Sphere spectrophotometer versus human evaluation of tooth shade

The purpose of this study was to compare an objective to a subjective metho d of tooth shade evaluation using the SP78 sphere spectrophotometer and hum an visual analysis. Twenty extracted fully developed human maxillary teeth had their L* values (lightness) read by the SP78 on day 1 and then again on day 14. Using a blind method, five human evaluators then attempted to matc h shade tabs from a six-tab experimental Vita shade guide to the same teeth on days 1 and 14. The SP78 L* values read for each tooth were evaluated fo r a match between those obtained on day 1 and those read on day 14. The res ults of human evaluation of tooth shade were compared among the evaluators and then between themselves over time. Finally, the ability of human evalua tors to match tooth shade was compared with the results obtained with the S P78. The SP78 reproduced L* readings within the standard error of the machi ne (less than or equal to 1.0) in 16 of 20 (80%) teeth. In contrast, intere valuator agreement expressed as majority agreement (3, 4, or 5 of 5 evaluat ors agreeing) was only 10 of 20 (50%) teeth on day 1 and 13 of 20 (65%) tee th on day 14. Intraevaluator agreement over the experimental period ranged from 20 to 60%. The results of this study confirm that human evaluation of tooth shade is unreliable and that the SP78 sphere spectrophotometer can pr ovide a more predictable and accurate method of evaluating tooth shade in v itro. This finding opens up a new avenue of investigation for testing the e ffectiveness of materials and techniques in bleaching discolored teeth.