| Experiment One:Comparative analysis of shedding rate of the brackets bonding to normal and fluorotic teethObjective:To study the difference in bonding strength of brackets adhering to normal and fluorotic teeth by clinical comparative analysis of the shedding rate.Methods:30 orthodontic patients in our department with moderate fluorotic teeth were selected randomly as experimental group while 30 patients with normal teeth were selected as control group.For each subject,two quadrants(the left side of maxilla and right side of mandible or the right side of maxilla and left side of mandible) were selected to bond brackets with Jingjin ceramic adhesive.Brackets in the other quadrants were bonded with Charisma Light-cured Resin adhesive.Conventional ligation was done and reviewed once a month to record the shedding of brackets in every patient(only the first time of shedding was recorded on each tooth).Analyzed the shedding rate of the brackets bonding to normal and fluorotic teeth and compared the shedding rate of the two adhesives.Results:1.Shedding rate of the brackets bonding to the normal teeth(Jingjin Ceramic Adhesive group--10.90%,Charisma adhesive group----9.42%) was lower than fluorotic teeth(Jingjin Ceramic Adhesive group--22.10%,Charisma adhesive group--14.13%)(P<0.05).2.There is no significant difference in the bracket shedding rate of normal teeth between Jingjin Ceramic Adhesive group(10.90%) and Charisma adhesive group(9.42%).But the shedding rate of normal teeth Jingjin Ceramic Adhesive group(22.10%) is higher than Charisma adhesive group(14.13%)(P <0.05).3.Generally speaking,the tooth with the highest shedding rate is the second premolar in mandible. Experiment Two:Interface Observation of the Adhesive Bonding to the Fluorotic Teeth by Scanning electronic microscopeObjective:To observe the adhesive interface through scanning electron microscope to affirm if there is obvious statistics difference between different adhesives.Methods:39 normal premolar teeth and 39 fluorotic teeth which need to be taken out by orthodontic operation were selected as experimental group and control group. Patients aged between 12 and 16 were required.The dental crown was complete, without any dental caries and cracks that could be seen by visual inspection and the pulp was not subjected to any chemical treatment.The selected fluorotic teeth were diagnosed as moderate fluorosis by visual inspection according to Classification on Fluorotic teeth in VI grades.Three normal teeth and three fluorotic teeth with similar crown were selected from normal teeth and fluorotic teeth and brackets were bonded with 3M unite XT,GC Fuji Ortho LC and Unite Bonding adhesive.Teeth were splitted into two halves after 24 hours from the lingual surface to the labial surface.After being coated,the adhesive interface was observed under the scanning electronic microscope.Results:The internal texture of 3M unite XT resin was well-distributed with few particles and/or air bubbles.The internal quality of Unite Bonding Adhesive was loose and with big particles.The internal structure of GC Fuji Ortho LC was mixed pretty well but with big particles.Lots of round-shaped air bubbles with a size of 10-30um can be seen in the internal of Unite Bonding adhesive and GC Fuji LC under scanning electron microscope.The bonding interface between 3M unites XT and the normal tooth was the tightest,which could hardly be seen.The bonding interface between 3M Unite XT and fluorotic tooth was obvious.Compared with the bonding interface between normal teeth and 3M unite XT,3M unite XT,the bonding interface between fluorotic teeth and 3M unite XT could be identified easily.Long and obvious cracks were seen in the bonding interface between GC Fuji Ortho LC and fluorotic teeth. Cracks also existed in the bonding interface between GC Fuji Ortho LC and normal teeth,but are getting smaller and narrower.Small cracks were seen in the bonding interface between the Unite Bonding Adhesive and fluorotic teeth.But the interface between Unite Bonding Adhesive and normal teeth was identified easily. Experiment Three:Evaluation of the shearing strength of brackets bonding to fluorotic teeth by three different adhesivesObjective:To