The quality of coronal restoration will directly influence the survival and success of ETT [2, 17, 19]. Though inadequate coronal restoration is a major risk to survival, a small proportion of teeth do not receive any restoration after the completion of root canal treatment [20–22]. It is not surprising to find a few clinical cases of ETT with coronal contamination, which might require root canal retreatment. After all, root canal retreatment is a comparatively difficult operation due to unforeseen factors [22, 23]. The ability to obtain good outcomes in ETT with coronal contamination with no root canal retreatment is desirable. In this clinical investigation, the 23 recalled patients with less than 12 months of coronal contamination achieved success by only a single-visit coronal restoration.
It is acknowledged that coronal leakage may adversely influence the long-term success of ETT because bacteria possibly reach the periapical tissue through the root canal system [24, 25]. Coronal contamination can potentially result in periapical infection, but not certainly. A sufficient number of pathogens in periapical tissue is a prerequisite for the occurrence of apical periodontitis [26, 27]. An in vitro study (1991) considered that root canal retreatment should be performed if obturated root canals are exposed for more than three months . A few researchers even speculated that the contamination of root canals occurred within a month in an in vitro model [12, 28, 29]. The studies did not yet present clear clinical evidence because the in vitro root-filling infection models were based on tracers such as dye, India ink, and methylene blue, which could not mimic the clinical conditions, and the size, type and penetrative ability were also significantly different from those of live oral bacteria.
Some bacteria or saliva were also employed in the in vitro experimental model, but the tracer alone was not able to provide evidence [11, 30]. Many studies have deemed that the quality of root canal filling is the most critical factor for the treatment outcome of ETT [1, 31, 32]. Compact obturation and adequate depth of root filling block the penetration of oral bacteria into the root canal. Furthermore, in the clinic and in experiments, acceptable antibacterial activity and sealing ability of root canal sealers create an inadequate environment for the viability of bacterial organisms [33–36]. In the in vitro model of other studies, if even small amounts of bacteria in saliva entered the apical root through coronal sealing, turbid culture medium in which the apical root was immerged was noted [37, 38]. Even so, this did not imply the occurrence of apical periodontitis. The small amounts of bacteria could not multiply or propagate in a compactly obturated root canal after effective coronal sealing. If the small amounts of bacteria reach the periapical tissue, they may still be removed by a healthy immune system. Therefore, defective teeth with coronal contamination should undergo coronal restoration as early as possible, provided that the primary root canal treatment is effective to prevent more bacteria from entering the root canal. Our pilot retrospective study indicated that 23 patients with ETT recalled with less than 12 months of coronal contamination treated with only a single-visit coronal coverage restoration were categorized as having treatment success; therefore, 3 months of coronal contamination may not be considered decisive evidence to support root canal retreatment.
The timing of the coronal restoration of ETT depends upon multiple factors: the pre-existing endodontic status, the quality of root canal filling, the position of the tooth, the type of restoration, the preoperative lesion size, and indecisive diagnosis [17, 39]. The consideration of retreatment should not be conjectural by the time of bacterial penetration; rather, it should be based on evidence of healing. A case report noted that endodontically treated teeth showed evidence of periradicular healing after more than 2.5 years by temporary restorations . In our clinical investigation, to ensure a successful outcome, the period of coronal contamination was limited to less than a year, a comparatively safe time. None of the treatments failed with only a single-visit coronal restoration, though our study lacks sufficient sample size. This study suggested that retreatment was not necessary for well-obturated root canals with coronal leakage.