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The crisis in orthodontia
My objection to the ling~~al awh, which ctsttwds from the molar to t hc irlc*isors without any supporl, has always lichen that it is not stable. 1 havr t.lltx same objection to the lingual springs that arc not supportt~d by bands or spurs. Without such stability ;LIL cud result <~iLLLLLot lw achiewd. I do not donbt but that the nonsupported lingual arch with free springs is also ;~ble to charLgt~ the posit,ion of the teeth, Inul the cxad ;rL~tl dcsircd change in position and tilt‘ stability of the anchor tet.1 h is frctquently lacking. 1 fully subscribe to Mershon‘s statement : “If it wrc possible to obtain accurate data, 1 helievc that today tht?rc is as much harm king done by the 11s~of orthotlontic~ appliances as thwt~ is good. ’ ’ The harmful results art’ tlot o1r1~~t ho result of the intensity of the force--since WC11 esttwsivc da171ilgYt ma)- cX\;i~t~tl~ally1W c*om1)1(4cl~-rtLl)a.ired-but iilS0 of the changes in the dirwtion of the Eowc~. Thtl fa(at that to the wpcated change of thr *From tine I)\?p:wtmt~nt i,f 0rthw;ontia cif tl~t: Ucwt:ll Tnstitutrx of the Irnivetsity of Vienna. j-Translated from Zeitschrift fiit’ ISto?nftfo2o!~i~. Kos. 7 and 8. 1933. Lmblishcd by ‘lirbarr 8nti Srhwwzenberg, Vienna and Berlin. $Oppenheim? : “From ‘thv characteristic tr:tnsfornlation of the bone whic*h aceompanitw the movement cf teeth, we can llraw the conclusion that before any treatment is started, the kind and direction of tooth movement hi?ve to he determined ter’y cwefully in order to avoid :I later change of direction once movement has been started. If such a change is introduced into the treatment. the neccssary repeated tr:lnSformation of the? hone must necessarily interfew with the definite reorzsnization of the boric strurturc ?nd is no doubt responsible for man;\ failures.” Opwnheiml* (Quotation from Dr. Angle’s letter of May 23. 1929. to Dr. Oppcnheim) : “The remedy (for root resorption) seems to me clear, tinat is, ar, even and steady movement as gassible in the ooze direction requirtd. . .” WiLson’6: “Tooth movement must bc continuous in one dirrction.” Hawleyas: “A moYemen$ once it haa been started should br c’ontinwd : intermission*r-tpermissible, but never a mown.g back in the opposite direction.”
ligatures, which produced minute changes in the direction of pull and irregulariin the direction of force. In addition to the changes in the direction, the actual intensity of the force is also supposed to be of great importance. In the experiments of Schwarz” an attempt has been made t,o find definite figures for the intensit)y of orthodontic force. There arc several objections to the validit,> of such figures. In the first place, the force exerted by a finger spring will depend largely upon its position on the surface of the tooth. If the spring lies on the tuberculum it will have a tendency to become displaced in an incisal direction; thereby the intensity of force will be decreased. On the other hand, if the force of mastication displaces the lingual arch or the individual spring; in an apical direction, this will automatically increase the intensity o’f force, hence the necessity of cutting grooves in the teeth in Schwarz’s experiments to stabilize the posit,ion of the finger springs. Schwarz’s formula. for the biologic limit of orthodontic force reads as follows:” “ These experiments already show empirically that forces up to 20 grams intensity at the start still conform to the biological optimum, but that forces whose intensity at the start is greater, eve,,
tics
be it only slightly, are dangerous to the root, to say nothing of the intermittent character of such forces, which ha.s already been mentioned.” Schwarz’s formula, for the permissible force is as follows : “The capillary blood pressure in man and in most, mammalian animals is 15 to 20 mm. Hg per square centimeter, i.e., a pressure of 20 to 26 grams per square centimeter will just suppress the capillary pulsation. . . . the root surface of a fully developed mandibular premolar under pressure in lateral movement may roughly be estimated as being one square centimeter, whereby part of the pressure is taken up by the elastic soft tissues of the gingival tissues and the periosteum. . . . Taking into account a certain safety reduction we arrive, for single-rooted teeth, at a maximum permissible pressure averaging 15 to 20 grams per average root in tipping movement,. ” To this formula the objection must be raised that the area of the root surfact of t,he mandibular premolar which is under pressure in labial movement is only about one-ninth of a square centimeter. If a in Fig. 22 indicates the average width of a mandibular premolar (4.9 mm.) and b the average length of a root (13.8 mm.), the approximate surface of the labial periphery of the root is about 0.34 sq. cm., or in other words, a lit,tle more than 1L3sq. cm. If the tooth is moved labially, practically only the upper third of its surface is subject to pressure; so the figure for the square area under pressure would hare to be reduced to 0.11 sq. cm. The biologic limit of force would then have to
