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A Report Concerning the Etiology of Dental Caries*
A REPORT CONCERNING THE ETIOLOGY OF DENTAL CARIES* By H. E. FRIESELL, D.D.S., and C. C. VOGT, Pittsburgh, Pennsylvania
A C T IO N
O F D I L U T E A C ID S O N T H E
E N A M E L OF T H E TE E T H
E V E R A L investigators have shown that lactic acid solutions containing 1 part acid to 2 0 ,0 0 0 parts o f w ater w ill soften the enamel o f a tooth to some extent in three or fo u r days, but no tests have been reported in which the concentrations o f acid are compar able to those usually fou n d in saliva, which is norm ally either practically neutral or only very slightly acid. In the experiments re ferre d to, the acid solutions used were not stirred or kept in motion constantly, so that fresh por tions o f acid w ould be brought contin uously in contact w ith the surfaces o f enamel exposed to its action. Studies o f this kind give considerable inform ation regarding the action o f acids on enamel, but it seems preferable to conduct tests in which the solutions are made to flow slo w ly over the tooth, thus sim ulating to a greater degree the conditions in the mouth, w here saliva continuously bathes the teeth. T h ere fo re , an apparatus which w ould permit the flow ing o f dilute acid solutions over
S
*R ea d b e fo re the Section on H isto lo g y , P h y sio lo g y , P a th o lo g y , B a cte rio lo g y and C hem istry (R esea rch ) at the Sixty-Seventh A n n u al Session o f the A m erican D en tal A sso ciation , L ou isv ille, K y ., Sept. 23, 1925. Jour. A . V . A ., June, 1926
the tooth was constructed. T h e rate o f flow approximated that o f the secretion o f saliva, i. e., about 1 liter per day. T h is rate o f flow is so slow that, w hile the solution is constantly renewed in the vicinity o f the tooth, there is no danger o f w ear on the tooth by any mechanical action o f the solution itself. T h e apparatus consisted o f a 7-liter reservoir bottle containing the solution under test. T h is bottle was connected by a siphon tube to a 5 0 c.c. E rlenm eyer flask, fitted w ith a tw o-hole rubber stopper. T h e end o f the siphon tube reached to the bottom o f the flask, so that there could not be any mechanical action o f the solution on the tooth. A n outflow tube was placed about tw othirds o f the distance to the top o f the flask so that the excess solution was a l low ed to flow out continuously, a con stant level being thus maintained in the flask. Such an arrangem ent permits the gradual renew al o f the acid solution in a m anner that does not produce any mechanical effects, but does insure com plete freedom o f action by the acid on the enamel by continuously bathing the enamel surfaces w ith fresh portions o f the acid solution. T h e first set o f experiments was made on the action o f w ater saturated w ith carbonic acid gas on tooth enamel.
