Biomedical subjects
Publications and source records attributed to J B Moser.
Luminescence spectra of several non-radioactive luminophors that may be suitable for dental porcelain have been obtained. It was found that porcelain composition and maturation temperature have large effects on excitation and emission spectra. Most of the luminophors had excitation maxima lower in wavelength than have been observed for natural teeth.
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These static creep characteristics indicate that under functional loads Coe-Comfort could behave satisfactorily as a tissue-conditioning material for periods up to 1 week, particularly for the first 24 hours postinsertion. However, the absence of published data on the tissue loads exerted by dentures in their resting state precludes making judgments as to the absolute efficiency of any of these materials as tissue-conditioning agents. When the present results are considered along with those obtained in an earlier study (Part I), the following general conclusions can be made: 1. Coe-Comfort should exhibit the best tissue-conditioning characteristics of the materials tested. 2. F.I.T.T. should perform as the best functional impression material. 3. Lynal is distinctly different from the other two materials in its mechanical properties. Its much greater stiffness coupled with much lower plasticity precludes a prediction of its relative clinical efficacy.
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Impressions of a laboratory model of an edentulous ridge were made with three commercial tissue conditioners (FITT, Hydro-Cast and Coe-Comfort). Combinations of undercut dimensions and tray relief were tested by using three different sized trays with each tissue conditioner. Greater tray relief increased the accuracy of all materials tested; increasing ageing time from 7 to 24 h resulted in little change of accuracy of the stone models poured from the impressions taken.
Permanent deformation, strain in compression, flow, dimensional stability, reproduction of detail and gypsum compatibility of three commercial tissue conditioners (Coe-Comfort, FITT and Hydro-cast) and one polysulphide base Type I impression material (Coe-flex) were measured according to ADA Specification No. 19. Although the tissue conditioners generally exhibited higher deformations and lower gypsum compatibility than specified by ADA Specification No. 19, the materials can, in all probability, be considered adequate for the present. It would appear that the development of international standards for tissue conditioners and functional impression materials is badly needed.
An indirect extrusion viscometer has been used to assess the shear rate dependence of viscosity of a range of pastes supplied for elastomeric impression materials. A suggested specification for these pastes has been proposed.
A previous clinical evaluation indicated that semiprecious metals had a definite place in the construction of dowels and cores in endodontically treated teeth. 2 The results from the present in vitro study suggest that those alloys do have a place in the fabrication of single castings as type III and IV gold alloy substitutes. Although when compared with a type III gold alloy the behavior of the semiprecious alloys tested was less like that of a noble alloy, the semiprecious alloys appeared less active than the base-metal alloy. This suggests that the semiprecious alloys should be acceptably resistant to corrosion in the oral environment.
Colorimetric measurements were made on four composite resins before and after controlled immersion treatments. The four composite resins were: Adaptic (Johnson and Johnson), Prestige (Lee Pharmaceuticals), Addent XV (3M Mfg. Co.) and Smile (Kerr Mfg. Co.). Specimens of each material were prepared with mylar surfaces and with abraded finished surfaces. Separate groups of specimens of the four materials were immersed in three separate solutions for 12 days at 55c. The three solutions used were: a control solution of distilled water and coffee and a solution of distilled water and tea. For all materials and surface finishes, immersion in coffee and tea produced significantly greater colour changes than distilled water. Coffee produced significantly greater colour changes than tea with the exception of 'Prestige' and 'Addent XV' with finished surfaces. When immersed in a tea solution, specimens of the same material with differing surface finishes showed greater differences in colour change than when immersed in control and coffee solutions. The relative colour changes of the four materials due to the immersion procedures were as follows: 'Adaptic' showed the least colour changes and "Smile' showed the most. 'Addent XV' and 'Prestige' tended to vary between the former two. Comparison and correlation of colorimetry results with visual assessment scores allowed for the expression of the objective measures in subjective terms suitable for clinical purposes.
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1. The surface yielded by the acrylic resin formed against tinfoil provided better retention for the rubber base than any other surface tested. 2. Wax consistently gave the worst results in spite of careful boiling out. 3. The use of wax or asbestos spacers would not degrade the resin surface if tinfoil, or presumably the more easily obtainable aluminum foil, were used as a separating medium. 4. For drying times of between 15 minutes and 72 hours, no significant change was found in bond strength of elastomer to tray material. 5. Drying times of less than 15 minutes were found to be inadequate and to decrease bond strength; they are clinically inadvisable. 6. If, as a result of unavoidable delay, a tray is painted and then left for a number of days prior to making the impression, satisfactory bonding will still occur. However, if the dentist wishes to apply a second coat and dry it for 15 minutes, an increase in bond strength is likely to occur. 7. In the six systems tested, failure occurred at varied levels, from a low of 20 p.s.i. to a high of 80 p.s.i. 8. In the silicone and polyether systems, cohesive failure of the elastomer occurred before the adhesive bond between elastomer and tray failed. This finding correlates with the clinical observation that silicones and polyethers are more difficult to remove completely from acrylic resin trays when an impression has to be repeated.
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The influence of both imposed anodic potential in Ringer's solution and surface finish on the fatigue lives of annealed 316 type stainless steel and annealed pure titanium were measured and statistically compared to fatigue data run in air. The applied potentials in simulated extracellular fluid approximated conditions existing within the body while also producing the types of surface defects actually found on removed long time implants within the time interval of the accelerated R. R. Moor fatigue tests. Differentiating tests were run at single levels of applied cyclic stress well above the endurance limits. In Ringer's solution, the fatigue life of the 316 stainless steel decreased with increasing applied potential, and at +500 mV was significantly shorter than when run in air. At each condition, the 316 stainless steel was independent of initial surface finish. In contrast, the fatigue life of titanium improved rapidly with increasingly fine surface finishes. Furthermore, compared to air, the application of +500 mV in Ringer's solution improved the life of the rough surface finished material and markedly increased to number of cycles to failure for the electopolished specimens.
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