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Cavity Preparation with Special Reference to Pulp Protection, for Various Filling Materials *
Byrnes— Cavity Preparation and atten tio n is given to correct diagnosis, design and construction, th e tim e and ability applied to th e details of fitting, p lacing and m aintenance of the cast
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p artial dentures w ill, w ith b u t few ex ceptions, elim inate th e failures th a t have occurred in th e past. 185 North Wabash Avenue.
C A V IT Y P R E P A R A T IO N W IT H S P E C IA L R E F E R E N C E T O P U L P P R O T E C T IO N , FO R V A R IO U S F IL L IN G M A T E R IA L S * By RALPH R. BYRNES, D.D.S., F.A.C.D., Atlanta, Ga.
N this paper, dealing w ith cavity prep aratio n , I shall n o t attem p t to give the operative procedure in detail, as th a t is a phase of d entistry w hich in itself could be the subject of a very long paper. In stead, I shall deal w ith general p rin ciples of cavity preparation, and discuss certain aspects w hich, though less com m only considered in the w ritin g of dental papers, have an im p o rta n t bearing on the subject, directly o r indirectly.
I
I t is obvious th a t any one attem pting cavity preparation should have a know l edge of the anatom y of the pulp, if he has fo r his objective the preservation of th a t delicate, vascular tissue. I t seems appro priate, therefore, to begin this paper w ith a b rief description of the pulp, m acro scopic and microscopic. A s a g eneral rule, th e shape of the pulp of a tooth conform s ro u ghly to th e shape of the cro w n of the tooth, b u t there are enough m inor differ ences to w a rra n t a brief description of th e pulps of th e individual teeth. I n this description, I shall take as m y guide B lack’s D e n ta l A natom y. •Read by William Edgar Coleman, Atlanta, Ga., in the absence of the author. •Read before the Section on Operative Dentistry at the Midwinter Clinic of the Chicago Dental Society, Jan. 14, 1930.
Jour. A .D . A., March, 1931
P U L P S OF T H E U P P E R INCISORS
In th e incisors, th ere is no sharp d if ferentiatio n in th e pulp of th e coronal portion an d th a t of the ro o t portion. T h e pulp is broadest m esiodistally, and tapers gently as th e root portion is ap proached. T h e pulp cham bers of th e cen tra l and la te ra l incisors are so sim ilar th a t a description of one w ill do for both. T h e largest diam eter o f th e p ulp cavity occurs about the level o f the gingival line on the labial surface. B lack says th a t in young incisors ju st erupting, he has found the diam eter of th e p ulp a t th e gingival line to be from on e-fo u rth to one-third th e diam eter of th e neck of the tooth. H e says fu rth e r th a t, in early a d u lt age, the pulp m ay average about one-fourth th e diam eter of th e neck of th e tooth, w ith a range, w ith approaching age, to one-fifth, one-sixth or, in th e extrem e, to one-tenth. T h e cham bers and canals in th e la te ra l incisors are, of course, a little sm aller th an those of the ce n tral incisors, b u t they are pro p o rtio n ately larg er w hen the size of th e to o th is considered. T h is fact accounts fo r the freq u en t exposure of pulps in the la te ra l incisors d u rin g cavity p rep aratio n . I n very young teeth, three sh o rt horns are often present, cor
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responding m am elons.
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P U L P OF T H E U P P E R C U S P ID
T h e re is n o t a g reat deal of difference in the general shape of the pulp of the u p per cuspid and th a t of the upper in cisors. T h e coronal extrem ity of the pulp of th e cuspid has a ce n tral h o rn w hich is n o t present in the incisors. T h is horn extends to w ard th e cusp of th e tooth, the m esial and la te ra l horns being practically o bliterated. T h e pulp cham ber extends to w ard the cu ttin g edge of th e tooth ab out tw o -thirds the length of th e crow n. T h e pulp is proportionately sm aller than th a t of the incisors, and its greatest diam eter is at the gingival line, from labial to lingual. T h e proportionately sm aller size of the pulp of this tooth and the tapering of the coronal p o rtion of the pulp accounts fo r th e extensive cavity p reparation th a t can be done on a cuspid to o th w ith o u t in ju ry to the pulp. P U L P CH A M B E R OF T H E LOW ER CU SPID
A t the neck of th e tooth, th e labial p o rtion of th e pulp is w ider th a n the lingual, and the long diam eter of the pulp is from labial to lingual aspect. T h e coronal portion traverses about tw o -thirds th e length of the crow n to w ard the point of the cusp, w here it ends in a point, or horn, w hich is usually very slender. H ere again, proportionately extensive prep ara tio n m ay be done w ith o u t encroaching on th e pulp. P U L P C H A M BERS OF T H E LOWER
extends to w ard the cu ttin g edge about tw o -th ird s th e len g th of the crow n. C avity p rep aratio n in these teeth is m ost delicate. P U L P C H A M B E R OF T H E U P P E R FIRST B IC U SPID
In this tooth, th e re is a sharp differen tiation betw een th e pulp of the crow n and th a t of the ro o t portion, w hich is n o t the case w ith th e incisors and th e cuspids. T h e p ulp cham ber of this to o th is cen tra lly placed in th e long axis of the crow n. T h e axial w alls are about equal in thickness, b u t the occlusal w alls are thicker th a n th e axial, th e ir thickness varying from one-th ird to tw o-thirds the length of the crow n. T o w a rd the apex of each cusp, a h o rn extends. T h e height and th e sharpness of th e cusps determ ine the height and sharpness of th e horns of the pulp. In teeth w ith very high and w ellpronounced cusps, such as w e often see in new ly erupted bicuspids, th ere are often very long and slender horns. Black has reported th a t, in some bicuspids w ith very pronounced cusps, th is h o rn has ex tended alm ost to the enam el. O f course, these horns become sh o rter as age ad vances. H ere, etern al vigilance m ust be exercised to avoid the area of the reces sional lines of th e horns, w hich are the lines along w hich the pulp recedes as the age of the tooth advances, and a t times there m ay be a tra c t containing a filam ent of the pulp tissue, the strik in g of w hich gives us the equivalent of an exposure.
INCISORS
P U L P C H A M B E R OF T H E U P P E R
A t the level of the gingival line, the long diam eter of the pulp is from labial to lingual aspect. A s the coronal ex trem ity of th e pulp is approached, the diam eter gradually diminishes labiallylingually, increases m esially-distally and ends in a th in edge. T h e pulp cham ber
T h e re is little difference betw een the shape of the pulp of this tooth and th a t of th e upper first bicuspid. T h e horns of the pulp of this to o th are usually shorter, and the recessional lines are n ot so pro nounced n o r so likely to in ject them -
SECOND BICUSPID
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Byrnes— Cavity Preparation selves into the p reparation of th e cavity, as in the first bicuspid. P U L P C H A M BERS OF T H E LOW ER BICUSPIDS
T h e pulp cham ber of th e low er first bicuspid ends in a horn extending to w ard the point of the buccal cusp. T h e re is no definite h o rn extending to w a rd the lin g u al cusp, although a p rotrusion of the p u lp in th a t direction is discernible. T h ese teeth seldom show a definite line of dem arcation betw een th e coronal pulp and th a t of the root canals. I n th e low er second bicuspid, the pulp extends into a lingual horn as w ell as in to a buccal horn, and the lin g u al horn m ay sometimes be very slender, especially in young teeth. In the low er bicuspids having three cusps, tw o horns of the pulp extend on the lingual side, spreading to w ard the mesial and distal aspects. T h o u g h th e horns themselves a re usually short, th e ir protrusion brings them nearer the surface of the tooth th a n other horns of th e pulp. T h is accounts for the greater likelihood of opening into th a t portion of the pulp in excavating proxim al cavities. P U L P CH A M BERS OF T H E U P P E R
ness of the w alls of this tooth accounts fo r the ra th e r extensive cavity p rep ara tion w hich can be m ade on the to o th ; hence, th e to o th serves w ell as an ab u t m ent for bridges in th e form of crow ns and inlays. P U L P CH A M BERS OF T H E LOWER MOLARS
T h e pulp cham bers of these teeth, though they correspond to th e general shape of the crow ns, as is the case w ith the other m olars, are som ew hat m ore an g u lar. T h e occlusal w all of the pulp cham ber shows a convexity to w ard the pulp. F ro m th e extrem e angles of the pulp, the horns extend to w ard each cusp. T h e diam eter of the pulp cham ber of this too th varies g reatly according to the age of the individual. In youth, it may be as m uch as tw o-fifths the diam eter of the crow n, and it is seldom less th an oneth ird . T h e diam eter of the pulp decreases greatly in old age, ow ing to the deposit of secondary dentin, a result of abrasion, and th e pulp cham ber in old individuals m ay often be alm ost obliterated. H ere, then, the age of the p atien t is an im por ta n t factor in d eterm ining the extent of cavity preparation.