748
Friesell-Vogt— The Etiology of Dental Caries I t was found that w hen w ater fu lly carbonated at atmospheric pressure was perm itted to flow slo w ly over the enamel surface o f a tooth fo r tw o days, several opaque white spots appeared that suggested very definite etching action. A t the end o f the third day, the entire surface o f the enamel was opaque, which indicated very rapid action. T o be sure, these teeth did not have the pro tective action - due to the presence o f saliva; nevertheless, the quantity o f etching produced was surprisingly large, much greater than that found in the non-flow method o f testing, reports o f which have appeared fro m time to time in dental literature. In all the experi ments described in this com munication, the roots were coated w ith paraffin, so that only the enamel o f the tooth was exposed to the action o f the reagent. O th er studies by the flow method w ere made on the action o f very dilute citric and lactic acid solutions on tooth enamel. T h e solutions w ere made with distilled w ater through which carbon dioxid fre e air had been allow ed to bubble fo r at least tw elve hours; hence they w ere practically carbon dioxid fre e. T hese solutions w ere as dilute as 1 part acid to fro m 1 ,1 0 0 ,0 0 0 to 1 .4 0 0 .0 0 0 parts w ater. O th er more concentrated solutions w ere also used, 1 part acid to fro m 5 0 0 ,0 0 0 to 7 0 0 ,0 0 0 parts w ater, and 1 part acid to fro m 1 1 0 .0 0 0 to 1 4 0 ,0 0 0 parts w ater. These concentrations o f acid w ere chosen be cause they approximate those found in saliva itself. F o r example, the 1 part lactic acid to 1 ,1 0 0 ,0 0 0 parts w ater solution has a pB o f approxim ately 6 .6 , a degree o f acidity o ften encountered in saliva. T h e term pB has been adopted as a convenient method fo r ex
749
pressing the concentration o f hydrogen ion, and it w ill be remembered that ionic hydrogen is the substance which imparts to acids their characteristic properties. B y p h y sic o c h e m ic al m e th o d s, it h as been sh ow n th a t one lite r o f p u re d istille d w a te r c o n ta in s one te n m illio n th g ra m o f h y d ro g e n ion. E xp ressed m a th e m a tic a lly , th is con c e n tra tio n is e q u a l to t o . o o V . o o o o r T o 7. o r, to a v o id fra c tio n s , 1 x 10'7. T h is is th e n e u tra l p o in t, w h ere a su b stan ce o r a so lu tio n is n e ith e r acid n o r a lk a lin e in its re a c tio n . In o rd e r to av o id th e re p e titio n o f th e te rm 1 x 10 ‘x in ex p ressin g a c id ity , biologic ch em ists h a v e agreed to m a k e use o f o n ly th e in d ex n u m b e r “ x ” as in d ic a tiv e o f th e h y d ro g en ion con cen tra tio n . T h u s, p a — 7 m eans th a t th e h y d ro g e n ion c o n c e n tra tio n o f th a t so lu tio n is e q u a l to 1 x 10'7 o r T o . o o T M n n r , i- e ., it c o n ta in s a ten m illio n th g ra m of h y d ro g e n ion in 1 lite r. p u = 6 m ean s th a t t h e h y d ro g e n ion c o n c e n tra tio n o f th a t so lu tio n is e q u a l to lx lO '6, o r Tiooi,ooo) o r th a t th e re is 1 m illio n th gram o f h y d ro g e n ion in 1 lite r, w h ich is ten tim es th e h y d ro g e n ion c o n c e n tra tion o f a so lu tio n w ith p a= l ■ H ence, a so lu tio n w ith p n = 6 is te n tim es as acid as one w ith p tL= l ■ P k — % m eans th a t th e c o n c e n tra tio n o f h y d ro g en ion o f th a t so lu tio n is 1 x 10"8, o r x o o .o k o o o , w h ich ex presses m a th e m a tic a lly th e fa c t th a t th e re is a one h u n d re d m illio n th gram o f h y d ro g en ion in 1 lite r o f one te n th o f th e h y d ro g e n ion c o n c e n tra tio n o f a so lu tio n w ith p u = 7. T h e re fo re , a so lu tio n w ith p B = 8 is o n ly one te n th as acid as one w ith p B = 7.
750
The Journal of the American Dental Association
These examples show that since f a = 7 represents the neutral point, all solutions having a f s less than 7 w ill be on the acid side o f neutrality, w hile a ll solutions having a fu more than 7 w ill be on the alkaline side o f the neutral point. T h e quantities o f acid or alkali met w ith in biologic fluids are usually very slight— most o f these fluids being neutral or n early neutral— so that the fn range is lim ited. T h is method -o f expressing the acidity o f solutions has come to be the usual one in biologic chem istry, dentistry, medicine and re lated sciences. In every case, by the end o f six weeks, a definite etching o f the enamel was observed. Etching o f the enam el o f teeth by solutions o f acid concentrations comparable to those found in saliva is particularly inter esting since it throw s additional light on the susceptibility o f enamel to the action o f very dilute acids, when fresh portions o f acid are brought con tinuously into contact w ith the enamel. T h e enamel o f teeth was also ex posed to the action o f pure distilled w ater freed fro m carbon dioxid by the method described above. I t was found at the end o f eight weeks that opaque spots had been form ed on the enam el, which indicated some solvent action by w ater. Sample teeth fro m a ll these treat ments w ere stained w ith silver nitrate, sectioned and examined. In every case, the white opaque spots stained more deeply and in the sections had the same appearance as a stained section o f a tooth w here there is an area o f the first stage o f dental caries.
