The purpose of this study was to determine if a colour difference exists between teeth that had orthodontic appliances bonded to and debonded from them and untreated controls subjected to whitening with 10 per cent carbamide peroxide. The sample consisted of 20 pairs of first and second premolars extracted for orthodontic reasons. The contralateral surfaces were divided into an experimental and control group. The experimental group underwent orthodontic bonding/debonding procedures. Both groups were subjected to 4 hour whitening and 20 hour hydration sessions for 30 days. The L*a*b*colour system was chosen to evaluate any colour change and these changes were calculated by determining the ΔE from the L*a*b* values using a colorimeter. Colour change readings were taken before and after each 4 hour whitening. Additional readings were taken at 48 hour intervals for 30 days following the cessation of active whitening. The results were analysed using statistical (ANOVA) and graphical analyses (α = 0.05). A colour change difference of 2 CIELAB units was set as being clinically significant.

A mean clinical colour difference was found for enamel surfaces subjected to orthodontic bonding/debonding of attachments relative to control sites after whitening. Bonding and debonding procedures resulted in a significant colour difference between orthodontic bonded and control sites at the end of the active period, which became insignificant at the end of the 30 day period of monitoring. Both the control and debonded sites responded to whitening; however, the control sites responded initially to a greater extent; the orthodontic debonded sites did not respond until after 2 weeks of continuous whitening. After the 2 week period the improved response of the debonded sites decreased the colour difference between the two groups.