ABSTRACT
T-loop is one of the most popular closing loops in orthodontic profession. However its activation is in the contrary to Bouschinger effect theory, since the formed bends would be opened during activation. The purpose of this study was to add a helix in a way to be more respondent to the Bouschinger effect theory.To compare the load deflection, maximal elastic load and range between three different types of T-loop.5 sample of each 3 different designs of T-loop [group 1: original T-loop, group 2: T-loop with the two inner helices, group 3: T-loop with the two helices constructed outside the horizontal part] had been tested with universal testing machine [Instron]. The load -deflection curves was plotted and the mechanical properties [load deflection, maximal elastic load and range] were measured. One way ANOVA was used to identify statistical differences between designs.The mean value of maximal elastic load in group 1 [6.02 +/- 0.27] was significantly higher than group 2 [5.16 +/- 0.46] and in group 2 were significantly higher than group3 [4.35 +/- 0.25] [p<0.001]. A significantly higher load deflection was reported in group 1 [0.73 +/- 0.36] in comparison to group2 [0.56 +/- 0.74] and group 3[0.56 +/- 0.69] [p=0.002], with no significant difference between two latest groups [p=0.999]. The mean range in group 3 [4.15 +/- 0.10] was significantly lower than group 1[5.43 +/- 0.13] and group 2 [5.59 +/- 0.15] [p=<0.001] with no significant difference between group 1 and 2 [p=0.149].The results revealed that increasing length of T-loop with helices will decrease Load deflection rate the place and design of helices might not be a crucial factor. The new design of T-loop with helices relevant to Bouschinger effect theory needs a further survey regarding their position
ABSTRACT
Decalcification of the enamel in orthodontic patients mainly follows plaque accumulation, but it is promoted by appliance components and the materials used for bonding. This study was designed to compare the microleakage beneath metallic orthodontics brackets, using two different methods of enamel preparation. Sixty bovine deciduous lower incisors were collected, and divided into two equal groups. For bonding the stainless steel brackets using Transbond XT as light cured composite, the surface enamel preparation of each group was as follows: Group I: Acid etch+Transbond XT primer and Group II: self-etching primer. After immersion in fuchsin basic 0.5% for 24 hours, each group was randomly divided into two subgroups of 15 samples and placed in acrylic block, in order to have mesiodistal and buccolingual sectioning. The sectioned teeth were evaluated under stereomicroscope and both enamel-adhesive and adhesive-bracket interfaces were scored for the micropleakage. Kruskal-Wallis and Mann-Whitney U tests were used for statistical analysis for compare the groups. The level of significance was set at p<0.05. No significant differences in the microleakage scores on the gingival and incisal sides were observed in the interfaces between the groups [p>0.05]. Mesiodistal margins of the self-etching groups showed significantly lower scores for microleakage in the enamel-adhesive interface in comparison with acid etch group [p<.o5]. With the limitation of this study using the self-etch primers in enamel preparation for bonding of the orthodontic brackets seems acceptable if all the margins of the brackets are cured directly