- Email: [email protected]
Fixed and Semifixed Bridges*
FIXED AND SEMIFIXED BRIDGES By STANLEY D . TY LM A N , B.S., D.D .S., Chicago, Illinois D IS C U S S I O N o f the p artial d en tu re (fix ed and rem ovable) problem usually finds the discus sers an d the audience divided, each claim in g superiority f o r his choice. O n e group w ill uphold the fixed resto ration ; the other, the rem ovable in one fo rm or an other. Interspersed w ill be fo u n d m any w ho are n o t bound to the one or the o th e r; they fo llo w the golden m ean, using either type w here indicated. In this problem , there should be a m eans o f guidance fo r the dentist to arriv e at a judicious selection o f the type o f restoration to be used in a given case. I t is n o t o f such im portance w h eth er it be a fixed or a rem ovable bridge, b u t it is o f vital im portance w h eth er the appliance placed in the p atien t’s m outh w ill, in addition to re storing lost teeth , help to restore and m ain tain h ealth an d fu n ctio n . I t is not so m uch a question w h eth e r w e use an inlay or crow n f o r the fixed bridge attach m en t, or a clasp or other fric tio n a l attach m en ts fo r th e rem ovable resto ra tion, as it is a question o f restoring n o rm al fu n ctio n and correct stru ctu ra l fo rm . T h e problem s o f the fixed group are the problem s o f the rem ovable group. E ach m ust restore m issing te eth ; each m ust place an appliance th a t w ill be
A
* R ead b e fo re th e M id w in te r C lin ic o f the C h ica g o D e n ta l Society, J a n . 27, 1926. J o u r . A .D .A ., F eb ru a ry , 1927
sanitary, efficient and esthetic. A n u n biased survey w ill reveal th a t unless c a re fu l ju d g m e n t is exercised in the selection o f type and an o rdinary am o u n t o f skill is em ployed in the con struction o f the appliance, n eith er the fixed n o r the rem ovable d en tu re w ill be able to w ith stan d co n tin u ed use and strains. T h e task th a t c o n fro n ts us is n o t only to restore lost m asticating efficiency; m ore is involved: the appli ance should be p a rt o f a therapeutic rem edy th a t w ill aid the p atien t in his fig h t against f u rth e r loss o f teeth , an d , i f possible, p ro tect the edentulous areas against undue d egeneration. T o say th a t these results can be se cured by one or an o th er type o f prosthe sis only is presum ing a g reat deal. Such claim s have been and are now being m ade by certain operators, w h o ' disregard the fa c t th a t, u n d er certain conditions, the fixed and the sem i-fixed bridge w ill f u lfil the desired req u ire m ents. I t is tru e th at, in the past, there have been, and there m ay be no w , g la r ing failu re s o f the fixed resto ratio n , but le t us stop and consider the causes of these failu res. W h a t do w e find? A disregard o f the basic law s o f biology, physics and m echanics. Y o u w ill g ran t th a t a sim ilar lack o f application o f these principles w ill resu lt likew ise in the fa ilu re o f the rem ovable type o f appliance. I f u n d erly in g principles
307
308
The Journal of the American Dental Association
are grasped and m astered, m ethods need n o t h in d e r, b u t w ill ra th e r assist, us. P rio r to u n d erta k in g reconstructive w o rk o f any type in the m o u th , there are three facto rs w hich m ust activate o u r final decision; nam ely, the vital, the physical an d the m echanical. Since no stru ctu re is stro n g er th an its fo u n d a tion, this phase should receive, m ore a t tention th an has been o rd in arily allo tted to it. W e cannot fa il to appreciate the f a c t th a t the h u m an body, in its entirety, is th e real fo u n d atio n o f any m edical or d ental effort a t reconstruction, and unless w e evaluate it as such, our efforts w ill f a il; f o r it is possible to have stru c tu ra l fo rm w ith o u t n o rm a l fu n c tion. F o r this reason, w here it is deem ed necessary, a thorough physical exam ination o f the p atien t should n o t be o m itted ; f o r fre q u en tly our diagnosis fa ils to take into consideration the etiology o f the present im p airm en t o f th e m outh. Im p o rta n t as it is to know h o w to restore m issing teeth, it is o f g re a te r im portance to un d erstan d w h y they w ere lost so th a t w e m ay rem ove th e causes and prev en t additional losses. H a v in g ascertained the condition o f th e body, w e are prepared to proceed w ith o u t en d an g erin g the body w ith added strain. N o t all patients are fav o rab le subjects f o r p artial restora tions, either fixed or rem ovable, and it is w ith these th a t w e m ust exercise the utm ost care. O u r u ltim ate success or fa ilu re de pends also on how thoroughly and how accurately w e have diagnosed the m o u th condition, w hich is the im m e diate fo u n d atio n o f any appliance. T h e r e are certain guides to fo llo w and p itfa lls to avoid, in o rd er to arriv e at a co rrect diagnosis. A n exhaustive o cu lar, digital an d radiographic survey
o f the teeth , p arad en tal tissues and the ed entulous areas should be m ade, to g eth er w ith fu ll-m o u th study m odels. U sin g these diagnostic aids, w h at should be our objectives? D o we m erely observe w hich teeth have defi n ite g ran u lo m as, pockets o r cysts, to enable us to convince the p atien t th at certain teeth o u g h t to be rem oved and a certain type o f restoration inserted? I f this is the prim e reason f o r our ex am in atio n , then w e are losing 90 per ce n t o f the f u ll diagnostic potentialities. I f our vision carries beyond this point, an d our purpose is u ltim ate ra th e r than im m ediate, w e can then proceed to es tablish the tonicity o f the supporting an d investing tissues. W e should d eter m ine, as accurately as possible, the pres ence o f pathologic lesions, acute or chronic, and w h eth e r they have chan g ed the n o rm al fu n ctio n s o f the tooth w ith its p arad en tal tissues; also, to w h a t degree these lesions have altered th e ir stru ctu ra l fo rm . H a v in g established these facts, the n e x t step is to determ in e w hich teeth can sa fe ly be retained as abutm ents and w hich not. A vital tooth w hose su r ro u n d in g tissues are stru c tu ra lly and fu n c tio n a lly n o rm a l is the ideal ab u t m e n t or pier. H av in g this ideal b efo re us, w e are m ore read ily able to decide w hich teeth are to be retain ed and w hich rem oved. A t this tim e, le t us test the tooth fo r lu x atio n , d eterm in in g w h eth e r the excessive m obility is due to a th in or a m issing buccal alveolar plate, or w h eth e r it is due to trau m atic occlusion. I f the fo rm e r, use o f the tooth as an ab u tm en t is co n train d icated ; i f the la tte r, the trau m a m ay be recti fied. T h e teeth should also be exam ined w ith referen c e to th eir physical m akeup.
