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Microscopic investigation of root canal diameters
Microscopic investigation of root canal diameters Edward N . G reen, D .D .S ., M .S ., M iam i, Fla.
Today, greater emphasis is placed on conserving teeth by m eans of endodontic treatm en t th an was previously, and the need for research in this field has also increased. O ne of the phases of study th a t has been neglected until recently is the accurate determ ination of root canal size and taper. T h e minuteness and ir regularity of canals have caused most in vestigators to abandon any attem pt at actually m aking m easurem ents through a microscope, although the volumes of root canals have been determ ined by other m ethods .1,2 Nevertheless, inform ation on sizes and tapers can be of great value to the endodontist by aiding him in visual izing the dimensions of root canals before and during the procedures of preparing and filling them . T h e success of endo dontic treatm ent, as w ith any other operation, depends to a large degree on the dentist’s knowledge of the anatom y of the region involved. Furtherm ore, such d a ta are needed for correlation w ith the sizes of files, ream ers, silver cones, g u tta p ercha cones, pluggers and broaches and m ay provide the m anufacturer of these instrum ents and m aterials w ith a basis m ore precise th an trial and error for the determ ination of the necessary diameters. Scant m ention of root canal sizes is m ade in the literature. In 1867 Latim er" observed the sizes of the foramens of m andibular m olar roots, not the canals, which he said were impossible to classify
on paper. In 1925, B arrett 4 reported a study of 512 sectioned perm anent teeth an d stated, w ithout fu rther elucidation, th a t “the canals vary greatly in size, ranging from about 20 to 35 m icrons to 250 m icrons for the larger examples.” In 1933, M ueller 5 tabulated root canal sizes under the heading, “Range in M illi m eters of C anal Size in Gingival T h ird .” T h e table provides figures for incisors, cuspids and bicuspids only, and there is no m ention of the sizes of the canals in th e m iddle third or apical third of the roots. M eyer and Scheele 6 examined root canals by m aking serial cross sections of the roots, the canals of which were then reproduced in wax. According to their observations, histological preparations show th a t the m ajor canal may be m oder ately narrow and its ramifications may
Presented before the annual m eeting of the In ter national A sso ciatio n for Dental Research, A tla n tic C ity , N . J . , M arch 22, 1957. This p a p e r is part o f a thesis, subm itted in p a rtia l fu lfillm e n t o f the requirem ents fo r the d e gre e of M aster o f Science, H o ra c e H . Rackham Sch ool of G ra d u a te Studies, U niversity of M ich igan . 1. Stew art, G . G . _ Determ ination of the a p p ro x i m ate volum es o f m ed ication used in en d od on tic tre a t ment. J . D. Res. 27:24 Feb. 1948. 2. D ietz, V. H . Personal com m unication. 3. Latim er, C . E. In ferior m olar pulps. D. Cosm os 9:243 D ec. 1867. 4. Barrett, M. T. The internal anatom y o f the teeth with sp e cia l reference to the p u lp and its branches. D. Cosm os 67:581 Ju n e 1925. 5. M ueller, A . H . A n a to m y o f the root can a ls of the incisors, cusp id s and b icu sp id s o f the perm anent teeth. J . A .D .A . 20:1361 A u g . 1933. 6. M eyer, W .t and Scheele, E. Die A n a to m ie der W u rze lkan a le . Deut. zah n arztl. Zsch r. 9:497 M ay I, 1954.
636
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be extremely fine, in the order of 0.025 to 0.5 mm. (25 to 500 m icrons). M easurem ents of root canals were ob tained by K u ttler 7 by exam ining 268 teeth from cadavers. A t th e dentinocem ental junction, the average diam eter of all canals was approxim ately 300 microns for teeth from persons less th an 25 years of age' and 270 microns for teeth from persons who were m ore than 55 years of age. T h e m easurem ents of all teeth, anterior and posterior, were averaged together. David G reen 8 exam ined the root apexes of 100 m andibular m olars through a stereomicroscope and reported th a t the average diam eter of the m ajo r apical foramens of the mesial roots was 0.52 mm. (520 m icrons), whereas th a t of the distal roots was 0.64 mm. (640 m icro n s). Considering the d a ta of Grove ,9 Coolidge ,10 D avis 11 and others, there is strong evidence th a t the funneling of the apical foram en can be verified by m easurem ent, since the figures given for th e diam eter of the foram inal opening at the surface of the cem entum are usually up to double those given for the diam eter ^ to 1 mm. inside the foramen. PRO CED U RE
Prelim inary screening of several p ro cedures was carried out so th a t th e best one could be selected. F or exam ple, sagit tal sections were prepared and m easured, but the greatest diam eter of the canal was difficult to determ ine accurately when sagittal grinding h ad been carried out. Furtherm ore, the diam eter of the canal could be m easured in only one d i rection. A n attem pt to m easure the cross sections of roots th a t h ad been prepared previously by dental students was unsuc cessful because, u n d er microscopic exam i nation, the teeth, as well as canals which had been subjected to filing or otherwise disturbed, revealed cracks and im perfec tions. M oreover, no positive identifica tion as to level of the cut could be m ade,
VOLU M E 57, NOVEM BER 1958 • 637
since m any cross-sectional cuts had been m ade close together. T he effect which drying of the teeth had on canal size was determ ined by a pilot study in a small num ber of teeth. This study showed th a t the specimens could not be allowed to dry before exam ination if measurements were to be accurate. A fter the decision to m easure the cross-sectional diam eters of the root canals of wet teeth was m ade, the n u m ber and levels of the cuts h ad to be de term ined. O ne cross section at 5 to 6 m m. from the apex was decided on im mediately, as the dentist who is carrying o ut endodontic therapy is most interested in the apical third of the root canal. Prior to establishing the level of the second cross section, which was to be m ade closer to the apex, m easurem ents of apical cem entum were m ade. T he ce m entum thickness was found generally to range from 200 to 1,000 microns and seldom to exceed 1 mm. These figures supported the findings of other investiga tors .7,1214 In this regard, the discussions by Grove 9 and Coolidge 10 relative to the presence of an apical constriction were evaluated. T horough consideration of th e factors m entioned led to the selection of the m ethod. A section was m ade /i to 1 mm. from the apical foram en and 5 to 6 mm. from the foram en so as to ex pose th e canal for measurements which would reveal the true canal size (Fig. 1). 7. Kuttler, Yu ry. M icro sco p ic in vestigation o f root apexes. J . A .D .A . 50:544 M ay 1955. 8. G reen, D a v id . Ste re o -b in o cu lar m icro sco p ic study of the root a p ice s and surroundlnq areas o f m an d ib u lar m olars. A p re lim in ary study. O ra l S u rg ., O ra l M ed . & O ra l Path. 8:1298 D ec. 1955. 9. G rove , C a r l J . N atu re's method o f m aking perfect root fillin g s fo llo w in g p u lp rem oval, with a b rie f consideration o f the d e velop m en t o f secondary c e mentum. D. Cosm os 63:968 O c t. 1921. 10. C o o lid g e , E d g a r D. A n a to m y o f the root a p e x In relation to treatm ent p roblem s. J . A .D .A . 16:1456 A u g . 1929. 11. D avis, W . C ly d e . A n a to m y o f the a p ic a l third of the roots o f teeth. D. Item s Int. 45:649 Sept. 1923. 12. Box, H . K . Dentinal cem ental ¡unction, b u lletin 3. Toronto, C a n a d ia n Dental Research Foundation, 1922. 13. H opew ell-Sm ith , A . C o n ce rn in g human cem entum . J . D. Res. 2:59 Ja n . 1920. 14. O rb a n , Balint, e d ito r. O r a l h istoloq y and em b ryo lo g y, ed 2. St. Louis, C . V. M osby C o ., 1949, p. 160.