be reduced to about 3 grams. 1 realize that, I am not justified in t]Fing to gl1-t. nny definite figures for the forctl. l~cctr~tsi rrt!y wbcdufions w-e ilist l/s m rtclr 0 m.atter of conjectuw (1s fllosc of Schlorrr;. In addition 10 t hcscx mat hcmat ic*ill fallacies we know still less about the amount, of ~rrcssu~c whiclt is t;tkthrl 111)II~ tir(L tension of the fibers of the periodontal membrane on the side of pull and t-1~’th+: increased resist,ancc of the tissues on the side of prt~ar~ as the forcch incrc~asc~s. Therefore, it is inzposrilde bo gilye c’l*zn approximatel!/ ilr, figures t//c p rmis We must not forget tllat wt’ :I~Y’ sible total force auhich, should not be erccdcd. dealing with living tissues and that each i ndividua 1 has his particular individual reaction. Consequently, we cannot give au- standard figures 01’ data f‘ot’ ;ltl!therapy. N. W. Kingsley expressed this thought as follows: ‘. 12t~ntly t/1( statement has been made that a tooth should bc moved only a certain tlistarrcsc within a certa,in length of time in order to avoid complications: bllt it is cluitc, evident that any mathemat,ic formula for ~~hysiologic or pa.thologic~ c+hangrs i, absurd. ” Xalamon17 states. ,l . “We shall never be able to dctcrminc the force of tilt‘ angle arch mathematically, because WC arc dealing with living tissurs. .’ “Treatment. in orthodontia cannot be worked out as a mathematical formula. ’ ’ (Mershon.“) “The’ reaction of the organism is not only different in individuals. but it is also different in t,he same individual at different Cmes. ” (Winkler. I.*) A definite standard force is by no mcians the clue to success; 011 the> COIItrary, in addition to the knowledge about, the fundamental principle of appliances, which knowledge may be acquired by studyin g and reading, flr,e s~crel of success is only the extent of experience, the numb of cases trea,ted, und the number of successes ad failwres. Particularly the latter are the best teachers for us. Orthodontia is neither a technica, nor a mathematical science with definite formulas and regulations; orthodontia deals with living tissues which are subject to constant changes and for which there are no strict rules. 0 st>hodontia is purely a science of experience.* Another argument in dental literature deals with the position of the fulcrum. Some authors (Schwarz) claim that t,he fulcrum is located in the apical third of the root, others at the alveolar margin (Ba,uer and Lang2”), and still otlkers at t,he apex. However, sometimes one author has changed his opinions SOrat,idly that it is difficult to decide just what his latest opinion on the subject actuall~~ is. Schwarzg in 1928, stated: ‘ ‘A ligature producing gentle force will graduall) tip the tooth in such a way t,hat the fulcrum is located at the apex. If the same ligature is applied in the same place and in the same direction, but with greattir force? the fulcrum is located farther crownward. ” “Even ;L weCakforce In 1932, Schwarz12 comes to the following conclusion: can tip a tooth inside its alveolus around an axis situated above the apex. The comparatively small displacement of the apex nevertheless brings about slow *opp,pler 38 “In the use of our orthodontic tional factor, and therefore, we are still working concerned. despite the data given by Schwarz.”
appliances in the dark
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the
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changes in the structure which are by far surpassed by the marginal changes, so that in favorable cases the apex can remain approximately undisturbed.” I have again proved the fact that the fulcrum is located at the apex, and I stated in 1911” and a.gain in 192918: “Under the influence of gentle forces we find that the bone is resorbed on the side of pressure by ost,eoclasts, while new bone is being built on the spicules on the side of pull. These changes can be found extending almost to the apex, which indicates that the crown does not deviate in an opposite direction from the root.” (See Figs. 3 and 15 of this article.) The results of Gottlieb, Breitner, and Johnson can be explained in only one way : The reason these authors found a deviation of the apex is that they worked with eery strong forces; thus their findings corroborate Schwarz’s conclusions, who also has worked with excessive forces. As far as t,he book of Gottlieb and Orban is concerned, the fact that excessive forces were used is indicated in the very title. BreitneF has restricted the application of his findings in animal experiments to man by stating: “It is known from orthodontic practice that teeth are tipped much less with very gentle forces and very slow movements.” Johnson, Appleton and Rittershofer32 also used excessive force in their experiments. since their springs, according to the examination by Dr. Irish Pittsburgh, exerted a continlrous force of 64 grams for twenty-six and forty days. This is a very great force, especially in view of t,he fact that it was continuous, and necessarily would bring about a deviation of the apex. Schwarz quot,es Johnson as proof of the correctness of his own statement, that in biologic treatment with continuous forces the apex always shows an excursion in the opposite direction of the crawn. But although Schwarz worked with much less force than Johnson, he found necrosis of the periodontal tissues and the presence of deep resorption in the dentin, which indicates that his force also was excessive. The fulcrum in tipping movement is located at the apex, if such gentle forces are applied that bone resorption cm keep pace with the movement of the tooth. If the force is so strong that on the side of pressure there is contact between root and bone, then this point of contact will of necessity act as the fulcrum, and the apex must deviate in the opposite direction of the crown. Whenever this condition is found, it is definite proof that the movement has been carried on faster than the bone on t,he side of pressure could be eliminated by resorption. Since all forces, ellen if in our opinion they are as gentle as possible, are still gl,eater than the forces of natm*al growth and bone development, the rule requliring the gentkst intemaittent forces, the use of intermissions during the active period of trentnzent, and the elivninntion of continuous forces cannot be overemphasized.