Tylman— Fixed and Semifixed Bridges W e very fre q u en tly find a tooth, the co ron al p ortion o f w hich is en tirely o u t o f proportion to the len g th o f the root an d its attach m en t. W e re w e to use a tooth w ith a lo n g cro w n an d a short root, our restoration w ould be doom ed to fa ilu re in a short tim e, ow in g to the resu ltan t excessive leverage. Y et the m ere fa c t th a t the tooth has a lo n g root does n o t suffice; it m ust have a healthy an d adequate periodontal a ttac h m e n t to the alveolus; otherw ise, its use as an ab u tm en t is contraindicated. T h e po sition o f the tooth in the arch and its relatio n to the teeth o f the other arch m u st likew ise be considered a t this tim e. E lo n g a tio n , m arked convergence, di vergence or other m alposition o f the teeth m ay necessitate th eir rem oval, or at least ch an g in g the prescribed denture fro m a fixed to a rem ovable. A n o th er im p o rta n t consideration is the n u m b er an d distribution o f ab u t m ents in th e arch. T h e pontics should n o t g reatly o utnum ber the abutm ents w hen a fixed restoration is contem plated. T h e distribution o f the ab u t m ents m ust be fav o rab le both in relation to other teeth, and in relation to the abu tm en ts o f the opposite arch. W h e n w e find th a t the axis direction o f the abutm ents is n o t reasonably n ea r to be ing p ara llel, the fixed restoration is subordinate to the rem ovable. Subsequently, the study m odels and the teeth are exam ined f o r im properly placed fillings, crow ns an d fixed res torations. A ll th a t do n o t m eet the requirem ents o f hygiene, occlusion and co n to u r should be rem oved w ith o u t hesitation. A n o th er question th a t has co n fro n te d the d en tal profession f o r some tim e is th a t o f stress. W e are told th a t m ore teeth have been lost thro u g h overload
309
than thro u g h any o th er cause. Y o u and I have accepted as fa c t th e statem en t th a t the ab u tm en t teeth carry the cu m u lative poundage o f the en tire bridge. T o illu stra te : in a fo u r-to o th bridge resto rin g tw o bicuspids, it has been stated th a t the cuspid an d the m o lar abutm ents, in addition to th e ir ow n load, carried the added 2 0 0 pounds o f the tw o bicuspids, m ak in g a to ta l load o f approxim ately 4 0 0 pounds. L e t us v e rify this to see w h eth e r w e have n o t been condem nin g overload instead o f leverage. T h e re are th ree possible directions in w hich a tooth m ay m ove; v ertically, or into the socket; b u ccolingually, and m esiodistally. Since N a tu re n o rm ally has provided co n tact points betw een the teeth an terio r to the th ird m olars, it can be presum ed th a t this m esiodistal m ovem ent is negligible. T h e buccolin g u a l m ovem ent m ay become p ro nounced w hen the n o rm al articu latio n and occlusion have been disturbed, w ith a resu ltan t trau m atic incoordination o f occlusal surfaces. T h e v ertical d irec tion, then, is the one to be m ost affected by the supposed overload. M o st o f us have tried to crack a n u t betw een ou r teeth. Som etim es w e w ere successful, but o fte n e r w e w ere com pelled to stop b efo re atta in in g o u r end. D id w e stop because w e w ere unable to bite w ith sufficient force? H a d the muscles o f m astication reached th eir m axim um pow er? O r w as it because w e f e lt a slig h t pain in the periodontal m em brane? I f N a tu re had n o t been so farsig h ted in h e r plan an d had she placed the roots in rig id co n tact w ith the ja w bone instead o f interposing a resilient, sensitive p erio d o n tal m em brane, m any teeth w o u ld be irreparably and prem atu rely dam aged. A s it is.
310
The Journal of the American Dental Association
teeth w ill endure only as m uch fo rce as the periodontal m em brane can com fo rta b ly bear. W h e n this is exceeded, w e are fo rced to stop because o f the pain experienced. A tooth w ill n o t en d ure co m fo rta b ly pressure g rea ter than th a t f o r w hich it was suited, although its pow er o f endurance w ill be increased g rad u a lly w ith the continuance o f the increased load. . C onsequently, w hen a fo u r-to o th bridge is placed, extending fro m a cuspid to the first m o la r, w e are able, a t the tim e, to exert only such force on the bridge as the abut m en t can co m fo rtab ly bear by itself. Of several hun d red bridge cases th a t have been c a re fu lly recorded and observed, in n o t one instance has the patient been able to bite to a g rea ter poundage on the bridge th an could be registered on the corresponding n atu ra l teeth o f the opposite side o f the arch. A s a f u rth e r diagnostic m easure, let us study the occlusion in each case. A ccurate study m odels, m ounted care fu lly on an adjustable a rticu la to r, are indispensable f o r this purpose. T h is w ill also aid us in classifying the m an dibulom axillary relation, as w ell as in disclosing unevenly distributed forces. I f the bite is a close one, w e can decide w heth er a hygienic, fixed appliance can be placed w ith o u t opening the bite. I f n ot, a rem ovable is indicated. L ast, but by no m eans u n im p o rta n t, the vitality o f a ll pulps should be established and the teeth given a thorough prophylactic treatm en t. H av in g m ade the diagnosis, w e are b etter qualified to proceed w ith the de sign and the construction o f the bridge. J u s t as the autom otive m echanic u n d e r stands the m o to r an d its com ponent parts w ith th eir individual fu n ctio n s as related to the fu n ctio n o f the assembled
m o to r, so also should w e un d erstan d the m asticatory apparatus, its elem ents, and th eir stru ctu re an d fu n ctio n s, in d i v idually, collectively an d relatively. A f te r a study o f the fo u n d atio n or body o f w hich the ab u tm en t tooth is a p art, le t us consider the types an d in d i cations o f the various attach m en ts, pontics an d connecters. T h e in te rm e diary connection betw een the ab u tm en t tooth an d the pontic o f a d en tal bridge is called the attach m en t, be it fo r a fixed or fo r a rem ovable appliance. T h e ideal has certain qualities th a t should be em bodied, as f a r as possible, in all our attachm ents. A s tim e does n ot p erm it am plification, they w ill only be enu m erated . F irs t am o n g these in im portance is pulp conservation; sec ond, the least am o u n t o f tooth destruc tion consistent w ith extension fo r p re v e n tio n ; th ird , sufficient m echanical reten tio n to w ith stan d the displacing forces o f continued an d successive stresses; fo u rth , restoration th a t w ill restore the tooth to its n o rm al f o rm ; fifth , sim plicity o f preparation an d con stru ctio n ; sixth, safety , d u rin g prepara tion, to the p arad en tal tissues; seventh, esthetics; eighth, easy fittin g and placing. ' T h e fu n c tio n o f any attac h m e n t is tw o fo ld : reten tiv e an d prophylactic. I t m ust hold the bridge proper to the ab u tm en t teeth , at the same tim e pre v en tin g in ju ry to the tooth and its su r ro u n d in g tissues. Since the types o f abutm ents an d the conditions u n d er w hich they are fo u n d in the m outh vary g reatly , it is necessary to use a t tachm ents to m eet these varied de m ands. In certain cases, w eaker types w ill suffice, w h ile in others the strongest w ill scarcely fu lfil the requirem ents. T h e attach m en ts at o u r disposal are
