Influence of varying a spectrophotometer's angulations on shade-selection accuracy

It is not clear how precise the positioning of a spectrophotometer to the tooth must follow manufacturers' recommendations. Objective: to assess the effect of various angulations of a spectrophotometer on shade-selection accuracy. The specific aims were to determine whether there were differences in the CIE L*a*b* coordinates of cervical, body, and incisal thirds of shade-tabs when the spectrophotometer was positioned on the shade-tab according to manufacturer's recommendations and at four other angulations. METHODS: Shade measurements of 20 shade-tabs (Chromascope, Ivoclar, Liechtenstein) were taken with a spectrophotometer (Crystaleye, Olympus, Japan) at different angulations: The following groups were tested: (a) control group according to manufacturer recommendations, and at (b) 0°, (c) 15°, (d) 30°, and (e) 45° to the perpendicular to the surface on which the shade-tab was secured. CIE L*a*b* coordinates from the cervical, body, and incisor thirds were obtained thrice then averaged. RESULTS: Intraclass correlation coefficients for measurements taken thrice were high (>0.9); therefore, averages were used for all subsequent calculations and analyses. ANOVA tests revealed differences between the recommended and the 30° and 45° positions. DE values below the clinically noticeable threshold of 3.6 were considered acceptable. DE calculations suggested there were none-to-few clinical differences between recommended and 0° and 15°, and few differences at 30° positions. The 45° position was generally unacceptable in cervical, body, and incisor measurements.

	DE Cervical		DE Body		DE Incisor
Position	A*	Un-A**	A*	Un-A**	A*	Un-A**
00	20	0	20	0	19	1
150	20	0	20	0	19	1
300	2	18	19	1	16	4
450	0	20	2	18	0	20

* A=Acceptable DE <3.6, **Un-A=Unacceptable DE >3.6

CONCLUSION: Variations in angulations of this spectrophotometer of up to 15° from the manufacture's recommendations do not appear to affect clinical results.