December 1, 2000
by Stephen Johal, DMD
A 43-year-old woman saw her dentist complaining of a toothache. Her medical history was not significant. The maxillary left lateral incisor was diagnosed as the cause of her complaint. There was no sinus tract or buccal swelling, EPT gave a negative response, and radiographic examination revealed the presence of periapical radiolucency and deficiencies in the coronal restorations (mesial and distal composite resin fillings with evidence of secondary decay underneath). Root canal treatment was started using standard techniques including a palatal access, rubber dam isolation and copious sodium hypochlorite irrigation. The tooth was cleaned, shaped, dressed and the patient was re-appointed for completion of the root canal treatment for the next visit. Unfortunately, the symptoms did not resolve after the initiation of treatment. She had to return twice after the first visit as her toothache persisted. On each occasion the root canal was given a thorough cleaning and redressed, but it remained uncomfortable, A course of Pen V was also prescribed but provided little relief. The tooth was now very tender to percussion and the buccal sulcus was tender to palpation. Consequently, her general dental practitioner referred her. Diagnosis for Treatment Failure: Coronal Leakage Due to Deficient Composite Resin Filling and Lack of Coronal Seal (Courtesy of Bun San Chong, JOE, 1995)1
Apical leakage is considered a common reason for the clinical failure of endodontic therapy. An inadequate apical seal allows the periapical exudate to percolate into the root canal system and to adversely affect the prognosis of the endodontic treatment.2 The question that then arises is what role might coronal microleakage play in the prognosis of the root canal treatment?
Sealed root canals can be coronally recontaminated under several circumstances:3
1. Recurrent decay exposing the endodontic filling material.
2. The filling materials and/or tooth structures have fractured or been lost.
3. Leakage through the temporary restoration.
When this occurs, the coronal portion of the root canal system is exposed to the oral flora, which can allow bacteria to penetrate to the periapical tissues. Consequently, these bacteria and bacterial byproducts may result in pathosis that could necessitate retreatment or surgical intervention with the added expense, time, and possible discomfort for the patient.
Coronal microleakage is a major factor in the etiology of treatment failure, therefore; materials and techniques must be examined for their ability to minimize this leakage. Numerous factors may affect coronal leakage in root canal treatment including:
1. The oral flora/saliva
2. The root canal sealer
3. The smear layer
4. The coronal restoration
The purpose of this report is to present and evaluate these factors based on clinical studies.
EFFECTS OF THE ORAL FLORA/SALIVA
Maintaining a coronal seal is important throughout endodontic treatment. The coronal seal prevents saliva, bacteria, and bacterial byproducts in the oral cavity from invading the canal system and gaining access to the periradicular tissues. The question is how quickly the entire root canal system becomes recontaminated to the point that retreatment of the canal may be necessary.
Swanson and Madison (1987) were the first to evaluate the length of time that the obturation material could be exposed to artificial saliva before compromising the integrity of the seal.4 They exposed the coronal portion of the obturated root canals to artificial saliva for various time periods and then immersed them in Pelikan ink for 48 hours. They found that the dye penetrated from 79 to 85% of the root length in all exposed specimens after 3 days exposure. There was no leakage in the control group, which was not exposed to artificial saliva, but was placed in contact with ink for 48 hours. They showed that the extent of leakage seen in the canal space after only three days of exposure was not significantly different from the microleakage observed after eight weeks of exposure.
However, Madison and Wilcox (1988) performed an in vivo study on monkeys that did not confirm their in vitro studies. They found that some of the positive controls (no sealers) did not show microleakage, while some of the negative controls (temporary not removed) showed dye penetration.5
Nevertheless, bacterial leakage studies might be more meaningful and clinically relevant. Dyes are good substances for comparing relative leakage, but because of their small molecules, they may not give a true picture of the leakage of bacteria or their by-products.6
Torabinejad et al. (1990) used two species of bacteria, Staphylococcus epidermis (highly motile) and Proteus vulgaris (non-motile), to evaluate the coronal leakage of obturated teeth.7 Eighty percent of the root canals were completely contaminated with in 30 days of exposure to S. epidermis and 85% with in 66 days of exposure to P. vulgaris. This study also suggested that motility of the bacteria may not be factor in rate of penetration to the apices.
