The effect of dowel preparation on the apical seal of endodontically treated teeth Ross L. Neagley, Commander (DC) USN NAVAL
he most common method of restoring the pulpless single-rooted tooth is by means of a cast post crown which is cemented into the prepared root canal space,l However, there have been no published investigations to indicate what effect the actual post preparation has on the apical seal of the endodontically treated tooth. The following questions need to be answered: (1) How much of the root canal filling can be removed in post crown preparation without endangering the apical seal? (2) Wh.at root-filling technique is best suited for a tooth which subsequently may require a post crown! It is the purpose of this article to try to answer these questions. The cardinal principle of endodontics is total sealing of the root canal from the periapical environment. The major cause of endodontic failure is inadequate sealing of the root canal. Incomplete obliteration, unfilled canals, and inadvertently removed silver points accounted for 63.4 per cent of the endodontic failures in the Washington study. Other categories of failure which actually involve apical perculation are accessory canals, adjacent pulpless teeth, root perforations, and broken instruments. These categories increase the rate of failures that are directly or indirectly related to inadequate root sealing to 75 per cent.2y3 The various methods of sealing root canals have been investigated by Dow and Ingle4 and Marshall and Massler. 5 In both investigations it was found that poorly obturated root canals showed penetration when subjected to leakage studies with radioisotopes. Dye-penetration studies to indicate Ieakage were first utilized by Grossman6 to study the seal of temporary filling materials. Stewart7 immersed root canal filling materials in methylene blue dye to study permeability. In a The opinions and assertCons contained herein are those of the author and are not to be construed as official or as reflecting the views of the Navy Department or the naval service at large.
recent unpublished stutly, Kitzmiller” also used mcthplcne blue as an indicator of leakage following apicoectomy. Numerous texts and articles bar-c presented, in great detail, various techniques for preparing a post crown. However, there is a grclat deal of controversy as to the desired depth of the post hole in the root and the preferred material to be utilized for the apical seal. Barabanl has stated that one half of the root canal is needed for the construction of the post crown and that the root canal should preferably be filled with gutta-percha. Others, 9, lo have advocated the use of the twist-off silver cone in teeth to be rcstorcd by a dowel drown. Soltanoff and Parr2 have stated that a dowel space as long as the clinical crown should be allowed. Deubert’l believes that the dowel preparation should be 11/z times the crown length, with only 6hc apical 2 to 3 mm. remaining sealed, whereas Metrickl” has advocated an apicoeetomy be performed after dowel. crown insertion to eliminate the need for relying on the previous apical seal. Frank2 has cautioned against dislodging the root canal filling in dowel preparation, particularly when silver points have been used. Kronfeld13 has warned that the post preparation should not encroach on the apical third, lest failure result from disturbing the apical seal, He also stated that the use of solvents with reamers to remove gutta-pcrcha would cause shrinkage of the root canal filling and thereby destroy the apical seal. A recent unpublished study by ZeiglcrlJ dealt with the effect of removing one half the root canal filling (as in dowel preparation) on the apical seal. The results of the invest,igation showed complete penetration along the remaining root canal filling in 14 per cent of the teeth treated with lateral 20 per cent of Ihe teeth obturated with single condensat,ion of gutta-percha, Cones of gutta-percha ancl scaler, and 6 per cent of the cases in which silver points and sealer were used. The present study was designed to evaluate the effect on the apical seal of the three most popular root sealing techniques when subjected to dowel preparations that permitted remaining root fillings 4 mm. and 8 mm. in length. A retrograde amalgam technique was also included. MATERIALS
One hundred single-rooted anterior teeth were collected immediately following extraction and stored in a dilute solution of sodium hypochlorite for approximately 7 days at 7’ C. The teeth were then transferred to an isotonic saline solution and stored at 7O C. until needed. The crowns of the tcet,h were removed to facilitate access, and the roots were dipped in collodian to seal the accessory canals. The root canals were instrumented with reamers and files* to at least two sizes larger than the instrument which would initially bind in the apex. The teeth were divided into three groups of thirty teet,h each and one group of ten teeth. They were stored in isotonic saline solution at 37’ C. until used. *Kerr
on apical seal
Group A. Sectional silver cone. The thirty teeth in Group A were fitted with silver cones which were notched 5 mm. from the apex. The root canals were dried with paper points. The silver cone was well coated with Rickert’s sealer,” seated, and twisted off at the working distance under pressure. Zinc oxide and eugenol were spun into the remainder of the canal with a lentulo spiral. Group B. Gutta-percha lateral condensation. The thirty teeth in Group B were fitted with a master cone of gutta-percha, dried with paper points, and filled with the prepared cone, using lateral condensation of multiple guttapercha points and Rickert ‘s sealer. Group C. Warm gutta-percha. The thirty teeth in Group C were fitted with a master cone of gutta-percha and dried with paper points, and the mast,er cone was cemented with Rickert’s sealer. The root canal was then completely filled by warming and condensing the gutta-percha as advocated by Schilder.15 Group D. Retrograde amalgam. The apices of the ten teeth in Group D were beveled facially-lingually with a tapered fissue bur, and a retrograde amalgam preparation w,as made to a depth of 3 mm. The preparation was air-dried, and a zinc-free silver amalgam alloy was condensed and burnished into place. A temporary filling of Cavitt was placed in the access openings of all the teeth in Groups A, B, C, and D, and the teeth were stored for at least 7 days in 100 per cent humidity at 37’ C. before Phase II was initiated. Phase
