# Automated Global Positioning Layout (GPL) for accuracy assessment in CAD-CAM mandibular reconstruction – Method validation

## TL;DR

A new automated method called GPL is validated for accurately measuring surgical outcomes in mandibular reconstruction, offering better reliability than existing techniques.

## Contribution

The study introduces and validates a fully automated, reproducible protocol (GPL) for 3D accuracy assessment in mandibular reconstruction.

## Key findings

- The GPL method showed complete reproducibility with no inter- or intra-operator variability.
- GPL provides a spatially-oriented assessment of deviations, overcoming limitations of landmark- and surface-based methods.
- GPL is more reliable and applicable than existing methods, especially after surgical resection.

## Abstract

The lack of a standardized methodology complicates accuracy assessment in computer-assisted mandibular reconstruction. Existing landmark-based methods are susceptible to operator variability, while surface-based comparisons can mask local deviations. This study validates a novel, automated protocol, the Global Positioning Layout (GPL), to quantify the 3D discrepancy between the virtual surgical plan and the postoperative outcome, by comparing its performance and reliability against Methods A and B. A retrospective cohort of 17 patients was analysed, with three operators performing all measurements on two occasions. The GPL method demonstrated complete reproducibility, with no inter- or intra-operator variability, providing a detailed, spatially-oriented assessment of deviations. In contrast, the landmark-based method showed poor reproducibility and systematic bias and was often inapplicable due to the absence of landmarks after resection. The surface-based method, while objective for its mean error metric, was operator-dependent for initial alignment and its non-directional output masked significant localized deviations. This study validates GPL as a robust and fully reproducible tool that overcomes the critical limitations of established techniques. The GPL method provides a strong foundation for a standardized protocol, essential for the reliable comparison of surgical outcomes, refinement of surgical techniques, and improvement of long-term patient outcomes.

The online version contains supplementary material available at 10.1038/s41598-025-30516-1.