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.

Leaching of nickel, chromium, and beryllium ions from base metal alloy in an artificial oral environment.

The use of base metal alloys in dentistry has gained wide popularity in recent years. However, claims of their safety have not been universally accepted. An artificial oral environment capable of reproducing three-dimensional force-movement cycles of human mastication was used to determine whether nickel, chromium, and beryllium ions were leached from base metal alloy. Twelve pairs of crowns were articulated in the following combinations: metal versus metal, metal versus enamel, metal versus porcelain, and metal versus metal without chewing as a control. In a simulated 1-year period of mastication, the results showed that nickel and beryllium metals were released both by dissolution and occlusal wear. These findings suggest that if these conditions occur in the oral cavity, the stability of base-metal alloys is subject to question. Further studies are needed to determine whether the leaching reported has long-term consequences for patients receiving base metal restorations.

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.

Shade color discrimination by men and women.

Women have traditionally been believed to be more capable of matching colors than men. Because of this factor women should tend to agree with one another more often than men regarding tooth shade selection. This study tested differences in dental color perception between men and women. Six women and six men, all dental students, were selected and given the Farnsworth-Munsell 100 Hue test and the Farnsworth D15 test to rule out any inherent color deficiences. The students then used three different shade guides and three different light sources to match each others' teeth. Students selected shades for the gingival third and incisal third sites of selected maxillary anterior teeth. The students rotated use of the different shade guides and light sources. Descriptive statistics and ANOVA were performed on the data. Generally, there were no statistically significant findings with the use of three light sources and two shade guides for men at the p less than 0.05 level. For women, the light source made a difference. The men, as a group, showed borderline more (63% to 58%) uniform shade selection than the women.

Deformation of crowns during cementation.

Deformation of crowns during cementation was investigated by a simple loading system of defined crowns with silicone fluids as cements. Deformation of the crowns was measured by long stain gauges that encircled the cervical margins. Die spacing was simulated by etching the die. Venting was simulated by removing a small screw. Deformation of the crowns was decreased by decreasing the viscosity of fluid, increasing the thickness of the crowns, and venting. Etching the die decreased the seating times of the crowns, but did not alter the level of deformation. Terminal cementation with zinc phosphate cement confirmed the presence of crown deformation during cementation. The results have consequences for bonded and all-ceramic crowns, and explain several clinical phenomena. It is suggested that low viscosity cements, low seating forces, and die spacing be used to decrease the deformation of crowns during seating. The importance of passive fitting of the crown to the tooth is stressed.

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.

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.

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.

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.

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.

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.