Evaluation Of The Efficacy Of 532 Nm And 671 Nm Laser Treatments For Color-stained Teeth

Since the coloring of teeth is very important to the appearance,the bleaching of teeth has become the appeal of most people.The principle of tooth bleaching is essentially a redox reaction,in which hydrogen peroxide(HP)or urea peroxide(CP)in the bleaching gel acts as an oxidizing agent.On this basis,photodynamic bleaching is applied to colored teeth with laser and photosensitizer.When the laser is applied to the bleaching gel,it will produce a photothermal effect: the molecules in the teeth absorb the energy of the laser and cause local heating.This heating effect will increase the temperature in the gel or teeth,and then promote the rate of redox reaction,release a large number of free radicals in a short time,and oxidize the dark long-chain molecules to the light-colored short-chain molecules,thus significantly improving the bleaching efficiency.And the photosensitizer can absorb specific wavelengths of light,photochemical reaction,produce a large number of reactive oxygen species,reactive oxygen species has a strong oxidation,which can significantly improve the bleaching efficiency.Laser bleaching has many advantages over traditional bleaching methods: it can shorten the treatment time,reduce tooth sensitivity and so on.The objective of this study was to explore the bleaching effect of bleaching gel combined with photodynamic treatment on colored teeth under 532 nm laser and 671 nm laser irradiation,and to evaluate the thermal effect of photodynamic bleaching on colored teeth.It provides a new basis for the treatment of clinical pigmented teeth.The main work of this paper is as follows:1.A pulp cavity temperature model was established using human isolated teeth.Two different wavelengths of laser,532 nm and 671 nm,were used to irradiate the isolated teeth.A K-type thermocouple was used to measure the pulp cavity temperature of the isolated teeth in real time with or without bleaching gel and photosensitization agent,and the relationship curve between pulp cavity temperature and irradiation time was drawn.Under the condition of laser irradiation,adding photosensitizer and bleaching gel can reduce the temperature increase of tooth pulp cavity.The thermal effect of photodynamic bleaching on colored teeth was evaluated by the pulp cavity temperature experiment,which provided a basis for evaluating the safety of photodynamic bleaching in vitro colored teeth.2.An isolated tooth coloring model was prepared by using human isolated teeth,and three groups of bleaching experiments were carried out on the isolated tooth coloring model.The bleaching of colored teeth in vitro under 532 nm laser and 671 nm laser irradiation was studied by colorimetric experiments before and after bleaching(the laser irradiation group added the corresponding photosensitizer).Through data processing and statistical analysis,the results showed that under 671 nm laser irradiation,the total color difference ΔE,brightness change |ΔL| and hue change |Δa| of the photodynamic combined bleaching gel group before and after bleaching were the largest,indicating that the photodynamic combined bleaching gel group had the best treatment effect on colored teeth under 671 nm laser irradiation.In conclusion,this study provides a new experimental basis for the treatment of clinical pigmented teeth.The color value of teeth was significantly improved by photodynamic combined bleaching gel.The method has the advantages of simple operation,safety and reliability,and is suitable for various types of discolored teeth treatment.Compared with 532 nm laser,671 nm laser has a more significant bleaching effect on discolored teeth,and it was found that under laser irradiation,adding photosensitizer or bleaching gel can reduce the temperature rise of pulp,thereby improving the safety of treatment.In addition,our evaluation of the experimental results suggests the need for proper control of light duration and power when performing photodynamic therapy.