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A Comparative Study in Root Resorption in Permanent Teeth*
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The Journal of the American Dental Association
needle. T h e relaxed muscles o f the bu c cal orifice a llo w the corn er o f the m outh to be retracted sufficiently far laterally and posteriorly to perm it the needle to fo llo w along the zygom atic surface o f the m axilla instead o f being carried into the interior o f the pterygom andibular fossa, w here are located num erous arteries and venous plexuses. T h e needle is usually-in serted m uch deeper than is necessary. T h e attachment o f the structures form in g the buccal forn ix is very high in this region. Insertion o f the needle n ot m ore than h alf an inch beyond the upper attach ment o f the cheek opposite the second and third m olars w ill effectively block the branches o f the posterior dental nerve. In extensive cysts in volvin g the entire ram u s; in fractures in volvin g the ramus, coron oid process or condyloid process; in depressed fractures o f the zygom atic a r c h ; in infection o f this region, an exact kn ow led ge o f the pterygom andibular fossa is o f an inestimable im portance. H eretofore, the study o f the pterygo m andibular fossa has been made by the usual dissection methods, w hich, w hile
com m endable, leave much to be desired in gaining a surgical appreciation o f this little kn ow n part o f the body. A n atom ic reconstructions made from actual dissec tions show ing the relations o f the muscles and principal structures are invaluable aids in gaining fam iliarity w ith the field. O n reconstructions o f vulcan ite and m e tallic castings, such as are show n in the accom panying illustrations, operative technic may be planned in advance or clearly dem onstrated in teaching. T h e pterygom andibular fossa is a w elldefined region w h ich peculiarly belongs to dentistry. T h e muscles form in g its boundaries m otivate the m andible. T h e blood coursing through its arteries sup plies the oral structures. T h e nerves passing through it are concerned m ore than any other w ith condu ctive anes thesia. T h e pterygoid plexus o f veins, when* punctured, furnishes one o f the chief com plications. In ord er to prevent and to correct u ntow ard su rgical com p li cations in volvin g this fossa, its anatomy should be clearly understood by every oral surgeon.
A C O M P A R A T IV E S T U D Y IN R O O T R E SO R P TIO N IN P E R M A N E N T TEETH* B y C . E. R U D O L P H , D .D .S ., M in n ea p olis, M in n .
T w o u ld be impossible to make even a close guess as to w hen men first o b served the results o f root absorption. N o dou bt, the loss o f the deciduous teeth w ent on fo r years w ith ou t num ber before men finally understood that at one time
I
*Read before the Section on Orthodontia at the Seventy-Seventh Annual Session o f the American Dental Association, New Orleans, La., Nov. 6, 1935. Jour. À .D .A ., Vol. 23, M ay, 1936
the tem porary teeth had roots similar to those o f the perm anent teeth. W e are not so m uch interested in the ch ron ology o f the different steps in the natural loss o f the deciduous teeth as ob served by students. W e have the facts n ow as related by scientific observers and, generally speaking, m ost people in the civilized w o rld understand them . It is possible that facts yet to be discovered
Rudolph— Comparative Study in Root Resorption may change some o f the theories o f the present. Students o f histology and anat om y are ever on the alert fo r n ew in form ation . W e kn ow considerably less about ro o t resorption in permanent teeth. In com parison, little actual scientific study o f permanent root resorption has been carried on to date. Q u ite naturally, the advent o f the roentgen rays has m ade it possible to make certain observations, but, strangely enough, fe w men have given a great deal o f thought to the sub ject. A t present, a scattered, lim ited num ber are interested enough to give o f their best efforts to the observance and possible explanation o f the phenom enon. It is n ot the purpose o f this paper to review the bibliography pertaining to the su bject o f root resorption, but rather to report some statistical findings o f the w ork done at the School o f D entistry, U niversity o f M innesota. In passing, it is a pleasure to com plim ent those men w h o have been, and w h o are, interested in the subject to the degree o f having laid at least a partial foundation fo r fu r ther study. Perhaps it w o u ld be w ell to attem pt a w ord picture o f root form ation and root resorption. Some may have forgotten that, in a child o f 10 years, the roots o f a num ber o f permanent teeth that are in place in the arch have not reached their m axim um size. F o r instance, the average first bicuspid, w hich may be erupted at this age, may be, and usually is, about three-fourths the length it w ill be w hen fu lly m atured. T h e g row th o f the root proceeds in such a manner as to make a crater-shaped opening w here the pulp o f the tooth enters. Peripheral g row th con tinues tow ard the apex until the crater shaped opening is closed w ith the excep tion o f the foram en. F inal developm ent o f the root proceeds on the pulpal w a ll until it is fu lly form ed. In view in g a roentgen-ray picture o f a root such as I
