an attitude should be subject to modification. O b viously, lack of care in the use of amal gam is due to carelessness, and is gen erally the result of a belief on the part of the dentist th at he is dealing with an inferior filling material which it is not necessary for him to manipulate with precision. I t is not the purpose of this paper to champion amalgam over and above its value; yet it is only fair to state that amalgam deserves a high rating as a tooth-saving material. M ost practitioners agree th at gold is the filling material par excellence; yet Pond states th at he believes amalgam to be a better restorative material than in-'
Fig. 3.—More orthodox and desirable types of outline form than that shown in Figure 2.
Fig. 4.—Comparison between amalgam bevel illustrated at A and bevel for gold illustrated at B. T he amalgam bevel should be three-quarters to full length of the enamel wall, varying but slightly in its direction from the cavity wall.
im portant. O ne cannot fairly make such a differentiation; for both are important, and w ithout both, excellent results can not be obtained. I t is apparent, therefore, th at many failures w ith amalgam are traced by those responsible to the chemical and physical properties of the alloy when only a poor technic is responsible. F aults such as poor condensation, ill-shaped contours, cervi cal excesses and overhangs cannot be properly attributed to the use of a lowstandard alloy. Broadly speaking, it would seem th a t the average dentist is
lays made of gold. C ertain it is th at thousands if not millions of teeth are saved yearly in this country by the use of amalgam. Amalgam has its faults— plenty of them— but if the material is understood and its physical properties ob served, many of these deficiencies can be sufficiently controlled to give us very good results. Some of the disadvantages which may be attributed to amalgam are: relatively low tensile and edge stren g th ; a crystal line make-up, which defeats attempts to burnish it; expansion and shrinkage; a
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tendency to discolor in the mouth, and therm al conductivity. Spheroiding is not mentioned in the foregoing list because it is quite probable that this phenomenon should be properly included in the vol ume changing factors of expansion and shrinkage. L et us discuss briefly the defi ciencies above related and attem pt to point out the seriousness of each, taking them in the order of their importance. Shrinkage is without doubt the most det rimental physical characteristic which amalgam possesses. I t has the eifect of pulling the restoration away from its cavity walls, thereby exposing such areas to bacteria and decay— not to mention the discoloration which results when these surfaces are exposed to the fluids of the
condensation of the filling. Such residual excess mercury w ill produce serious vol ume changes; which, in turn, will ad versely affect the durability of the resto ration. T h e crystalline physical characteristic prevents the burnishing of the margins of the filling as is done when using gold. This, to a large extent, precludes good adaptation to the cavity walls if an error has been made at the cavosurface angle in carving or preparing the cavity. T his point illustrates definitely the precision required in the technic. T h e disadvan tages of this crystalline makeup can be controlled by employment of the amal-
Fig. 5.— Use of spiral plane fissure bur No. 56 or 57 for finishing enamel wall.
mouth. Shrinkage also impairs the mechanical structure of the restoration by draw ing the amalgam away from its supporting w alls; but shrinkage can be controlled to a large extent by the selec tion of a high-silver-content alloy and by the complete removal of excess mercury, accomplished by thorough condensation. T h e next most important physical dis advantage associated w ith amalgam is its apparent crystalline formation. This type of structure hinders us in the re moval of the excess mercury owing to the evident temper which the amalgam ex hibits when exposed to pressure during
Fig. 6.—Above, hardened cement base with amalgam ready to adapt to cavity. There is a flat floor and clean walls. Below, amalgam in soft mass of cement showing irregular floor and inevitable result when pressure, as indi cated by arrow, is applied.
gam before the initial crystallization has started and by the use of suitable pres sures at the proper times during conden sation of the filling. T h e low tensile and edge strengths are factors in the failure of restorations when beveling of the enamel walls of the prepared cavity necessitates the drawing out of the amalgam into thin edges. Such edges will, of course, fracture, imperfect
Tingley— Ideal Amalgam Restoration margins resulting. T his characteristic can be controlled to a large degree by proper treatm ent of the enamel wall. W here tensile strength is needed for retentive purposes, a sufficient bulk should be given to the preparation to pro vide essential strength to the filling material at that point. T h e discoloration of amalgam and, subsequently, of the tooth structure, which is indeed a serious fault, implies that its use should be confined mostly to the posterior teeth. Some years ago, G. V. Black pointed out th at discoloration of the tooth structure resulting from the placing of amalgam occurs only where there are leaky margins. H e advanced
Fig. 7.—Carving direction with spoon or carving instrument, from tooth structure toward central part of restoration area.
the theory that the metallic salts and hydrogen sulphide would penetrate the dentinal tubules only when moisture was present. Comparatively nothing has been brought out in recent years for or against this theory, which indicates that the con trol of this condition may be accomplished by adopting a technic th at w ill insure im permeable margins. T h e discoloration resulting from the presence of unsup ported enamel can best be controlled by its removal or by the use of a light col ored cement lining. T h e discoloring ten dency of amalgam is indeed unfortunate, and, accordingly, the use of this material
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should be confined to teeth and surfaces of teeth which are not exposed to view. T h e use of amalgam in the lingual pits of maxillary anterior teeth is dangerous in this respect, and for these cases no better m aterial than gold can be found. I t is apparent th at expansion is not an unfavorable factor except in poorly bal anced alloys; i. e., alloys which have an unusually high silver content, and there are none of these on the market. P ro longed expansion up to a period of a tenday ultimate expansion is desirable. If there is need of controlling expansion, it should be done by selecting an alloy which is not above 70 per cent in silver content. T herm al conductivity is undesirable in any filling material, since lasting injury to the pulp may result. T h e thermal con ductivity of amalgam is, I believe, suffi ciently below that of gold to be more desirable material in this respect. T h e r mal conductivity should always be con sidered when impending irritation to the pulp is anticipated. Cavity lining and cement are probably the best means of insulation in these cases. In addition to the above-mentioned physical and chemical shortcomings of amalgam, considerable attention has been given in the dental literature to flow, spheroiding and mercurial poisoning. In a discussion of alloys of high silver con tent, flow ceases to be a factor to any dangerous extent. T h e presence of, let us say, 68 per cent silver, 26 per cent tin, 5 per cent copper and 1 per cent zinc raises the crushing strength sufficiently to eliminate flow from any great practi cal consideration. M uch has been w rit ten about that unusual and inexplicable phenomenon, spheroiding. T h e theory has been advanced that any alloy contain ing mercury tends to become spheroidal because mercury in its separate and un combined state has that tendency. T he