This opinion is supported by a statement of Korkhaus ? “ Strange as it may seem, we have not yet seen too weak forces in orthodontia, because even the most. gentle force brings about some form of reaction; the least amount of force has not yet, been determined. ”
My findings have also been corroborated in the study of ii human tool Ii following orthodontic trcatmc~ut. which was pnblisht~tl }),I, Ile~zbr~~~~.‘~” I((* tt~tr fomld ncilr the apex 011 th side of’ pull ‘. nt~wl~- formc~d bent: ;11*1xriptl iir I tic. general direction Of tllc fibt>Y bmldlc~s 01’ ttlt, ~)t~~iOdOtlf ill rric~rrrhr;r ttt’ iii 1 hi-. region. ” kltlc forctY3 had hYl1 usctl. ilutt colrsc‘c(uclltl~~ 111
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vessels aud IICWW ;tt that :IIWS is ncvc~ tiisturbccl. :Rcgar*tllcw of 1 II(’ r+n1r$ys that may occur in the position during t ht> ptrysiologic ~~rocessc~s 01’ qowth ~1111 movrment, the apex will remain stationary. “The t,jl)ping of teeth is OII~J-;III evidence of 011~‘s inability t.o handle iI dt~li~at(~ ;r~~l)liancr ;Illtl wtl t~spt*c~ssiotlot OI~P’Slack of knowledge of growing and dc~vclo~~ingprocesses. ” (Iuerxhon. 1 The correctness of m,v opinion WII b(’ R~UWII tl(Jt only by tlic’ ~~hotornitdrographs (Figs. 2. 3, and 1.5) of thi 5 article hut also by ;i siml)lc espt+rnc~nt. If it is trur-and we know it is true-thf btmc watts to tllcs gc.ntlw1 t‘owt~ 1)~ resorption and thus seems to rccedc from the force, then the raoot ulil>v f.~areprosented by a stick which stands with tnl(’ ~ntl OJI s till)lc ;r~lti the ot hcsr talltl tit’ which is moved laterally without me&n% an! resistance during this trm\:(~mt’n~. Then the lower thnd of the stick will rtmaill in its ~)l;rcc~witho(lt ;rn,v ckviatit)tr ita the opposite> dirwtimi of tl~r 11ppcr PIIJI, All authors hare agrec~l that cxperimc>nts on models or mathematical formulas cannot prove the position of the fulcrum of thtl root. \Vh~th~r Schwarz and other authors used soft plaster, ruhbrr; soft clay, or any otht>r plastic, mirterial for their experiments to prove t,lie cxcursioli of the ;ipcs ii1 il direct,ioir opposite to that of the crown, tlrc?y roll o~yrZookcd 1//c. i)~l.~~tcr~t /‘c,cf fl~crl f//f. CkongcS
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bow, udzich rcncts to 111~gvntlcst stimwli II~C%the wndi~io~b of w/l icll ~~~~d~~t~qof’s basic chcrny~s (IS SOONIIS an!/ force is csc~?(d upon if. If the movement of’ the t&h is not t’astcr ttta]J the tr.unsi’orrnatioll of t ht. bone can take place, in other words, if lhc tooth does not mret any rt~sistanc*c~ iri the direction of its movt~mcnt, Ihen the changes in hone hi, no mea7ls co1 respond t,o those produced cspcrimcntally by Schwarz. The fact that Schwarz considers the excursion of the a~lex in a direction opposite to the direction of the crown as a tdorrect procedure in orthodontic tooth moveme77t proves, in itself that, he has used too strong forces. HP illSO Stllt(‘SZ “Any f0rc.e that displaces the apex must al first dt9troy the xpica t fibclrs which are the natural anchorage of the apex.” If teeth have inadvcrlcntly been tipped h> pcntle forces during or1 hodontic~ treatment in such a \\-a>that thcrt> is no tlcviation of the apex-, t-hen f77ndion and other natural forccx will gradnall~- st raightcn the teeth >lnd restore them to their normal position as soon as the orthodontic appliance has been removed. If, however, the apex has deviated, if the t&h have been tipped too rapidly ant1 estensivcly. then natural forces will not he sufficient, to restore the tcdh to t tit4v
normal position, and orthodontic procedures will become necessary to correct their position, which will necessitate a chamge in the direction of movement and risk the danger of root resorption. There can be no doubt but that in orthodontic treatment displacement of the apex opposite to that of the crown is not a biologic process. In discussing Johnson’s animal experiments,“” Boedecker expressed t,he following opinion concerning the diffcrcnce in the findings of Johnson (excursion of thr apex) illid my own findings (apex stationary) : “Why this should be SO is difficult to say; but, if we think of the matter logically, we would suppose that Oppenheim is correct, that it was a single-arm lever, and I believe the answer to the questiort is the degree of pressure used in moving a tooth. . . .” Stallard”” has expressed the opinion that I am not justified in drawing conclusions from my experiments as to the changes in man, because I did not move teeth from a wrong position to a correct one, but from a correct position to an incorrect, one. I have already answered this criticism by saying that there are no monkeys, with malocclusions that can be corrected. Furthermore the recent investigations of Hcrzbcrg Q have shown that the findings in human teeth are analogous to those in monkeys. A basic difference now between the various orthodontic schools is their attitude toward the problem whether continuous or intermittent forces should be used. Many investigators, among them prominent physiologists, havn sta.tcd that devclopmcnt and qcncral growth arc not continuous, but. intermittent processes. Also, for the structural arrangcmcnt of the jaw, intermittent forces are of paramount importance, that is, the effect of occlusion and mastication. If nature works with intermittent forces and if the principle of the best form of treatment is imitation of nature, with what justification has intermittent orthodontic trcatmcnt been called ‘ ‘ unbiologic ’ ’ 1 The question whether intermittent or continuous forces are the best for orthodontia is perhaps best cspressed in a letter written to me on this subject by Professor Salamon of Budapest. He states: “As far as the problem, ‘intermittent force-biologic action, ’ is concernnd, one thing is certain: it has never been proved experimentally that intermittent forces are ‘unbiologie.’ This has only been stated in order to support the assumption that continuous forens are ‘biologic. ’ In my opinion the latter statement, too, has never been proved but has only been broadcast as truth. I think I can characterize t,his problem as follows: there are no ‘biologic’ or ‘unbiologic’ appliances or methods, but onI?/ ‘biologic’ or ‘unbiologic’ ortkodontists. With every appliance one can work biologically as well as unbiologicallp. T do not think that this problem can be decided histologically, and Schwarz’s theory of capillary pressure also seems to be open to criticism. ” In none of the textbooks of orthodontia which have appeared within the last few years do we find proof of the statements contained in them by a dcmonstration of pewnanent results (Dewey, Gallavardin, Herbst, Izard, Kantorowicz, Korkhaus, Kranz, I&her, McCoy, Oppler, Pfaff, Quintero, Simon, Walkhoff, and Winkler). I do not include Angle and Case in this list, because I ‘nave been
256
