CDEN0210

I 31 research _ bleaching I cosmeticdentistry 2_2010 the mean L* for the control group increased sig- nificantly between baseline and final measure- ments and the Chlortetracycline, Doxycycline and Minocycline groups’ mean L* decreased, these differences were even greater at the final evalua- tion period (Table Ia). While these changes explain the significant differences between the four groups, they do not indicate a positive whitening effect. There was a significant association between C* and treatment group, evaluation and the interac- tion term, treatment group x evaluation (two-way ANOVA; p < 0.003, p < 0.001 and p = 0.002, re- spectively). From the baseline to final evaluation, all four groups demonstrated a significant reduc- tion in C* (Holm-Sidak Multiple Comparisons Test; all comparisons to baseline; p < 0.05; Table Ib). With the C* data, we once again see that there was a significant difference between the control group and the Chlortetracycline group at baseline, with the Chlortetracycline group significantly more chromatic. At the final evaluation, the reduction in C* for the Chlortetracycline, Minocycline and Doxycy- clinegroupswassodramaticthatthecontrolgroup was significantly more chromatic than these three groups (Holm-Sidak Multiple Comparisons Test; p < 0.05). There was no significant association be- tween H* data and the evaluation period (Table Ic). There was a significant association between treat- ment group and H*. Comparing the means for the three experimental groups to the control, the hue value for Chlortetracycline was significantly lower (that is, more blue). The mean values for the four groups include data from both the baseline and final evaluations. It does not indicate there was asignificantchangeinH*,onlythattheChlortetra- cycline teeth were more blue than the other three groups. _Discussion Bleaching treatment is considered to be the most conservative procedure for treating dis- colouredandstainedteethwhencomparedtolam- inate and crown restorations. Moreover, bleaching can be used to reduce the colour of dark teeth before preparation and placement of aesthetic indirect restorations. Therefore, depending on colour reduction, the tooth preparation can be moreconservativeandpreservemoresounddental tissues.7,12–14 Doxycycline Baseline 1st week 3rd week 5th week 7th week Fig. 3c Fig. 3d Minocycline Baseline 1st week 3rd week 5th week 7th week