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The bacteriologic status of the pulp chambers in intact teeth found to be nonvital following trauma
THE BACTERIOLOGIC STATUS OF THE PULP CHAMBERS INTACT TEETH FOUND TO BE NONVITAL FOLLOWING TRAUMA ?JOMN
13. MACDONAL~D, il.
IV.
I).I>.S., 8. %‘OOD,
N.S., PH.D., GEORUE C, HARE! I).T).S., TOROSTO, ONT.?RIO
L).I).S.,
IN
ASI)
MPACT injury to teeth, unaccompanied by fract.ure, is a common occurrence. According to Ellis,6 the degree of “shock” to t,he pulp in such instances may be greater than when fracture occurs. Such teeth frequently become nonvital, as evidenced by discoloration and negative response to electrical pulp testing. Nevertheless, they commonly are p(~rmittc~tl to rcinkain in situ without trcatmerit,, although t,his practice is not ~ccoIIIIIL~~~~(‘~.” Little data exist relative to the bacteriologic* status of intact traumat,ically devitalized teeth. Ellis” cultured the contents of the canals of an unstated number of symptomlcss nonvital t&h and apparently was unimprcsscd by the significance of organisms which htl recovered. Tic obsc~rvt~l. howcvcr, tha.t operative disturbance of the pulp cont,cnts in thcsc CRSCSis followed often by evidence of an acute abscess. Stewart’? reportcY1 bacteriologic findings on fourteen teeth devitalized following trauma. Tn all but, one, a sinus had bec>n established. Organisms WCTCrccovercd from all fourteen. Results of animal studies indicate, however, that it is the rule rather thrill the exception to find organisms in the pulp chamber where inflammation has been induced. Robinson and Rolingl” irritated t,hc pulps of the teeth in cats by cavity preparation and croton oil or phenol. Known organisms were introduced into the circulation by hypodermic needle in SOIHCcases; in others, the animals were carrying a natural infection. Organisms were rccorercd from the pulp chambers (post mortem) from forty-six of sixt,y-four operated t,eeth (inflamed pulps) and only six of seventy-one nontreated teeth. Csernye? demonstrated the localization of intravenously introduced bacteria (Bmcel7a abortus) at the a.pex of nonvital guinea pig t&h. Genvert, Miller, and Burn’ recovered a variety of organisl:ls from teeth and periapical tissues of monkeys in which the pulps were cxposc~l under aseptic conditions and subscqucntly sealccl. The present report clcals with thrb oc~~umxlcc of cultivable bacteria in th(a pulp contents of intact human t&h found to bc nonvital following mechanical in jury.
I
k;;;;;;71;l
PULP
CHAMBERS
IN
INTACT
NONVITAL
TEETH
AFTER
TRAUMA
319
Material and Methods The contents of the pulp chambers of forty-six teeth were examined bacteriologically. The teeth were observed over a period of three years and were There was a history of chosen in accordance with the following criteria: trauma. The teeth were nonvital, as evidenced by discoloration or failure to respond to thermal stimulation and electrical pulp testing, or bot,h. They were not fractured. There was no evidence of caries and the teeth were free from restorations. In nineteen instances the periapical area appeared normal radiographically. In twenty-seven there was periapical rarefaction varying from a mere thickening of the periodontal membrane t,o the presence of areas All were anterior teeth; thirty-nine of rarefaction up to 1 cm. in diameter. were permanent and seven were deciduous teeth. All patients were children or young adults (ages 3 to 34)) with the exception of a 5%year-old woman from whom two teeth were studied. The interval between the occurrence of injury and that time when cultures were obtained from the nonvital pulps varied from two weeks to twenty years. TARIX T.