638 • THE JO U R N A L O F THE A M E R IC A N DEN TAL A S S O C IA T IO N
Fig . I • Drawings of m axillary first bicuspid (le ft), m axillary m olar (center) and m andibular m olar (rig h t) showing levels at which cross sections were made to expose root canals fo r m icroscopic measurement
T he root canals of 110 extracted h u m an teeth were exam ined, giving a total of 260 roots, approxim ately 300 canals, and approxim ately 1200 cross-sectional m easurem ents (two diam eters at each of two levels), w hich were tabulated and analyzed. Included were 30 m axillary first bicuspids, 20 m axillary first molars, 20 m axillary second molars, 20 m andib ular first molars and 20 m andibular sec ond molars. These particu lar teeth werç selected for study because of their ex tremely fine canals, w hich present diffi cult problems of endodontic instrum en tation. T h e root apexes of the specimens revealed no evidence of resorption or fracture under magnification. Individually labeled J/j ounce bottles partly filled w ith 10 per cent Form alin were utilized to keep the teeth w et and separated. T eeth of the same type were kept in a group by means of a coding system of colored dots, and each tooth was given a number. A specimen was removed from the bottle, and Masson trichrom e stain, which contains fast green, was placed on the root apex to reveal the foram en or foram ens more clearly. W ith a saw-edged disk, m easuring approxim ately 120 m i crons in thickness and m ounted in a m andrel in a straight handpiece, a cut was m ade to 1 mm. from the apical
foram en and as nearly as possible at right angles to the long axis of the m ain canal. I n the usual instance in which the fo ra m en opened at or close to the root apex, th e cut was m ade a t right angles to the long axis of the root. In those instances in which the foram en did not open di rectly on the apex, the section was m ade a t a slight angle, in an attem p t to cut perpendicular to the canal. Even w hen m ore th an one foram en was evident on th e root surface, usually only one canal appeared a t the level of section. This shows th a t these additional foram ens were often the ends of short accessory canals which join the m ain canal 1 mm. o r less from the root tip and were conse quently cut away. W hen a canal in addi tion to the m ajor canal appeared a t the level of section, a notation was m ade in the tables. A fter the root tips of a tooth were sec tioned, the tooth was replaced in its bottle. No attem pt was m ade to remove the pulp tissue from the canals a t any time, nor was the canal itself disturbed. For m easurem ent of the canal diam e ter at the i/i> to 1 mm. level, a tooth was removed from its bottle, dried w ith tissue paper, and m ounted on a microscope slide w ith the roots up, the crown being fastened to the slide with soft utility wax (Fig. 2 ). T he crowns were left intact
GREEN
F ig . 2 • M axillary molar, with roots sectioned 5 to 6 mm. from ap ical foram ens, mounted upright with soft wax on glass slide prior to examination
throughout the investigation to facilitate handling and m ounting and to serve as a reference for orientation under the m icro scope. All bicuspids w ere m ounted w ith the buccal root on the right and all molars so th a t the m esiobuccal canal appeared in the upper right-hand corner. This a r rangem ent, which was arbitrary b u t sys tem atic, was im portant in the correlation of the m easurem ents at the two levels and later proved helpful during photo m icrography of the canal cross sections. T he cu t surface was stained, and the specimen was laid aside while a second tooth root was stained, thereby allow ing the dye on the first tooth to penetrate sufficiently to outline the canal clearly. T he first tooth specimen was placed on the platform of th e microm eter-measuring microscope, w hich provides a 32 diam eter m agnification (Fig. 3 ). T he microscope was focused on the cut sur face (Fig. 4 ) , and the hairline in the eyepiece was lined u p tangential to the circum ference of th e canal and a t right angles to a line across th e widest or the narrowest a p p aren t diam eter of the canal. T h e microscope is designed so
. VO LU M E 57, NOVEM BER 1958 • 639
th a t revolution of the adjustm ent knob moves the whole optical u n it in which the m easuring m echanism is incorporated m echanically, until the hairline arrives tangential to the opposite side of the canal circum ference, w ith the tooth re m aining stationary. Subtraction of the readings taken from the scales before an d after rotation of the optical unit gave the diam eter of the canal in microns. T h e m ounted tooth was then rotated, usually about 90 degrees, and a second m easurem ent of the canal diam eter m ade (Fig. 5 ). These two num bers were re corded as “N ” and “W ,” the narrowest an d widest diam eters of the canal. T he accuracy of this m ethod is ± 1 per cent. A fter com pletion of the m easurements at the ]/i to 1 mm. level, the roots were sectioned 5 to 6 mm. from the apex. They were placed on a m illim eter ruler and were sectioned w ith a disk as described previously perpendicularly to the long
Fig. 3 • M icrom eter-m easuring m icroscope. I. Eyepiece containing hairline. 2. Focusing knob. 3. Adjustm ent knob fo r m oving o ptical unit laterally during measurement. 4. H ousing containing measuring mechanism. 5. Tooth in position on platform
640 • TH E JO U R N A L O F TH E A M E R IC A N DEN TAL A S S O C IA T IO N
Fig . 4 • C ro ss sections of two canals as seen through m icroscope. Section on left was ma de '/2 +o I mm. from ap ical foram en and that on right was made 5 to 6 mm. from foram en
axis of the root w ith allowance being m ade for the length of the root tip th a t had already been removed. T h e cut sur faces w ere stained an d measured, and the d a ta were tabulated. M easurem ents of irregularly shaped canals w ere som ew hat more difficult to obtain th a n those of canals w ith round or oval shapes. In the mesial roots of m an dibular molars, the canal as revealed by the cross section was often the shape of a dum bbell or hourglass, and three or four m easurem ents could be determ ined— the widest portion, th e narrow est portion (isthm us), and the diam eter of the two ends of the ribbon, w hich represent con tinuations of the mesiobuccal and mesiolingual canals. A t least two m easure ments, representing the narrow est and widest portions of the canal, were ob tained for each cross section. RESU LTS
Microscope readings were in microns, one thousandth of a m illim eter. A p proxim ately 25.4 m illim eters equal one inch. T o aid the reader in visualizing the root canal sizes by com paring them w ith a known factor, K e rr root canal files were measured. O ne m illim eter from the tip,
three no. 1 files averaged 120 m icrons; three no. 3 files, 230 m icrons; and three no. 5 files, 420 microns. M easurem ents taken a t 6 m m . from the tips of three no. 1 files averaged 200 m icrons; three no. 3 files, 310 m icrons; and three no. 5 files, 570 microns. T h e diam eters of the root canals of individual teeth were tabulated, and the m ean diam eters were calculated by adding the individual m easurem ents to gether and by dividing by the num ber of canals. These d a ta were tabulated and graphs were m ade to facilitate easy com parison of one canal w ith another and of the canals of one tooth with those of a n other (Fig. 6 and 7). In both graphs the narrow m ean di am eter in microns is indicated by the first b a r of the three bars. T he m iddle bar represents the average of the narrow and wide diam eters, and the last bar rep resents the wide m ean diam eter of the canal. T h e diam eters of the canals of the m axillary first bicuspid are given in Fig. 6 . Also given in Fig. 6 are the diam eters of the smaller canals of the molars. T he diam eters of the larger canal in th e lingual root of m axillary molars and in the distal root of m andibular m olars are given in Fig. 7.