T hese “ flow m ethod” experiments w ere made during the progress o f some w ork on the chem istry o f dental caries, and the results obtained w ere so striking that they seemed w orth re cording. T o be sure, no saliva was present so that its protective action w ould be available, but the continuous slow solvent action o f dilute acids and o f w ater on tooth enamel merits some consideration. O ne m ight fo rm the hypothesis that when the saliva, which bathes the teeth continuously, is unsaturated w ith re spect to calcium and phosphate, it has the pow er to dissolve some o f the cal cium phosphate fro m the enamel o f the tooth, thus producing some very slight etching o f its surface. E xperi m ental p ro o f fo r this hypothesis is lacking, but it certainly is reasonable to assume that there must be some close relationship between the compo sition o f saliva and oral conditions. N O TE ON T H E D E G R E E OF A L K A L IN IT Y OF
THE
S A L IV A
OF
PREGNANT
W OMEN
D u rin g the course o f the research on the etiology o f dental caries, in which the School o f D entistry o f the U n i versity o f Pittsburgh is cooperating w ith M ello n Institute, a study o f the relation which the composition o f saliva bears to oral conditions has been undertaken. T h e fo llo w in g general plan o f at tack has been adopted: A c a re fu l ex am ination o f the teeth and mouth is made and recorded by a member o f the clinical staff o f the School o f D entistry. A sample o f saliva is then taken fo r the determ ination o f cal
FrieseUr-Vogt— The Etiology of Dental Caries cium and phosphorus. A f a determ ina tion by a slight modification o f the colorim etric method described by S ta rr1 is also made o f fresh saliva, as soon as it is collected. T h e w ork as planned includes the study o f the saliva and the oral con ditions o f both children and adults. A s considerable trouble w ith the teeth occurs during pregnancy, especial atten tion is being accorded to the compo sition o f the saliva and to the general oral conditions o f gestating wom en. T h ro u gh the courtesy o f the de partm ent o f obstetrics o f the School o f M edicine o f the U n iversity o f Pitts burgh, arrangem ents have been made to examine the mouths o f some o f the clinic patients at M agee M atern ity Hospital. A m p le opportunity is a f forded fo r the compilation o f com plete case histories o f these patients. W h ile , as yet, it is too early to a r rive at any definite generalizations 1. Starr, H . E . : J. B io l. 4 3 -5 4 , 5 5 -6 4 (S e p t.) 1922.
C hem .,
54:
751
fio m the results o f these salivary analyses, it is o f interest to call atten tion to the observations made up to this time on the degree o f alkalinity o f saliva o f pregnant wom en whose mouths have been examined. T h e fn o f the saliva o f ninety-seven gestating wom en has been determined, and only eight samples showed a' f>n o f 6 .8 or above, w h ile the rem aining eighty-nine had a fn o f 6 .7 or below. T h e average pH o f the ninety-seven samples was 6 .6 1 , a figure practically 0 .2 lo w er than the average figure o f approximately 6 .8 obtained on samples o f saliva fro m various types o f individ uals, but not fro m pregnant women. W h e th e r the slightly higher acidity o f saliva has anything to do w ith the incidence o f dental caries is an open question, but, at any rate, the observa tions re fe rre d to seem w orthy o f record. I t is to be understood that this is m erely a prelim inary note, and that, at a later date, the results o f f u r ther research w ill possibly necessitate its revision.
