Methods: Six Vita Lumin Vacuum tabs, shades B1, A3 and C4, from 2 different shade guides had their metal holders removed and were mounted on a Bachmann Articulator. The method of calibration of the machine was verified. The same three shades were selected from each guide and three tabs from one guide had a 3mm2 flat surface smoothed on their front surfaces. The examiner was blinded to all shade selections and the original shade tab designations. The tabs were each measured 31 times in a dark room and in ambient lighting on day 1 using the articulators' arm to hold the probe. The same measurements were recorded on day 2 at the same location on each tab with ambient lighting only. All experiments were repeated with the measuring probe being hand-held by an experienced operator. The Cronbach á reliability coefficient was used to analyze the overall data.
Results: The machine was repeatable regardless of calibration method. The intra-oral spectrophotometer was 100% repeatable under different lighting conditions and over time when fully mounted in an articulator regardless of tab surface type. 100% repeatability was shown when hand-held in both lighting conditions. Repeatability over time for conventional and ground tabs was 98% (reliability á value 0.9980) and 99% (reliability á value 0.9999) respectively for all shades. It was 100% repeatable for shade tabs A3 and C4 across all experiments but 93% for conventional tab B1 and 97% for ground tab B1.
Conclusions: Within the limitations of this study the intra-oral spectrophotometer studied is a reliable method of recording the basic shade of prefabricated shade tabs.