ticular method; I have tried all new methods and appliances of the ~WI: years with varying results. and 1 do not hc3ilirtc to wcdvcpt improvemcrrts of dci methods, as long as these improvements art’ snfficientl,v justified by clinical rt%dts. ht t!Jf? pe”nJnf3eJJt results tlJat IliJ\‘r brcan reportetl so far by the* advocates of the J~ern nJr~tlJotls are so swmA that I haw swn no ~-P~SOII to discont,inrxe my method of treatment, as tli(!tatctl by the findings in my irnimal experiments; t,lic permanciic~y of my results warrants this pcrsist~cnt:~. There is no “modem ” and IJO “oiit-of-(late” t~rtl~t~dt~r~tia. There is t-ml, an orthodontia which is successful or one that cannot rtlport prmanrnt results. l‘hc repeated cluotIng of comnlonplaces. such as biologic reaction only with continuous forces, the danger of osteoid ill intt~rmittcnt forcc>s, or the ;tppii:1ncdl1 which causes only I)rcssurt~, should ilt I:ist l)(L tliscontinucd. This does not t’oI3tribute to the progress of orthodont-iii. My conclusions of 191 1 do iiot riced any modification. All I can do is add ~Jpon them in sc>vcral rcspec’tx : I. The histologic changes which were clescribetl more t,han twenty years ago as the result of the activity of osteoclasts itlid ostcoblasts under the influence of gentle, intermittent, elast,itJ, orthodontic forces still retain their validity today. The same is true of the reaction of the tissues to strong forces (ort.hodontically speaking). 2. The animal experiments carried out ill fully drvalopcd, intact deciduous teeth are couivalent to the experiments on fully developed permanent teeth. The bone transformation which is produced by forces of known dir&ion is so characteristic that it can never be confused with any changes (shedding) which might be found in deciduous teeth that wcrc not subject to such forces. 3. The influence of masticatory function is a factor which helps our orthodontic procedures. This principle, laid tlow~J bp Angle. applies to the properly used labial arch just as well as to the lingual arch. 4. The Angle arch (pulling force) can work biologically just as well as the lingua.1 arch (pushing force). In both cases the orthodontist only is responsible for the kind of result obtained. 5. Besides the short intervals resulting from the use of intermittent, forces, our orthodontic cases are often markedly benefited 1)~ long intervals of rest during the t,reatment. 6. General growt,h and development do not take place continuously, hut. periodically. The stimuli which are constantly acting upon the jaws during growth and development, namely, t,he forces of mastication, arc of decidedly intermittent character. SORIC points to them and enlarge
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7. Only the gentlest, elastic, intermittent forces, acting always in a uniform direction, should be applied in practice,: such forces give the tissues time and opportunity to recotler from the orthodontic forces which, under all circumstances, are too strong if compared to the natural forces of growth and dcvelopmerit. Only after the use of such forces, during the interruptions of the treatment, can osteoid form on the side of pull, can there be the new formation of periodontal fibers and their attachment to the bone on the side of pressure, which processes prevent the loosening and soreness of the tooth and restore its resistance to ma.sticatory forces. Firmness and absence of soreness during treatment are the clinical criteria for properly gauged and properly applied forces.
8. A further rule of paramount importance for the undisturbed development of the tissue changes is the absolutely stabilized position of the appliance, in order to avoid jiggling and changes in the direction of the force. A change in the direction, once treatment is started, should be avoided if possible because, as I have already emphasized in 1911: ‘ ‘ From the characteristic transformation of the bone which accompanies the movement of teeth, we can draw the conclusion that before any treatment is started, the kind and direction of tooth movement has to be determined very carefully in order to avoid a later change of direction once movement has been started. If such a change is introduced into the treatment, the necessary repeated transformation of the bone must necessarily interfere with the definite reorganization of the bone structure and is no doubt responsible for many failures.” 9. If strong forces or sudden movements are used, the periodontal membrane is damaged by hemorrhages, tearing of fibers, and disturbance’ of circulation to such an extent that it can no longer react normally to mechanical stimuli. A periodontal membrane that has undergone such pathologic changes requires a long time to regain its normal physiologic properties and its power to react t,o functional stimuli. Rapid movement and the use of strong forces do not lead to more rapid progress in the treatment, but rather to the contrary. Not only the bone reaction is disturbed by strong and rapid forces, but also the resistance of the cementum is lessened by the disturbed circulation, and thus the cementum shows a definite disposition to resorption. Still another factor speaks against rapid and forceful orthodontic movcment. After the force has been discontinued, a tooth that has been moved slowly may return to some extent toward its previous position; but it will never go back entirely, because during the slow orthodontic movement a transformation This of the bone has taken place which will hold the tooth in its new position. transformation does not take place in rapid movement. The thickening of the alveolar bone plate, which always occurs under the influence of gentle forces of pressure and pull, accounts for the observation that anterior teeth may be moved labially over a great distance without danger of destroying the very delicate labial bone plate. Hence the rule that if considerable resistance is met during treatment, we should not increase the force, but merely prolong the time of the action of the force. Impatience
is the greatest enemy of the orthodontist.
I’rolonged
use of continuous
fores
has the same effect as f hc USPof strong
forces.
10. The tooth represents a single-arm lever with thr* fulcrun~ al the upc’b. In my specimens I could find along almost t Ire! cntiw lcugtl~ Of the root the tissue ehangcs produced by orthodontic forces, but with the most marked changes near the alveolar margin and the Icust marked near the nyrx. The IWIW immediatcl~ surrouslding the apex- does not show any c4~:mg~ The bone on t IIV xi& oi pressure c&mot ilct 31sa fillerurn for the loath, bctraua~ this lww is iti ;I of transformation. If very gent.le forces are applied. tlwe will bc only a sido of pressart~. but not an area of prcssurci. If an arca of pressure develops, then the tooth is transformed into a double-arm lever, and the apex must. necessarily d&ate in th<* direvt.ion opposite to the c’rown. This forced displac~emcnt of the apical fora.mc!n is a pathologic process. Il. The ostcoid formed during the intermissions is not eupablr of harminp the rementum, as has bet&n claimed by some authors, providing p~ntlt~, intermit,tent, dilSti(? force9 are used. 12. Occasional small resorptions of thr ccmentum are without significallcc~, since they arc almost invariably rcpairchd b? a reparative doposition of secondery ccmcntum. IX There is no such thing aa a definite amount of force which c~~uld be used for all et~ses and whic*h at the same time would rcprescnt an optimum for nil cases. SliItc*
I~EFERENCIW a. 27. Nerahon, T.. V.: Orthodontia b Its Relation to Dentistry, Dent. C~OSIIIOR, Drennber, 1930. 48. Oppler, Y.: Paradentose und Orthodontic wm Standpunkt der I’bcrl:tstung, Xahnarxtl. Rdsch., I>. 261, 193::. 29. Baner, W., and Lang, 3’. J. : l’lwr das \f'm~dcw~ dw Ziihne. ~~rtljsschr. F. Zulmh. 44: 321, 1928. 39. Korkhaus, G.: Die Grnndlagen der orthodontiwhen Behandlung de& Ih%wdrn GvBiswRin Scheff ‘a Handbuck d. Zabnheilkundo 6: 503, 1931. V~rSnderung der rnesiodistalen Brxiehngen der ~hvrc~~~~md Xl. Breitner, C.: Experimentelle untcren Zahnreihen, Ztsrhr. f. Stomatol. II. Gw, 1930. 32. .Johnson, A. T,eRog, Appleton. J. L., Jr., and Hittershofw, L. S.: ‘l’issw (‘llanges I urolred in Tooth ,Movcmcwt, I KTERNAT. J. OWIIOD. OHAI, &-au. (YFRanrou. 12: 8x!). 1926. 33. Hwzberg, R. T,.: Bono Changrs Tncident to Orthodontic Tooth Yovcnwnt in MIIII, .I’. :\. I). A. 19: 1777, 1932. 34. Mallard, H.: A Criticism of Oplwnhc+m ‘w l!U 1 Ihywrt, INTICRNAT. .I. ~HTIIOI~. ORAL 81:~~. & RADIOG. 14: 87% l!E8.
