Quantitative Three-Dimensional Morphometry of Temporomandibular Joint Related Muscles

Objectives: The objective of this study was to quantify variation in temporomandibular joint (TMJ) related muscles attachments by determining changes in muscle size, spatial location and orientation.
Methods: 23 cadaver heads, 11 females (age 71.7±13.6 years) and 12 males (age 71.4±10.7 years), with no sign of pathology underwent CBCT scanning before muscle dissection. Skeletal and surface models were generated from image segmentation using Amira. Temporomandibular muscles were sequentially dissected (masseter, temporalis, lateral pterygoid, medial pterygoid) by trained oral surgeons. As each muscle was dissected, a custom tracking probe digitized muscle origins and insertions using a motion capture system (OptiTrack) at 200Hz. The spatial location of 13 anatomical landmarks and a reference marker set were also recorded. 3D surfaces of each muscle were generated from the co-registered muscle attachment sites and skeletal model using Geomagic Studio. Morphometric analysis of each muscle was performed by bounding box method using MATLAB.
Results: Muscle attachments were successfully digitized and registered with the skeletal model. 3D surface models of muscle attachments were reconstructed and descriptive statistics determined. For the temporalis muscle origin, bounding box length, width and height (indicating muscle size) are 106.4±11.7mm, 79.9±9.1mm and 20.5±4.0mm, respectively. Off-center distances for the temporalis muscle origin bounding box center (indicating muscle location) was 73.1±4.5mm. The angle between the major side of the temporalis muscle origin bounding box for each specimen to a reference specimen (indicating relative orientation) was 20.1±5°.
Conclusions: Morphology of TMJ related muscles’ attachments varies among populations, characterized by differences in muscle size, location and orientation. In order to develop a patient specific musculoskeletal model of the temporomandibular joint, understanding the natural variation in muscle attachments is necessary.