| Experiment 1 Effect of different adhesive removal methods on enamel microstructure and shear bond strength of bracketsObjective:To compare the effects of five removal methods of residual adhesives on the microscopic morphology of tooth enamel and the shear bond strength of brackets,and to provide clinical guidance for the removal methods of residual adhesives on tooth surfaces after orthodontic treatment.Methods:A total of 66 extracted premolars were selected,and resin blocks(length 4mm× width 3mm × thickness 1mm)were bonded on the lip surface of extracted premolars using resin filling template.The teeth randomly divided into 6 groups with 11 teeth in each group.Group A:blank group,without any treatment;Group B:rotary needle treatment group;Group C:green sand treatment group;Group D:slow tungsten drill treatment group;Group E:slow speed tungsten drill+polishing cup treatment group;The same amount of cement samples in each group were removed by the above treatment method,and the operation time was recorded.The enamel surface was qualitatively and quantitatively evaluated by Scanning electron microscopy(SEM)and surface roughness meter,respectively.The shear bond strength(SBS)and adhesive residual index(ARI)of each group were measured by using a universal mechanical tester.Results:Group B and C have higher removal efficiency,while Group E has the lowest efficiency;SEM showed that the morphology of enamel in Group F was the closest to that of Group A;Group F has the lowest surface roughness(0.48±0.13)μ m,There was no statistical difference between Group A and Group F(P>0.05);The SBS of bracket in Group D was the highest(16.61 ± 1.99)MPa,significantly higher than that in Group A(P<0.05);There was no significant difference in ARI index after bracket removal in each group(P>0.05).Conclusions:Slow tungsten drilling combined with silicon particle polishing has the lowest damage to the enamel,and the removal efficiency is acceptable.Experiment 2 Effect of diode laser with different parameters on bonding strength and pulp cavity temperature of a novel laser-induced reversible cementObjective:To compare the influence of different diode laser irradiation modes on the SBS and pulpal temperature of a novel laser-induced reversible cement(LRC),and to evaluate the optimal irradiation parameters of diode laser and the influence on pulpal safety.Methods:70 premolars were randomly divided into 7 groups with 10 in each group using LRC bonded monocrystalline brackets.According to different laser parameters,they were divided into:Group A(blank group):0W,0s;Group B:2W,1s;Group C:2W,2s;Group D:3W,1s;Group E:3W,2s;Group F:5W,1s;Group G:5W,2s;The temperature of the pulp chamber was measured by a thermocouple probe multimeter.SBS was measured and ARI index was analyzed.Results:The ΔT in Group B was the lowest(2.42±0.67)℃,the ΔT in Group E was(3.74±0.52)℃,which was located in the safty zone,and the ΔT in Group G was the highest(5.77±0.46)℃,which was beyond the safty zone.The SBS value of Group B was not significantly different from that of Group A(P>0.05),the other groups were significantly different from that of Group A(P<0.05).The ARI index of each group was statistically significant(P<0.05).The ARI values of Group A and Group B were concentrated at 3-5 points,and the ARI values of the remaining groups were concentrated at 1-3 points.Conclusions:The irradiation power and time of diode laser are positively correlated with the change of pulpal cavity temperature.After screening,it is safe to use diode laser power of 3 W and irradiate for 2 seconds,and easy to remove the LRC.Experiment 3 Evaluation of the effect of novel laser-induced reversible cement on the orthodontic bracketsObjective:To compare the effects of the novel laser-induced reversible cement(LRC)and the traditional orthodontic cement(TOC)with three different types of brackets on the shear bond strength,adhesive removal efficiency,aerosol concentration and enamel damage.Methods:Bracket were luted onto the buccal side of 90 isolated premolars.The teeth randomly divided into 9 groups with 10 teeth per group according to the type of binder,bracket type and whether laser irradiation was used.Group A:metal bracket+TOC;Group B:metal bracket+LRC;Group C:metal bracket+LRC+L;Group D:poly crystalline bracket+TOC;Group E:polycrystalline bracket+LRC;Group F:polycrystalline bracket+LRC+ L;Group G:monocrystalline bracket+TOC;Group H:monocrystalline bracket+LRC;Group I:monocrystalline bracket+LRC+L;Where(+L group)refers to the support groove after bonding with diode laser irradiation for 2 seconds,the power is 3 W.The SBS value of the brackets of each group was measured by a universal mechanical tester,and the ARI index was analyzed by a microscope.Another 30 extracted premolars were randomly divided into 3 groups with 10 in each group.Resin filling templates were used to bond resin blocks(length 4mm×width 3mm × thickness 1mm)on the lip surface of extracted teeth according to different types of adhesives.The three groups of adhesives were as follows:Group J was TOC,Group K was LRC,and Group M was LRC+L.The adhesives of group J～M were removed by using a slow speed tungsten steel drill with silicon particles.The removal efficiency of adhesives of each group was evaluated by time.The spatial and temporal distribution of PM1,PM2.5 and PM 10 concentrations near the chair during the removal of cement was detected by the micro air detector,and the air pollution during the removal of cement was evaluated.The enamel morphology after the removal of cement was observed by SEM.Results:There was no statistical difference between SBS and TOC when LRC was used to bond metal,monocrystalline and polycrystalline brackets(P>0.05),both of which could meet the clinical requirements of orthodontic bonding.After diode laser irradiation,the SBS value of monocrystalline bracket was significantly decreased(P<0.05),but the SBS value of metal and polycrystalline bracket was not significantly changed(P>0.05).ARI index was statistically significant among all groups(P<0.05).ARI index was concentrated in 3-5 points in the group without laser treatment,and 1-3 points in the group after laser irradiation,with less residual adhesive.Aerosol detection results indicated that there were statistical differences in PM2.5 and PM 10 concentrations in Group J before and after treatment(P<0.05),while there were no statistical differences in PM2.5 and PM 10 concentrations in Group M(P>0.05).The removal efficiency of Group J was the lowest,and that of Group M was the highest,and there was a significant difference between the two groups(P<0.05).SEM results indicated that no obvious enamel damage was found on the tooth surface of the Group J～M.Conclusions:1.Laser reversible cement can meet the adhesive strength requirement of cement in clinic.2.After diode laser irradiation,the SBS of LRC glued to the back of monocrystalline brackets decrease significantly,but the SBS of LRC glued to the back of polycrystalline brackets and metal brackets have no significant change,which may be related to the difference in light transmission performance of brackets.3.Compared with traditional orthodontic cement,laser reversible cement has higher removal efficiency,less aerosol and less pollution to the clinic.There was no obvious damage on the enamel surface after removing the residual cement. |
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