A Preliminary In vitro Model Assessing Tooth Whitening Agent Effectiveness

Objectives: To develop an in vitro model for whitening agent performance assessment using a spectrophotometer; to correlate the contribution of tooth dehydration states to the peroxide whitening effect.

Methods: 50 prepared molars were divided into 5 groups (n=10). Groups1-2 were treated with 35% hydrogen peroxide (HP) whitening agent (OpalescenceXtra Ultradent, Inc.). Following treatment, teeth in Group-1 were submerged in water and teeth in Group-2 were left to dehydrate at room temperature. Groups 3, 4 and 5 did not receive whitening treatment. Group-3 was submerged in water. Group-4 was dehydrated at room temperature; Group-5 was dehydrated at room temperature for 45 minutes and then submerged in water. Measurements at timed intervals on the lingual surface were taken for all groups using a new intraoral spectrophotometer (SpectroShade™ Micro, MHT Italy). Data were recorded as CIE-L*a*b*. Delta-E shade change was calculated from baseline. Significant shade change was determined if Delta-E was 2.7 or above.

Results: Tooth shade was affected by both dehydration and whitening agent treatment. Statistically significant shade changes from baseline were found in Groups1-2 and 4. In Group-5 a significant shade change occurred in the first 3 readings. In Group-1, shade change attributed to HP was found 30 minutes following treatment and increased for 2 days. For Group-2, a significant shade change attributed to HP was observed 6 hours following treatment and continued for a month. L*-value was influenced mostly by dehydration. a*-value was influenced mostly by HP, and b*-value was influenced partly by HP and partly by dehydration.

Conclusions: This model may be used to initially assess whitening agent effectiveness in wet (shorter evaluation period) or dry conditions (longer evaluation period). Initial shade change following whitening treatment was attributed to tooth dehydration while HP affected shade change at a later stage. CIE-L*a*b* values responded to tooth dehydration or HP treatment.