Research On 2.8μm Laser And Its Application In Dentin Ablation

The MIR 2.8μm laser is located near the absorption peak of water molecule and hydroxyapatite.In the field of biomedicine,it can accurately perform minimally invasive treatment on target tissues,with advantages of shallow penetration depth,small thermal damage range and high surgical accuracy.Therefore,it has broad clinical application prospect in dentistry,orthopedics,pain and other fields.At present,medical mid-infrared laser is mostly used in clinical static mode.The pulse width of static laser is large,which will cause excessive thermal load and thermal stress in the process of ablation,cause damage or carbonization of surrounding healthy tissues.Qswitched laser has the advantages of high peak power and narrow pulse width,which can ensure the ablation efficiency and effectively reduce the occurrence of thermal damage.Therefore,in this thesis,the output of Q-switched 2.8μm narrow pulse laser is realized successfully by using electro-optical Q-switched technique,and the ablation experiment of dentine tissue is carried out by the Q-switched 2.8μm laser source.Firstly,the optical properties and ablation mechanism of dentin were studied based on laser dentin ablation theory.Using COMSOL Multiphysics software,the laser ablation model was established and the temperature field was calculated.The simulation results show that the pulse width of the compressed laser can effectively reduce the temperature of the irradiation zone,effectively limit the high temperature zone and avoid the thermal damage of the surrounding healthy tissue.Secondly,in the experimental research,we select the laser device in a specific way,and set up the Testing lamp pump Er,Cr;YSGG electro-optic Q-switched laser experimental device.When the laser operates at 5Hz repetition rate,the maximum static pulse output energy of 545 m J is obtained,and the corresponding center output wavelength is 2797.6nm.Using LGS crystal as the depressurized Q-switched element,the maximum dynamic pulse energy of 126 m J and pulse width of 37.58 ns can be obtained under the working condition of 45 J pump energy and 5Hz repetition rate.Corresponding to the peak power of 3.35 MW,for the follow-up dentine ablation experiment provided a high peak power,narrow pulse width Q-switched laser source.Finally,in order to verify the accuracy of the simulation model,a self-developed Q-switched 2.8μm Er,Cr:YSGG laser system was used to ablate the dentine tissue in vitro in static and Q-switched modes.Scanning Electron Microscope(SEM)was used to observe the surface morphology and pit changes of the dentine after ablation,and thermocouple was used to measure the temperature distribution of the pulp cavity.The results showed that compared with static laser,Q-switched laser could improve the ablation precision and obtain better ablation appearance,and the temperature of pulp cavity was lower than 5.6 ℃ during ablation,which reduced the thermal damage range and ensured the biological activity of pulp tissue.At the same time,the effect of different doses of water mist on the ablation effect of Q-switched laser dentin was also studied.The results showed that the proper water mist flow could improve the surface structure of dentin,enhance the ablation effect,and be more beneficial to the opening of dentinal tubules.