A C T IO N
O F D I L U T E A C ID S O N T H E
E N A M E L OF T H E TE E T H
E V E R A L investigators have shown that lactic acid solutions containing 1 part acid to 2 0 ,0 0 0 parts o f w ater w ill soften the enamel o f a tooth to some extent in three or fo u r days, but no tests have been reported in which the concentrations o f acid are compar able to those usually fou n d in saliva, which is norm ally either practically neutral or only very slightly acid. In the experiments re ferre d to, the acid solutions used were not stirred or kept in motion constantly, so that fresh por tions o f acid w ould be brought contin uously in contact w ith the surfaces o f enamel exposed to its action. Studies o f this kind give considerable inform ation regarding the action o f acids on enamel, but it seems preferable to conduct tests in which the solutions are made to flow slo w ly over the tooth, thus sim ulating to a greater degree the conditions in the mouth, w here saliva continuously bathes the teeth. T h ere fo re , an apparatus which w ould permit the flow ing o f dilute acid solutions over
S
*R ea d b e fo re the Section on H isto lo g y , P h y sio lo g y , P a th o lo g y , B a cte rio lo g y and C hem istry (R esea rch ) at the Sixty-Seventh A n n u al Session o f the A m erican D en tal A sso ciation , L ou isv ille, K y ., Sept. 23, 1925. Jour. A . V . A ., June, 1926
the tooth was constructed. T h e rate o f flow approximated that o f the secretion o f saliva, i. e., about 1 liter per day. T h is rate o f flow is so slow that, w hile the solution is constantly renewed in the vicinity o f the tooth, there is no danger o f w ear on the tooth by any mechanical action o f the solution itself. T h e apparatus consisted o f a 7-liter reservoir bottle containing the solution under test. T h is bottle was connected by a siphon tube to a 5 0 c.c. E rlenm eyer flask, fitted w ith a tw o-hole rubber stopper. T h e end o f the siphon tube reached to the bottom o f the flask, so that there could not be any mechanical action o f the solution on the tooth. A n outflow tube was placed about tw othirds o f the distance to the top o f the flask so that the excess solution was a l low ed to flow out continuously, a con stant level being thus maintained in the flask. Such an arrangem ent permits the gradual renew al o f the acid solution in a m anner that does not produce any mechanical effects, but does insure com plete freedom o f action by the acid on the enamel by continuously bathing the enamel surfaces w ith fresh portions o f the acid solution. T h e first set o f experiments was made on the action o f w ater saturated w ith carbonic acid gas on tooth enamel.
748
Friesell-Vogt— The Etiology of Dental Caries I t was found that w hen w ater fu lly carbonated at atmospheric pressure was perm itted to flow slo w ly over the enamel surface o f a tooth fo r tw o days, several opaque white spots appeared that suggested very definite etching action. A t the end o f the third day, the entire surface o f the enamel was opaque, which indicated very rapid action. T o be sure, these teeth did not have the pro tective action - due to the presence o f saliva; nevertheless, the quantity o f etching produced was surprisingly large, much greater than that found in the non-flow method o f testing, reports o f which have appeared fro m time to time in dental literature. In all the experi ments described in this com munication, the roots were coated w ith paraffin, so that only the enamel o f the tooth was exposed to the action o f the reagent. O th er studies by the flow method w ere made on the action o f very dilute citric and lactic acid solutions on tooth enamel. T h e solutions w ere made with distilled w ater through which carbon dioxid fre e air had been allow ed to bubble fo r at least tw elve hours; hence they w ere practically carbon dioxid fre e. T hese solutions w ere as dilute as 1 part acid to fro m 1 ,1 0 0 ,0 0 0 to 1 .4 0 0 .0 0 0 parts w ater. O th er more concentrated solutions w ere also used, 1 part acid to fro m 5 0 0 ,0 0 0 to 7 0 0 ,0 0 0 parts w ater, and 1 part acid to fro m 1 1 0 .0 0 0 to 1 4 0 ,0 0 0 parts w ater. These concentrations o f acid w ere chosen be cause they approximate those found in saliva itself. F o r example, the 1 part lactic acid to 1 ,1 0 0 ,0 0 0 parts w ater solution has a pB o f approxim ately 6 .6 , a degree o f acidity o ften encountered in saliva. T h e term pB has been adopted as a convenient method fo r ex