Tylman— Fixed and Semifixed Bridges o f tw o g eneral kinds, inlays and crow ns. O f the inlay group, the tw o su rface types are considered the w eakest and are used only in places w here there are no dislodging forces an d w here the inlay is to receive a rest or lug. I t is n o t used w hen a soldered jo in t exists betw een it an d the pontic. I n exceptional cases, it m ay be used w ith a soldered connection i f the opposing arch carries an artificial rem ovable den tu re. M oreo v er, w hen the ab u tm en t tooth is extrem ely short, a tw o su rfa ce inlay should n o t be used u n d e r any circum stances. T h e n ex t stro n g er type o f attach m en t is the th ree -su rfac e type. T h ese attach m ents m ay be used w ith soldered joints or connections provided the tooth is o f sufficient len g th occlusogingivally. I t is im p o rta n t to have sufficient su rface contact betw een the gold casting and the tooth stru ctu re to obtain a tensofric tio n a l grip. Should the stress o f occlusion or the span or type o f tooth dem and a stro n g er type, the n ex t choice is the three q u arter crow n. T h is is an ideal preparation an d can be used alm ost universally. I t meets all the requirem ents o f an ideal attach m en t. O u r debt to D r. T in k e r is im m easurable. In its present state o f refin em en t, due to his efforts, w e have an attac h m e n t th a t frees us fro m the constant dread o f pulp involvem ent. Its em ploym ent m akes it unnecessary to encroach on the pulp in o rd er to obtain m echanical retention. The sm all am o u n t o f tooth stru ctu re rem oved makes possible thin castings o f hard gold. W ith this attach m en t, the d an g er o f th e rm al shock is reduced to a m in im u m . T h e beveled m a rg in at the g in g iv al is m ore practical th an a pro nounced shoulder, since it is easier to prepare and involves the rem oval o f
311
less tooth stru ctu re th an w hen a shoulder is cut. T h is type o f attach m e n t is also highly esthetic, since its m argins are n o t m ore ev ident th an the m argins o f a typical mesiodistoclusal inlay. F in a lly , it does n o t require a superdentist n o r a superdegree o f tech nical skill to do this type o f w ork. T h e instru m en tatio n and technic are quite sim ple, b rin g in g it w ith in the scope o f every m an. A t this tim e, the so-called “ slice” preparatio n m ig h t be m entioned. O ccasionally, even the three qu arter a ttac h m e n t is deem ed too w eak. W e are then com pelled to reso rt to the next stro n g er type, the f u ll cro w n . T h is is by f a r the stro n g est a ttac h m e n t th a t w e have, but it should be used only w hen the others f a ll short o f the necessary requirem ents. I t is indicated w h ere the tooth is very sh o rt occlusogingivally or w here the coronal portion o f the tooth is im p e rfe ct in stru ctu re , fo rm or posi tion. T h e teeth m ost com m only em ployed are the second an d th ird m olars and o fte n the lo w er first bicuspids. O u r n ex t consideration is the pontic. T h e construction o f pontics or so called dum m ies has received less ca refu l study and less tim e th an any o th er p art o f the dental bridge. P ontics m ay be constructed o f g old o r porcelain, or gold an d porcelain. T h e fo rm e r tw o have th e ir lim itations, b u t it is the goldporcelain com bination type th a t is m ore g eneral in its application. Since a pontic is the artificial substitute fo r the lost n a tu ra l tooth, it fo llo w s th a t the ideal pontic should sim ulate the n atural tooth as closely as possible. U p to a very recen t period, w e placed bridges the pontics o f w hich consisted o f a porcelain fac in g g ro u n d to fit a scraped cast, then backed, soldered and assem bled in one operation. L ittle or
312
The Journal of the American Dental Association
no atten tio n w as paid to the occlusion, contour, cusp relations, contact points, em brasures o r hygiene. N o w o n d er th a t, in the course o f a year or m ore, these cases w ould re tu rn to us in such a condition as justified some the diatribes launched against A m erican dentistry. W e m ust n o t lose sight o f the fa c t th a t the pontic is the prim e objective o f the bridge. W e have had pioneers in this field w ho spent a g rea t am o u n t o f tim e and effo rt in p ointing out the essentials o f a p erm a n en t, esthetic and hygienic pontic. L e t us consider these essentials, briefly. I n the first place, no porcelain, unless it has been glazed previously, should come in contact w ith the mucosa. U nless reg la ze d , g round porcelain w ill absorb the fluids o f the m outh, w hich fe rm e n tin g act as an irrita n t to the m ucous m em brane. G la z e d porcelain is n o t only im pervious to m oisture, but, being highly g lazed , it presents a sm ooth, n o n irrita tin g su rface to the tis sues w ith no d an g er o f m echanical irri tation. W e w ill find th a t a tip o f porcelain, convex in a ll directions and b rou g h t into close contact w ith o u t pres sure on the tissues, a f te r a fe w years w ill be clean an d the tissues su rro u n d ing it n o rm al. I t m ig h t n o t be am iss to designate some o f the dangers encountered w ith this type o f pontic. G en e ra lly speak ing, there are tw o types em ployed: the root an d the p lain tip. T h e f o rm e r is placed w ith in the alveolar socket, the la tte r in contact w ith the crest o f the ridge a f te r it has healed. A fe w years ago, the possibilities o f the porcelain root created g re a t enthusiasm . W e all tried it, and some o f us w ith o u t c a re fu l study, I am a fra id , placed it in discrim i nately. N o t lo n g a f te r th at, w e en countered trouble. Secondary infections,
recessions an d m o n u m en t-lik e cones stared us in the face. Im m e d iate ly the “ an v il chorus” w as sounded, the p rin ciple w as “ a ll w ro n g .” A s w ith every th in g else, w e soon learn ed th at this type o f pontic had its lim itations. W e set about to find o u t w h a t they w ere an d , am o n g o th er things, fo u n d th a t it w as necessary to have a sound alv eo lar plate o f bone; also th a t ex trem e care in extraction w as essential in o rd er n o t to in ju re the ad jac en t tis sues. M o reo v er, the root could n ot extend into the socket to a g rea ter depth th an o n e-th ird its distance. C are had to be exercised n o t to have the porce lain im pinge against the bone an d to elim in ate its use w here th ere was an extensive’ pathologic condition. A f te r reco g n izin g its lim itations and using it w here indicated, w e realized its f u ll benefits. I n co n stru ctin g a pontic o f the baked tip variety , th ere are several points to be rem em b ered : first, th a t the w idest p a rt o f the pontic, m esiodistally, is th ro u g h the contact points ju st lin g u a l to the fac in g , an d th a t the contact points are in g old an d n o t in the porce lain fac in g s; secondly, th a t the pontic is n arro w e d m esiodistally in its lin g u al h a lf. T h is results in w ide em brasures on the lin g u a l su rface, w ith a resu ltan t reduction o f the occlusal su rfa ce and stress. A ideal pontic tapers fro m the contact points to a g in g iv al end. T h e tip o f the porcelain rests on the center o f the rid g e or a trifle to the buccal side. T h e contour o f the fac in g m ust alw ays h arm o n ize w ith the rem a in in g teeth. A t this tim e, I w ish to stress an o th er phase, the selection an d g rin d in g o f the fac in g . T h e edentulous space should n o t be filled en tirely m esiodistally by
Tylman— Fixed and Semifixed Bridges