but
ORGAKISMS RECOVERED FROM PULP CHAMBERS OF FORTY-SIX TRAUMATICALLY DEVITALIZED TEETH
ORGANISM Alpha streptococci Gamma streptococci Anaerobic gram-positive cocci Staphylococcus albus Staphylococcus aweus Other micrococci Neisseria Bacteroidest Pseudomonas Fusobacterium: Pibrio sputorum Escherichia co% Aerobic gram-positive bacilli Anaerobic gram-positive bacilli Yeast *Two strains, arbitrarily included, appeared in broth did not grow on blood agar. tAnaerobic
lone
strain
gram-negative
was identified
bacilli otherwise as Fbsobacterium
I
NUMBER OF' STRAINS 17* 3 12 6 4 6 4 5 2 2 1 1 i 1
as gram-positive
chain-forming
cocci
unidentified.
girans.”
In each case satisfying the above criteria, the tooth was isolated by rubber dam and its surface was sterilized with either tincture of iodine or aqueous benzalkonium chloride (1 :l,OOO) . The opening was made into the pulp chamber with sterile burs. Sterile paper points were introduced into the pulp chamber to adsorb some of the contents. One point was transferred to a tube of Connaught penicillinase dextrose broth, a second to a tube of Difco thioglycollate broth (B236). The tubes were incubated at 3F’ C., the former aerobically for forty-eight hours and the latter anaerobically in a Brewer jar reduced with hydrogen for ninety-six hours, at which time growth, if any, was recorded. The contents of tubes were examined by gram stain and by dark-field microscopy. Samples of a.11tubes were transferred to heart infusion
320
JfBCI)ONALl~,
HAHF:.
.4X1)
\\.()()I)
agar containing 10 per cent defibrinated sheep’s blood. Subcultures from tht’ Connaught medium were incubated aerobically and those from the thioglycollate medium, anaerobically, for two and four days, respectively. Colonies were examined and the appearance of gram-stained cells was recorded. Each type of colony recovered from plates incubated anaerobically was subculturctl to blood agar for aerobic incubation to detcrminc those which required anaIl?.obic conditions. In most instances organisms were classified according to the scheme shown in Table 1 on the basis of t,he n.bovc findings. When it appearctl to be warrant,ed, additional examinations were made, including fcrmentat,ion of dextrose and lactose, methyl red test, Voges-Proskauer test, growth ill citrate medium, product.ion of indole and hydrogen sulfitlc, reduction o!’ nitrates, production of ammonia, a,nd gelatin liquefaction. Tests of reliability of the method of collecting the sample, in terms OF freedom from contamination, >v(‘re performed on eight cases. Moistenecl sterile paper points were applied to the exposed dentine before oprninp into the pulp. Incubation of points in broth, a,ccording to the above procedurc7 resulted in no growth.
Results Of the forty-six cases, thirty-eight ber of strains recovered in individual TABLE
IT.
DISTKIBUTION
NUMBER OF STRAINS RECOVEREI) 0 1 2 3 4 5 6
yielded growth (Table 11). ‘l’hcb I~UIIIcases varied from none t,o six.
OF RACTERIBL STRAINS IN E'ORTY-SIX. DEYITAJJZE~ TEETH ---~_I_-I
.Nl~bIKJm OI' CASES 8 16 14 3 1 1 1
I
_
~RAlJAIATICAI~I~V __---~
F'EK('I:.v'~Al:E
-~ ~~ OF ('A2SE.S
I7 35 30 11 2 2 .I
The organisms recovered are listed in Table I. A total of seventy-onca strains were isolated, The largest single group consisted of the aerobic streptococci (a total of t,wcnty strains). This was followed by Nicrococci (fifteen strains). Anaerobic cocci constituted the third largest group (twelve strains). Twenty-three, or 32 per cent, of the strains were anaerobes. There appeared to be no relationship between the bacteriologic status of the pulps and the radiographic appearance of the periapical area. Of the eight cases from which no organisms were recovered, t,he periapical tissue apRarefaction was evident in five. peared radiographically normal in three. In one of the latter, an area of rarefying osteitis about 4 mm. by 5 mm. radiated from the root tip. Fifteen cases from which bacteria were isolated were normal radiographically and twenty-three exhibited evidence of rarefaction. There was no apparent relationship between the bacteriologic status and the length of the interval between injury and cultivation. One case cultivated fourteen days following injury yielded three different strains of organisms.
