Three-dimensional color coordinates of natural teeth compared with three shade guides.

The three-dimensional color coordinates of 2832 human teeth were measured in vivo and were plotted in a cylindrical Hue, Value/Chroma space, using a program in BASIC. The commonly used Vita, and Bioform shade guides, and a surviving shade guide of E. B. Clark were compared with these natural teeth. The shade guides did not match well with the color space of the human teeth, and the anticipated deficiencies were in the yellow-red Hues, higher Values, and higher Chromas. However, the points for natural teeth were in a narrow flounder-like configuration, suggesting that a representative shade guide matching natural teeth could be generated with limited samples.

Spectrophotometric study of five porcelain shades relative to the dimensions of color, porcelain thickness, and repeated firings.

A total of 125 ceramo-metal samples were used representing: 1. Five different porcelain shades a. Ceramco shades A3, B2, and D3. b. Vita B2. c. Biobond B62. 2. Thicknesses of 1, 2, and 3 mm for each shade fired two times 3. Additional 2 mm samples for each shade fired five and 10 times. Each sample was analyzed by a recording spectrophotometer. Data received was converted to Munsell notation for evaluation of the dimensions of color, i.e., Hue, Chroma, and Value, as related to (1) shade differences, (2) thickness of porcelain, and (3) numbers of firings.

Teaching of color in predoctoral and postdoctoral dental education in 1988.

This is a report of a 1988 survey of faculty involved in undergraduate and graduate programs concerning the teaching of color science. This survey indicates that the dental profession is making progress in color theory, application, and research in the dental curriculum. Manufacturers have been slow to respond to the needs of the profession. The majority of dentists surveyed indicated a need for the development of a new and systematic shade guide.

A status report of possible risks of base metal alloys and their components.

Sensitivity to base metal alloys and the components, both generalized skin reactions and local reactions, has been well documented. With the present trend toward increased use of these alloys by the dental profession, the short- and long-term implications of their use needs to be investigated. This article reviews the background, intake, and current use of two of the most commonly used metal alloys and their components. It also describes their mechanisms of action at the cellular level, the hazard to technicians, patients, and dentists, and the current health standards for airborne exposure in dental laboratories.

Design and technique variables affecting fracture resistance of metal-ceramic restorations.

An attempt was made in this study to make a clinically meaningful measure of fracture resistance in metal-ceramic restorations. Forty-four solid metal-ceramic crown forms were fabricated and subjected to compressive load testings. Variables included the presence or absence of a metal coating agent, the type of metal preparation (using stones of different abrasives), and three designs of the underlying metal. The following conclusions were arrived at: (1) The design of the underlying metal structure had a significant relation to the ultimate fracture strength. (2) A design with a definite acuteness of the underlying metal structure failed at significantly lower ultimate fracture strengths. (3) A metal conditioning agent did not decrease fracture resistance if applied properly. (4) Fracture strength was severely decreased when (a) improper thickness of the coating agent was used and (b) porcelain was fused to an unoxidized metal surface. (5) Bond strength, although a contributing factor, may not be as important as metal design and proper manipulation of materials during fabrication of the restoration.

Bond strength studies of precious, semiprecious, and nonprecious ceramic-metal alloys with two porcelains.

One-hundred cylindrical pull-through ceramic-metal test specimens were subjected to shear loading forces. Two porcelain systems were treated in association with five ceramic alloys--one precious, one semiprecious, and three nonprecious alloys. 1. There was no significant difference in bond strength between Ceramco and Vita porcelains. 2. The various alloys tested demonstrated significantly different bond strengths. 3. Differential statistical tests suggested that nonprecious alloys performed better with Ceramco porcelain than with Vita porcelain. 4. The bond strength of Ceramco porcelain fused to nonprecious alloy N-C2 was significantly greater than that of Ceramic and traditional gold-based alloys. 5. Nonprecious alloy N-C1 produced significantly less bond strength than the traditional gold-based alloys. 6. Semiprecious alloy W produced high bond strengths with both Ceramco and Vita porcelains. 7. The cylindrical pull-through test was a reliable, reproducible method of testing ceramic-metal bond shear strength. 8. The surface roughness appears to be the one common factor in nonprecious alloys that relates to large differences in bond strength. Additional tests must be made to verify this hypothesis.

Corrosion-fatigue of the bond between nickel-chrome casting alloys and porcelain.

This study was designed to determine if corrosion-fatigue might play a part in early failure of the porcelain-fused-to-metal bonds with Ni-Cr alloys. A qualitative test was used that compared the bond strengths of a control group with those of samples subjected to corrosion-fatigue. One Au-Pd alloy was used for comparison with the Ni-Cr alloys. The bond strengths were determined with a shear-push through test in an M.T.S. hydraulic testing machine. Two additional groups of samples were tested with corrosion only and fatigue only. All samples except those used for controls were placed in an oral environment chamber that had an aerated artificial saliva circulating through it maintained at 37 degrees C. (Samples subjected to fatigue only used unaerated distilled water). Corrosion was accelerated by enforcing a potential of approximately 500 mV on the test samples. The samples subjected to fatigue were stressed with a haversine waveform with a force between 5 and 45 pounds at a rate of 200 Hz for 10(6) cycles.

An investigation of tensile strength of dental solder joints.