G R EEN . . . VO LU M E 57, NOVEM BER 1958 • 641
* O nly bi cuspids w ith two distinct roots were se lected for this study. All 30 teeth h ad canals th a t were evident a t both 1 an d 6 mm. levels in both roots. Some canals were nearly round, w hereas others h ad distinctly oval shapes. Com parison of the m ean diam eters shows th a t the narrow m ean diam eter was less for the buccal canal at each level, whereas the wide m ean diam eter was g reater for the buccal canal a t each level. Therefore, on the average, the lingual canals were m ore nearly round th a n th e buccal canals, al though their average diam eters (m iddle bars on the g rap h in Fig. 6 ) were ap proxim ately equal. M axillary First Bicuspids
M axillary M olars • T h e m axillary first
molars h ad mesiobuccal canals which were fairly consistent in shape n ear the apex b u t slightly variable at the 6 mm. level, w here the shapes revealed by the cross sections definitely were compressed and ribbon shaped. This observation makes ap p aren t the reason for difficulties in negotiating and cleansing this canal and also shows th a t a better seal can be expected by filling the canal to the apical foram en. T h e distobuccal canals were slightly larger at both levels th a n the mesiobuccal canals b u t h ad similar shapes (Fig. 6 ). T h e lingual root canals were, of course, considerably larger as well as somewhat rounder and fairly evenly tapered (Fig. 7 ). T he size of the root canals of the maxillary second m olars showed a tendency opposite to th a t of root canals of the first molars, the distobuccal canals appearing sm aller a t both levels th a n the mesiobuccal canals. N earer the apex, the canals tended to be less oval, whereas, at the 6 mm. level, the outlines often ap peared m ore oval. Comparisons • Com parison of the canals of m axillary first and second molars shows th a t the mesiobuccal canals of each had sim ilar m ean narrow and wide
F ig . 5 • Root canal outlines showing how narrow ( " N ” ) and wide (" W " ) diam eters o f canal cross sections were measured
diam eters at the apex. At the 6 mm. level, however, the narrow m ean diam e ter of th e mesiobuccal canals of the sec ond m olar was slightly greater, and the w ide m ean diam eter was m uch greater. O n the average, the distobuccal canal of th e first m olar was larger th an th a t of the second m olar near the apex and also 6 mm. from the apex. Furtherm ore, com parison of the canal tapers shows th a t m ore binding of a file in the disto buccal canal of the m axillary second m olars could be expected th an in the other canals. T he lingual canals of the m axillary second molars were very m uch larger th an those of the first molars, ex cept th a t, a t 5/2 to 1 mm. from the apex, the wide m ean diam eters were approxi m ately equal. In this study, the two buccal canals of m axillary second molars were sm aller th a n those of the first
642 • T H E JO U R N A L O F T H E A M E R IC A N D EN TAL A S S O C IA T IO N
microns
1 mm.
6 mm.
Maxillary First Bicuspid
1 mm.
6 mm.
1 mm.
Maxillary First Molar
6 mm.
Maxillary Second Molar
1 mm.
6 mm.
Mandibular First Molar
1 mm.
6 mm.
Mandibular Second Molar
Fig. 6 • G ra p h showing mean diam eters in m icrons o f root canals in m axillary bicuspid and of sm aller canals in molars. First o f three bars represents narrow mean diam eter o f canals, and third b ar represents wide mean diam eter. M iddle b ar gives average of narrow and wide mean diam eters. The letter "B" refers to buccal, " L " to lingual, "M B " to m esiobuccal, "D B " to distobuccal and "M L " to m esiolingual
molars, although th e tended to be larger.