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amount of uncombined mercury in an amalgam restoration would, of course, vary w ith the technic of manipulation. I t is hard to believe th at a sufficient amount of free mercury exists in a well-condensed filling to allow this action to take place. T his statement is made guardedly, as there is no proof for it at hand; but it would seem that, for our answer, we should look to the volume changes which might result from extreme tem perature variations in the mouth. F or example, there is a considerable tem perature spread between a cup of hot coffee and a dish of sherbet, and the relative volume coeffi cient value of amalgam is high for the metals. T ay lo r states that measuring by thermocouple the tem perature of an amalgam mix triturated in a mechanical mixer showed a rise in tem perature of from 20 to 25 degrees Centigrade, and the amalgam did not behave well after wards. If this is true, is it not a logical deduction th at greater temperature vari ations, such as are found in the mouth, will inevitably cause much volume change in amalgam restorations? A t the present time in this country, there seems to be no general belief that mercurial poisoning may result from the presence of silver amalgams, although Germ any has many adherents to this theory. Saliva in which silver amalgam was immersed for six weeks showed no mercury and only slight traces of tin. As the salts of tin are not particularly harm ful, if these experiments were exact, m er curial poisoning may be dismissed from our minds. As regards this point, a num ber of G erm an investigators have shown th at copper amalgam gives off mercury in proportionally large quantities. T here also have been several cases reported of severe poisoning, but it must be remem bered in this connection that copper amalgam is much less stable than silver, especially in the fluids of the mouth. Cop
per amalgam is well on the road to being discarded in this country, although abroad it is still in general use. I t was heralded in the past on its supposed germicidal merits and became touted as the panacea for all ills in children’s teeth. T ru e, it may have had germicidal merits, but its instability in the fluids of the mouth ren der it generally unfit for use. Before proceeding w ith an advocated technic, let us consider briefly the makeup of an alloy and also the phenomenon of w hat is called the setting of the amalgam. M ost high-test alloys have an element content which compares closely w ith the following form ula: silver 68 per cent, tin 26 per cent, copper 5 per cent and zinc 1 per cent. Every alloy should have a high silver content; which promotes ex pansion, thereby controlling excessive shrinkage. T h e use of silver also in creases edge strength, controls flow and hastens setting. T h e tin contracts and its employment decreases edge strength, increases flow, retards setting and adds plasticity. T h e use of copper increases edge strength, at 5 per cent or less, hastens setting and decreases flow and there is little change in volume. T he zinc content increases edge strength, les sens flow, improves color and adds smoothness to the amalgam. Silver and copper unite with mercury with greater difficulty than does tin or zinc, and tin has an exceptional affinity for mercury; which makes it a dangerous factor in this respect. A high silver alloy w ill not work so smoothly as one containing a large amount of tin, but shrinkage can be con trolled only by using a high silver con tent. Practitioners should, therefore, avoid excessively smooth amalgams as these usually shrink greatly on account of the high content of tin. T h e trituration of an amalgam in the m ortar and the subsequent mulling in the hand are accompanied by shrinkage which
Tingley— Ideal Amalgam Restoration is the result of the fact that alloy filings go into solution w ith the mercury. This, which is called the primary shrinkage, is followed by a primary expansion which is the result of the crystallization marked at the start by a slight crepitus in the mass. T h e duration of this primary ex pansion period is approximately twentyfour hours, after which the residual ex cess mercury diffuses through the amal gam and the remaining particles of alloy go into solution, this causing a secondary shrinkage. T h e subsequent crystalliza tion, which is known as secondary ex pansion, is desired at the end of approxi mately ten days. If this sequence of events occurs as claimed, any margin th at is finished before the expiration of th at time will fail. T h ere is a period which lasts from the completion of the mixing until about ten minutes have elapsed, during which time the amalgam is more easily adapted to the cavity walls. T his period, which is called the period of adaptable plasticity, varies in length w ith the type of alloy employed, being of shorter duration in high-silver-content amalgams. T here should be relatively little crepitus in the amalgam during the period of adaptable plasticity. Immediately following this, there is a period of lessened plasticity, which continues until the amalgam ceases to be workable. T his is called the period of workable plasticity. D uring this period, the amalgam may still be used, but good adaptation to the cavity walls will not be effected and difficulty w ill be experienced in removing excess mercury. T h e foregoing facts are practical points, easily demonstrable by experimentation. T h e greatest success is obtained only by exercising regard for these periods in the setting of the amalgam. Cavity preparation is an important p art of amalgam technic. Restorations usually fail if preceded by poor cavity
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preparations. T here is no step in amal gam technic that is more important. Fundam ental principles of cavity prep aration must be followed, and such prin ciples should evolve from a complete familiarity w ith the anatomy, histology and pathology of the tooth. T here are, briefly, two types of dental caries: the pit and fissure type and the smooth surface type. T h e former attacks the tooth through structural defects; the latter, by the formation of plaques on the smooth surface of the enamel within the vulnerable or especially susceptible areas. In the first type, the limits of the caries are not usually known until the cavity is partially prepared and, obviously, two cavities of the first type in the same tooth should not be filled separately until it has been definitely established that they are not intercommunicating. In the pit and fissure type, caries seldom spreads on the surface of the tooth, and this fact makes it unnecessary to “extend for pre vention” except to include pits, fissures and deep grooves. In the smooth surface type, the operator should not, of course, limit the extension of the cavity outline until all carious and susceptible areas have been included. In this respect, special attention should be given to cavi ties on gingival third of the tooth, as de calcified enamel w ill not be detected un less the surface of the tooth is dry. Cavi ties of this type present a problem in mouths wherein caries susceptibility is high. G enerally speaking, their outline forms should be proportionately extensive. T h e direction of the enamel rods modifies the treatm ent of the enamel and the directional placement of the cavity walls. T h e rods radiate from the pulp, converge in approaching grooves and change direction acutely at cusps and ridges. Accordingly, cavity enamel walls are stronger when placed near the grooves.
