Study On Erbium Laser Technique With Sub-pulse Sequence Mode And Its Ablation Of Tooth Hard Tissue

3 ?m laser has been widely used in biomedical,military and other fields.3?m laser is closed to the infrared absorption peaks of water and hydroxyapatite.Compared with other wavelengths,it has incomparable advantages in ablation of biological tissues and cutting of hard tissues such as bone and teeth.As far as the current erbium laser is concerned,the frequency of erbium dental laser on the market is relatively low,with the highest frequency no more than 50 Hz,which leads to low cutting and ablation efficiency and little advantage over the traditional dental therapeutic apparatus.In addition,the static(free-running)mode and dynamic(Q-switched)modes are mostly used in clinical applications of erbium laser.However,the free-running erbium laser has a pulse width of few hundred microseconds.When such a long-pulsed radiation is applied to the affected areas,the excess heat diffuses into the surrounding healthy tissues,causing damage or necrosis.Due to the low gain of 3 ?m laser,it is difficult to obtain Q-switched erbium lasers with high pulse energy at high repetition frequency.The low ablation efficiency due to low pulse energy limits the dental treatment effectiveness.To solve the problems mentioned above,3 ?m laser in sub-pulse sequence mode has been developed and carried out experiments of laser ablation of dentin of human teeth.Meanwhile,the erbium laser control system has been developed to improve the feasibility of erbium laser ablation.The main research contents of this thesis are as follows:1.The control system of sub-pulse sequence mode laser was developed.We discussed the chip selection,detection circuit and function module program of the control system in detail,and developed the overall program design and each function module program.In this paper,the laser control system mainly realized the following functions:man-machine interaction module,water mist control module,A/D conversion module,power control module,data storage module,pulse output module.While realizing the basic functions of each module,the control system also communicated with the power source through RS232 to obtain the corresponding parameters such as laser frequency,pulse width and pulse energy.2.The resonator design principle of solid state laser and the sub-pulse sequence mode was introduced,which laid a theoretical foundation for the development of the sub-pulse sequence mode laser.The Er:YAG and Cr,Er:YSGG laser in sub-pulse sequence mode was developed.The comparison experiment of monopulse and sub-pulse sequence mode laser was carried out.High frequency and high energy laser outputs of 80 and 100 sub-pulses per second were obtained by modulating the envelope of long laser discharge pulse.3.The experiment of laser dentin ablation with sub-pulse sequence mode was studied theoretically.The absorption of laser energy by cooling water mist was investigated in the experiment,and the temporal evolution of the ablation cloud during ablation of dentin was observed by high-speed camera.The effects of sub-pulse width on erbium laser ablation in sub-pulse sequence mode were investigated.The experiment used an erbium laser in pulse sequence mode with a repetition rate of 20 Hz,pulse energy of 45 mJ and pulse widths of the sub-pulses 20 ?s,30 ?s,40 ?s and 50 ?s.The influence of sub-pulse width on the ablation mass,the temperature rise in the pulp Chamber and the microstructure of dentin ablation,without using cooling water mist,were compared.The results indicated that shorting sub-pulse width can increase the ablation mass,reduce the temperature rise in the pulp chamber,prolong the operation time and improve the efficiency.In addition,better microstructure of dentin ablation and more opened dentinal tubules can be obtained,which is beneficial to adhesive repair and treatment.