| Objective:To study the effectiveness and safety of the laser combined with two different bleaching gel on tooth bleaching in vitro.The gels were irradiated with a low-power 532 nm laser,this experiment will provide a basis for clinical application.Methods:Two different bleaching gels were used in the experiment: Opalescence Boost(38% hydrogen peroxide)and Opalescence PF(15% carbamide peroxide).A 532 nm laser with a power of 600 mW was used.Pulp chamber temperature experiment:15 extracted maxillary central incisors were randomly divided into three groups.Group A: Opalescence Boost(38% HP)combined with 532 nm laser irradiation(n=5);group B: Opalescence PF(15% CP)combined with 532 nm laser irradiation(n=5);and group C: 532 nm laser irradiation alone as a control group to observe the temperature change in the pulp cavity within 60 s.Record temperature every ten seconds for a total of 6 times,and compare the temperature between groups.Experiment of efficacy of tooth bleaching:20 extracted maxillary central incisors were selected and an in vitro tooth staining model was established using Acid Orange II.The model specimens were randomly divided into 4 groups,group A: Opalescence Boost(38% HP)combined with 532 nm laser irradiation(n=5);group B: Opalescence PF(15% CP)combined with 532 nm laser irradiation(n=5);group C: Opalescence Boost(38% HP)(n=5)alone and group D: Opalescence PF(15% CP)alone(n=5).After 20 s of irradiation time and 5 min of bleaching,color parameters L*,a* and b* were measured with a spectrophotometer immediately,day7,day15,day30 after bleaching,respectively,to analyze the amount of color change,?E.Results:Pulp chamber temperature experiment: With the increase of irradiation time,Pulp temperature shows an rising trend in each group.Within the irradiation time of 20 s,temperature changes is 5.41±0.10? in group A,2.66±0.18? in group B,4.09±0.28? in group C.Temperature changes at all time points were significantly higher in group A(P<0.05)than that in the other two groups,and significantly lower in group B(P<0.05)than that in the other two groups.Experiment of efficacy of tooth bleaching: Significant color changes were observed in all groups after bleaching;the ?E at all time points in group A was higher than the other three groups(P<0.05);immediately after bleaching,?E of group B(14.9±1.84)was higher than that in group C(9.59±2.32),but no statistically significant difference was found between the two groups in day 7,day 15,day 30(P>0.05).The ?E at all time points in group D is lower than the other three groups(P<0.05).The ?E on day 30(13.48±1.33)in group A is lower than that immediately after bleaching(19.68±3.98)(t=3.300,P=0.011);The ?E on day30(10.79±3.14)in group B is lower than that immediately after bleaching(14.96±1.84)(t=2.562,P=0.033).Conclusion:The following experimental results were obtained after irradiation of tooth using a 532 nm laser power of 600 mW combined with two bleaching gels.1.In pulp chamber temperature experiment,within the irradiation time of 20 s,temperature changes in all groups did not exceed the safety threshold of 5.6 °C.Thus irradiation time of 20 s can be considered within the safety range.When the teeth were irradiated with 532 nm laser,the application of Opalescence Boost(38% HP)increased the temperature of the pulp chamber.Using opalescence PF(15%CP)slowed down the temperature increase in the pulp chamber.2.In efficacy of tooth bleaching experiment,the bleaching effects of Opalescence Boost(38% HP)and Opalescence PF(15% CP)were enhanced during the 20 s' irradiation time.An ideal efficacy was obtained immediately after bleaching,although color recurrence was found with time.Being observed for 30 days after bleaching,Opalescence Boost(38% HP)combined with 532 nm laser irradiation was found to have the best bleaching efficacy,Opalescence PF(15%CP)combined with 532 nm laser had similar bleaching effect as Opalescence Boost(38% HP)alone. |
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