ligatures, which produced minute changes in the direction of pull and irregulariin the direction of force. In addition to the changes in the direction, the actual intensity of the force is also supposed to be of great importance. In the experiments of Schwarz” an attempt has been made t,o find definite figures for the intensit)y of orthodontic force. There arc several objections to the validit,> of such figures. In the first place, the force exerted by a finger spring will depend largely upon its position on the surface of the tooth. If the spring lies on the tuberculum it will have a tendency to become displaced in an incisal direction; thereby the intensity of force will be decreased. On the other hand, if the force of mastication displaces the lingual arch or the individual spring; in an apical direction, this will automatically increase the intensity o’f force, hence the necessity of cutting grooves in the teeth in Schwarz’s experiments to stabilize the posit,ion of the finger springs. Schwarz’s formula. for the biologic limit of orthodontic force reads as follows:” “ These experiments already show empirically that forces up to 20 grams intensity at the start still conform to the biological optimum, but that forces whose intensity at the start is greater, eve,,
tics
be it only slightly, are dangerous to the root, to say nothing of the intermittent character of such forces, which ha.s already been mentioned.” Schwarz’s formula, for the permissible force is as follows : “The capillary blood pressure in man and in most, mammalian animals is 15 to 20 mm. Hg per square centimeter, i.e., a pressure of 20 to 26 grams per square centimeter will just suppress the capillary pulsation. . . . the root surface of a fully developed mandibular premolar under pressure in lateral movement may roughly be estimated as being one square centimeter, whereby part of the pressure is taken up by the elastic soft tissues of the gingival tissues and the periosteum. . . . Taking into account a certain safety reduction we arrive, for single-rooted teeth, at a maximum permissible pressure averaging 15 to 20 grams per average root in tipping movement,. ” To this formula the objection must be raised that the area of the root surfact of t,he mandibular premolar which is under pressure in labial movement is only about one-ninth of a square centimeter. If a in Fig. 22 indicates the average width of a mandibular premolar (4.9 mm.) and b the average length of a root (13.8 mm.), the approximate surface of the labial periphery of the root is about 0.34 sq. cm., or in other words, a lit,tle more than 1L3sq. cm. If the tooth is moved labially, practically only the upper third of its surface is subject to pressure; so the figure for the square area under pressure would hare to be reduced to 0.11 sq. cm. The biologic limit of force would then have to
be reduced to about 3 grams. 1 realize that, I am not justified in t]Fing to gl1-t. nny definite figures for the forctl. l~cctr~tsi rrt!y wbcdufions w-e ilist l/s m rtclr 0 m.atter of conjectuw (1s fllosc of Schlorrr;. In addition 10 t hcscx mat hcmat ic*ill fallacies we know still less about the amount, of ~rrcssu~c whiclt is t;tkthrl 111)II~ tir(L tension of the fibers of the periodontal membrane on the side of pull and t-1~’th+: increased resist,ancc of the tissues on the side of prt~ar~ as the forcch incrc~asc~s. Therefore, it is inzposrilde bo gilye c’l*zn approximatel!/ ilr, figures t//c p rmis We must not forget tllat wt’ :I~Y’ sible total force auhich, should not be erccdcd. dealing with living tissues and that each i ndividua 1 has his particular individual reaction. Consequently, we cannot give au- standard figures 01’ data f‘ot’ ;ltl!therapy. N. W. Kingsley expressed this thought as follows: ‘. 12t~ntly t/1( statement has been made that a tooth should bc moved only a certain tlistarrcsc within a certa,in length of time in order to avoid complications: bllt it is cluitc, evident that any mathemat,ic formula for ~~hysiologic or pa.thologic~ c+hangrs i, absurd. ” Xalamon17 states. ,l . “We shall never be able to dctcrminc the force of tilt‘ angle arch mathematically, because WC arc dealing with living tissurs. .’ “Treatment. in orthodontia cannot be worked out as a mathematical formula. ’ ’ (Mershon.“) “The’ reaction of the organism is not only different in individuals. but it is also different in t,he same individual at different Cmes. ” (Winkler. I.*) A definite standard force is by no mcians the clue to success; 011 the> COIItrary, in addition to the knowledge about, the fundamental principle of appliances, which knowledge may be acquired by studyin g and reading, flr,e s~crel of success is only the extent of experience, the numb of cases trea,ted, und the number of successes ad failwres. Particularly the latter are the best teachers for us. Orthodontia is neither a technica, nor a mathematical science with definite formulas and regulations; orthodontia deals with living tissues which are subject to constant changes and for which there are no strict rules. 0 st>hodontia is purely a science of experience.* Another argument in dental literature deals with the position of the fulcrum. Some authors (Schwarz) claim that t,he fulcrum is located in the apical third of the root, others at the alveolar margin (Ba,uer and Lang2”), and still otlkers at t,he apex. However, sometimes one author has changed his opinions SOrat,idly that it is difficult to decide just what his latest opinion on the subject actuall~~ is. Schwarzg in 1928, stated: ‘ ‘A ligature producing gentle force will graduall) tip the tooth in such a way t,hat the fulcrum is located at the apex. If the same ligature is applied in the same place and in the same direction, but with greattir force? the fulcrum is located farther crownward. ” “Even ;L weCakforce In 1932, Schwarz12 comes to the following conclusion: can tip a tooth inside its alveolus around an axis situated above the apex. The comparatively small displacement of the apex nevertheless brings about slow *opp,pler 38 “In the use of our orthodontic tional factor, and therefore, we are still working concerned. despite the data given by Schwarz.”
