Unpolymerized Material Research Articles

The effect of various base/core materials on the setting of a polyvinyl siloxane impression material

Five resin-modified glass ionomers and amalgam, used as a base or core buildup material, were clinically evaluated for whether they effected polymerization of a low viscosity (light body) regular set polyvinyl siloxane impression material. A total of 20 samples per group was prepared according to the manufacturer's recommendations. Ten samples from each group were handled with latex gloves during mixing and the other 10 were handled with vinyl gloves. Five of the 10 samples had the outer surface prepared with a round diamond wheel. Impressions were made of all the samples. The impression materials were visually scored inhibited or noninhibited. Inhibited impression materials met at least one following criterion: (1) an oily substance on the surface of the impression readily collected on a sterile explorer tine as it was moved across the impression surface; (2) a rippled appearance on the surface of the impression material; or (3) unpolymerized impression material adherent to the prepared sample surface. If none of the criteria were observed, the impression was scored noninhibited. The data were analyzed with the chi square analysis (level of significance p = 0.05). Total chi square analysis revealed a significant difference between brands ( p = 0.0001) and between prepared and non-prepared samples ( p = 0.001). Interrater reliability data were analyzed with the kappa correlation analysis. Raters were in complete agreement (kappa = +1). The prepared samples of Vitrebond material had an inhibitory effect on the polymerization of Express impression material.

Microwave Induced Polymerization of Monomer Impregnated Hardened Cement

ABSTRACTIt is well known that when pores of hardened cement are filled with a suitable polymer, desirable properties are greatly enhanced. With microwave induced polymerization, significant increases in compressive strength are observed.Mortar samples with a sand cement ratio of 2.5 and water cement ratios, 0.3, 0.4, and 0.5, were molded and hardened. After sufficient hydration, they were evacuated, filled with MMA and pressurized. The samples were then processed in a dynamic multimode applicator. Temperature was monitored and they were processed until the temperature exceeded 85°C.The principal result is the increase in compressive strength as compared to an untreated sample. For a W/C=0.5, and a sample hydrated for one day, the strength increased by a factor of6.0. In addition, the highly porous 1 day polymerized samples exhibited significantly greater strength than 28 day unpolymerized material.

Physical properties and repair bond strength of direct and indirect composite resins

Use of composite resins now includes indirect curing methods. Surface chemistry, repair bond strength, plus location of failure and five physical properties of two direct and three indirect composite resins were determined. There were statistically significant differences in flexural strength of materials and in hardness values. Repair bond strength failures were not significantly different; failures occurred primarily at the interface. Multiple internal reflection spectroscopy confirmed the presence of unpolymerized material after cure in all products. Indirect cure of the direct composite resin increased the degree of cure.

Residual monomer in acrylic polymers

Three proprietary dental resins were found to include acrylates (as distinct from methacrylates). As acrylates are well known to have adverse skin reactions, the nature and content of the acrylates were obtained. One resin contained methyl acrylate, and the other two ethyl acrylate. Also, the extractable free monomer from one proprietary and one experimental bone cement was determined as a function of time. This was carried out: (a) on unpolymerized material as soon as it formed a coherent dough; and (b) on already polymerized material. The extraction of n-butyl methacrylate from the experimental bone cement was very much less than that of methyl methacrylate from the proprietary bone cement. In both cases, whilst the kinetics of loss for short times appeared to conform to diffusion theory, subsequent loss did not; this was attributable to both continued polymerization of the monomer and to the concentration dependence of the diffusion coefficient.

Materials Science

The unpolymerized material extracted from cured orthodontic bonding resin was analyzed by UV spectrophotometry. Under certain conditions, substantial amounts of the material (approximately 14%) were leached from bracketed teeth. The possible carcinogenicity of these unpolymerized materials is discussed.

The denaturation of orosomucoid

Highly purified human orosomucoid exhibits apparent multistate behavior on thermal denaturation, with Δ H(cal) for the transition being 119 kcal/mol at pH 7.4. Asialoorosomucoid denatured similarly. A domain structure could not be demonstrated for orosomucoid with cyanogen bromide fragments, although some reannealing of these did occur. It is suggested that the source of the apparent multistate behavior may lie in the existence of polypeptide variants, known to be present in orosomucoid. Although some polymerization occurs on heating, the unpolymerized material shows reversible thermal denaturation behavior. The presence of low concentrations of ethanol induces a significant endotherm which moves to lower temperatures with increasing ethanol concentration. This endotherm was irreversible in the continued presence of ethanol.