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T he Journal of the American D ental Association
P it and fissure cavities should be ex tended to include all caries, pits, fissures and deep grooves, as it is almost impos sible to finish properly the m argin of a restoration which crosses a deep groove. M arginal ridges should not be en croached on or undermined w ith inverted cone burs. T here should be no sharp angles in the outline form and the floors should be flat; in a parallel plane to the surface of the tooth, and always well seated in the dentin. T h e walls should be parallel and at right angles to the floor, w ith the exception of the slight re tentive form made at the floor w ith an inverted cone bur and sharp hand instru ments. T h e enamel margins should be beveled from three quarters to the full length of the enamel rods, flaring but little from the direction of the wall. A plain spiral fissure bur of moderate size is, I believe, the best instrum ent for this purpose. T h e occlusal dovetail, the chief source of retention in compound cavities in the posterior teeth, should follow the groove tow ard the buccal aspect. Especially is this true in the maxillary teeth. Con stricted portions of the cavity should be made sufficiently wide and deep to com pensate for the low tensile strength of amalgam. Buccal and lingual walls should be extended to self-cleansing areas and, if possible, should be kept w ithin the angles of the tooth. Gingivally, the extension for prevention is made to a point under the normal free gingival margin. T h e gingival w all should be at right angles w ith the axial w all, as well as parallel to the floor of the dove tail. Amalgam requires somewhat more re tention than malleted g o ld ; and owing to this fact, substantial retentive points are placed in the proximal portion. T h e buc cal and lingual enamel walls are finished by planing w ith sharp chisels, and at the
gingival enamel wall, Black’s gingival margin trimmers are used. Caries frequently is extensive and, in such cases, an intermediate filling ma terial is indicated for the protection of the pulp. Zinc oxyphosphate cement seems best for this purpose. G uttapercha should not be used, because of its tre mendous coefficient of expansion; i.e., 198, as compared with a tooth substance value of 8 and an amalgam value of 25, to say nothing of a mercury value of 60. L ittle is known of the volumetric change of zinc-oxide and eugenol and, as an in termediate, it should probably be con fined to simple cavities. Pond states th at he prefers to cement all his amalgam restorations w ith a soft mix of cement. I believe th at it is better to allow the cement base to harden before attem pting to place the amalgam, for the following reasons: 1. Cement is usually indicated as an intermediate filling when insulation from therm al shock and pro tection from pressure of condensation is needed. A thicker layer of cement should give greater protection from both of these factors. 2. O ne of the objects of conden sation is to eliminate as much excess mercury as possible, and it seems more feasible to have a flat floor against which orderly condensation may be directed. It is extremely difficult to express mercury from an amalgam filling in a cavity which has a concave floor. 3. T here is always the danger of touching the m atrix band or cavity margins w ith the soft ce ment. M atrices are necessary in compound cavities and for general use “ivory” 1, 4 and 8 are recommended. “Ivory” 1 and 4 may be used on mesioclusal and distoocclusal cavities, while 8 is quite suitable in mesioclusodistal and larger restora tions. T h e separation of the teeth and the adaptation of the 1 and 8 matrices at the gingival aspect is obtained by using
Tingley— Ideal Amalgam Restoration a wooden wedge for this purpose, a round toothpick properly trimmed being suit able in the average case. I t usually is best to trim the m atrix band to suit the case at hand and the bands may be burnished to obtain the desired contour, proximal or otherwise. T h e tension on the m atrix band should be released slightly when the height of the filling reaches the con tact point. T his helps in obtaining the proper contact. T h e m atrix band should be removed as soon as the condensation of the filling is complete as the friability of the amalgam increases very rapidly as crystallization progresses. T h e m atrix should be rotated tow ard the gingival as pect and from buccal to lingual, but never tow ard the occlusal. I t is best to cut the m atrix band as near the contact point as possible before attem pting its removal, and pressure should be kept on the filling during this procedure to pre vent the displacement of a portion of the filling material. In the mixing of the amalgam, known volumes, measured by weight, of mercury and alloy filings are placed in the m ortar. T h e proportion of the mercury to the al loy is not especially important except that it should be constant. T h e time of mix is exceedingly important, as prolonged trituration and vigorous grinding pro mote shrinkage. T h e mercury content should be reduced slightly when multiple portions are used, and this reduction does away w ith any excess of mercury in the mix. I t is best to use the proportions rec ommended by the alloy manufacturers. T h e proportions of eight parts mercury to five parts alloy are suitable for most high grade alloys. Crepitus should not be present in the mix, yet the mixture should not be excessively thin. A good consistency test may be made by dropping the spherical mass of the mix onto a flat surface from a height of 6 or 8 inches; after which the mass should be flattened
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out approximately one-half its diameter. T h e alloy and mercury should be lightly triturated in the m ortar for two minutes and m ulled in the hand for one minute. T h is procedure should be timed and the mixing should not exceed three minutes. Condensation is accomplished by plac ing in the cavity the first portion of the amalgam from which no mercury has been removed and carefully tamping it to place. T am ping adapts the amalgam to the walls, as well as sharp angles, and this process should not be confused w ith forceful condensation. A small amount of mercury is then removed from the sec ond portion, which is placed in the cavity. A t this point, condensation is started. O r derly packing of the amalgam is accom plished by starting in the center of the cavity and packing toward the walls, overlapping the previously condensed area w ith each thrust of the instrument, and continually driving the mercury in one direction. A strong force of from nine to sixteen points pressure should be applied. T his method carries the mercury tow ard the walls, where it is finally ex pelled by the filling instrument. T he above-described process is repeated, ex pelling more and more mercury from the amalgam before it is inserted in the cav ity. Still more mercury is expelled in the process of condensation. T h e last por tion of the amalgam used should be very dry and packed into the cavity with great force of the hand instrument, if not malleted. A t the completion of the condensa tion, a substantial excess of amalgam should always exist for the convenience of carving. T h e whole purpose of thor ough condensation is to effect proper adaptation to the cavity and to expel as much mercury as possible. T h e behavior of the finished filling is largely dependent on the thoroughness of this process of eliminating excess mercury. Volume, crushing strength, marginal friability, all
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T h e Journal of the American D ental Association
will be affected if the excess mercury is not removed. T h e function of amalgam restorations is to restore anatomically lost tooth struc ture, in order to preserve the health of and restore function to the teeth and their investing tissues. By the same token, anatomic form must be reproduced in order to restore the teeth to their orig inal use and function. Proper contact points should be made w ith the approxi mating teeth and should be located well toward the buccal third of the tooth. If the contact point is not normally present, it is best to improve on nature by devel oping a contact, when the distance is not too great. Such a contact point should be convex and not a broad surface, in order to preclude decay of the adjacent tooth. T h e operator will, by obtaining a contact point, prevent the impaction of food and stabilize the tooth as to its normal posi tion and mobility. M arginal ridges are restored to an equivalent height of the m arginal ridge of the adjacent tooth as this will further prevent the wedging of the food into the interproximal space. Buccal and lingual embrasures are made to resemble wide open V-shaped spaces and should not be reduced to the narrow places which are often caused by too great convexity of either the buccal or the lingual aspects of the approximal surface. T h e cusps should be reproduced as to their original form, the tips being placed well tow ard the center of the tooth. Es pecially should this be done in the cases of buccal cusps of the lower and lingual cusps of the upper molars. T h e principal grooves should be reproduced, particu larly grooves separating cusps, as well as the triangular grooves which are present in practically all mesial and distal fossae of the posterior teeth. Spillways may be reproduced when the approximal surfaces are broad. Interproxim al spaces should
.be preserved to allow the interdental papilla to take its natural position. O n the whole, anatomic form must be under stood before it can be reproduced, and the occasional carving of a tooth serves to keep the practitioner interested in the production of good tooth form. T he study of dental anatomy may be elemen tary but is certainly fundamental. If condensation has been accomplished, carving may be started at once. T he carving instrum ent should always be di rected from the tooth structure to the amalgam, and burnishing should not be attempted, reports to the contrary not withstanding. Excessively deep grooves should be avoided and marginal ridges should be made the lowest points on the surface of the tooth, w ith the exception of pits, fissures and grooves. T h e finishing and polishing should not be attempted for tw enty-four hours, or, better still, ten days. T h e technic of fin ishing consists of trimming the occlusal margins w ith finishing burs until they are flush w ith the surface of the enamel. T his operation should be repeatedly checked with a sharp explorer and there should be no catches. O n the proximal aspect, the buccal and the lingual margins are trimmed with sandpaper disks, then the gingival margin is surfaced w ith fine sandpaper strips. T h e entire proximal surface is finished w ith fine cuttlefish strips and the occlusal with midget disks. A t this point, all scratches w ill have been removed and the occlusal surface is fu r ther finished w ith rubber cups, moist pumice being used as an abrasive. T his is followed by moist whiting, and the polish ing is done by using nearly dry tin oxide powder. T h e same procedure is followed for the proximal, linen strips carrying the polishing material. If each step is fol lowed in the proper sequence,, a restora tion of high luster and flawless margins will result.
