The Influence In Intrapulpal Temperature And Tissue Structure After Er：YAG Laser Irradiation On The Tooth Hard Tissue

Backgrounds and ObjectiveCurrently Treatment of caries and cavity preparation mostly still rely on the turbine.Because of its own limitations, it results in many patients suffering from dental phobia.In recent years, laser technology is widely used in the medical field, especially in theoral medicine. The function of laser in romoving necrotic tissue and Treating cavitypreparation have been confirmed.Er: YAG laser have the effect of no noise、no vibrationand no pain that traditional turbines can not achieve, And Er: YAG laser in treatmentdon’t touch tieeue which minimizes infection and aching feeling and relieves tension. It isa new treatment method for the treatment of oral diseases.The function of using Er: YAG laser in the tissue is mainly heating induced by laserlight which is very important for the soft pulp tissue.Different from other laser, Er: YAGlaser’s wavelength is2940nm and its absorption coefficient is close to the water absorptionpeak, and absorbed by water and hydroxyapatite of the dental hard tissue, So it caneffectively cut the dental hard tissue. The main inorganic constituents of dental hard tissueare calcium and phosphorus, According to the mechanism of action of Er: YAG laser,irradiation of dental hard tissue can cause the the change of surface composition andstructure.In this study, observe the change of the morphology and composition、ablationdiameter, depth, and the medullary cavity temperature of dental hard tissue by differentlaser energy and illumination time,to find the maximum ablation rate and ablation accuracyon the basis of avoiding or reducing unnecessary heat damage directly or indirectly, and toprovide theoretical and experimental basis for the initially identification of effective andsafe laser dose range. Materials and methods1Collected52premolars with complete crowns, caries-free and no cracks which areput out from15to25-year-old volunteers for orthodontic decrease，randomly divided intoenamel and dentin group of each26. Pulp in1mm place under cemento-enamel junction ofthe neck of extracted tooth,entrance diameter of about1mm, exposed to the canal.Preparation of each104samples of enamel and dentin. Randomly selected8from104samples for blank control group (C group). the remaining96samples were randomlydivided into A (irradiation for10s) and B (irradiation for20s) two groups. Each group wasrandomly divided into1,2,3,4,5,6W six subgroups by power, each subgroup of eightsamples. Use Er: YAG laser in20HZ frequency for illuminating relevant samples,at thesame time use the digital thermometer to measure temperature change of pulp cavity.2Collected52premolars with complete crowns, caries-free and no cracks which areput out from15to25-year-old volunteers for orthodontic decrease, randomly divided intoenamel and dentin group of each26. Intercept the root of cemento-enamel junction,preparation of each104samples of enamel and dentin with the size of4mm×4mm×2.5mm。Divided into group same as the last test.. After the completion of the irradiation ofEr: YAG laser using scanning microscope imaging system for measuring the diameter anddepth (the distance from the edge to the bottom of pit hole)of the pits of A and B twogroups.3Collected52premolars same as the last test.Randomly selected8from104samplesfor blank control group (C group). the remaining96samples were randomly divided into A(irradiation for10s) and B (irradiation for20s) two groups. Each group was randomlydivided into1,2,3,4,5,6W six subgroups by power, each subgroup of eight samples.After the completion of the illuminate randomly selected4samples from each power groupfor observation by scanning electron microscopy, representative samples were selectedcontrast4Collected52premolars same as the last. Intercept the root of cemento-enameljunction, preparation of each104samples of enamel and dentin with the size of4mm×4mm×2.5mm. Randomly selected8from104samples for blank control group (C group).the remaining96samples were randomly divided into A (irradiation10s) and B (irradiationfor20s) two groups. Each group was randomly divided into1,2,3,4,5,6W six subgroupsby power, each subgroup of eight samples. After the completion of the radiation, select thepit site of the experimental group and surface parts of the blank group by the scanning electron microscope, Use the energy dispersion type of X-ray fluorescence analyzer forfixed-point measurement of Ca, P contentResults1In this experiment, along with the increase of the laser energy and irradiation timethe temperature of the medullary cavity also shows ascendant trend. In the highestfrequency20HZ,6W illuminate for20s, pulp cavity temperature rise but was not over thescope of the medullary cavity safety threshold5.5°C.2In this experiment, along with the laser energy and irradiation time increases thedepth change of the pits is not just increased, but fluctuated within a certain range.3In this experiment, with the increase of the laser energy and irradiation time,displaydifferent pit sizes, surface of enamel pits produce different levels of coarse particles, similarto the scaly. With large doses of irradiation, enamel column can not be clearly observed,and produce ablation depression, the pit at the bottom of showing uneven and high-energyappearance of cracks. After laser irradiation, Dentin surface is rough and clean, dentinaltubule is open state, tube around the dentin is prominent on the surface, and dentin is indepression between the pipes, the phenomenon of melting and charring does not appear inthe large doses of irradiation.4In this experiment, the Ca, P content of the enamel experimental group compared tocontrol group has significant difference, After the laser irradiation, the Ca, P content of theEnamel experimental group is higher than the blank control group, the Ca/P ratios of theEnamel experimental group compared with control group has no significant difference. theCa, P content of the dentin experimental group compared to control group has significantdifference, After the laser irradiation, the Ca, P content of the Enamel experimental groupcompared to control group has the decreasing trend, the Ca/P ratios of the Enamelexperimental group compared with control group has significant difference in the Highdoses of radiation.Conclusions1With the Er: YAG laser ultrashort pulse illumination, Choose ultrashort Er: YAGlaser pulse of10HZ、20HZ frequency, energy1W~6W to radiate tooth enamel andnature within10s-20s,it will not cause harm to the dental pulp, that provides experimentalbasis for clinical application. 2With the Er: YAG laser ultrashort pulse illumination, Choose ultrashort Er: YAGlaser pulse of10HZ、20HZ frequency, energy1W~6W to radiate tooth enamel andnature within10s~20s, With the increase of laser energy and irradiation time, the pit depthof enamel and dentin increases. But pit diameter does not increase with the increase in laserenergy and irradiation time.3With the Er: YAG laser ultrashort pulse illumination, Choose ultrashort Er: YAGlaser pulse of10HZ、20HZ frequency, energy1W~6W to radiate tooth enamel andnature within10s-20s, Enamel and dentin doesn’t has degeneration and carbonizationchange,and under certain energy scaly structure of the enamel and dentinal tubules areclearly visible.4With the Er: YAG laser ultrashort pulse illumination,Choose very short Er: YAGlaser pulse of20HZ frequency, energy1W~6W to radiate with10s~20s, the componentof enamel and dentin changed...