Analytical Investigation On The Measurements Of Healthy Young Adults’ Temporalmandibular Joint By MRI And CBCT

Objectives:1. In order to explore the best scanning sequences and parameters of MRI of temporalmandibular joint (TMJ), we compared different scanning sequences of TMJ MRI of young adults with individual normal occlusion.2.Compare the measurement results of MRI and CBCT scans of healthy young adults with individual normal occlusion, in order to find the differences of TMJ articular discs and joint spaces measured by these two different methods, and finally provide data references for basic research, clinical diagnosis and treatment of temporomandibular joint diseases.Materials and methods:1.With the help of Phillips Achieva 3.0T (a superconduct magnetic resonance imaging system) and flexible surface coil, we scanned young adults’TMJ at the position of axial, oblique-axial and oblique-coronal plane, measured their structures and recorded the measurements.2.With the help of NewTom VG CBCT, the software was used to reconstruct layers and to set up a way to measure and record TMJs by axial position, sagittal position, coronal position, and oblique position perpendicular to and parallel to the condyle long axis.3.Images of structure and measurements of TMJ from MRI were compared with those from CBCT.Results:1. Phillips Achieva 3.0T did a better job of showing the anatomical structure and morphological character of articular disc, and PDWI sequence get the highest score for the image effect of articular disc.2. Measurements at the position of axial plane:The maximum diameter of mandibular condyle is 19.75±1.25mm(from inner to outer) and 8.12±0.50mm(anteroposteriorly).The distance from condyle process to sagittal axis is 61.11±2.62mm.The angle makes of long axis and middle axle of condyle process is 74.31±6.15±.The normal range of crossed long axis angle of young adults is141.4±5.42°.Measurements at the position of oblique-axial plane when mouth closed:The anteroposteriorly maximum diameter of mandibular condyle is 7.96±0.47mm,The thicknesses of fore, mid and hind ligament of articular disc respectively are 1.91±0.17mm,0.98±0.11mm and 2.95±0.39mm, The angers made of condyle process and fore, mid, hind ligament of articular disc respectively are 91.87±4.41°,56.78±2.72°and4.74±1.05°.MRI measurements at the position of oblique —axial plane with mouth opening:The thicknesses of fore, mid and hind ligament of articular disc respectively are2.65±0.14mm,1.66±0.32mm and 3.52±0.27mm.Measurements at the position of oblique-coronal plane:The maximum diameter of mandibular condyle is 19.89±2.05mm(from inner to outer). The inner distance from TMJ articular disc to condyle process is 0.19±1.41mm,and the outer distance is-0.14±1.13mm.Comparison is made of data above between left and right side. (P>0.05), and there was no statistical significance.The distance from the outside of condyle process to sagittal axis at the position of axial plane is 61.07±2.20mm,The diameter of mandibular condyle from inner to outer at oblique — coronal plane is 19.53 ±1.63mm, The anteroposteriorly diameter of mandibular condyle is at oblique-axial plane is 8.28±0.75 mm,The joint space with a 30°lexion is 2.42±0.41mm.The joint space with a 60°lexion is 2.42±0.41mm.The joint space with a 90°flexion is 2.93±0.52mm.The joint space with a 120°flexion is 2.04±0.37mm.The joint space with a 150°flexion is 2.19±0.54mm.3. MRI is good at showing articular disc with soft tissue. Bone structure of condyle process, especial the trabecular structure, is clearly displayed by CBCT. It is impossible for MRI to display cortical bone, but bone marrow is displayed with high signal.Conclusions:1. Dedicated surface coil for TMJ is the first choice when we scan the TMJ by MRI. We also can use flexible surface coil as the second choice because it can clearly display images of articular disc’s anatomical structure and morphological character on PDWI sequence.2. In this research, image data of temporomandibular joint at the position of axial, oblique coronal and oblique sagittal plane were produced by MRI and CBCT, which can provide evidences for the comparison of the position relation between the articular disc and the condyle in orthodontic treatment. The measurement values of articular disc and joint space can provide data references for TMD clinical diagnosis.