QUANTITATIVE DIGITAL SUBTRACTION RADIOGRAPHY FOR THE DETERMINATION OFSMALL CHANGES IN BONE THICKNESS - AN IN-VITRO STUDY

Objective. The objective of this study was to determine the ability of quantitative digital subtraction radiography to detect small changes in bone thickness adjacent to tooth roots. Study design. A series of c ortical or cancellous bone slices with a 50 mu m-stepwise increasing t hickness were attached to 4 porcine mandible sections covering buccal and interproximal ''defect'' regions. Standardized radiographs were qu antitatively evaluated for radiographic density changes with the use o f digital subtraction radiography. Furthermore, all radiographs were c onventionally evaluated by 10 clinicians. The Wilcoxon signed-rank tes t and the Mann-Whitney U test were used for statistical analysis (alph a = 0.05). Results. A high linear correlation was found between the ac tual thickness of bone slices and radiographic density changes (cortic al bone: r(2) = 0.89 to 0.99; cancellous bone r(2) = 0.61 to 0.86, p l ess than or equal to 0.001). A certain increase in bone thickness caus ed a 3 times higher increase in radiographic density for cortical bone than for cancellous bone (p less than or equal to 0.05). The detectio n limits of digital subtraction radiography were 200 mu m for cortical and 500 mu m for cancellous bone, whereas the detection limits of con ventional radiography were 600 mu m and 2850 mu m, respectively. Concl usions. This in vitro study demonstrated a very high correlation betwe en the objective, quantitative assessment of subtle changes in alveola r bone by digital subtraction radiography and the true changes in bone thickness.