Segmented Indirect Versus Direct Bracket Bonding

Background and rationale: Direct bonding, in which orthodontic brackets are positioned and light-cured individually on each tooth, remains the most common technique but depends heavily on operator visibility and isolation at the moment of placement, which is constrained on posterior teeth. Indirect bonding positions brackets on a working cast under direct vision and transfers them to the dentition in a tray, and has been proposed to improve placement and reduce chairside time. Whether indirect bonding reduces clinical bond failure compared with direct bonding is not established, and clinical failure data for low-cost analogue (hot-glue) transfer-tray methods are limited.

Objective: To compare time to bracket bond failure (primary outcome) and bond-failure rate (secondary outcome) between conventional direct bonding and a segmented modified indirect bonding technique, and to examine whether failure varied by tooth type, arch, or side.

Design: Prospective, parallel-arm, single-center randomized clinical trial. Participants were allocated by simple randomization from a computer-generated sequence to direct bonding or segmented modified indirect bonding. The trial was open-label, as the bonding technique could not be masked from the operator.

Setting: Orthodontic clinics, Riyadh Elm University, Riyadh, Saudi Arabia. Participants: Patients seeking fixed-appliance orthodontic treatment were screened against eligibility criteria. Patients with overbite greater than 3 mm; with crowns, bridges, veneers, restorations, or enamel hypoplasia on the teeth to be bonded; with severely rotated or blocked-out teeth; or with partially erupted teeth were excluded. Eighteen participants were enrolled after written informed consent.

Interventions: In the direct group, teeth were pumiced, etched with 37% phosphoric acid (Meta Etchant, Meta Biomed), rinsed thoroughly, and excess water was removed; Ortho Solo Universal Sealant and Bond Enhancer (Ormco) was applied, and brackets were bonded with Enlight light-cured adhesive (Ormco), then light-cured for 20 seconds occlusally and 20 seconds gingivally. In the modified indirect group, alginate impressions were poured in dental stone; brackets were fixed to the casts in planned positions; segmented transfer trays (separate segments for molars, premolar-canine, and lateral/central incisors per quadrant) were fabricated with thermal (hot) glue covering the occlusal and partial lingual surfaces, leaving the bracket exposed below the slot. Teeth were pumiced, etched with the same 37% phosphoric acid, rinsed thoroughly, and excess water was removed; Ortho Solo Universal Sealant and Bond Enhancer was applied to the etched teeth and Enlight adhesive to the bracket bases before tray insertion; the trays were then seated and light-cured for 20 seconds before removal. The same bracket type and adhesive system were used in both arms.

Outcomes: The primary outcome was time to bracket bond failure (days from bonding to first debonding); the secondary outcome was the bond-failure rate. Each event was recorded with the tooth, arch (maxilla/mandible), side (right/left), date, and time from bonding to failure in days. The unit of analysis was the individual bracket. Participants were reviewed every four weeks for six months; debonded brackets were re-bonded directly.

Analysis: Time to failure was analysed with Kaplan-Meier estimates, the log-rank test and Cox proportional-hazards regression. Failure rates were compared with chi-square and exact tests and Firth penalized logistic regression, with an exploratory Holm-corrected analysis of technique by tooth type and side.