Formulation and evaluation of a hydrophobic composite plastic

A hydrophobic co-polymer, heptafluorobutylmethacrylate co-para vinyl phenol, was compounded with ethylene glycol dimethacrylate and silanated quartz to produce a hydrophobic composite. The experimental composite had satisfactory working properties and had mechanical properties comparable to commercial composite but a higher modulus of resilience. The wear resistance was equal to or greater than the commercial composite depending on whether a two-body abrasion test or a track width versus normal load test was used for the evaluation. The thermal coefficient of expansion and water sorption values were somewhat higher than those of commercial composites.

Physical properties of a pigmented silicone maxillofacial material as a function of accelerated aging

The effects of accelerated aging on a pigmented elastomer were evaluated by using a weathering chamber. Silastic 44210, a maxillofacial material with proven color and physical property stability, was chosen for pigmentation with 11 maxillofacial pigments. The values of ultimate tensile strength, maximum percent elongation, shear strength, Shore A hardness, and permanent deformation were determined for the pigmented elastomer before and after accelerated aging for 900 h. Results obtained indicate that the incorporation of 0.2% by weight of pigments can alter the physical and mechanical properties of the base elastomer. Accelerated aging had no effect on the physical properties of the pigment/elastomer combinations.

Physical properties of maxillofacial elastomers under conditions of accelerated aging

The stability of the physical properties of various commercially available maxillofacial prosthetic materials was evaluated with the use of an accelerated aging chamber. The tensile strength, maximum percent elongation, shear strength, tear energy, and Shore A hardness were determined before and after accelerated aging. Results indicate that silicone 44210, a RTV rubber, is a promising elastomer for maxillofacial application.

In vitro wear of microfilled and visible light-cured composites

Wear of microfilled composites, a visible light-cured composite, and a conventional composite were characterized by two-body abrasion and single-pass sliding. There were differences in abrasion rates among the materials. Tangential forces, wear track widths, and surface failure modes were different among materials. Wear characteristics are combinations of these properties.

A new composite restorative based on a hydrophobic matrix

A hydrophobic restorative composite based on a fluorocarbon analog of an alkyl methacrylate and a bisphenol adduct was formulated into a one-paste system, which polymerized in the presence of blue light. Physical, mechanical and water-related properties were determined. High contact angles and low water sorption were shown by the experimental composite. Capillary penetration of oral fluids around restorations, therefore, could be prevented in the presence of this highly hydrophobic surface. The physical and mechanical properties of the experimental composite were either comparable to or somewhat less favorable than commercial Bis-GMA composites.

Viscoelastic and dynamic properties of soft liners and tissue conditioners

The creep compliance and dynamic modulus of two tissue conditioners and five soft liners were determined after storage in water at 37 degrees C. Under static conditions the tissue conditioners functioned like viscous liquids, whereas the soft liners were more elastic. In general, linear viscoelasticity was not observed. Under dynamic conditions, the materials were stiffer.

Color stability of a pigmented elastomer for maxillofacial appliances

The color stability of a series of eleven maxillofacial pigments was determined after accelerated aging using reflection spectrophotometry. The results indicate that seven of the pigments demonstrated good to excellent color stability, while four of the pigments were less promising for clinical use.

Stain resistance of maxillofacial materials

The resistance of three silicone and one polyvinyl chloride maxillofacial materials to staining by tea, lipstick, and disclosing solution was measured by reflectance spectrophotometry. Changes in color caused by staining were larger than changes caused by color instability of the base elastomers or pigments under conditions of accelerated aging.

Modifying the setting rate of an addition-type silicone impression material

Two methods for controlling the working time of an addition-type silicone impression material are presented. The progress of the polymerization reaction of this modified system was studied using viscosity and a new "compression set" technique. The physical properties are presented and compared to those typical of condensation silicones, and a method of clinical use is suggested.

Wear of composites by abrasives of varying hardness

The relationship between the wear of three composite resins and the hardness of the abrasive was studied by a two-body abrasion test. The wear rates of the composites increased linearly with abrasive hardness from 530 to 2080 KHN. Measurement of the slope of the wear rate versus abrasive hardness over this range provided a sensitive method for ranking the composites.

Comparison of the accuracy of denture bases by a non-parametric method

A comparison of the accuracy of denture bases made from a conventional acrylic and four modified acrylic resins was made with the use of a non-parametric method. Twenty-five identical maxillary stone casts were made and five dentures for each resin were processed by conventional compression moulding techniques. The fit of each denture at the molar-to-molar region on its cast was evaluated by five evaluators who independently ranked the twenty-five dentures from best to worst fit after processing, after polishing, and after storage in water at 37 degrees C for 42 days. The ranking data were analysed by Kendall's coefficient of concordance, the Kruskal-Wallis statistic, and the Mann-Whitney test. Excellent agreement among observers was obtained. After storage in water, two modified acrylic resins, Hydrocryl and Vitalon II, had a better fit on their casts than the conventional acrylic, Lucitone Hypro. Luciton 199 had the same and Hircoe had a poorer fit than Lucitone Hypro.

Characterization of enamel surfaces prepared with commercial and experimental etchants

Polished enamel surfaces were etched with various commercial and experimental etching solutions and evaluated for changes in surface profile and topography. Enamel surfaces that were exposed to solutions of phosphoric acid in a concentration between 37% and 50% for a minute gave the most suitable surfaces for retention of the polymer. Enamel surfaces that were roughened with a diamond stone were not etched uniformly. Enamel that was exposed to acid etching solutions was better protected by a polycarboxylate cement than by either calcium hydroxide or zinc phosphate.

