The aim of this study was to validate the use of digitized periapical radiographs in evaluating orthodontically induced apical root resorption against micro-computed tomography (micro-CT) scanning as a criterion standard test. In a standardized experimental protocol, 29 premolars in 16 subjects were tipped buccally for 8 wk. Nineteen contralateral premolars not subjected to orthodontic movement served as controls. Standardized periapical radiographs were taken before and after the experimental period (Rx method). These teeth were extracted and scanned using a micro-CT technique with a 9 mum resolution. Two calibrated examiners assessed blindly the presence or absence of apical root resorption on digitized radiographs and three-dimensional reconstructions of the scans. Significant differences were detected between the orthodontically moved teeth and controls: 86% of the orthodontically moved teeth and 21% of the control teeth showed apical root resorption when using micro-CT as a validation method. A total of 55% of the experimental teeth and 5% of the control teeth showed resorption when assessed using Rx method. The Rx method showed a specificity of 78% and a sensitivity of 44%, which means that less than half of the cases with root resorption identified using a CT scanner were identified by radiography. Nearly all the orthodontically moved teeth showed apical root resorption. Apical root resorption may be underestimated when evaluated using digitized periapical radiographs.

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The development of the cholinergic system in the human forebrain, cerebral cortex and cerebellum was studied in post mortem material by estimating activity of choline acetyltransferase (CAT) and the binding capacity for quinuclidinyl benzilate (QNB) as markers for cholinergic nerve terminals and muscarinic receptors respectively; also the activity of acetylcholinesterase (AchE) was determined. The age periods were as follows (number of specimens in parentheses): fetal period, 18–22 weeks gestational age(GA; 8). perinatal period, 26–44 weeks GA (5–15 depending on brain part), early postnatal period, 2–15 months (4), and adult life, 58–70 years (4). Total protein and DNA were estimated in all specimens, and whole organ weights were obtained for the forebrain and most of the cerebellum specimens, allowing assessment of total organ parameters. Marked differences were observed in the ontogenesis of the cholinergic system in the cerebrum and the cerebellum. In the cerebral cortex and the forebrain from 18 weeks gestation towards term there was an increase in the concentration of CAT activity, which, however, had not reached adult concentrations at birth; on the other hand, receptor development was more advanced, since QNB binding site concentration reached adult levels by term. In sharp contrast, in the cerebellum maximal CAT activity was attained in the 26–42 weeks GA group. In comparison with the concentration of this presynaptic marker at that age period, the estimates in the postnatal samples were only 10–18%, the precipitous decline occurring during the early postnatal period. The highest concentration of the cholinergic ligand binding sites was also reached during gestation, but the peak was attained earlier (18–22 weeks GA) and the fall in concentration with age was less sharp. In contrast to the developmental changes in the concentration of the muscarinic receptor the affinity for the ligand was apparently the same throughout the age period studied. AchE activity in cerebral cortex increased with development to a level higher than that found in the adult, while the cerebellum was much richer in AchE and there was a modest developmental increase, the highest concentrations being found in adult cerebellum.