lingual
canals
M andibular M olars • N ineteen of the
20 m an d ib u lar first m olars h a d two canals in the mesial root. Five of th e 20 teeth also h ad tw o distinct canals in the distal root. T h e mesiobuccal canals were fairly round a t both levels, although, at the 6 m m . level, the canals were joined in some instances w ith the mesiolingual canal by a very fine corridor, measuring 20 or 30 microns. T h e mesiolingual canals, on the average, were also fairly round, an d they were the finest of all the canals m easured. Some distal roots had two canals, and, in these instances, the distobuccal canal was usually the smaller of the two, indicating th a t the m ain canal of th e distal root should be sought in a som ew hat lingual position. I t is of practical value to note th a t w hen a distal canal is found to be small, another canal should be sought in th a t root, and, if such a canal is present, it is likely to be
buccal to the one previously discovered. D istolingual canals, in such instances, were rath er small a t the 6 mm. level, whereas single distal canals usually a p peared large and frequently appeared ribbon shaped. A lthough they were rounded near the apex, the distal canals showed distinct oval or elongated diam e ters at the 6 mm. level, indicating an angular taper. T h e mesiobuccal canals of the m an d ib u lar second molars were usually larger th a n the mesiolingual canals. In 4 of the 20 teeth, only one canal could be found in the mesial root at the l/> to 1 mm. level; 8 of the 20 teeth h ad distinctly ribbon shaped canals, indicating joining of the m esiobuccal and mesiolingual canals by a corridor of variable w idth. O nly 6 of the 20 teeth revealed distinct mesiobuccal a n d mesiolingual canals a t both levels. W hen only one mesial canal was present, it was usually nearly as large as the distal canal. T h e m andibular second molars w ere the only group in w hich there was
G R EEN . . . VO LU M E 57, NOVEM BER 1958 • 643
an exception to the otherwise consistent ratios of narrow and wide m ean diam e ters, w ith th e wide m ean diam eter of the mesiolingual canals being less than the wide m ean diam eter of the mesiobuccal canals n ear the apex b u t greater at the 6 mm. level. Such a deviation can be explained by the fact th a t m easurem ents of larger single canals, w hich were found occasionally in mesial roots of m andib ular second molars, were included in cal culating th e m ean diam eters of the mesio buccal canals because they were usually found in th a t position. T he num ber of figures available for calculating the m ean wide diam eter of the mesiolingual canals at the 6 m m . level was thereby consider ably reduced. T h e distal roots had only one canal, w hich was considerably larger th an the canals of the mesial roots. Al though canals in the distal roots were quite round at the apex, they were some w hat flattened a t the 6 mm. level, w ith the wide diam eter being more th an 1 mm. in 8 of the 20 teeth. This fact em phasizes the necessity for ‘ obtaining a tight seal in the apical region, and the desirability of lateral condensation to obliterate th e w ider portion of the canal. Comparisons • Com parison of m andib ular first an d second m olars shows th a t the second m olars h ad mesiobuccal canals somewhat larger on the average than those of th e first m olars at the /i to 1 mm. level, b u t this disparity was found to be less a t the 6 mm. level. Mesiolingual canals at th e apical section of the second molars were almost identical in dim en sion w ith those of the first molars, but a t the 6 mm. level they were larger and less regular in shape. C O N C L U S IO N S
W ith all of the d a ta being considered, it is evident th a t the small canals of molars and m axillary bicuspids did not differ greatly in size n ear the apical foramen from one too th to another, nor did the
larger canals of the molars vary greatly, w ith certain exceptions. T he slight varia tions th a t did exist, however, would be im p o rtan t to the practitioner of endodontics, and the following conclusions can be m ade : 1. Both the narrow and wide diam e ters of root canals should be considered w hen discussing canal debridem ent, be cause the file or ream er cuts dentin in a straight canal w hen the instrum ent is as large as the narrow diam eter of the canal, whereas all organic m atter and debris are not rem oved until its wide diam eter is reached by the instrum ent. Since com plete debridem ent is the objective of in strum entation and irrigation, a knowl edge of canal diam eters can aid in judging microns 1,000
•
LINGUAL ROOT
DISTAL ROOT
W W
200
1 mm. 6 mm. 1 mm. 6 mm.
1 mm. 6 mm. 1 mm. 6 mm.
Maxillary Maxillary First Molar Second Molar
Mandibular Mandibular First Molar Second Molar
F ig . 7 • G rap h of mean diam eters in microns of large canals in lingua! roots of m axillary molars and distal roots o f m andibular molars. " N " bars represent narrow mean diam eters, " W " bars rep resent wide mean diam eters and m iddle bars represent average of these two measurements
444 • TH E JO U R N A L O F TH E A M E R IC A N D EN TAL A S S O C IA T IO N
the am ount of filing and ream ing neces sary to cleanse the canal, although fine canals are usually curved an d often have constrictions and although certain physi cal lim itations are imposed by the con struction of the instrum ents. 2. T h e m ajority of th e fine canals would have been adequately debrided by a no. 3 file, but a very few would have been sufficiently cleansed by a file smaller than no. 3. In several instances, filing with a no. 4 file, though rarely w ith a larger file, would have been necessary to completely debride the small canals. 3. T h e m ajority of the large m olar canals would have been debrided ade quately by a no. 5 file, b u t in a very few instances a sm aller instrum ent would have been adequate. Some of the large m olar canals would have required filing w ith a no. 6 or larger file for thorough debridem ent. 4. It should be kept in m ind th a t in dividual teeth present specific variations of canal anatom y depending on natural characteristics and secondary dentin for m ation, w hich is related to age, caries, occlusion, trau m a and other factors which the clinician'm ust evaluate to the best of his ability preparatory to and during endodontic treatm ent. SUM M ARY
An investigation was undertaken to de term ine the cross-sectional diameters, wide an d narrow , of the root canals of extracted hum an m olar and m axillary bi cuspid teeth. These teeth were chosen for study because of their extremely fine canals, w hich offer problem s in endo dontic treatm ent. T h e 110 specimens were k ept separated in ounce bottles, partly filled w ith 10 p er cent Form alin and individually labeled. T h e roots were sectioned at right angles to th e root canal
at two levels: /i to 1 mm. and 5 to 6 mm. from the apical foram en. P rior to exam ination, each tooth was m ounted on a glass slide, and M asson trichrom e stain which contains fast green was used to delineate the canal m ore clearly. M eas urem ents were m ade w ith a m icrom eterm easuring microscope at 32 diameters magnification. A pproxim ately 1200 m easurem ents of 300 root canals were tabulated and m ean diam eters were calculated. G raphs were prepared to facilitate study and com pari son. T h e observations were as follows: 1. T h e buccal and palatal canals of m axillary first bicuspids were sim ilar in size close to the apical foram en as well as 5 to 6 mm. from it. 2. T he distobuccal canals of m axil lary first molars were found to be slightly larger th an the mesiobuccal canals, p a r ticularly when m easurem ents were m ade 6 mm. from the root apex. T he maxillary second m olars exhibited the opposite tendency— the mesiobuccal canals being larger th an the distobuccal canals. 3. T h e mesiobuccal canals of m an dibular first m olars were slightly larger th an the mesiolingual canals. This was found to an even greater degree in the mesial canals of m andibular second molars near the apex, b u t at the 6 mm. level the wide dimension of the mesio lingual canals was slightly larger than the mesiobuccal canals and the narrow dim ension was slightly smaller. 4. T he lingual root canals of m axil lary first molars were somewhat smaller th an those of m axillary second molars. 5. T h e distal root canals of m andib u lar first molars and second molars were similar in size close to the apex, b u t at th e 6 mm. level the distal root canals of the m andibular first molars were smaller th a n those of the second molars. P.O. B ox 4339
