Quantitative analysis of changes in the three-dimensional position of the condyle in the intercuspal position and the myocentric position before and after transcutaneous electrical nerve stimulation

Although the concept of myocentric position (MCP), proposed by neuromuscular dentistry (NMD), remains controversial in clinical practice, its precise location and the corresponding changes in the condylar space have not been fully quantified. This study aims to objectively analyze the spatial relationship between the intercuspal position (ICP) to MCP, and to quantify condylar displacement and movement patterns via three-dimensional measurements. Thirty voluntary participants with normal dentition were recruited, mean age 24.93 ± 2.27 years. Baseline data of resting jaw position were collected and cone-beam computed tomography (CBCT) was taken at ICP. After 45 min of transcutaneous electrical nerve stimulation (TENS), resting jaw position were recorded again and CBCT was taken after recording MCP using silicone registration material. Model of the condyle above the mandibular sigmoid notch intercepted after three-dimensional reconstruction of CBCT data. The three-dimensional positional changes of the condyle during ICP-MCP were quantified by calculating the computer-generated changes in the center of gravity of the condyle, and assess the movement pattern of the condyle by measuring the angles on the surface of the condyle model. Following TENS intervention, the freeway space significantly increased in 30 subjects (1.70 ± 0.65 mm vs. 1.12 ± 0.51 mm, P < 0.001), confirming that TENS effectively guides the masticatory muscles to a physiological resting position (PRP) with lower muscle tension. The MCP is located on average 0.78 mm below and 0.60 mm anterior to the ICP. A small range of movement and rotation of the condyle occurred bilaterally from the ICP to the MCP. The average downward displacement was 0.61 mm, forward displacement was 0.83 mm, and outward displacement was 0.09 mm. The average change in the downward angle was 0.45° downward, forward angle was 0.20°, and outward angle was 0.20°. This displacement belongs within the physiological range of the condylar process. This study describes the three-dimensional spatial characteristics of MCP and condylar position induced by TENS in individuals with normal occlusion. It provides methodological and quantitative reference data for the measurement of condylar displacement and supports further evidence-based investigations of MCP-related concepts.