Jaw closing movement and sex differences in temporomandibular joint energy densities.

Energy densities (ED, mJ/mm3 ) quantify mechanical work imposed on articular cartilages during function. This cross-sectional study examined differences in temporomandibular joint (TMJ) ED during asymmetric versus symmetric jaw closing in healthy females versus males. ED component variables were tested for differences between and within sexes for two types of jaw closing. Seventeen female and 17 male subjects gave informed consent to participate. Diagnostic criteria for temporomandibular disorders and images (magnetic resonance (MR), computed tomography) were used to confirm healthy TMJ status. Numerical modelling predicted TMJ loads (Fnormal ) consequent to unilateral canine biting. Dynamic stereometry combined MR imaging and jaw-tracking data to measure ED component variables during 10 trials of each type of jaw closing in each subject's TMJs. These data were then used to calculate TMJ ED during jaw closing asymmetrically and symmetrically. Paired and Student's t tests assessed ED between jaw closing movements and sexes, respectively. Multivariate data analyses assessed ED component variable differences between jaw closing movements and sexes (α = 0.05). Contralateral TMJ ED were 3.6-fold and significantly larger (P < .0001) during asymmetric versus symmetric jaw closing, due to significantly larger (P ≤ .001) distances of TMJ stress-field translation in asymmetric versus symmetric movement. During asymmetric jaw closing, contralateral TMJ ED were twofold and significantly larger (P = .036) in females versus males, due to 1.5-fold and significantly smaller (P ≤ .010) TMJ disc cartilage volumes under stress fields in females versus males. These results suggest that in healthy individuals, asymmetric compared to symmetric jaw closure in females compared to males has higher TMJ mechanical fatigue liabilities.

Effect of rheumatoid arthritis and age on metacarpal bone shaft geometry and density: A longitudinal pQCT study in postmenopausal women.

OBJECTIVE: This study aimed to elucidate the effects of changes in the geometry and density of the metacarpal bone of patients with rheumatoid arthritis (RA). METHODS: This prospective study included consecutive postmenopausal RA patients who met the American College of Rheumatology Criteria and healthy controls (HC). Peripheral quantitative computed tomography scans at 50% of the total metacarpal shaft (third metacarpal bone) were obtained at baseline and follow-ups. Use of bisphosphonates (BP), glucocorticoids (GC), biologics, and disease-modifying anti-rheumatic drugs (DMARD) was monitored (baseline to follow-up). Total cross-sectional area (CSA), cortical-transitional zone and compact zone CSA, cortical volumetric bone mineral density, and compact cortex porosity were measured. A linear mixed-effects model was used to determine significant differences in the rate of change in the RA and control groups and in RA patient subgroups. RESULTS: Thirty-nine RA patients and 42 consecutive postmenopausal HC were followed for 63 months. RA and HC depicted a time-dependent increase of medullary CSA (+0.41 mm2/year, P < 0.0001), while total CSA remained stable (P = 0.2). RA status was associated with a loss of cortical bone mineral density (interaction: -3.08 mg/mm3; P = 0.014). In RA subgroup analysis, GC use ≥5 mg/day was positively correlated with a fourfold increase of medullary CSA (0.67 mm2/year P = 0.009), which resulted in a three- to fourfold loss of cortical density (-6.6 mg/mm3/year; P = 0.002) and cortical CSA (-0.57 mm2/year, P = 0.004). Patients with high disease activity and high GC dose at baseline demonstrated an increase in the total CSA (0.29 mm2/y; P = 0.049) and a loss of cortical BMD (-5.73 mg/mm3/y; P = 0.05) despite good clinical response. CONCLUSION: Increase in medullary metacarpal CSA and thinning of the cortical CSA are physiological and time dependent. RA status is associated with loss in cortical density. Even upon biological therapy, low glucocorticoid dose affects metacarpal bone shaft geometry and density over time.