Scanning electron microscopic study of root canal obturation using thermoplasticized gutta-percha

Scanning electron microscopic study of root canal obturation using thermoplasticized gutta-percha

JOURNALOF ENDODONTICS i VOL 4, NO 8, AUGUST 1978 Scanning Electron Microscopic Study of Root Canal Obturation using Thermoplasticized Gutta-percha M...

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Scanning Electron Microscopic Study of Root Canal Obturation using Thermoplasticized Gutta-percha

M a h m o u d Torabinejad, DMD, MSD; Ziedonis Skobe, MS, PhD; Paul L. Trombly, MA; Alvin Arlen Krakow, DDS; Poul G r i n , DMD; and Jay Marlin, DMD, Boston

Forty teeth with single canals w e r e b i o m e c h a n i c a l l y p r e p a r e d for r o o t canal o b t u r a t i o n . T e n teeth w e r e o b t u r a t e d b y i n j e c t i o n of t h e r m o p l a s t i c i z e d g u t t a - p e r c h a w i t h use of a p r e s s u r e syringe. T h e r e m a i n i n g 30 teeth w e r e d i v i d e d into t h r e e e q u a l g r o u p s and w e r e o b t u r a t e d using lateral c o n d e n s a t i o n , w a r m g u t t a - p e r c h a with vertical c o n d e n s a t i o n , and K l o r o p e r k a , respectively. T h e a d a p t a t i o n of the r o o t canal fillings to the s u r r o u n d i n g dentinal walls was e x a m i n e d u n d e r the s c a n n i n g e l e c t r o n m i c r o s c o p e with use of freeze f r a c t u r i n g in liquid n i t r o g e n to p r o d u c e samples s h o w i n g the g u t t a - p e r c h a - d e n t i n interface. T h e findings indicated that the i n j e c t i o n - m o l d i n g t e c h n i q u e r e s u l t e d in o b t u r a t i o n of the root canal system, w h i c h was at least c o m p a r a b l e to that o b t a i n e d in other c o n v e n t i o n a l a p p r o a c h e s .

Complete obturation of the entire root canal system with a nonirritating agent is a major objective of modern endodontic therapy. Ingle ~ showed that nearly 60% of endodontic failures were caused by incomplete obturation of the canal space. Many techniques have been advocated for filling the root canal systemS-" In the past, assay of the various approaches has been based primarily on clinical studies? ~ which are few and require long periods of observation to be meaningful. Other methods of evaluation include assessment of dye or radiotracer penetration, ~-2~ visual inspection of the root canal filling with or without the aid of the microscope, 2'~a'''7 and,

more recently, observations with the scanning electron microscope (SEM). 2~ This latter technique is particularly suitable for studying irregular characteristics of the surface because of the depth of the focal field and the degree of magnification obtainable. 2~ Collectively, the information in the literature emphasizes the importance of complete obturation of the root canal space for successful endodontic therapy. In the current study, the SEM was used to evaluate a new technique for root canal obturation that involves the use of thermoplasticized guttapercha introduced into the root canal space with a pressure syringe? ~ The adaptation of the experimental

root canal filling material to the surrounding dentin walls was compared with that obtained with three more commonly used gutta-percha techniques, namely lateral condensation, 2 vertical condensation with warm gutta-percha, 3 and Kloroperka. 9

METHODS A N D MATERIALS Forty teeth with single canals were divided into four equal groups. Thirty teeth were prepared for obturation by one of us who also obturated "lateral condensation" teeth and "experimental" teeth. Kloroperka teeth were obturated by another one



Fig 1--Three specimens prepared for spontaneous fracture. Longitudinal grooves have been cut so deeply that root canal filling can be seen through remaining thin layer of dentin.

Fig 2--Composite scanning electron micrograph of representative sample of obturation obtained with injected thermoplasticized gutta-percha technique. Adaptation of filling to canal walls is close and uniform thin layer of sealer is seen at interface. Surface of filling material shows impression-like reproduction of irregularities of canal wall. A minor void may be seen between filling and wall near apex and close to coronal termination of filling (arrows) (Orig mag X 50).

of us, who uses this technique extensively in his practice. The root canal sealer used for all groups except "Kloroperka" teeth was AH-26. After the canals were obturated, radiographs were taken to show the faciolingual and mesiodistal views. The access openings were closed with Cavit* and the teeth were stored in water for seven days to allow the root canal sealer to set. The clinical crowns were removed at the cemento-enamel junction. Longitudinal grooves were cut on the root surfaces as deeply as possible without disturbing the gutta-percha-dentin interface (Fig 1). The roots were immersed in liquid nitrogen which caused some roots to fracture spontaneously whereas the remaining roots 9 were fractured by means of pliers. The specimens were mounted on aluminum stubs, coated with palladium gold in the H u m m e r II~" sputtering system, and viewed with a J E O L JSM-U3:~ scanning electron microscope. The electron micrographs were inspected to determine the adaptation of the filling material to the root canal wall, the presence of voids, the extent and thickness of root canal sealer, and the reproduction of irregularities of the canal wall on the surface of the filling material.