Christiansen— Professional Trends C O N C L U S IO N S
1. I t is essential to use a high test alloy w ith an adequate silver content. 2. A good standardized technic is as im portant as the selection of the alloy. 3. Cavity preparations should be care fully made. 4. A ll excess mercury possible must be removed to insure nominal volume changes. 5. Amalgam has such structural com
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position and physical characteristics that it becomes necessary for the practitioner to exercise great care in its use to obtain good results in the restoration of the teeth. 6. G reat good would result from a conference of the leaders in amalgam work in the profession, and such a conference would be of value in the development and improvement of amalgam technic. 12 Bay State Road.
TH E RELATION OF CERTAIN PROFESSIONAL TRENDS T O PRIVATE PRACTICE* By JOHN F. CHRISTIANSEN, M.S., D.D.S., F.A.C.D., Los Angeles, Calif. H E N income gradually decreases over a prolonged period of time, the mental conception th at a “safe refuge lies somewhere in socialism” seems to need but little support to bring belief in its plausibility and trustworthiness. Thus, the concept of socialism becomes rather falsely idealistic to a proportion of the profession and, perhaps, an in teresting topic for academic discussion to us all. I t may not be well understood, nor acknowledged, that limited socialized health service already exists, and th at the extension of the form now established will make socialization only more nearly complete. T h e long-established United States Public H ealth Service and the state boards of health render service of a socialized type in that they provide free diagnostic clinics and afford hospitaliza tion, and their staffs offer free assistance in making diagnoses from free bacteri-
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*Read before the Utah State Dental So ciety, Salt Lake City, June 1, 1934. Jour. A .D .A ., October, 1934
ologic examinations. A ll the dentists and physicians on the government payrolls are thus practicing a form of limited socialized health service. Incidentally, our public school system is socialized, even if it is supported by public taxation ; and the army is the height of socialism. Likewise, all other similar boards or de partm ents paid out of the public treasury, such as fire and police departments, are socialized according to the ordinary meaning of the term. A t the present time, the government does not interfere w ith private medical or dental practice except to the extent th a t private practices necessarily contrib ute indirectly to the expenses of the medical budget of the government. A sympathetic inclination toward socialized dentistry means, of course, among other things, being attuned toward control of our profession and its activities by the government. Presumably, central con trol would provide a regular income, and designate quite acceptable working hours.
the effect of prophylactic vitamin D ther apy on dental structure. W e have such a group of about 450 children who have received viosterol in infancy, many of whom are now getting their permanent teeth. Unlike the rachitic group, which is composed mostly of colored children, the prophylactic group contains about an equal number of w hite children; hence, it will be possible to ascertain the correct ness of the supposed predisposition of the white race to dental decay. T h e plan, for next year, therefore, is to study the
1753
group in the same manner that the rachitic group was investigated this year, namely, a physical examination, dental roentgenographic examination and a study of malocclusion, hypoplasia and caries. As in the rachitic group, each child in the prophylactic group has had a series of roentgenograms during infancy and the absence of rickets in each one is therefore definitely known. Respectfully submitted, H a r r y E. K e l s e y , Advisor.
TH E IDEAL AMALGAM RESTORATION* By H A R O L D E. TIN G LEY , D .M .D ., B oston, Mass.
E B S T E R defines the adjective “ideal” as m eaning “conforming to a standard of perfection.” W hile it is difficult to qualify perfection in anything, we should do so, I believe, when we allude to perfection in amalgam work. It is doubtful th a t any authority believes a state of perfection to exist in amalgam restorations. T his lack of ac complishment is due mainly to the com plexity of the m ultiple physical and chemical factors involved and to an in different technic. Since its adoption in the field of den tistry, amalgam has been the subject of many empiricisms; which is one of the reasons that the scientific study of amalgam has progressed so slowly until comparatively recent years. A t the present time, the laboratory
W
*R ead at the S ev en ty -F ifth A n n u al Session o f the A m erican D en ta l A ssociation in con junction w ith the C h ica g o C entennial D ental Congress, A u g. 11, 1933.
Jour. A .D .A ., October, 1934
study of the physical and chemical prop erties of amalgam is, I believe, ahead of our study of the development of an accu rate and a scientific technic. Pond states that 75 per cent of restora tions are today made with amalgam. If this is true, amalgam is a material which deserves all the study th at can be given it. It has been said many times, and I hesi tate to repeat it, that “amalgam is the most widely used and abused of filling materials.” If this statement is true, and it undoubtedly is, the time has come when empiricism should be cast aside and amalgam restorations made according to the latest scientific knowledge on the sub ject. Paffenbarger and Sweeney sta te: The Research Commission has directed its research associates to purchase in the open market materials that are guaranteed by their makers to meet the various American Dental Association specifications and to test these materials for compliance with these specifica tions. Thus, by these check tests, the profes sion will be further protected against inferior
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T he Journal of the American D en ta l Association
products. Likewise, the manufacturer who is actually producing specification materials and has adequate testing facilities will also be pro tected against unfair trade practice.