Group A. Sectional si;!ver cone. The thirty teeth in Group A were separated into three subgroups of ten teeth each. The teeth were roentgenographed from a proximal direction to determine the completeness of the root canal obturation. The root canal fillings in the ten teeth in Group A-l were removed with a tapered fissure bur to a point where an apical filling of 8 mm. remained. The root canal fillings in the ten teeth in Group A-2 were removed with a tapered fissure bur to a point where an apical filling of 4 mm. remained. The root canal fillings in the ten teeth in Group A-2 were removed from the 5 mm. silver cone.) The ten teeth in Group A-3 served as controls. Group B. Gutta-per&a lateral condensation. The thirty teeth in Group B were separated into three subgroups of ten teeth each. The teeth were roentgenographed from the proximal aspect to determine completeness of root canal obturation. The ten teeth in Group B-l served as the controls. The root canal fillings in the ten teeth in Group B-2 were removed with a piso reamer to a point where an apical filling of 4 mm. remained. The root canal fillings in the ten teeth in Group B-3 were removed with a piso reamer to a point where an apical filling of 8 mm. remained. Group C. Warm gutta-percha. The thirty teeth in Group C were separated into three subgroups of ten teeth each. The teeth were roentgenographed from the proximal aspect to determine the completeness of root canal obturation. “Kerr’s root canal sealer. tPremier Dental Productri
O.S., O.M. & 0.1’. Novemhcr, 1969
742 Neagley Table
I. Leakage induced by dowel preparation 4 m/m.
Filling material Sectional silver cone
Lateral condensation of guttapercha
*Denotes complete leakage.
The root canal fillings in the ten teeth in Group C-l were removed with a piso reamer to a point where an apical filling of 8 mm. remained. The ten teeth in Group C-2 served as the controls. The root canal fillings in the ten teeth in Group C-3 were removed to a point where an apical filling of 4 mm. remained. Group D. Retrograde amalgam. The ten teeth in Group D were left undisturbed, as the canals were already empty to the level of the apical amalgam. Phase
A temporary filling of Cavit was placed in the access openings of all the teeth. The teeth were stored in 100 per cent humidity for at least 24 hours to permit the temporary filling to cure. The teeth were then placed in a bath of rhodamine B dye+ at room temperature for 48 hours. The teeth were removed, dried, and sectioned at approximately 1.5 mm. intervals until at least five serial sections were obtained. The sections were mounted on index cards and coded for evaluation. The specimens were evaluated for leakage under ultraviolet light, in total darkness, by four endodontists. The evaluators were instructed to note on a mimeographed form which sections contained dye, the etiology of the dye, if present, and whether in their opinion the root canal filling was sealing the canal or was permitting the dye to penetrate along the entire length of the root canal filling. RESULTS
The results of this investigation Group
appear in Table I.
The partial removal of the zinc oxide and eugenol coronal to the sectional silver cone did not have any noticeable effect on the apical seal. However, when all of the zinc oxide and 1 mm. of the sectional silver cone were complete dye penetration occurred in removed during dowel preparation, eight of nine specimens. *Hartman-Leddon
Effect of dowel preparation condensation
on a~pical seal
There was no increased incidence of leakage after dowel preparation in the canals obturated with lateral condensation of gutta-percha. Those teeth in which a dowel preparation was made to a depth of within either 4 mm. or 8 mm. from the apex compared favorably with the controls. Group
The control teeth that were filled with the warm gutta-percha exhibited less leakage than teeth treated by any other technique used in the investigation. However, complete leakage was produced in three of seven specimens and in three of ten specimens in the two groups of experimental teeth. Group
Seven of eight teeth in which showed complete dye penetration.
The results of this investigation indicate that the twist-off silver cone technique (Group A), advocatede-10 specifically for teeth that are to receive dowel crowns, is the most vulnerable to abuse. If the restoring dentist encroached upon the 5 mm. sectional silver cone (“I cut until I hit silver”), the cutting instrument, with its rotational forces, disturbed the cone sufficiently to permit leakage from the apex in eight out of the nine specimens. However, when the silver cone was not disturbed by the cutting instrument and a 3 mm. layer of zinc oxide and eugenol was left coronal to the silver cone, the root canal fillings were as well sealed as the controls. The laterally condensed gutta-percha (Group B) root canal fillings showed no trend toward increased leakage following post preparation. On the contrary, the dowel preparations t.hat were cut to within 4 mm. of the apex showed a slightly better seal than in the controls. The warm gutta-percha root canal fillings (Group C) presented a somewhat different picture. The controls gave the beat results of any root canal filling technique used in the study. However, dowel preparation to either experimental depth induced leaka,ge in six of seventeen specimens. A possible explanation may be that considerably less sealer is used in this technique and that the rotational force of the piso reamer may dislodge the remaining root canal filling more readily, gutta-percha alone6 being one of the poorest sealing agents. The use of a ret,rograde amalgam alone to seal the root end appeared to be inadequate. Complete dy: penetration was noted in seven of eight cases. However, it is possible that the corrosion products produced by the leakage might actually seal retrograde a.malgams well in clinical cases. The root canal filling,, were judged as either sealing or not sealing the root canal. Each root canal filling was placed in that category chosen by the majority of the evaluators. There was an equal division among the evaluators as to the seal of the root canal filling in sixteen of the teeth, so these teeth were deleted from the study.
