Effect of impression technique on bond strength.

If the effects of surface preparation (eg, acid etching, laser preparation, crystal growth) are to be investigated on the same tooth from which the bond strength is recorded, a method of surface replication is required that does not affect the subsequent bond. This study investigated the effect of 2 different methods of taking impressions on bond strength. Three groups of 11 mandibular incisors were used. The labial enamel was etched with 37% phosphoric acid for 30 seconds. Group A (control) had no impression taken; in group B (silicone), impressions were taken with silicone impression material before bonding; in group C (polyether), an impression was taken with polyether before bonding. After the impressions were taken, GAC brackets (A Company, San Diego, Calif) were bonded to the labial surfaces of the etched enamel with Transbond XT light-cured composite (3M Unitek, Monrovia, Calif). Teeth with bonded brackets were stored in water at 37 degrees C for 24 hours, and then bond strength was measured on a testing machine. The adhesive remnant index (ARI) was also recorded. The lowest bond strength was found after silicone replication (mean [standard deviation]: 8.6 [1.7] MPa) and the highest in the control group (21.2 [4.0] MPa). There was no significant difference between the control group and the polyether replication group (19.1 [4.7] MPa). The surface detail replications of polyether and silicone were found to be identical. It was concluded that polyether had no significant effect on bond strength and was suitable for surface replication before bonding. Polyether allows replication of the enamel surface without a significant effect on bond strength, and this technique could be used to examine the relationship between enamel preparation techniques and subsequent bond strength between composite and enamel.