I believe that every practitioner is in sympathy w ith the above-mentioned re port. Such precautions are bound to be re flected in an improved product, and no stone should be left unturned to improve our dental materials. T h e last sentence of the last paragraph of this report seems to me the most pertinent: “ It is felt that these safeguards will protect the dentist in the purchase of satisfactory materials. It is then his duty to employ them cor rectly.” A
Fig. 1.—Above, A , frail enamel, which is likely to fracture under stress. The enamel margin at B is much stronger. Below, shaded areas indicating probable enamel fractures resulting from placing margins in critical location ; i.e., near tips of cusps.
T h e implication from the foregoing sentence is, I believe, a challenge to the dentist to exert his best efforts in the use of dental materials. In the last analysis, this means th at the use of the materials should be based on scientific findings. One has only to refer to W a rd and Scott’s recent report to learn th at even the use of a differently surfaced m ortar and pestle will make a measurable difference in volumetric behavior of amalgam.
Knowledge of physics and chemistry is sufficiently complete at this time to as sure us safe materials and safe technic. By safe, I mean materials and a technic which w ill give us more accurate clinical results than were ever before obtained. C redit and recognition should be given to all the investigators of amalgam, but especial appreciation should be accorded the m en at the Bureau of Standards. T he efforts of Souder, Taylor, Sweeney and Paffenbarger were unquestionably of out standing m erit; for their contributions definitely improved the quality of dental alloys on the market today. T h e recent work of W ard and Scott
Fig. 2.—Above, A , B and C, points making adaptation and finishing a difficult task. Below, sharp, irregular angles in outline form, which make adaptation and finishing difficult.
deserves mention and recognition. T he report recently made by them was an other milestone in our progress toward ideal amalgam restorations. H arper should receive great credit for his contri butions and untiring efforts in the field of amalgam. H e has undoubtedly done more than any other investigator to im prove the amalgam technic of dentists. I t is unquestionable that the higher grade alloys must be available for the dental profession. H igh silver alloys of favorable proportional contents are the
Tingley— Ideal Amalgam Restoration only safe materials to use, since the best clinical results can be obtained only from high grade alloys of a known and favor able physical behavior. Volume changes alone vary sufficiently in alloys selected at random to make it necessary to choose a high-grade alloy in order to insure good results. An accurate and painstaking technic is of little help if the basis of the technic is the employment of a poor alloy; yet, con versely, the use of a high-grade alloy com bined w ith an inferior technic w ill not give satisfactory results either. T h e ques tion at once arises as to w hether the use of a good alloy or good technic is the more
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far more interested in the selection of a proper alloy than in the utilization of an improved technic, and such an attitude should be subject to modification. O b viously, lack of care in the use of amal gam is due to carelessness, and is gen erally the result of a belief on the part of the dentist th at he is dealing with an inferior filling material which it is not necessary for him to manipulate with precision. I t is not the purpose of this paper to champion amalgam over and above its value; yet it is only fair to state that amalgam deserves a high rating as a tooth-saving material. M ost practitioners agree th at gold is the filling material par excellence; yet Pond states th at he believes amalgam to be a better restorative material than in-'
Fig. 3.—More orthodox and desirable types of outline form than that shown in Figure 2.
Fig. 4.—Comparison between amalgam bevel illustrated at A and bevel for gold illustrated at B. T he amalgam bevel should be three-quarters to full length of the enamel wall, varying but slightly in its direction from the cavity wall.
im portant. O ne cannot fairly make such a differentiation; for both are important, and w ithout both, excellent results can not be obtained. I t is apparent, therefore, th at many failures w ith amalgam are traced by those responsible to the chemical and physical properties of the alloy when only a poor technic is responsible. F aults such as poor condensation, ill-shaped contours, cervi cal excesses and overhangs cannot be properly attributed to the use of a lowstandard alloy. Broadly speaking, it would seem th a t the average dentist is
lays made of gold. C ertain it is th at thousands if not millions of teeth are saved yearly in this country by the use of amalgam. Amalgam has its faults— plenty of them— but if the material is understood and its physical properties ob served, many of these deficiencies can be sufficiently controlled to give us very good results. Some of the disadvantages which may be attributed to amalgam are: relatively low tensile and edge stren g th ; a crystal line make-up, which defeats attempts to burnish it; expansion and shrinkage; a
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T he Journal of the American D ental Association
tendency to discolor in the mouth, and therm al conductivity. Spheroiding is not mentioned in the foregoing list because it is quite probable that this phenomenon should be properly included in the vol ume changing factors of expansion and shrinkage. L et us discuss briefly the defi ciencies above related and attem pt to point out the seriousness of each, taking them in the order of their importance. Shrinkage is without doubt the most det rimental physical characteristic which amalgam possesses. I t has the eifect of pulling the restoration away from its cavity walls, thereby exposing such areas to bacteria and decay— not to mention the discoloration which results when these surfaces are exposed to the fluids of the
condensation of the filling. Such residual excess mercury w ill produce serious vol ume changes; which, in turn, will ad versely affect the durability of the resto ration. T h e crystalline physical characteristic prevents the burnishing of the margins of the filling as is done when using gold. This, to a large extent, precludes good adaptation to the cavity walls if an error has been made at the cavosurface angle in carving or preparing the cavity. T his point illustrates definitely the precision required in the technic. T h e disadvan tages of this crystalline makeup can be controlled by employment of the amal-
Fig. 5.— Use of spiral plane fissure bur No. 56 or 57 for finishing enamel wall.
mouth. Shrinkage also impairs the mechanical structure of the restoration by draw ing the amalgam away from its supporting w alls; but shrinkage can be controlled to a large extent by the selec tion of a high-silver-content alloy and by the complete removal of excess mercury, accomplished by thorough condensation. T h e next most important physical dis advantage associated w ith amalgam is its apparent crystalline formation. This type of structure hinders us in the re moval of the excess mercury owing to the evident temper which the amalgam ex hibits when exposed to pressure during
Fig. 6.—Above, hardened cement base with amalgam ready to adapt to cavity. There is a flat floor and clean walls. Below, amalgam in soft mass of cement showing irregular floor and inevitable result when pressure, as indi cated by arrow, is applied.