the facing. The pontic, mesiodistally, is widest in the gold just lingual to the facings. If the facing is as wide as the distance through the contact points, after soldering, the joint, instead of as suming a circular form, will be much wider buccolingually than the desired form. Should it be impossible to obtain a facing narrow enough, the grinding must be done at the expense of the buccal surface. Similarly, if the gingivoclusal length is to be shortened, it is done at the expense of the buccal and not by increasing the occlusal bevel of the facing. One of the important things over looked in the construction of a pontic is tooth form. How many of us have stopped to note the comparative distance between the buccal and the lingual cusps of a lower first molar and its greatest buccolingual diameter? Those who have will recall that, if the greatest buccolingual diameter measured 12 mm., the distance from the buccal to the lingual cusp point was about 6.5 mm., or nearly one-half. Yet how many bridges are placed on which the distances from cusp to cusp almost equal the greatest buccolingual diameter? Let me emphasize the significance of this arrangement as found in Nature. We are aware of the fact that doubling the diameter of a water pipe increases its capacity four times, while doubling the diameter of a sphere increases its content eight times. The same is true of a sphere. Consequently, an orange with a 4 inch diameter has four times the contents of one 2 inches in diameter. Similarly, doubling one di mension of a square will double the surface area, but doubling both dimen sions increases the square area four times. We can readily draw the anal
313
ogy existing between these measure ments and the importance of proper occlusal cusp relations and occlusal surface areas. Another point to stress is the impor tance of marginal ridges and grooves. Unless the marginal ridges are well formed and properly placed, a lowdegree inflammation in the interproximal tissues will result. Grooves that are regularly found in teeth should be accentuated. Other supplementary ones are placed where they will aid the escape of food. The latter are usually cut through the marginal ridges from the central groove over into the lingual embrasures. The final unit of the fixed bridge to be considered is the connecter or the means of uniting the pontic with the attachment. There are two types: the rigid or the soldered joint, and the flex ible or the rest or lug type. The ques tion is often asked: when is one type indicated and when the other? We are led to believe that the stress-breaker type of rest or lug should be used uni versally except where the span is too long or where the teeth are loose. We cannot lose sight of the fact that there is a certain amount of individual movement in teeth, but not to the degree claimed by some. Even when both attachments are soldered to the pontics, there1is still a certain amount of mobility. To say that fixed bridges produce pathologic changes is not com patible with our clinical and radiographic findings. Although we place a removable restoration where it is indi cated, we must admit that a restoration is efficient in mastication only in pro portion to its stability during function. Hence, all other things being equal, the
314
The Journal of the American Dental Association
fixed appliance gives greater service in masticating food. An appreciation of the vital factors is of far more concern in partial prosthesis than an appreciation of the mechanical. More good bridges are lost because they were placed on poor foundations than because of the type of attachment used. Disregard of tooth form, absence of embrasures and im proper occlusion will overcome any ad vantages of glazed porcelain, accurate castings or methods of retention. 25
E ast W a sh in g to n
St.
DISCUSSION
Albert P. Grunn, Chicago, III.:
T h e r e are m an y types o f re m o va b le b rid g e s, som e sim ple and some co m p licated . W e fin d m en w h o are a b so lu te ly set on one type or a noth er and w h o seem to be sincere in th eir b e lie f that th ey are r ig h t, and w e fin d as m an y w h o a d v o cate the fix e d ty p e o f b rid g e and the e lim in atio n o f n e a rly a ll rem o va b le a p pliances. W h o can say th at a fix e d b rid g e th at has stood the test o f tw e n ty o r m ore »years has been a fa ilu re ? A n d w h o can co n dem n a rem o va b le typ e th at has answ ered e v e ry req u irem en t fr o m the stan d poin t o f m astica to ry efficiency? T h e r e are m a n y p ro b lem s th at c o n fr o n t us in b r id g e w o r k w h ich m ake it d ifficu lt to determ ine the typ e o f b rid g e to be b u ilt; y et i f w e stu d y o u r cases fr o m e v e ry a n g le , as D r . T y lm a n su ggests, ta k in g a d v a n ta g e o f the a id o f the roen tgen r a y , and o b se rv in g the la w s o f physics and m echanics, w e can ach ieve the success w e desire, w ith a th o ro u g h u n d ersta n d in g o f w h a t w e are d o in g , because w e h av e m as tered the u n d e rly in g p rin cip les th at m ake suc cess possible. T h e use o f f u l l m outh study m odels as an a id in d iagn osis is a p oin t w o rth rem em b erin g. In fix e d b rid g e w o rk , certain basic rules are fu n d a m e n ta l to suc
ce ssfu l a p p lica tio n , such as fa v o r a b le co n d i tions, g o o d h ealth , p ro p e r sa n itation , sound m ech an ical p rin cip les, p ro p e r d istrib u tion o f abutm ents fa v o r a b le to stress and stren gth req u ired , and m an y oth er w h ich h ave a l re a d y been m en tion ed. O f the tw o types o f a ttachm en ts, the cast g o ld in la y c e rta in ly has been a r a y o f sunshine to the dentist, m a k in g possible the p la c in g o f b rid ge s on v it a l teeth w h ere f o r m e r ly em p loym en t o f a cro w n and d e v ita liz a tio n w ere im p e rativ e . T h e threeq u arter cro w n ca stin g has com e to stay, and, w hen p r o p e rly fitted , it seems to m eet the g e n e ra l requirem ents f o r an id eal a tta ch m ent. T h e sem ifixed b rid g e , w ith lu g or rest a t one end, has p ro v e d sa tisfa c to ry in most cases. In la y b rid ges, cem ented a t both ends, h av e p ro v e d u n satisfacto ry, excep t w hen the c a v ity p rep aration w as deep en ou gh to resist la te r a l m ovem en t o f the teeth. I w as g la d to h ear D r . T y lm a n speak so fa v o r a b ly o f the th ree-q u arter cro w n ca stin g as an a t tach m en t f o r b rid g e w o rk . M a n y m en are d o in g b e a u tifu l w o r k in this lin e. W h en a f u l l cro w n is in d icated , either a cast ja c k e t o r, i f a sh ell is used, a band o f 34 g a g e pure g o ld is c a r e fu lly fitted , the top split and bent d o w n on top o f the ro o t, and an im pression taken , a rticu late d , w a x e d and cast. T h is m akes a w e ll- fittin g cro w n and can be ca rv e d and con tou red in the w a x to re p rodu ce n a tu ra l tooth fo r m . T h is type o f c ro w n , w ith p ro p e r root p rep ara tio n , is p r e f erable to the h eav ier 2 2-carat g o ld band o f the o ld type sh ell c ro w n , because o f the sn u g -fittin g p u re g o ld band. T h e p o in t o f c a r v in g to reprodu ce tooth fo r m is im p o r tan t, also the g la z in g o f a ll p o rcelain co m in g in co n tact w ith the m ucosa. T h e use o f a re m o va b le o r a rep laceab le type o f p orcelain fa c in g s m akes it possible f o r e v e ry dentist to f o l l o w ou t this p roced u re. A polished p orcelain tip w ill n o t close the pores, as w e m ig h t be led to b elieve. I am g la d th a t D r . T y lm a n tou ched on the p orcelain ro o t, w h ich caused tro u b le f o r m an y u n til th ey learn ed to bake it sh orter. O v e rlo a d in g o f ab u t m ents w as an oth er p o in t w e ll covered.
