CDE0211

22 I I research _ bleaching _Tooth-whiteningprocedureshavebeenasso- ciated with morphological changes in the enamel surface. As early as 1993, Shannon et al. reported significantsurfacetopographicalterationsinenamel slabsthathadbeentreatedwithbleachingsolutions for four weeks.1 These findings were confirmed in another study with 30 % H2O2 mixed with PBS.2 Teeth that were bleached in vivo with 35 % car- bamide peroxide lost the aprismatic enamel layer and the damage was not repaired after 90 days.3 A confocal laser scanning microscopic study evalu- atingthemicro-roughnessofenamelsurfacesafter bleaching procedures with 10 and 16 % carbamide peroxidefoundroughnesstobesignificantlyhigher than in control surfaces.4 However, another study reported no or minimal changes in the enamel surface after bleaching. Leonard etal. evaluated casts made from impressions of teeth bleached with 10 % carbamideperoxideforeighttotenhours per day for 14 days, and found no or minimal changes in the enamel surface.5 Their findings may be explained by the limits of the methodology, in which there was inadequate reproduction of the mi- nor enamel alterations in the impression. Other in vitro SEM studies published recently have also revealed no enamel irregularities after bleaching.6,7 In general, recent literature supports the theory that a high concentration of carbamide peroxide is detrimental to enamel surface integrity, while low con- centrations were found to produce no changes.8–11 A clinical implication of these findings may be that the teeth are more susceptible to extrinsic discolouration after bleaching due to increased surface roughness. The changes may be deeper than superficial. Using infrared spectroscopic analysis, Oltu and Gürgan reported that in vitro treatment of ex- tracted teeth with 35 % carbamide peroxide for 30 minutes per day for four days changed the inorganic composition of the enamel, whereas 10 and 16 % concentrations did not.12 Cavalli etal. also demonstrated that bleached dentine could lose inorganic components, resulting in ultra- structural alterations.13 Studies have demonstrated a dynamic process ofdemineralisationofhumanenamelintra-orally.14 Inthesestudies,theexistenceofsubsurfaceenamel pores, which increase and decrease in size in rela- tion to this de- and remineralisation process, has been demonstrated. Amorphous calcium phosphate (ACP)hasbeenshowntoshiftthede-/remineralisa- tion balance towards remineralisation, resulting in a decrease in size and/or number of pores.15 It has been theorised that bleaching creates subsurface cosmeticdentistry 2_2011 Figs. 1a–f_Pre-op view of one of the incisors selected for the study (a). Flattened area (≈ 4 x 5 mm) created by serial polishing with sandpaper up to 1,200 grit (b). A piece of water- resistant tape is applied to one-half of the tooth and burnished (c). The edge of the tape is sealed by painting it with a transparent nail varnish (d). Bleaching gel is applied to the exposed area (e). Diagrammatic representation of the control and treated areas (f). Table I_Bleaching agents used in the study. Fig. 1a Fig. 1b Fig. 1c Fig. 1d Fig. 1e Fig. 1f Confocalmicroscopyinvestigation of enamel subsurface structure following bleaching Authors_ Prof Daniel C. N. Chan, Prof William D. Browning, Prof Albert Kwok-Hung Chung & Prof So-Ran Kwon, USA & Korea Bleaching agent Main ingredient and concentration Manufacturer Nite White Excel 3 with ACP 16 % hydrogen peroxide (+ ACP) Discus Dental Opalescence PF 10 % carbamide peroxide Ultradent (+ fluoride and potassium nitrate) Table I