MOLARS
T h e pulp cham bers and the root canals of these teeth are sharply differentiated, th e root canals being m inute openings in to the pulp cham ber. T h e average diam eter of the pulp cham ber of this to o th is about equal to the thickness of th e axial w all by w hich it is surrounded. T h e occlusal w alls are usually consider ably thicker th an the axial. T h e pulp cham ber corresponds in form to the cro w n of th e tooth w ith horns of the pu lp extending to w ard each cusp. T h ese horns are usually very pronounced in young teeth, and, of course, w ea r dow n o r recede w ith advancing age. T h e thick
GROSS ANATOM Y
A thorough know ledge of the gross anatom y of the pulp w ill enable the oper ato r to avoid exposing pulps needlessly. Likewise, a thorough know ledge of the histologic or microscopic stru ctu re of the pulp w ill aid him in applying his k n o w l edge of m ateria m edica in the treatm en t of diseased pulps. T h e tooth pulp is an em bryonic con nective tissue consisting of fine reticu lar tissue and a m ucoid m a trix containing com paratively few cells. T h is tissue, or “nerve,” as it is com m only called by the laity, is exceedingly vascular, containing
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num erous capillaries w hich term inate in a plexus im m ediately beneath the odontoblasts lining th e periphery of the p ulp on all sides. T h e nerves of th e pulp have the same general distrib u tio n as th e blood vessels, and end in a plexus of filam ents ju s t beneath the odontoblasts. T h e nerve fibers are m edullated in the body of the pulp, b u t lose th e ir m edullary sheaths as th e periphery of th e pulp is approached. T h e fact th a t th e w alls of th e capillaries are exceedingly th in and th e ir lum ens large, and th e fu rth e r fact th a t the pulp is so richly supplied w ith nerves, accounts fo r the extrem e sensitiv ity of the pulp to bacterial infection and to irrita n ts. T h e lining cells, o r the odontoblasts, are responsible fo r th e de posit of secondary dentin w h en such unfavorable conditions as abrasion and b acterial infection through caries are en countered. D en tists are too prone to condem n a p ulp w hen it m anifests sym ptom s of dis ease o r irritatio n . O n e w ould not th in k of enucleating th e eye sim ply because of an iritis o r a conjunctivitis. T h e efforts of the physician w ould be directed first to w ard relieving the condition by rem edial m easures. T h o u g h th e pulp has probably less resistance th an th e eye to infection, it nevertheless possesses the pow er of recuperation w hen th e cause of th e disturbance is rem oved. W h ile it is tru e th a t pulpectom y is th e only relief fo r very badly diseased pulps, it does not follow th a t extirpation of th e pulp is nec essary in a ll cases of diseased o r irritated pulps. Indeed, the pulp of any tooth h a r boring caries in th e den tin m u st become infected, a t least in a degree, as it is a w ell k now n fact th a t the m icro-organism s of caries penetrate and extend th ro u g h the organic m a tte r of the dentinal tubules w ith apparent ease.
U n lik e m ost of th e o th er tissues of the body, the p ulp is enclosed w ith in an u n yielding w all. W h e n hyperem ia of the pulp occurs, th e tissue has no room in w hich to e x p a n d ; hence, the clinical sym ptom s are definite an d sharp, and sometim es re su lt in an exaggeration of th e seriousness of th e tro u b le in th e den tis t’s m ind. Insufficient consideration is given th e p ulp in cavity prep aratio n and in the tre a tm e n t of th a t organ. I f one is to prepare cavities properly, he should k now m ore th an th e gross a n a t omy and the histology of the pulp. A know ledge of th e histology of th e enam el and dentin is of u tm ost im portance. I shall n o t take the tim e in this paper to attem p t an exhaustive histologic descrip tion of th e enam el and dentin, as th a t w ould be w ith o u t the scope of this treatise. Suffice it to recall to your m inds th a t the enam el consists of enam el prisms or rods. T h e direction of these rods is usually a t rig h t angles to th e surface of the tooth in w hich they are found. T h e rods are held together by a cem ent sub stance w hich is softer th an the rods them selves ; therefore, w e have th a t ch aracter istic of enam el know n as cleavage. T h e re is com paratively little organic m a tte r in the enam el. T h e various calcium salts constitute th e b ulk of th e enam el sub stance, an d a re present in th e follow ing proportions (o th e r constituents are also given) : calcium phosphate an d fluorid, 89.82 per c e n t; calcium carbonate, 4.37 ; m agnesium phosphate, 1 .3 4 ; other salts,
0 . 88. T h e rest of the enam el substance, w hich is organic m atter, is present in the percentage of only 3.59. T h o u g h the dentin contains practically the same chem ical constituents as the enamel, it contains organic m a tte r in the percentage of 27.61, w hich is approxim ately nine tim es the am oun t found in th e enam el. I t is w ell
Byrnes— Cavity Preparation
know n th a t bacteria a ttac k organic m a t te r m uch m ore rapidly th a n inorganic; hence, it is easy to und erstan d w hy caries penetrates the dentin m ore rapidly th an the enam el. T h e d en tin al tubules contain organic m a tte r principally in the form of fine nerve filam ents fro m the odontoblasts around th e periphery of th e pulp. T h is organic m a tte r is readily attacked by the organism s of caries, and a rapid invasion takes place in the direction of the pulp. O nce the dentin is reached, th e decay also spreads la terally alo n g th e dentinoenam el jun ctio n , ow ing to the presence of the g ra n u la r layer of T om es in th a t location and to the increased am ount of organic m a tte r. I t therefore follow s th a t caries involving the enam el only does not require rem oval of so m uch tooth stru c tu re as th a t involving both the enam el and the dentin, an d th a t it is m anifestly m ore logical to fill the tooth w hen the carious area is sm all th an to w ait u n til the dentin is invaded. T R E A T M E N T O F FISSURES
O n e of the surest w ays to conserve the pulps in teeth is by filling those teeth before decay becomes extensive, or, b etter still, by filling them before caries even begins. In his “ L e tte r of E xplanation A bout Fissures” T h a d d e u s P . H y a tt, d ental director of the M e tro p o lita n L ife Insurance Com pany, states th a t “ there are 2,500 chances to one th a t a fissure w ill decay in less th a n tw en ty years.” H e says fu rth e r: “ P rofessor C . F . Bodecker also has show n in his article in the D e n ta l Ite m s o f In te re st fo r N ovem ber, 1926, th a t 2,400,000,000 bacteria can find lodg m ent in the average-sized fissure. I leave it to you to decide on the m orality of exposing any child to such odds. I also leave to you the decision if an occlusal pin-hole filling is as dangerous to the to o th as is an open and unfilled occlusal
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fissure.” D r. H y a tt also states th a t “in the exam ination of over 50,000 cases, w e find th a t here in o u r country, and in our present state of civilization, less th an onetw en tieth of one per cent are im m une to caries; also, th a t these persons w ho are im m une have teeth th a t a re practically free fro m pits o r fissures.” A n d D r. H y a tt very aptly ad d s: “ Please m ake your ow n deductions.” U n fo rtu n a tely , the public has n ot yet been convinced of the im portance of fill ing fissures in new ly eru p ted teeth, and m ost dentists m u st still be confronted w ith th e necessity of filling teeth afte r caries has become extensive. W ith refer ence to the m an n er in w hich caries occurs, there are tw o g reat groups of cavities, nam ely, p it and fissure cavities, and smooth surface cavities. T h e form er are found w h erev er pits and fissures occur, and th e la tte r, as th e nam e indicates, are found on portions of the surfaces of teeth w hich do n o t present pits an d fissures for th e beginning of the process of caries. T h is process, as fa r as the dentin is con cerned, is identical in both of these groups, b u t the processes in the enam el are quite different an d require different treatm en t in cavity preparation w ith reference to extension fo r prevention. P it an d fissure cavities begin in pits, grooves o r fissures. H ere, they cover themselves w ith a gelatinoid substance, w hich makes th eir hid in g place secure, so to speak. T h e ir nest or nidus is thus form ed, an d they grow and m ultiply. T h e ir acid products dissolve o u t the lime salts w hich hold th e enam el rods together, and thus form a channel fo r th e progress of the m icro-organism s to w ard the dentin and induce a general u n d erm in in g of the enam el beneath th e surface. T h is u n d er m ining along th e dentino-enam el ju n ctio n is sometimes term ed “ backw ard decay.” T h e only evidence, on the surface, of such
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a process, may be a darkened line in the groove, or a spot in th e pit, pressure on w hich w ith a c u ttin g instru m en t m ay cause the surface to cave in. T h e process, on reaching the dentino-enam el junction, finds less resistance here th an in the enam el, and the spread is m ore rapid. Because of the inclination of the enam el rods to w ard a groove or pit, we have the cone-shaped area of decay in the enam el here, w ith its apex to w ard the surface and its base to w ard the dentino-enam el ju n ction. T h e cone o f decay is la rg e r in the dentin than in th e enam el because the dentin is m ore vulnerable. T h e cone of decay in the dentin alw ays has its base a t the dentino-enam el junction, and its apex tow ard the pulp. In the preparation of cavities of the pit and fissure group, it is necessary only to remove the enam el covering the area underm ined by caries and form the cavity in th e dentin. F u rth e r extension fo r pre vention of recurrence of caries is not nec essary, except w here it may be required to follow o u t deep grooves to places w here a smooth m argin may be given the filling, or restoration. Sm ooth surface cavities have th eir be ginnings in surfaces w hich are free from stru c tu ra l defects. M icro-organism s m ust, therefore, attach them selves to th e su r faces in areas w hich are m ore or less hid den from the excursions of the food and saliva, as in th e proxim al surfaces and in the habitually unclean areas, le ft so by inadequate use of the toothbrush, as at the gingival m argin of the buccal and labial surfaces. H ere, again, th e m icro-organism s col lect and cover them selves w ith a gelatinoid substance, th e ir acid products dis solving o u t the lim e salts of the e n a m e l; b u t because of the difference in the incli nation of the enam el rods here as com pared to those su rro u n d in g a groove, th e
