An Evaluation of the Bond Strength and Failure Site of Two Orthodontic Direct Bonding Systems

Abstract

Two commercially available orthodontic direct bonding systems were evaluated for ultimate tensile strength and failure site. Both Endur (Ormco Corp.) and Solo-Tach (L. D. Caulk Co.) are Bis-GMA resin adhesives, but only Endur required the use of a sealant prior to bonding. Metal brackets intended for use with Endur are backed by a thin stainless steel pad and fine wire mesh. Bracket bases for use with Solo-Tach were fully perforated stainless steel pads (GAC International, Inc.). Two hundred human bicuspid teeth were divided into four groups to test the four combinations of bracket and adhesive types. Half of each group was tested 30 minutes after bonding and half was tested after 3 weeks, with thermocycling in the final week. Failure sites were completely opposite for these two adhesives regardless of which bracket type was used. Endur (sealant and adhesive) failed primarily at the bracket-adhesive interface, while Solo-Tach (adhesive only) failed primarily at the enamel-adhesive interface. The sealant-adhesive seems to form a more tenacious bond to enamel. Mesh bracket bases formed a significantly (p<.025) stronger bond than fully perforated bracket bases with either adhesive. Some difference was still apparent after correcting for the difference in base area between mesh and perforated base types. No significant difference in tensile bond strength were found between the two adhesives or between 30-minute and 3-week tests. It was noted that several other factors, such as protection of oral tissues, working time, and ease of manipulation must be evaluated in chasing a satisfactory bonding system.