ABSTRACT
Crustaceans are known for their hard, calcified exoskeleton; however some regions appear different in colour and opacity. These include leg and cheliped tips in the grapsid crab, Metopograpsus frontalis. The chelipeds and leg tips contain only trace levels of calcium but a significant mass of the halogens, chlorine (Cl) and bromine (Br). In contrast, the carapace is heavily calcified and contains only a trace mass of Cl and no Br. In transverse section across the non-calcified tip regions of cheliped and leg the mass percent of halogens varies with position. As such, the exoskeleton of M. frontalis provides a useful model to examine a possible correlation of halogen concentration with the physical properties of hardness (H) and reduced elastic modulus (E(r)), within a chitin-based matrix. Previously published work suggests a correlation exists between Cl concentration and hardness in similar tissues that contain a metal (e.g. zinc). However, in M. frontalis H and E(r) did not vary significantly across cheliped or leg tip despite differences in halogen concentration. The non-calcified regions of M. frontalis are less hard and less stiff than the carapace but equivalent to values found for insect cuticle lacking metals. Cheliped tips showed a complex morphological layering that differed from leg tips.
Subject(s)
Crustacea/anatomy & histology , Crustacea/physiology , Animal Structures , Animals , Behavior, Animal , Elastic Modulus , Elasticity , Halogens/metabolism , Hardness , Microscopy, Electron, Scanning/methods , Tensile Strength , X-Ray DiffractionABSTRACT
Although this system requires the use of some different impression techniques, it provides the dentist and technician a unique and simple method to restore a missing tooth with an implant-retained crown. The Straumann ITI impression coping and analog system allow the fabrication of a hybrid die for predictable results.
Subject(s)
Crowns , Dental Abutments , Dental Implants, Single-Tooth , Dental Prosthesis Design , Dental Impression Technique , Humans , IncisorABSTRACT
Fabricating a crown and bridge for the ITI Solid Abutment can be easier than conventional units if a few changes in technique are accomplished. Burnout times and temperatures are extremely important. Devesting and finishing the casting must be carried out following the manufactures instructions.
Subject(s)
Crowns , Dental Abutments , Dental Implants , Dental Prosthesis Design , Dental Casting Technique , Dental Polishing , Denture, Partial , Hot Temperature , Humans , Laboratories, DentalABSTRACT
Langmuir-Blodgett (LB) films of omega-tricosenoic acid are deposited onto side-polished optical fibers, resulting in wavelength-selective elements. The wavelength response is shown to be strongly dependent on film thickness, giving a shift in central wavelength with film thickness of Deltalambda(0)/Deltad = 2.4, in agreement with a simple phasematching model. It is demonstrated that an alternative polishing technique, requiring no substrates or epoxy, allows more repeatable LB deposition and produces devices with similar characteristics. This is the only technique that will allow deposition of more complex electro-optic LB film-forming molecules.