~l;~~r:” ”
PULP
CHAMBERS
IN
INTACT
NONVITAT,
TEETH
AFTER
TRAUMA
321
The interval between injury and cultivation in the eight cases in which no growth occurred varied between one month and three years. In the thirtyeight cases in which growth occurred, the interval varied between two weeks and twenty years.
Discussion It is clear from the findings that ‘bacteria can be recovered from the pulp chambers of the majority of traumatically devitalized teeth, even though there is no direct communication between the pulps and the oral cavity. The percentage from which organisms were recovered in this series was about 83. Furthermore, it seems likely that at least some of the eight cases reported here to be negative actually may have contained viable organisms. The media and methods would not disclose spirochetes or many organisms requiring more cnriched media or periods of incubation l.onger than ninety-six hours. It should be noted that the nature of this study made it impractical to include a negative control; that is, cultures were not taken from the pulps of normal uninjured human teeth. Evidence is available, however, that such pulps usually are free from organisms.” Henrici and Hartzell1° failed to obtain growth from the pulps of any of twenty-two teeth free from caries and periodontal disease. Dutton and Cameron” obtained growth from only 2.7 per cent of the pulps of 108 clinically normal teeth. Gunter and associates9 obtained no growth from forty-six pulps of normal teeth; Burke’? obtained growth from only three of fifty-four pulps examined in situ at autopsy. An anachoretic effect was probably responsible for the occurrence of organisms in the pulp chambers of the thirty-eight nonvital teeth. The tendency of bacteria and other particulate matter to become fixed in areas of inflammation has been described freqnently. The literature is reviewed by Robinson and Boling.15 The bacteria recovered in the present study, on the whole, were representative of the oral flora, and it seems likely that this was the source for most of them. Representatives of most of the groups isolated are found regularly in the oral cavity,16 and at least one (Vibrio sputorum) has rarely, if ever, been found elsewhere.12 On the other hand, some (for example, Pseudomonas species and 8:. coli) are not routinely recoverable from the mouth. Assuming the oral cavity as the most common source for bacteria within the pulp chambers of intact teeth, it is probable that they reach the pulp from the gingival sulcus via the lymphatics and blood vessels of the periodontium. That organisms can reach the pulp in this way has been pointed out frequently.‘g 7l I4 It is possible that bacteria may be the cause of pulp necrosis in some cases of trauma without fracture. Menkin13 showed that blood-borne bacteria may localize in areas of inflammation within thirty minutes after injury. Lewis’l observed, following intravenous injection, that there was a very rapid appearance and concentration of trypan red in the aqueous humor of congested *It is clear that early reports of the presence of bacteria introduction of organisms during extraction (see Appletonl).
