Microbial contamination of laboratory constructed removable orthodontic appliances

OBJECTIVES: This study aims to determine whether laboratory constructed removable orthodontic appliances are free from microbial contamination prior to clinical use and to evaluate the dental hospital cross-infection procedures to ensure that patient-derived contamination does not enter the construction process, thereby propagating a cycle of cross-contamination.MATERIALS AND METHODS: The construction process of removable orthodontic appliances from three individuals was evaluated at every stage, from impression to final delivery of the appliance using molecular microbiological techniques. The bacterial profiles at each stage of appliance construction were obtained using denaturing gradient gel electrophoresis, along with the bacterial profiles of the three participants' saliva. This enabled the bacterial profiles found at each stage of construction to be compared directly with the saliva of the person for whom the appliance was being constructed. Bacteria were identified at each stage using 16S rDNA PCR amplification and sequence phylogeny.RESULTS: There was no evidence of bacterial cross-contamination from patients to the laboratory. The current process of disinfection of impression appears to be adequate. Contamination was found on the final removable appliances (0.97 × 10(2)-1.52 × 10(3) cfu ml(-1)), and this contamination occurred from within the laboratory itself.CONCLUSIONS: Every effort is made to reduce potential cross-infection to patients and dental professionals. Newly constructed removable appliances were shown not to be free from contamination with bacteria prior to clinical use, but this contamination is environmental. Further studies would be required to determine the level of risk this poses to patients.CLINICAL SIGNIFICANCE: Dental professionals have a duty of care to minimise or eradicate potential risks of cross-infection to patients and other members of the team. To date, much less attention has been paid to contamination from the orthodontic laboratory, so contamination and infection risks are unknown.</p

Fracture behaviour of plant epicuticular wax crystals and its role in preventing insect attachment: a theoretical approach

It is known that attachment ability of insects depends among others on the texture of the substrate. On plant surfaces, covered with microscopic epicuticular wax crystals, insect attachment was found to be highly reduced for many insect species. In some plants, this effect may be explained by the contamination of insect adhesive organs (pads) by wax crystals. In the present study, mechanics of the wax crystals fracture during contact formation between insect adhesive pads and plant surface is examined, in order to explain the observed contamination of pads by wax. It is shown that mechanisms of the wax crystal fracture may be rather different, depending on the slenderness ratio of the crystals. Crystals with high values of the ratio may buckle elastically or in an elastic-plastic way. For five plant species under consideration, the critical value of the slenderness ratio for elastic buckling is 26.5, while for elastic-plastic buckling it is 18.7. If the values of the slenderness ratio are lower than the critical values, one has to consider bending of the crystals under the weight of insects. Although this study considered only crystals of a tubular shape, the general approach is valid also for crystals of other shapes