Comparison between flowable and flowable bulk-fill composites in the manufacture of attachments for orthodontic aligners: a split-mouth randomized clinical trial

INTRODUCTION: Orthodontic aligner attachments are crucial for enhancing dental movements that aligners alone cannot achieve. With recent advancements in design and materials, treatment precision and efficacy are improving. This study aimed to compare conventional and bulk-fill flowable composites in fabricating orthodontic attachments to determine their loss rate and clinical outcomes. METHODS: This split-mouth randomized clinical trial enrolled 50 participants (21 men and 29 women; mean age 37.86 ± 6.90 years), who were allocated to two treatment sequences (25 participants per group). In Group 1, the right side received 3 M Filtek Supreme Flowable and the left side received 3 M Filtek Bulk Fill Flowable; in Group 2, the allocation was reversed. This design allowed an intra-individual comparison between materials. RESULTS: After 140 days of follow-up, 150 of 800 attachments had been lost and rebonded, corresponding to an overall failure rate of 18.75%. No statistically significant differences were found between materials when evaluating individual teeth, contralateral teeth, or time to failure. Cox regression showed no significant difference between groups (HR = 0.84; 95% CI, 0.60-1.16; p = 0.293). CONCLUSION: Flowable and flowable bulk-fill composites showed similar clinical performance and attachment survival. REGISTRATION: This clinical trial was registered under UTN U1111-1303-5576 at the Brazilian Registry of Clinical Trials (ReBEC).