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have described, one w o u ld notice this crater-shaped opening at the unfinished end o f the root. T h e size o f the opening depends on the point o f developm ent at w hich the picture w as taken. Resorption takes place in a num ber o f w ays. T h e usual one, w hich is most easily noted, is that w hich seems to attack the root tip and travel tow ard the crow n o f the tooth, m aking w hat w e have term ed a “ shed r o o f” effect to the root. T h e por tion o f the root nearest the pulp appears to be the last to give w ay. T h is process is exactly opposite to that o f root form a tion. Resorption o f permanent roots may be the result o f other stimuli than tooth m ovem ent by appliances. N o t in fre quently, loss o f root structure is due to im paction pressures. W h e n R ich m on d or other d ow el crow ns are used, resorption occurs frequently. R esorption in this type o f case may be irregular and jagged, w ith no typical features such as are fou nd in orthodontia. In m y judgm ent, there are num erous other stim uli causing resorption than those m entioned. T h ese are simply examples. I t became evident, by casual observa tion at first, in the orth odontia clinic at M in n esota U niversity that the incidence o f resorption o f treated perm anent tooth roots w as frequent enough to w arrant fu rther study. W e w ere on ly m ildly in terested, until it occurred to us that per haps a com parison between persons w h o had had treatm ent and those w h o had had n o treatm ent m ight be enlightening. A ccord in g ly , a large num ber o f fu ll m outh roentgenogram s w ere studied. A ll o f the fu ll m outh films taken in the diag nostic clin ic over a given period, exclu d in g on ly those w hich had a history o f orth odon tic treatment, w ere taken as a sample. T h ese roentgenogram s, repre senting all age groups fro m 7 to 70 years, num bered 4,560.
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The Journal of the American Dental Association
T h e incidence o f resorption from all causes in this group is 12.6 per cent o f the num ber o f cases in volved. W e have tried to classify these affected teeth ac cord in g to w hat m ight be the cause fo r resorption in each case. W e realize the
appliances w ere em ployed, no one type predom inating. T h e average age o f pa tients treated by the postgraduate group w as a trifle greater than that o f the regu lar undergraduate clin ic patients. T h e incidence o f resorption in both groups is
possibility o f error in the procedure, since w e have no histories to v erify ou r ju d g ment. T h e data presented from the treated orth odon tic group are gathered in the orth odontic undergraduate and postgrad uate clinics o f the Sch ool o f D entistry, U niversity o f M inn esota. T h e operating has been and is being carried on by the senior students under the direct super vision o f instructors. T h e type o f appli ance used in m ost cases is the simple la bial arch w ith bands m ade directly in the m outh and tied to the arch by w ire liga tures. Bite-planes, both vulcanite re m ovable and m etal fixed, are used w here indicated. In term axillary and intram axillary forces by rubber bands are used as cases require them. B ite-blocks and splints are used infrequently. M ov em en t o f the teeth is usually co m paratively slow . Student w ork makes steady progress in m ovem ent difficult in com parison to results obtained by most experienced practitioners. Q u ite neces sarily, w ith inexperienced operators such as the undergraduate student body, there w ou ld be a larger incidence o f error in m aking adjustm ents in actual treatment even under supervision, and this fact may have some bearing on the percentages. T h e num ber o f orth odon tic cases used in this study is 439. T h is num ber consti tutes all the cases treated and under treatment fo r a given time in the teach in g clin ic. T h e large m a jority have been o r are being treated by undergraduate students during the senior year. A fe w have been treated by postgraduate stu dents o f the same time period. In those treated by the latter, various types o f
