An In Vitro Study Of Bond－strength Of Orthodontic Brackets

A significant change in orthodontics over the last 30 years has been the replacement of bands by directly bonded orthodontic brackets. The orthodontic success is directly determined by the result of brackets bonding. This paper studied the bond-strengths of brackets in following 4 aspects.Study 1: An in vitro bond-strength evaluation of orthodontic bracket bonding for several timesobjective The aim of this study was to compare the tensile and shear bond strength of orthodontic bracket bonding for several times. Methods Sixty extracted human premolars were randomly and evenly divided into the following 6 groups: (1) and (2) acid etching and bracket bonding for the first time ;(3) and (4) for the second time ;(5) and (6) for the third time. The tensile bond strength of (1) (3) (5) groups and the shear bond strength of (2) (4) (6) groups were tested by material testing machine after 24 hours. The adhesive remnant index was recorded and the enamel surface was observed with scanning electron microscope after debonding. Result There were no statistically significant differences among either 3 groups. Conclusions In vitro bond strength of acid etching and bracket bonding for second and third time had reached the first level.Study 2: A comparative study of bond strength for orthodontic bracket between immediate and 24 hours bondingObjective The aim of this study was to compare the bond strength of orthodontic bracket between immediate and 24 hours bonding. Methods Forty extracted human premolars were randomly and evenly divided into 4 groups. Edgewise bracket was bonded on each tooth. The immediate shear bond strength was tested in group 1; the immediate tensile bond strength in group 2; the 24 hours shear bond strength in group 3; the 24 hours tensile bond strength in group 4. The adhesive remnant index was recorded. Result There were statistically significant differences in both shear and tensile bond strength between immediate groups and 24 hours groups. Conclusions In vitro, bond strength in immediate bonding was significantly lower than that in 24 hours bonding.Study 3: Bond strengths with two bracket base design: an in vitro comparative study. objective The purpose of this study was to compare the bond strengths between swallow-tailed base and foil mesh base bracket . Methods Forty extracted human premolars were randomly and evenly divided into 4 groups. Swallow-tailed base brackets were bonded on group 1,3; and foil mesh base brackets on group 2,4. The immediate shear bond strengths were tested in group 1,2; the immediate tensile bond strengths in group 3,4. The adhesive remnant index was recorded. Result There were no statistically significant differences in both shear and tensile bond strengths between the tow kinds of bracket base design. Conclusions In vitro study indicates that there is no evident difference between the tow kinds of brackets which are used in clinic most often. Study 4: A study of shear bond strength of recycled metal bracketsobjective The purpose of the study was to evaluate the shear bond strengths of recycled brackets ,and to compare tow base-cure methods of recycled bracket. Methods Extracted human premolars were selected as samples. The edgewise brackets of swallow-tailed base (orsu) were bonded on each tooth, then rebonded after 24 hours. The teeth were cleaned and randomly divided into 3groups. There were 10 teeth in each group. Group 1 were bonded with new brackets; group 2 with recycled brackets whose adhesive remnant were burned and got rid of; group 3 with recycled brackets whose adhesive remnant in the groove of the bases were stored. After 24 hours , the shear bond strengths were tested with material testing machine. Result There were no statistically significant differences among 3 groups. Conclusions In vitro study indicates that the recycled metal brackets can reach good bond strength; and that maybe there is strong chemical bonding between new and old adhesives.