Abstract: Objective To study the effect of different chairside heat bleaching times on the healthy central upper incisors.Methods The subjects were treated with chairside heat bleaching for three times (an interval of one day),45 minutes each time.Color parameters of the six healthy central upper incisors before and after each time of bleaching by Wy10 were determined using a dental colorimeter and a VITA classical shade guide.The statistical analysis of the results was performed using paired t-test.Results Paired t-test showed that L* and W(Lab)parameters of all the central upper incisors increased(P<0.05) and b* demonstrated a negative trend(P<0.05),which meant that whiteness and brightness of the teeth improved and the incisors exhibited a blue-trend .The margin grewwith the increase in the number of operation times.Color difference after each time of bleaching could be identified by the human eye(ΔE>1.7).Conclusions The increase in the number of operation times leads to the improvement of the heat bleaching effect.

Key words: bleaching, color, tooth