essentially the same. In the fo llo w in g discussion, the orth o dontic group w ill be understood to in clude all cases treated or under treat m ent fo r the designated time o f this study. R outine diagnosis o f each o f the orth o dontic cases includes a fu ll m outh roentgen-ray exam ination. F o r children in the clinic, a fu ll m outh roentgen-ray exam ination calls fo r from tw elv e to fourteen films as the case m ay require. A t oneyear intervals du ring treatm ent, fu ll m outh roentgenogram s w ere taken o f each case. T h e total num ber o f begin ning roentgen-ray exam inations w as 439. T h e total num ber o f second roentgeno grams, those taken at the end o f the first year o f treatm ent, w as 439. T h e num ber at the second year o f treatm ent was 277 ; the num ber at the third year o f treatment, 121, and the num ber at the end o f the fourth' year, 34. N o perma nent root resorption w as noted in the be ginning roentgen-ray exam ination. A t the end o f the first year o f treatment, 48 .74 per cent o f the total num ber w ere m ore or less affected. T h e third examina tion, w hich includes 277 cases, showed resorption in 74.63 per cent o f these cases. T h e age range o f these patients w as 7 to 21 years. T h e average age o f patients at the beginning o f treatm ent w as ap proxim ately 10 years. D ivision o f the 439 patients show s 209 male and 23 0 fem ale. U p to the time these data w ere tabulated, 135 cases show no resorption ; 3 0 4 cases show resorption ; 209 males show a percentage o f resorption o f 64 .59 ; 2 3 0 females show a percentage o f resorption o f 73.47. T h e
Rudolph— Comparative Study in Root Resorption com bined group o f 439 cases show s a per centage o f resorption o f 69.24. In ex planation o f the foregoin g statement, o f the 135 cases show ing no resorption, som e o f these are finished and som e are yet under treatment. A lso, no attem pt has been made as yet to estimate the de gree o f resorption in this series o f cases. T h e percentages show n deal w ith the num ber o f cases in volved and not w ith the num ber o f teeth. T h e con trol group, or those studied w h o had no history o f orth odon tic treat ment, ranged in age from 7 to 79 years. F rom 7 to 30 years inclusive, there are 1,609. F rom 31 to 55 years inclusive, there are 2,557. F rom 56 to 79 years inclusive, there are 394. In taking the age grou p o f these com parable to the age group o f the orthodontia patients studied, there are from 7 to 21 years o f age, 739 cases. T h irty-eigh t o f the 739 cases show resorption from some cause, a per centage o f 5.14. A ll o f these cases o f re sorption are fou nd in the age group from 13 to 21 years inclusive. T w en ty-th ree o f these cases o f resorption are to be fou n d at the ages o f 18 to 21 years in clusive. In the beginning, no one o f the 439 orth odontia cases showed resorption o f any permanent roots. O f the 739 cases w ith no orth odontic history, no pa tient 13 years o f age or under show ed resorption. I t is interesting to note the distribu tion o f resorption in each o f the groups studied. In the con trol group (those hav ing no orth odontic treatment h istory ), w e find that the tooth least apt to be affected is the lo w e r cuspid. T h e inci dence o f resorption in this tooth in the entire group is 0.55 per cent. T h e other teeth in order o f their incidence o f re sorption a r e : low er lateral, low er central, upper cuspid, low er bicuspids, upper m o lars, low er molars, upper central incisors, upper lateral incisors and upper bicus
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pids. N o definite explanation fo r this curious sequence can be offered. It is not know n w h y the upper bicuspids are a f fected m ore often than the other teeth. It w ill probably take a great deal o f study o f anatom y and histology, as w e ll as tooth analysis, along w ith study and experim entation in functional stresses throughout the m outh, to arrive at an ac ceptable explanation. Q u ite logically, the percentage o f resorption runs high est between the ages o f 25 and 45 years. In this interval, too, the largest num ber o f erupted perm anent teeth have been exposed to disease and treatm ent by restorative procedures. Betw een these ages, people appear to have the largest num ber o f serious dental operations per form ed. It seems that, in many cases, resorption is directly attributable to the dental restoration in and on the teeth. T o return to the orth odontic