Some degree of relapse was recorded in 13% of the measurements on average, even in patients with some form of long-term retention. However, it may be possible to reduce the relapse rate by taking account of the following criteria: Retention time should be increased in cases of short-term therapy, since relapse was found to occur more often on average (19%) when the treatment time was less than 3 years than when it was longer than 4 years (13%). As the highest relapse rate registered was 24% when therapy was started between the ages of 9 and 12 years, but was up to 42% in younger and older patients, there should be more extensive retention in these latter cases. Where there is a risk of relapse in the anterior arch, fixed lingual retainers should be given preference over removable ones. This is especially applicable to male patients and to non-extraction patients, as relapses in the anterior segment occurred more often or were more marked in these cases. The use of removable retainers is necessary when the transverse stability of the buccal segment is at risk. When only fixed retainers were used in the anterior area, relapses were recorded 6-31% more frequently in the interpremolar distance in the maxilla (21%) and the mandible (35%), and in the lower intermolar distance (27%). In particular, the use of a removable mandibular retainer should not be dispensed with after bicuspid extractions, transverse expansion and, in female patients, in the lower jaw, as relapse in the buccal segment was more marked or more common in such cases. On the basis of our clinical findings and of earlier studies, the retention time should be at least 2 years. The retainer type used has been found to be just as important as the retention time. If optimum relapse prevention is aimed at, fixed maxillary and mandibular retainers in the anterior region should be combined with a removable retainer and worn until the patients reach their late twenties.

No abstract

The type-2 depleted form of ascorbate oxidase from zucchini has been prepared in crystals and characterised by X-ray crystallography and EPR spectroscopy. The X-ray structure analysis by difference-Fourier techniques and refinement shows that, on average, about 1.3 Cu atomslascorbate oxidase monomer are removed. The copper is lost from the trinuclear site whereby the EPR-active type-2 copper is depleted most; type-1 copper is not affected. This observation indicates preferential formation of a 1 Cu-depleted form with the hole equally distributed over all three copper sites. Each of these 1 Cu-depleted species may represent an anti-ferromagnetically coupled copper pair which is EPR-silent and could explain the disappearance of the type-2 EPR signal.Ascorbate oxidase is a blue multicopper oxidase that catalyses the four-electron reduction of dioxygen to water with concomitant one-electron oxidation of the organic substrate The 0.25-nm X-ray structure of the oxidised form of ascorbate oxidase from zucchini showed the polypeptide fold and the coordination of the mononuclear blue copper site; in addition, an unprecedented trinuclear copper site has been discovered consisting of three Cu atoms within 0.37 nm of each other [6]. The structure has now been refined to 0.19 nm and its detailed description and implications for the catalytic mechanism have been the subject of a further publication [7].The structural relationship to the other blue copper oxidases, laccase and ceruloplasmin, has been demonstrated by amino acid sequence alignment based on the spatial structure of ascorbate oxidase from zucchini [8]. All canonical copper ligands are strictly conserved with the exception of the methio- Abbreviations. T2D, type-2 depleted; FO, observed structure factor amplitude; FC, calculated structure factor amplitude; g,,, parallel component of g-tensor; g,, perpendicular component of g-tensor; All, parallel component of the electron-nuclear hyperfine tensor; A,, perpendicular component of the electron-nuclear hyperfine tensor.Enzymes. Ascorbate oxidase

We present accurate electromechanical measurements on a balanced push-pull dielectric elastomer actuator, demonstrating submicrometer accurate position control. An analytical model based on a simplified pure-shear dielectric elastomer film with prestretch is found to capture the voltage-displacement behavior, with reduced output due to the boundary conditions. Two complementary experiments show that actuation coefficients of 0.5–1 nm/V2 are obtainable with the demonstrated device, enabling motion control with submicrometer accuracy in a voltage range below 200 V.