Color stability of elastomers for maxillofacial appliances

The color stability of polyvinyl chloride, polyurethane, and silicone polymers for maxillofacial applications was determined after accelerated aging using reflectance spectrophotometry. On the basis of color stability after accelerated aging, and ease of processing, several silicone materials were the most promising.

Sintered hydroxyapatite ceramic for wear studies

A sintered hydroxyapatite (HAP) ceramic for use in wear studies was prepared from a commercial tricalcium phosphate. The sintered HAP had physical properties close to those of human enamel. The coefficient of friction and wear of the sintered HAP ceramic as characterized by tangential force, track width, and surface failure data, approximated those of human enamel.

Characterization of hydroxyapatite powders and compacts at room temperature and after sintering at 1200 degrees C

Synthetic HAP made in the laboratory as 'synthetic bone' may be a possible replacement or repair material, since the mineral phase of dental hard tissue and bone is essentially hydroxyapatite in form. Hydroxyapatite or modified compositions of HAP appear to offer possibilities as a substitute for the original material provided by nature. A high surface area (70.4 m2/g) commercially available hydroxyapatite (HAP) of poor crystallinity was converted to a highly crystalline HAP through sintering at 1200 degrees C in an atmosphere of steam and nitrogen. Compacts were made of the powdered HAP from 500 to 25,000 psi and sintered under the same conditions. The changes in the resulting pore volumes, pore sizes, pore size distributions, densities, and surface areas of the sintered compacts were determined by mercury porosimetry. A 20-fold reduction in open pore volume for sintered compacts was observed. For compacts made at pressures above 5000 psi, the reduction in open pore volume was compensated for by the formation of closed pore volume. The sintering mechanism was attributed mainly to neck formation, growth between particles, diffusion, and plastic deformation.

Polyurethane elastomers as maxillofacial prosthetic materials

A series of polyurethane elastomers based on an aliphatic diisocyanate and a polyether macroglycol was polymerized with various cross-link densities and OH/NCO ratios. Stoichiometries yielding between 8,600 and 12,900 gm/mole/crosslink and an OH/NCO ratio of 1.1 resulted in polymers with the low modulus, yet high strength and elongation necessary for maxillofacial applications.

Viscoelastic properties of elastomeric impression materials: polysulphide, silicone and polyether rubbers

Creep compliance measurements were shown to be effective in characterizing the elastic, retarded elastic, and viscous properties of polysulphide, silicone, and polyether impression materials. The test is particularly valuable in that the creep compliance was independent of load, allowing the mechanical properties to be represented by a single total creep compliance curve which can be used to determine the various creep components. The total recovered compliance was shown to be independent of time provided the polymerization had progressed sufficiently before testing was done. The retarded elastic and viscous compliances contributed proportionally to the total creep compliance and thus did not affect the rankings of materials. The viscous compliance of polysulphide A decreased enough after 1 h so that the creep compliance of A and D were not different. The creep compliance measurements showed that the polysulphide materials were the most viscoelastic followed by silicone and polyether impression materials. The polyether was the most nearly ideal elastic material but it had a flexibility comparable to heavy body polysulphide. Of particular interest was the observation that polyether with thinner in ratios up to 1 : 1 by length had no practical effect on the viscoelastic properties.

Stresses from loading distal-extension removable partial dentures

A concentrated load of 222 N in the region of the central fossa of the second molar resulted in stresses in the supporting bone which increased gradually from zero in the region of the retromolar pad to about 25 MN/m2 distal to the second molar. Stresses in the alveolar bone supporting the second premolar were about 30 MN/m2 at the cemento-enamel junction, decreased to about 20 MN/m2 distal to the apex of the root, increased to 100 MN/m2 at the apex, and decreased to 3 MN/m2 near the mesial upper third of the root surface. When a distributed load of 222 N was applied to the first and second molar region, the stress distribution was similar to that observed for the concentrated load, and stress magnitudes were about 20% lower. Dramatic decreases in stress, with the maximum stress at the apex being 40 MN/m2, occurred when a 222 N load was distributed in the area of the marginal ridge.

Thermal analysis of dental impression waxes

Ten dental impression waxes were characterized by penetration and differential thermal analysis. Penetration and initial transition temperatures were directly correlated. Penetration at 37 C ranged from 2.5 to 22% for bite waxes and was 100% for corrective waxes. Distortion of an impression wax may occur upon removal from the mouth.

Vapor phase adsorption of water on hydroxyapatite

Water vapor adsorption isotherms were determined gravimetrically on three hydroxyapatite sampel differing in preparation and with surface areas of 70.4, 22.5, and 3.0 M2/gm, respectively. Heats of adsorption for the first layer of water were found to be 13.3, 13.2, and 13.9 kcal/mole on these hydroxypatites. From repeated thermal desorption and adsorption cycles of water, stepwise adsorption was observed which diminished with each outgassing cycle until it disappeared after the fourth cycle. Cross-sectional area of adsorbed water molecule on hydroxyapatite surface was estimated at 11.5 A2. Standard free energies, isosteric heats, changes in enthalpy, and entropy of adsorption of water on HAP samples outgassed at 300 C were determined.