caries spreads la terally on the surface, each p a r t of the w idened area of begin n ing caries p en etratin g the line of the length of th e enam el rods. T h is gives a conical area of caries, w ith the base of the cone a t th e surface an d th e apex to w ard the pulp. T h is is ju s t the reverse of the process h aving its inception in the enam el su r roundin g a groove, fissure or pit, w hile the decay in the dentin is id en tical; or, to repeat, im m ediately th e enam el is pene tra te d , caries spreads la terally along the dentino-enam el ju n ctio n in every direc tion. T h e extension of the m argins of gin gival th ird cavities from the center of the surface fa r to w ard the mesial and distal angles of the tooth is so necessary th a t the rule should be to cu t them close to the angles in every case, b u t never past the angles. H erein alone lies safety ; fo r if this is n ot done, and susceptibility to caries continues, caries is alm ost certain to recur a t the mesial o r distal aspect, or a t both, th e filling being lost, an d the pulp fu rth e r disturbed by the preparation of a m ore extended cavity. W h y to the angles ? Because these are areas of n a tu ra l im m unity. I m ig h t m ention th a t, in a record of 1 0 , 0 0 0 cases exam ined in the dental clinic of N o rth w e ste rn U n iv er sity, Chicago, only nine presented caries beginning a t these angles of the to o th ; and, in all of these, th ere w as some n a tu ra l or acquired fa u lt of occlusion, i. e., teeth tw isted, n o t occluding, lost or abscessed, n o rm al use being thereby pre vented. In laying the gingival w all of a cavity, w e should be guided by the age of the patient. I f such cavities are filled in young persons w ith o u t pushing the gin givae w ell back so th a t the m argin of the cavity can be extended w ell u n d er the gingivae, as age advances an exposure of
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Byrnes— Cavity Preparation the enam el betw een the gingivae and the filling w ill result. Such an exposure may resu lt in fu rth e r caries, necessitating fu rth e r cavity preparation and atten d a n t needless irritatio n of the pulp, all of w hich could have been prevented by m ak ing the first preparation extensive enough. T o o th stru c tu re is not saved by inade q uate cavity preparation, nor is the pulp preserved. I shall now take up briefly the prepa ration of cavities in the various teeth, and m ention a few general principles bearing on the relation of proper cavity prep ara tion to pulp conservation. INCISORS AND CUSPIDS
I n a h orizontal section thro u g h an in cisor or cuspid, the enam el rods are cut p arallel w ith their length in all their parts, b u t they do n o t all stand at rig h t angles to th e surface of the tooth. T h e deviation is greatest as the angles are reached in passing from the proxim al to the lingual surfaces. T h is, interpreted in its application to cavity preparation, means th a t it is not safe to lay cavity m argins a t these angles, as th e rods w ill m ost likely be le ft unsupported. I f the decay reaches these m argins, the m argins of the cavity m ust be carried over to the lingual surface. I n the preparation of proxim al cavities for foil in the incisors and cuspids, care should be taken in placing convenience points. T hese should not be cu t into the gingival w all, b u t into the labial and lin gual w alls. T h e reason for this is obvious w hen one considers the closer proxim ity of the pulp in the gingival portion of the cavity. L arg e convenience points in cav ities are unnecessary. T h ese points, w hen filled, convey th erm al changes to the pulp in the same m anner th a t the general body of the restoration w ould. T h e re is also frequent danger of ru n n in g into the
horns of the pulp w ith large convenience points. In the upper incisors, p articu larly the lateral, th ere is very often a pit in the cingulum w hich extends to quite a depth. I t is not good procedure to carry the floor of the cavity to the depth of this pit of decay. T h is is obviated by follow ing out the area of decay w ith a sm all round bur, and, w hen this operation is completed, filling this channel w ith cement. I t is also w ell to rem em ber th a t, in proxim al cavities in the incisors and cus pids, w here caries has underm ined por tions of the labial and lin g u al surfaces, the carious process in the dentin in the ce n tral portion of th e cavity is often checked. In such cavities, it is necessary to cu t around the pulp to the labial and lingual aspect. T h is w ill give a rounded pulpal floor to the cavity, and w ill avoid the exposure of the pulp w hich w ould resu lt if the pulpal floor in such cavities w ere m ade flat. B ICU SPID
TEETH
R ecalling the gross anatom y of the pulp of the bicuspid tooth, w e w ill re m em ber th a t the horns of the pulp, p a r ticularly in the upper bicuspids, and in the low er second bicuspid, are prom inent and slender, and th a t recessional lines of the horns of the pulp often extend to w ard the cusps fo r a considerable distance. T h e location of these should be carefully studied an d avoided, if possible, in cavity preparation in these teeth. I t is here th a t unintentio n al exposure of the pulp often occurs, for the reason th at, in the process of the developm ent and recession of the pulp, this tra c t is not alw ays com pletely closed, and a slender th rea d of pulp tissue w ill often persist in the tra c t. O f course, even the m ost m inute portion of an ex posed pulp is sufficient fo r the beginning of an infectious process w hen such p art
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is brought in contact w ith the m icro organism s of the m outh. A point to be rem em bered in the prep aratio n of occlusal cavities in th e bi cuspids, p articu larly the upper bicuspids, is th a t such cavities call fo r a very shal low preparation in the ce n tral line of the groove, because of the very deep inclined planes from the cusps. W h e n th e cavity is w idened buccally-lingually, the line angles of the floor m ay strik e the horns of the pulp. MOLAR T E E T H
In very deep occlusal cavities, it is not necessary to carry the floor of the cavity to th e depth of the decay. T h e caries in the center of the floor m ay be removed, and this cupped-out area filled w ith cem ent. Exposures often resu lt from the o p erato r’s attem p tin g to flatten out the floor of the cavity to correspond to the depth of the sm all area of caries in the central portion of the cavity, thereby in vading the area of the horns or the reces sional lines of the pulp. In mesial cavities of upper m olars, the occlusal step m ay be m ade broader than it could be in distal cavities of the upper m olars or in m esial and distal cavities of th e low er m olars, because th e lingual h orn of the pulp in the upper m olars is situated fa rth e r distally. T h is affords m ore room in th e neighborhood of the m esial surface. Black says, “ In the preparation of proxim o-occlusal cavities th e re is usually room to occupy one-third of the buccolingual breadth of the tooth in a step w ith o u t interfering w ith the pulpal horns, provided the step is not cut too deep, i. e., deeper th a n necessary fo r substantial stren g th .” I t m u st be rem em bered in th e prepara tion of cavities in m olar teeth th a t the
pulpal horns in the m esial portion are longer, and th a t there is m ore danger of cu ttin g in to the recessional lines in the mesial portion th a n in th e distal. I should like to recall to your m inds a few points of a general n a tu re w hich, simple though they are, are often over looked by dentists in the course of cavity preparation. M e ta l fillings cannot be placed so near the pulp as can porcelain inlays, for the reason th a t m etal conducts therm al con ditions m ore readily to the pulp. F o r the same reason, an inlay m ay be placed n ear er the p ulp th an a gold foil filling may. T h o u g h the layer of cem ent betw een the inlay and th e floor of the cavity m ay be exceedingly thin, it is nevertheless suffi cient to in te rru p t the transm ission of changing th erm al conditions to the pulp. B u t it m ust also be borne in m ind th a t cem ent itself is irrita tin g to the pulp. A cavity for a porcelain inlay m ay be made so deep th a t the irritatio n of th e cem ent may counterbalance the h arm resulting from a m etal filling of th e same depth. G enerally speaking, th e use of procain is a dangerous th in g in cavity preparation. In elim inating pain, it does aw ay w ith the signals w hich w arn the operator of the close proxim ity of the pulp. T h e re are times w hen its use is indicated, b u t the occasions are rare. T h e dentist seeking to relieve th e p atien t of pain incident to cavity preparation should employ other methods. T h e use of tepid w a te r during cavity preparation, the use of sharp burs and a m ore extended use of the cu ttin g instrum ents w ill accomplish much in th a t direction. T h e use of sharp burs in the preparation of cavities keeps dow n u n necessary friction, thus preventing th e r m al shock and consequent pain. T h e w ate r also keeps dow n friction. I f it is tepid, its tem p eratu re w ill n ot act as a pulp irrita n t.