A
* R ead b e fo re th e M id w in te r C lin ic o f the C h ica g o D e n ta l Society, J a n . 27, 1926. J o u r . A .D .A ., F eb ru a ry , 1927
sanitary, efficient and esthetic. A n u n biased survey w ill reveal th a t unless c a re fu l ju d g m e n t is exercised in the selection o f type and an o rdinary am o u n t o f skill is em ployed in the con struction o f the appliance, n eith er the fixed n o r the rem ovable d en tu re w ill be able to w ith stan d co n tin u ed use and strains. T h e task th a t c o n fro n ts us is n o t only to restore lost m asticating efficiency; m ore is involved: the appli ance should be p a rt o f a therapeutic rem edy th a t w ill aid the p atien t in his fig h t against f u rth e r loss o f teeth , an d , i f possible, p ro tect the edentulous areas against undue d egeneration. T o say th a t these results can be se cured by one or an o th er type o f prosthe sis only is presum ing a g reat deal. Such claim s have been and are now being m ade by certain operators, w h o ' disregard the fa c t th a t, u n d er certain conditions, the fixed and the sem i-fixed bridge w ill f u lfil the desired req u ire m ents. I t is tru e th at, in the past, there have been, and there m ay be no w , g la r ing failu re s o f the fixed resto ratio n , but le t us stop and consider the causes of these failu res. W h a t do w e find? A disregard o f the basic law s o f biology, physics and m echanics. Y o u w ill g ran t th a t a sim ilar lack o f application o f these principles w ill resu lt likew ise in the fa ilu re o f the rem ovable type o f appliance. I f u n d erly in g principles
307
308
The Journal of the American Dental Association
are grasped and m astered, m ethods need n o t h in d e r, b u t w ill ra th e r assist, us. P rio r to u n d erta k in g reconstructive w o rk o f any type in the m o u th , there are three facto rs w hich m ust activate o u r final decision; nam ely, the vital, the physical an d the m echanical. Since no stru ctu re is stro n g er th an its fo u n d a tion, this phase should receive, m ore a t tention th an has been o rd in arily allo tted to it. W e cannot fa il to appreciate the f a c t th a t the h u m an body, in its entirety, is th e real fo u n d atio n o f any m edical or d ental effort a t reconstruction, and unless w e evaluate it as such, our efforts w ill f a il; f o r it is possible to have stru c tu ra l fo rm w ith o u t n o rm a l fu n c tion. F o r this reason, w here it is deem ed necessary, a thorough physical exam ination o f the p atien t should n o t be o m itted ; f o r fre q u en tly our diagnosis fa ils to take into consideration the etiology o f the present im p airm en t o f th e m outh. Im p o rta n t as it is to know h o w to restore m issing teeth, it is o f g re a te r im portance to un d erstan d w h y they w ere lost so th a t w e m ay rem ove th e causes and prev en t additional losses. H a v in g ascertained the condition o f th e body, w e are prepared to proceed w ith o u t en d an g erin g the body w ith added strain. N o t all patients are fav o rab le subjects f o r p artial restora tions, either fixed or rem ovable, and it is w ith these th a t w e m ust exercise the utm ost care. O u r u ltim ate success or fa ilu re de pends also on how thoroughly and how accurately w e have diagnosed the m o u th condition, w hich is the im m e diate fo u n d atio n o f any appliance. T h e r e are certain guides to fo llo w and p itfa lls to avoid, in o rd er to arriv e at a co rrect diagnosis. A n exhaustive o cu lar, digital an d radiographic survey
o f the teeth , p arad en tal tissues and the ed entulous areas should be m ade, to g eth er w ith fu ll-m o u th study m odels. U sin g these diagnostic aids, w h at should be our objectives? D o we m erely observe w hich teeth have defi n ite g ran u lo m as, pockets o r cysts, to enable us to convince the p atien t th at certain teeth o u g h t to be rem oved and a certain type o f restoration inserted? I f this is the prim e reason f o r our ex am in atio n , then w e are losing 90 per ce n t o f the f u ll diagnostic potentialities. I f our vision carries beyond this point, an d our purpose is u ltim ate ra th e r than im m ediate, w e can then proceed to es tablish the tonicity o f the supporting an d investing tissues. W e should d eter m ine, as accurately as possible, the pres ence o f pathologic lesions, acute or chronic, and w h eth e r they have chan g ed the n o rm al fu n ctio n s o f the tooth w ith its p arad en tal tissues; also, to w h a t degree these lesions have altered th e ir stru ctu ra l fo rm . H a v in g established these facts, the n e x t step is to determ in e w hich teeth can sa fe ly be retained as abutm ents and w hich not. A vital tooth w hose su r ro u n d in g tissues are stru c tu ra lly and fu n c tio n a lly n o rm a l is the ideal ab u t m e n t or pier. H av in g this ideal b efo re us, w e are m ore read ily able to decide w hich teeth are to be retain ed and w hich rem oved. A t this tim e, le t us test the tooth fo r lu x atio n , d eterm in in g w h eth e r the excessive m obility is due to a th in or a m issing buccal alveolar plate, or w h eth e r it is due to trau m atic occlusion. I f the fo rm e r, use o f the tooth as an ab u tm en t is co n train d icated ; i f the la tte r, the trau m a m ay be recti fied. T h e teeth should also be exam ined w ith referen c e to th eir physical m akeup.
