Dr Elmaasarawi, what three instrumentation protocols did you compare?
The first protocol used hand K-files from the Dentsply Sirona brand VDW, accompanied by conventional irrigation with sodium hypochlorite. Working length was determined using conventional radiographs. Dentsply Sirona’s AH Plus sealer was used, and lateral compaction was the obturation technique. In total, 5,450 teeth were treated this way between 1999 and 2007.

For the second protocol, starting in 2008, 1,667 teeth were treated with FKG’s RaCe and BioRaCe rotary instruments after manual glide path preparation using hand K-files. Sodium hypochlorite and citric acid were used as irrigants, and passive ultrasonic irrigation was used after mechanical preparation. Working length was determined using both radiographs and electronic apex locators, and the same obturation approach as for the first protocol was used.

For the third protocol, starting in 2011, 7,116 teeth were treated with VDW’s Reciproc instruments without glide path preparation. In the few cases in which the Reciproc file could not reach the working length, a glide path was prepared manually. Preparation was accompanied by passive ultrasonic irrigation, and working length was determined using electronic apex locators. AH Plus sealer was used in the beginning, as for the first two protocols, but from 2020 onwards, it was replaced by a bioceramic sealer. Similarly, lateral compaction was used at first, but in recent years, the third protocol moved to warm vertical compaction.

What was the reason for undertaking the study?
It was my PhD supervisor, Dr Andreas Bartols, who made this extensive analysis possible. He had identified a gap in the research: few published papers had compared different files and mechanical preparation techniques regarding tooth survival and the success of root canal treatment. On that basis, we decided to dig deeper into this.

Fortunately, we had a large amount of data that had been collected for quality assurance reasons from the dental clinic of the Akademie für Zahnärztliche Fortbildung Karlsruhe in Germany. We used this data to analyse how the three different protocols affected the outcome of root canal treatment, specifically the survival of teeth.

The study included 14,233 teeth in total. This large number makes the results more reliable. Statistically speaking, the higher the number of teeth included, the more reliable the results. The 25 years of data reflect the improvement of mechanical preparation over time: hand file preparation was followed by rotary instrumentation and then reciprocating instrumentation. This advancement mirrors the history of endodontic treatment, which is why I believe that the results are reliable and well founded.

In our retrospective analysis, the groups in the database were not necessarily comparable in terms of their baseline characteristics. Therefore, we used advanced statistical methods to make the groups more comparable. Even after this adjustment, the protocol that incorporated the Reciproc and Reciproc Blue files had a much higher tooth survival rate compared with the protocols that used the hand files or rotary files.

In the study, you differentiated between “tooth survival” and “survival without further intervention”. Why is this distinction important for clinical practice?
We addressed two outcomes. The first was survival until the first further intervention—non-surgical retreatment, surgical retreatment or extraction. We evaluated the effect of the protocol up to the point when one of those events occurred.

The second outcome was tooth survival until extraction, regardless of whether surgical or non-surgical retreatment had taken place in the meantime. This is also important because the longer the tooth survives, the better it is for the patient.