in normal
pulps resulted
from
322
MACDONAI,I),
HARE,
ASI)
\VOOl)
0. s , 0. M.. & 0. P. If:,,
eyes of rabbits. It seems likely, t,heref’orc,, that in many inst,ances bactet*i:r While the rapidly become established in the pulp tissue following in,jury. mere presence in the pulp of bacteria, even known pathogclns, does not nclc*essarily lead to disease (SW, for example, Dcnuy ant1 Thomas’), it stems safe to conclude that the presenccl of bacteria in pulps alrc~atly inflanlctl relight W~Ipound the injury and lead to pulp necrosis. Summary The bacteriologic status of the pulp chambers of forty-six intact t&h found to be nonvital following impact injury was investigated by aerobic ant1 anaerobic cultural methods. Growth was obtain4 from thirty-eight teeth. The number of strains recovered in individual casts varied bctwecn one ant1 six. A total of seventy-one strains were isolated, of which twenty-three were anaerobes. It is postulated that most of these organisms reached t.he pull) from the oral cavity via the lymphatics ant1 blood vessels of the periotlontium. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Appleton, J. L. T.: Bacterial Infect.ion, Philadelphia, 1!)51), Lea & Febiger. Burket, L. W.: J. D. Res. 21: 9, 1942. Csernyei, J.: .T. D. Res. 18: 527, 1939. Denny, F. IV., ant1 Thomas, L.: Proc. Sot. l’;xper. Hiol. ti- ,\fe,l. 88: %iO, l$J.‘i5. Dutton, E. M., and Cameron, G. C.: Canad. J. Pub. Health 23: 436, 1932. Ellis, R. 0.: The Classification and Treatment of Injuries to the Teeth of Children, Chicago, 1952, The Year Book Publishers, Inc. Fish, W. F., and MacLean, I.: Brit. Dent. J. 61: 336, 1936. Genvert, H., Miller, H., and Burn, C. G.: Tale J. Biol. & Xed. 13: 649, 1941. Gunter, J. H., Appleton, J. L. T., Strong, .I., Reatler, ,J. (‘., Zimnlerman, E:. ;I., a1111 Brooks. J. J.: J. D. Rtts. 16: 310 3937. Henrici, A. *., and H&zell, T. B.: .J. D. R&. 1: 419, 1919. Lewis, P. A.: J. Exper. Med. 23: 669, 1916. The Motile Non-Sporulating Anaerobic Rods of the Oral Cavity, Macdonald, J. B.: Toronto, 1953, University of Toronto Press. Dynamics of Inflammation, New York, 1940, The illacmillan Company. Menkin, V.: Rickert, U. G.: J. Am. Dent. A. 8: 411, 1931. Robinson, H. B. G., and Boling, L. R.: J. Am. Dent. -4. 28: 26S, 1941. Rosebury, T., in Dubos, R. 5.: Bacterial and Mycotic Infections of Man, Philadelphia, 1952, J. B. Lippineott Company. Stewart, G. G.: J. Endodontia 2: 8, 191;.
13. MACDONAL~D, il.
IV.
I).I>.S., 8. %‘OOD,
N.S., PH.D., GEORUE C, HARE! I).T).S., TOROSTO, ONT.?RIO
L).I).S.,
IN
ASI)
MPACT injury to teeth, unaccompanied by fract.ure, is a common occurrence. According to Ellis,6 the degree of “shock” to t,he pulp in such instances may be greater than when fracture occurs. Such teeth frequently become nonvital, as evidenced by discoloration and negative response to electrical pulp testing. Nevertheless, they commonly are p(~rmittc~tl to rcinkain in situ without trcatmerit,, although t,his practice is not ~ccoIIIIIL~~~~(‘~.” Little data exist relative to the bacteriologic* status of intact traumat,ically devitalized teeth. Ellis” cultured the contents of the canals of an unstated number of symptomlcss nonvital t&h and apparently was unimprcsscd by the significance of organisms which htl recovered. Tic obsc~rvt~l. howcvcr, tha.t operative disturbance of the pulp cont,cnts in thcsc CRSCSis followed often by evidence of an acute abscess. Stewart’? reportcY1 bacteriologic findings on fourteen teeth devitalized following trauma. Tn all but, one, a sinus had bec>n established. Organisms WCTCrccovercd from all fourteen. Results of animal studies indicate, however, that it is the rule rather thrill the exception to find organisms in the pulp chamber where inflammation has been induced. Robinson and Rolingl” irritated t,hc pulps of the teeth in cats by cavity preparation and croton oil or phenol. Known organisms were introduced into the circulation by hypodermic needle in SOIHCcases; in others, the animals were carrying a natural infection. Organisms were rccorercd from the pulp chambers (post mortem) from forty-six of sixt,y-four operated t,eeth (inflamed pulps) and only six of seventy-one nontreated teeth. Csernye? demonstrated the localization of intravenously introduced bacteria (Bmcel7a abortus) at the a.pex of nonvital guinea pig t&h. Genvert, Miller, and Burn’ recovered a variety of organisl:ls from teeth and periapical tissues of monkeys in which the pulps were cxposc~l under aseptic conditions and subscqucntly sealccl. The present report clcals with thrb oc~~umxlcc of cultivable bacteria in th(a pulp contents of intact human t&h found to bc nonvital following mechanical in jury.
