| Tooth fracture is always leading to the most catastrophic failure results from the destruction of the dental hard tissue,for which the extraction of the involved tooth is always inevitable.As shown in a recent published investigation,,62% of the teeth extraction were caused by the vertical fracture while that caused by dental caries and periodontitis were 7% and 5%.Therefore,efforts to improve the mechanical properties of the tooth,thus to enhance the resistance to tooth fracture has drawn wide interest among the researchers.Mainly of the dental hard tissue is consisted of dentin,in which the type I collagen was encapsulated by highly mineralized HAP crystal Research shows that space structure improved by dentin constituent could maintain its mechanical property to improve fracture resistance of tooth tissue.It provides new solution to keep bad tooth with badly coloboma.Recently,laser technology developed rapidly and dentistry laser is widely used in each area of mouth cavity clinic treatment.Laser on the tooth could be through fusing,micro explosion to change tissue constituent and space structure of tooth causing related change for teeth hard sclerous mechanical property owing to rather penetrating power for tooth and mouth cavity special tissues.Diode laser(DL)of dentistry belongs to near infrared laser with low energy called as low energy laser or semiconductor laser with wave length 800 to 980 nm.It is safer and more effective without damage of hyperpyrexia comparing to traditional laser,and it overcomes absorbing optical media by coating of laser operation and continued water cooling with the simple usage at a wide using in treatment area of tooth and dental pulp.Research shows that diode laser irradiation of 980 nm could promote crystal structure change of dentin HAP and inorganic substrate to penetrate in dentinal canaliculi to close for improving its mechanical property.It shows the excellent using background to improve mechanical property and tooth tissue to change space structure by physical method based on the above-mentioned situation.The research promotes the penetrating on the dentin coating sodium fluoride,magnesium hydrate,calcium hydroxide by diode laser role.Comparing influence of mechanical property of dentin micro hardness of diode laser with different energy and researching improving mechanism of dentin mechanical property of diode laser,mechanical property could provide theory base to enhance mechanical property on dentin supplying new solution for clinical repair of tooth.ObjectiveThis project aims to study proper condition and mechanism of diode laser and inorganic substance as a effective way to improve the resilience of dentin.The project proposes to use 980 nm diode laser in oral treatment which can melt inorganic substance with biological activity,to facilitates its penetration in dentinal tubules,inducing the reactive ion penetration into the dentin surface to improve the mechanical properties.This idea is based on development in recent research,which proves that physicochemical treatment such as heat and UV light can change the spatial structure and mechanical properties of dentin collagen.Method1.The preparation and group division of dentin sampleCollect complete permanent molars extracted recently.Prepare pieces of dentin sample of 2mm from the middle of the tooth along the direction vertical to the longitude.Then the samples are polished under flowing water.Finally,the dentin samples are divided into four groups,identified by different inorganic substance applied on the surface: a blank contrast group,Na F group,Mg(OH)2 group and Ca(OH)2 group2.Test of microhardness of the dentin sampleThe center of the sample surface is marked with a cross-shape and divided into four regions of approximately same area.Clockwise name the top-left,top-right,bottom-right,bottom-left regions as region A,B,C,D respectively.Apply evenly distilled water(contrast group),Na F,Mg(OH)2 and Ca(OH)2 to the surface of the samples according to its group assignment,with rubber cup at low polishing speed.980 nm diode laser is irradiated onto region A,B,C and D of the surface of dentin samples with power as 0W,1.0W,1.5W and 2.0W.Knoops microhardness tester is used to record the KHN value of different regions of he samples.All the collected data is processed with SPSS for two-factored variance analysis.3.Observation of microstructure change of the dentin samplePlace the treated samples under SEM for observation.Record and compare the microstructure change of the surface of Na F group,Mg(OH)2 and Ca(OH)2 group after irradiation of laser of the same power and study the mechanism of the change.Result1.Two effective treatment conditions are found from the hardness test in this study,namely: 1.1.5W diode laser with continuous wave mode,applied onto Ca(OH)2 group.2.1.0W diode laser with continuous wave mode,applied onto Mg(OH)2 group.Between the two conditions,in tems of hardness improvement,the latter is significantly more effective than the former group.Another fact is improvement of hardness is observed on all regions of the Mg(OH)2 group.2.Observation of dole fluorine,Mg(OH)2 and Ca(OH)2 with SEM shows that:1)dole fluorine mainly covers the dentin surface,even after treatment with 1.0W and 1.5W diode laser,the substrace still cannot penetrate into the dentinal tubules.But as the laser power is increased to 2.0W,dole fluorine is observed to penetrate and fill dentinal tubules.2)For Mg(OH)2 group with 1.0W,1.5W an 2.0W laser irradiation,Mg(OH)2 can largely melt with the dentin or penetrate and fill dentinal tubules.Especially for 1.0W laser group,the substrace fully fills the dentinal tubules.3)For Ca(OH)2 group with different laser power,crater-like change of the dentin is observed.Ca(OH)2 fills the dentinal tubules with moderate degree.This proves diode laser can be combined with the three inorganic substrates for effective penetration of dentinal tubules.Conclusion:1.Treating the surface of dentin samples with diode lalser combined with inorganic substrace can significantly improve the hardness of the surface.In this study,the hardness of dentin samples is improved in Mg(OH)2 group with different laser irradiation,among which 1.0W laser with continous wave mode has the best result.2.Scanning electron microscopy shows that under treatment of 980 nm diode laser,The “micro morphology homogenization” of the inorganic substrates sealed and fused in dentinal tubule,and the “mechanical property homogenization” of the inorganic substrates fused and deposited on the surface of intertubular dentin.This mechanism can be leveraged to improve the hardness of dentin surface.3.Diode laser processing the dentin surface in combination with inorganic substances could obviously strengthen the hardness of dentin surface,this has provided reliableexperimental basis for clinical application of diode laser to strengthen the mechanical property of dentin,and provided new strategies for preservation and restoration of the residual root and crown. |
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