gam before the initial crystallization has started and by the use of suitable pres sures at the proper times during conden sation of the filling. T h e low tensile and edge strengths are factors in the failure of restorations when beveling of the enamel walls of the prepared cavity necessitates the drawing out of the amalgam into thin edges. Such edges will, of course, fracture, imperfect
Tingley— Ideal Amalgam Restoration margins resulting. T his characteristic can be controlled to a large degree by proper treatm ent of the enamel wall. W here tensile strength is needed for retentive purposes, a sufficient bulk should be given to the preparation to pro vide essential strength to the filling material at that point. T h e discoloration of amalgam and, subsequently, of the tooth structure, which is indeed a serious fault, implies that its use should be confined mostly to the posterior teeth. Some years ago, G. V. Black pointed out th at discoloration of the tooth structure resulting from the placing of amalgam occurs only where there are leaky margins. H e advanced
Fig. 7.—Carving direction with spoon or carving instrument, from tooth structure toward central part of restoration area.
the theory that the metallic salts and hydrogen sulphide would penetrate the dentinal tubules only when moisture was present. Comparatively nothing has been brought out in recent years for or against this theory, which indicates that the con trol of this condition may be accomplished by adopting a technic th at w ill insure im permeable margins. T h e discoloration resulting from the presence of unsup ported enamel can best be controlled by its removal or by the use of a light col ored cement lining. T h e discoloring ten dency of amalgam is indeed unfortunate, and, accordingly, the use of this material
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should be confined to teeth and surfaces of teeth which are not exposed to view. T h e use of amalgam in the lingual pits of maxillary anterior teeth is dangerous in this respect, and for these cases no better m aterial than gold can be found. I t is apparent th at expansion is not an unfavorable factor except in poorly bal anced alloys; i. e., alloys which have an unusually high silver content, and there are none of these on the market. P ro longed expansion up to a period of a tenday ultimate expansion is desirable. If there is need of controlling expansion, it should be done by selecting an alloy which is not above 70 per cent in silver content. T herm al conductivity is undesirable in any filling material, since lasting injury to the pulp may result. T h e thermal con ductivity of amalgam is, I believe, suffi ciently below that of gold to be more desirable material in this respect. T h e r mal conductivity should always be con sidered when impending irritation to the pulp is anticipated. Cavity lining and cement are probably the best means of insulation in these cases. In addition to the above-mentioned physical and chemical shortcomings of amalgam, considerable attention has been given in the dental literature to flow, spheroiding and mercurial poisoning. In a discussion of alloys of high silver con tent, flow ceases to be a factor to any dangerous extent. T h e presence of, let us say, 68 per cent silver, 26 per cent tin, 5 per cent copper and 1 per cent zinc raises the crushing strength sufficiently to eliminate flow from any great practi cal consideration. M uch has been w rit ten about that unusual and inexplicable phenomenon, spheroiding. T h e theory has been advanced that any alloy contain ing mercury tends to become spheroidal because mercury in its separate and un combined state has that tendency. T he
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T h e Journal of the American D ental Association
amount of uncombined mercury in an amalgam restoration would, of course, vary w ith the technic of manipulation. I t is hard to believe th at a sufficient amount of free mercury exists in a well-condensed filling to allow this action to take place. T his statement is made guardedly, as there is no proof for it at hand; but it would seem that, for our answer, we should look to the volume changes which might result from extreme tem perature variations in the mouth. F or example, there is a considerable tem perature spread between a cup of hot coffee and a dish of sherbet, and the relative volume coeffi cient value of amalgam is high for the metals. T ay lo r states that measuring by thermocouple the tem perature of an amalgam mix triturated in a mechanical mixer showed a rise in tem perature of from 20 to 25 degrees Centigrade, and the amalgam did not behave well after wards. If this is true, is it not a logical deduction th at greater temperature vari ations, such as are found in the mouth, will inevitably cause much volume change in amalgam restorations? A t the present time in this country, there seems to be no general belief that mercurial poisoning may result from the presence of silver amalgams, although Germ any has many adherents to this theory. Saliva in which silver amalgam was immersed for six weeks showed no mercury and only slight traces of tin. As the salts of tin are not particularly harm ful, if these experiments were exact, m er curial poisoning may be dismissed from our minds. As regards this point, a num ber of G erm an investigators have shown th at copper amalgam gives off mercury in proportionally large quantities. T here also have been several cases reported of severe poisoning, but it must be remem bered in this connection that copper amalgam is much less stable than silver, especially in the fluids of the mouth. Cop
per amalgam is well on the road to being discarded in this country, although abroad it is still in general use. I t was heralded in the past on its supposed germicidal merits and became touted as the panacea for all ills in children’s teeth. T ru e, it may have had germicidal merits, but its instability in the fluids of the mouth ren der it generally unfit for use. Before proceeding w ith an advocated technic, let us consider briefly the makeup of an alloy and also the phenomenon of w hat is called the setting of the amalgam. M ost high-test alloys have an element content which compares closely w ith the following form ula: silver 68 per cent, tin 26 per cent, copper 5 per cent and zinc 1 per cent. Every alloy should have a high silver content; which promotes ex pansion, thereby controlling excessive shrinkage. T h e use of silver also in creases edge strength, controls flow and hastens setting. T h e tin contracts and its employment decreases edge strength, increases flow, retards setting and adds plasticity. T h e use of copper increases edge strength, at 5 per cent or less, hastens setting and decreases flow and there is little change in volume. T he zinc content increases edge strength, les sens flow, improves color and adds smoothness to the amalgam. Silver and copper unite with mercury with greater difficulty than does tin or zinc, and tin has an exceptional affinity for mercury; which makes it a dangerous factor in this respect. A high silver alloy w ill not work so smoothly as one containing a large amount of tin, but shrinkage can be con trolled only by using a high silver con tent. Practitioners should, therefore, avoid excessively smooth amalgams as these usually shrink greatly on account of the high content of tin. T h e trituration of an amalgam in the m ortar and the subsequent mulling in the hand are accompanied by shrinkage which
Tingley— Ideal Amalgam Restoration is the result of the fact that alloy filings go into solution w ith the mercury. This, which is called the primary shrinkage, is followed by a primary expansion which is the result of the crystallization marked at the start by a slight crepitus in the mass. T h e duration of this primary ex pansion period is approximately twentyfour hours, after which the residual ex cess mercury diffuses through the amal gam and the remaining particles of alloy go into solution, this causing a secondary shrinkage. T h e subsequent crystalliza tion, which is known as secondary ex pansion, is desired at the end of approxi mately ten days. If this sequence of events occurs as claimed, any margin th at is finished before the expiration of th at time will fail. T h ere is a period which lasts from the completion of the mixing until about ten minutes have elapsed, during which time the amalgam is more easily adapted to the cavity walls. T his period, which is called the period of adaptable plasticity, varies in length w ith the type of alloy employed, being of shorter duration in high-silver-content amalgams. T here should be relatively little crepitus in the amalgam during the period of adaptable plasticity. Immediately following this, there is a period of lessened plasticity, which continues until the amalgam ceases to be workable. T his is called the period of workable plasticity. D uring this period, the amalgam may still be used, but good adaptation to the cavity walls will not be effected and difficulty w ill be experienced in removing excess mercury. T h e foregoing facts are practical points, easily demonstrable by experimentation. T h e greatest success is obtained only by exercising regard for these periods in the setting of the amalgam. Cavity preparation is an important p art of amalgam technic. Restorations usually fail if preceded by poor cavity
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preparations. T here is no step in amal gam technic that is more important. Fundam ental principles of cavity prep aration must be followed, and such prin ciples should evolve from a complete familiarity w ith the anatomy, histology and pathology of the tooth. T here are, briefly, two types of dental caries: the pit and fissure type and the smooth surface type. T h e former attacks the tooth through structural defects; the latter, by the formation of plaques on the smooth surface of the enamel within the vulnerable or especially susceptible areas. In the first type, the limits of the caries are not usually known until the cavity is partially prepared and, obviously, two cavities of the first type in the same tooth should not be filled separately until it has been definitely established that they are not intercommunicating. In the pit and fissure type, caries seldom spreads on the surface of the tooth, and this fact makes it unnecessary to “extend for pre vention” except to include pits, fissures and deep grooves. In the smooth surface type, the operator should not, of course, limit the extension of the cavity outline until all carious and susceptible areas have been included. In this respect, special attention should be given to cavi ties on gingival third of the tooth, as de calcified enamel w ill not be detected un less the surface of the tooth is dry. Cavi ties of this type present a problem in mouths wherein caries susceptibility is high. G enerally speaking, their outline forms should be proportionately extensive. T h e direction of the enamel rods modifies the treatm ent of the enamel and the directional placement of the cavity walls. T h e rods radiate from the pulp, converge in approaching grooves and change direction acutely at cusps and ridges. Accordingly, cavity enamel walls are stronger when placed near the grooves.
