Abstract

This in vitro study compared the bond strength performance and adhesive remnant characteristics of two metallic orthodontic pre-coated bracket systems: APC™ Plus and APC™ Flash Free. Forty extracted human premolars were randomly allocated to two groups (n = 20). Following enamel etching with 37% phosphoric acid, brackets were bonded according to the manufacturers’ recommendations. Bond strength testing was performed using a custom-made apparatus in which failure was induced through a progressively increasing load. Because the experimental setup generated a combined loading configuration involving shear, tensile, and bending components, the measured values should be interpreted as comparative bond strength measurements rather than absolute shear bond strength values. Adhesive Remnant Index (ARI) scores were recorded after debonding to evaluate failure patterns. Median bond strength values were 17.75 MPa (IQR: 13.53–21.98) for APC™ Plus and 14.28 MPa (IQR: 9.81–18.74) for APC™ Flash Free. No statistically significant difference was found between groups (Mann–Whitney U test, p = 0.102). In contrast, ARI score distributions differed significantly (Fisher’s exact test, p = 0.001). APC™ Plus brackets predominantly exhibited ARI scores of 2–3, whereas APC™ Flash Free brackets mainly demonstrated ARI scores of 1–2, indicating less adhesive remaining on the enamel surface after debonding. Three enamel fractures were observed in the APC™ Plus group, while none occurred in the APC™ Flash Free group; however, no statistically significant association between bracket type and enamel fracture was identified. Within the limitations of this in vitro study, both bracket systems demonstrated comparable bond strength performance under the experimental conditions investigated. APC™ Flash Free brackets were associated with reduced adhesive remnants on enamel, which may facilitate post-debonding cleanup. Further studies using standardized testing methods and prospective clinical investigations are required to confirm these findings and determine their clinical relevance.

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