Clinical evaluation of perceptibility of color differences between natural teeth and all-ceramic crowns

Color matching still remains as one of the most challenging tasks in clinical dentistry. With the advancement of intraoral color matching instruments the importance of the development of color thresholds becomes increasingly important. The objective of this study was to set a gold standard for the color difference (DeltaE) at which all-ceramic crowns cannot be distinguished from natural teeth.

All-ceramic crowns with a zirconia coping (LAVA, 3M ESPE, St. Paul, MN, USA) and layered porcelain (Cerabien CZR, Noritake, Nagoya, Japan) fabricated to match contralateral maxillary central incisors were assessed by experienced observers. Eleven all-ceramic crowns (AC) were assessed as "excellent/perfect matches;" these crowns were then measured using a spectrophotometer and compared to their natural counterparts. Unrestored natural maxillary teeth (NT) were compared to unrestored contralateral teeth in 22 subjects. Six areas were measured in both groups to determine color differences (DeltaE*).

Mean DeltaE* value between the restorations and natural teeth was 1.6. Mean DeltaE* between contralateral natural teeth was 0.9. Incisal areas of natural teeth exhibited greater differences in color than other compared areas.

A DeltaE*=1.6 represented the color difference that could not be detected by the human eye.