Residual mercury content and leaching of mercury and silver from used amalgam capsules

OBJECTIVE

The objective of this investigation was to carry out residual mercury (Hg) determinations and toxicity characteristic leaching procedure (TCLP) analysis of used amalgam capsules.

METHODS

For residual Hg analysis, 25 capsules (20 capsules for one brand) from each of 10 different brands of amalgam were analyzed. Total residual Hg levels per capsule were determined using United States Environmental Protection Agency (USEPA) Method 7471. For TCLP analysis, 25 amalgam capsules for each of 10 brands were extracted using a modification of USEPA Method 1311. Hg analysis of the TCLP extracts was done with USEPA Method 7470A. Analysis of silver (Ag) concentrations in the TCLP extract was done with USEPA Method 6010B.

RESULTS

Analysis of the residual Hg data resulted in the segregation of brands into three groups: Dispersalloy capsules, Group A, retained the most Hg (1.225 mg/capsule). These capsules were the only ones to include a pestle. Group B capsules, Valliant PhD, Optaloy II, Megalloy and Valliant Snap Set, retained the next highest amount of Hg (0.534-0.770 mg/capsule), and were characterized by a groove in the inside of the capsule. Group C, Tytin regular set double-spill, Tytin FC, Contour, Sybraloy regular set, and Tytin regular set single-spill retained the least amount of Hg (0.125-0.266 mg/capsule). TCLP analysis of the triturated capsules showed Sybraloy and Contour leached Hg at greater than the 0.2 mg/l Resource Conservation and Recovery Act (RCRA) limit.

SIGNIFICANCE

This study demonstrated that residual mercury may be related to capsule design features and that TCLP extracts from these capsules could, in some brands, exceed RCRA Hg limits, making their disposal problematic. At current RCRA limits, the leaching of Ag is not a problem.

Minimum color differences for discriminating mismatch between composite and tooth color

PURPOSE

The purpose of this study was to determine if there are differences between patients and dental professionals in their ability to identify small color differences (deltaE) in composite resin restorative materials in vitro and to determine the deltaE that would indicate acceptability of color match between a restoration and an adjacent tooth.

MATERIALS AND METHODS

Subjects were asked to evaluate composite resin disks to distinguish acceptability of deltaE between disk pairs. Color difference discrimination of dental professionals groups D1 (dentists, n = 12) and D2 (dental auxiliaries, n = 12) was compared to that of dental patient groups P1 (patients, n = 12) and P2 (scientists, n = 12). Each group was pretested for normal color vision. Color differences between a standard and restoration disks of composite were measured in Colour Measurement Committee (CMC) (1:1) color units. Data were analyzed by logistic regression, and results were used to calculate a probability level for minimal acceptance or rejection of AE for all observers. Mean 50:50 deltaE replacement points (RP) for each group were obtained and analyzed by analysis of variance, and the Tukey pairwise comparison test was applied (alpha = 0.05 for all statistical analyses).

RESULTS

There were significant differences found between the experimental groups (p = .020). Group D2 (mean 50:50 deltaE RP = 1.78) proved to be more discriminating in accepting differences between tooth and composite resin restorative material color than group P1 (mean 50:50 deltaE RP = 2.69). The mean 50:50 deltaE RP for all subjects was 2.29 CMC (1:1) units.

CLINICAL SIGNIFICANCE

The ability to generate an excellent color match between a tooth-colored restoration and the tooth is critical to esthetic success. This study demonstrates that patients are not as discriminating in their ability to identify small color differences between composite restorations and the tooth as are dental professionals. Dental auxiliaries proved to be more discriminating in accepting differences between tooth and composite resin restorative material color than were patients.

Accuracy of Kubelka-Munk reflectance theory applied to human dentin and enamel

The Kubelka-Munk (K-M) theory provides a reflectance model for translucent materials placed on backings of different colors. We hypothesize that Kubelka-Munk (K-M) theoretical diffuse reflectance spectra of dentin and enamel are in good agreement with observed diffuse reflectance. The aim of this study was to measure the reflectance of enamel and dentin specimens and to compare the measured values of reflectance with K-M theoretical values. Disc-shaped specimens of enamel, dentin, and enamel/dentin were prepared from extracted teeth. Diffuse reflectance spectra were measured on three backings by means of a reflectance spectrophotometer over every wavelength (lambda) from 400 to 700 nm at three thicknesses. The measured reflectance values were fit by non-linear regression to corrected K-M theory. The low value of the reported errors associated with the application of K-M theory illustrated that the theoretical diffuse reflectance spectra of dentin and enamel are in good agreement with the observed diffuse reflectance.

Detail reproduction, contact angles, and die hardness of elastomeric impression and gypsum die material combinations

PURPOSE

This study compared surface detail parameters, interfacial contact angles, and die hardness for some combinations of elastomeric impression and die materials.

MATERIALS AND METHODS

Representative polyvinyl siloxanes, polyether, polysulfide, and reversible hydrocolloid impression materials and Type IV, Type V, and resin reinforced-Type IV die materials were evaluated using a factorial design. For the evaluation of surface detail reproduction, the width of the thinnest continuous line observed and the visually observed shape of the thick line were determined from samples formed using a master die conforming to American Dental Association specification 19. The contact angle of freshly mixed die material on the set impression was measured using a contact angle goniometer. Finally, hardness of the die material was determined. After conversion of the data to ranks if necessary, 2-way analysis of variance with Ryan-Einot-Gabriel-Welsch (REGWQ) multiple comparison tests where appropriate were used to determine statistical significance.

RESULTS

The thinnest continuous line demonstrated statistically significant impression material effects, and the observed shape of the thick line showed both statistically significant impression material and die material effects. For both contact angle and die hardness, a statistically significant interaction between the impression and die materials was found.

CONCLUSION

Although statistically significant differences in each property were found, no specific combination of impression and die materials was identified as superior to another for all surface properties studied.

Photoelastic stress analysis of self-threading pins

In this laboratory study six self-threading retention pins were evaluated using the two-dimensional photoelastic technique. The experimental samples consisted of 60 blocks of PSM-1 photoelastic material measuring 1" by 1" by 1/4". The samples were divided into six groups of 10 blocks each, with each group representing one of the pins used in the study. Pins were inserted and cores of amalgam and composite were fabricated over the pins. The samples were observed in the polariscope and photographed after pin insertion and after loading the cores with a constant, compressive force of 20 pounds. Using magnification, fringe orders were counted and rounded to the highest 0.5 fringe order. Each sample was evaluated for apical and shoulder stress. All statistical analyses were done using ANOVA at the P = 0.05 significance level. It was concluded from this study that the insertion of self-threading retention pins results in stress at the apical and shoulder areas of the pin. Pin design features, such as shoulder stops, significantly affect the magnitude and location of stress. There were no significant differences in either the apical or shoulder stresses induced when cores were made of either amalgam or composite resin.