Magura et al. (1991) evaluated the coronal leakage of human saliva in endodontically treated teeth.8 They reported that saliva penetration at 90 days was significantly greater than seen at 2, 7, 14, and 28 days. This study recommended that obturated root canals that have been exposed to the oral environment for longer than three months should be retreated before placement of a permanent coronal restoration. They also challenged the findings of Madison et al (1987) where they concluded that retreatment should be considered if the obturated canal was exposed to the oral environment for more than 3 days. They argued that aqueous solutions have been shown to penetrate farther than viscous saliva, therefore; dye studies may give inflated values for leakage.
Khayat et al (1993) studied the length of time for bacteria present in natural human saliva to penetrate through the entire root canal system obturated by lateral and vertical condensation techniques.9 They found that a root canals were recontaminated in less than 30 days and that there was no statistical significance between lateral and vertical condensation.
Chailertvantikul et al (1996) showed that acid end-products of gram negative bacteria (Fusobacterium. nucleatum) could penetrate a seemingly well obturated root canal with in a 12 week period.10 Their findings showed that microleakage of the small molecules (butyric acid or methylene blue dye) could not be prevented.
It is obvious that several studies have been performed to evaluate the coronal leakage phenomenon. Unfortunately an obstacle that many of these studies encounter is they cannot show whether or not the microorganisms penetrate through the obturated canals and produce their acid end products in the apical chamber or that their acid end products diffuse through the obturated canal. Regardless if a dye or bacterial system is used, a consistent finding has been that coronal leakage occurs, but at varying rates.
ROOT CANAL SEALERS
In root canal treatment, root canal sealers serve to fill voids and minor discrepancies of fit between the gutta percha filling and the root canal wall. Leakage along a root canal filling may be expected to occur between the sealer and dentin, between sealer and gutta percha or through the sealer itself. The sealer could therefore be regarded as the weak link in long-term successful obturation of the root canal.11
An important property of a root canal sealer is that it should be insoluble and provide a good long – term barrier to bacterial penetration of the root canal system. Many studies have reported that AH26 (an epoxy resin-based sealer) provides a better apical seal than other types of sealer.12 However, the zinc oxide-eugenol based sealers have more antimicrobial activity than other types.13
Chailertvantikul et al (1996) showed that AH26, Apexit or Tubliseal EWT sealers had no significant effect on the leakage of S. sanguis along obturated canals, after a 90 day experimental period.14 In a later study, Chailertvantikul et al (1997)
showed that lateral condensation of cold gutta percha with two different sealers was unable to prevent coronal ingress of a mixed microbial flora. (S. sanguis and P. intermedia) after a 90 day experimental period.15
It is clear from many studies that the presence of a root canal filling of gutta-percha with a sealer merely delays invasion by microorganisms. More importantly, this implies that it is necessary to provide a suitable coronal restoration after the root canal treatment has been completed to reduce the likelihood of contamination.
Coronal root canal has a number of susceptible interfaces where leakage may occur. One of these interfaces includes the presence of the smear layer. The smear layer is created during instrumentation and the compression of the resulting crumbs against the root canal wall during filing.16 It is primarily composed of inorganic particles of calcified tissue and organic elements.
Some investigators have proposed that the smear layer contains bacteria or bacterial products that might provide a reservoir of irritants. Thus, complete removal of the smear layer would be consistent with elimination of irritants from the root canal system. Furthermore, the presence of the smear layer may hinder the adaptation of the root canal filling and prevent tubular penetration of the filling materials, thereby increase the likelihood of leakage.17
Saunders and Saunders (1992) investigated the influence of the smear layer on coronal leakage of teeth filled with different sealers.18 They concluded that removal of the smear layer increases the resistance of a gutta percha root filling to coronal leakage. Taylor et al (1997) also concluded that removal of the smear layer, plus the use of dentin-adhering sealers (AH26 and Ketac-Endo) had cumulative effects in decreasing coronal leakage.19
On the other hand, other investigators argue that the smear layer should be left intact as it may block dentinal tubules from bacterial penetration and/or fluids by altering dentin permeability. Recently, a study by Chailertvantikul et al (1996) showed that the presence or absence of the smear layer had no significant effect on the leakage of Streptococcus sanguis.20 Another study by this group concluded that the presence or absence of the smear layer did not affect bacterial leakage either with cold lateral condensation of gutta percha or thermally softened injectable guitta percha.21
If the pulp chamber becomes contaminated, it may serve as a reservoir of microorganisms and toxins. This could cause a problem in either two ways. First, the apical seal may be affected adversely and cause the root canal treatment to fail. Second, movement of microorganisms and toxins through the accessory canals in the floor of the pulp chamber may result in periodontal furcation involvement. Therefore, again it implies the need to provide a suitable coronal restoration from the beginning to the end of root canal treatment.
