Round Wire Clasp as Applied to Partial Dentures*

R O U N D WIRE CLASP AS APPLIED T O PA R TIA L DENTURES* By LEO G. POLLOCK, D.D.S., New York City N F ebruary, 1924, H e n ry W . G ille tt1 introduced a form of p a rtia l den tu re restoration w hich employed the round w ire clasp fo r retention and a stabilizing lu g to counteract the forces of m astica­ tion. I should like you to consider my p aper as a supplem ent to his, an d I shall also endeavor to give you the technic for th e construction of such a p a rtia l den­ tu re . In D r. G ille tt’s paper, th e advan­ tages of this restoration over o th e r types of rem ovable appliances are stated so clearly th a t a brief review w ill provide a background fo r a clear understan d in g of this subject. I am in fu ll accord w ith D r. G ille tt’s opinions, except w here such differences are stated. D r. G ille tt dismisses the fixed bridge as being inadequate except in sm all cases because of the “ inability to keep it clean enough to insure stability o f abutm ents an d health of gingival tissues, w ith in th e lim its of tim e and effort th a t patients a re w illin g to give to it.” T h e buccolingual precision attac h ­ m ents, in o rd er to have sufficient strength to endure for some time, m ust necessarily be large, and therefore require cavities so deep a t the cervical portion th a t the p ulp is endangered, especially w h en cav­ ities are prepared in previously sound

I

teeth. H e also calls our atten tio n to th e r­ m al shock from large inlays w hich have a “ d riv in g fit” to hold these inlays against the p u ll of th e attachm ent. T h e presence of extension attachm ents w hich overlie th e gingival tissue, in ad ­ dition to th e terrific strain on the ab u t­ m ents, makes the m aintenance of cleanli­ ness m ore difficult. T h e w ide cast clasp, w hile an adequate retain in g device, causes so m uch destruc­ tion of enam el in m ost m ouths th a t its use should be em phatically decried. In sum m ing up, D r. G ille tt says: I t is self-evident th a t w h a te v e r risks th ere m ay be of m alinfluence on pulps o f v ita l teeth, by reason of the size of inlays needed, o r th e ir close approach to pulp a n d sensitive a re a s in the case of th e ir use as receptacles for the box elem ents of split attachm ents, this fe atu re w ill d isa p p ea r, if split attachm ents fo r v ita l teeth be discard ed and the re ta in e rs used be a p ­ plicable to the ex terio r of the tooth. It is also self-evident th a t from the stan d p o in t of e x er­ cising a n influence fa v o ra b le to caries, the n a rro w e r the a re a of contact betw een any extern ally a cting device, a n d the surface of the norm al tooth, the less the risk. T h is, of course, points a t once to the clasp m ade of round w ire, of an alloy capable of m ain tain ­ ing an elastic tension, fo r long periods, w ith ­ out noticeable deterio ratio n .

I t m ust be borne in m ind th a t round w ire clasps of sm all gage having g reat *R ead before the Section on P a r tia l D en ­ elasticity w ill fall sh o rt of the m ark u n ­ tu re Prosthesis a t the Seventy-Second A nnual less w e use w ith them stabilizing lugs of Session of the A m erican D ental A ssociation, such design th a t stresses due to th e forces D en v er, Colo., Ju ly 22, 1930. 1. G illett, H . W . : D ent. Item s Int., 46:126 of m astication as w ell as la te ra l strain s are counteracted. T h is a t once throw s in (F eb.) 1924. Jour. A . D. A ., July, 1931

1233

1234

T h e Jo u rn a l of the A m erican D e n ta l Association

th e discard the occlusal rest placed over th e m arg in al ridge of the abutm ent teeth. T h e r e are selected places w here an occlu­ sal rest m ay be used in conjunction w ith th e stabilizing lug, b u t they should never be used alone. T h e rec tan g u lar lug relieves the clasp of m uch of the dem and m ade on it if no lu g is u se d ; o r if th e occlusal rest is selected, th e lug takes care of th e stresses so th a t the only function of the clasp is to sup port upper pieces against g ravity an d a ll of them against trac tio n of ad­ hesive foods. B u t little retentive force is required fo r this. T h e stabilizing lug should have a defi­ nite rec tan g u lar form w ith w ell-defined stra ig h t sides and floor b u t som ew hat sm aller a t th e cervical th a n at the occlu­ sal surface. T h e lug m ust have a seat in an ab u tm en t restoration, w hich usually should be an inlay. A t once, th e advocates of the precision attachm ents raise the point as to w hy, if we m u st have inlays, we should not insert a precision attachm ent and do aw ay w ith the clasp entirely. I adm it th a t w hen the ab u tm en t teeth have large deep cavities o r la rg e fillings or inlays of lo n g sta n d ­ ing, so th a t little if any new cu ttin g is necessary, and if the crow ns of th e ab u t­ m en t teeth are n o t too short, the precision attach m en t m ay be used to advantage. In the case of sound ab u tm en t teeth, there is a g reat difference. A n inlay cav­ ity can be prepared w hich is so shallow a t the cervical portion th a t th e sm allest (an d therefore the w eakest) precision a t­ tach m ent cannot be inserted w ith in its border, and yet there w ill be am ple room in w hich to place a lug seat in an inlay m ade for the same cavity. I t is this con­ servation of v ita l tooth substance a t the to o th ’s m ost vulnerable point w hich dic­ tates th e selection of the lug and round w ire clasp as the u ltim ate attachm ent in