g ro u p : T h e percentage o f resorption runs as fo l low s, beginning w ith the least affected tooth and nam ing the teeth in o rd e r: low er bicuspids, upper bicuspids, upper first m olar, low er cuspid, low er first m olar, upper cuspid, low er lateral in cisor, low er central incisor, upper central incisor and upper lateral incisor. R e sorption is m ost prevalent in the upper and low er anterior fou r teeth. T h ese teeth' suffer the greatest am ount o f root loss also. A lth ou g h the curve o f esti mated tissue loss has n ot yet been w orked out, it takes but little study to be con vinced that the anterior fou r teeth, up per and low er, sustain the largest loss. B y far the largest num ber o f cases o f resorption occu r in patients treated du r ing and after the age o f 11 years. T h e percentage o f resorption increases rapidly from this age to the age lim it o f treat m ent in ou r clinic. A lth ou g h the data available have not yet been tabulated, it seems apparent that gentle forces on teeth not fu lly form ed have little effect on
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The Journal of the American Dental Association
their predestined size. In other w ords, the teeth not fu lly form ed seem to keep on grow in g n orm ally w hen treated du r ing the naturally fast g row th periods o f the child, especially in the youn ger age lim its o f childhood. It is thought that some teeth may be stunted in length g row th if treated vigorou sly du ring the later age lim its o f childhood. T h e r e is som e evidence o f this phenom enon. M a n y questions arise in the study and analysis o f these groups. I am attem pting to prove on ly that resorption occurs m ore frequently in patients treated orthodontically than in those o f the same age group w h o have had no orth odon tic treatment. B oth the groups studied are, as nearly as w e can tell, in the same eco nom ic group and on the same health level. O u r data are as yet m eager in relation to the largeness o f the problem . Y ears o f study and com pilation o f m any data are necessary. O n e intriguing phase, o f the m any one m ight discuss, is the actual damage the resultant resorption really causes. N o data bearing on this are available. So far, w e can on ly guess. I t is log ical to conclu de that a cuspid root foreshortened one-half w ill n ot carry a definite type o f restoration as lon g as one n ot so affected, other conditions being equal. O n the other hand, there is on ly a con jectu re as to the am ount o f dam age to the m outh and health o f the patient that m ight have occurred had n o orth odon tic treatm ent been given. T h o se o f us w h o have prac ticed general dentistry sufficiently lon g to gain a proper background o f experi ence can recall and visualize m any cases wherein the w reck in g o f the masticatory apparatus seemed due to m alocclusion alone. It is possible that the foreshorten
ing o f a fe w roots, o w in g to orth odon tic treatment, m ight n ot in these cases have been too large a price to pay fo r other advantages gained by treatm ent. T h is statement is n ot m eant to condon e the resultant resorption, fo r it m ust be ou r business to avoid such results in treat ment. T h e question is, h o w ? T h e w ork at the U n iversity o f M in nesota C lin ic is reported fo r the reason that it is the beginning o f a thorough questioning o f methods o f teaching and practice o f orth odontia and n ot an in dictm ent o f the practice o f orth odontia. W e w o u ld be happy to consult w ith any individual o r institution analyzing this problem w h o believes that a scientific analysis is desirable and necessary. I shall m ention ju st a fe w o f the many angles o f the problem that are being, or perhaps should be, studied. T h e correct age at w hich to have treatm ent is a broad field o f study. P roper diet constitutes an in triguing field. T h e type o f appliance and rapidity o f m ovem ent need much study. T h e com bination o f forces to be applied at a given time m ight in itself keep an investigator busy fo r years. N o attem pt to state these phases o f .the problem in the order o f their im portance is intended. A thorough study o f the problem as a w hole by a com petent group is necessary in ord er that proper research can be carried ou t and the resorption o f roots due to orth odon tic treatm ent can be com pletely elim inated. I t is n ot m y belief that the phases m entioned are by any means all the angles o f the subject to be studied. Some o f these fields are be ing investigated n o w and every en cou r agem ent should be given the m en and w om en w h o are devotin g their tim e and energy to such service.
