Evaluation by digital subtraction radiography of induced changes in the bone density of the female rat mandible.

OBJECTIVES: To verify whether changes in bone mass induced by glucocorticoid and bisphosphonate can be detected by digital subtraction radiography of lateral X-rays in female rat mandibles. METHODS: 36 Rattus norvegicus (Wistar) females were randomly allocated to three groups: Group 1, control (n = 12); Group 2, induced osteopaenia (n = 12); and Group 3, induced osteopaenia plus risedronate (n = 12). Group 1 received subcutaneous saline solution (2 ml kg(-1)) injections for 12 weeks. Group 2 received 1 mg kg(-1) methylprednisolone acetate for 12 weeks. Group 3 received the same treatment as Group 2, plus 3 mg kg(-1) risedronate sodium for a further 12 weeks. A radiograph of the left mandible was taken on day 0 and after 12 weeks. A third radiograph was taken in Group 3 after risedronate treatment. Digital subtraction of the radiographs was used to compare the intensity of pixels in the control area and the test area. The animals were killed and the same area assessed by subtraction was histologically evaluated. RESULTS: ANOVA revealed statistically significant histological differences between the three groups. Tukey's multiple comparisons test showed that Group 2 had the smallest mean proportion of bone trabeculae per field and Group 3 the largest (F = 37.56; P < 0.01). Radiographic subtraction revealed a higher mean pixel intensity in Groups 1 and 3 vs Group 2. In Group 3, glucocorticoid caused a significant loss in radiographic density, and risedronate restored that loss (Friedman's non-parametric test). CONCLUSIONS: Subtraction radiography was able to detect changes in bone mass induced by glucocorticoid and bisphosphonate.

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.