The effect of metal ceramic restoration framework design on tooth color

Statement of problem: The opacity of the metal framework in metal ceramic restorations results in reduced light transmission through the tooth that diminishes the esthetics of the tooth. Purpose: The purpose of this study was to investigate the color change that occurs apically to a metal ceramic restoration as a result of altering the metal framework design. Material and methods: Color change relative to the unprepared tooth (ΔE) between various metal ceramic restorations was determined using computer imaging and CIELAB coordinates and compared to previously determined levels of clinical acceptability. Color change was evaluated by examining 2 conditions (the metal copings and the completed metal ceramic restorations), 4 framework designs (metal collar and porcelain margins with 0-mm, 1-mm, or 2-mm cutbacks), and 2 locations on the tooth apical to the margin of the restoration, using an imaging system developed at the Minnesota Dental Research Center for Biomaterials and Biomechanics. The data were analyzed statistically using repeated measures analysis of variance (P=.05). Results: For metal ceramic restorations there exists a significant (P=.001) color change (ΔE) between all framework designs except for the 0-mm and 1-mm cutbacks. Color change (ΔE) in the location above the cemento-enamel junction was significantly greater (P=.004) than below the cemento-enamel junction. Conclusions: The framework design for metal ceramic restorations can affect the esthetics of the adjacent natural tooth. A minimum 2-mm facial cutback of the metal framework is necessary for there to be a significant difference in color change. (J Prosthet Dent 2008;99:468-476).