The effect of a natural extract-based experimental bleaching gel upon the colour and surface roughness of a composite resin--an in vitro study

Objective: To evaluate the bleaching effect and the changing in the surface roughness of one experimental natural-based bleaching gel and of three commercial bleaching gels, namely: Opalescence PF 16%, Ultradent, Opalescence Quick PF 45%, Ultradent (based on carbamide peroxide CP) and Philips Zoom DayWhite 6% HP light activated (based on hydrogen peroxide HP) upon A3 body shade Filtek Supreme, 3M Espe nanocomposite. Material and methods: Thirty disks of the A3 body shade Filtek Supreme, 3M Espe, were immersed in a coffee solution and further divided into 6 groups: group 1 was kept as control, while groups 2-6 underwent a certain bleaching protocol, with different materials and exposure time, as follows: group 2: experimental gel, five sessions, 6 hours each; group 3: Opalescence PF 16 % (Ultradent), five sessions 6 hours each; group 4: Opalescence Quick PF 45% (Ultradent), 2 sessions, 30 min each; group 5: Opalescence Quick PF 45%--2 applications/30 min and Opalescence PF 16% - 5 applications/6h and group 6 was bleached using an in office gel containing HP 6% (Philips Zoom DayWhite 6% HP light-activated 2 applications/30min). CIE [L.sup.*][a.sup.*][b.sup.*] parameters and surface roughness were recorded before and after bleaching. Data were analyzed using one-way repeated measures ANOVA, and multiple comparisons were adjusted using the Bonferroni method (p