The aim of this in vitro study was to investigate the effect of remineralization and time on the color and
microhardness change of bleached teeth using 10 % carbamide peroxide (CP) and 40 % hydrogen peroxide (HP).
Seventy-two 6x6x2 mm3 enamel slabs were prepared from human premolars. The specimens’ color and Vickers’
microhardness were recorded at baseline (T0). The specimens were divided into six groups: twelve specimens per
group. Two groups were treated with 10 % CP with or without casein phosphopeptides and amorphous calcium
phosphate (CPP-ACP) (10 % CP and 10 % CP/CPP-ACP, respectively), two groups were treated with 40 % HP with or
without CPP-ACP (40 % HP and 40 % HP/CPP-ACP, respectively), one group received no bleaching (CON) and
another group received only CPP-ACP treatment without bleaching, (CON/CPP-ACP). The CPP-ACP groups were
treated with CPP-ACP twice daily for five minutes for seven days after completing their respective protocol. The
color change and Vickers’ microhardness were recorded at three time points after treatment; one day (T1), two
weeks (T2), and one month (T3). After one month, the tooth color changed (ΔE) in all groups at every time point;
however, significant ΔE was found only at T3 for the 10 % CP and the CON/CPP-ACP groups (p<0.05). Microhardness
tended to decrease from the baseline (T0) value at each time point. There were significant differences between
time points in microhardness (ΔVHN) in the 40 % HP, CON, and CON/CPP-ACP groups. A relationship between ΔE
and ΔVHN was found in the 10 % CP and 10 % CP/CPP-ACP groups. In summary, tooth whiteness decreased in the
10 % CP group from T1 to T3. CPP-ACP can prevent color relapse in the 10 % CP/CPP-ACP and CON/CPP-ACP groups.
Microhardness improved in the 10 % CP/CPP-ACP group compared with the 10 % CP group at T3. Both tooth whiteness
and microhardness were stable for at least one month when CPP-ACP was used as an intervention in the 10 % CP/
CPP-ACP group.