I
k;;;;;;71;l
PULP
CHAMBERS
IN
INTACT
NONVITAL
TEETH
AFTER
TRAUMA
319
Material and Methods The contents of the pulp chambers of forty-six teeth were examined bacteriologically. The teeth were observed over a period of three years and were There was a history of chosen in accordance with the following criteria: trauma. The teeth were nonvital, as evidenced by discoloration or failure to respond to thermal stimulation and electrical pulp testing, or bot,h. They were not fractured. There was no evidence of caries and the teeth were free from restorations. In nineteen instances the periapical area appeared normal radiographically. In twenty-seven there was periapical rarefaction varying from a mere thickening of the periodontal membrane t,o the presence of areas All were anterior teeth; thirty-nine of rarefaction up to 1 cm. in diameter. were permanent and seven were deciduous teeth. All patients were children or young adults (ages 3 to 34)) with the exception of a 5%year-old woman from whom two teeth were studied. The interval between the occurrence of injury and that time when cultures were obtained from the nonvital pulps varied from two weeks to twenty years. TARIX T.
but
ORGAKISMS RECOVERED FROM PULP CHAMBERS OF FORTY-SIX TRAUMATICALLY DEVITALIZED TEETH
ORGANISM Alpha streptococci Gamma streptococci Anaerobic gram-positive cocci Staphylococcus albus Staphylococcus aweus Other micrococci Neisseria Bacteroidest Pseudomonas Fusobacterium: Pibrio sputorum Escherichia co% Aerobic gram-positive bacilli Anaerobic gram-positive bacilli Yeast *Two strains, arbitrarily included, appeared in broth did not grow on blood agar. tAnaerobic
lone
strain
gram-negative
was identified
bacilli otherwise as Fbsobacterium
I
NUMBER OF' STRAINS 17* 3 12 6 4 6 4 5 2 2 1 1 i 1
as gram-positive
chain-forming
cocci
unidentified.
girans.”
In each case satisfying the above criteria, the tooth was isolated by rubber dam and its surface was sterilized with either tincture of iodine or aqueous benzalkonium chloride (1 :l,OOO) . The opening was made into the pulp chamber with sterile burs. Sterile paper points were introduced into the pulp chamber to adsorb some of the contents. One point was transferred to a tube of Connaught penicillinase dextrose broth, a second to a tube of Difco thioglycollate broth (B236). The tubes were incubated at 3F’ C., the former aerobically for forty-eight hours and the latter anaerobically in a Brewer jar reduced with hydrogen for ninety-six hours, at which time growth, if any, was recorded. The contents of tubes were examined by gram stain and by dark-field microscopy. Samples of a.11tubes were transferred to heart infusion
320
JfBCI)ONALl~,
HAHF:.
.4X1)
\\.()()I)
agar containing 10 per cent defibrinated sheep’s blood. Subcultures from tht’ Connaught medium were incubated aerobically and those from the thioglycollate medium, anaerobically, for two and four days, respectively. Colonies were examined and the appearance of gram-stained cells was recorded. Each type of colony recovered from plates incubated anaerobically was subculturctl to blood agar for aerobic incubation to detcrminc those which required anaIl?.obic conditions. In most instances organisms were classified according to the scheme shown in Table 1 on the basis of t,he n.bovc findings. When it appearctl to be warrant,ed, additional examinations were made, including fcrmentat,ion of dextrose and lactose, methyl red test, Voges-Proskauer test, growth ill citrate medium, product.ion of indole and hydrogen sulfitlc, reduction o!’ nitrates, production of ammonia, a,nd gelatin liquefaction. Tests of reliability of the method of collecting the sample, in terms OF freedom from contamination, >v(‘re performed on eight cases. Moistenecl sterile paper points were applied to the exposed dentine before oprninp into the pulp. Incubation of points in broth, a,ccording to the above procedurc7 resulted in no growth.