all cases w here th e ab u tm en t teeth are sound. D r. G ille tt advocated the use of 16, 17, 18 and 19 gage ro u n d w ire. Since th a t tim e, research in gold alloys contain­ ing high percentages of p latin u m and m etals of th e p latin u m group has m ade it possible to use sm aller gage w ire, chiefly 19, 20 and 21. I t is fittin g th a t w e pause for a m om ent and pay trib u te to th e m em ory of th e late L ouis J . W ein stein , w hose researches in dental m etallu rg y lately conducted in association w ith the B u reau of S tandards a t W ash in g to n , D . C ., have m ade these im provem ents possible. H is co n trib u ­ tions to prosthetic d en tistry have been num erous and his u n tim ely death leaves a place in d en tal research w hich it w ill be difficult to fill. W h a t is th e advantage in using sm aller gage w ire? One of the g o v e rn in g law s of elasticity is th a t deflection v a rie s in v ersely as the fourth pow er of diam eter. A n o th e r is th a t deflection v a rie s as the th ird p ow er of length. T r a n s ­ latin g this into practice, w e find th a t the sm aller the w ire and th e longer the clasp we can use fo r a n in d iv id u a l case, the g re a te r the deflection possible, a n d consequently the g re a te r the fa cto r o f sa fety fo r a sm all d e ­ flection. T h is, in tu rn , calls fo r a w ire o f the highest possible elasticity and the g reatest ad ap tab ility to h e at treatm en t, because a sm all w ire w ith these qualities w ill h a v e the sam e retention v alu e as the la rg e r w ire w ith ­ out them . A nd, in addition, it can be de­ pended upon to d isp lay the re q u ire d am ount o f deflection to p erm it the clasp to pass o ver the contour of the tooth, a n d close up a g ain to the desired sm aller size, a g re a t num ber of tim es w ithout perm anent defo rm atio n and consequent loss of retention v a lu e .2 T E C H N I C FO R D E N T U R E C O N S T R U C T IO N

L et us now take up th e construction of a typical tw o-arm ed clasp denture w here a first m o lar and second bicuspid 2. G illett, H . W .: R etain ers in P a rtia l Prostheses, J. D ent. Res. (Sept.) 1927, p. 189.

P ollock— R o u n d W ir e Clasp are m issing and the adjacent teeth are sound. T h e prelim inary survey having been m ade, and this type of restoration selected, typical inlay cavities are pre­ pared in the distal portion of the first bicuspid and th e m esial of th e second m olar. By typical inlay cavities, I m ean cavities w hich are not any deeper or w id er th an w o u ld be em ployed if these teeth had the sm allest in terproxim al cav­ ities th a t could be detected by a ro en t­ genogram . In d ire c t cavity impressions and a w ax bite are taken and th e cavities closed w ith a tem porary filling. W h e n the w ax p attern s are being constructed in the laboratory, sm all rec tan g u lar seats are carved o u t of th e w ax and th e inlays are cast, finished and polished. In la y gold should be the very h ardest th a t can be obtained. M e tallu rg ists have proved th a t no gold has yet been alloyed w hich is so h ard as dental e n a m e l; and recently some of the leading periodontists have stated th a t there is less trau m atic occlusion from h a rd gold th a n from the soft golds w hich flow u n d er th e stress of m astication, and do not w ea r dow n so readily n o r so u n i­ form ly as the h a rd e r alloys. T h e floor of the lu g seat should be inclined slightly rootw ise a t its axial end, and the side w alls should also be inclined som ew hat to give a tapering form , this m aking the lug sm aller a t th e cervical th a n a t th e occlusal p art. T h e general form of the lug seat is such th a t the lug enters its seat easily and yet tends to re ­ m ain seated w hen in place. T h e lug p attern s are then w axed on the finished inlay, leaving an apron about 1 m m . w ide on the proxim al surface. T h e sprue is inserted in th e occlusal su r­ face, and th e lu g is cast. In cu ttin g the lu g from the residue button, a short por­ tion of the sprue is left attached to the lug. T h is w ill serve as a handle and also

