CDEN0210

28 I I research _ bleaching _While nightguard vital bleaching is the most used treatment modality for whitening of discoloured teeth, in-office tooth whitening pro- cedures that use a concentration of higher than 10 % carbamide peroxide have been advocated as acceptable alternatives. Patients often choose in- office bleaching when they desire more rapid whitening of their teeth and/or when they do not desire to wear bleaching trays for at-home tech- niques.1 Although manufacturers indicate that most in-office bleaching agents can be used with- outlightirradiation,studieshavereportedthatlight activation can enhance the results of the bleaching procedures.2 The light energy increases the rate of hydrogenperoxidedegradationtoformoxygenfree radicals, leading to an enhancement of the bleach- ing process.2–5 Introducedin1948,tetracyclines(TCN)arebroad- spectrum antibiotics that may be used in the treat- ment of many common infections in children and adults.Oneofthenegativeside-effectsofTCNisin- corporation into tissues that are calcifying at the timeofdrugadministration,suchasteeth,cartilage and bone. A resulting permanent discolouration of both the primary and permanent dentitions can vary, such as yellow or grey or brown, depending on thedosageandthetypeofthedrugreceived,aswell as the duration of exposure to the drug.6,7 In recent literature, it has been noted that Mino- cycline, a semi-synthetic member of the TCN family widely used in the treatment of acne, also causes abnormal pigmentation of collagenous tissues such as the skin, thyroid gland, nails, bone, sclera and conjunctiva in adults. The pigment is the product of an oxidation reaction, and laboratory studies have shownthatthepigmentformationcanbeinducedby exposure to ultraviolet light in the presence of air.8 Similarly, Minocycline has been shown to cause a blue-greytogreydiscolourationoftheteethofadults. Thisappearstobelinkedtothecycleofdemineralisa- tion and remineralisation of the enamel surface, and can produce staining that is clinically indistinguish- able from staining during tooth development.9 As a continuation of what was reported by Harada10 , we recently described an effective invitro method to produce standardised discolouration of extracted human molar teeth using Chlortetra- cycline and its analogs.11 Utilising this technique, a readily available source of discoloured teeth can be produced to evaluate the efficacy of various bleaching protocols. Thepurposeofthepresentstudywastoevaluate the effects of one in-office tooth whitening proce- dure (Zoom 2, Discus Dental) on such standardised discolouredteethtoassesstheirusefulnessasmod- els for bleaching research. Our hypothesis was that the teeth discoloured by the in vitro technique cosmeticdentistry 2_2010 In vitro bleaching study with a 20 % hydrogen-peroxide system Authors_ Dr Daniel C.N. Chan, Dr Albert Kwok-Hung Chung, Dr William D. Browning & Dr So-Ran Kwon, USA Fig. 2 Fig. 1b Fig. 1a Figs. 1a & b_Stained teeth before and after application of the 20 % whitening gel. Fig. 2_Stained teeth demonstrating application of the mercury metal halide light. Note the way that all the stained teeth fit inside the scope of the light.