Results Of the forty-six cases, thirty-eight ber of strains recovered in individual TABLE
IT.
DISTKIBUTION
NUMBER OF STRAINS RECOVEREI) 0 1 2 3 4 5 6
yielded growth (Table 11). ‘l’hcb I~UIIIcases varied from none t,o six.
OF RACTERIBL STRAINS IN E'ORTY-SIX. DEYITAJJZE~ TEETH ---~_I_-I
.Nl~bIKJm OI' CASES 8 16 14 3 1 1 1
I
_
~RAlJAIATICAI~I~V __---~
F'EK('I:.v'~Al:E
-~ ~~ OF ('A2SE.S
I7 35 30 11 2 2 .I
The organisms recovered are listed in Table I. A total of seventy-onca strains were isolated, The largest single group consisted of the aerobic streptococci (a total of t,wcnty strains). This was followed by Nicrococci (fifteen strains). Anaerobic cocci constituted the third largest group (twelve strains). Twenty-three, or 32 per cent, of the strains were anaerobes. There appeared to be no relationship between the bacteriologic status of the pulps and the radiographic appearance of the periapical area. Of the eight cases from which no organisms were recovered, t,he periapical tissue apRarefaction was evident in five. peared radiographically normal in three. In one of the latter, an area of rarefying osteitis about 4 mm. by 5 mm. radiated from the root tip. Fifteen cases from which bacteria were isolated were normal radiographically and twenty-three exhibited evidence of rarefaction. There was no apparent relationship between the bacteriologic status and the length of the interval between injury and cultivation. One case cultivated fourteen days following injury yielded three different strains of organisms.
~l;~~r:” ”
PULP
CHAMBERS
IN
INTACT
NONVITAT,
TEETH
AFTER
TRAUMA
321
The interval between injury and cultivation in the eight cases in which no growth occurred varied between one month and three years. In the thirtyeight cases in which growth occurred, the interval varied between two weeks and twenty years.
Discussion It is clear from the findings that ‘bacteria can be recovered from the pulp chambers of the majority of traumatically devitalized teeth, even though there is no direct communication between the pulps and the oral cavity. The percentage from which organisms were recovered in this series was about 83. Furthermore, it seems likely that at least some of the eight cases reported here to be negative actually may have contained viable organisms. The media and methods would not disclose spirochetes or many organisms requiring more cnriched media or periods of incubation l.onger than ninety-six hours. It should be noted that the nature of this study made it impractical to include a negative control; that is, cultures were not taken from the pulps of normal uninjured human teeth. Evidence is available, however, that such pulps usually are free from organisms.” Henrici and Hartzell1° failed to obtain growth from the pulps of any of twenty-two teeth free from caries and periodontal disease. Dutton and Cameron” obtained growth from only 2.7 per cent of the pulps of 108 clinically normal teeth. Gunter and associates9 obtained no growth from forty-six pulps of normal teeth; Burke’? obtained growth from only three of fifty-four pulps examined in situ at autopsy. An anachoretic effect was probably responsible for the occurrence of organisms in the pulp chambers of the thirty-eight nonvital teeth. The tendency of bacteria and other particulate matter to become fixed in areas of inflammation has been described freqnently. The literature is reviewed by Robinson and Boling.15 The bacteria recovered in the present study, on the whole, were representative of the oral flora, and it seems likely that this was the source for most of them. Representatives of most of the groups isolated are found regularly in the oral cavity,16 and at least one (Vibrio sputorum) has rarely, if ever, been found elsewhere.12 On the other hand, some (for example, Pseudomonas species and 8:. coli) are not routinely recoverable from the mouth. Assuming the oral cavity as the most common source for bacteria within the pulp chambers of intact teeth, it is probable that they reach the pulp from the gingival sulcus via the lymphatics and blood vessels of the periodontium. That organisms can reach the pulp in this way has been pointed out frequently.‘g 7l I4 It is possible that bacteria may be the cause of pulp necrosis in some cases of trauma without fracture. Menkin13 showed that blood-borne bacteria may localize in areas of inflammation within thirty minutes after injury. Lewis’l observed, following intravenous injection, that there was a very rapid appearance and concentration of trypan red in the aqueous humor of congested *It is clear that early reports of the presence of bacteria introduction of organisms during extraction (see Appletonl).
