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Titanium screw implants in optimization of radiographic evaluation of facial growth in longitudinal animal studies.

The aim of this study was to develop a method that optimizes the reliability of longitudinal radiographic evaluation of small and fast-growing animals, such as the rabbit. Because the use of conventional cephalometric methods, including superimposition of serial radiographs, is more problematic in small animals than in humans, two titanium-alloy screws were placed 10 mm apart in the sagittal crest of the parietal bone in 10 growing New Zealand white rabbits. The anterior screw served as holder for a steel pin that, in turn, secured the fixation of the rabbit's head to a specially designed cephalostat. A lateral cephalogram of each animal was exposed on four occasions at one-month intervals. Computer-aided superimpositions were made of all four cephalograms from each animal using the screws in the calvarium as reference structures. To evaluate the method, the superimpositions were repeated after three to eight weeks, and the superimposition reproducibility was calculated. From the results, it can be concluded that the method allows congruent positioning of the animal skull relative to the film-focus assembly at repeated radiographic examinations. Furthermore, it introduces readily identified reference structures in the animal skull that can be used at high-precision superimposition of serial radiographs.