appliances in the dark
WC hare to consider as far ns the intensity
the
constiluof form (5
The
Crisis
in
Orthodolztia
253
changes in the structure which are by far surpassed by the marginal changes, so that in favorable cases the apex can remain approximately undisturbed.” I have again proved the fact that the fulcrum is located at the apex, and I stated in 1911” and a.gain in 192918: “Under the influence of gentle forces we find that the bone is resorbed on the side of pressure by ost,eoclasts, while new bone is being built on the spicules on the side of pull. These changes can be found extending almost to the apex, which indicates that the crown does not deviate in an opposite direction from the root.” (See Figs. 3 and 15 of this article.) The results of Gottlieb, Breitner, and Johnson can be explained in only one way : The reason these authors found a deviation of the apex is that they worked with eery strong forces; thus their findings corroborate Schwarz’s conclusions, who also has worked with excessive forces. As far as t,he book of Gottlieb and Orban is concerned, the fact that excessive forces were used is indicated in the very title. BreitneF has restricted the application of his findings in animal experiments to man by stating: “It is known from orthodontic practice that teeth are tipped much less with very gentle forces and very slow movements.” Johnson, Appleton and Rittershofer32 also used excessive force in their experiments. since their springs, according to the examination by Dr. Irish Pittsburgh, exerted a continlrous force of 64 grams for twenty-six and forty days. This is a very great force, especially in view of t,he fact that it was continuous, and necessarily would bring about a deviation of the apex. Schwarz quot,es Johnson as proof of the correctness of his own statement, that in biologic treatment with continuous forces the apex always shows an excursion in the opposite direction of the crawn. But although Schwarz worked with much less force than Johnson, he found necrosis of the periodontal tissues and the presence of deep resorption in the dentin, which indicates that his force also was excessive. The fulcrum in tipping movement is located at the apex, if such gentle forces are applied that bone resorption cm keep pace with the movement of the tooth. If the force is so strong that on the side of pressure there is contact between root and bone, then this point of contact will of necessity act as the fulcrum, and the apex must deviate in the opposite direction of the crown. Whenever this condition is found, it is definite proof that the movement has been carried on faster than the bone on t,he side of pressure could be eliminated by resorption. Since all forces, ellen if in our opinion they are as gentle as possible, are still gl,eater than the forces of natm*al growth and bone development, the rule requliring the gentkst intemaittent forces, the use of intermissions during the active period of trentnzent, and the elivninntion of continuous forces cannot be overemphasized.
This opinion is supported by a statement of Korkhaus ? “ Strange as it may seem, we have not yet seen too weak forces in orthodontia, because even the most. gentle force brings about some form of reaction; the least amount of force has not yet, been determined. ”
My findings have also been corroborated in the study of ii human tool Ii following orthodontic trcatmc~ut. which was pnblisht~tl }),I, Ile~zbr~~~~.‘~” I((* tt~tr fomld ncilr the apex 011 th side of’ pull ‘. nt~wl~- formc~d bent: ;11*1xriptl iir I tic. general direction Of tllc fibt>Y bmldlc~s 01’ ttlt, ~)t~~iOdOtlf ill rric~rrrhr;r ttt’ iii 1 hi-. region. ” kltlc forctY3 had hYl1 usctl. ilutt colrsc‘c(uclltl~~ 111
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vessels aud IICWW ;tt that :IIWS is ncvc~ tiisturbccl. :Rcgar*tllcw of 1 II(’ r+n1r$ys that may occur in the position during t ht> ptrysiologic ~~rocessc~s 01’ qowth ~1111 movrment, the apex will remain stationary. “The t,jl)ping of teeth is OII~J-;III evidence of 011~‘s inability t.o handle iI dt~li~at(~ ;r~~l)liancr ;Illtl wtl t~spt*c~ssiotlot OI~P’Slack of knowledge of growing and dc~vclo~~ingprocesses. ” (Iuerxhon. 1 The correctness of m,v opinion WII b(’ R~UWII tl(Jt only by tlic’ ~~hotornitdrographs (Figs. 2. 3, and 1.5) of thi 5 article hut also by ;i siml)lc espt+rnc~nt. If it is trur-and we know it is true-thf btmc watts to tllcs gc.ntlw1 t‘owt~ 1)~ resorption and thus seems to rccedc from the force, then the raoot ulil>v f.~areprosented by a stick which stands with tnl(’ ~ntl OJI s till)lc ;r~lti the ot hcsr talltl tit’ which is moved laterally without me&n% an! resistance during this trm\:(~mt’n~. Then the lower thnd of the stick will rtmaill in its ~)l;rcc~witho(lt ;rn,v ckviatit)tr ita the opposite> dirwtimi of tl~r 11ppcr PIIJI, All authors hare agrec~l that cxperimc>nts on models or mathematical formulas cannot prove the position of the fulcrum of thtl root. \Vh~th~r Schwarz and other authors used soft plaster, ruhbrr; soft clay, or any otht>r plastic, mirterial for their experiments to prove t,lie cxcursioli of the ;ipcs ii1 il direct,ioir opposite to that of the crown, tlrc?y roll o~yrZookcd 1//c. i)~l.~~tcr~t /‘c,cf fl~crl f//f. CkongcS
in.
