In the same week, two lower molars arrived on my screen. Both were previously treated. Both require new crowns. Both with the same request: “Please retreat this tooth” My reply, however, was not the same.
Case 1 – Leave Well Alone (Unless Proven Otherwise)
Radiographically, Case 1 shows a long-standing root filling beneath a crown. The periapical image is not of diagnostic quality, so my first step is a CBCT scan. Not to justify treatment, but to justify restraint.
Modern evidence consistently shows that when a root-treated tooth is asymptomatic and exhibits no periapical radiolucency, the prognosis is generally favourable. The classic epidemiological data from Sjögren et al. (1990) demonstrated that the presence or absence of apical periodontitis is the dominant prognostic factor. More recently, Ng et al. (2008, 2011 systematic reviews) confirmed that teeth without pre-operative apical periodontitis have a significantly higher success rate.
If a scan reveals no periapical changes, the biological message is clear:
There is no active disease.
We sometimes worry about coronal exposure. Yet studies on coronal leakage show that bacteria do not “tunnel” deterministically through gutta-percha in the absence of nutrients and fluid exchange. Leakage models demonstrate that regrowth requires residual intraradicular bacteria combined with a fluid pathway. If neither is biologically active enough to create apical inflammation, intervention may introduce more risk than benefit.
Retreatment is not benign. It carries procedural risks:
- Canal transportation
- Instrument separation
- Perforation
- Microfracture propagation
- Crown damage
In a tooth with no disease, retreatment becomes preventive surgery without pathology. So in Case 1, I scan. If clean, I monitor. Experience teaches that sometimes the bravest act is to put the file back in the drawer.
Case 2 – A Different Biological Reality
Case 2 tells a different story before we even scan.
The mesial canal shows poorly condensed gutta-percha confined to the coronal third. The apical and middle thirds are inadequately sealed and virtually empty. Regardless of whether a periapical radiolucency is present, the seal is fundamentally compromised.
Here, the evidence base shifts.
Ray and Trope (1995) demonstrated that both apical and coronal quality significantly influence periapical status. Subsequent work has repeatedly shown that poorly filled canals are associated with higher rates of apical periodontitis, even when asymptomatic. An inadequately sealed canal is not a neutral environment. It is a nutrient corridor waiting for colonisation.
Even if the CBCT shows no PDL widening today, the structural weakness of the seal makes future bacterial penetration highly probable. In this scenario, we are not intervening in health. We are correcting a structural risk factor with a strong evidence base linking it to disease.
Therefore, in Case 2:
- I would scan to assess existing periapical status and for anatomical canal considerations.
- I would retreat irrespective of radiographic findings.
Because the biological architecture is flawed.
The Principle at Work
Both teeth may look “treated.” Only one looks biologically secure. Endodontics has moved beyond judging beauty by radiographic density alone. With CBCT as a diagnostic gold standard, we now separate aesthetics from pathology.
A root filling that looks imperfect but is disease-free may deserve respect. A root filling that looks compromised in critical zones deserves correction. The goal is not to create textbook radiographs. The goal is to manage bacterial risk.
Forty years of practice has taught me that sometimes intervention prevents disease. And sometimes intervention creates it. The art lies in knowing which is which.
