The contemporary use of removable orthodontic appliances.

Although apparently simple and efficient to use, removable appliances are no longer the appliance of choice for comprehensive orthodontic treatment in the permanent dentition. Their mechanical properties result in simple tipping of teeth, therefore multiple simultaneous tooth movements with apical control are not possible. It is for these and other reasons that removable appliances are usually only indicated for specific interventions in the mixed dentition, and as an adjunct to more complex fixed appliance treatment. Removable appliances, once popular because of their case of use, are no longer seen as the appliance of choice. This article discusses the rationale behind this statement and indicates cases suitable for removable appliance treatment.

A randomized clinical trial to compare three methods of orthodontic space closure.

AIM: To compare the rates of orthodontic space closure for: Active ligatures, polyurethane powerchain (Rocky Mountain Orthodontics, RMO Europe, Parc d'Innovation, Rue Geiler de Kaysersberg, 67400 Illkirch-Graffenstaden, Strasbourg, France) and nickel titanium springs. SAMPLE: Patients entering the space closure phase of fixed orthodontic treatment attending six orthodontic providers. Twelve patients received active ligatures (48 quadrants), 10 patients received powerchain (40 quadrants) and 11 patients, nickel-titanium springs (44 quadrants). METHOD: Patients were randomly allocated for treatment with active ligatures, powerchain or nickel titanium springs. Upper and lower study models were collected at the start of space closure (T(o)) and 4 months later (T(1)). We recorded whether the patient wore Class II or Class III elastics. Space present in all four quadrants was measured, by a calibrated examiner, using Vernier callipers at T(o) and T(1.) The rate of space closure, in millimetres per month (4 weeks) and a 4-monthly rate, was then calculated. Examiner reliability was assessed at least 2 weeks later. RESULTS: Mean rates of space closure were 0.35 mm/month for active ligatures, 0.58 mm/month for powerchain, and 0.81 mm/month for NiTi springs. No statistically significant differences were found between any methods with the exception of NiTi springs showing more rapid space closure than active ligatures (P < 0.05). There was no effect of inter-arch elastics on rate of space closure. CONCLUSIONS: NiTi springs gave the most rapid rate of space closure and may be considered the treatment of choice. However, powerchain provides a cheaper treatment option that is as effective. The use of inter-arch elastics does not appear to influence rate of space closure.

The integration of functional and fixed appliance treatment.

This article describes a functional appliance system to correct Class II problems, which is clipped on to bands, cemented to the teeth. This appliance has several advantages, as the patient cannot remove it. It acts on the teeth and jaws for 24 hours each day, patient co-operation is not a problem, and as a result the treatment time is short. Any fixed appliance system can be added while the functional phase is being completed so allowing full integration of the two treatment systems.

The effectiveness and efficiency of hygienists in carrying out orthodontic auxiliary procedures.

The aim of this study was to compare the ability and efficiency of dental hygienists, after preliminary training as orthodontic auxiliaries, with post-graduate orthodontists. The study was cross-sectional and prospective. The sample consisted of five second-year hygienists and five qualified orthodontists from Manchester University Dental Hospital. All subjects carried out a range of orthodontic exercises on phantom head typodonts. The ability and efficiency for each task was measured, and comparison made between hygienists and orthodontic groups. There was no statistically significant differences between hygienists and orthodontists in terms of their ability to carry out potential orthodontic auxiliary procedures. However, orthodontists were more efficient (P < 0.05). The ability of hygienists to carry out potential orthodontic auxiliary tasks after appropriate training is supported. Trained orthodontists are more efficient than newly trained hygienists in carrying out potential orthodontic auxiliary tasks.

Light cured direct bonding--is it necessary to use a primer?

A study was undertaken to assess the influence of a low viscosity unfilled 'primer' resin upon the shear bond strength of a bracket adhesive combination to etched enamel and at the separate interfaces of the bonding system, namely the bracket/adhesive and the enamel/adhesive interfaces. No significant differences were detected between the bond strengths when an unfilled resin phase was utilized (P greater than 0.05).

A clinical trial of an indirect bonding technique with a visible light-cured adhesive.

A trial was carried out to evaluate the clinical performance of a visible light-cured adhesive when used with a foil mesh base in an indirect bonding technique. Thirty-seven patients entered the trial, and a total of 407 brackets were placed. The incidence and site of bond failure were recorded. The overall failure rate was 6.5%. There were no significant differences detected between the failure rates for either the upper or the lower arches or for the anterior and the posterior segments of the arches (p less than 0.01).

Inactivation of the Escherichia coli heat-labile enterotoxin by in vitro mutagenesis of the A-subunit gene.

