title: Quantitative evaluation of masseter muscle stiffness in patients with temporomandibular disorders using shear wave elastography.
abstract: OBJECTIVE
  The aim of this study was to quantify masseter muscle stiffness in patients with masticatory myofascial pain.
  
  
  METHODS
  Stiffness was measured using shear wave elastography, which expresses stiffness as shear wave velocity (Vs). A phantom study was conducted to confirm the reliability of the measuring device. The study participants were 26 females with bilateral masseter muscle pain who were classified into either Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) group Ia (myofascial pain; n=13) or RDC/TMD group Ib (myofascial pain with limited opening; n=13). Healthy controls consisted of 24 female volunteers with normal teeth and jaws, who were not classified into groups I/II/III by RDC/TMD.
  
  
  RESULTS
  Muscle stiffness was 1.96m/s (12.5kPa) in 13 patients in group Ia, 2.00m/s (13.0kPa) in 13 patients in group Ib and 1.27m/s (5.25kPa) in 24 control subjects. Vs was significantly greater in groups Ia and Ib than in the control group (p<0.05). Characteristic pain intensity (CPI) became clear as an independent factor impacting Vs (partial regression coefficient=0.714; multiple regression analysis , p<0.05). Masseter muscle stiffness was positively correlated with CPI (p< 0.05) and negatively correlated with maximum assisted mouth opening (p<0.05) and painless mouth opening (p<0.05).
  
  
  CONCLUSIONS
  Shear wave elastography is useful to quantify masticatory muscle stiffness. Masseter muscle stiffness of females measured using shear wave elastography was about two-fold greater in group Ia and Ib than in the healthy control group.
authors.affiliation: Temporomandibular Joint Clinic, Niigata University Medical and Dental Hospital, Niigata, Japan.
authors.forename: Makiko
authors.initials: M
authors.lastname: Takashima
authors.affiliation: Temporomandibular Joint Clinic, Niigata University Medical and Dental Hospital, Niigata, Japan. Electronic address: ara@dent.niigata-u.ac.jp.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Arai
authors.affiliation: Temporomandibular Joint Clinic, Niigata University Medical and Dental Hospital, Niigata, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kawamura
authors.affiliation: Division of Oral and Maxillofacial Radiology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Hayashi
authors.affiliation: Temporomandibular Joint Clinic, Niigata University Medical and Dental Hospital, Niigata, Japan; Division of Oral and Maxillofacial Surgery, Niigata Graduate School of Medical and Dental Sciences, Niigata, Japan.
authors.forename: Ritsuo
authors.initials: R
authors.lastname: Takagi
mesh_terms: D000293:Adolescent; D000328:Adult; D004548:Elasticity; D054459:Elasticity Imaging Techniques / Q000379:methods*; D005260:Female; D006801:Humans; D008406:Masseter Muscle / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008875:Middle Aged; D019047:Phantoms, Imaging; D013705:Temporomandibular Joint Disorders / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D055815:Young Adult
keywords: Masseter muscle; Masticatory myofascial pain; Shear wave elastography; Stiffness; Temporomandibular disorders