A comparison of ultraviolet-curing and self-curing polymers in preventive, restorative and orthodontic dentistry.

Both self-cured and UV-cured resin-base dental materials are used in preventive, restorative, and orthodontic dentistry. Polymerization is initiated in both systems by free radicals. Self-curing materials generate free radicals by means of chemical compounds included in their formulation. UV-curing systems rely upon externally-supplied, long wavelength, ultraviolet radiation to produce free radicals within the material. Therefore, although the major chemical components of both systems are similar in many respects, each system has particular advantages and disadvantages over the other, which must be recognized by the practitioner. Substantial differences exist, for example, in the color stability of these two types of materials, because of the fact that the UV-cured system cannot include UV absorbers, which protect the self-cured systems from discoloration after exposure to sunlight. UV-cured systems require a limitation on the maximum depth of filled restorative that can be cured at one time, since the filler particles attenuate UV radiation. The limit-layer is generally established as 1-1-5 mm maximum thickness. Therefore, UV-cured filled systems are more time-consuming in restorations of deeper cavities. This liability is also in evidence as it affects the degree of polymerization of UV-cured filled systems. The uncertainty of complete polymerization is apparently responsible for highly erratic compressive strength data found with UV-cured restoratives. Normally, the amount of unpolymerized monomer is much less predictable in UV-cured systems, over that which is obtained in self-cured materials. The presence of a larger fraction of unpolymerized monomer creates a greater potential for pulpal injury from UV-cured restorative materials. The catalyst used in several UV-cured systems is benzoin methyl ether, a compound of rather high toxicity (LD50:300 mg/kg). The safety of using UV radiation in the vicinity of oral mucosa has not been firmly established. The design of the UV lamp should provide for focusing all radiation onto hard tissue. However, UV-cured systems do offer several advantages over self-cured systems. They normally are one-component systems and therefore are more convenient to use in certain types of applications, e.g., fissure sealing. UV-cured systems also provide an unlimited working time, an important advantage for specific applications.

An adhesive paint-on restorative for tooth surface defects.

The physical properties of an adhesive paint-on restorative material have been examined and it is shown that the adhesion to enamel is good, its compressive strength about equal to silicate, hardness is less than for composite resins, and stain resistance is good.

Properties of a new carvable composite dental filling material.

The chemical principles and physical properties of a new composite system, which apparently cures in a two-step process to allow time for hand carving to the proper anatomic contours, are described. The new material appears to have better in vitro wear resistance than an older composite filling material.

Histological studies of an adhesive paint-on restorative for cervical erosions.

A histological study of the response in the pulps of human teeth to cervical restorations made with a composite resin following etching of the enamel for 2 minutes with 50 per cent phosphoric acid showed moderate inflammation after 14 days. Three specimens showed normal structure after 98 days. Teeth restored without etching showed only slight inflammation.

Surface roughness of composite filling materials.

Seven commercial composite filling materials were studied as regards 1) differences in their ability to take a smooth polish as measured by an electronic roughness gauge and 2) their relative loss in smoothness due to toothbrushing. A series of test formulations indicated that polishability and ability to retain a good polish are interrelated and are functions of filler particle size and filler hardness. Optimization in the filler particles from the point of view of polishability also results in improved wear resistance to toothbrushing.

Immunochemical characterization of Nocardia asteroides antigens: support for a single species concept.

Nocardia asteroides strains are highly heterogeneous. They show morphological, physiological, and immunological differences. In a previous study, we delineated seven immunotypes of N. asteroides. In the present study, we compared the culture filtrate antigens of these immunotypes by antigen-antibody crossed-immunoelectrophoresis and by rocket electrophoresis. We have also compared the antigen preparations by two-dimensional electrophoresis. While unique components constitute the major portion of the components, the results indicate that similar components are present in the culture filtrates of all strains. This finding supports the view of retaining all the immunotypes in the species Nocardia asteroides rather than designating different species such as N. farcinica and N. sebivorans.