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bow, udzich rcncts to 111~gvntlcst stimwli II~C%the wndi~io~b of w/l icll ~~~~d~~t~qof’s basic chcrny~s (IS SOONIIS an!/ force is csc~?(d upon if. If the movement of’ the t&h is not t’astcr ttta]J the tr.unsi’orrnatioll of t ht. bone can take place, in other words, if lhc tooth does not mret any rt~sistanc*c~ iri the direction of its movt~mcnt, Ihen the changes in hone hi, no mea7ls co1 respond t,o those produced cspcrimcntally by Schwarz. The fact that Schwarz considers the excursion of the a~lex in a direction opposite to the direction of the crown as a tdorrect procedure in orthodontic tooth moveme77t proves, in itself that, he has used too strong forces. HP illSO Stllt(‘SZ “Any f0rc.e that displaces the apex must al first dt9troy the xpica t fibclrs which are the natural anchorage of the apex.” If teeth have inadvcrlcntly been tipped h> pcntle forces during or1 hodontic~ treatment in such a \\-a>that thcrt> is no tlcviation of the apex-, t-hen f77ndion and other natural forccx will gradnall~- st raightcn the teeth >lnd restore them to their normal position as soon as the orthodontic appliance has been removed. If, however, the apex has deviated, if the t&h have been tipped too rapidly ant1 estensivcly. then natural forces will not he sufficient, to restore the tcdh to t tit4v
normal position, and orthodontic procedures will become necessary to correct their position, which will necessitate a chamge in the direction of movement and risk the danger of root resorption. There can be no doubt but that in orthodontic treatment displacement of the apex opposite to that of the crown is not a biologic process. In discussing Johnson’s animal experiments,“” Boedecker expressed t,he following opinion concerning the diffcrcnce in the findings of Johnson (excursion of thr apex) illid my own findings (apex stationary) : “Why this should be SO is difficult to say; but, if we think of the matter logically, we would suppose that Oppenheim is correct, that it was a single-arm lever, and I believe the answer to the questiort is the degree of pressure used in moving a tooth. . . .” Stallard”” has expressed the opinion that I am not justified in drawing conclusions from my experiments as to the changes in man, because I did not move teeth from a wrong position to a correct one, but from a correct position to an incorrect, one. I have already answered this criticism by saying that there are no monkeys, with malocclusions that can be corrected. Furthermore the recent investigations of Hcrzbcrg Q have shown that the findings in human teeth are analogous to those in monkeys. A basic difference now between the various orthodontic schools is their attitude toward the problem whether continuous or intermittent forces should be used. Many investigators, among them prominent physiologists, havn sta.tcd that devclopmcnt and qcncral growth arc not continuous, but. intermittent processes. Also, for the structural arrangcmcnt of the jaw, intermittent forces are of paramount importance, that is, the effect of occlusion and mastication. If nature works with intermittent forces and if the principle of the best form of treatment is imitation of nature, with what justification has intermittent orthodontic trcatmcnt been called ‘ ‘ unbiologic ’ ’ 1 The question whether intermittent or continuous forces are the best for orthodontia is perhaps best cspressed in a letter written to me on this subject by Professor Salamon of Budapest. He states: “As far as the problem, ‘intermittent force-biologic action, ’ is concernnd, one thing is certain: it has never been proved experimentally that intermittent forces are ‘unbiologie.’ This has only been stated in order to support the assumption that continuous forens are ‘biologic. ’ In my opinion the latter statement, too, has never been proved but has only been broadcast as truth. I think I can characterize t,his problem as follows: there are no ‘biologic’ or ‘unbiologic’ appliances or methods, but onI?/ ‘biologic’ or ‘unbiologic’ ortkodontists. With every appliance one can work biologically as well as unbiologicallp. T do not think that this problem can be decided histologically, and Schwarz’s theory of capillary pressure also seems to be open to criticism. ” In none of the textbooks of orthodontia which have appeared within the last few years do we find proof of the statements contained in them by a dcmonstration of pewnanent results (Dewey, Gallavardin, Herbst, Izard, Kantorowicz, Korkhaus, Kranz, I&her, McCoy, Oppler, Pfaff, Quintero, Simon, Walkhoff, and Winkler). I do not include Angle and Case in this list, because I ‘nave been
256
ticular method; I have tried all new methods and appliances of the ~WI: years with varying results. and 1 do not hc3ilirtc to wcdvcpt improvemcrrts of dci methods, as long as these improvements art’ snfficientl,v justified by clinical rt%dts. ht t!Jf? pe”nJnf3eJJt results tlJat IliJ\‘r brcan reportetl so far by the* advocates of the J~ern nJr~tlJotls are so swmA that I haw swn no ~-P~SOII to discont,inrxe my method of treatment, as tli(!tatctl by the findings in my irnimal experiments; t,lic permanciic~y of my results warrants this pcrsist~cnt:~. There is no “modem ” and IJO “oiit-of-(late” t~rtl~t~dt~r~tia. There is t-ml, an orthodontia which is successful or one that cannot rtlport prmanrnt results. l‘hc repeated cluotIng of comnlonplaces. such as biologic reaction only with continuous forces, the danger of osteoid ill intt~rmittcnt forcc>s, or the ;tppii:1ncdl1 which causes only I)rcssurt~, should ilt I:ist l)(L tliscontinucd. This does not t’oI3tribute to the progress of orthodont-iii. My conclusions of 191 1 do iiot riced any modification. All I can do is add ~Jpon them in sc>vcral rcspec’tx : I. The histologic changes which were clescribetl more t,han twenty years ago as the result of the activity of osteoclasts itlid ostcoblasts under the influence of gentle, intermittent, elast,itJ, orthodontic forces still retain their validity today. The same is true of the reaction of the tissues to strong forces (ort.hodontically speaking). 2. The animal experiments carried out ill fully drvalopcd, intact deciduous teeth are couivalent to the experiments on fully developed permanent teeth. The bone transformation which is produced by forces of known dir&ion is so characteristic that it can never be confused with any changes (shedding) which might be found in deciduous teeth that wcrc not subject to such forces. 3. The influence of masticatory function is a factor which helps our orthodontic procedures. This principle, laid tlow~J bp Angle. applies to the properly used labial arch just as well as to the lingual arch. 4. The Angle arch (pulling force) can work biologically just as well as the lingua.1 arch (pushing force). In both cases the orthodontist only is responsible for the kind of result obtained. 5. Besides the short intervals resulting from the use of intermittent, forces, our orthodontic cases are often markedly benefited 1)~ long intervals of rest during the t,reatment. 6. General growt,h and development do not take place continuously, hut. periodically. The stimuli which are constantly acting upon the jaws during growth and development, namely, t,he forces of mastication, arc of decidedly intermittent character. SORIC points to them and enlarge
The
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7. Only the gentlest, elastic, intermittent forces, acting always in a uniform direction, should be applied in practice,: such forces give the tissues time and opportunity to recotler from the orthodontic forces which, under all circumstances, are too strong if compared to the natural forces of growth and dcvelopmerit. Only after the use of such forces, during the interruptions of the treatment, can osteoid form on the side of pull, can there be the new formation of periodontal fibers and their attachment to the bone on the side of pressure, which processes prevent the loosening and soreness of the tooth and restore its resistance to ma.sticatory forces. Firmness and absence of soreness during treatment are the clinical criteria for properly gauged and properly applied forces.