1235

as an aid in seating th e lu g in a plaster impression. T h e p atien t is now seen fo r th e second appointm ent. T h e inlays are adjusted for occlusion an d cem ented in to th e cavities, and an o th er w a x bite is taken. T h e lugs are then w axed in th e ir respective seats. I dry the lu g seat in th e in la y ; and grasp­ ing th e han d le of th e lu g w ith a p air of pliers, gently h ea t th e lu g in a sm all bunsen flame, an d touch th e cavity side of th e lu g to a stick of w ax, allow ing only a sm all q u an tity of w ax to adhere to the lug, an d quickly place in position in the inlay. F o r this, I use a sticky w ax th a t is n ot too adhesive and w ill allow the lu g to come aw ay w ith the plaster impression, being certain to get an accu­ rate impression of th e teeth to be clasped. A t th is tim e, I also take th e shade. T h e lugs are now replaced in th e im ­ pression, if they have become loose, and all traces of w a x rem oved from them . F usible m etal is poured into the a b u t­ m ent teeth, care being exercised so th a t no m etal ru n s o nto th e saddle area. Sm all iron loops should be inserted in to the fusible m etal to secure it in the model. A fte r th e m etal h as been cast, th e rem ain ­ ing surface of th e im pression is coated w ith shellac an d th en sandarac an d al­ low ed to d ry thoroughly. T h e impression is then poured, a good artificial stone being employed. Y o u are probably w on d erin g w hy the impression w as n o t taken w ith the inlays uncem ented so th a t th e bridge could be constructed directly upon th e inlays in the m odel. T h e re is a tw o fo ld reason fo r th is: (1 ) th e cem enting of the inlay a fte r th e case is constructed w ould tend to raise th e denture, perhaps only slightly, b u t this is en tirely elim inated by settin g th e inlays before tak in g the im pression; and (2 ) th e slig h t film of w ax on the lug allow s fo r ju st th a t am o u n t of com pres­

1236

T h e Jo u rn a l of the A m erican D e n ta l A ssociation

sion w hen the d en tu re has been com ­ pleted. T h e impression is then separated, the lugs are removed from the m odel and the case is articulated. T h e porcelain crow ns are ground nearly to fit the m odel, w here th e saddle w ill la te r be constructed, and approxim ately to occlusion, being le ft a little longer th an required to allow for th e final adjustm ents. A space equal to the gage of the w ire to be used for the clasps m ust be le ft betw een th e porcelains and th e ab u tm en t teeth. T h is space w ill be occupied by the uprights. A plaster key is m ade to hold th e porcelains in place on th e model. T h e porcelains are n o w ground fo r th e boxings, a space about 26 gage being le ft betw een them and the model fo r the saddle. T h e saddle section, consisting of the saddle, the boxings for the porcelain crow ns and the u prights is now form ed in w ax on th e model, th e plaster key be­ ing used to hold the porcelains in place in so doing. T h is section is cast w ith a h a rd elastic gold and rough finished but n o t polished. T h e saddle section is then placed back on the m odel and the lugs are n o w to be soldered to the section. I t is advisable to solder one lu g a t a tim e. T h e sm all h an ­ dle on the lug is again useful in steadying th e lu g in the soldering investm ent. A fter the lugs have been soldered and a ll joints betw een lugs and section nicely finished an d polished, the lug handles are ground aw ay and th e den tu re is ground to exact occlusion. W ith a suitable bur, a groove is cut across the occlusal aspect to the uprights. T h is groove is to be ju s t w ide enough and deep enough to house the round w ire clasp. W e now come to the bending and shap­ ing of th e clasps, w hich is n o t a difficult