Saunders and Saunders (1990) study indicated that pulp chambers restored with glass ionmer, cermet cement, or amalgam leaked significantly less than those filled with gutta percha and root canal sealer.22 Magura et al (1991) suggested that when temporizing the access opening of an endodontically treated tooth; consideration must be given to the material chosen to fill the void.23 Their results suggested that a thickness of IRM greater than 3mrn should be used or the clinician should use a double seal, possibly Cavit and IRM to ensure the integrity of the root canal filling. A recent study by Chailertvanitkul et al (1997) also demonstrated that glass ionmer was an effective barrier in preventing microbial leakage, while teeth in which the gutta percha had been removed from the pulp chamber before testing showed extensive leakage.24
There are many approaches in the methods and techniques used in leakage studies in an effort to improve the experimental conditions. The use of dyes, for example, is considered to increase the reliability of the results with respect to the penetration level. On the other hand, bacterial leakage studies seem to be more clinically relevant.
With many studies, the speed of penetration by bacteria and/or dyes varies. Many factors could affect penetration including:25
1. The model design
2. The canal preparation and obturation technique
3. The type of dye/bacteria used
4. The nature of solutions to which the coronal portion was exposed
5. The methods for detecting penetration
Unfortunately a major concern with most bacterial studies are that they are qualitative rather than quantitative. If only one bacterium passes through the obturated root canal, it may multiply in the enriched broth and cause turbidity. Consequently, the results of the study may be misleading.
In any case, most techniques are laboratory rather than clinically based which underlines the need for “in vivo” studies.
A review of the large number of leakage studies published points to general agreement that leakage occurs mainly between the root filling and root canal wall. Clinically, it is likely that passage of bacteria or bacterial by-products follows the dissolution or disintegration of the root canal sealer and smear layer. However, the clinical significance of the smear layer and the relevance of its removal remain controversial.
Successful root canal treatment is dependent on cleaning, shaping and filling of the root canal system There is now increasing realization that the coronal seal is important in root canal treatment. Coronal leakage leads to canal contamination, preventing the satisfactory completion of each stage in root canal treatment.
ral Health welcomes this original article.
1.B. Chong, “Coronal Leakage and Treatment Failure.” Journal of Endodontics March 1995: 159
2.L. Vassiliadis, “Effect of Smear Layer on Coronal Microleakage.” Oral Surgery, Oral Medicine, Oral Pathology, Sept. 1996: 315.
3.M. Torabinejad, “In vitro Bacterial Penetration of Coronally Unsealed Endodontically Treated Teeth.” Journal of Endodontics Dec. 1990: 566.
4.K. Swanson and S. Swanson, “An Evaluation of Coronal Microleakage in Endodontically Treated Teeth. Part 1. Time Periods.” Journal of Endodontic Feb. 1987: 56.
5.S. Madison and L. Wilcox, “An Evaluation of Coronal Microleakage in Endodontically Treated Teeth. Part III. In Vivo Study.” Journal of Endodontics Sept. 1988: 455.
6.A. Khayat, “Human Saliva Penetration of Coronally Unsealed Obturated Root Canals.” Journal of Endodontics Sept. 1993: 458.
7.M. Torabinejad 556.
8.M. Magura, “Human Saliva Coronal Microleakage in Obturated Root Canals: In Vitro Study.” Journal of Endodontics July 1991: 324.
9.A. Khayat 459.
10.P. Chailertvantikul, “An in vitro study of the coronal leakage of two root canal sealers using an obligate anaerobe microbial marker.” International Endodontic Journal 1996: 249.