RESULTS Fig 3-Scanning electron micrograph showing detail of apical void m Figure 2. Void does not extend to apex and measures less than 51z at its greatest width (Orig mag X 200).


The root canal fillings resulting from injection of thermoplasticized gutta-percha showed close adaptation to the dentin wails with only an occasional minor void. A representative filling is shown in Figure 2. The sealer was generally dispersed uniformly in a thin layer at the interface. Irregularities of the canal walls appeared clearly reproduced on the


surface of the fillings. A higher magnification of a section of the apical area (Fig 3) shows a small void, which does not extend to the apex. The fillings produced by the lateral condensation technique showed poorer adaptation to the dentin walls than those in the experimental group except in the apical few millimeters where they were comparable (Fig 4). Narrow voids w e r e observed frequently along the filling-dentin wall interface. The voids rarely extended to the apical termination of the fillhag. The most coronal part of the filling was generally well adapted. One of the ten specimens had a dentinal crack perpendicular to a void. Root canal sealer was sometimes discerned in the midsection of the root canal and was always seen at and near the apex. Striations and other irregularities appeared to be reproduced on the Surface of the filling. A higher magnification of the apical area (Fig 5) shows close adaptation with sealer present at the filling-wall interface. Fillings produced by vertical condensation of warm gutta-percha were closely adapted to the dentin walls in the apical and middle thirds of the roots (Fig 6). Voids were often seen in the coronal third. Two of ten specimens in the group showed dentinal cracks associated with these voids (Fig 7). Root canal sealer was not always apparent at the interface but it could be seen on the surface of the gutta-percha. The surface of the filling appeared to reproduce the irregularities of the root canal walls. A feature peculiar to the group is the presence of occasional seams, which might represent the union of different gutta-percha segments. These Seams were sometimes filled with

Fig 4--Composite scanning electron micrograph of representative sample of obturation obtained with laterally condensed gutta-percha technique. Adaptation of filling to canal wall is close in apical area but narrow voids are present elsewhere. Sealer is not prominent at interface but a layer is apparent on surface of filling in midroot area. Irregularities in root canal wall are reproduced on surface filling (Orig Mag • 50).

Fig 5~Scanning electron micrograph of apical part of specimen in Figure 4. Sealer is shown at fillingwall interface and adaptation of filling is close (Orig mag X 200).

Fig 6-Composite scanning electron micrograph of representative sample of obturation obtained with warm gutta-percha technique. Adaptation of filhng to canal walls is close and narrow voids are only seen in coronal third. Sealer is recognizable as discrete patches in filling surface and in minimal amounts along filling-canat walt interface. Surface of fiUing is apparent reproduction of irregularities of root canal walls. Prominent is occasional seam (arrow) which, in this case, is filled with sealer. (Orig mag • 247

Fig 7--Scanning electron micrograph of dentinal crackfound m root obturated with warm guttapercha technique. Filling-root canal wall interface traverses lower part of Figure. Seams are apparent on gutta-percha surface close to crack where a void is present at interface. Crack goes through the dentin (Orig mag X 200).

root canal sealer. A higher magnification of the apex emphasizes the close adaptation of filling material to the canal wall in the area (Fig 8). The features generally characteristic to the Kloroperka technique are seen in Figure 9. The filling showed good adaptation within the apical few millimeters, where the irregulariL ties of the canal walls were reproduced on the surface. Voids were frequently found coronal .to this section. The surface often appeared somewhat wrinkled. A higher-power electronmicrograph of the apical area confirmed the close adaptation and the presence of wrinkles (Fig 10). Furthermore, filamentous-like extensions from the gutta-percha are discernable. The radiographs did not disclose any discernable difference in the quality of root canal obturation of the fillings obtained with the various techniques.


Fig 8--Scanning electron micrograph showing higher magnification of apical part of specimen in Figure 6. Filling is slightly short of apex on one side and slightly overextended on other side as seen in Figure 8 Top and Bottom, respectively. Adaptation offilling to walls is close. Surface of filling appears finely wrinkled. (Orig mag X200).