task b u t one w hich m ust be carried out w ith carefu l a tte n tio n to details. T h e first step is to secure round w ire w hich has been carefu lly m an u factu red and accurately d raw n . A suitable length of the w ire (gage 19 fo r the m o lar and 20 fo r th e bicuspid) is quenched. T h is renders th e w ire soft and pliable so th a t it can be b en t to shape w ith o u t being nicked or u n d u ly compressed a t an y point. I t is m ost im p o rta n t to use pliers from w hich all sharp corners have been re­ moved by g rinding. I like to begin th e bending of the clasp by form ing the lin g u al arm , w hich i§ placed n ear the gingival m arg in b u t not im pinging it. T h is is tried against the fusible m etal to o th and the w ire b en t to form the vertical segm ent of th e lingual arm . Each tim e a bend is m ade, the w ire is broug h t back to th e model an d held securely in place, to determ ine th a t each segm ent fits properly. T h e vertical seg­ m ents of th e clasp m ust n ot touch the m odel. T h e y m u st be kept in th e center of the em brasure and slightly aw ay from the m etal tooth. T h e n ex t bend is a rig h t angle to form th e occlusal segm ent of the clasp. T h is segm ent fits into th e buccolingual groove w hich w as m ade on the oc­ clusal aspect of th e u p rig h t next to the lug. N o w w e bend the w ire to form the v ertical segm ent of th e buccal arm , and finally bend it to fit into th e angle form ed by the buccal surface of the tooth and the gum m argin, being carefu l to keep it from im pinging on th e gum . Especial care is needed to avoid allow ing the angle betw een the h o rizo n tal an d perpendicular segm ents to bear against th e gum . Y ou w ill observe th a t th e clasp has an occlusal segm ent, a buccal and a lingual v ertical segm ent extending from th e oc­ clusal to th e gingival border of th e tooth and a buccal an d a lingual h o rizo n tal segm ent a t nearly rig h t ‘a ngles to the v er­

P ollock— R o u n d W ir e Clasp tical segm ent. W h e n the clasp is opened to pass over the highest convexity of the tooth, th e horizo n tal arm s exhibit flexure elasticity. T h e vertical arm s are also flexed to a slight degree, b u t bring into play another form of elasticity know n as torsional elasticity, w hich is even m ore im p o rtan t th an flexure elasticity. T h e com pleted clasps are then placed in th eir respective grooves and a sm all plaster key is m ade w hich covers the clasps and saddle section. Before the clasps are set back into the key, they should be boiled in 30 per cent nitric acid to remove all traces of the fusible m etal w ith w hich they w ould otherw ise become contam inated. T h e key contain­ ing the clasps and saddle section is treated like an impression, and a soldering in­ vestm ent m odel is m ade fro m it. T h e clasps are soldered a t th e point w here they rest in th e ir grooves. A very sm all piece of solder is used and ju st enough heat to flow it. W e m ust n o t overheat the case no r unite any m ore th a n the occlusal segm ent of the clasp. If, per­ chance, any solder flows onto the vertical segments, the clasp has been spoiled and w ill have to be detached and discarded. A fte r the clasps are soldered to the saddle section, m inor adjustm ents in the fit of the clasps are m ade and the denture is again boiled in 30 per cent nitric acid. T h is brings us to the final operation of producing m axim um resiliency of the w ire, or “heat tre a tm e n t.” H EAT TREATM EN T

U n til recently, this m axim um resil­ iency w as obtained by heat trea tin g the finished denture in an electric oven. D u r ­ ing the past year, I have been allow ing the case to cool slow ly in its investm ent afte r the final soldering. Several years ago, through the cour­ tesy of M r . Colem an, then of the B ureau

1237

of Standards, I w as p erm itted to make m any tests w ith w ires in the quenched, air-cooled and oven-cooled states. Some of the m aterials tested show ed rem ark ­ able im provem ent a fte r h eat treatm en t. T h is same w ire w hen soldered to the den tu re and heat trea ted in my lab o ra­ tory became extrem ely b rittle. U n d o u b t­ edly, heat trea tm e n t has a m arked effect on these elastic wires, and fu rth e r re­ search is needed to produce a definite technic w hich w ill give m axim um resil­ iency w ith o u t brittleness. Jo h n S. Shell3 says, “T h e problem of h eat trea tm e n t of dental alloys w ill be found eventually to be a ra th e r com plicated procedure, re­ quiring a special technic for each alloy.” T h e oxids w hich have been form ed on the den tu re w hile it w as being soldered m ay be removed a fte r h eat trea tm e n t or air-cooling by boiling in d ilu te hydro­ chloric or sulphuric acid. T h is does not affect the properties of the w ire. In a one or even a tw o to o th denture such as I have described, one can dispense w ith the buccal arm of the bicuspid clasp if it should be too obtrusive. In designing clasps, w e should rem em ­ ber th a t only the final th ird of the h o ri­ zontal segm ent should m ake contact w ith the tooth. T h e v ertical segments m ust never come in contact w ith the tooth. If a vertical segm ent of a clasp impinges on the tooth in either rem oving or in sert­ ing a denture, the clasp w ill be u n d u ly strained and its life w ill be short. A n im p o rtan t clasp is th e “G ille tt crib,” w hich is attached to the saddle at its lingual end and rests in an occlusal em brasure and has its buccal arm free. T h is type is generally used w ith a canti­ lever saddle w here only one definite lug seat can be obtained. 3. Shell, J. S.: H e at T re a tm e n t of G oldNickel Alloys, J. A. D. A., 17:409 (M a rch ) 1930.

