Measurement of discolouration of orthodontic elastomeric modules with a digital camera

The objective of this study was to measure discolouration using a digital camera on various types of clear orthodontic elastic modules, immersion solutions, and time periods to determine whether the cause of discolouration of these modules was due to simple staining, chemical degradation, or both. Three types of clear orthodontic elastomeric modules were investigated [Plastic ligatures (AO); Power 'O's 012 (OC); dispense-A-tie (TP)]. The elastomeric modules were immersed in the stretched condition in distilled water (control group) and in 75 per cent ethanol for chemical degradation and 2 per cent methylene blue for simple staining. After 0, 1, 2, 3, 6, 9, 12, 15, 18, and 21 hours and 1, 2, 3, 4, and 5 days of immersion, digital images of the modules were taken and processed using commercial software. The differences in colour changes depending on the type of elastomeric modules, immersion solution, and immersion period were analysed using a three-way analysis of variance and Tukey's multiple comparison test. The colour changes in the ethanol and methylene blue solutions by immersion period were analysed with regression analysis. There were significant differences in discolouration depending on the type of elastomeric modules, immersion solution, and immersion period (P < 0.05). The range of colour changes (Delta E* ab) was 1.0-20.0 units for AO, 0.6-30.0 units for OC, and 1.1-18.8 units for TP, independent of immersion solution and time. Methylene blue resulted in the greatest colour change. Discolouration due to chemical degradation by the ethanol solution mainly occurred in the first few hours, reached a plateau with no further increase over time, and was greater than staining by methylene blue in that period. Discolouration due to staining by methylene blue, however, continued to increase over the whole immersion period. Therefore, discolouration of elastomeric modules was a result of chemical degradation as well as staining in the early stages but in the later stages was due only to simple staining.