Consider two molars, both with an apical radiolucency. In the first, the canals have been prepared, irrigated and dried. In the second, successive paper points come out wet as exudate collects again in the canal. The distinction matters when deciding how to end the appointment. Before I consider calcium hydroxide, I ask why this particular tooth needs a second visit. [1][2]
Which teeth might need an interappointment dressing?
The European Society of Endodontology’s 2023 S3 guideline provides a starting point. For permanent teeth with asymptomatic apical periodontitis, it recommends single-visit treatment without interappointment calcium hydroxide when the necessary clinical procedures have been carried out adequately. This strong recommendation draws on studies of radiographic healing. Applying it requires knowing the diagnosis and considering which stages of treatment the clinician was able to complete that day. [2]
A regenerative procedure in a tooth with a necrotic pulp and an immature apex follows a different sequence. The American Association of Endodontists lists calcium hydroxide as one option for intracanal medication at the first visit. The response to initial treatment is assessed at the second. An open apex therefore needs to be considered alongside the intended procedure and its aim. The patient’s ability to attend follow-up appointments is also one of the document’s case-selection criteria. [3]
How does canal drainage affect the decision?
When colleagues ask about exudate, I distinguish a trace on the tip of a paper point from persistent, copious drainage. In the latter situation, I defer calcium hydroxide at the initial visit and reassess once the drainage subsides. Recording its initial volume and whether the canal could be dried gives the next clinician a more informative comparison than an entry that simply says “drainage present”. [1]
In earlier posts I also discussed my choice of formulation. In some cases in which I mixed powder and liquid to a thicker consistency, I found the exudate easier to control at the second visit. That observation explains my preference in those cases. The patients’ initial findings, the products used and the conditions of application were not matched for comparison. The observation alone cannot establish that powder–liquid formulations outperform all premixed pastes. [1]
Keeping the dressing within the canal
A colleague asked which of two distances short of working length to use when placing the paste. I did not propose a distance in millimetres. My concern was to keep the material inside the canal. In another reply, I noted that a patient may feel no immediate pain even if material has been extruded. Particularly under local anaesthesia, comfort during placement tells the clinician little about the location of the paste. [1]
The relationship between the root apices of mandibular posterior teeth and the mandibular canal matters here. Gluskin and colleagues described five cases of serious neurological injury after needle delivery resulted in substantial extrusion of calcium hydroxide into the space occupied by the inferior alveolar nerve. Without a denominator, the series cannot establish how often this complication occurs. It does illustrate the severity of the injury. Assess the proximity of the apex to neurovascular structures before placement and choose a technique that allows controlled delivery. [5]
When to review the patient and what to assess
Antibacterial activity measured in a study and a patient’s readiness for obturation are distinct outcomes. In a frequently cited study, Sjögren and colleagues compared ten minutes with seven days of calcium hydroxide dressing in teeth with periapical lesions. The seven-day application showed activity against bacteria that had survived initial canal preparation. The researchers did not compare recall intervals of two, three and four weeks. Interpretation depends on the durations actually studied and the outcome measured. [4]
Some of my patients who initially presented with a sinus tract or drainage still had a patent tract or a canal I could not dry when they returned as scheduled. I subsequently changed my recall intervals. Two findings can be followed directly. Has the sinus tract opening seen at the first visit closed? Is the canal still draining when reopened? The date of the visit can be arranged in advance, but these findings require reassessment of the patient. [1]
For a regenerative procedure, the AAE document’s interval of one to four weeks refers to the planned second appointment in selected immature teeth. If signs of persistent infection are present at that visit, the document allows for reconsidering the duration or choice of antimicrobial treatment. The planned date and the clinical findings that would support proceeding to the next stage can be recorded separately in the patient’s notes. [3]
What does prolonged exposure mean for root dentine?
When discussing applications lasting several months, document the stage of root development, root wall thickness and the reason treatment has been prolonged. In my posts I discussed immature teeth with particularly thin walls. A smaller lesion on a radiograph of a single patient returning late for review gives no measure of the mechanical strength of that tooth’s root dentine. Radiographic follow-up and tests of a material’s effects on dentine address different questions. [1][7]
Sunlakawit and colleagues included 27 laboratory studies measuring fracture resistance in specimens of human permanent teeth or roots in their network meta-analysis. In experiments on mature teeth, exposure periods of four weeks or longer affected fracture resistance. Studies simulating immature teeth did not identify a specific time threshold. Risk of bias ranged from moderate to high. These findings cannot predict the day an individual patient’s root might fracture or establish that shorter exposure carries no risk. [7]
Removing the dressing before obturation
An interappointment dressing plan also needs to address how to remove the paste. Ma and colleagues used micro-CT to measure residual calcium hydroxide after attempted removal from 30 extracted mandibular second molars with C-shaped canals. All three techniques left some material. Mean residual volume was lower with sonic or ultrasonic activation than with irrigation without activation. The apical third retained the greatest proportion of material. [6]
A C-shaped canal may appear clean coronally while paste remains apically. Canal anatomy therefore matters when planning both placement and removal. In the same study, residual material did not differ significantly between the sonic and ultrasonic groups. The outcome measured was the volume of residual dressing. This experiment cannot rank the methods by clinical success of obturation or by periapical healing. [6]
What should we compare at the review appointment?
Recording the initial finding that prompted a second visit clarifies what to reassess. For persistent drainage, compare its volume and whether the canal can be dried. For a sinus tract, compare the soft-tissue findings. For a regenerative procedure, review the course of the signs of infection. When the patient returns, distinguish persistence of the original finding from the onset of a new symptom. The record can then explain to the treating clinician and any colleague taking over the case why the interval, treatment stage or diagnosis needs reconsideration. [1][3]