X-ray beam angulation can compromise 2-dimensional diagnosis of interradicular space for mini-implants

The aim of this research was to evaluate the influence of x-ray projection geometry on interradicular space of the posterior maxillary arch.

Cone-beam computed tomography (CBCT) scans of 32 patients (16.85 ± 4.93 years) who met the selection criteria were enrolled. One hundred ninety-two interradicular sites of the posterior maxillary arch were evaluated. Before measurements, each side of the maxillary arch was orientated in all 3 planes of space to obtain CBCT synthesized periapical radiographs with 0° projection geometry (orthogonal x-ray beam-orthogonal X-ray angulation [OX]). Standardized CBCT axial rotations (10°, 20°, -10°, and -20°) were used to simulate periapical radiographs taken with mesial and distal angulation of the x-ray beam (mesial x-ray angulation [MX] and distal x-ray angulation [DX]). Interradicular space widths were measured on OX, MX, and DX CBCT synthesized periapical radiographs. Measurements were performed parallel to the occlusal plane at 3 mm and 6 mm apical to the midpoint of the alveolar crest. Interradicular distances were statistically compared (P <0.05).

Interradicular distances measured on MX and DX CBCT synthesized periapical radiographs were significantly smaller than those measured on OX. Interradicular distance was significantly correlated with the horizontal angulation of the x-ray beam. X-ray projection angle was the most influential variable on interradicular distance. About 30% reduction in interradicular space was observed for every 10° of deviation from orthogonal x-ray.

Two-dimensional radiographs obtained away from the 0° projection geometry can reduce the actual interradicular space for mini-implants, inducing misdiagnosis.