749
pressing the concentration o f hydrogen ion, and it w ill be remembered that ionic hydrogen is the substance which imparts to acids their characteristic properties. B y p h y sic o c h e m ic al m e th o d s, it h as been sh ow n th a t one lite r o f p u re d istille d w a te r c o n ta in s one te n m illio n th g ra m o f h y d ro g e n ion. E xp ressed m a th e m a tic a lly , th is con c e n tra tio n is e q u a l to t o . o o V . o o o o r T o 7. o r, to a v o id fra c tio n s , 1 x 10'7. T h is is th e n e u tra l p o in t, w h ere a su b stan ce o r a so lu tio n is n e ith e r acid n o r a lk a lin e in its re a c tio n . In o rd e r to av o id th e re p e titio n o f th e te rm 1 x 10 ‘x in ex p ressin g a c id ity , biologic ch em ists h a v e agreed to m a k e use o f o n ly th e in d ex n u m b e r “ x ” as in d ic a tiv e o f th e h y d ro g en ion con cen tra tio n . T h u s, p a — 7 m eans th a t th e h y d ro g e n ion c o n c e n tra tio n o f th a t so lu tio n is e q u a l to 1 x 10'7 o r T o . o o T M n n r , i- e ., it c o n ta in s a ten m illio n th g ra m of h y d ro g e n ion in 1 lite r. p u = 6 m ean s th a t t h e h y d ro g e n ion c o n c e n tra tio n o f th a t so lu tio n is e q u a l to lx lO '6, o r Tiooi,ooo) o r th a t th e re is 1 m illio n th gram o f h y d ro g e n ion in 1 lite r, w h ich is ten tim es th e h y d ro g e n ion c o n c e n tra tion o f a so lu tio n w ith p a= l ■ H ence, a so lu tio n w ith p n = 6 is te n tim es as acid as one w ith p tL= l ■ P k — % m eans th a t th e c o n c e n tra tio n o f h y d ro g en ion o f th a t so lu tio n is 1 x 10"8, o r x o o .o k o o o , w h ich ex presses m a th e m a tic a lly th e fa c t th a t th e re is a one h u n d re d m illio n th gram o f h y d ro g en ion in 1 lite r o f one te n th o f th e h y d ro g e n ion c o n c e n tra tio n o f a so lu tio n w ith p u = 7. T h e re fo re , a so lu tio n w ith p B = 8 is o n ly one te n th as acid as one w ith p B = 7.
750
The Journal of the American Dental Association
These examples show that since f a = 7 represents the neutral point, all solutions having a f s less than 7 w ill be on the acid side o f neutrality, w hile a ll solutions having a fu more than 7 w ill be on the alkaline side o f the neutral point. T h e quantities o f acid or alkali met w ith in biologic fluids are usually very slight— most o f these fluids being neutral or n early neutral— so that the fn range is lim ited. T h is method -o f expressing the acidity o f solutions has come to be the usual one in biologic chem istry, dentistry, medicine and re lated sciences. In every case, by the end o f six weeks, a definite etching o f the enamel was observed. Etching o f the enam el o f teeth by solutions o f acid concentrations comparable to those found in saliva is particularly inter esting since it throw s additional light on the susceptibility o f enamel to the action o f very dilute acids, when fresh portions o f acid are brought con tinuously into contact w ith the enamel. T h e enamel o f teeth was also ex posed to the action o f pure distilled w ater freed fro m carbon dioxid by the method described above. I t was found at the end o f eight weeks that opaque spots had been form ed on the enam el, which indicated some solvent action by w ater. Sample teeth fro m a ll these treat ments w ere stained w ith silver nitrate, sectioned and examined. In every case, the white opaque spots stained more deeply and in the sections had the same appearance as a stained section o f a tooth w here there is an area o f the first stage o f dental caries.
