Validating an uncoupled laser-aiming device for serial implant radiography

Precision of bone level measurements adjacent to implants in longitudinal studies is, in part, dependent on the accurate reproduction of the relationships of the central x-ray beam, object, and film. The purpose of this study was to test the precision of a prototype aiming device consisting of three laser pointers symmetrically mounted on an x-ray cone, a ring supporting three mirrors aligned to reflect the laser light onto a grid on the x-ray head, and a custom film holder to align the film with the implant and the mirrors. Multiple regression analysis revealed a very high correlation between the angular change of the central ray and the position of the reflected light beam (R2 = 0.999, sig. < 0.001). Precision of the aiming device was determined from measurements made on digitized serial radiographs, exposed by two operators, of three dental implants in dried mandibles. The interthread distances and thread widths on each radiograph were measured using the NIH Image program. Chi-square tests demonstrated that the clinical use of the aiming device was independent of the operators and clinically applicable in all areas of the jaw. These tests also revealed that the significant errors found were directly related to the measurement of the thread width. This indicates a measurement technique problem rather than a deficiency with the aiming device. Additionally, none of the errors was greater than 0.032 mm, which is less than the accepted standard of 0.2 mm annual bone loss, and therefore should not be clinically significant. These results support the feasibility of using a three-beam reflected-light aiming device for precision of x-ray geometry in serial studies.