Optimal parameters for lateral oblique radiographs of rat mandibles

OBJECTIVE: To establish optimal exposure parameters for lateral oblique radiographs of rat mandibles using an intraoral X-ray machine. METHODS: A positioning apparatus, previously tested for its reproducibility, was used to obtain radiographs of four heads of formaldehyde-preserved Wistar rats. Radiographs were exposed at 50 kV and 8 mA using four size 2 films (Insight, Ektaspeed Plus, Ultraspeed and D-Speed; Eastman Kodak Co., Rochester, NY), two focal distances (30 cm and 60 cm) and seven exposure times (0.6 s, 0.7 s, 0.8 s, 1.0 s, 1.5 s, 2.0 s and 2.5 s). The radiographs were evaluated by two examiners and scored for image quality: 1, very poor; 2, poor; 3, fair; 4, good; and 5, excellent. The evaluations were repeated at 30 days. RESULTS: Intraobserver reproducibility was substantial (kappa = 0.798 and 0.667). Also, the two examiners showed substantial agreement (kappa = 0.726). There was a significant difference (alpha = 1%) between the scores for the films under study. At a 30 cm distance, E-speed films had mean scores of 4 and 5 at 0.8 s and 1 s exposure times, and D-speed films, at 1.5 s, 2 s and 2.5 s exposure times. At a 60 cm distance, the best results were found for E-speed films at 2.0 s and 2.5 s exposure times. CONCLUSION: The films under study did not show any significant difference in the quality of rat mandible images as long as exposure times were adequate to their sensitivity and focal distance.