J.B. Moser

The bonding properties of elastomer tray adhesives

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.

Forces and efficacy in endodontic irrigation systems

Measurements of the pressure necessary to activate three commercially available types of endodontic irrigation systems were obtained from an in vitro testing procedure. In addition, the irrigation process was observed in simulated 1 mm. diameter root canals prepared in clear acrylic. Except for one patented system, the force necessary to depress the plunger of an irrigation syringe was found to increase as the size of the needle decreased. the most effective irrigation was observed when the larger needles of a blunted, open-end design were inserted to the full length of the preparation.

Biological and physical properties of an experimentalroot canal sealer without eugenol

Abstract The working time, setting time, set hardness, setting pH, sealing potential, and biocompatibility of an experimental root canal sealer without eugenol were compared with those of two other root canal sealers that contain eugenol. The working and setting times for the sealer without eugenol were longer than those for the sealers with eugenol at 25 C. The setting times for all sealers were similar at approximately 37 C. Set hardness, pH, and sealing ability were similar for all the sealers tested. At less than 96 hours, the sealer without eugenol was more tissue-compatible than the sealers containing eugenol. After six months, the biocompatibility of all the sealers tested was similar.

Adhesive properties of several impression material systems: Part II

The effect of saliva contamination on the tensile adhesive bond strengths of four impression adhesive systems, (1) polysulfide, (2) polyether, (3) polyvinylsiloxane, and (4) condensation silicone impression adhesive, was studied. Standard acrylic resin tray samples of 1-inch square surface were made. Tray surfaces were contaminated with saliva either before or after the application of tray adhesives. Tensile tests were performed with a Universal Load testing machine. The tensile adhesive bond strengths of contaminated tray surface and contaminated adhesive were compared with a group of control. Contamination of all impression adhesives resulted in significantly lower bond strength. Except for the polyvinylsiloxane and polysulfide impression adhesive systems, saliva contamination of tray material significantly decreased adhesive bond strengths. Impression trays should be tried in the mouth, rinsed, and dried before adhesive is applied.

Development of dental Pd-Ti alloys.

Abstract Alloys, in which the main constituents are palladium and titanium, have the following potential advantages for dental application: corrosion resistance, biocompatibility and acceptable casting temperatures for porcelainfused-to-metal dental prostheses. Alloy compositions chosen for investigation were as follows: 30 w/o Ti which lies in the 5% single-phase region near TiPd, 50 w/o Ti which lies near the 1120°C melting temperature minimum of the Pd−Ti system, and 70% Ti which minimizes Pd content while still in a relatively low melting range (1300°C). Analysis of the X-ray diffraction of 70%Pd30%Ti showed mostly PdTi with some Pd5Ti3; in 50%Pd50%Ti mostly PdTi2 was observed with some PdTi; in 30%Pd70%Ti mostly PdTi2 was found with some alpha Ti and PdTi4. The amounts of the minor phases in each of the 3 alloys depended on heat treatment. The Knoop hardness of the alloys ranged from 300–500 KHN for the as-melted condition; after heat treatment the maximum hardness values were 400 KHN. After centrifugal casting, hardness values increased to a range of 350 to 560 KHN, depending on composition. These values exceed those obtained for the pure metals which were in the neighborhood of 100 KHN. From anodic potentiodynamic scans the breakdown potentials in Ringers solution for 70%Pd30%Ti, 50%Pd50%Ti and 30%Pd70%Ti were 600, 650 and 500 (SCE); the repassivation potentials for the same alloys are 450, 300 and 350 (SCE), respectively. These are all above oral potential. The Pd−Ti system investigated was, thus, found to have adequate corrosion resistance and hardness. Therefore, it can be considered of good potential as a dental prosthetic alloy.

Effect of repeated firing on fluorescence of porcelain-fused-to-metal porcelains

T o simulate the bluish-white fluorescence of natural teeth under ultraviolet light,‘-’ dental manufacturers use fluorophors of proprietary composition. Uranium oxides were often used in the past in combination with cerium to impart a realistic fluorescence to dental porcelain.* Uranium is no longer used as a result of increased awareness of possible radiation effects on oral tissues.‘.” Fluorescent dental porcelains are often patented; for example, fluorescence activators for Shofu porcelain (Shofu Dental Corp., Monrovia, Calif.) include combinations of rare earths such as europium, cerium, and ytterbium.” Both natural and artificial teeth are exposed to ultraviolet (UV) light routinely. Not only does sunlight contain a significant UV component, but so do certain fluorescent lights, photoflash lights, high intensity studio lights, and entertainment lights. The bluish-white fluorescence of natural teeth is the result of a broad emission band with a diffuse peak at 410 to 420 nm when subjected to near UV excitation of approximately 340 nm (Fig. l).13 It appears that both the organic and inorganic portions of tooth structure are involved, but that for enamel the organic component predominates.‘4 In 1978, the luminescence spectra of many dental porcelains and acrylic resins commercially available were published.13 At that time, the effect of repeated firing on fluorescence was not investigated, and a clear distinction among the characteristics of opaque, body, and enamel porcelains was not made. It was felt, therefore, that a new study on presently used commercial porcelain was worthwhile.

Color comparisons of composite resins of various shade designations

Abstract The purpose of this investigation was to compare the measured color of commercial composite resins of various shade designations (L, LG, LY, Y, U). Three samples of 11 composite resins were prepared according to manufacturers instructions. Diffuse reflectance measurements were made on a Pye Unicam dual-beam spectrophotometer equipped with an integrating sphere to provide CIE 1976 L * a * b * values using both black and white backgrounds. Differences within shade designations were as follows: ΔL * varied from 19.45 for Y to 4.75 for LG; Δa * ranged from 7.46 for U to 3.26 for LG: and Δb * ranged from 16.23 for Y to 4.73 for LY. Total color difference was greatest within the Y shade designation and least for the LY shade. Contrast ratios ranged from 0.811 for Command (LG) to 0.961 for Spectrafil (Y) and varied considerably within shade designations. Color differences between brands of identical shade designations were visually perceptiable in all groups. The results of this study indicate the need for improved standardization of shade designations for composite resins.

Mechanical properties of tissue conditioners. Part II: Creep characteristics

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.

A clinical evaluation of semiprecious alloys for dowels and cores

The semiprecious metals investigated and hard dental gold alloys may be manipulated in a similar manner. The semiprecious metals produced accurate and well-fitted dowels needing minimal adjustment. Being harder than type III gold alloy, they would be ideal for casting dowels and cores. Before considering these semiprecious alloys as final restorations, however, they must be further examined for resistance to tarnish and corrosion and their marginal adaptability and burnishability.

Visual and instrumental discrimination steps between two adjacent porcelain shades

Two different porcelain systems were compared over the B1 to B2 shade ranges visually and spectrophotometrically. Six samples of each porcelain were made by blending weighed increments of opaque and body porcelain and firing the blended compositions onto Option metal disks according to manufacturers instructions. Compositional blends varied incrementally by 20% in steps. Selective blending of porcelain shades was shown to have an effect in improving the range of choices within the shade guide system. The human eye was capable of detecting small-step changes between two steps of the Vita shade guide. Systematic color changes occurred with compositional changes between B1 and B2. It appears from the overall results observed that a desired blending of porcelains at smaller intervals than full shade guide steps could be done more easily with Jelenko than with Vita porcelain. The visual rankings agreed more closely with the manufacturers expectations than did the instrumental measurements.