In Vivo-Ex Vivo Evaluation of the Root ZX3 for Working-Length Determination

Accurate determination of root canal working length is essential for successful endodontic treatment because instrumentation and obturation should terminate at an appropriate apical endpoint. Electronic apex locators have become widely used to improve working-length determination and reduce reliance on radiographic methods. The Root ZX3 is a third-generation electronic apex locator that has demonstrated promising accuracy; however, limited evidence exists regarding its performance under different pulpal and periapical conditions using microscopic actual working length as the reference standard.

This prospective mixed in vivo-ex vivo diagnostic accuracy study evaluates the accuracy and repeatability of the Root ZX3 electronic apex locator in single-rooted permanent teeth indicated for extraction. Adult participants requiring extraction of teeth for prosthodontic, periodontal, orthodontic, or non-restorable reasons and requiring primary nonsurgical root canal treatment are enrolled after providing informed consent.

Before tooth extraction, electronic working length is determined using the Root ZX3 according to the manufacturer's instructions with a standardized coronal reference point. Pulpal and periapical diagnoses are recorded clinically. After extraction, limited field-of-view CBCT imaging is performed, and working length is measured using standardized imaging protocols. The actual working length is then determined microscopically by directly identifying the apical foramen and is used as the reference standard.

The primary outcome is the diagnostic accuracy of the Root ZX3 compared with the microscopic actual working length. Accuracy is evaluated as the proportion of measurements within ±0.5 mm and ±1.0 mm of the reference standard. Agreement between measurement methods is assessed using Bland-Altman analysis, Lin's concordance correlation coefficient, and the intraclass correlation coefficient. Repeatability of electronic measurements is also evaluated.

Inclusion criteria

• * Adults (≥18 years) requiring extraction of a single-rooted permanent tooth for prosthodontic, periodontal, orthodontic, or non-restorable reasons.

• Tooth requiring primary nonsurgical root canal treatment.
• Fully formed root with a closed apex.
• Ability to provide written informed consent.

Exclusion criteria

• Teeth with root resorption (internal or external).

• Teeth with root perforation or previous endodontic treatment.
• Teeth with immature (open) apices.
• Teeth with root fractures.
• Teeth in which apical patency could not be achieved.
• Teeth with no electronic working-length measurement obtained using the Root ZX3.
• Teeth that fractured during extraction, preventing microscopic determination of the actual working length.