In vitro mutagenesis of the LTA gene, encoding the A subunit of the Escherichia coli heat-labile enterotoxin, has been used to obtain A subunits deficient in enzymic activity. One inactive A-subunit mutant which contained two amino acid substitutions, was shown to associate with native B subunits to form a holotoxoid lacking toxin activity. A serine to phenylalanine mutation appears to be responsible for the loss of toxicity.

A visible light-activated direct-bonding material: an in vivo comparative study.

A clinical trial was carried out to evaluate and compare the clinical performance of a visible light-cured material with a chemically cured adhesive. This was used in combination with two types of bracket base. Fifty-two patients entered the trial and 542 bracket bases were placed. The incidence and site of bond failure were recorded. The overall failure rate for the light-cured material in combination with both types of bracket was 4.7% and 6% for the chemical-cured adhesive. There were no significant differences detected between the failure rates for both types of adhesive in combination with either bracket base, and no bracket base/adhesive combination proved superior (p greater than 0.05). When the data were examined in an overall manner, a significantly higher posterior tooth failure rate was detected for all adhesive/base combinations (p less than 0.001).

Residual debris and bond strength--is there a relationship?

A study was undertaken to test the theory that there is a relationship between bond strength at the separate interfaces of the direct bonding system and the amount of residual debris remaining on the enamel surface following removal of a bonded appliance. In separate experiments, shear loads were applied at the complete direct bonding system and at the separate interfaces--namely, those at the adhesive/enamel and the adhesive/bracket base--using a chemically cured and a visible light-cured materials in combination with two designs of bracket bases. An assessment of residual debris following bond failure was made. For the complete direct bonding system, analysis showed that a foil mesh/chemically cured adhesive combination produces significantly more residual debris on the enamel than any other combination (P less than 0.05). No significant differences (P greater than 0.05) in shear bond strengths were detected for any bracket base/adhesive/enamel combination. Furthermore, no significant differences (P greater than 0.05) were detected between the shear bond strengths at the adhesive/enamel and adhesive/bracket base interfaces. These results suggest that the amount of residual debris following removal of the bonded bracket is not related to the shear bond strength at the separate interfaces but is governed by factors caused by bracket base design and properties of the adhesive used.

An investigation into the reliability of the timing headgear.

Thirteen cervical timing headgears, then commercially available, were subjected to testing under laboratory conditions. Continuous and intermittent forces were applied, these being varied between 200 and 1000 gm. Forces were applied by attaching the cervical straps to a cylindrical drum, to activate the timer switch. Each headgear showed only moderate variation in accuracy under different phases of the testing, although timing accuracy varied considerably between individual headgears. The overall performances produced mean timing accuracy values exceeding 90 per cent in only four appliances, indicating that these 'Patient Motivators' did not provide a consistently dependable recording of headgear usage.

Indirect bonding using a visible light cured adhesive.

A method of indirect bonding using a visible light cured adhesive is described in detail. The advantages include convenience and rapid placing of many brackets to a predetermined position. The ease of removal of the brackets and the material following treatment is also a major benefit of this technique.

Nucleotide sequences of four variants of the K88 gene of porcine enterotoxigenic Escherichia coli.

The nucleotide sequences of four variants of the Escherichia coli K88 antigen gene, K88ab1, K88ab2, K88ac, and K88ad, have been determined. The K88ab2 and K88ac sequences have not been reported previously. The K88ab1 sequence is very similar to that determined by other workers, but the K88ad sequence differs considerably from that described in a previous report. Comparison of the amino acid sequences inferred from the gene sequences revealed certain clusters of amino acid substitutions which have been correlated with areas of potential antigenicity in the mature proteins.

M13 clones carrying point mutations: identification by solution hybridization.

A solution hybridization procedure for the rapid identification of M13 clones carrying a particular sequence is described. The method, which employs a radiolabeled oligonucleotide probe, can discriminate between sequences which differ by only a single base, and can therefore be used for the identification of mutant sequences created by oligonucleotide-directed mutagenesis. Samples of phage-containing supernatant from cultures of M13-infected Escherichia coli are incubated with radiolabeled probe in the presence of sodium dodecyl sulfate. The mixtures are then subjected to agarose gel electrophoresis to separate hybrid molecules from unbound probe and hybridization is detected by autoradiography. This solution hybridization procedure is quicker and more convenient than membrane hybridization and has the added advantage that more than one probe can be used on a given gel.

The bonding of orthodontic attachments using a visible light cured adhesive.

The bonding of orthodontic attachments using a visible-light cured adhesive is described. The material is a Urethane Dimethacrylate resin with a glass filler which sets when exposed to visible light. This gives the material the advantage that the operator can decide when the material should set. This command setting at the appropriate moment gives increased working time and improves the accuracy of bracket positioning. These properties have been used in the development of a new technique for the direct placing of bonded retainers.