Tylman— Fixed and Semifixed Bridges W e very fre q u en tly find a tooth, the co ron al p ortion o f w hich is en tirely o u t o f proportion to the len g th o f the root an d its attach m en t. W e re w e to use a tooth w ith a lo n g cro w n an d a short root, our restoration w ould be doom ed to fa ilu re in a short tim e, ow in g to the resu ltan t excessive leverage. Y et the m ere fa c t th a t the tooth has a lo n g root does n o t suffice; it m ust have a healthy an d adequate periodontal a ttac h m e n t to the alveolus; otherw ise, its use as an ab u tm en t is contraindicated. T h e po sition o f the tooth in the arch and its relatio n to the teeth o f the other arch m u st likew ise be considered a t this tim e. E lo n g a tio n , m arked convergence, di vergence or other m alposition o f the teeth m ay necessitate th eir rem oval, or at least ch an g in g the prescribed denture fro m a fixed to a rem ovable. A n o th er im p o rta n t consideration is the n u m b er an d distribution o f ab u t m ents in th e arch. T h e pontics should n o t g reatly o utnum ber the abutm ents w hen a fixed restoration is contem plated. T h e distribution o f the ab u t m ents m ust be fav o rab le both in relation to other teeth, and in relation to the abu tm en ts o f the opposite arch. W h e n w e find th a t the axis direction o f the abutm ents is n o t reasonably n ea r to be ing p ara llel, the fixed restoration is subordinate to the rem ovable. Subsequently, the study m odels and the teeth are exam ined f o r im properly placed fillings, crow ns an d fixed res torations. A ll th a t do n o t m eet the requirem ents o f hygiene, occlusion and co n to u r should be rem oved w ith o u t hesitation. A n o th er question th a t has co n fro n te d the d en tal profession f o r some tim e is th a t o f stress. W e are told th a t m ore teeth have been lost thro u g h overload
309
than thro u g h any o th er cause. Y o u and I have accepted as fa c t th e statem en t th a t the ab u tm en t teeth carry the cu m u lative poundage o f the en tire bridge. T o illu stra te : in a fo u r-to o th bridge resto rin g tw o bicuspids, it has been stated th a t the cuspid an d the m o lar abutm ents, in addition to th e ir ow n load, carried the added 2 0 0 pounds o f the tw o bicuspids, m ak in g a to ta l load o f approxim ately 4 0 0 pounds. L e t us v e rify this to see w h eth e r w e have n o t been condem nin g overload instead o f leverage. T h e re are th ree possible directions in w hich a tooth m ay m ove; v ertically, or into the socket; b u ccolingually, and m esiodistally. Since N a tu re n o rm ally has provided co n tact points betw een the teeth an terio r to the th ird m olars, it can be presum ed th a t this m esiodistal m ovem ent is negligible. T h e buccolin g u a l m ovem ent m ay become p ro nounced w hen the n o rm al articu latio n and occlusion have been disturbed, w ith a resu ltan t trau m atic incoordination o f occlusal surfaces. T h e v ertical d irec tion, then, is the one to be m ost affected by the supposed overload. M o st o f us have tried to crack a n u t betw een ou r teeth. Som etim es w e w ere successful, but o fte n e r w e w ere com pelled to stop b efo re atta in in g o u r end. D id w e stop because w e w ere unable to bite w ith sufficient force? H a d the muscles o f m astication reached th eir m axim um pow er? O r w as it because w e f e lt a slig h t pain in the periodontal m em brane? I f N a tu re had n o t been so farsig h ted in h e r plan an d had she placed the roots in rig id co n tact w ith the ja w bone instead o f interposing a resilient, sensitive p erio d o n tal m em brane, m any teeth w o u ld be irreparably and prem atu rely dam aged. A s it is.
310
The Journal of the American Dental Association
teeth w ill endure only as m uch fo rce as the periodontal m em brane can com fo rta b ly bear. W h e n this is exceeded, w e are fo rced to stop because o f the pain experienced. A tooth w ill n o t en d ure co m fo rta b ly pressure g rea ter than th a t f o r w hich it was suited, although its pow er o f endurance w ill be increased g rad u a lly w ith the continuance o f the increased load. . C onsequently, w hen a fo u r-to o th bridge is placed, extending fro m a cuspid to the first m o la r, w e are able, a t the tim e, to exert only such force on the bridge as the abut m en t can co m fo rtab ly bear by itself. Of several hun d red bridge cases th a t have been c a re fu lly recorded and observed, in n o t one instance has the patient been able to bite to a g rea ter poundage on the bridge th an could be registered on the corresponding n atu ra l teeth o f the opposite side o f the arch. A s a f u rth e r diagnostic m easure, let us study the occlusion in each case. A ccurate study m odels, m ounted care fu lly on an adjustable a rticu la to r, are indispensable f o r this purpose. T h is w ill also aid us in classifying the m an dibulom axillary relation, as w ell as in disclosing unevenly distributed forces. I f the bite is a close one, w e can decide w heth er a hygienic, fixed appliance can be placed w ith o u t opening the bite. I f n ot, a rem ovable is indicated. L ast, but by no m eans u n im p o rta n t, the vitality o f a ll pulps should be established and the teeth given a thorough prophylactic treatm en t. H av in g m ade the diagnosis, w e are b etter qualified to proceed w ith the de sign and the construction o f the bridge. J u s t as the autom otive m echanic u n d e r stands the m o to r an d its com ponent parts w ith th eir individual fu n ctio n s as related to the fu n ctio n o f the assembled
m o to r, so also should w e un d erstan d the m asticatory apparatus, its elem ents, and th eir stru ctu re an d fu n ctio n s, in d i v idually, collectively an d relatively. A f te r a study o f the fo u n d atio n or body o f w hich the ab u tm en t tooth is a p art, le t us consider the types an d in d i cations o f the various attach m en ts, pontics an d connecters. T h e in te rm e diary connection betw een the ab u tm en t tooth an d the pontic o f a d en tal bridge is called the attach m en t, be it fo r a fixed or fo r a rem ovable appliance. T h e ideal has certain qualities th a t should be em bodied, as f a r as possible, in all our attachm ents. A s tim e does n ot p erm it am plification, they w ill only be enu m erated . F irs t am o n g these in im portance is pulp conservation; sec ond, the least am o u n t o f tooth destruc tion consistent w ith extension fo r p re v e n tio n ; th ird , sufficient m echanical reten tio n to w ith stan d the displacing forces o f continued an d successive stresses; fo u rth , restoration th a t w ill restore the tooth to its n o rm al f o rm ; fifth , sim plicity o f preparation an d con stru ctio n ; sixth, safety , d u rin g prepara tion, to the p arad en tal tissues; seventh, esthetics; eighth, easy fittin g and placing. ' T h e fu n c tio n o f any attac h m e n t is tw o fo ld : reten tiv e an d prophylactic. I t m ust hold the bridge proper to the ab u tm en t teeth , at the same tim e pre v en tin g in ju ry to the tooth and its su r ro u n d in g tissues. Since the types o f abutm ents an d the conditions u n d er w hich they are fo u n d in the m outh vary g reatly , it is necessary to use a t tachm ents to m eet these varied de m ands. In certain cases, w eaker types w ill suffice, w h ile in others the strongest w ill scarcely fu lfil the requirem ents. T h e attach m en ts at o u r disposal are
