Thread Depth Effects on Stability and Positional Accuracy in Guided Immediate Implants: A Randomized Controlled Trial

OBJECTIVES: To evaluate the influence of implant thread depth on implant stability and positional accuracy in fully guided immediate implant placement. MATERIALS AND METHODS: Fifty-four patients received a reference tapered (BLT), a standard-thread (MST), or a deep-thread implant (MDT). Fifty-four implants were placed using fully guided surgery and evaluated over 1-year follow-up. Primary outcomes were implant stability (insertion torque, ISQ, ISV). Secondary outcomes included positional accuracy and marginal bone level (MBL) at 12 months. RESULTS: Primary and longitudinal stability were comparable across groups. Insertion torque was highest for MDT implants, followed by MST and BLT implants (BLT: 35.28 ± 11.18; MST: 40.00 ± 11.88; MDT: 43.89 ± 10.92 Ncm; p = 0.062). A higher proportion of MDT implants achieved insertion torque ≥ 40 Ncm (MDT: 14/18; MST: 12/18; BLT: 8/18). Angular deviation differed among implant groups (MDT: 5.57° ± 3.71°; BLT: 4.73° ± 2.46°; MST: 3.58° ± 1.81°; p = 0.062). In subgroup analysis comparing implants differing only in thread depth (MST vs. MDT), angular deviation was significantly greater for MDT (p = 0.029), particularly in molar sites. At 12 months, MBL did not differ significantly among groups. CONCLUSIONS: In fully guided immediate implant placement, deeper-thread implants showed higher insertion torque values but were associated with greater angular deviation, while longitudinal stability and marginal bone levels remained comparable. Deeper-thread designs may be beneficial when enhanced primary stability is required, provided careful angulation control is ensured. TRIAL REGISTRATION: cris.nih.go.kr Identifier: KCT0009402; This clinical trial was not registered prior to participant recruitment and randomization.