| Objective: To study the effect of different force and time on tooth color by fixed orthodontic treatment.Methods: 50 canines from 18 patients who were treated with 4 premolars extraction and maximum anchorage were measured for the base value of L*,a*,b* of the teeth before experiment.Teeth in the study underwent maxillary canine retraction using mini-implants as anchorage for every month,respectively with 100 g and 200 g of force applied via elastic chain in group A and group B.During retraction,The chromaticity parameters of the experimental teeth were measured by the above method at the time of a monthly visit.The canines were measured for 4 months in a row.The value of L*,a*,b* respectively in group A and group B were statistically analysed using two-way ANOVA repeated measures.Results:(1)The each color coordinate of enamel surface before treating were analyzed using one-way analysis of variance by group.There were no significant differences between the groups in each of the color coordinates(P>0.05).(2)The chromaticity parameters of 4 months in all groups were significant different from the base value.Besides,group A and group B showed clinically unacceptable colour difference.(ΔE*>3.3).(3)The value of L*,a*,b* respectively in group A and group B were statistically analysed using two-way ANOVA repeated measures: The values in group A had no significant differences comparing to group B in the cervical regions(P>0.05).The value of L*,a*,b* which in the cervical regions had a significant difference statistically at every time within 4 months in group A and group B(P<0.05).The value of L* had no interaction between group and time(P>0.05).The value of a*,b* had interaction between group and time(P<0.05).The value of L* in group A had difference comparing to group B in the body regions(P<0.05).The value of a*,b* in group A had no difference comparing to group B in the body regions(P>0.05).The value of L*,b* which in the body regions had a significant difference statistically at every time within 4 months(P<0.05).However,no difference was found in the body regions about the value of a* among the experiment time(P>0.05).The value of L*,a*,b* had no interaction between group and time(P>0.05).The value of L*,a*,b* in group A had no difference comparing to group B in the incisal regions(P>0.05).The value of L*,a*,b* which in the incisal regions had a significant difference at every time within 4 months in group A and group B(P<0.05).The value of L* had interaction between group and time(P<0.05).The value of a*,b* had no interaction between group and time(P>0.05).(4)The value of L*,a*,b* in all regions were generally decreasing along with the extension of time.Conclusion:(1)The fixed orthodontic treatment can cause changes in teeth color,and the reasons are related to the orthodontic force and time.(2)The orthodontic force affects the chromaticity of the tooth,but there is no significant difference between the group 100 g and group 200 g.(3)The chromaticity parameters are generally decreasing along with the extension of time.The teeth will become more darker and the tone will change to be smaller. |
