Sir, a 32-year-old male, from Donetsk (Ukraine) presented for a general check-up at the Manchester University Dental Hospital. Clinical examination revealed an asymptomatic upper right premolar with a characteristic pink/red burgundy discolouration which is frequently described as a symptom of internal resorption, caries, pulp polyp or dental trauma (Fig. 1).1 Medical history was non-contributory. Dental anamnesis and radiographic examination evidenced that, previously, this tooth was inadequately endodontically treated, with the obturation material being significantly short from the radiological apex. Further investigation indicated that a resorcinol-formaldehyde (RF) hard-setting paste was used to fill the canals, which resulted in pink/red staining of dentine and enamel over the time.2

Fig. 1
figure 1

The asymptomatic upper right premolar with a pink/red burgundy discolouration

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This method was widely used in Russia, other post-Soviet countries and China for many years to manage irreversible pulpitis and chronic apical periodontitis, and to perform pulpotomies. RF paste is a mixture of an antimicrobial formaldehyde agent and a resorcinol white crystalline powder that arrests dental caries.3,4 When RF is introduced into the root canal system, it not only destroys infection and 'resinifies' residual pulp tissues, but it also obturates the canals as it sets 'brick' hard, preventing further reinfection.2,3 The only advantage of the described obturation method, besides its bactericidal effect, is that it permits incomplete pulp tissue removal at the stage of cleaning and shaping. It must be noted that the described method is now rarely used due to the high toxicity of the paste and associated tooth staining.2

This case highlights the importance of accurate diagnosis prior to initiating treatment on teeth with abnormal staining. Teeth treated with RF paste often have red/pink discolouration and can be mistaken for being affected by gross caries, potentially resulting in imprudent tooth tissue removal.5 Moreover, in order to avoid misdiagnosing, a careful radiographic assessment must be undertaken. As a hard-setting white obturation paste, RF can significantly obstruct access to the root canal system, making the conventional retreatment unpredictable.3,4 Combined utilisation of ultrasonic files, burs, endodontic solvents, rotary Ni-Ti instruments and an operative microscope can be helpful in removing hard-setting cements.1 In clinical situations where retreatment is difficult, an apicoectomy with retrograde obturation may be considered.5