# Optimization of the size and location of the FOVs for CBCT capture of impacted lower third molars

## TL;DR

This study determines the smallest radiation-exposing area for imaging impacted wisdom teeth using CBCT, aiming to reduce patient exposure.

## Contribution

The study provides optimized field-of-view dimensions for unilateral and bilateral imaging of impacted third molars in best- and worst-case patient positioning scenarios.

## Key findings

- Minimal FOVs for lower third molars were 23.5mm × 35.4mm in best-case and 35.4mm × 36.6mm in worst-case scenarios.
- Bilateral imaging of all four third molars required a best-case FOV of 44.8mm × 84.8mm and a worst-case FOV of 51.7mm × 85.6mm.
- Optimized FOVs aim to reduce radiation exposure while maintaining diagnostic quality for impacted wisdom teeth.

## Abstract

Cone beam computed tomography (CBCT) is an established diagnostic tool for impacted wisdom teeth (third molars (3 M)) in proximity of the mandibular nerve canal. This study aims to define the minimum field-of-view (FOV) size and its localization to reduce radiation exposure. As reference, the chin rest of the CBCT device was used.

Three-dimensional CBCT data sets were used to analyze the bilateral positions and dimensions of the wisdom teeth. A total of 215 wisdom teeth from a study population with a mean age of 21 years, including data from 82 male and 58 female patients, were mapped. By transformation into a common coordinate space using the device’s chin rest as a joint denominator, the optimal size and location for uni- and bilateral capture of the wisdom teeth were determined, for both best-case and worst-case scenarios with regard to patient positioning.

The minimal FOVs for the lower 3 M capture were H 23.5 mm × R 35.4 mm in the best-case scenario assuming optimal patient positioning and H 35.4 mm × R 36.6 mm in the worst-case scenario with rotational deviation along the transversal axis. For the upper 3 M, the minimal FOVs were H 29.9 mm × R 29.2 mm in the best-case scenario and H 38.6 mm × R 35.6 mm in the worst-case scenario. Unilateral capture of both the upper and lower 3 M required FOV dimensions of H 51.7 mm × R 39.8 mm and H 44.8 mm × R 36.8 mm, respectively. For bilateral capture of all four 3 M, the best-case FOV was H 44.8 mm × R 84.8 mm and the worst-case FOV was H 51.7 mm × R 85.6 mm.

This research provides indication-specific FOVs for uni- and bilateral imaging of the upper and lower 3 M. Taking into account optimal clinical practices for CBCT imaging, this study aims to propose clinically feasible FOV dimensions while meeting the technical specifications of commonly used CBCT devices. Clinical application of the results may help reduce radiation exposure of patients receiving CBCT imaging of the wisdom teeth. Transfer of the present results to other CBCT devices requires further research.

The study is registered in the German Trial Register with the number DRKS00026149, 2024/02/21.