in normal
pulps resulted
from
322
MACDONAI,I),
HARE,
ASI)
\VOOl)
0. s , 0. M.. & 0. P. If:,,
eyes of rabbits. It seems likely, t,heref’orc,, that in many inst,ances bactet*i:r While the rapidly become established in the pulp tissue following in,jury. mere presence in the pulp of bacteria, even known pathogclns, does not nclc*essarily lead to disease (SW, for example, Dcnuy ant1 Thomas’), it stems safe to conclude that the presenccl of bacteria in pulps alrc~atly inflanlctl relight W~Ipound the injury and lead to pulp necrosis. Summary The bacteriologic status of the pulp chambers of forty-six intact t&h found to be nonvital following impact injury was investigated by aerobic ant1 anaerobic cultural methods. Growth was obtain4 from thirty-eight teeth. The number of strains recovered in individual casts varied bctwecn one ant1 six. A total of seventy-one strains were isolated, of which twenty-three were anaerobes. It is postulated that most of these organisms reached t.he pull) from the oral cavity via the lymphatics ant1 blood vessels of the periotlontium. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Appleton, J. L. T.: Bacterial Infect.ion, Philadelphia, 1!)51), Lea & Febiger. Burket, L. W.: J. D. Res. 21: 9, 1942. Csernyei, J.: .T. D. Res. 18: 527, 1939. Denny, F. IV., ant1 Thomas, L.: Proc. Sot. l’;xper. Hiol. ti- ,\fe,l. 88: %iO, l$J.‘i5. Dutton, E. M., and Cameron, G. C.: Canad. J. Pub. Health 23: 436, 1932. Ellis, R. 0.: The Classification and Treatment of Injuries to the Teeth of Children, Chicago, 1952, The Year Book Publishers, Inc. Fish, W. F., and MacLean, I.: Brit. Dent. J. 61: 336, 1936. Genvert, H., Miller, H., and Burn, C. G.: Tale J. Biol. & Xed. 13: 649, 1941. Gunter, J. H., Appleton, J. L. T., Strong, .I., Reatler, ,J. (‘., Zimnlerman, E:. ;I., a1111 Brooks. J. J.: J. D. Rtts. 16: 310 3937. Henrici, A. *., and H&zell, T. B.: .J. D. R&. 1: 419, 1919. Lewis, P. A.: J. Exper. Med. 23: 669, 1916. The Motile Non-Sporulating Anaerobic Rods of the Oral Cavity, Macdonald, J. B.: Toronto, 1953, University of Toronto Press. Dynamics of Inflammation, New York, 1940, The illacmillan Company. Menkin, V.: Rickert, U. G.: J. Am. Dent. A. 8: 411, 1931. Robinson, H. B. G., and Boling, L. R.: J. Am. Dent. -4. 28: 26S, 1941. Rosebury, T., in Dubos, R. 5.: Bacterial and Mycotic Infections of Man, Philadelphia, 1952, J. B. Lippineott Company. Stewart, G. G.: J. Endodontia 2: 8, 191;.