|Year : 2016 | Volume
| Issue : 3 | Page : 71-75
Importance of coronal seal: Preventing coronal leakage in endodontics
Department of Conservative Dentistry and Endodontics, D Y Patil University School of Dentistry, Navi Mumbai, Maharashtra, India
|Date of Web Publication||10-Aug-2016|
Department of Conservative Dentistry and Endodontics, D Y Patil University School of Dentistry, Nerul, Navi Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
The primary goal of endodontic treatment is to keep the pulpal space free of microorganisms and to prevent recurrent infection. Oral bacteria and their by-products can penetrate this space if there is inadequate coronal or apical seal. Apical leakage leading to reinfection of an obturated canal has been the major cause of failed endodontic treatment. However, recently, attention has been drawn to the significance of coronal seal in endodontic success. Microbial contamination through the occlusal surface, leading to coronal leakage constitutes a large percentage of failed root canal treatments. This paper highlights the clinical and biological implications of coronal leakage and the means to prevent the same.
Keywords: Coronal leakage, coronal seal, oral bacteria
|How to cite this article:|
Mandke L. Importance of coronal seal: Preventing coronal leakage in endodontics. J Res Dent 2016;4:71-5
| Introduction|| |
Oral bacteria and their by-products play a major role in the production of pulpal and periradicular diseases. Keeping the pulpal space free of these microorganisms is a challenging task as these microorganisms have the capacity to penetrate through the minutest of spaces. A thorough debridement and shaping of the root canal along with a "fluid-tight" obturation can prevent bacterial ingress and ensure a favorable endodontic outcome.
For years, the focus of endodontists has been on the apical third of the root canal. No doubt, it is a proven fact that apical leakage leads to reinfection, thus causing maximum endodontic failures. So then, why do we find a 20-30% failure rate in well-sealed teeth? 
The apical third of the root canal has an intricate anatomy, it cannot be seen with naked eyes and is difficult to seal.
The coronal part of the canal, on the other hand, has a more predictable anatomy, it can be visualized and therefore is easy to seal. Hence, unknowingly, the coronal seal was taken for granted.
However, in the last few years, there has been a significant focus on the coronal seal of the root canal. The penetration of microorganisms through the coronal end of the root canal, causing recontamination and subsequent failure, is a disturbing revelation. That coronal leakage can affect the outcome of endodontic treatment, is now a proven fact.
| Etiology|| |
Salivary microleakage with bacterial penetration can be considered a major cause of loss of coronal seal. A contaminated pulp chamber acts as a reservoir of bacteria and their endotoxins.  These bacteria can penetrate in two ways. First, they can diffuse along the interface between the obturation material and the root canal wall. Thus, they penetrate corono-apically, affect the apical seal, and cause reinfection. Second, they can also penetrate through the accessory canals present in the floor of the pulp chamber of multirooted teeth, causing periodontal furcation involvement. 
Coronal leakage can occur in the following instances:
- Delay in placement of coronal restoration following root canal treatment:
- Compromised or inadequate temporary filling
- Tooth fracture
- Leakage during post placement
- Failure of final restoration
- Recurrent decay at restoration margins. 
| Early Studies|| |
The concept of coronal leakage causing endodontic failure is not a new one. In 1961, Marshall and Massler speculated on the role of the occlusal seal on the outcome of endodontic treatment.  They undertook a study with a radioactive tracer and showed the presence of coronal leakage in spite of the presence of a temporary restoration. Further studies by other researchers led to similar inferences. ,,,
In 1990, two landmark studies served as an eye-opener for clinicians and academicians. Torabinejad et al. studied the penetration of different microorganisms on single-rooted obturated teeth but without coronal restoration. In 19 days, 50% of the canals were contaminated to their full length after being exposed to Staphylococcus epidermidis. Proteus vulgaris took 52 days for the same outcome. 
In the same year, Saunders and Saunders studied coronal leakage in root-filled molars. They showed that the common practice of packing excess gutta-percha in the floor of the pulp chamber provided an inadequate seal. They recommended the removal of this excess gutta-percha, leaving only that on the root canal orifices, and sealing the floor with a restorative material like amalgam or glass polyalkanoate. ,
In 1995, Ray and Trope published a retrospective clinical study based on the radiographic assessment of patients with high incidence of apical pathology.  More than 1000 patients participated in this study. For the first time, the absence of apical pathology (success percentage) was compared to the quality of coronal seal [Table 1]. They concluded that "the quality of the coronal restoration is significantly more important than the quality of the endodontic treatment for periapical health." This conclusion ruffled quite a few feathers. Till then, the postendodontic restoration was considered as a requirement only for restoring the tooth to function. The fact that it could affect the outcome of endodontic treatment; moreover, it could be more important than the obturation, was a startling revelation. This assessment also sort of undermined the importance of a good obturation.
