In this study the clinical usefulness of a light-curing (Heliosit) and a chemically-curing composite (Concise) for orthodontic bracket bonding were compared. A sample of 37 patients to be treated with full Edgewise (FE) appliance in one or both arches (in total 52 dental arches) were randomly selected to have brackets on the left or right side of the dental arch bonded either with Concise or with Heliosit. In 12 patients, two teeth were extracted before orthodontic treatment and 25 patients were treated non-extraction. Impressions (Impregum) of the tooth surface and the bracket were made immediately after bracket loss. Frequency scores of bracket loss were noted for both composites and scanning microscopic evaluation of the tooth/composite surface was performed. Significant differences in bracket loss could be demonstrated between the two composites as a whole, and between the anterior and posterior parts of the dentition. For Heliosit bracket loss was observed predominantly in the posterior region, while for Concise it was distributed more equally over the dental arches. It was, however, demonstrated that in the clinical situation of bracket bonding the chemically-cured Concise failed significantly less than Heliosit in the overall frequency score.