8. A further rule of paramount importance for the undisturbed development of the tissue changes is the absolutely stabilized position of the appliance, in order to avoid jiggling and changes in the direction of the force. A change in the direction, once treatment is started, should be avoided if possible because, as I have already emphasized in 1911: ‘ ‘ From the characteristic transformation of the bone which accompanies the movement of teeth, we can draw the conclusion that before any treatment is started, the kind and direction of tooth movement has to be determined very carefully in order to avoid a later change of direction once movement has been started. If such a change is introduced into the treatment, the necessary repeated transformation of the bone must necessarily interfere with the definite reorganization of the bone structure and is no doubt responsible for many failures.” 9. If strong forces or sudden movements are used, the periodontal membrane is damaged by hemorrhages, tearing of fibers, and disturbance’ of circulation to such an extent that it can no longer react normally to mechanical stimuli. A periodontal membrane that has undergone such pathologic changes requires a long time to regain its normal physiologic properties and its power to react t,o functional stimuli. Rapid movement and the use of strong forces do not lead to more rapid progress in the treatment, but rather to the contrary. Not only the bone reaction is disturbed by strong and rapid forces, but also the resistance of the cementum is lessened by the disturbed circulation, and thus the cementum shows a definite disposition to resorption. Still another factor speaks against rapid and forceful orthodontic movcment. After the force has been discontinued, a tooth that has been moved slowly may return to some extent toward its previous position; but it will never go back entirely, because during the slow orthodontic movement a transformation This of the bone has taken place which will hold the tooth in its new position. transformation does not take place in rapid movement. The thickening of the alveolar bone plate, which always occurs under the influence of gentle forces of pressure and pull, accounts for the observation that anterior teeth may be moved labially over a great distance without danger of destroying the very delicate labial bone plate. Hence the rule that if considerable resistance is met during treatment, we should not increase the force, but merely prolong the time of the action of the force. Impatience
is the greatest enemy of the orthodontist.
I’rolonged
use of continuous
fores
has the same effect as f hc USPof strong
forces.
10. The tooth represents a single-arm lever with thr* fulcrun~ al the upc’b. In my specimens I could find along almost t Ire! cntiw lcugtl~ Of the root the tissue ehangcs produced by orthodontic forces, but with the most marked changes near the alveolar margin and the Icust marked near the nyrx. The IWIW immediatcl~ surrouslding the apex- does not show any c4~:mg~ The bone on t IIV xi& oi pressure c&mot ilct 31sa fillerurn for the loath, bctraua~ this lww is iti ;I of transformation. If very gent.le forces are applied. tlwe will bc only a sido of pressart~. but not an area of prcssurci. If an arca of pressure develops, then the tooth is transformed into a double-arm lever, and the apex must. necessarily d&ate in th<* direvt.ion opposite to the c’rown. This forced displac~emcnt of the apical fora.mc!n is a pathologic process. Il. The ostcoid formed during the intermissions is not eupablr of harminp the rementum, as has bet&n claimed by some authors, providing p~ntlt~, intermit,tent, dilSti(? force9 are used. 12. Occasional small resorptions of thr ccmentum are without significallcc~, since they arc almost invariably rcpairchd b? a reparative doposition of secondery ccmcntum. IX There is no such thing aa a definite amount of force which c~~uld be used for all et~ses and whic*h at the same time would rcprescnt an optimum for nil cases. SliItc*
I~EFERENCIW a. 27. Nerahon, T.. V.: Orthodontia b Its Relation to Dentistry, Dent. C~OSIIIOR, Drennber, 1930. 48. Oppler, Y.: Paradentose und Orthodontic wm Standpunkt der I’bcrl:tstung, Xahnarxtl. Rdsch., I>. 261, 193::. 29. Baner, W., and Lang, 3’. J. : l’lwr das \f'm~dcw~ dw Ziihne. ~~rtljsschr. F. Zulmh. 44: 321, 1928. 39. Korkhaus, G.: Die Grnndlagen der orthodontiwhen Behandlung de& Ih%wdrn GvBiswRin Scheff ‘a Handbuck d. Zabnheilkundo 6: 503, 1931. V~rSnderung der rnesiodistalen Brxiehngen der ~hvrc~~~~md Xl. Breitner, C.: Experimentelle untcren Zahnreihen, Ztsrhr. f. Stomatol. II. Gw, 1930. 32. .Johnson, A. T,eRog, Appleton. J. L., Jr., and Hittershofw, L. S.: ‘l’issw (‘llanges I urolred in Tooth ,Movcmcwt, I KTERNAT. J. OWIIOD. OHAI, &-au. (YFRanrou. 12: 8x!). 1926. 33. Hwzberg, R. T,.: Bono Changrs Tncident to Orthodontic Tooth Yovcnwnt in MIIII, .I’. :\. I). A. 19: 1777, 1932. 34. Mallard, H.: A Criticism of Oplwnhc+m ‘w l!U 1 Ihywrt, INTICRNAT. .I. ~HTIIOI~. ORAL 81:~~. & RADIOG. 14: 87% l!E8.