In Vitro Study Of Phthalocyanine Photosensitizers For Tooth Bleaching

Objectives:Current tooth bleaching materials perform satisfactory clinical effect and long-term stability,but may accompany some adverse effects,such as tooth sensitivity,soft tissue irritation and enamel surface morphology changes.The purpose of this study was to explore the bleaching effect of pentalysineβ-carbonylphthalocyanine zinc（ZnPc（Lys）₅）in vitro and evaluate its effects on enamel surface in order to provide a new selective bleaching scheme for clinical patients.Materials and methods:Extracted human third permanent molars and premolars were used in this study.Teeth that had no caries,were intact and had uniform color distribution were included in the study although tetracycline teeth and those with fluorosis were excluded.The study also ensured that the included teeth had a vita-color shade of A2 or darker.The roots of the collected teeth were cut off at the enamel-cemental junction using a slow hard tissue cutter.In addition,the crown was divided into the buccal and lingual hard tissues along the mesial and distal direction before removing the dental pulp tissue.After ultrasonic shock for 20 minutes,the hard tissues of buccal and lingual teeth were embedded in polymethyl methacrylate resin with a unified mold,a total of 126 samples were prepared.Among them,36 samples were used to explore the effect of tooth bleaching with different concentrations of photosensitizers.The rest samples were randomly divided into 3 groups（A,B and C）with different treatment schemes,including negative control group（group A,physiological saline）,experimental group（group B,ZnPc（Lys）₅）,and the positive control group（group C,hydrogen peroxide gel）.Three materials were added in the sample surface,and a LED red light source was irradiated vertically at samples for 30 minutes,2 times continuously bleached,7 days as one cycle,and bleaching with 2 cycles.Tooth color,surface microhardness（SMH）and roughness（SR）measurement was performed at the baseline,immediately after the first phase of bleaching,immediately after the second phase of bleaching,1 week and 1 month after the bleaching treatment,and evaluated the temperature variation on the surface of samples after the activity of the three groups of materials.Finally,one sample was randomly selected in each group to evaluate the surface morphology and structure changes by using scanning electron microscope（SEM）.Results:ZnPc（Lys）₅ has satisfied tooth bleaching ability,and the most suitable bleaching concentration is 20μM.After two bleaching cycles,theΔE value of group B（7.10±1.03）and group C（12.22±2.35）were significantly higher than those in group A（0.93±0.30）（P<0.05）,and no color recovery occurred at 1 week and 1 month post-bleaching.The whiteness index in group B（66.90±3.42）and group C（71.18±3.23）was significantly higher than that at baseline（P<0.05）,but there was no significant difference in group A（59.38±3.80）（P=0.905）.There was no significant change in SMH in group A and B before and after bleaching（P>0.05）,while that in group C decreased significantly（P<0.05）.In addition,SR increased significantly in group C after bleaching,but no significant change was observed in group A and group B（P>0.05）.SEM images also indicated that the surface morphology of group B enamel samples after bleaching showed corrosive enamel changes and micro-roughness increased.No morphological changes were detected during the experimental time in group A and C.Finally,no significant difference was found in enamel surface temperature among the three groups during bleaching process（P>0.05）.Conclusion:ZnPc（Lys）₅ performs a satisfactory bleaching effect,and has no obvious side effects on the enamel surface,expected to become a new type of tooth bleaching material.