Are Dental Radiometers Useful?

Objectives: This study evaluated the accuracy of fifteen models of commercial dental radiometer (DR) in measuring the light output of LED light curing units (LCUs) compared to a ‘gold standard’ laboratory grade spectrometer integrating-sphere assembly (IS).

Methods: Ten type I (light guide) and eight type II (light source in head) LED LCUs were tested. Gold standard (GS) output measurements (n=3) were taken using IS and confirmed with a laboratory grade thermopile (Coherent PM10-19C). One model of radiometer (Bluephase Mark II, Ivoclar - BPII) allowed power (mW) to be recorded as well as irradiance (mW/cm²). DR output measurements (n=3) were made of the LCUs and compared to IS derived irradiance (mW/cm²) values. Individual LCU mean irradiance values were normalised against GS figures.
Results: The IS sphere method yielded reproducible data with a pooled Coefficient of Variation of 0.4% for the LCUs. Mean power values ranged from 0.27W to 1.7W. Average power values for the thermopile and BPII meter were within 5% and 10% respectively of GS values. Power values of all three tested examples of BPII meter were significantly higher (ANOVA 2P < 0.05) than GS for five type II LED LCUs. Tested BPII meters were the only meter type within 20% of GS irradiance values overall. Ten out of fifteen tested models of radiometer failed to give any irradiance reading with one or more LCU. Individual LCU/DR combinations overestimated GS irradiance up to 471% and underestimated irradiance by up to 90%.
Conclusions: Dentists have no accurate way of measuring light output in their surgery. Sufficient light exposure is critical for successful curing of dental resins. Massive discrepancies may occur between valid and estimated irradiance values of dental LCUs with individual LCU/DR combinations. Manufacturers accuracy claims for DRs should specify specific tested LCUs.