Byrnes— Cavity Preparation O n e of the redeem ing features of the inlay is th a t it does aw ay w ith the need fo r the deep portions of cavities, often m ade necessary by the use of oth er filling m aterials, for the sake of retention. D IS E A S E D O R E X P O S E D P U L P S
L astly, w e come to the tre a tm e n t of diseased or exposed pulps. W h e n a dentist speaks of preventing caries, he usually has in m ind the prevention of ex tern al or ap p arent caries. T o o little atten tio n is given to the caries in the floor of th e cav ity. M o st of the m icro-organism s of the m outh are facultative, and can thrive w ith or w ith o u t the presence of free oxygen. I f it is impossible to rem ove all th e carious dentin w ith o u t exposing the pulp, it is very necessary th a t the rem ain ing dentin be treated in a m a n n er th a t w ill inhibit the progress of f u rth e r caries. T h is is done best by sterilizing the re m aining dentin and at the same tim e placing some agent in the cavity w hich w ill allay the irritatio n and soothe the pulp. W h ile it is tru e th a t in m ost cases w here caries extends to the pulp th e re m oval of th a t organ is necessitated, there is a possibility of preserving the pulp in some instances, particularly in the teeth of young individuals. Even the sm all per centage of cases w hich w ould respond to p ulp trea tm e n t should w a rra n t ou r ef forts along the line of pulp preservation. W h a t trea tm e n t should be given the pulp w hen the rem oval of all caries is not possible w ith o u t exposing o r endan gering it? V arious m ethods have been successfully used by dentists in the past, a few of w hich I shall outline. Silver n itra te m ay be used extensively in the trea tm e n t of rem aining carious d entin. W h e n applied to the dentin, it form s a h ard coagulum w hich resists caries. C are and precaution should be exercised in its use, and a ru b b er dam
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should be placed over the to o th w herever it is possible to do so. T h e silver n itra te is placed on the carious d en tin w ith a pledget of cotton. I t m ay be precipitated w ith oil of cloves, and should n o t be placed by itself in very deep cavities. O v er this may be placed a eugenol-cem ent base; th a t is, a th in m ix of “ silver B ” cem ent, w ith eugenol as th e liquid instead of the reg u lar liquid furnished by the m a n u factu rer. O v e r this pulp-capping, the reg u lar cem ent base m ay be placed. T h e tooth should be left alone fo r a w eek or more, fo r purposes of observation. If, at the end of th a t tim e, it gives no fu rth e r symptoms of p ulp irritatio n , a regular, perm anent filling m ay th en be placed. Some dentists have found th e use of black copper cem ent effective in the tre a t m ent of pulps. T h e black oxid of copper content in this cem ent is about 90 per cent. Copper salts are know n to have an inhibitory effect on caries. T h e principal objection to this k ind of cement is the discoloration to th e tooth w hich follow s its use. T h e re are also various proprie ta ry preparations on the m ark et, some of w hich possess decided virtues. P erhaps the to o th m ost com m only the seat of caries and p ulp tro u b le is the first perm anent m olar. E a rly caries in this tooth is a serious m a tte r, for, if the pulp is involved, the d en tist is confronted w ith the question as to w h eth e r to attem p t to save the pulp or to remove it. I t is prac tically impossible to place a good root canal filling in this tooth before the ninth year, a t w hich tim e the apex has usually attained its final form . O n the other hand, the chance of saving the pulp through tre a tm e n t is com paratively sm all. T h e dentist m ust take m any things into consideration before he m akes his final decision. T h e ideal th in g is to obviate the necessity fo r such a situation arising. A s I m entioned earlier in this paper, it is
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m uch b etter to fill undecayed pits and fissures in these teeth than to pursue the policy of w atc h fu l w aiting. T h e re are various ways th a t these undecayed pits an d fissures m ay be treated. A side from actual cavity preparation involving these pits and fissures (w hich w ould seem m ore lo g ical), a m ethod w hich has found favor w ith some is as fo llo w s: 1. Rem ove debris w ith a stiff brush and a needle-pointed explorer. 2. D ry out w ith alcohol. 3. A p ply silver n itra te for three m inutes. 4. P recip itate w ith solution of form aldehyd, U .S .P ., if quick precipitation is desired. 5. W ip e out w ith a pledget of cotton. 6 . A pply good cement. (P la ce the cem ent a t the m arginal ridges of the tooth, and w o rk it dow n into the pits and fissures w ith an explorer.) 7. W ith fingers coated
w ith cocoa b u tte r, apply pressure to the cem ent. D u rin g the en tire procedure, the tooth should, of course, be kept perfectly dry w ith a ru b b er dam . I t is m y observation th a t dentists in the past have given entirely too little a tte n tion to th e trea tm e n t and conservation of the pulp. T h e pulp of a tooth is w o rth saving, and, in cavity preparation, as w ell as in the specific trea tm e n t of the pulp, its value as a v ita l tissue should be real ized by th e dentist. I have endeavored here to stress a few principles w hich, w hen applied either directly, as in the case of pulp treatm en t, or indirectly, as in the case of cavity preparation, w ill result in a fu rth e r conservation of the pulp. 106 F o rrest A venue, N. E.
TH E WRITINGS A N D ACTIVITIES OF DR. ALFRED OWRE IN RELATION TO THE STATUS OF DENTISTRY: A CRITICAL ANALYSIS By BISSELL B. PALMER, D.D.S., F.A.C.D., N ew York City H E very foundations of the A m eri can republic w ere b u ilt upon to ler ance and the rig h t of the individual to form , hold and express his opinions on any and all subjects. T h a t privilege is recognized today. T h e re is a m arked distinction, however, betw een to leration of an opinion and toleration of an effort to enforce th a t opinion and bring about an undesired end. F o r example, one could tolerate the view th a t'th e U n ited S tates should again become a colony of G re a t B ritain, b u t one could n o t justly be term ed into leran t if he believed such a step to be undesirable and opposed
T
Jotir. A . t>. A ., M arch, 19
every effort to b rin g about such a con dition. T h e foregoing statem en t of principle is presented as prelim inary to this an a lytic study of the w ritin g s and activities of D r. A lfre d O w re in relatio n to the status of dentistry, so th a t the reader m ay un d erstan d th a t there is no question about the rig h t of D r. O w re the indi vidual to form and express any opinion. I t is believed, how ever, th a t the opinions of D r. O w re, expressed officially as dean of the School of D e n ta l and O ra l S u r gery of Colum bia U niversity, and any ef forts to enforce those opinions on ap
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p artial dentures w ill, w ith b u t few ex ceptions, elim inate th e failures th a t have occurred in th e past. 185 North Wabash Avenue.
