EFFECTS OF VARIOUS METHODS OF CHLORHEXIDINE APPLICATION ON SHEAR BONDSTRENGTH

Chlorhexidine has been applied on the teeth and over orthodontic appli ances during treatment in order to reduce bacterial colonization. The purpose of this study was to determine whether the application of chlo rhexidine with or without a sealant, to the etched enamel will affect the shear bond strength and the bracket/adhesive failure modes of orth odontic brackets. A total of 132 extracted third molars were cleaned a nd then divided into 6 groups of at least 20 teeth each, The teeth wer e etched with a 37% phosphoric acid gel and a sealant was applied in 5 of the groups, Stainless steel orthodontic brackets were then bonded with the Transbond XT bending system. The chlorhexidine was applied to the teeth either as a prophylactic paste or as a varnish under the fo llowing conditions: (1) as a varnish over the bracket and tooth surfac es after the bonding procedure was completed; (2) as a prophylactic pa ste containing 0.12% chlorhexidine over the intact enamel i.e., before etching; (3) mixed with the sealant and applied to the etched enamel before bonding, (4) as a varnish applied to the etched enamel with no sealant used; (5) as a varnish over the light cured sealant; and (6) a s a varnish over the sealant before the sealant was light cured. All t eeth were mounted in phenolic rings and stored in deionized water at 3 7 degrees C for 48 hours. A Zwick Universal Testing Machine was used t o determine shear bond strengths, The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index, The analysis of variance and chi square tests were used to compare the six groups. Si gnificance was predetermined at the p less than or equal to 0.05. The findings in this study indicated that shear bond strength was not sign ificantly affected when chlorhexidine was applied; (1) over the bracke t and tooth surfaces after the bonding procedure was completed ((x) ov er bar = 12.3 +/- 3.1 MPa), (2) as a prophylactic paste over the unetc hed enamel surface before the bonding procedure is initiated ((x) over bar = 9.6 +/- 2.3 MPa), and (3) when the varnish was premixed with th e sealant and applied on the etched enamel surface ((x) over bar 11.8 +/- 2.1 MPa). On the other hand, in all the experimental groups in whi ch the chlorhexidine varnish was applied as a layer on the etched enam el surface or over the sealant, shear bond strength values and bracket failure rates were of a magnitude that made them clinically unaccepta ble.