EFFECT OF AN ACIDIC PRIMER ON SHEAR BOND STRENGTH OF ORTHODONTIC BRACKETS

A unique characteristic of some new etching systems is that they combi ne the conditioning and priming agents into a single acidic primer sol ution. The purpose of this study was to determine the effects on the s hear bond strength and the bracket/adhesive failure mode when an acidi c primer and other enamel etchants were used to condition the enamel s urface before bonding. The brackets were bonded to extracted human tee th according to one of four protocols following the manufacturers inst ructions. Group I, teeth were etched with 37% phosphoric acid, the bra ckets were then bonded with System 1+ adhesive (Ormco Corporation. Ora nge, Calif.); group II, teeth were etched with 10% maleic acid, the br ackets were also bonded with System 1+ adhesive; group III, an acidic primer that contains both the acid (phenyl-P) and the primer (hema and dimethacrylate) were placed on the enamel for 30 seconds. The adhesiv e used on this group was a lightly filled resin that contains Bis-GMA and HEMA. (Clearfil Liner Bond 2. J.C. Moritta, Kuraway, Japan); Group IV, the same acidic primer was used as in group Ill, the adhesive use d was highly filled (Panavia 21. J.C. Moritta) and contains Bis-GMA. T he present in vitro findings indicated that the use of acidic primers to bond orthodontic brackets to the enamel surface could provide clini cally acceptable shear bond forces ((x) over bar = 10.4 +/- 4.4 MPa) w hen used with a highly (77%) filled adhesive (Panavia 21). These debon ding forces were comparable to those obtained when the enamel was cond itioned with either Phosphoric ((x) over bar = 11.8 +/- 4.1 MPa) or Ma leic ((x) over bar = 10.9 +/- 4.4 MPa) acids. With the use of a lightl y (10%) filled adhesive (Clearfil Liner Bond 2), the shear bond streng th was significantly lower ((x) over bar = 5.9 +/- 5.6 MPa). It is of interest to note that there was a tendency to have less residual adhes ive remaining on the tooth when an acid primer was used than when phos phoric and maleic acids were used. This might be of advantage to the c linician because it will require less time to clean the teeth after de bonding.