C A V IT Y P R E P A R A T IO N W IT H S P E C IA L R E F E R E N C E T O P U L P P R O T E C T IO N , FO R V A R IO U S F IL L IN G M A T E R IA L S * By RALPH R. BYRNES, D.D.S., F.A.C.D., Atlanta, Ga.
N this paper, dealing w ith cavity prep aratio n , I shall n o t attem p t to give the operative procedure in detail, as th a t is a phase of d entistry w hich in itself could be the subject of a very long paper. In stead, I shall deal w ith general p rin ciples of cavity preparation, and discuss certain aspects w hich, though less com m only considered in the w ritin g of dental papers, have an im p o rta n t bearing on the subject, directly o r indirectly.
I
I t is obvious th a t any one attem pting cavity preparation should have a know l edge of the anatom y of the pulp, if he has fo r his objective the preservation of th a t delicate, vascular tissue. I t seems appro priate, therefore, to begin this paper w ith a b rief description of the pulp, m acro scopic and microscopic. A s a g eneral rule, th e shape of the pulp of a tooth conform s ro u ghly to th e shape of the cro w n of the tooth, b u t there are enough m inor differ ences to w a rra n t a brief description of th e pulps of th e individual teeth. I n this description, I shall take as m y guide B lack’s D e n ta l A natom y. •Read by William Edgar Coleman, Atlanta, Ga., in the absence of the author. •Read before the Section on Operative Dentistry at the Midwinter Clinic of the Chicago Dental Society, Jan. 14, 1930.
Jour. A .D . A., March, 1931
P U L P S OF T H E U P P E R INCISORS
In th e incisors, th ere is no sharp d if ferentiatio n in th e pulp of th e coronal portion an d th a t of the ro o t portion. T h e pulp is broadest m esiodistally, and tapers gently as th e root portion is ap proached. T h e pulp cham bers of th e cen tra l and la te ra l incisors are so sim ilar th a t a description of one w ill do for both. T h e largest diam eter o f th e p ulp cavity occurs about the level o f the gingival line on the labial surface. B lack says th a t in young incisors ju st erupting, he has found the diam eter of th e p ulp a t th e gingival line to be from on e-fo u rth to one-third th e diam eter of th e neck of the tooth. H e says fu rth e r th a t, in early a d u lt age, the pulp m ay average about one-fourth th e diam eter of th e neck of th e tooth, w ith a range, w ith approaching age, to one-fifth, one-sixth or, in th e extrem e, to one-tenth. T h e cham bers and canals in th e la te ra l incisors are, of course, a little sm aller th an those of the ce n tral incisors, b u t they are pro p o rtio n ately larg er w hen the size of th e to o th is considered. T h is fact accounts fo r the freq u en t exposure of pulps in the la te ra l incisors d u rin g cavity p rep aratio n . I n very young teeth, three sh o rt horns are often present, cor
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responding m am elons.
to
the
position
of
the
P U L P OF T H E U P P E R C U S P ID
T h e re is n o t a g reat deal of difference in the general shape of the pulp of the u p per cuspid and th a t of the upper in cisors. T h e coronal extrem ity of the pulp of th e cuspid has a ce n tral h o rn w hich is n o t present in the incisors. T h is horn extends to w ard th e cusp of th e tooth, the m esial and la te ra l horns being practically o bliterated. T h e pulp cham ber extends to w ard the cu ttin g edge of th e tooth ab out tw o -thirds the length of th e crow n. T h e pulp is proportionately sm aller than th a t of the incisors, and its greatest diam eter is at the gingival line, from labial to lingual. T h e proportionately sm aller size of the pulp of this tooth and the tapering of the coronal p o rtion of the pulp accounts fo r th e extensive cavity p reparation th a t can be done on a cuspid to o th w ith o u t in ju ry to the pulp. P U L P CH A M B E R OF T H E LOW ER CU SPID
A t the neck of th e tooth, th e labial p o rtion of th e pulp is w ider th a n the lingual, and the long diam eter of the pulp is from labial to lingual aspect. T h e coronal portion traverses about tw o -thirds th e length of the crow n to w ard the point of the cusp, w here it ends in a point, or horn, w hich is usually very slender. H ere again, proportionately extensive prep ara tio n m ay be done w ith o u t encroaching on th e pulp. P U L P C H A M BERS OF T H E LOWER
extends to w ard the cu ttin g edge about tw o -th ird s th e len g th of the crow n. C avity p rep aratio n in these teeth is m ost delicate. P U L P C H A M B E R OF T H E U P P E R FIRST B IC U SPID
In this tooth, th e re is a sharp differen tiation betw een th e pulp of the crow n and th a t of the ro o t portion, w hich is n o t the case w ith th e incisors and th e cuspids. T h e p ulp cham ber of this to o th is cen tra lly placed in th e long axis of the crow n. T h e axial w alls are about equal in thickness, b u t the occlusal w alls are thicker th a n th e axial, th e ir thickness varying from one-th ird to tw o-thirds the length of the crow n. T o w a rd the apex of each cusp, a h o rn extends. T h e height and th e sharpness of th e cusps determ ine the height and sharpness of th e horns of the pulp. In teeth w ith very high and w ellpronounced cusps, such as w e often see in new ly erupted bicuspids, th ere are often very long and slender horns. Black has reported th a t, in some bicuspids w ith very pronounced cusps, th is h o rn has ex tended alm ost to the enam el. O f course, these horns become sh o rter as age ad vances. H ere, etern al vigilance m ust be exercised to avoid the area of the reces sional lines of th e horns, w hich are the lines along w hich the pulp recedes as the age of the tooth advances, and a t times there m ay be a tra c t containing a filam ent of the pulp tissue, the strik in g of w hich gives us the equivalent of an exposure.
INCISORS
P U L P C H A M B E R OF T H E U P P E R
A t the level of the gingival line, the long diam eter of the pulp is from labial to lingual aspect. A s the coronal ex trem ity of th e pulp is approached, the diam eter gradually diminishes labiallylingually, increases m esially-distally and ends in a th in edge. T h e pulp cham ber
T h e re is little difference betw een the shape of the pulp of this tooth and th a t of th e upper first bicuspid. T h e horns of the pulp of this to o th are usually shorter, and the recessional lines are n ot so pro nounced n o r so likely to in ject them -
SECOND BICUSPID
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Byrnes— Cavity Preparation selves into the p reparation of th e cavity, as in the first bicuspid. P U L P C H A M BERS OF T H E LOW ER BICUSPIDS
T h e pulp cham ber of th e low er first bicuspid ends in a horn extending to w ard the point of the buccal cusp. T h e re is no definite h o rn extending to w a rd the lin g u al cusp, although a p rotrusion of the p u lp in th a t direction is discernible. T h ese teeth seldom show a definite line of dem arcation betw een th e coronal pulp and th a t of the root canals. I n th e low er second bicuspid, the pulp extends into a lingual horn as w ell as in to a buccal horn, and the lin g u al horn m ay sometimes be very slender, especially in young teeth. In the low er bicuspids having three cusps, tw o horns of the pulp extend on the lingual side, spreading to w ard the mesial and distal aspects. T h o u g h th e horns themselves a re usually short, th e ir protrusion brings them nearer the surface of the tooth th a n other horns of th e pulp. T h is accounts for the greater likelihood of opening into th a t portion of the pulp in excavating proxim al cavities. P U L P CH A M BERS OF T H E U P P E R
ness of the w alls of this tooth accounts fo r the ra th e r extensive cavity p rep ara tion w hich can be m ade on the to o th ; hence, th e to o th serves w ell as an ab u t m ent for bridges in th e form of crow ns and inlays. P U L P CH A M BERS OF T H E LOWER MOLARS
T h e pulp cham bers of these teeth, though they correspond to th e general shape of the crow ns, as is the case w ith the other m olars, are som ew hat m ore an g u lar. T h e occlusal w all of the pulp cham ber shows a convexity to w ard the pulp. F ro m th e extrem e angles of the pulp, the horns extend to w ard each cusp. T h e diam eter of the pulp cham ber of this too th varies g reatly according to the age of the individual. In youth, it may be as m uch as tw o-fifths the diam eter of the crow n, and it is seldom less th an oneth ird . T h e diam eter of the pulp decreases greatly in old age, ow ing to the deposit of secondary dentin, a result of abrasion, and th e pulp cham ber in old individuals m ay often be alm ost obliterated. H ere, then, the age of the p atien t is an im por ta n t factor in d eterm ining the extent of cavity preparation.