Today, greater emphasis is placed on conserving teeth by m eans of endodontic treatm en t th an was previously, and the need for research in this field has also increased. O ne of the phases of study th a t has been neglected until recently is the accurate determ ination of root canal size and taper. T h e minuteness and ir regularity of canals have caused most in vestigators to abandon any attem pt at actually m aking m easurem ents through a microscope, although the volumes of root canals have been determ ined by other m ethods .1,2 Nevertheless, inform ation on sizes and tapers can be of great value to the endodontist by aiding him in visual izing the dimensions of root canals before and during the procedures of preparing and filling them . T h e success of endo dontic treatm ent, as w ith any other operation, depends to a large degree on the dentist’s knowledge of the anatom y of the region involved. Furtherm ore, such d a ta are needed for correlation w ith the sizes of files, ream ers, silver cones, g u tta p ercha cones, pluggers and broaches and m ay provide the m anufacturer of these instrum ents and m aterials w ith a basis m ore precise th an trial and error for the determ ination of the necessary diameters. Scant m ention of root canal sizes is m ade in the literature. In 1867 Latim er" observed the sizes of the foramens of m andibular m olar roots, not the canals, which he said were impossible to classify
on paper. In 1925, B arrett 4 reported a study of 512 sectioned perm anent teeth an d stated, w ithout fu rther elucidation, th a t “the canals vary greatly in size, ranging from about 20 to 35 m icrons to 250 m icrons for the larger examples.” In 1933, M ueller 5 tabulated root canal sizes under the heading, “Range in M illi m eters of C anal Size in Gingival T h ird .” T h e table provides figures for incisors, cuspids and bicuspids only, and there is no m ention of the sizes of the canals in th e m iddle third or apical third of the roots. M eyer and Scheele 6 examined root canals by m aking serial cross sections of the roots, the canals of which were then reproduced in wax. According to their observations, histological preparations show th a t the m ajor canal may be m oder ately narrow and its ramifications may
Presented before the annual m eeting of the In ter national A sso ciatio n for Dental Research, A tla n tic C ity , N . J . , M arch 22, 1957. This p a p e r is part o f a thesis, subm itted in p a rtia l fu lfillm e n t o f the requirem ents fo r the d e gre e of M aster o f Science, H o ra c e H . Rackham Sch ool of G ra d u a te Studies, U niversity of M ich igan . 1. Stew art, G . G . _ Determ ination of the a p p ro x i m ate volum es o f m ed ication used in en d od on tic tre a t ment. J . D. Res. 27:24 Feb. 1948. 2. D ietz, V. H . Personal com m unication. 3. Latim er, C . E. In ferior m olar pulps. D. Cosm os 9:243 D ec. 1867. 4. Barrett, M. T. The internal anatom y o f the teeth with sp e cia l reference to the p u lp and its branches. D. Cosm os 67:581 Ju n e 1925. 5. M ueller, A . H . A n a to m y o f the root can a ls of the incisors, cusp id s and b icu sp id s o f the perm anent teeth. J . A .D .A . 20:1361 A u g . 1933. 6. M eyer, W .t and Scheele, E. Die A n a to m ie der W u rze lkan a le . Deut. zah n arztl. Zsch r. 9:497 M ay I, 1954.
636
GREEN
be extremely fine, in the order of 0.025 to 0.5 mm. (25 to 500 m icrons). M easurem ents of root canals were ob tained by K u ttler 7 by exam ining 268 teeth from cadavers. A t th e dentinocem ental junction, the average diam eter of all canals was approxim ately 300 microns for teeth from persons less th an 25 years of age' and 270 microns for teeth from persons who were m ore than 55 years of age. T h e m easurem ents of all teeth, anterior and posterior, were averaged together. David G reen 8 exam ined the root apexes of 100 m andibular m olars through a stereomicroscope and reported th a t the average diam eter of the m ajo r apical foramens of the mesial roots was 0.52 mm. (520 m icrons), whereas th a t of the distal roots was 0.64 mm. (640 m icro n s). Considering the d a ta of Grove ,9 Coolidge ,10 D avis 11 and others, there is strong evidence th a t the funneling of the apical foram en can be verified by m easurem ent, since the figures given for th e diam eter of the foram inal opening at the surface of the cem entum are usually up to double those given for the diam eter ^ to 1 mm. inside the foramen. PRO CED U RE
Prelim inary screening of several p ro cedures was carried out so th a t th e best one could be selected. F or exam ple, sagit tal sections were prepared and m easured, but the greatest diam eter of the canal was difficult to determ ine accurately when sagittal grinding h ad been carried out. Furtherm ore, the diam eter of the canal could be m easured in only one d i rection. A n attem pt to m easure the cross sections of roots th a t h ad been prepared previously by dental students was unsuc cessful because, u n d er microscopic exam i nation, the teeth, as well as canals which had been subjected to filing or otherwise disturbed, revealed cracks and im perfec tions. M oreover, no positive identifica tion as to level of the cut could be m ade,
VOLU M E 57, NOVEM BER 1958 • 637
since m any cross-sectional cuts had been m ade close together. T he effect which drying of the teeth had on canal size was determ ined by a pilot study in a small num ber of teeth. This study showed th a t the specimens could not be allowed to dry before exam ination if measurements were to be accurate. A fter the decision to m easure the cross-sectional diam eters of the root canals of wet teeth was m ade, the n u m ber and levels of the cuts h ad to be de term ined. O ne cross section at 5 to 6 m m. from the apex was decided on im mediately, as the dentist who is carrying o ut endodontic therapy is most interested in the apical third of the root canal. Prior to establishing the level of the second cross section, which was to be m ade closer to the apex, m easurem ents of apical cem entum were m ade. T he ce m entum thickness was found generally to range from 200 to 1,000 microns and seldom to exceed 1 mm. These figures supported the findings of other investiga tors .7,1214 In this regard, the discussions by Grove 9 and Coolidge 10 relative to the presence of an apical constriction were evaluated. T horough consideration of th e factors m entioned led to the selection of the m ethod. A section was m ade /i to 1 mm. from the apical foram en and 5 to 6 mm. from the foram en so as to ex pose th e canal for measurements which would reveal the true canal size (Fig. 1). 7. Kuttler, Yu ry. M icro sco p ic in vestigation o f root apexes. J . A .D .A . 50:544 M ay 1955. 8. G reen, D a v id . Ste re o -b in o cu lar m icro sco p ic study of the root a p ice s and surroundlnq areas o f m an d ib u lar m olars. A p re lim in ary study. O ra l S u rg ., O ra l M ed . & O ra l Path. 8:1298 D ec. 1955. 9. G rove , C a r l J . N atu re's method o f m aking perfect root fillin g s fo llo w in g p u lp rem oval, with a b rie f consideration o f the d e velop m en t o f secondary c e mentum. D. Cosm os 63:968 O c t. 1921. 10. C o o lid g e , E d g a r D. A n a to m y o f the root a p e x In relation to treatm ent p roblem s. J . A .D .A . 16:1456 A u g . 1929. 11. D avis, W . C ly d e . A n a to m y o f the a p ic a l third of the roots o f teeth. D. Item s Int. 45:649 Sept. 1923. 12. Box, H . K . Dentinal cem ental ¡unction, b u lletin 3. Toronto, C a n a d ia n Dental Research Foundation, 1922. 13. H opew ell-Sm ith , A . C o n ce rn in g human cem entum . J . D. Res. 2:59 Ja n . 1920. 14. O rb a n , Balint, e d ito r. O r a l h istoloq y and em b ryo lo g y, ed 2. St. Louis, C . V. M osby C o ., 1949, p. 160.
