Sir, regarding working length determination, the European Society of Endodontology recommends the use of an electronic apex locator followed by confirmation of the canal length with an undistorted periapical radiograph during root canal treatment (usually using a file instrument).1Additionally, they recommend use of a master cone radiograph to verify working length but only in 'some cases'. Thus, guidance involving master GP radiographs is open to interpretation.

I completed an in-practice audit which showed that master GP radiographs were taken in 61% of completed RCT cases. When considering cases which met criteria regarding obturation length, master GP radiographs were present 73% of the time. In comparison, master GP radiographs were present only 33% of the time in cases failing to meet standards.

The literature clearly demonstrates the impact obturation length has upon RCT 'success'. For every millimetre not instrumented, there is a 12% reduction in success, meanwhile overextended root fillings reduce success by 62%.2 Furthermore, short root fillings had 3.1% higher odds of being associated with periapical lesions.3

The practice provides outreach placements to students at the University of Sheffield and interestingly, both the students and foundation dentists seemed far more likely to obtain master GP radiographs than the associates. This may be explained due to the former coming straight from dental school, where all stages are taught as radiographically required.

Research highlights that apex locators can reduce the need for mid-treatment radiographs, thus reducing the time taken to complete endodontic procedures.4 Being subject to increased time constraints may account for why associates may choose not to utilise master GP radiographs. Furthermore, with modern apex locators reporting accuracies as high as 99.85%5 some experienced clinicians may wish to avoid exposing the patient to unnecessary radiation.

Despite demonstrating a variety of reasons why master GP radiographs may be deemed unnecessary, the fundamental point stands that collectively, the practice achieved better obturation lengths when using master cone periapical radiographs. Thus, it is certainly worth considering obtaining these as part of normal endodontic treatment protocol.