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No medicament versus calcium hydroxide976IntroductionRoot canal treatments are often performed in more than one visit. Patients may return to the clinic between the scheduled visits due to pain or swelling, which is defined as an interappointment emergency [1,2]. An interappointment emergency is not only unpleasant for the patient as well as the dentist, but also demands extra materials and costs, and contributes to the carbon footprint [3]. It is possible that root canals are not prepared and irrigated thoroughly during the first visit of a root canal treatment, resulting in tissue remnants or persisting infection that may cause an interappointment emergency [4]. Even though incomplete preparation itself is not necessarily related to a higher incidence of interappointment emergencies [5], one might consider the use of an intracanal medicament in such situations more relevant. Using calcium hydroxide as an intracanal medicament has become common practice in root canal treatment [6]. Calcium hydroxide is believed to play a significant role in disinfecting the root canal system [7], and in preventing regrowth of microorganisms [8]. Healing of apical periodontitis upon finishing a root canal treatment has been partly attributed to the use of calcium hydroxide [9]. The ascribed benefits of calcium hydroxide as an intracanal medicament in root canal treatment, however, remain questionable. Healing of apical periodontitis following single-visit root canal treatment appears to be similar to both the healing following multiple-visit root canal treatment with calcium hydroxide as an intracanal medicament [10] and the healing following two-visit root canal treatment without the use of an intracanal medicament [11]. Microorganisms can regrow between visits, even when calcium hydroxide is enclosed as an intracanal medicament [11]. To exert its disinfecting properties, calcium hydroxide has to be brought into direct contact with the microorganisms, which is not possible in all parts of the root canal system or in the dentinal tubules [12]. Besides, most microorganisms inhabiting the root canal system live in biofilms that make them more resistant to alkaline stress [13] and, therefore, less vulnerable to the effect of calcium hydroxide. Calcium hydroxide may even enable opportunistic microorganisms to proliferate and cause a shift in biofilm composition towards more resilient species [14], and it may lead to an enhanced biofilm mass production [15]. There is no scientific evidence on which to assess whether calcium hydroxide has any therapeutic effect in root canal treatment [16]. Besides, the complete removal of calcium hydroxide from the root canal system is very difficult or impossible to achieve [17], and the presence of its remnants in the root canal Annemarie Baaij.indd 97 28-06-2023 12:26