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T he Journal of the American D ental Association
P it and fissure cavities should be ex tended to include all caries, pits, fissures and deep grooves, as it is almost impos sible to finish properly the m argin of a restoration which crosses a deep groove. M arginal ridges should not be en croached on or undermined w ith inverted cone burs. T here should be no sharp angles in the outline form and the floors should be flat; in a parallel plane to the surface of the tooth, and always well seated in the dentin. T h e walls should be parallel and at right angles to the floor, w ith the exception of the slight re tentive form made at the floor w ith an inverted cone bur and sharp hand instru ments. T h e enamel margins should be beveled from three quarters to the full length of the enamel rods, flaring but little from the direction of the wall. A plain spiral fissure bur of moderate size is, I believe, the best instrum ent for this purpose. T h e occlusal dovetail, the chief source of retention in compound cavities in the posterior teeth, should follow the groove tow ard the buccal aspect. Especially is this true in the maxillary teeth. Con stricted portions of the cavity should be made sufficiently wide and deep to com pensate for the low tensile strength of amalgam. Buccal and lingual walls should be extended to self-cleansing areas and, if possible, should be kept w ithin the angles of the tooth. Gingivally, the extension for prevention is made to a point under the normal free gingival margin. T h e gingival w all should be at right angles w ith the axial w all, as well as parallel to the floor of the dove tail. Amalgam requires somewhat more re tention than malleted g o ld ; and owing to this fact, substantial retentive points are placed in the proximal portion. T h e buc cal and lingual enamel walls are finished by planing w ith sharp chisels, and at the
gingival enamel wall, Black’s gingival margin trimmers are used. Caries frequently is extensive and, in such cases, an intermediate filling ma terial is indicated for the protection of the pulp. Zinc oxyphosphate cement seems best for this purpose. G uttapercha should not be used, because of its tre mendous coefficient of expansion; i.e., 198, as compared with a tooth substance value of 8 and an amalgam value of 25, to say nothing of a mercury value of 60. L ittle is known of the volumetric change of zinc-oxide and eugenol and, as an in termediate, it should probably be con fined to simple cavities. Pond states th at he prefers to cement all his amalgam restorations w ith a soft mix of cement. I believe th at it is better to allow the cement base to harden before attem pting to place the amalgam, for the following reasons: 1. Cement is usually indicated as an intermediate filling when insulation from therm al shock and pro tection from pressure of condensation is needed. A thicker layer of cement should give greater protection from both of these factors. 2. O ne of the objects of conden sation is to eliminate as much excess mercury as possible, and it seems more feasible to have a flat floor against which orderly condensation may be directed. It is extremely difficult to express mercury from an amalgam filling in a cavity which has a concave floor. 3. T here is always the danger of touching the m atrix band or cavity margins w ith the soft ce ment. M atrices are necessary in compound cavities and for general use “ivory” 1, 4 and 8 are recommended. “Ivory” 1 and 4 may be used on mesioclusal and distoocclusal cavities, while 8 is quite suitable in mesioclusodistal and larger restora tions. T h e separation of the teeth and the adaptation of the 1 and 8 matrices at the gingival aspect is obtained by using
Tingley— Ideal Amalgam Restoration a wooden wedge for this purpose, a round toothpick properly trimmed being suit able in the average case. I t usually is best to trim the m atrix band to suit the case at hand and the bands may be burnished to obtain the desired contour, proximal or otherwise. T h e tension on the m atrix band should be released slightly when the height of the filling reaches the con tact point. T his helps in obtaining the proper contact. T h e m atrix band should be removed as soon as the condensation of the filling is complete as the friability of the amalgam increases very rapidly as crystallization progresses. T h e m atrix should be rotated tow ard the gingival as pect and from buccal to lingual, but never tow ard the occlusal. I t is best to cut the m atrix band as near the contact point as possible before attem pting its removal, and pressure should be kept on the filling during this procedure to pre vent the displacement of a portion of the filling material. In the mixing of the amalgam, known volumes, measured by weight, of mercury and alloy filings are placed in the m ortar. T h e proportion of the mercury to the al loy is not especially important except that it should be constant. T h e time of mix is exceedingly important, as prolonged trituration and vigorous grinding pro mote shrinkage. T h e mercury content should be reduced slightly when multiple portions are used, and this reduction does away w ith any excess of mercury in the mix. I t is best to use the proportions rec ommended by the alloy manufacturers. T h e proportions of eight parts mercury to five parts alloy are suitable for most high grade alloys. Crepitus should not be present in the mix, yet the mixture should not be excessively thin. A good consistency test may be made by dropping the spherical mass of the mix onto a flat surface from a height of 6 or 8 inches; after which the mass should be flattened
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out approximately one-half its diameter. T h e alloy and mercury should be lightly triturated in the m ortar for two minutes and m ulled in the hand for one minute. T h is procedure should be timed and the mixing should not exceed three minutes. Condensation is accomplished by plac ing in the cavity the first portion of the amalgam from which no mercury has been removed and carefully tamping it to place. T am ping adapts the amalgam to the walls, as well as sharp angles, and this process should not be confused w ith forceful condensation. A small amount of mercury is then removed from the sec ond portion, which is placed in the cavity. A t this point, condensation is started. O r derly packing of the amalgam is accom plished by starting in the center of the cavity and packing toward the walls, overlapping the previously condensed area w ith each thrust of the instrument, and continually driving the mercury in one direction. A strong force of from nine to sixteen points pressure should be applied. T his method carries the mercury tow ard the walls, where it is finally ex pelled by the filling instrument. T he above-described process is repeated, ex pelling more and more mercury from the amalgam before it is inserted in the cav ity. Still more mercury is expelled in the process of condensation. T h e last por tion of the amalgam used should be very dry and packed into the cavity with great force of the hand instrument, if not malleted. A t the completion of the condensa tion, a substantial excess of amalgam should always exist for the convenience of carving. T h e whole purpose of thor ough condensation is to effect proper adaptation to the cavity and to expel as much mercury as possible. T h e behavior of the finished filling is largely dependent on the thoroughness of this process of eliminating excess mercury. Volume, crushing strength, marginal friability, all