The findings in the current study confirm the earlier observation that injection of thermoplasticized guttapercha in conjunction with the use of a sealer represents a practical approach to obturation of the root canal space in vitro? ~ We further show that, when observed with the scanning electron microscope, adaptation of the injected thermoplasticized gutta-percha root canal fillings is equal or superior to that of fillings produced by the other generally accepted procedures that were tested and that are known to be clinically successful. A consistent observation was that the intricacies of the root canal space were reproduced in an impression-like manner by the injection molded thermoplasticized gutta-percha fillings with only few


pig 9-Composite scanning electron micrograph of representative sample of obturation obtained ith Kloroperka technique. Adaptation is close only in apical few millimeters. Discrete voids cur intermittently coronal to this section. Surface is somewhat wrinkled in appearance except apical part where irregularities of canal walls are reproduced (Ortg mag X 50).



Fig lO-Scanning electron micrograph showing higher magnification of apical part of specimen shown in Figure 9. Filamentous-like extensions from gutta-percha are prominent. Adaptation of gutta-percha to root canal wall is close and surface appears finely wrinkled ( Orig mag x 2oo). minor voids occasionally present. These voids could not be recognized on radiographs and may be attributable to entrapment of air during the loading of the pressure syringe. The frequency and extent of voids between root canal walls and filling was greater in all three groups of Conventionally obturated root ca-

nals. A particular pattern of voids was frequently noticed in the case of lateral condensation where the fillings adapted reasonably well at the apical and coronal parts and showed longitudinal voids in the mid-root section, thus confirming earlier findings by Goldman and associates. '-'''-''~ The seams, which were observed in

the specimens obtained by the vertical condensation with warm guttapercha, may be due to the inadequate warming of some of the guttapercha segments. The wrinkles, which were noticeable on the surface of the Kloroperka fillings, are probably due to shrinkage of the material. The cracks observed in three roots in the current study may not be attributable to the specific techniques used (vertical warm gutta-percha and lateral condensation) for their obturation but may be related to the freeze-fracturing technique used because Seltzer (personal communication, 1977) and Rubin '~1 have described similar findings in roots that were instrumented but not obturated. Other investigators have had difficulty with the freeze-fracturing technique. Coviello and others 29 abandoned freeze fracturing because of separation of filling materials from the canals and excessive fragmentation and distortion. We did not encounter these problems in the study; one reason may be that the roots were carefully grooved longitudinally as deeply as was consistent with maintaining the integrity of the root canal filling. The roots that had not fractured spontaneously when immersed in liquid nitrogen separated readily when the pliers with which the roots were held were tapped. A potential advantage of the filling technique of injecting thermoplasticized gutta-percha is that the plastic filling material flows both vertically and laterally during the injection. The fact that we found a 9uniquely even dispersion of sealer at the interface between the root canal wall and the filling in the experimental group lends support to this



concept of lateral pressure and lateral flow o f t h e filling d u r i n g t h e injection. The sealer was unevenly distribu t e d r e l a t i v e to t h e fillings r e s u l t i n g from vertical and lateral condensat i o n . T h i s in v i t r o s t u d y i n d i c a t e s t h a t t h e r o o t c a n a l s y s t e m is o b t u r a t e d a t least as well b y t h e i n j e c t i o n o f t h e r m o p l a s t i c i z e d g u t t a - p e r c h a as by generally accepted methods of o b t u r a t i o n . C l i n i c a l s t u d i e s a r e in p r o g r e s s to c o m p a r e t h i s n e w a p proach with conventional methods. *Premier Dental Products Co., Philadelphia, Pa 19107. ~'Technics, Alexandria, Va 22310. ~JEOL, Medford, Mass 02155. The authors thank Dr. Lester Goldsmith for his assistance in obturating the teeth in the Kloroperka group. This study was supported in part by funds from a General Research Support Grant from the US Public Health Service to the Forsyth Dental Center. Dr. Torabinejad, formerly assistant clinical professor of endodontics at the Forsyth Dental Center, is currently associate professor of endodontics at Loma Linda University, Loma Linda, Calif. Dr. Skobe is head of electronmicroscopy and an assistant staff member at Forsyth Dental Center. Dr. Krakow is chairman of the department of endodontics at Harvard School of Dental Medicine and Forsyth Dental Center. Dr. Grin is a senior staff member at Forsyth Dental Center, and Dr. Marlin is an assistant clinical professor of endodontics at Forsyth Dental Center and a lecturer on endodontics at Harvard School of Dental Medicine. Request for reprints should be directed to Dr. Alvin Krakow, Department of Endodontics, Forsyth Dental Center, 140 The Fenway, Boston, Mass 02115.

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