| BackgroundDental caries is a common disease and frequently encountered disease of oral.At present,the dentist often use a turbine to remove the decay tooth tissues in clinical,the negative pressure which produced by the high speed turbine lead to dentine hypersensitivity and even pain,the noise and vibration is increased in patients with dental fear.In 1997,the Food and Drug Administration(FDA)approved Erbium:Yttrium-Aluminum-Garnet(Er:YAG)laser can be used in the treatment of dental hard tissue diseases,since then,Er:YAG laser is used in the treatment of dental caries.When using the Er:YAG laser to ablate dental tissues,there are no noise,no vibration,painless,precise cutting,etc,therefore the Er:YAG laser accepted and recognized by more and more patients.Although the Er:YAG laser has many advantages,but how to improve the Er:YAG laser cutting efficiency on the dental hard tissue is a hotspot of current research.The cutting efficiency of dental hard tissue irradiated with Er:YAG laser was mainly influenced by energy,frequency,irradiation time,water spray and so on.Now,the experimental research and clinical operation through changing the Er:YAG laser's energy to improve the cutting efficiency,however,few studies have reported the Er:YAG laser frequency to influence the cutting efficiency of dental hard tissue.ObjectiveIn this study,measure the pits of enamel and dentin surface diameter,depth under Er:YAG laser different frequency and irradiation time,at the same time observe surface morphology change,in order to obtain the Er:YAG laser ablate dental hard tissue optimal parameters of frequency and time,to improve the Er:YAG laser cutting efficiency and safety of provide the scientific basis.Materials and methods1.Collecting 80 complete premolars which were took with orthodontic treatment,required the crowns is completed,no decay,no crack,no spot on tooth surface,preparation into 80 enamel samples and 80 dentin samples(4 mm ×4 mm× 2.5 mm).According to the different irradiation time,the 80 enamel samples and 80 dentin samples were randomly with random number table divided into 10 s and 20 s two groups,each group of 40 samples,then,each group divided into five subgroups(according to the Er:YAG laser frequency of 10 Hz,15 Hz,20 Hz,25 Hz,and 30 Hz),each group of 8 samples.Using the Er:YAG laser to irradiate each sample according to the above groups,Er:YAG laser energy fixed to 200 mJ.After irradiation,using a stereoscopic microscope to observe and measure the diameter and depth of the pits.2.Collecting 80 complete premolars with the above requirements,preparation into 80 enamel samples and 80 dentin samples(4 mm ×4 mm× 2.5 mm),divided into group same as the first test,after irradiation,selected two samples in each subgroup to observe the surface morphology under Scaning Electron Microscopy(SEM)and choose the representative area to take photos.3.30 patients between 12-55 years with dental caries accepted treatment in endodontics department of our hospital from October 2015 to March 2016 were selected,for patients in the mouth have at least two molar similar caries on same or opposite jaws(the standard of caries diagnosis refer to endodontics edited by Fan Minwen),patients with symptom of pulpitis? periarthritis and unwilling to accept the Er:YAG laser treatment were ruled out.Then 30 patients were divided into two groups: Er:YAG laser(Er:YAG laser energy is 200 m J and frequency is 20 Hz)and high speed turbine,to record the the used time respectively after removing caries,using the Visual Analogue ScaleScore(VAS)to observe and record the pain degree of patients,after bottom,using Z350 composite resin to fill the cavity,grinding and polishing.Informing all patients to review after 1 month,3 months,6 months and 12 months,to observe whether the edge of filling material's discoloration,the filling material was lost,and presence of secondary caries.Result1.After Er:YAG laser irradiation,with the increase of frequency and the extension of irradiation time,the diameter and depth of pits on the enamel and dentin surface are increased.When the irradiation time is same and the frequency is 10-20 Hz,the diameter and depth of pits on the enamel and dentin surface increased fast the difference was statistically significant(P<0.05),while the frequency increased to 25-30 Hz,the diameter and depth of pits on enamel and dentin surface increased relatively flat,there was no statistically significant difference(P>0.05).When the frequency is same,the diameter and depth of pits on enamel and dentin surface which irradiation by 10 s were significantly less than the diameter and depth of pits on enamel and dentin surface which irradiation by 20 s,the difference has statistical significance(P<0.05).2.After Er:YAG laser irradiation,the surface of enamel show different sizes of the pits under SEM.When the frequency is 10-20 Hz,the surface of the pits were rough and irregular,enamel prisms were scales sample,With the increase of frequency,when frequency reaches 25-30 Hz,the surface of pits became slightly flat,the scales of the enamel prisms were lost,and there can be seen cracks and melting phenomenon on the surface of pits.The surface of dentin is clean,no smear layer,the dentin tubules were open.With the increase of frequency and the extension of irradiation time,more and more dentin tubules opened,When frequency is 25 Hz and irradiation time is 20 s,cracks can be seen on dentin surface,as frequency increased to 30 Hz,irradiation time is 10 s and 20 s,cracks became deeper,molten dentine blocked lumen,reduce the number of opened dentin t ubules.3.The average time to remove caries of Er:YAG laser(158.4±32.8s)was more than that of high-speed turbine(93.6±42.5s),the difference was statistically significant(P<0.05),VAS showed that the patients are more likely to accept Er: YAG laser(P<0.05),after 1 month,3 months,6 months and 12 months,the review showed that the edge of filling material's discoloration? filling material's lose and secondary caries have no statistical difference between Er: YAG laser and high speed turbine(P>0.05).Conclusion1.Using Er: YAG laser to irradiate dental hard tissue,choosing energy of 200 mJ,frequency for 10-30 Hz,and irradiation time 10 s and 20 s,with increase of frequency an d extension of irradiation time,diameter and depth of pits on enamel and dentin are increased.2.Choosing Er: YAG laser energy of 200 m J,frequency of 10-20 Hz,irradiation time 10 s and 20 s,enamel and dentin surface will not appear crack and melt thermal damage phenomenon;However using high frequency of Er: YAG laser(25-30Hz)to irradiate enamel and dentin after 10 s and 20 s,the surface has the thermal damage such as cracks and melting phenomenon.3.When the frequency of Er: YAG laser is 20 Hz and irradiation time is 20 s,the dental hard tissue can obtain effective and safety ablation.4.Compared to high speed turbine,Er: YAG laser can obviously relieve the pain of the patients,and the long-term effect of filling material within both treatment have no statistical difference. |
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