11.P. Chailertvantikul, “An evaluation of microbial coronal leakage in the restored pulp chamber of root canal treated multirooted teeth.” International Endodontic Journal 199T 318.
12.P. Chailertvantikul (#10) 250.
13.p. Chailertvantikul (#10) 250.
14.P. Chailertvantikul, “An assessment of microbial coronal leakage in teeth root-fifled with gutta percha and three different sealers.” International Endodontic Journal 1996: 388.
15.P. Chailertvantikul, “Coronal Leakage of Obturated Root Canals After Long-term Storage using a Polymicrobial Marker.” Journal of Endodontics 1997: 611.
16.L. Vassiliadis 316.
17.P. Chailertvantikul, “The effect of smear layer on microbial coronal leakage of gutta percha root fillings.” International Endodontic Journal 1996: 242.
18.L. Vassiliadis 316.
19.J. Taylor, “Coronal Leakage: Effects of Smear Layer, Obturation Technique, and Sealer.” Journal of Endodontics Aug. 1997: 508.
20.P.Chailertvantikul (#10) 251.
21.P. Chailertvantikul (# 17) 243.
22.W.P. Saunders and E.M. Saunders, “Assessment of Leakage in the Restored Pulp Chamber of Endodontically Treated Multirooted Teeth.” International Endodontic Journal 1990: 28.
24.P. Chailertvantikul (#11) 318.
25.P. Chailertvantikul (#14) 388.
Chailertvanitkul, P. et al. “An in vitro study of the coronal leakage of two root canal sealers using an obligate anacrobic microbial marker.” International Endodontic Journal 1996: 249.
Chailertvanitkul, P. et al. “Coronal Leakage of Obturated Root Canals After Long-term Storage using a Polymicrobial Marker.” Journal of Endodontic 1997: 610.
Chailertvanitkul, P. et al. “An assessment of microbial coronal leakage in teeth root-filled with gutta percha and three different sealers.” International Endodontic Journal 1996: 387.
Chailertvanitkul, P. et al. “The effect of smear layer on microbial coronal leakage of gutta percha root fillings.” ImcmationW Endodontic Journal 1996: 242.
Chailertvanitkul, P. et al. “An evaluation of microbial coronal leakage in the restored pulp chamber of rootcanal treated multirooted teeth.” International Endodontic Jounial 1997 318.
Chong, B. “Coronal Leak-age and Treatment Failure.” Journal of Endodontics March 1995: 159.
Khayat, A. et al. “Human Saliva Penetration of Coronally Unsealed Obturated Root Canals.” Journal of Endodontics Sept. 1993: 458.
Madison, S. et al. “An Evaluation of Coronal Microleakage in Endodontically Treated Teeth. Part 1. Time Periods.” Journal of Endodontics Feb. 1987: 56.
Madison, S. et al. “An Evaluation of Coronal Microleakage in Endodontically Treated Teeth. Part 11. Sealer Types.” Journal of Endodontics Mar. 198T 109.
Madison, S. et al. “An Evaluation of Coronal Microleakage in Endodontically Treated Teeth. Part III. In Vivo Study.” Journal of Endodontics Sept- 1988: 455.
Magura, M. et al. “Human Saliva Coronal Microleakage in Obturated Root Canals: In Vitro Study.” Journal of Endodontics July 1991: 324.
Malone, K. “An In Vitro Evaluation of Coronal Microleakage in Obturated Root Canals without Coronal Restorations.”. Journal of Endodontics Jan. 1997: 35.
Saunders, W.P. “Assessment of Leakage in the Restored Pulp Chamber of Endodontically Treated Multirooted Teeth.” Interriational Endodontic Journal 1990: 28.
Torabinejad, M. et al. “In vitro Bacterial Penetration of Coronally Unsealed Endodontically Treated Teeth.” Journal of Endodontics Dec. 1990: 566.
Taylor, J. “Coronal Leakage: Effects of Smear Layer, Obturation Technique, and Sealer.” Journal of Endodontics Aug. 1997: 508.
Vassiliadis, L. “Effect of Smear Layer on Coronal Microleakage.” Oral Surgery, Oral Medicine, Oral Pathology Sept. 1996- 315.