The Journal of the American Dental Association
needle. T h e relaxed muscles o f the bu c cal orifice a llo w the corn er o f the m outh to be retracted sufficiently far laterally and posteriorly to perm it the needle to fo llo w along the zygom atic surface o f the m axilla instead o f being carried into the interior o f the pterygom andibular fossa, w here are located num erous arteries and venous plexuses. T h e needle is usually-in serted m uch deeper than is necessary. T h e attachment o f the structures form in g the buccal forn ix is very high in this region. Insertion o f the needle n ot m ore than h alf an inch beyond the upper attach ment o f the cheek opposite the second and third m olars w ill effectively block the branches o f the posterior dental nerve. In extensive cysts in volvin g the entire ram u s; in fractures in volvin g the ramus, coron oid process or condyloid process; in depressed fractures o f the zygom atic a r c h ; in infection o f this region, an exact kn ow led ge o f the pterygom andibular fossa is o f an inestimable im portance. H eretofore, the study o f the pterygo m andibular fossa has been made by the usual dissection methods, w hich, w hile
com m endable, leave much to be desired in gaining a surgical appreciation o f this little kn ow n part o f the body. A n atom ic reconstructions made from actual dissec tions show ing the relations o f the muscles and principal structures are invaluable aids in gaining fam iliarity w ith the field. O n reconstructions o f vulcan ite and m e tallic castings, such as are show n in the accom panying illustrations, operative technic may be planned in advance or clearly dem onstrated in teaching. T h e pterygom andibular fossa is a w elldefined region w h ich peculiarly belongs to dentistry. T h e muscles form in g its boundaries m otivate the m andible. T h e blood coursing through its arteries sup plies the oral structures. T h e nerves passing through it are concerned m ore than any other w ith condu ctive anes thesia. T h e pterygoid plexus o f veins, when* punctured, furnishes one o f the chief com plications. In ord er to prevent and to correct u ntow ard su rgical com p li cations in volvin g this fossa, its anatomy should be clearly understood by every oral surgeon.
A C O M P A R A T IV E S T U D Y IN R O O T R E SO R P TIO N IN P E R M A N E N T TEETH* B y C . E. R U D O L P H , D .D .S ., M in n ea p olis, M in n .
T w o u ld be impossible to make even a close guess as to w hen men first o b served the results o f root absorption. N o dou bt, the loss o f the deciduous teeth w ent on fo r years w ith ou t num ber before men finally understood that at one time
I
*Read before the Section on Orthodontia at the Seventy-Seventh Annual Session o f the American Dental Association, New Orleans, La., Nov. 6, 1935. Jour. À .D .A ., Vol. 23, M ay, 1936
the tem porary teeth had roots similar to those o f the perm anent teeth. W e are not so m uch interested in the ch ron ology o f the different steps in the natural loss o f the deciduous teeth as ob served by students. W e have the facts n ow as related by scientific observers and, generally speaking, m ost people in the civilized w o rld understand them . It is possible that facts yet to be discovered
Rudolph— Comparative Study in Root Resorption may change some o f the theories o f the present. Students o f histology and anat om y are ever on the alert fo r n ew in form ation . W e kn ow considerably less about ro o t resorption in permanent teeth. In com parison, little actual scientific study o f permanent root resorption has been carried on to date. Q u ite naturally, the advent o f the roentgen rays has m ade it possible to make certain observations, but, strangely enough, fe w men have given a great deal o f thought to the sub ject. A t present, a scattered, lim ited num ber are interested enough to give o f their best efforts to the observance and possible explanation o f the phenom enon. It is n ot the purpose o f this paper to review the bibliography pertaining to the su bject o f root resorption, but rather to report some statistical findings o f the w ork done at the School o f D entistry, U niversity o f M innesota. In passing, it is a pleasure to com plim ent those men w h o have been, and w h o are, interested in the subject to the degree o f having laid at least a partial foundation fo r fu r ther study. Perhaps it w o u ld be w ell to attem pt a w ord picture o f root form ation and root resorption. Some may have forgotten that, in a child o f 10 years, the roots o f a num ber o f permanent teeth that are in place in the arch have not reached their m axim um size. F o r instance, the average first bicuspid, w hich may be erupted at this age, may be, and usually is, about three-fourths the length it w ill be w hen fu lly m atured. T h e g row th o f the root proceeds in such a manner as to make a crater-shaped opening w here the pulp o f the tooth enters. Peripheral g row th con tinues tow ard the apex until the crater shaped opening is closed w ith the excep tion o f the foram en. F inal developm ent o f the root proceeds on the pulpal w a ll until it is fu lly form ed. In view in g a roentgen-ray picture o f a root such as I