MOLARS
T h e pulp cham bers and the root canals of these teeth are sharply differentiated, th e root canals being m inute openings in to the pulp cham ber. T h e average diam eter of the pulp cham ber of this to o th is about equal to the thickness of th e axial w all by w hich it is surrounded. T h e occlusal w alls are usually consider ably thicker th an the axial. T h e pulp cham ber corresponds in form to the cro w n of th e tooth w ith horns of the pu lp extending to w ard each cusp. T h ese horns are usually very pronounced in young teeth, and, of course, w ea r dow n o r recede w ith advancing age. T h e thick
GROSS ANATOM Y
A thorough know ledge of the gross anatom y of the pulp w ill enable the oper ato r to avoid exposing pulps needlessly. Likewise, a thorough know ledge of the histologic or microscopic stru ctu re of the pulp w ill aid him in applying his k n o w l edge of m ateria m edica in the treatm en t of diseased pulps. T h e tooth pulp is an em bryonic con nective tissue consisting of fine reticu lar tissue and a m ucoid m a trix containing com paratively few cells. T h is tissue, or “nerve,” as it is com m only called by the laity, is exceedingly vascular, containing
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num erous capillaries w hich term inate in a plexus im m ediately beneath the odontoblasts lining th e periphery of the p ulp on all sides. T h e nerves of th e pulp have the same general distrib u tio n as th e blood vessels, and end in a plexus of filam ents ju s t beneath the odontoblasts. T h e nerve fibers are m edullated in the body of the pulp, b u t lose th e ir m edullary sheaths as th e periphery of th e pulp is approached. T h e fact th a t th e w alls of th e capillaries are exceedingly th in and th e ir lum ens large, and th e fu rth e r fact th a t the pulp is so richly supplied w ith nerves, accounts fo r the extrem e sensitiv ity of the pulp to bacterial infection and to irrita n ts. T h e lining cells, o r the odontoblasts, are responsible fo r th e de posit of secondary dentin w h en such unfavorable conditions as abrasion and b acterial infection through caries are en countered. D en tists are too prone to condem n a p ulp w hen it m anifests sym ptom s of dis ease o r irritatio n . O n e w ould not th in k of enucleating th e eye sim ply because of an iritis o r a conjunctivitis. T h e efforts of the physician w ould be directed first to w ard relieving the condition by rem edial m easures. T h o u g h th e pulp has probably less resistance th an th e eye to infection, it nevertheless possesses the pow er of recuperation w hen th e cause of th e disturbance is rem oved. W h ile it is tru e th a t pulpectom y is th e only relief fo r very badly diseased pulps, it does not follow th a t extirpation of th e pulp is nec essary in a ll cases of diseased o r irritated pulps. Indeed, the pulp of any tooth h a r boring caries in th e den tin m u st become infected, a t least in a degree, as it is a w ell k now n fact th a t the m icro-organism s of caries penetrate and extend th ro u g h the organic m a tte r of the dentinal tubules w ith apparent ease.
U n lik e m ost of th e o th er tissues of the body, the p ulp is enclosed w ith in an u n yielding w all. W h e n hyperem ia of the pulp occurs, th e tissue has no room in w hich to e x p a n d ; hence, the clinical sym ptom s are definite an d sharp, and sometim es re su lt in an exaggeration of th e seriousness of th e tro u b le in th e den tis t’s m ind. Insufficient consideration is given th e p ulp in cavity prep aratio n and in the tre a tm e n t of th a t organ. I f one is to prepare cavities properly, he should k now m ore th an th e gross a n a t omy and the histology of the pulp. A know ledge of th e histology of th e enam el and dentin is of u tm ost im portance. I shall n o t take the tim e in this paper to attem p t an exhaustive histologic descrip tion of th e enam el and dentin, as th a t w ould be w ith o u t the scope of this treatise. Suffice it to recall to your m inds th a t the enam el consists of enam el prisms or rods. T h e direction of these rods is usually a t rig h t angles to th e surface of the tooth in w hich they are found. T h e rods are held together by a cem ent sub stance w hich is softer th an the rods them selves ; therefore, w e have th a t ch aracter istic of enam el know n as cleavage. T h e re is com paratively little organic m a tte r in the enam el. T h e various calcium salts constitute th e b ulk of th e enam el sub stance, an d a re present in th e follow ing proportions (o th e r constituents are also given) : calcium phosphate an d fluorid, 89.82 per c e n t; calcium carbonate, 4.37 ; m agnesium phosphate, 1 .3 4 ; other salts,
0 . 88. T h e rest of the enam el substance, w hich is organic m atter, is present in the percentage of only 3.59. T h o u g h the dentin contains practically the same chem ical constituents as the enamel, it contains organic m a tte r in the percentage of 27.61, w hich is approxim ately nine tim es the am oun t found in th e enam el. I t is w ell
Byrnes— Cavity Preparation
know n th a t bacteria a ttac k organic m a t te r m uch m ore rapidly th a n inorganic; hence, it is easy to und erstan d w hy caries penetrates the dentin m ore rapidly th an the enam el. T h e d en tin al tubules contain organic m a tte r principally in the form of fine nerve filam ents fro m the odontoblasts around th e periphery of th e pulp. T h is organic m a tte r is readily attacked by the organism s of caries, and a rapid invasion takes place in the direction of the pulp. O nce the dentin is reached, th e decay also spreads la terally alo n g th e dentinoenam el jun ctio n , ow ing to the presence of the g ra n u la r layer of T om es in th a t location and to the increased am ount of organic m a tte r. I t therefore follow s th a t caries involving the enam el only does not require rem oval of so m uch tooth stru c tu re as th a t involving both the enam el and the dentin, an d th a t it is m anifestly m ore logical to fill the tooth w hen the carious area is sm all th an to w ait u n til the dentin is invaded. T R E A T M E N T O F FISSURES
O n e of the surest w ays to conserve the pulps in teeth is by filling those teeth before decay becomes extensive, or, b etter still, by filling them before caries even begins. In his “ L e tte r of E xplanation A bout Fissures” T h a d d e u s P . H y a tt, d ental director of the M e tro p o lita n L ife Insurance Com pany, states th a t “ there are 2,500 chances to one th a t a fissure w ill decay in less th a n tw en ty years.” H e says fu rth e r: “ P rofessor C . F . Bodecker also has show n in his article in the D e n ta l Ite m s o f In te re st fo r N ovem ber, 1926, th a t 2,400,000,000 bacteria can find lodg m ent in the average-sized fissure. I leave it to you to decide on the m orality of exposing any child to such odds. I also leave to you the decision if an occlusal pin-hole filling is as dangerous to the to o th as is an open and unfilled occlusal
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fissure.” D r. H y a tt also states th a t “in the exam ination of over 50,000 cases, w e find th a t here in o u r country, and in our present state of civilization, less th an onetw en tieth of one per cent are im m une to caries; also, th a t these persons w ho are im m une have teeth th a t a re practically free fro m pits o r fissures.” A n d D r. H y a tt very aptly ad d s: “ Please m ake your ow n deductions.” U n fo rtu n a tely , the public has n ot yet been convinced of the im portance of fill ing fissures in new ly eru p ted teeth, and m ost dentists m u st still be confronted w ith th e necessity of filling teeth afte r caries has become extensive. W ith refer ence to the m an n er in w hich caries occurs, there are tw o g reat groups of cavities, nam ely, p it and fissure cavities, and smooth surface cavities. T h e form er are found w h erev er pits and fissures occur, and th e la tte r, as th e nam e indicates, are found on portions of the surfaces of teeth w hich do n o t present pits an d fissures for th e beginning of the process of caries. T h is process, as fa r as the dentin is con cerned, is identical in both of these groups, b u t the processes in the enam el are quite different an d require different treatm en t in cavity preparation w ith reference to extension fo r prevention. P it an d fissure cavities begin in pits, grooves o r fissures. H ere, they cover themselves w ith a gelatinoid substance, w hich makes th eir hid in g place secure, so to speak. T h e ir nest or nidus is thus form ed, an d they grow and m ultiply. T h e ir acid products dissolve o u t the lime salts w hich hold th e enam el rods together, and thus form a channel fo r th e progress of the m icro-organism s to w ard the dentin and induce a general u n d erm in in g of the enam el beneath th e surface. T h is u n d er m ining along th e dentino-enam el ju n ctio n is sometimes term ed “ backw ard decay.” T h e only evidence, on the surface, of such
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a process, may be a darkened line in the groove, or a spot in th e pit, pressure on w hich w ith a c u ttin g instru m en t m ay cause the surface to cave in. T h e process, on reaching the dentino-enam el junction, finds less resistance here th an in the enam el, and the spread is m ore rapid. Because of the inclination of the enam el rods to w ard a groove or pit, we have the cone-shaped area of decay in the enam el here, w ith its apex to w ard the surface and its base to w ard the dentino-enam el ju n ction. T h e cone o f decay is la rg e r in the dentin than in th e enam el because the dentin is m ore vulnerable. T h e cone of decay in the dentin alw ays has its base a t the dentino-enam el junction, and its apex tow ard the pulp. In the preparation of cavities of the pit and fissure group, it is necessary only to remove the enam el covering the area underm ined by caries and form the cavity in th e dentin. F u rth e r extension fo r pre vention of recurrence of caries is not nec essary, except w here it may be required to follow o u t deep grooves to places w here a smooth m argin may be given the filling, or restoration. Sm ooth surface cavities have th eir be ginnings in surfaces w hich are free from stru c tu ra l defects. M icro-organism s m ust, therefore, attach them selves to th e su r faces in areas w hich are m ore or less hid den from the excursions of the food and saliva, as in th e proxim al surfaces and in the habitually unclean areas, le ft so by inadequate use of the toothbrush, as at the gingival m argin of the buccal and labial surfaces. H ere, again, th e m icro-organism s col lect and cover them selves w ith a gelatinoid substance, th e ir acid products dis solving o u t the lim e salts of the e n a m e l; b u t because of the difference in the incli nation of the enam el rods here as com pared to those su rro u n d in g a groove, th e