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6: 0.1’. 1969
Five root canal fillings which appeared on the proximal roentenogram a,s not completely obliterating the root canal space were als,o deleted from the study. The use of collodion to seal the accessory canals proved to be inadequate. The manipulative procedures involved in the investigation resulted in the peeling off of sections of the collodion. This allowed dye penetration into many of the accessory canals, making interpretation of the results more difficult. Rhodamine B dye was selected after a preliminary study indicated that it was superior to other dyes tested because of its excellent fluorescent quality. It was thought that the sectioned roots could be evaluated more accurately if t.he fluorescent dye and ultraviolet light were used to detect leakage. Further areas for investigation are noted: (1) How do different methods of root filling removal effect the seal! (2) What is the minimum amount of guttapercha that can be left in the canal and still seal the canal hermetically? (3) What is the effect on the root canal filling if the coronal portion is removed immediately after placement P The clinical considerations of this investigation are as follows: (1) Those teeth which require a post crown (or may require one in the future) should be filled with a laterally condensed gutta-percha filling. If the anatomy of the root contraindica,tes the use of gutta-percha, a sectional silver cone should be placed and the restoring dentist informed of the maximum distance allowed for post preparation. The use of only a root end amalgam to seal the canal should be discouraged. SUMMARY
The effect of dowel preparation on root canals sealed with either guttapercha, sectional silver cones, or root-end amalgam fillings has been investigated. The dowel preparations were terminated at depths of 4 and 8 mm. coronal to the apex. The prepared teeth were placed in a dye bath for 48 hours; then they were coded, sectioned, and evaluated for dye penetration along the remaining root canal filling. The results of the investigation revealed that cutting 1 mm. from a 5 mm. sectional silver cone permitted complete dye penetration in eight of nine teeth. However, no increased incidence of leakage was noted if the silver cone was not reduced in length. Root canals sealed with the lateral condensation of guttapercha showed no adverse leakage effect due to dowel preparation. Root canals sealed by the warm gutta-percha technique presented a slightly increased incidence of leakage following dowel preparation. The root canals sealed with only a root-end amalgam permitted complete dye penetration in seven of eight teeth. REFERENCES
of Pulpless Teeth, D. Clin. North America, November, 1. Baraban, D. J.: The Restoration 1967, pp. 633-653. 2. Ingle, J. I.: Endodontics, ed. 1, Philadelphia, 1965, Lea & Febiger, pp. 63-65, 614. 3. Ingle, J. I.: Root Canal Obturation, J. Am. Dent. A. 53: 47-57, 1956. 4. Dow, P. R., and Ingle, J. I.: Isotope Determination of Root Canal Failure, ORAL SURG., ORAL MED.& ORAL PATH. 8: llOO-1104,1955. With 5. Marshall, F. J., and Massler, M.: The Sealing of Pulpless Teeth Evaluated Radioisotopes, J. D. Med. 16: 172-184, 1961. Fillings as Hermetic Sealing Agents, J. D. Res. 6. Grossman, L. I.: A Study of Temporary 18: 67-71, 1939.
Effect of dowel preparation
G. G.: A Comparative
ORAL MED.& 0~
on apical seal
of Three Root Canal Sealing8
PATH. 11: 1029-1041,1958.
8. Kitzmiller, J. 8.: Unpublished data. 9. Soltanoff, W., and Parris, L.: Controlled Silver Point Filling Technic for Endodontically Involved Teeth, J. Am. Dent. A. 65: 301-310, 1962. 10. Nicholls, E.: Sectional Root Fillings With Silver Points, D. Practitioner 8: 241-245, 1958. 11. Deubert, L. W.: An Operative and Laboratory Technic for an Acrylic Faced Post Crown, Australian D. J. 5: 9-13, 1,960. 12. Metrick, L.: Root Canal Obliteration With a Post Crown, J. Canad. D. A. 27: 585-586, 1961. 13. Kronfeld, M.: Mouth Rehabilitation, St. Louis, 1967, The C. V. Mosby Company, vol. 1, pp. 170-171. 14. Zeigler, P. E.: The Effects of Instrumentation for a Post Preparation on the Apical Seal of Endodontically Filled Teeth, Research Project, U. 5. Naval Hospital, San Diego, Calif., 1965. 15. Schilder, H.: Filling Root Canals in Three Dimensions, D. Clin. North America, November, 1967, pp. 723-744.