638 • THE JO U R N A L O F THE A M E R IC A N DEN TAL A S S O C IA T IO N
Fig . I • Drawings of m axillary first bicuspid (le ft), m axillary m olar (center) and m andibular m olar (rig h t) showing levels at which cross sections were made to expose root canals fo r m icroscopic measurement
T he root canals of 110 extracted h u m an teeth were exam ined, giving a total of 260 roots, approxim ately 300 canals, and approxim ately 1200 cross-sectional m easurem ents (two diam eters at each of two levels), w hich were tabulated and analyzed. Included were 30 m axillary first bicuspids, 20 m axillary first molars, 20 m axillary second molars, 20 m andib ular first molars and 20 m andibular sec ond molars. These particu lar teeth werç selected for study because of their ex tremely fine canals, w hich present diffi cult problems of endodontic instrum en tation. T h e root apexes of the specimens revealed no evidence of resorption or fracture under magnification. Individually labeled J/j ounce bottles partly filled w ith 10 per cent Form alin were utilized to keep the teeth w et and separated. T eeth of the same type were kept in a group by means of a coding system of colored dots, and each tooth was given a number. A specimen was removed from the bottle, and Masson trichrom e stain, which contains fast green, was placed on the root apex to reveal the foram en or foram ens more clearly. W ith a saw-edged disk, m easuring approxim ately 120 m i crons in thickness and m ounted in a m andrel in a straight handpiece, a cut was m ade to 1 mm. from the apical
foram en and as nearly as possible at right angles to the long axis of the m ain canal. I n the usual instance in which the fo ra m en opened at or close to the root apex, th e cut was m ade a t right angles to the long axis of the root. In those instances in which the foram en did not open di rectly on the apex, the section was m ade a t a slight angle, in an attem p t to cut perpendicular to the canal. Even w hen m ore th an one foram en was evident on th e root surface, usually only one canal appeared a t the level of section. This shows th a t these additional foram ens were often the ends of short accessory canals which join the m ain canal 1 mm. o r less from the root tip and were conse quently cut away. W hen a canal in addi tion to the m ajor canal appeared a t the level of section, a notation was m ade in the tables. A fter the root tips of a tooth were sec tioned, the tooth was replaced in its bottle. No attem pt was m ade to remove the pulp tissue from the canals a t any time, nor was the canal itself disturbed. For m easurem ent of the canal diam e ter at the i/i> to 1 mm. level, a tooth was removed from its bottle, dried w ith tissue paper, and m ounted on a microscope slide w ith the roots up, the crown being fastened to the slide with soft utility wax (Fig. 2 ). T he crowns were left intact
GREEN
F ig . 2 • M axillary molar, with roots sectioned 5 to 6 mm. from ap ical foram ens, mounted upright with soft wax on glass slide prior to examination
throughout the investigation to facilitate handling and m ounting and to serve as a reference for orientation under the m icro scope. All bicuspids w ere m ounted w ith the buccal root on the right and all molars so th a t the m esiobuccal canal appeared in the upper right-hand corner. This a r rangem ent, which was arbitrary b u t sys tem atic, was im portant in the correlation of the m easurem ents at the two levels and later proved helpful during photo m icrography of the canal cross sections. T he cu t surface was stained, and the specimen was laid aside while a second tooth root was stained, thereby allow ing the dye on the first tooth to penetrate sufficiently to outline the canal clearly. T he first tooth specimen was placed on the platform of th e microm eter-measuring microscope, w hich provides a 32 diam eter m agnification (Fig. 3 ). T he microscope was focused on the cut sur face (Fig. 4 ) , and the hairline in the eyepiece was lined u p tangential to the circum ference of th e canal and a t right angles to a line across th e widest or the narrowest a p p aren t diam eter of the canal. T h e microscope is designed so
. VO LU M E 57, NOVEM BER 1958 • 639
th a t revolution of the adjustm ent knob moves the whole optical u n it in which the m easuring m echanism is incorporated m echanically, until the hairline arrives tangential to the opposite side of the canal circum ference, w ith the tooth re m aining stationary. Subtraction of the readings taken from the scales before an d after rotation of the optical unit gave the diam eter of the canal in microns. T h e m ounted tooth was then rotated, usually about 90 degrees, and a second m easurem ent of the canal diam eter m ade (Fig. 5 ). These two num bers were re corded as “N ” and “W ,” the narrowest an d widest diam eters of the canal. T he accuracy of this m ethod is ± 1 per cent. A fter com pletion of the m easurements at the ]/i to 1 mm. level, the roots were sectioned 5 to 6 mm. from the apex. They were placed on a m illim eter ruler and were sectioned w ith a disk as described previously perpendicularly to the long
Fig. 3 • M icrom eter-m easuring m icroscope. I. Eyepiece containing hairline. 2. Focusing knob. 3. Adjustm ent knob fo r m oving o ptical unit laterally during measurement. 4. H ousing containing measuring mechanism. 5. Tooth in position on platform
640 • TH E JO U R N A L O F TH E A M E R IC A N DEN TAL A S S O C IA T IO N
Fig . 4 • C ro ss sections of two canals as seen through m icroscope. Section on left was ma de '/2 +o I mm. from ap ical foram en and that on right was made 5 to 6 mm. from foram en
axis of the root w ith allowance being m ade for the length of the root tip th a t had already been removed. T h e cut sur faces w ere stained an d measured, and the d a ta were tabulated. M easurem ents of irregularly shaped canals w ere som ew hat more difficult to obtain th a n those of canals w ith round or oval shapes. In the mesial roots of m an dibular molars, the canal as revealed by the cross section was often the shape of a dum bbell or hourglass, and three or four m easurem ents could be determ ined— the widest portion, th e narrow est portion (isthm us), and the diam eter of the two ends of the ribbon, w hich represent con tinuations of the mesiobuccal and mesiolingual canals. A t least two m easure ments, representing the narrow est and widest portions of the canal, were ob tained for each cross section. RESU LTS
Microscope readings were in microns, one thousandth of a m illim eter. A p proxim ately 25.4 m illim eters equal one inch. T o aid the reader in visualizing the root canal sizes by com paring them w ith a known factor, K e rr root canal files were measured. O ne m illim eter from the tip,
three no. 1 files averaged 120 m icrons; three no. 3 files, 230 m icrons; and three no. 5 files, 420 microns. M easurem ents taken a t 6 m m . from the tips of three no. 1 files averaged 200 m icrons; three no. 3 files, 310 m icrons; and three no. 5 files, 570 microns. T h e diam eters of the root canals of individual teeth were tabulated, and the m ean diam eters were calculated by adding the individual m easurem ents to gether and by dividing by the num ber of canals. These d a ta were tabulated and graphs were m ade to facilitate easy com parison of one canal w ith another and of the canals of one tooth with those of a n other (Fig. 6 and 7). In both graphs the narrow m ean di am eter in microns is indicated by the first b a r of the three bars. T he m iddle bar represents the average of the narrow and wide diam eters, and the last bar rep resents the wide m ean diam eter of the canal. T h e diam eters of the canals of the m axillary first bicuspid are given in Fig. 6 . Also given in Fig. 6 are the diam eters of the smaller canals of the molars. T he diam eters of the larger canal in th e lingual root of m axillary molars and in the distal root of m andibular m olars are given in Fig. 7.
