A methodological approach to standardize and control the quality of the position and alignment of lamina implants on two-dimensional radiographs

Objectives We sought to validate a new method to detect the degree of correlation between simulated and real tilted blade implants as they appear on a single two-dimensional radiograph. Methods The angular correction factor (CF^) was defined as the coupling of two subsequent angle transformations, a set of five angular values describing the theoretical radiographic appearance of the blade implant: (1) three consecutive rotations about the axes of the blade ( φ , θ , and ψ , standing for pitch, roll, and yaw, respectively) to represent the polarization directions; (2) a two-dimensional projection defined by two angles ( λ and ϕ , respectively, longitude and latitude) to represent the vector of the X-ray beam intersecting the detector plate. Data of patients who received fixed prostheses supported by blade-form implants were employed to calculate a dimensional correction factor (CF°), a specific length through the major axis. The simulation of a distorted radiograph of a blade positioned in space was compared with the real radiograph. Differences in the angular measurements served as an initial test to assess the effectiveness of the method. Results In the acquired sets of periapical radiographs, mean misalignments of + 3.58° in longitude and − 0.04° in latitude were registered. The following variations were detected during the accuracy testing: the absolute error was 0.1 ± 7.5° for angle φ ; 2.4 ± 6.7° for angle θ ; − 1.0 ± 3.7° for angle ψ ; 4.5 ± 8.6° for angle λ ; and 2.0 ± 9.3° for angle ϕ . The linear dependence between CF° and CF^ was estimated by a robust linear regression: slope + 0.991, intercept + 0.007, and adjusted R 2 0.992. Conclusions This a posteriori analysis introduces the explicit trigonometric equations of the theoretical standard (CF^) used to describe the blade implant radiographic position and misalignment on two-dimensional radiographs.