evaluate the shearing strength and adhesive remnant index(ARI) and select the right adhesive suitable for orthodontic use that provides sufficient adhesive strength for brackets bonding to fluorotic teeth.Methods:36 normal teeth and 36 fluorotic teeth were divided into six groups,namely Group A(3M unite XT-normal teeth);Group B(GC Fuji Ortho LC-normal teeth); Group C(Unite Bonding adhesive -normal teeth);Group D(3M unite XT-fluorotic teeth);Group E(GC Fuji Ortho LC-fluorotic teeth) and Group F(Unite Bonding adhesive-fluorotic teeth).15-second polishing and 60-second acid etching were carried out and the bonding of brackets was performed according to the instruction of each adhesive.The second premolar brackets produced by the Hangzhou Xihu Biological Material Limited company were bonded to teeth and then soaked in distilled water of 37(?).24 hours later evaluated the shearing bonding strength and ARIResults:1.The average anti-shearing strength of six groups were as follows:the Normal teeth 3M unite XT Group—13.2631Mpa;the GC Fuji Ortho LC Group—8.0286Mpa;the Unite Bonding Adhesive Group—11.6740Mpa;the Fluorotic Teeth 3M unite XT Group—6.4258Mpa;the GC Fuji Ortho LC Group—6.0313Mpa;the Unite Bonding Adhesive Group-2.1959Mpa.When 3M unite XT,GC Fuji Ortho LC and Unite Bonding Adhesive were used for the bonding of brackets on normal teeth,no statistics difference was found.All these three adhesives met the minimal requirement of orthodontic treatment in terms of bonding strength(6-8Mpa).2.When 3M unite XT,GC Fuji Ortho LC and Unite Bonding Adhesive were used for the bonding of brackets on fluorotic teeth,the shearing bonding strength of 3M unite XT and GC Fuji Ortho LC was enough for orthodontic treatment while Unite Bonding Adhesive could not meet the requirement and not suitable for fluorotic teeth.3.When used in normal teeth group and fluorotic teeth group,the shearing bonding strength of 3M unite XT reached 13.2631 Mpa and 6.4258 Mpa respectively,and there was no statistic difference(P>0.05).When used in normal teeth and fluorotic teeth groups,the shearing strength of GC Fuji Ortho LC were 11.6740 Mpa and 2.1959 Mpa respectively, and no statistic difference existed(P>0.05).When used in the normal teeth group and fluorotic teeth group,the average shearing strength of GC Fuji Ortho LC were 8.0286 M pa and 6.0313 M pa respectively,and no obvious statistics difference existed(P>0.05).4.Marks of ARI:In group A---four teeth merited 3 points,two teeth merited 2 points and one tooth merited 1 point.In group B---four teeth merited 3 points,one tooth merited 2 points and one tooth merited 1 point.In group C----six teeth merit 3 points.In group D---three teeth merited 4 points,three teeth merited 3 points;In group E---two teeth merit 4 points,three teeth merited 3 points and one tooth merited 2 points;In Group F---four teeth merited 5 points,and two teeth merited 4 points.ARI of three adhesives for normal teeth have no remarkable statistic difference(P>0.05) and that the ARI of these three adhesives for fluorotic teeth have no notable statistic difference(P>0.05).When used in normal teeth and fluorotic teeth groups,the ARI of 3M unite XT has notable statistic difference(P<0.05);When used in normal teeth and fluorotic teeth groups,the ARI of Unite Bonding Adhesive has notable statistic difference(P<0.05);When used in normal teeth and fluorotic teeth groups,the ARI of GC Fuji Ortho LC has no remarkable statistic difference(P>0.05).Conclusions:1.Shedding rate of the brackets bonding to fluorotic teeth is significantly higher than that to normal teeth.2.Shedding rate of the Unite Bonding Adhesive brackets bonding to the fluorotic teeth is higher than that of Charisma Resin Adhesive.3.Bracket shedding rate of the second premolar tooth is the highest.4.3M unite XT,GC Fuji Ortho LC and Unite Bonding Adhesive can all meet the clinical orthodontic strength requirement for normal teeth brackets.5.3M unite XT,GC Fuji Ortho LC and Unite Bonding Adhesive can meet the lowest clinical orthodontic strength requirement for fluorotic teeth brackets,Unite Bonding Adhesive do not fit in the brackets bonding to fluorotic teeth.
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