|Table 1: Percentage of success in endodontic treatment, depending on the quality of the treatment, and the quality of the coronal restoration (Ray and Trope 1995) |
Click here to view
Further studies were carried out in subsequent years to assess coronal leakage during post and core procedures. Their recommendation was equivocal. "It is preferable to restore the tooth as early as possible with a post followed by a core build up to prevent coronal leakage". ,,,,
A major concern for all clinicians was the speed at which coronal leakage and recontamination occurred thus requiring retreatment. The big question asked was, "how long is too long?" When, after the coronal seal is compromised is it necessary to do retreatment? There has been no consensus as to the timeline in this instance. Here, time alone should not be considered the only factor since leakage can occur because of other factors too. A good solution would be to correlate the quality of the endodontic treatment to the time of coronal exposure and then decide when and whether to do retreatment.
| Preventing Coronal Leakage|| |
A clinician gets several opportunities to prevent coronal leakage during root canal treatment. They are as follows:
Any endodontic treatment should be started keeping the end in mind. It is not advisable to start endodontic treatment in a tooth which is nonrestorable. If the postendodontic restoration fails, coronal leakage can lead to endodontic failure. As a thumb rule, at least 2 mm of sound tooth structure must be present circumferentially for ferrule effect. Only if the clinician can visualize a sound postendodontic restoration, should he begin an endodontic treatment.
Preendodontic tooth preparation
The following are predisposing factors for coronal leakage and should be checked:
- Ensuring complete removal of caries or defective restorations
- Examining the tooth carefully for any cracks or fractures. This can be done with transillumination or dyes
- Establishing sound tooth margins above gingival tissues
- Isolation with rubber dam is necessary to reduce microbial contamination.
A preendodontic buildup of the coronal structure, i.e., building up the missing walls of the tooth has many advantages. It strengthens the tooth, provides better isolation, limits microbial ingress, helps better stabilization of rubber dam clamps, and thus helps in limiting coronal leakage. However, care should be taken that the restorative material does not clog the root canals.
Access cavity preparation
Retention of as much sound tooth structure as possible to enhance structural integrity limits coronal leakage.
Protecting cusps in the areas of significant function also minimize the crown fracture thus maintaining occlusal seal.
Cleaning and shaping of the root canals
A thorough cleaning and shaping with copious irrigation are mandatory to prevent leakage. A clinician has an array of instruments and materials to aid him in effectively performing this step.
Smear layer serves as a major hindrance to a perfect seal. Smear layer is a microcrystalline layer of debris, which covers the root canal walls after cleaning and shaping. If not removed, it can serve as a pathway for bacterial leakage. It also clogs the dentinal tubules, preventing sealer penetration. This in turn aids leakage. Smear layer comprises an organic part, which can be removed by irrigants such as sodium hypochlorite and an inorganic part, which requires chelating agents such as 17% ethylenediaminetetraacetic acid for its removal. Removal of this layer opens the dentinal tubules and enhances the adaptation of the obturating material to the canal walls. Alternating the above-mentioned irrigating solutions along with adequate instrumentation will aid in removing the smear layer. ,
The main goals of obturation are to prevent microorganisms from re-entering the root canals and to isolate the remaining microorganisms in the canal space from nutrition from tissue fluids.
No matter how well we seal the root canal, if the coronal end is not adequately sealed, "crown-down bacterial leakage" will occur in no time. Clinicians should try to attain as near - perfect seal as is possible to prevent this complication. Single cone obturations or short, incomplete obturations should be avoided for the same reason.
After obturation, all excess gutta-percha in the floor of the pulp chamber should be removed which can serve as a pathway for bacterial ingress. Some advocate placement of a layer of resin-modified glass ionomer cement (GIC) or adhesive resin immediately after obturation to seal accessory canals in furcation area. 
Root canal sealers are as important as the obturation materials. They help in sealing the discrepancies between the obturation material and the canal walls, seal lateral and accessory canals, and help in better adaptation. Improper sealer usage or lack of sealer usage is an invitation to leakage and subsequent failure. Zinc oxide eugenol and calcium hydroxide sealers exhibit solubility thus aiding leakage. Resin sealers have adhesive properties, but their shrinkage is a major disadvantage. On setting, shrinkage of the sealer allows it to pull away from the gutta-percha core, thus creating a microgap through which bacteria can pass. 
In short, no sealer or obturation material is capable of completely preventing leakage.
A temporary or provisional restoration is required either in between appointments for a multivisit root canal treatment, or is required after obturation, before placing a permanent restoration.
A faulty temporary restoration is one of the major causes of coronal leakage. It can be due to:
- Inadequate thickness - Usually, a large cotton plug is placed in the pulp chamber over which a thin layer of temporary restoration is placed. This does not produce an adequate seal. A minimum 4-5 mm thickness of temporary is recommended to prevent leakage. This thickness also prevents potential lifting or dislodgement of the temporary
- Improper placement - Unfortunately, scant attention is given to temporary placement, which is a critical step. It should be properly placed so that it seals all avenues of leakage. It should be placed incrementally with no gaps or voids
- Failure to evaluate occlusion after placement - This will lead to fracture of the provisional restoration and in turn promote coronal leakage. Hence, it is important to check the occlusion before relieving the patient.
