Study Of The Effect On The Shear Bond Strength Of Orthodontic Brackets Of Different Concentration Fluorided Etching Fluid

Enamel demineralization that occurs adjacent to directly bonded orthodontic attachments is of great concern to orthodontists. It had long been known that fluoride has a remarkable ability to reduce the incidence of dental caries. Several methods of topical fluoride application in the dental clinic are as follows: (1) pretreatment with topical fluoride before etching; ( 2 ) incorporation of fluoride in the etching solution ; (3) topical application of fluoride to the etched enamel surface before bonding. Among these,We 11 talk about the second method;use fluoride to the phosphoric acid(H3PO4) etching solution. The purpose of this study were to evaluate the effect of various fluoride concentration in H3PO4 on the sheer bond strength of an Jing - jin orthodontic bonding resin and to evaluate the effect of four etching solution on debonding surface of the enamel by 16 * microscopy.MethodSolution of 35% H3PO4 containing 0% and approximately 1. 23% ,2% and 3% fluoride were prepare. Sixty - four the first maxillary premolars were randomly divided into four groups of 16 teeth each group. Each tooth was polished with a fine pumice powder and waterpaste for 15 seconds,then dried. In preparation for bonding,the buccal enamel of the first group teeth were etched with35% H3PO4 incoropo-rated with 1. 23% NaF for 30 seconds; the second group teeth were etched with35% H3PO4 incoroporated with 2% NaF'for 30 seconds; the third group teeth were etched with 35% H3PO4 incoroporated with 3% NaF for 30 seconds and the control group teeth were etched with 35% H3PO4 only. To standarize the bonding area of the resin ,the outline of the bracket base was marked on the etched enamel with a pencil before bonding. The area outside the encircled area was coated with red neil polish. The brackets were then bonded on the labial surface of the crown of four groups of teeth. All specimens were in cubated in a 37℃ water bath. After one week ,four week, twelve week, twenty -four week, every time four specimens were selected to be tested with bond strength machine to determine the shear bond strength, as well as to detect the debonding interface with 16 * microscope.ResultThe mean shear bond strength of the control group(0% fluoride) was 14. 1123 ℃2. 3186MPA; the first group(1. 23% fluoride) was 14.0719 ℃2.0481 MPA; the second group(2% fluoride) was 14. 4431 ℃2.7106MPA ; the third group (3% fluoride) was 6.3606 ℃0. 8636.ConclusionAlthough the mean shear bond sthength of all the groups were within the clinic acceptable range, the third group (3% fluorid) wassignificantly lower than the first group (1. 23% fluorid) ,the second group (2% fluorid) and the control group (0% fluorid) . The mean shear bond sthength between the first , the second and the control group has no statiscally significant difference. The chisquare test results indicated that there was no significant difference between the four groups.