Tylman— Fixed and Semifixed Bridges o f tw o g eneral kinds, inlays and crow ns. O f the inlay group, the tw o su rface types are considered the w eakest and are used only in places w here there are no dislodging forces an d w here the inlay is to receive a rest or lug. I t is n o t used w hen a soldered jo in t exists betw een it an d the pontic. I n exceptional cases, it m ay be used w ith a soldered connection i f the opposing arch carries an artificial rem ovable den tu re. M oreo v er, w hen the ab u tm en t tooth is extrem ely short, a tw o su rfa ce inlay should n o t be used u n d e r any circum stances. T h e n ex t stro n g er type o f attach m en t is the th ree -su rfac e type. T h ese attach m ents m ay be used w ith soldered joints or connections provided the tooth is o f sufficient len g th occlusogingivally. I t is im p o rta n t to have sufficient su rface contact betw een the gold casting and the tooth stru ctu re to obtain a tensofric tio n a l grip. Should the stress o f occlusion or the span or type o f tooth dem and a stro n g er type, the n ex t choice is the three q u arter crow n. T h is is an ideal preparation an d can be used alm ost universally. I t meets all the requirem ents o f an ideal attach m en t. O u r debt to D r. T in k e r is im m easurable. In its present state o f refin em en t, due to his efforts, w e have an attac h m e n t th a t frees us fro m the constant dread o f pulp involvem ent. Its em ploym ent m akes it unnecessary to encroach on the pulp in o rd er to obtain m echanical retention. The sm all am o u n t o f tooth stru ctu re rem oved makes possible thin castings o f hard gold. W ith this attach m en t, the d an g er o f th e rm al shock is reduced to a m in im u m . T h e beveled m a rg in at the g in g iv al is m ore practical th an a pro nounced shoulder, since it is easier to prepare and involves the rem oval o f
311
less tooth stru ctu re th an w hen a shoulder is cut. T h is type o f attach m e n t is also highly esthetic, since its m argins are n o t m ore ev ident th an the m argins o f a typical mesiodistoclusal inlay. F in a lly , it does n o t require a superdentist n o r a superdegree o f tech nical skill to do this type o f w ork. T h e instru m en tatio n and technic are quite sim ple, b rin g in g it w ith in the scope o f every m an. A t this tim e, the so-called “ slice” preparatio n m ig h t be m entioned. O ccasionally, even the three qu arter a ttac h m e n t is deem ed too w eak. W e are then com pelled to reso rt to the next stro n g er type, the f u ll cro w n . T h is is by f a r the stro n g est a ttac h m e n t th a t w e have, but it should be used only w hen the others f a ll short o f the necessary requirem ents. I t is indicated w h ere the tooth is very sh o rt occlusogingivally or w here the coronal portion o f the tooth is im p e rfe ct in stru ctu re , fo rm or posi tion. T h e teeth m ost com m only em ployed are the second an d th ird m olars and o fte n the lo w er first bicuspids. O u r n ex t consideration is the pontic. T h e construction o f pontics or so called dum m ies has received less ca refu l study and less tim e th an any o th er p art o f the dental bridge. P ontics m ay be constructed o f g old o r porcelain, or gold an d porcelain. T h e fo rm e r tw o have th e ir lim itations, b u t it is the goldporcelain com bination type th a t is m ore g eneral in its application. Since a pontic is the artificial substitute fo r the lost n a tu ra l tooth, it fo llo w s th a t the ideal pontic should sim ulate the n atural tooth as closely as possible. U p to a very recen t period, w e placed bridges the pontics o f w hich consisted o f a porcelain fac in g g ro u n d to fit a scraped cast, then backed, soldered and assem bled in one operation. L ittle or
312
The Journal of the American Dental Association
no atten tio n w as paid to the occlusion, contour, cusp relations, contact points, em brasures o r hygiene. N o w o n d er th a t, in the course o f a year or m ore, these cases w ould re tu rn to us in such a condition as justified some the diatribes launched against A m erican dentistry. W e m ust n o t lose sight o f the fa c t th a t the pontic is the prim e objective o f the bridge. W e have had pioneers in this field w ho spent a g rea t am o u n t o f tim e and effo rt in p ointing out the essentials o f a p erm a n en t, esthetic and hygienic pontic. L e t us consider these essentials, briefly. I n the first place, no porcelain, unless it has been glazed previously, should come in contact w ith the mucosa. U nless reg la ze d , g round porcelain w ill absorb the fluids o f the m outh, w hich fe rm e n tin g act as an irrita n t to the m ucous m em brane. G la z e d porcelain is n o t only im pervious to m oisture, but, being highly g lazed , it presents a sm ooth, n o n irrita tin g su rface to the tis sues w ith no d an g er o f m echanical irri tation. W e w ill find th a t a tip o f porcelain, convex in a ll directions and b rou g h t into close contact w ith o u t pres sure on the tissues, a f te r a fe w years w ill be clean an d the tissues su rro u n d ing it n o rm al. I t m ig h t n o t be am iss to designate some o f the dangers encountered w ith this type o f pontic. G en e ra lly speak ing, there are tw o types em ployed: the root an d the p lain tip. T h e f o rm e r is placed w ith in the alveolar socket, the la tte r in contact w ith the crest o f the ridge a f te r it has healed. A fe w years ago, the possibilities o f the porcelain root created g re a t enthusiasm . W e all tried it, and some o f us w ith o u t c a re fu l study, I am a fra id , placed it in discrim i nately. N o t lo n g a f te r th at, w e en countered trouble. Secondary infections,
recessions an d m o n u m en t-lik e cones stared us in the face. Im m e d iate ly the “ an v il chorus” w as sounded, the p rin ciple w as “ a ll w ro n g .” A s w ith every th in g else, w e soon learn ed th at this type o f pontic had its lim itations. W e set about to find o u t w h a t they w ere an d , am o n g o th er things, fo u n d th a t it w as necessary to have a sound alv eo lar plate o f bone; also th a t ex trem e care in extraction w as essential in o rd er n o t to in ju re the ad jac en t tis sues. M o reo v er, the root could n ot extend into the socket to a g rea ter depth th an o n e-th ird its distance. C are had to be exercised n o t to have the porce lain im pinge against the bone an d to elim in ate its use w here th ere was an extensive’ pathologic condition. A f te r reco g n izin g its lim itations and using it w here indicated, w e realized its f u ll benefits. I n co n stru ctin g a pontic o f the baked tip variety , th ere are several points to be rem em b ered : first, th a t the w idest p a rt o f the pontic, m esiodistally, is th ro u g h the contact points ju st lin g u a l to the fac in g , an d th a t the contact points are in g old an d n o t in the porce lain fac in g s; secondly, th a t the pontic is n arro w e d m esiodistally in its lin g u al h a lf. T h is results in w ide em brasures on the lin g u a l su rface, w ith a resu ltan t reduction o f the occlusal su rfa ce and stress. A ideal pontic tapers fro m the contact points to a g in g iv al end. T h e tip o f the porcelain rests on the center o f the rid g e or a trifle to the buccal side. T h e contour o f the fac in g m ust alw ays h arm o n ize w ith the rem a in in g teeth. A t this tim e, I w ish to stress an o th er phase, the selection an d g rin d in g o f the fac in g . T h e edentulous space should n o t be filled en tirely m esiodistally by
Tylman— Fixed and Semifixed Bridges
