ABSTRACT
The moments and forces delivered by round transpalatal arches of steel and of beta-titanium (TMA) for symmetrical derotation of molars were studied in laboratory experiments. Three sizes of arches were tested in two series. In the first series, the degree of activation was checked for symmetry in a computer-based strain-gauge measuring system. In the second series, the activation was carried out in a way simulating clinical use. The mesio-distal and transverse forces and the derotating moments at full activation and during derotation in steps of 5 degrees were measured. At full activation, the steel arches delivered relatively large moments which, however, decreased rapidly during deactivation. The TMA arches had a larger working range. It was not possible to achieve full symmetry of the moments at the two ends of the arch. The difference of the two moments resulted in forces acting on the two anchorage teeth in a mesio-distal direction. These forces were generally small but could reach clinically relevant magnitude. The derotation resulted in a contractive force of up to 2.7 N which has to be compensated for by expansion. The mode of activation simulating clinical use resulted in reasonably constant forces and moments. The use of a vice to hold the arch during activation was found to be of great help and is recommended in the clinical setting. Because of the larger working range, TMA arches are recommended if substantial derotation is needed.
Subject(s)
Molar , Orthodontic Appliance Design , Tooth Movement Techniques/instrumentation , Adolescent , Computer Simulation , Dental Alloys/chemistry , Dental Arch/anatomy & histology , Humans , Maxilla , Models, Biological , Molar/physiology , Palate/anatomy & histology , Rotation , Stainless Steel/chemistry , Stress, Mechanical , TitaniumABSTRACT
40 patients with sonographically detected diffuse liver diseases of different severity and 8 controls with normal ultrasound of the liver were evaluated for fasting concentrations of serum bile acids (SBA) using an enzymatic method. Differences of SBA levels were significant among 4 groups classified as to severity by ultrasonography; SBA levels above 4.6 mumol/l were specific for the more severe grades of liver disease. Measurement of SBA and the evaluation of echographic patterns may be helpful in the decision to perform a liver biopsy.