823
have described, one w o u ld notice this crater-shaped opening at the unfinished end o f the root. T h e size o f the opening depends on the point o f developm ent at w hich the picture w as taken. Resorption takes place in a num ber o f w ays. T h e usual one, w hich is most easily noted, is that w hich seems to attack the root tip and travel tow ard the crow n o f the tooth, m aking w hat w e have term ed a “ shed r o o f” effect to the root. T h e por tion o f the root nearest the pulp appears to be the last to give w ay. T h is process is exactly opposite to that o f root form a tion. Resorption o f permanent roots may be the result o f other stimuli than tooth m ovem ent by appliances. N o t in fre quently, loss o f root structure is due to im paction pressures. W h e n R ich m on d or other d ow el crow ns are used, resorption occurs frequently. R esorption in this type o f case may be irregular and jagged, w ith no typical features such as are fou nd in orthodontia. In m y judgm ent, there are num erous other stim uli causing resorption than those m entioned. T h ese are simply examples. I t became evident, by casual observa tion at first, in the orth odontia clinic at M in n esota U niversity that the incidence o f resorption o f treated perm anent tooth roots w as frequent enough to w arrant fu rther study. W e w ere on ly m ildly in terested, until it occurred to us that per haps a com parison between persons w h o had had treatm ent and those w h o had had n o treatm ent m ight be enlightening. A ccord in g ly , a large num ber o f fu ll m outh roentgenogram s w ere studied. A ll o f the fu ll m outh films taken in the diag nostic clin ic over a given period, exclu d in g on ly those w hich had a history o f orth odon tic treatment, w ere taken as a sample. T h ese roentgenogram s, repre senting all age groups fro m 7 to 70 years, num bered 4,560.
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The Journal of the American Dental Association
T h e incidence o f resorption from all causes in this group is 12.6 per cent o f the num ber o f cases in volved. W e have tried to classify these affected teeth ac cord in g to w hat m ight be the cause fo r resorption in each case. W e realize the
appliances w ere em ployed, no one type predom inating. T h e average age o f pa tients treated by the postgraduate group w as a trifle greater than that o f the regu lar undergraduate clin ic patients. T h e incidence o f resorption in both groups is
possibility o f error in the procedure, since w e have no histories to v erify ou r ju d g ment. T h e data presented from the treated orth odon tic group are gathered in the orth odontic undergraduate and postgrad uate clinics o f the Sch ool o f D entistry, U niversity o f M inn esota. T h e operating has been and is being carried on by the senior students under the direct super vision o f instructors. T h e type o f appli ance used in m ost cases is the simple la bial arch w ith bands m ade directly in the m outh and tied to the arch by w ire liga tures. Bite-planes, both vulcanite re m ovable and m etal fixed, are used w here indicated. In term axillary and intram axillary forces by rubber bands are used as cases require them. B ite-blocks and splints are used infrequently. M ov em en t o f the teeth is usually co m paratively slow . Student w ork makes steady progress in m ovem ent difficult in com parison to results obtained by most experienced practitioners. Q u ite neces sarily, w ith inexperienced operators such as the undergraduate student body, there w ou ld be a larger incidence o f error in m aking adjustm ents in actual treatment even under supervision, and this fact may have some bearing on the percentages. T h e num ber o f orth odon tic cases used in this study is 439. T h is num ber consti tutes all the cases treated and under treatment fo r a given time in the teach in g clin ic. T h e large m a jority have been o r are being treated by undergraduate students during the senior year. A fe w have been treated by postgraduate stu dents o f the same time period. In those treated by the latter, various types o f