the facing. The pontic, mesiodistally, is widest in the gold just lingual to the facings. If the facing is as wide as the distance through the contact points, after soldering, the joint, instead of as suming a circular form, will be much wider buccolingually than the desired form. Should it be impossible to obtain a facing narrow enough, the grinding must be done at the expense of the buccal surface. Similarly, if the gingivoclusal length is to be shortened, it is done at the expense of the buccal and not by increasing the occlusal bevel of the facing. One of the important things over looked in the construction of a pontic is tooth form. How many of us have stopped to note the comparative distance between the buccal and the lingual cusps of a lower first molar and its greatest buccolingual diameter? Those who have will recall that, if the greatest buccolingual diameter measured 12 mm., the distance from the buccal to the lingual cusp point was about 6.5 mm., or nearly one-half. Yet how many bridges are placed on which the distances from cusp to cusp almost equal the greatest buccolingual diameter? Let me emphasize the significance of this arrangement as found in Nature. We are aware of the fact that doubling the diameter of a water pipe increases its capacity four times, while doubling the diameter of a sphere increases its content eight times. The same is true of a sphere. Consequently, an orange with a 4 inch diameter has four times the contents of one 2 inches in diameter. Similarly, doubling one di mension of a square will double the surface area, but doubling both dimen sions increases the square area four times. We can readily draw the anal
313
ogy existing between these measure ments and the importance of proper occlusal cusp relations and occlusal surface areas. Another point to stress is the impor tance of marginal ridges and grooves. Unless the marginal ridges are well formed and properly placed, a lowdegree inflammation in the interproximal tissues will result. Grooves that are regularly found in teeth should be accentuated. Other supplementary ones are placed where they will aid the escape of food. The latter are usually cut through the marginal ridges from the central groove over into the lingual embrasures. The final unit of the fixed bridge to be considered is the connecter or the means of uniting the pontic with the attachment. There are two types: the rigid or the soldered joint, and the flex ible or the rest or lug type. The ques tion is often asked: when is one type indicated and when the other? We are led to believe that the stress-breaker type of rest or lug should be used uni versally except where the span is too long or where the teeth are loose. We cannot lose sight of the fact that there is a certain amount of individual movement in teeth, but not to the degree claimed by some. Even when both attachments are soldered to the pontics, there1is still a certain amount of mobility. To say that fixed bridges produce pathologic changes is not com patible with our clinical and radiographic findings. Although we place a removable restoration where it is indi cated, we must admit that a restoration is efficient in mastication only in pro portion to its stability during function. Hence, all other things being equal, the
314
The Journal of the American Dental Association
fixed appliance gives greater service in masticating food. An appreciation of the vital factors is of far more concern in partial prosthesis than an appreciation of the mechanical. More good bridges are lost because they were placed on poor foundations than because of the type of attachment used. Disregard of tooth form, absence of embrasures and im proper occlusion will overcome any ad vantages of glazed porcelain, accurate castings or methods of retention. 25
E ast W a sh in g to n
St.
DISCUSSION
Albert P. Grunn, Chicago, III.:
T h e r e are m an y types o f re m o va b le b rid g e s, som e sim ple and some co m p licated . W e fin d m en w h o are a b so lu te ly set on one type or a noth er and w h o seem to be sincere in th eir b e lie f that th ey are r ig h t, and w e fin d as m an y w h o a d v o cate the fix e d ty p e o f b rid g e and the e lim in atio n o f n e a rly a ll rem o va b le a p pliances. W h o can say th at a fix e d b rid g e th at has stood the test o f tw e n ty o r m ore »years has been a fa ilu re ? A n d w h o can co n dem n a rem o va b le typ e th at has answ ered e v e ry req u irem en t fr o m the stan d poin t o f m astica to ry efficiency? T h e r e are m a n y p ro b lem s th at c o n fr o n t us in b r id g e w o r k w h ich m ake it d ifficu lt to determ ine the typ e o f b rid g e to be b u ilt; y et i f w e stu d y o u r cases fr o m e v e ry a n g le , as D r . T y lm a n su ggests, ta k in g a d v a n ta g e o f the a id o f the roen tgen r a y , and o b se rv in g the la w s o f physics and m echanics, w e can ach ieve the success w e desire, w ith a th o ro u g h u n d ersta n d in g o f w h a t w e are d o in g , because w e h av e m as tered the u n d e rly in g p rin cip les th at m ake suc cess possible. T h e use o f f u l l m outh study m odels as an a id in d iagn osis is a p oin t w o rth rem em b erin g. In fix e d b rid g e w o rk , certain basic rules are fu n d a m e n ta l to suc
ce ssfu l a p p lica tio n , such as fa v o r a b le co n d i tions, g o o d h ealth , p ro p e r sa n itation , sound m ech an ical p rin cip les, p ro p e r d istrib u tion o f abutm ents fa v o r a b le to stress and stren gth req u ired , and m an y oth er w h ich h ave a l re a d y been m en tion ed. O f the tw o types o f a ttachm en ts, the cast g o ld in la y c e rta in ly has been a r a y o f sunshine to the dentist, m a k in g possible the p la c in g o f b rid ge s on v it a l teeth w h ere f o r m e r ly em p loym en t o f a cro w n and d e v ita liz a tio n w ere im p e rativ e . T h e threeq u arter cro w n ca stin g has com e to stay, and, w hen p r o p e rly fitted , it seems to m eet the g e n e ra l requirem ents f o r an id eal a tta ch m ent. T h e sem ifixed b rid g e , w ith lu g or rest a t one end, has p ro v e d sa tisfa c to ry in most cases. In la y b rid ges, cem ented a t both ends, h av e p ro v e d u n satisfacto ry, excep t w hen the c a v ity p rep aration w as deep en ou gh to resist la te r a l m ovem en t o f the teeth. I w as g la d to h ear D r . T y lm a n speak so fa v o r a b ly o f the th ree-q u arter cro w n ca stin g as an a t tach m en t f o r b rid g e w o rk . M a n y m en are d o in g b e a u tifu l w o r k in this lin e. W h en a f u l l cro w n is in d icated , either a cast ja c k e t o r, i f a sh ell is used, a band o f 34 g a g e pure g o ld is c a r e fu lly fitted , the top split and bent d o w n on top o f the ro o t, and an im pression taken , a rticu late d , w a x e d and cast. T h is m akes a w e ll- fittin g cro w n and can be ca rv e d and con tou red in the w a x to re p rodu ce n a tu ra l tooth fo r m . T h is type o f c ro w n , w ith p ro p e r root p rep ara tio n , is p r e f erable to the h eav ier 2 2-carat g o ld band o f the o ld type sh ell c ro w n , because o f the sn u g -fittin g p u re g o ld band. T h e p o in t o f c a r v in g to reprodu ce tooth fo r m is im p o r tan t, also the g la z in g o f a ll p o rcelain co m in g in co n tact w ith the m ucosa. T h e use o f a re m o va b le o r a rep laceab le type o f p orcelain fa c in g s m akes it possible f o r e v e ry dentist to f o l l o w ou t this p roced u re. A polished p orcelain tip w ill n o t close the pores, as w e m ig h t be led to b elieve. I am g la d th a t D r . T y lm a n tou ched on the p orcelain ro o t, w h ich caused tro u b le f o r m an y u n til th ey learn ed to bake it sh orter. O v e rlo a d in g o f ab u t m ents w as an oth er p o in t w e ll covered.