Comparison of dynamic high-frequency ultrasound-guided versus conventional manual determination of mandibular protrusion in the treatment of disc displacement with reduction: a prospective, stratified randomized controlled trial

Objectives: To compare the clinical and radiographic outcomes of dynamic high-frequency ultrasound guidance versus conventional manual techniques for determining the mandibular protrusive position of anterior repositioning splints (ARS) in the treatment of disc displacement with reduction (DDwR). Materials and methods: This prospective randomized controlled trial included 40 patients with DDwR, who were randomly and equally divided into an ultrasound-guided group (US-ARS) and a conventional manual group (M-ARS). Both groups received customized ARS therapy. At baseline and 3 months post-treatment, cone-beam computed tomography (CBCT) was used to evaluate joint spaces and condylar bone characteristics, while magnetic resonance imaging (MRI) was used to measure the disc-condyle angle and disc morphology. Results: After 3 months of treatment, there were no significant inter-group differences regarding the increase in CBCT joint spaces and the improvement in condylar bone scores (P > 0.05). However, in the MRI soft-tissue evaluation, the US-ARS group demonstrated a significantly greater reduction in the disc-condyle angle (-20.50° ± 7.50° vs. -12.00° ± 8.50°, P = 0.002) and a superior improvement in the disc morphology score (P = 0.001) compared to the M-ARS group. Conclusions: Compared to conventional empirical manual techniques, ultrasound guidance provides a more precise determination of the magnitude of mandibular protrusion. This achieves superior three-dimensional articular disc reduction and morphological remodeling at the soft-tissue level while maintaining equivalent hard-tissue decompression efficacy. Trial registration: MR5124001996. © The Author(s) under exclusive licence to Japanese Society for Oral and Maxillofacial Radiology 2026.