essentially the same. In the fo llo w in g discussion, the orth o dontic group w ill be understood to in clude all cases treated or under treat m ent fo r the designated time o f this study. R outine diagnosis o f each o f the orth o dontic cases includes a fu ll m outh roentgen-ray exam ination. F o r children in the clinic, a fu ll m outh roentgen-ray exam ination calls fo r from tw elv e to fourteen films as the case m ay require. A t oneyear intervals du ring treatm ent, fu ll m outh roentgenogram s w ere taken o f each case. T h e total num ber o f begin ning roentgen-ray exam inations w as 439. T h e total num ber o f second roentgeno grams, those taken at the end o f the first year o f treatm ent, w as 439. T h e num ber at the second year o f treatm ent was 277 ; the num ber at the third year o f treatment, 121, and the num ber at the end o f the fourth' year, 34. N o perma nent root resorption w as noted in the be ginning roentgen-ray exam ination. A t the end o f the first year o f treatment, 48 .74 per cent o f the total num ber w ere m ore or less affected. T h e third examina tion, w hich includes 277 cases, showed resorption in 74.63 per cent o f these cases. T h e age range o f these patients w as 7 to 21 years. T h e average age o f patients at the beginning o f treatm ent w as ap proxim ately 10 years. D ivision o f the 439 patients show s 209 male and 23 0 fem ale. U p to the time these data w ere tabulated, 135 cases show no resorption ; 3 0 4 cases show resorption ; 209 males show a percentage o f resorption o f 64 .59 ; 2 3 0 females show a percentage o f resorption o f 73.47. T h e
Rudolph— Comparative Study in Root Resorption com bined group o f 439 cases show s a per centage o f resorption o f 69.24. In ex planation o f the foregoin g statement, o f the 135 cases show ing no resorption, som e o f these are finished and som e are yet under treatment. A lso, no attem pt has been made as yet to estimate the de gree o f resorption in this series o f cases. T h e percentages show n deal w ith the num ber o f cases in volved and not w ith the num ber o f teeth. T h e con trol group, or those studied w h o had no history o f orth odon tic treat ment, ranged in age from 7 to 79 years. F rom 7 to 30 years inclusive, there are 1,609. F rom 31 to 55 years inclusive, there are 2,557. F rom 56 to 79 years inclusive, there are 394. In taking the age grou p o f these com parable to the age group o f the orthodontia patients studied, there are from 7 to 21 years o f age, 739 cases. T h irty-eigh t o f the 739 cases show resorption from some cause, a per centage o f 5.14. A ll o f these cases o f re sorption are fou nd in the age group from 13 to 21 years inclusive. T w en ty-th ree o f these cases o f resorption are to be fou n d at the ages o f 18 to 21 years in clusive. In the beginning, no one o f the 439 orth odontia cases showed resorption o f any permanent roots. O f the 739 cases w ith no orth odontic history, no pa tient 13 years o f age or under show ed resorption. I t is interesting to note the distribu tion o f resorption in each o f the groups studied. In the con trol group (those hav ing no orth odontic treatment h istory ), w e find that the tooth least apt to be affected is the lo w e r cuspid. T h e inci dence o f resorption in this tooth in the entire group is 0.55 per cent. T h e other teeth in order o f their incidence o f re sorption a r e : low er lateral, low er central, upper cuspid, low er bicuspids, upper m o lars, low er molars, upper central incisors, upper lateral incisors and upper bicus
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pids. N o definite explanation fo r this curious sequence can be offered. It is not know n w h y the upper bicuspids are a f fected m ore often than the other teeth. It w ill probably take a great deal o f study o f anatom y and histology, as w e ll as tooth analysis, along w ith study and experim entation in functional stresses throughout the m outh, to arrive at an ac ceptable explanation. Q u ite logically, the percentage o f resorption runs high est between the ages o f 25 and 45 years. In this interval, too, the largest num ber o f erupted perm anent teeth have been exposed to disease and treatm ent by restorative procedures. Betw een these ages, people appear to have the largest num ber o f serious dental operations per form ed. It seems that, in many cases, resorption is directly attributable to the dental restoration in and on the teeth. T o return to the orth odontic g ro u p : T h e percentage o f resorption runs as fo