Sensitized tissue response to an ethylene imine derivative transitional crown material

Routine clinical use of Scutan, an ethylene imine transitional crown material, over a 4-year period in approximately 2,000 applications resulted in two observed patients with allergic response to the unpolymerized material.

Microbiologic evaluation of poly-HEMA root canal filling material

This study was designed to determine whether poly-HEMA root canal filling material can support bacterial growth. Eight different microorganisms were tested against the polymerized material, as well as against the powder and paste components of the unpolymerized material. The results establish that this root canal filling material does not support bacterial growth.

Remaining methacrylate groups in composite restorative materials

The quantity of the remaining unreacted methacrylate groups in polymerized composite materials has been determined. Six proprietary composites were investigated by infrared multiple internal reflection spectroscopy. Infrared reflectance measurements were made before polymerization and repeated after the composites were subjected to polymerization at 37 degrees C for 24 hours. The quantities of remaining unreacted methacrylate groups were determined and the data expressed as percentages of the total amount of methacrylate groups in the unpolymerized materials. The specimens were specially prepared to ensure that the surface properties simulated the bulk properties of the polymerized composites. The quantities of remaining methacrylate groups in the six composites determined by this surface measuring technique ranged from 25 to 48%. The results demonstrate that commercially available composite materials exhibit different degrees of conversion 24 hours after the start of polymerization. These differences can be correlated to the different monomer compositions of the composite restorative resins.

An infrared spectroscopic study of sealants.

The aim of this work was to determine the quantity of remaining unreacted methacrylate groups in polymerized dental sealants. Eight brands of sealants were investigated by means of a grating infrared spectrophotometer. The infrared absorbance measurements were made before polymerization and repeated after the sealants had been polymerized at 37 degrees C for 24 h. The quantities of remaining unreacted methacrylate groups were determined and the data expressed as percentages of the total amount of methacrylate groups in the unpolymerized materials. The results demonstrate that commercially available sealants exhibit different degrees of conversion 24 h after the start of polymerization. The quantities of remaining methacrylate groups after polymerization under conditions comparable with optimal clinical conditions range from approximately 15% to approximately 35% in the different brands.

Heat-polymerization of human immunoglobulin G

When added to heated immunoglobulin G solution, rivanol precipitated polymerized immunoglobulin G, leaving the unpolymerized material in the supernate. Using this property of rivanol, kinetic studies on heat-polymerization of normal immunoglobulin G disclosed two types of immunoglobulin G differing in rate of polymerization by heat. Experiments using myeloma sera showed, however, that monoclonal immunoglobulins G exhibited a wide range of rate constant of heat-polymerization, which was not related to immunological subclass, L chain type or electrophoretic mobility. It appears that the two types present in polyclonal immunoglobulins G may correspond to two distributions of immunoglobulin G with different rate constant of heat-polymerization.

Annealing and Recrystallization in the Solid-state Polymerization in Solid Solutions of Methacrylamide and Isobutyramide

Abstract It is shown that lattice parameter changes that reflect the composition of the unpolymerized material occur during the solid-state polymerization of methacrylamide in solid solution with isobutyramide. In addition, phase changes also occur as is required by the phase diagram of the system. These results indicate that annealing and recrystallization must play an important role in this reaction and probably in other solid-state polymerizations. It is also likely that these effects are among the parameters that are important in determining the rate of solid-state polymerization.

Flame Retardants for Cotton Using APO and APS-THPC Resins

A new group of polymers made by reacting tris(1-aziridinyl)phosphine oxide, referred to as APO, or tris(1-aziridinyl)phosphine sulfide, referred to as APS, with tetrakis- (hydroxymethyl)phosphonium chloride, referred to as THPC, are good permanent-type flame retardants for cotton. All three of the compounds are water-soluble crystalline materials. The application of APO- or APS-THPC resins to textiles consists of padding fabric in an aqueous solution of the compounds, drying the fabric, curing it at about 140° C. for about 5 min. to polymerize the compounds, and then rinsing the fabric to remove any unpolymerized material. About 8% of the resins in 8-oz. cotton twill or sateen is adequate to make the fabric pass the vertical flame test before or after 15 launderings with synthetic detergents, followed by an acid fluoride sour after each laundering. The flame resistance is also very durable to boiling alkaline soap solutions. The properties of fabric treated with these new polymers are, in general, excellent. The hand and strength of the fabric is only slightly different from that of untreated fabric. The flame-resistant fabrics are resistant to rot and mildew.