caries spreads la terally on the surface, each p a r t of the w idened area of begin n ing caries p en etratin g the line of the length of th e enam el rods. T h is gives a conical area of caries, w ith the base of the cone a t th e surface an d th e apex to w ard the pulp. T h is is ju s t the reverse of the process h aving its inception in the enam el su r roundin g a groove, fissure or pit, w hile the decay in the dentin is id en tical; or, to repeat, im m ediately th e enam el is pene tra te d , caries spreads la terally along the dentino-enam el ju n ctio n in every direc tion. T h e extension of the m argins of gin gival th ird cavities from the center of the surface fa r to w ard the mesial and distal angles of the tooth is so necessary th a t the rule should be to cu t them close to the angles in every case, b u t never past the angles. H erein alone lies safety ; fo r if this is n ot done, and susceptibility to caries continues, caries is alm ost certain to recur a t the mesial o r distal aspect, or a t both, th e filling being lost, an d the pulp fu rth e r disturbed by the preparation of a m ore extended cavity. W h y to the angles ? Because these are areas of n a tu ra l im m unity. I m ig h t m ention th a t, in a record of 1 0 , 0 0 0 cases exam ined in the dental clinic of N o rth w e ste rn U n iv er sity, Chicago, only nine presented caries beginning a t these angles of the to o th ; and, in all of these, th ere w as some n a tu ra l or acquired fa u lt of occlusion, i. e., teeth tw isted, n o t occluding, lost or abscessed, n o rm al use being thereby pre vented. In laying the gingival w all of a cavity, w e should be guided by the age of the patient. I f such cavities are filled in young persons w ith o u t pushing the gin givae w ell back so th a t the m argin of the cavity can be extended w ell u n d er the gingivae, as age advances an exposure of
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Byrnes— Cavity Preparation the enam el betw een the gingivae and the filling w ill result. Such an exposure may resu lt in fu rth e r caries, necessitating fu rth e r cavity preparation and atten d a n t needless irritatio n of the pulp, all of w hich could have been prevented by m ak ing the first preparation extensive enough. T o o th stru c tu re is not saved by inade q uate cavity preparation, nor is the pulp preserved. I shall now take up briefly the prepa ration of cavities in the various teeth, and m ention a few general principles bearing on the relation of proper cavity prep ara tion to pulp conservation. INCISORS AND CUSPIDS
I n a h orizontal section thro u g h an in cisor or cuspid, the enam el rods are cut p arallel w ith their length in all their parts, b u t they do n o t all stand at rig h t angles to th e surface of the tooth. T h e deviation is greatest as the angles are reached in passing from the proxim al to the lingual surfaces. T h is, interpreted in its application to cavity preparation, means th a t it is not safe to lay cavity m argins a t these angles, as th e rods w ill m ost likely be le ft unsupported. I f the decay reaches these m argins, the m argins of the cavity m ust be carried over to the lingual surface. I n the preparation of proxim al cavities for foil in the incisors and cuspids, care should be taken in placing convenience points. T hese should not be cu t into the gingival w all, b u t into the labial and lin gual w alls. T h e reason for this is obvious w hen one considers the closer proxim ity of the pulp in the gingival portion of the cavity. L arg e convenience points in cav ities are unnecessary. T h ese points, w hen filled, convey th erm al changes to the pulp in the same m anner th a t the general body of the restoration w ould. T h e re is also frequent danger of ru n n in g into the
horns of the pulp w ith large convenience points. In the upper incisors, p articu larly the lateral, th ere is very often a pit in the cingulum w hich extends to quite a depth. I t is not good procedure to carry the floor of the cavity to the depth of this pit of decay. T h is is obviated by follow ing out the area of decay w ith a sm all round bur, and, w hen this operation is completed, filling this channel w ith cement. I t is also w ell to rem em ber th a t, in proxim al cavities in the incisors and cus pids, w here caries has underm ined por tions of the labial and lin g u al surfaces, the carious process in the dentin in the ce n tral portion of th e cavity is often checked. In such cavities, it is necessary to cu t around the pulp to the labial and lingual aspect. T h is w ill give a rounded pulpal floor to the cavity, and w ill avoid the exposure of the pulp w hich w ould resu lt if the pulpal floor in such cavities w ere m ade flat. B ICU SPID
TEETH
R ecalling the gross anatom y of the pulp of the bicuspid tooth, w e w ill re m em ber th a t the horns of the pulp, p a r ticularly in the upper bicuspids, and in the low er second bicuspid, are prom inent and slender, and th a t recessional lines of the horns of the pulp often extend to w ard the cusps fo r a considerable distance. T h e location of these should be carefully studied an d avoided, if possible, in cavity preparation in these teeth. I t is here th a t unintentio n al exposure of the pulp often occurs, for the reason th at, in the process of the developm ent and recession of the pulp, this tra c t is not alw ays com pletely closed, and a slender th rea d of pulp tissue w ill often persist in the tra c t. O f course, even the m ost m inute portion of an ex posed pulp is sufficient fo r the beginning of an infectious process w hen such p art
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is brought in contact w ith the m icro organism s of the m outh. A point to be rem em bered in the prep aratio n of occlusal cavities in th e bi cuspids, p articu larly the upper bicuspids, is th a t such cavities call fo r a very shal low preparation in the ce n tral line of the groove, because of the very deep inclined planes from the cusps. W h e n th e cavity is w idened buccally-lingually, the line angles of the floor m ay strik e the horns of the pulp. MOLAR T E E T H
In very deep occlusal cavities, it is not necessary to carry the floor of the cavity to th e depth of the decay. T h e caries in the center of the floor m ay be removed, and this cupped-out area filled w ith cem ent. Exposures often resu lt from the o p erato r’s attem p tin g to flatten out the floor of the cavity to correspond to the depth of the sm all area of caries in the central portion of the cavity, thereby in vading the area of the horns or the reces sional lines of the pulp. In mesial cavities of upper m olars, the occlusal step m ay be m ade broader than it could be in distal cavities of the upper m olars or in m esial and distal cavities of th e low er m olars, because th e lingual h orn of the pulp in the upper m olars is situated fa rth e r distally. T h is affords m ore room in th e neighborhood of the m esial surface. Black says, “ In the preparation of proxim o-occlusal cavities th e re is usually room to occupy one-third of the buccolingual breadth of the tooth in a step w ith o u t interfering w ith the pulpal horns, provided the step is not cut too deep, i. e., deeper th a n necessary fo r substantial stren g th .” I t m u st be rem em bered in th e prepara tion of cavities in m olar teeth th a t the
pulpal horns in the m esial portion are longer, and th a t there is m ore danger of cu ttin g in to the recessional lines in the mesial portion th a n in th e distal. I should like to recall to your m inds a few points of a general n a tu re w hich, simple though they are, are often over looked by dentists in the course of cavity preparation. M e ta l fillings cannot be placed so near the pulp as can porcelain inlays, for the reason th a t m etal conducts therm al con ditions m ore readily to the pulp. F o r the same reason, an inlay m ay be placed n ear er the p ulp th an a gold foil filling may. T h o u g h the layer of cem ent betw een the inlay and th e floor of the cavity m ay be exceedingly thin, it is nevertheless suffi cient to in te rru p t the transm ission of changing th erm al conditions to the pulp. B u t it m ust also be borne in m ind th a t cem ent itself is irrita tin g to the pulp. A cavity for a porcelain inlay m ay be made so deep th a t the irritatio n of th e cem ent may counterbalance the h arm resulting from a m etal filling of th e same depth. G enerally speaking, th e use of procain is a dangerous th in g in cavity preparation. In elim inating pain, it does aw ay w ith the signals w hich w arn the operator of the close proxim ity of the pulp. T h e re are times w hen its use is indicated, b u t the occasions are rare. T h e dentist seeking to relieve th e p atien t of pain incident to cavity preparation should employ other methods. T h e use of tepid w a te r during cavity preparation, the use of sharp burs and a m ore extended use of the cu ttin g instrum ents w ill accomplish much in th a t direction. T h e use of sharp burs in the preparation of cavities keeps dow n u n necessary friction, thus preventing th e r m al shock and consequent pain. T h e w ate r also keeps dow n friction. I f it is tepid, its tem p eratu re w ill n ot act as a pulp irrita n t.