l low s, beginning w ith the least affected tooth and nam ing the teeth in o rd e r: low er bicuspids, upper bicuspids, upper first m olar, low er cuspid, low er first m olar, upper cuspid, low er lateral in cisor, low er central incisor, upper central incisor and upper lateral incisor. R e sorption is m ost prevalent in the upper and low er anterior fou r teeth. T h ese teeth' suffer the greatest am ount o f root loss also. A lth ou g h the curve o f esti mated tissue loss has n ot yet been w orked out, it takes but little study to be con vinced that the anterior fou r teeth, up per and low er, sustain the largest loss. B y far the largest num ber o f cases o f resorption occu r in patients treated du r ing and after the age o f 11 years. T h e percentage o f resorption increases rapidly from this age to the age lim it o f treat m ent in ou r clinic. A lth ou g h the data available have not yet been tabulated, it seems apparent that gentle forces on teeth not fu lly form ed have little effect on
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The Journal of the American Dental Association
their predestined size. In other w ords, the teeth not fu lly form ed seem to keep on grow in g n orm ally w hen treated du r ing the naturally fast g row th periods o f the child, especially in the youn ger age lim its o f childhood. It is thought that some teeth may be stunted in length g row th if treated vigorou sly du ring the later age lim its o f childhood. T h e r e is som e evidence o f this phenom enon. M a n y questions arise in the study and analysis o f these groups. I am attem pting to prove on ly that resorption occurs m ore frequently in patients treated orthodontically than in those o f the same age group w h o have had no orth odon tic treatment. B oth the groups studied are, as nearly as w e can tell, in the same eco nom ic group and on the same health level. O u r data are as yet m eager in relation to the largeness o f the problem . Y ears o f study and com pilation o f m any data are necessary. O n e intriguing phase, o f the m any one m ight discuss, is the actual damage the resultant resorption really causes. N o data bearing on this are available. So far, w e can on ly guess. I t is log ical to conclu de that a cuspid root foreshortened one-half w ill n ot carry a definite type o f restoration as lon g as one n ot so affected, other conditions being equal. O n the other hand, there is on ly a con jectu re as to the am ount o f dam age to the m outh and health o f the patient that m ight have occurred had n o orth odon tic treatm ent been given. T h o se o f us w h o have prac ticed general dentistry sufficiently lon g to gain a proper background o f experi ence can recall and visualize m any cases wherein the w reck in g o f the masticatory apparatus seemed due to m alocclusion alone. It is possible that the foreshorten
ing o f a fe w roots, o w in g to orth odon tic treatment, m ight n ot in these cases have been too large a price to pay fo r other advantages gained by treatm ent. T h is statement is n ot m eant to condon e the resultant resorption, fo r it m ust be ou r business to avoid such results in treat ment. T h e question is, h o w ? T h e w ork at the U n iversity o f M in nesota C lin ic is reported fo r the reason that it is the beginning o f a thorough questioning o f methods o f teaching and practice o f orth odontia and n ot an in dictm ent o f the practice o f orth odontia. W e w o u ld be happy to consult w ith any individual o r institution analyzing this problem w h o believes that a scientific analysis is desirable and necessary. I shall m ention ju st a fe w o f the many angles o f the problem that are being, or perhaps should be, studied. T h e correct age at w hich to have treatm ent is a broad field o f study. P roper diet constitutes an in triguing field. T h e type o f appliance and rapidity o f m ovem ent need much study. T h e com bination o f forces to be applied at a given time m ight in itself keep an investigator busy fo r years. N o attem pt to state these phases o f .the problem in the order o f their im portance is intended. A thorough study o f the problem as a w hole by a com petent group is necessary in ord er that proper research can be carried ou t and the resorption o f roots due to orth odon tic treatm ent can be com pletely elim inated. I t is n ot m y belief that the phases m entioned are by any means all the angles o f the subject to be studied. Some o f these fields are be ing investigated n o w and every en cou r agem ent should be given the m en and w om en w h o are devotin g their tim e and energy to such service.