G R EEN . . . VO LU M E 57, NOVEM BER 1958 • 641
* O nly bi cuspids w ith two distinct roots were se lected for this study. All 30 teeth h ad canals th a t were evident a t both 1 an d 6 mm. levels in both roots. Some canals were nearly round, w hereas others h ad distinctly oval shapes. Com parison of the m ean diam eters shows th a t the narrow m ean diam eter was less for the buccal canal at each level, whereas the wide m ean diam eter was g reater for the buccal canal a t each level. Therefore, on the average, the lingual canals were m ore nearly round th a n th e buccal canals, al though their average diam eters (m iddle bars on the g rap h in Fig. 6 ) were ap proxim ately equal. M axillary First Bicuspids
M axillary M olars • T h e m axillary first
molars h ad mesiobuccal canals which were fairly consistent in shape n ear the apex b u t slightly variable at the 6 mm. level, w here the shapes revealed by the cross sections definitely were compressed and ribbon shaped. This observation makes ap p aren t the reason for difficulties in negotiating and cleansing this canal and also shows th a t a better seal can be expected by filling the canal to the apical foram en. T h e distobuccal canals were slightly larger at both levels th a n the mesiobuccal canals b u t h ad similar shapes (Fig. 6 ). T h e lingual root canals were, of course, considerably larger as well as somewhat rounder and fairly evenly tapered (Fig. 7 ). T he size of the root canals of the maxillary second m olars showed a tendency opposite to th a t of root canals of the first molars, the distobuccal canals appearing sm aller a t both levels th a n the mesiobuccal canals. N earer the apex, the canals tended to be less oval, whereas, at the 6 mm. level, the outlines often ap peared m ore oval. Comparisons • Com parison of the canals of m axillary first and second molars shows th a t the mesiobuccal canals of each had sim ilar m ean narrow and wide
F ig . 5 • Root canal outlines showing how narrow ( " N ” ) and wide (" W " ) diam eters o f canal cross sections were measured
diam eters at the apex. At the 6 mm. level, however, the narrow m ean diam e ter of th e mesiobuccal canals of the sec ond m olar was slightly greater, and the w ide m ean diam eter was m uch greater. O n the average, the distobuccal canal of th e first m olar was larger th an th a t of the second m olar near the apex and also 6 mm. from the apex. Furtherm ore, com parison of the canal tapers shows th a t m ore binding of a file in the disto buccal canal of the m axillary second m olars could be expected th an in the other canals. T he lingual canals of the m axillary second molars were very m uch larger th an those of the first molars, ex cept th a t, a t 5/2 to 1 mm. from the apex, the wide m ean diam eters were approxi m ately equal. In this study, the two buccal canals of m axillary second molars were sm aller th a n those of the first
642 • T H E JO U R N A L O F T H E A M E R IC A N D EN TAL A S S O C IA T IO N
microns
1 mm.
6 mm.
Maxillary First Bicuspid
1 mm.
6 mm.
1 mm.
Maxillary First Molar
6 mm.
Maxillary Second Molar
1 mm.
6 mm.
Mandibular First Molar
1 mm.
6 mm.
Mandibular Second Molar
Fig. 6 • G ra p h showing mean diam eters in m icrons o f root canals in m axillary bicuspid and of sm aller canals in molars. First o f three bars represents narrow mean diam eter o f canals, and third b ar represents wide mean diam eter. M iddle b ar gives average of narrow and wide mean diam eters. The letter "B" refers to buccal, " L " to lingual, "M B " to m esiobuccal, "D B " to distobuccal and "M L " to m esiolingual
molars, although th e tended to be larger.