Byrnes— Cavity Preparation O n e of the redeem ing features of the inlay is th a t it does aw ay w ith the need fo r the deep portions of cavities, often m ade necessary by the use of oth er filling m aterials, for the sake of retention. D IS E A S E D O R E X P O S E D P U L P S
L astly, w e come to the tre a tm e n t of diseased or exposed pulps. W h e n a dentist speaks of preventing caries, he usually has in m ind the prevention of ex tern al or ap p arent caries. T o o little atten tio n is given to the caries in the floor of th e cav ity. M o st of the m icro-organism s of the m outh are facultative, and can thrive w ith or w ith o u t the presence of free oxygen. I f it is impossible to rem ove all th e carious dentin w ith o u t exposing the pulp, it is very necessary th a t the rem ain ing dentin be treated in a m a n n er th a t w ill inhibit the progress of f u rth e r caries. T h is is done best by sterilizing the re m aining dentin and at the same tim e placing some agent in the cavity w hich w ill allay the irritatio n and soothe the pulp. W h ile it is tru e th a t in m ost cases w here caries extends to the pulp th e re m oval of th a t organ is necessitated, there is a possibility of preserving the pulp in some instances, particularly in the teeth of young individuals. Even the sm all per centage of cases w hich w ould respond to p ulp trea tm e n t should w a rra n t ou r ef forts along the line of pulp preservation. W h a t trea tm e n t should be given the pulp w hen the rem oval of all caries is not possible w ith o u t exposing o r endan gering it? V arious m ethods have been successfully used by dentists in the past, a few of w hich I shall outline. Silver n itra te m ay be used extensively in the trea tm e n t of rem aining carious d entin. W h e n applied to the dentin, it form s a h ard coagulum w hich resists caries. C are and precaution should be exercised in its use, and a ru b b er dam
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should be placed over the to o th w herever it is possible to do so. T h e silver n itra te is placed on the carious d en tin w ith a pledget of cotton. I t m ay be precipitated w ith oil of cloves, and should n o t be placed by itself in very deep cavities. O v er this may be placed a eugenol-cem ent base; th a t is, a th in m ix of “ silver B ” cem ent, w ith eugenol as th e liquid instead of the reg u lar liquid furnished by the m a n u factu rer. O v e r this pulp-capping, the reg u lar cem ent base m ay be placed. T h e tooth should be left alone fo r a w eek or more, fo r purposes of observation. If, at the end of th a t tim e, it gives no fu rth e r symptoms of p ulp irritatio n , a regular, perm anent filling m ay th en be placed. Some dentists have found th e use of black copper cem ent effective in the tre a t m ent of pulps. T h e black oxid of copper content in this cem ent is about 90 per cent. Copper salts are know n to have an inhibitory effect on caries. T h e principal objection to this k ind of cement is the discoloration to th e tooth w hich follow s its use. T h e re are also various proprie ta ry preparations on the m ark et, some of w hich possess decided virtues. P erhaps the to o th m ost com m only the seat of caries and p ulp tro u b le is the first perm anent m olar. E a rly caries in this tooth is a serious m a tte r, for, if the pulp is involved, the d en tist is confronted w ith the question as to w h eth e r to attem p t to save the pulp or to remove it. I t is prac tically impossible to place a good root canal filling in this tooth before the ninth year, a t w hich tim e the apex has usually attained its final form . O n the other hand, the chance of saving the pulp through tre a tm e n t is com paratively sm all. T h e dentist m ust take m any things into consideration before he m akes his final decision. T h e ideal th in g is to obviate the necessity fo r such a situation arising. A s I m entioned earlier in this paper, it is
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m uch b etter to fill undecayed pits and fissures in these teeth than to pursue the policy of w atc h fu l w aiting. T h e re are various ways th a t these undecayed pits an d fissures m ay be treated. A side from actual cavity preparation involving these pits and fissures (w hich w ould seem m ore lo g ical), a m ethod w hich has found favor w ith some is as fo llo w s: 1. Rem ove debris w ith a stiff brush and a needle-pointed explorer. 2. D ry out w ith alcohol. 3. A p ply silver n itra te for three m inutes. 4. P recip itate w ith solution of form aldehyd, U .S .P ., if quick precipitation is desired. 5. W ip e out w ith a pledget of cotton. 6 . A pply good cement. (P la ce the cem ent a t the m arginal ridges of the tooth, and w o rk it dow n into the pits and fissures w ith an explorer.) 7. W ith fingers coated
w ith cocoa b u tte r, apply pressure to the cem ent. D u rin g the en tire procedure, the tooth should, of course, be kept perfectly dry w ith a ru b b er dam . I t is m y observation th a t dentists in the past have given entirely too little a tte n tion to th e trea tm e n t and conservation of the pulp. T h e pulp of a tooth is w o rth saving, and, in cavity preparation, as w ell as in the specific trea tm e n t of the pulp, its value as a v ita l tissue should be real ized by th e dentist. I have endeavored here to stress a few principles w hich, w hen applied either directly, as in the case of pulp treatm en t, or indirectly, as in the case of cavity preparation, w ill result in a fu rth e r conservation of the pulp. 106 F o rrest A venue, N. E.
TH E WRITINGS A N D ACTIVITIES OF DR. ALFRED OWRE IN RELATION TO THE STATUS OF DENTISTRY: A CRITICAL ANALYSIS By BISSELL B. PALMER, D.D.S., F.A.C.D., N ew York City H E very foundations of the A m eri can republic w ere b u ilt upon to ler ance and the rig h t of the individual to form , hold and express his opinions on any and all subjects. T h a t privilege is recognized today. T h e re is a m arked distinction, however, betw een to leration of an opinion and toleration of an effort to enforce th a t opinion and bring about an undesired end. F o r example, one could tolerate the view th a t'th e U n ited S tates should again become a colony of G re a t B ritain, b u t one could n o t justly be term ed into leran t if he believed such a step to be undesirable and opposed
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every effort to b rin g about such a con dition. T h e foregoing statem en t of principle is presented as prelim inary to this an a lytic study of the w ritin g s and activities of D r. A lfre d O w re in relatio n to the status of dentistry, so th a t the reader m ay un d erstan d th a t there is no question about the rig h t of D r. O w re the indi vidual to form and express any opinion. I t is believed, how ever, th a t the opinions of D r. O w re, expressed officially as dean of the School of D e n ta l and O ra l S u r gery of Colum bia U niversity, and any ef forts to enforce those opinions on ap