Effect of an acidic primer on shear bond strength of orthodontic brackets

A unique characteristic of some new etching systems is that they combine the conditioning and priming agents into a single acidic primer solution. The purpose of this study was to determine the effects on the shear bond strength and the bracket/adhesive failure mode when an acidic primer and other enamel etchants were used to condition the enamel surface before bonding. The brackets were bonded to extracted human teeth according to one of four protocols following the manufacturers instructions. Group I, teeth were etched with 37% phosphoric acid, the brackets were then bonded with System 1+ adhesive (Ormco Corporation. Orange, Calif.); group II, teeth were etched with 10% maleic acid, the brackets 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 adhesive 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 used was highly filled (Panavia 21. J.C. Moritta) and contains Bis-GMA. The present in vitro findings indicated that the use of acidic primers to bond orthodontic brackets to the enamel surface could provide clinically acceptable shear bond forces ((x) over bar = 10.4 +/- 4.4 MPa) when used with a highly (77%) filled adhesive (Panavia 21). These debonding forces were comparable to those obtained when the enamel was conditioned with either Phosphoric ((x) over bar = 11.8 +/- 4.1 MPa) or Maleic ((x) over bar = 10.9 +/- 4.4 MPa) acids. With the use of a lightly (10%) filled adhesive (Clearfil Liner Bond 2), the shear bond strength 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 adhesive remaining on the tooth when an acid primer was used than when phosphoric and maleic acids were used. This might be of advantage to the clinician because it will require less time to clean the teeth after debonding.