T hese “ flow m ethod” experiments w ere made during the progress o f some w ork on the chem istry o f dental caries, and the results obtained w ere so striking that they seemed w orth re cording. T o be sure, no saliva was present so that its protective action w ould be available, but the continuous slow solvent action o f dilute acids and o f w ater on tooth enamel merits some consideration. O ne m ight fo rm the hypothesis that when the saliva, which bathes the teeth continuously, is unsaturated w ith re spect to calcium and phosphate, it has the pow er to dissolve some o f the cal cium phosphate fro m the enamel o f the tooth, thus producing some very slight etching o f its surface. E xperi m ental p ro o f fo r this hypothesis is lacking, but it certainly is reasonable to assume that there must be some close relationship between the compo sition o f saliva and oral conditions. N O TE ON T H E D E G R E E OF A L K A L IN IT Y OF
THE
S A L IV A
OF
PREGNANT
W OMEN
D u rin g the course o f the research on the etiology o f dental caries, in which the School o f D entistry o f the U n i versity o f Pittsburgh is cooperating w ith M ello n Institute, a study o f the relation which the composition o f saliva bears to oral conditions has been undertaken. T h e fo llo w in g general plan o f at tack has been adopted: A c a re fu l ex am ination o f the teeth and mouth is made and recorded by a member o f the clinical staff o f the School o f D entistry. A sample o f saliva is then taken fo r the determ ination o f cal
FrieseUr-Vogt— The Etiology of Dental Caries cium and phosphorus. A f a determ ina tion by a slight modification o f the colorim etric method described by S ta rr1 is also made o f fresh saliva, as soon as it is collected. T h e w ork as planned includes the study o f the saliva and the oral con ditions o f both children and adults. A s considerable trouble w ith the teeth occurs during pregnancy, especial atten tion is being accorded to the compo sition o f the saliva and to the general oral conditions o f gestating wom en. T h ro u gh the courtesy o f the de partm ent o f obstetrics o f the School o f M edicine o f the U n iversity o f Pitts burgh, arrangem ents have been made to examine the mouths o f some o f the clinic patients at M agee M atern ity Hospital. A m p le opportunity is a f forded fo r the compilation o f com plete case histories o f these patients. W h ile , as yet, it is too early to a r rive at any definite generalizations 1. Starr, H . E . : J. B io l. 4 3 -5 4 , 5 5 -6 4 (S e p t.) 1922.
C hem .,
54:
751
fio m the results o f these salivary analyses, it is o f interest to call atten tion to the observations made up to this time on the degree o f alkalinity o f saliva o f pregnant wom en whose mouths have been examined. T h e fn o f the saliva o f ninety-seven gestating wom en has been determined, and only eight samples showed a' f>n o f 6 .8 or above, w h ile the rem aining eighty-nine had a fn o f 6 .7 or below. T h e average pH o f the ninety-seven samples was 6 .6 1 , a figure practically 0 .2 lo w er than the average figure o f approximately 6 .8 obtained on samples o f saliva fro m various types o f individ uals, but not fro m pregnant women. W h e th e r the slightly higher acidity o f saliva has anything to do w ith the incidence o f dental caries is an open question, but, at any rate, the observa tions re fe rre d to seem w orthy o f record. I t is to be understood that this is m erely a prelim inary note, and that, at a later date, the results o f f u r ther research w ill possibly necessitate its revision.