1238

T h e Jo u rn a l o f the A m erican D e n ta l Association

T h e v ariety of shapes into w hich the ro und w ire clasp can be easily bent to overcome tipped abutm ents and extrem e convexities of crow ns m ake it an excel­ le n t attach m en t to be used in conjunction w ith m any other form s of retainers such as th e split pin or b ar and th e buccolingual precision devices. 200 W est F ifty-Seventh Street. D IS C U S S IO N

F. M . H ig h t, H ouston, T e x a s: I a g ree w ith D r. Pollock in m ost of his statem ents as to the use and a d v an tag e s of the w ire clasp. I am sure th a t w e h ave all w atch ed p a rtia l dentures w ith w ire clasps long enough to know th a t they function pretty w ell. T h e re is not anything perfect in dentistry, and of course im properly m ade p a rtia l den tu res w ith w ire clasps a re going to give trouble. T h e re a re m en to d ay th a t a re m aking one-piece castings th a t live up to p ractically ev ery fu n d am en tal th a t D r. Pollock has show n. O ne-piece cast­ ings can, I think, be cast in such w a y th a t the frictio n al contact or contact -with the clasp a g ain st the tooth w ill be no g re a te r th an w ith the w ire clasp, as has been show n. One th in g on w hich I w ould differ w ith D r. Pollock is the use of re c ta n g u la r grooves in the teeth. H e uses the flat seatin g base, w hich necessitates the placing of a gold in la y in each tooth th a t he uses the re st on. T h e reason th a t I w ould not agree to this placing of re c ta n g u la r c a v i­ ties in th ere is the fa ct th a t I believe w e m ight ju st as w ell place a sta tio n a ry b ridge in these sm all cases, because, as f a r as the stra in

is concerned, w e w ill get all the stra in on the abutm ent teeth w ith this type of lu g th a t we w ould g et w ith a sta tio n a ry bridge. In my ow n practice, I w ould p re fe r a lug w hich fits into a seat, p re fe ra b ly gro u n d into the en am ­ el, p rovided the enam el is thick enough, w h e re the occlusion w ill p erm it the placing of a lug, and I think th a t a lug placed in a saucer shaped groove, placed in the tooth so th a t the p a rtia l d enture o r the add ed teeth m ay m ove and the lug m ay move also, causes less tra u m a to the abutm ent teeth. A ccord­ ing to the pictures show n here, D r. Pollock is using w o nderful w ire. I h av e h a d m uch trouble w ith w ire clasps b reak in g w hen the expansion o r b ending occurs. D r. Pollock (clo sin g ): T h e re is not a n y ­ th in g w o nderful about the w ire th a t I use. A ny good w ire will, if pro p erly used and not abused, p erm it one to m ake all the necessary bends in them th a t a re required. O f course, w e m ust employ a w ire w hich, w hen quenched, w ill be quite soft. I f the w ire is soft enough, w e can bend it. W ith the ex­ ception of the little loops, m ost of the loops a re bent by hand, ju st bent aro u n d an oran g e wood stick and forced on the m etal. T h e w ire is v e ry soft w hen it is annealed o r quenched, and a fte r the final soldering fo r h e at tr e a t­ m ent, it re ta in s its orig in al elasticity. T h e re is no trick to th at. It is v e ry sim ple, and any good w ire w ill do th at. I h ave been w orking to reduce the size of the w ire th a t I use. As stated in the text, a t first I used 16 and 17 gage w ire. I am now using 19 and 20 gage fo r m olars and bicuspids, 18 g age fo r crib clasps and 21 gage for closed crib clasps.

BACTERIOLOGY OF V IN C E N T ’S INFECTION By FRANCIS H . DALEY, D.M.D., Boston, Mass. N a study of the bacteriology of any disease, there are certain fundam ental principles w hich m ust be follow ed. T h e c u ltu ra l and m orphologic character­ istics of the organism s m u st be studied. T h e ir relation to certain lesions m ust be

I

Jour. A . D. A ., July, 1931

definitely established. W h e th e r they tend to be saprophytic or parasitic is a factor. Some organism s liberate exotoxins. T h e Klebs-Loeffler bacillus is an exam ple of this type. O th e r organism s store up th eir toxic m aterials as endotoxins. A n ex-