Tensile specimens of dental solder joints were tested to determine the effect of gap distance on the strength of solder joints. Two dental alloys were used; a Type III gold alloy and a gold-palladium (Au-Pd) alloy. The Type III alloy was joined with the recommended gold solder. The Au-Pd alloy was joined using preceramic and postceramic application soldering techniques. Gap distances of 0.13 mm, 0.5 mm, and 1 mm were used with each soldering technique. All solder specimens were machined to a uniform diameter and then tested for tensile strength. It was concluded that: 1. There was a significant increase in strength for the Type III gold as the gap distance was increased. 2. The trend toward stronger joints at narrow gap distances for Au-Pd alloy joined with presolder was not statistically significant. 3. The trend toward stronger joints at wide gap distances for the Au-Pd alloy joined with the postsolder was not statistically significant. 4. The postsolder joints were statistically stronger than the presolder joints. 5. The trends observed could be partially explained in terms of competing effects of yield strength (triaxially), wettability, and void or inclusion content at the various gap distances.

Effects of opaque and porcelain surface texture on the color of ceramometal restorations.

This study demonstrated the difference between Hue, Chroma, and Value between Ceramco shades A3 and B1 when the porcelain and opaque textures were modified. Porcelain surface texture, whether rough or smooth, did not make a difference in Hue. However, the glossy type surface in the opaque layer shifted for shade A3 from yellow toward yellow-red, and toward yellow for shade B1. This study demonstrated that Chroma is greater for dull opaque than for glossy opaque with shade B1, but for shade A3 the statistical interaction between dull opaque and smooth porcelain texture decreased the Chroma. Value had essentially an additive effect of opaque and porcelain textures for shade A3. The smooth surface porcelain texture increased the Value of shade B1 compared to the rough porcelain surface. The interactions that occur between the texture of porcelain and opaque affecting color are complex phenomena. They may be related to the modification of light by transmission, absorption, refraction, scattering, and reflection.

Comparative study of two treatment methods for internal derangement of the temporomandibular joint.

Orthopedic mandibular repositioning and flat plane occlusal splint therapy were compared in the treatment of 20 patients with internal TMJ derangement with reduction. The following conclusions can be drawn. Mandibular repositioning treatment produces significant subjective and objective improvement in the dysfunction of patients with internal joint derangements with reduction. Flat plane occlusal splint treatment produces no significant change in the dysfunction level of patients with internal joint derangements with reduction. Mandibular repositioning treatment may eliminate the reciprocal click of internal joint derangement with reduction. To realize improvement in dysfunction of internal joint derangement, it appears that the reciprocal click must be eliminated. Mandibular repositioning treatment produces a significant improvement in muscle pain associated with internal joint derangement.

A shear test for the bond strength of ceramometals.

An innovative shear-testing method was introduced to study the effect of firing temperature, type of metal, and surface texture on the bond strength of the ceramometals. Two common ceramic/metal alloys were used: Olympia, a precious alloy, and Talladium, a base alloy. A Ceramco II Paint-O-Pake opaque was selected for the study. Each porcelain alloy was prepared in a similar manner before porcelain application to achieve uniform surfaces. A separate category of base alloy samples was subjected to etching after sandblasting. Each category was then divided into two groups. Opaque porcelain was fired according to the manufacturer's instructions in one group and 65 degrees F higher in the other. The bond strengths were compared by statistical analysis and post-tested samples were evaluated visually and microscopically with a scanning electron microscope.

The compressive strength of nonprecious versus precious ceramometal restorations with various frame designs.

This study was designed as a comparative analysis of the compressive strengths of precious versus nonprecious metals with various framework designs used in clinical restorations. One hundred thirty-five statistically uniform ceramometal restorations were fabricated. The restorations were cemented to the die and then subjected to stroke-control compression forces in an Instron loading machine. Simulated clinical failure was recorded by the Instron load cell recorder in pounds of load.

Interdependence of the hue, value, and chroma in the middle site of anterior human teeth.

PURPOSE: This study examines how the color coordinates of human teeth are related to each other and describes a mathematical relationship between Hue, Value, and Chroma of the middle site of anterior teeth. MATERIALS AND METHODS: The color coordinates obtained from a previous instrumental survey of the colors of vital teeth (see Goodkind and Schwabacher) were examined statistically, and equations were sought to describe their distribution in color space. The resulting single equation was applied to the colors of 100 extracted teeth. RESULTS: Correlations between Hue, Value, and Chroma were not significant for incisal and cervical sites. For the middle site, these Munsell color coordinates were highly correlated and closely confined to a planar region of the color space, described by a single equation. CONCLUSIONS: Human tooth color distribution seems to be relatively simple, at least for the middle site. It seems possible that a systematic method of shade selection (see Goodkind and Loupe) can be made available.

Residual stress in several ceramometal systems.

Residual stress caused by a mismatch of alloy-porcelain thermal contraction can contribute to clinical failure of a ceramometal restoration. This investigation assessed thermal compatibility of three ceramometal alloys and two opaque porcelains. Thermal expansions of the alloys and porcelains were measured by using a straight push-rod dilatometer. Porcelain glass transition temperatures and expansion values were derived from length-versus-temperature curves. Residual stress states in alloy-porcelain pairs were assessed by comparing expansion values of the components at the porcelain glass transition temperatures. Above that temperature the porcelain viscosity is low and stress relief is possible, whereas below the glass transition the porcelain acts as a stress-supporting solid. Expansion values were in general agreement and glass transition temperatures were slightly lower than values previously reported for similar materials. Alloy-porcelain thermal compatibility for the materials tested appeared more dependent on the opaque porcelain than the alloy.

The effect of the resilient-layer distal-extension partial denture on movement of the abutment teeth: a new methodology.

The new methodology presented in this article is simple, reliable, and accurate. The testing casts represented a reasonable simulation of human dentition. The artificial mouth reproduced major mandibular movement in a physiologic manner and applied controlled load instead of static load. The abutment movement sensor and the strain-gauge configurations suggested showed a higher level of sensitivity, accuracy, and reproducibility. This method was intended to be used for in vitro studies of RPD designs. It allowed recording of occlusal forces around the abutment tooth in the three axes of motion simultaneously.