Evaluation of color duplication in metal-ceramic complexes using visual and instrumental shade-matching systems.

This study was designed to evaluate color differences (DE) between intended and fabricated shades of various metal-ceramic complexes using visual and instrumental shade determination. Forty-two master disks were made to represent every tab in two shade guides. The shades of the master disks were determined visually and instrumentally. Accordingly, 84 experimental disks were fabricated. Color measurements of the master and fabricated disks were performed using a spectrophotometer. Visual shade determination showed a significantly lower DE value than the instrumental shade determination. However, all groups showed DE values exceeding 2.75, which could be considered perceivable and therefore clinically unacceptable. A reliable shade duplication of an existing metal-ceramic restoration cannot be ensured, regardless of the method of shade assessment.

The effect of two fit-indicating materials and various subsequent cleaning methods on the retention of simulated crowns.

STATEMENT OF PROBLEM: Different cleaning methods are recommended to remove residual fit-indicating materials before definitive cementation. There is little information in the dental literature regarding the effect of these cleaning methods on the eventual retention of crowns. PURPOSE: The purpose of this investigation was to evaluate the effect of various cleaning methods on the retention of simulated crowns after using disclosing wax and silicone as fit-indicating materials. MATERIAL AND METHODS: One hundred and ten specimens were divided into 11 groups (n=10) according to the fit indicators used (silicone and disclosing wax) and the methods of cleaning as follows: Group C, no fit indicator with airborne-particle abrasion and steam cleaning (control); Group S+0, silicone with no cleaning; Group S+CH, silicone with chemical cleaning; Group S+ST, silicone with steam cleaning; Group S+US, silicone with ultrasonic cleaning in distilled water; Group S+AA+ST, silicone with airborne-particle abrasion and steam cleaning; Group W+0, disclosing wax with no cleaning; Group W+CH, disclosing wax with chemical cleaning; Group W+ST, disclosing wax with steam cleaning; Group W+US, disclosing wax with ultrasonic cleaning in distilled water; Group W+AA+ST, disclosing wax with airborne-particle abrasion and steam cleaning. Solid acrylic resin blocks were machined to form the specimens. Each specimen consisted of a cylinder and a rod. The specimens were invested and cast using a nickel chromium alloy. The rod and the internal surface of the cylindrical part of each specimen were airborne-particle abraded using 100-mum aluminum oxide powder. After application of fit indicators and subsequent cleaning, all the rods were cemented into their perspective cylinders using zinc phosphate cement at a constant load of 5 kg for 10 minutes. Specimens were randomly assigned to all groups before cementation procedures. The sequence of cementation of all specimens was also performed randomly regardless of the groups to which they were assigned. The specimens were then stored in water at 37 degrees C for 1 month. All specimens were mounted in a universal testing machine and the rods were then pulled out of their respective cylinders at a crosshead speed of 0.05 mm/min. The ultimate load required for separation was recorded and expressed as MPa. The resultant data were statistically analyzed using 2-way ANOVA for fit-indicating materials/cleaning methods, and Tukey honestly significant difference (HSD) tests (alpha =.05). RESULTS: Two-way ANOVA showed significant interaction between the effects of fit-indicating materials tested and the method of cleaning on retention (P<.001). The Tukey HSD test indicated that wax and silicone fit indicators significantly reduced retention if not properly cleaned (P<.001). Retention was significantly improved when wax was used compared to silicone, regardless of the cleaning method (P<.001). Airborne-particle abrasion coupled with steam cleaning produced the highest retention values with both fit indicators tested (P<.001). However, when wax was used there was no significant difference between steam cleaning and airborne-particle abrasion along with steam cleaning. CONCLUSIONS: Wax and silicone fit indicators significantly reduced retention of simulated crowns if not properly cleaned. Airborne-particle abrasion, in addition to steam cleaning, was necessary to clean silicone. However, steam cleaning alone was sufficient for cleaning wax.