lingual
canals
M andibular M olars • N ineteen of the
20 m an d ib u lar first m olars h a d two canals in the mesial root. Five of th e 20 teeth also h ad tw o distinct canals in the distal root. T h e mesiobuccal canals were fairly round a t both levels, although, at the 6 m m . level, the canals were joined in some instances w ith the mesiolingual canal by a very fine corridor, measuring 20 or 30 microns. T h e mesiolingual canals, on the average, were also fairly round, an d they were the finest of all the canals m easured. Some distal roots had two canals, and, in these instances, the distobuccal canal was usually the smaller of the two, indicating th a t the m ain canal of th e distal root should be sought in a som ew hat lingual position. I t is of practical value to note th a t w hen a distal canal is found to be small, another canal should be sought in th a t root, and, if such a canal is present, it is likely to be
buccal to the one previously discovered. D istolingual canals, in such instances, were rath er small a t the 6 mm. level, whereas single distal canals usually a p peared large and frequently appeared ribbon shaped. A lthough they were rounded near the apex, the distal canals showed distinct oval or elongated diam e ters at the 6 mm. level, indicating an angular taper. T h e mesiobuccal canals of the m an d ib u lar second molars were usually larger th a n the mesiolingual canals. In 4 of the 20 teeth, only one canal could be found in the mesial root at the l/> to 1 mm. level; 8 of the 20 teeth h ad distinctly ribbon shaped canals, indicating joining of the m esiobuccal and mesiolingual canals by a corridor of variable w idth. O nly 6 of the 20 teeth revealed distinct mesiobuccal a n d mesiolingual canals a t both levels. W hen only one mesial canal was present, it was usually nearly as large as the distal canal. T h e m andibular second molars w ere the only group in w hich there was
G R EEN . . . VO LU M E 57, NOVEM BER 1958 • 643
an exception to the otherwise consistent ratios of narrow and wide m ean diam e ters, w ith th e wide m ean diam eter of the mesiolingual canals being less than the wide m ean diam eter of the mesiobuccal canals n ear the apex b u t greater at the 6 mm. level. Such a deviation can be explained by the fact th a t m easurem ents of larger single canals, w hich were found occasionally in mesial roots of m andib ular second molars, were included in cal culating th e m ean diam eters of the mesio buccal canals because they were usually found in th a t position. T he num ber of figures available for calculating the m ean wide diam eter of the mesiolingual canals at the 6 m m . level was thereby consider ably reduced. T h e distal roots had only one canal, w hich was considerably larger th an the canals of the mesial roots. Al though canals in the distal roots were quite round at the apex, they were some w hat flattened a t the 6 mm. level, w ith the wide diam eter being more th an 1 mm. in 8 of the 20 teeth. This fact em phasizes the necessity for ‘ obtaining a tight seal in the apical region, and the desirability of lateral condensation to obliterate th e w ider portion of the canal. Comparisons • Com parison of m andib ular first an d second m olars shows th a t the second m olars h ad mesiobuccal canals somewhat larger on the average than those of th e first m olars at the /i to 1 mm. level, b u t this disparity was found to be less a t the 6 mm. level. Mesiolingual canals at th e apical section of the second molars were almost identical in dim en sion w ith those of the first molars, but a t the 6 mm. level they were larger and less regular in shape. C O N C L U S IO N S
W ith all of the d a ta being considered, it is evident th a t the small canals of molars and m axillary bicuspids did not differ greatly in size n ear the apical foramen from one too th to another, nor did the
larger canals of the molars vary greatly, w ith certain exceptions. T he slight varia tions th a t did exist, however, would be im p o rtan t to the practitioner of endodontics, and the following conclusions can be m ade : 1. Both the narrow and wide diam e ters of root canals should be considered w hen discussing canal debridem ent, be cause the file or ream er cuts dentin in a straight canal w hen the instrum ent is as large as the narrow diam eter of the canal, whereas all organic m atter and debris are not rem oved until its wide diam eter is reached by the instrum ent. Since com plete debridem ent is the objective of in strum entation and irrigation, a knowl edge of canal diam eters can aid in judging microns 1,000
•
LINGUAL ROOT
DISTAL ROOT
W W
200
1 mm. 6 mm. 1 mm. 6 mm.
1 mm. 6 mm. 1 mm. 6 mm.
Maxillary Maxillary First Molar Second Molar
Mandibular Mandibular First Molar Second Molar
F ig . 7 • G rap h of mean diam eters in microns of large canals in lingua! roots of m axillary molars and distal roots o f m andibular molars. " N " bars represent narrow mean diam eters, " W " bars rep resent wide mean diam eters and m iddle bars represent average of these two measurements
444 • TH E JO U R N A L O F TH E A M E R IC A N D EN TAL A S S O C IA T IO N
the am ount of filing and ream ing neces sary to cleanse the canal, although fine canals are usually curved an d often have constrictions and although certain physi cal lim itations are imposed by the con struction of the instrum ents. 2. T h e m ajority of th e fine canals would have been adequately debrided by a no. 3 file, but a very few would have been sufficiently cleansed by a file smaller than no. 3. In several instances, filing with a no. 4 file, though rarely w ith a larger file, would have been necessary to completely debride the small canals. 3. T h e m ajority of the large m olar canals would have been debrided ade quately by a no. 5 file, b u t in a very few instances a sm aller instrum ent would have been adequate. Some of the large m olar canals would have required filing w ith a no. 6 or larger file for thorough debridem ent. 4. It should be kept in m ind th a t in dividual teeth present specific variations of canal anatom y depending on natural characteristics and secondary dentin for m ation, w hich is related to age, caries, occlusion, trau m a and other factors which the clinician'm ust evaluate to the best of his ability preparatory to and during endodontic treatm ent. SUM M ARY
An investigation was undertaken to de term ine the cross-sectional diameters, wide an d narrow , of the root canals of extracted hum an m olar and m axillary bi cuspid teeth. These teeth were chosen for study because of their extremely fine canals, w hich offer problem s in endo dontic treatm ent. T h e 110 specimens were k ept separated in ounce bottles, partly filled w ith 10 p er cent Form alin and individually labeled. T h e roots were sectioned at right angles to th e root canal
at two levels: /i to 1 mm. and 5 to 6 mm. from the apical foram en. P rior to exam ination, each tooth was m ounted on a glass slide, and M asson trichrom e stain which contains fast green was used to delineate the canal m ore clearly. M eas urem ents were m ade w ith a m icrom eterm easuring microscope at 32 diameters magnification. A pproxim ately 1200 m easurem ents of 300 root canals were tabulated and m ean diam eters were calculated. G raphs were prepared to facilitate study and com pari son. T h e observations were as follows: 1. T h e buccal and palatal canals of m axillary first bicuspids were sim ilar in size close to the apical foram en as well as 5 to 6 mm. from it. 2. T he distobuccal canals of m axil lary first molars were found to be slightly larger th an the mesiobuccal canals, p a r ticularly when m easurem ents were m ade 6 mm. from the root apex. T he maxillary second m olars exhibited the opposite tendency— the mesiobuccal canals being larger th an the distobuccal canals. 3. T h e mesiobuccal canals of m an dibular first m olars were slightly larger th an the mesiolingual canals. This was found to an even greater degree in the mesial canals of m andibular second molars near the apex, b u t at the 6 mm. level the wide dimension of the mesio lingual canals was slightly larger than the mesiobuccal canals and the narrow dim ension was slightly smaller. 4. T he lingual root canals of m axil lary first molars were somewhat smaller th an those of m axillary second molars. 5. T h e distal root canals of m andib u lar first molars and second molars were similar in size close to the apex, b u t at th e 6 mm. level the distal root canals of the m andibular first molars were smaller th a n those of the second molars. P.O. B ox 4339