CDEN0210

32 I I research _ bleaching Sinceitsintroductiontodentistryin1989,night- guard vital bleaching has been proven to be a sim- pleandsafeproceduretolightendiscolouredteeth. With extended treatment time, TCN-stained teeth can be expected to lighten in at least 86 % of cases. Side effects are usually mild and transient, disap- pearing within days of treatment completion with no long-term sequelae.15 Recent in-office tooth whitening procedures with 20 % hydrogen peroxide are gaining popular- ity as alternatives to at-home nightguard vital bleaching. The present study evaluated the efficacy of one such in-office whitening protocol on stan- dardised invitro stained human teeth. One of the most significant observations is that visuallythedarkcolouroftheTCN-stainedteethap- peared more intense as the treatment protocol pro- gressed(Figs.3a–d).Theenamelappearedtobemore translucent in all TCN groups, allowing the underly- ingdarkerdentineshadetobeexpressed.Thisiscon- firmed by the spectrophotometer readings in which the data shows a reduction in the L* values (Table II). One explanation is that the superficial enamel layer was affected much faster by the higher con- centration bleaching agent than the deeper den- tine. Haywood hypothesised that dentine can be bleached in the case of Chlortetracycline-stained teeth.16 Successwasachievedgenerallyaftertwoto six months of 10 % nightguard bleaching.17,18 In our case, the short treatment duration may not have resulted in sufficient contact time to effect dentine colour change. A slower process such as that sug- gestedbyHaywoodmaybeindicatedforteethmore intensely stained by tetracycline. Another explana- tion is that the colour of TCN-stained teeth became more intense in the artificial light owing to the photo-oxidation of this complex.19 However, there have been no studies on the efficacy or adverse effect of light in TCN-stained teeth. The results support the conclusion that Zoom 2 provided a positive whitening effect, as one would expecteitherareductionincoloursaturationand/or an increase in brightness. All four treatment groups demonstrated a reduction in C* from the baseline to final evaluations. Compared to the control group, the reduction in C* for the TCN groups was much more prominent. It is interesting to note that only the control group demonstrated an increase in brightness; all of the TCN groups decreased in brightness. _Conclusions Subjecting the standardised TCN-stained teeth to the Zoom 2 in-office bleaching system yielded results consistent with a whitening effect when considering changes in chroma. However, a re- duction in brightness was noted for all of the experimental groups, which is not consistent with the increase in brightness of the control group. Additionally, at the conclusion of the experimental period, the experimental groups attained a bluer hue when compared to their hue at the beginning of the experiment. No significant change in the hue of the control group was noted. Bleaching studies of teeth stained in the manner described in the present study may yield significantly different re- sults to studies of teeth stained by TCN while they are developing._ Editorial note: A complete list of references is available fromthepublisher. Table II_Means of colour difference at baseline and weeks 1, 3, 5 and 7. cosmeticdentistry 2_2010 Dr Daniel C.N.Chan University ofWashington School of Dentistry Office of Clinical Services Health Sciences Center,D322 P.O.Box 356365 Seattle,WA 98195,USA E-mail:dcnchan@u.washington.edu cosmeticdentistry _contact Baseline 1st week 3rd week 5th week 7th week L* C* H* L* C* H* L* C* H* L* C* H* L* C* H* Chlortetracycline 71.58 27.13 88.12 68.10 30.50 85.23 60.28 9.63 84.65 65.70 11.23 85.63 65.40 8.97 88.25 Control 81.73 20.17 100.03 82.07 23.02 94.48 73.20 11.97 97.77 87.25 16.98 101.33 85.52 15.33 99.60 Doxycycline 71.60 18.37 93.23 72.22 21.47 88.42 64.32 10.25 88.12 69.28 12.10 88.37 69.90 8.53 93.05 Minocycline 77.32 18.10 105.9 73.20 25.17 96.95 67.15 10.48 94.30 67.43 10.28 106.25 69.00 8.12 105.67 Table II