Intracanal medicament should be given in intermediate restorations. They act as a barrier to microbial ingress. Calcium hydroxide is the preferred material. However, intracanal medicament should not be used as a substitute for a well-placed temporary restoration.
Provisional restorations should be placed for the least possible time since they all leak. Any temporary can provide adequate seal for maximum up to 3 weeks. Beyond this period is an invitation to coronal leakage and failure.
Because of the drawbacks of provisional restorations, some researchers advocate using permanent restorative materials such as GIC or composite resin as a provisional restoration. 
Timing of permanent restoration
The earlier the tooth is permanently restored; the lesser will be the leakage. Safavi et al. advocated immediate placement of a permanent restoration after obturation. 
This immediate postendodontic buildup can prove to be advantageous. The clinician's knowledge of canal angulation, anatomy, and curvature is greatest immediately following endodontic obturation, making it the optimal time to place the buildup. Since rubber dam isolation is already present, the buildup becomes an extension, rather than an invasion, of the endodontic seal.
Delaying the permanent restoration allows teeth with periapical radiolucency to demonstrate healing before restoration. This is unnecessary in the current scenario because of the advancements in root canal treatment.
Of 41 articles published between 1969 and 1999 (majority in 1990s), the literature suggests that sealing the canals as soon as possible after endodontic therapy dramatically improves their long-term success rate. 
Choice and integrity of permanent restoration
The presence of adequate ferrule at the crown-root interface is critical for the long-term success of the crowned endodontically treated tooth. The ferrule is the circumferential ring of sound tooth structure that is enveloped by the cervical portion of the crown restoration. A minimum 2 mm of ferrule provides a bracing, casing, or hugging action to improve the integrity of the endodontically treated tooth.  This in turn helps in retaining an adequate coronal seal.
The clinician should ensure that the permanent restoration does not violate the biologic width. The correlation between coronal leakage and biologic width is that if the latter is impinged upon, the patient experiences discomfort, especially during brushing. Thus, he will not keep that area clean, leading to plaque accumulation, recurrent decay, and subsequently coronal leakage.
Ensure that the tooth is in atraumatic occlusion. A traumatic occlusion will cause disruption of occlusal seal or fracture of the tooth or final restoration.
The Nayyar core or bonded corono-radicular dowel and core technique serves as an effective postendodontic restoration.  In this technique, 2-4 mm of gutta-percha is removed from coronal portion of each canal. A restorative material like amalgam or composite resin is condensed into the root canals, pulp chamber, and the coronal portion of the tooth. Such type of restoration enhances the retention and resistance features and also limits coronal leakage.
A sandwich technique postendodontic restoration with GIC base and overlaying composite restoration is also an effective restoration. The GIC base also serves to seal the accessory canals in the furcation area of molars.
Post and core
Not all endodontic teeth require a post and core build up. Post and core procedures increase the chances of damaging the occlusal seal thus promoting leakage. Contemporary research has shown that bonded restorations or corono-radicular restorations provide adequate retention and also limit leakage. Only gross tooth destruction should warrant the use of posts.
If indicated, meticulous precautions should be taken during post and core procedures. Parallel, serrated, and threaded posts are preferred as they are able to distribute forces more evenly along the root. Postspace preparation should be done under isolation with a rubber dam to prevent contamination. Heat should be used to remove the bulk of gutta-percha from the root canal as rotary instruments can disrupt the apical seal. A 4-5 mm of apical gutta-percha should be retained to provide adequate seal. Post placement should be done immediately after postspace preparation, to limit contamination. Thus, prefabricated posts are preferred to custom posts as they can be cemented immediately. Core build up should be done as soon as possible after post cementation. 
Follow-up evaluation of all cases is imperative because coronal leakage does not manifest immediately. It can be observed only after a period. The concerned tooth should be evaluated for signs and symptoms, integrity of permanent restoration, the presence of recurrent decay, and apical pathologies. 
An important point to be noted here is that a root canal treated or pulpless tooth does not have any sensory innervation. Hence, leaking coronal restorations may go unnoticed for months since the patient does not feel pain or sensitivity initially. By the time, it gets noticed, the damage is already done.
Thus, coronal leakage is like a silent killer, which sneaks in unobtrusively and causes extensive damage. An awareness of the biological and clinical implications along with adequate precautions can help to overcome this hurdle.
| Conclusion|| |
Lack of coronal seal can lead to endodontic failure.
Coronal leakage can occur at any time right from the beginning of endodontic treatment, till the postendodontic restoration is completed. The lesser the time duration between access cavity preparation and permanent restoration, the lesser will be the leakage. Basic precautions taken during every step of treatment can prevent this complication and ensure endodontic success.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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