1762
T h e Journal of the American D ental Association
will be affected if the excess mercury is not removed. T h e function of amalgam restorations is to restore anatomically lost tooth struc ture, in order to preserve the health of and restore function to the teeth and their investing tissues. By the same token, anatomic form must be reproduced in order to restore the teeth to their orig inal use and function. Proper contact points should be made w ith the approxi mating teeth and should be located well toward the buccal third of the tooth. If the contact point is not normally present, it is best to improve on nature by devel oping a contact, when the distance is not too great. Such a contact point should be convex and not a broad surface, in order to preclude decay of the adjacent tooth. T h e operator will, by obtaining a contact point, prevent the impaction of food and stabilize the tooth as to its normal posi tion and mobility. M arginal ridges are restored to an equivalent height of the m arginal ridge of the adjacent tooth as this will further prevent the wedging of the food into the interproximal space. Buccal and lingual embrasures are made to resemble wide open V-shaped spaces and should not be reduced to the narrow places which are often caused by too great convexity of either the buccal or the lingual aspects of the approximal surface. T h e cusps should be reproduced as to their original form, the tips being placed well tow ard the center of the tooth. Es pecially should this be done in the cases of buccal cusps of the lower and lingual cusps of the upper molars. T h e principal grooves should be reproduced, particu larly grooves separating cusps, as well as the triangular grooves which are present in practically all mesial and distal fossae of the posterior teeth. Spillways may be reproduced when the approximal surfaces are broad. Interproxim al spaces should
.be preserved to allow the interdental papilla to take its natural position. O n the whole, anatomic form must be under stood before it can be reproduced, and the occasional carving of a tooth serves to keep the practitioner interested in the production of good tooth form. T he study of dental anatomy may be elemen tary but is certainly fundamental. If condensation has been accomplished, carving may be started at once. T he carving instrum ent should always be di rected from the tooth structure to the amalgam, and burnishing should not be attempted, reports to the contrary not withstanding. Excessively deep grooves should be avoided and marginal ridges should be made the lowest points on the surface of the tooth, w ith the exception of pits, fissures and grooves. T h e finishing and polishing should not be attempted for tw enty-four hours, or, better still, ten days. T h e technic of fin ishing consists of trimming the occlusal margins w ith finishing burs until they are flush w ith the surface of the enamel. T his operation should be repeatedly checked with a sharp explorer and there should be no catches. O n the proximal aspect, the buccal and the lingual margins are trimmed with sandpaper disks, then the gingival margin is surfaced w ith fine sandpaper strips. T h e entire proximal surface is finished w ith fine cuttlefish strips and the occlusal with midget disks. A t this point, all scratches w ill have been removed and the occlusal surface is fu r ther finished w ith rubber cups, moist pumice being used as an abrasive. T his is followed by moist whiting, and the polish ing is done by using nearly dry tin oxide powder. T h e same procedure is followed for the proximal, linen strips carrying the polishing material. If each step is fol lowed in the proper sequence,, a restora tion of high luster and flawless margins will result.
Christiansen— Professional Trends C O N C L U S IO N S
1. I t is essential to use a high test alloy w ith an adequate silver content. 2. A good standardized technic is as im portant as the selection of the alloy. 3. Cavity preparations should be care fully made. 4. A ll excess mercury possible must be removed to insure nominal volume changes. 5. Amalgam has such structural com
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position and physical characteristics that it becomes necessary for the practitioner to exercise great care in its use to obtain good results in the restoration of the teeth. 6. G reat good would result from a conference of the leaders in amalgam work in the profession, and such a conference would be of value in the development and improvement of amalgam technic. 12 Bay State Road.
TH E RELATION OF CERTAIN PROFESSIONAL TRENDS T O PRIVATE PRACTICE* By JOHN F. CHRISTIANSEN, M.S., D.D.S., F.A.C.D., Los Angeles, Calif. H E N income gradually decreases over a prolonged period of time, the mental conception th at a “safe refuge lies somewhere in socialism” seems to need but little support to bring belief in its plausibility and trustworthiness. Thus, the concept of socialism becomes rather falsely idealistic to a proportion of the profession and, perhaps, an in teresting topic for academic discussion to us all. I t may not be well understood, nor acknowledged, that limited socialized health service already exists, and th at the extension of the form now established will make socialization only more nearly complete. T h e long-established United States Public H ealth Service and the state boards of health render service of a socialized type in that they provide free diagnostic clinics and afford hospitaliza tion, and their staffs offer free assistance in making diagnoses from free bacteri-
W
*Read before the Utah State Dental So ciety, Salt Lake City, June 1, 1934. Jour. A .D .A ., October, 1934
ologic examinations. A ll the dentists and physicians on the government payrolls are thus practicing a form of limited socialized health service. Incidentally, our public school system is socialized, even if it is supported by public taxation ; and the army is the height of socialism. Likewise, all other similar boards or de partm ents paid out of the public treasury, such as fire and police departments, are socialized according to the ordinary meaning of the term. A t the present time, the government does not interfere w ith private medical or dental practice except to the extent th a t private practices necessarily contrib ute indirectly to the expenses of the medical budget of the government. A sympathetic inclination toward socialized dentistry means, of course, among other things, being attuned toward control of our profession and its activities by the government. Presumably, central con trol would provide a regular income, and designate quite acceptable working hours.