Determinants Of Enamel Discoloration During Simulated Orthodontic Treatment

Objective: The purpose of this study was to determine the relative effects thatphosphoric acid etching, composite resin adhesives and metal brackets have onenamel colour change during simulated orthodontic treatment;To determine theinfluence of the type of orthodontic adhesive system on the stain susceptibility ofenamel surface after orthodontic treatment. Methods：(1)one hundred recentlyextracted healthy premolars were used in this study．The teeth were randomly dividedinto five groups: Group A(etch only)was subjucted to37%phosporic acid gel,GroupB(etch+resin) were acid etched and a small pad of resin was placed on themid-surface of the tooth,Group C(etch+resin+bracket) were acid etched and a metalbracket was bonded on the mid-surface of the tooth using resin,Group D(noetch+resin)were a small pad of resin was placed on the mid-surface of thetooth.without acid etched,The teeth in group E (control) were untreated and served ascontrols.The enamel surfaces were colourimetrically evaluated before enamel treatingand after debonding and clean-up procedures.The color parameters of theCommission Internationale de L’Eclairage—L~*, a~*, and b~*were measured for eachgroup of tooth, and the corresponding color differences (△L~*、△a~*、△b~*、ΔE~*)were calculated.The effect of these parameters on color was assessed with one-wayanalysis of variance.(2)sixty recently extracted premolars were used in this study.Theteeth were divided into three groups averagely.Brakets were bonded with twodifferent orthodontic adhesive system,one was a composite resin adhesive and anotherwas a resin-modified glass ionomer,unbonded teeth were used as controls. The colorof each tooth was measured at three time intervals:before bracket bonding,afterdebonding and clean-up procedures,and after immersed in black tea for72hours. TheCIE colour parameters were recorded and the corresponding colour differences werecalculated.The results were statistically analysed using two-way ANOVA repeatedmeasures. Results:(1)The each color coordinate of enamel surface before treating were analyzed using one-way analysis of variance by group,There were no significantdifferences between the groups in each of the color coordinates (P>0.05).Teeth can beused for the experiment.1)At day7, All the groups have a significant differencestatistically(P≤0.05)with respect to△E~*comparing to the control group(P<0.05).Themean of color change in group C was significantly higher than the color change ingroup D(P<0.05).At day7,Group A and Group C show clinically unacceptable colourdifference(△E~*>3.3).2)At day30, all the groups have a significant differencestatistically(P≤0.05)with respect to△E~*comparing to the control group. Group Ahave a significant difference statistically(P≤0.05)with respect to△E~*comparing togroups C and D.For Group A and Group B, the mean values of color change have nosignificant difference statistically(P>0.05).The mean of color change in group C wassignificantly higher than the color change in groups B and D(P<0.05).At day30,with the exception of the control group,all the other groups show clinicallyunacceptable color difference(△E~*>3.3)．3)For Group A and Group C, at day7andday30, the mean values of color change have a significant difference statistically(P<0.05).For Group B, Group D and Group E, at day7and day30, the mean values ofcolor change have no significant difference statistically(P>0.05).(2)The each colorcoordinate of enamel surface before treating were analyzed using one-way analysis ofvariance by group,There were no significant differences between the groups in each ofthe color coordinates (P>0.05).Teeth can be used for the experiment.1)GroupsⅠandⅡhave an significant difference statistically(P<0.05)with respect to△E~*1and△E~*2comparing to groupⅢ.2)No difference was found with respect toE~*1between groupⅠand groupⅡ,and no difference was found with respect to△E~*2between groupⅠand groupⅡ.3)For groupⅠ, E~*1and△E~*2have a significantdifference statistically(P<0.05).For group Ⅱ and group Ⅲ, E~*1and△E~*2have nosignificant difference statistically(P>0.05).4)After debonding and clean-upprocedures,the color change in groupsⅠand Ⅱshow clinically undetectable(△E~*<3.3).After72hours of storage in Tea,groupsⅠand Ⅱshow clinically unacceptablecolor difference(△E~*>3.3). Conclusions：(1)Acid etching,composite resin adhesivesand metal brackets during treatment with fixed appliances increase enamel discoloration in vitro.(2)The time for orthodontic treatment may have an effection onenamel discoloration.(3)There were no significant differences two type oforthodontic adhesive system, resin adhesive and resin-modified glass ionomer,on thestain susceptibility of enamel surface.(4)Orthodontic bonding influences the colorstability of tooth surface after debonding in the external discoloration．...