[A comparative study of the upper airway changes of idiopathic condylar resorption and anterior open bite patients after bilateral temporomandibular joint prostheses surgery and bimaxillary orthognathic surgery]

Objective: To evaluate the 2-dimension and 3-dimension changes of upper airway of patients who were diagnosed with idiopathic condylar resorption (ICR) and anterior open bite as well as received bilateral temporomandibular joint (TMJ) prostheses replacement or bimaxillary orthognathic surgery. Methods: This study is a retrospective study. Seventeen patients diagnosed as ICR and anterior open bite in Department of Orthognathic and TMJ surgery, West China Hospital of Sichuan University were selected (January 2018 to December 2021) and divided into bilateral TMJ protheses replacement group (group R, n=8) and orthognathic group (group O, n=9), according to which surgery they have performed. In order to compare variation of upper airway before and after surgery in different dimensions and sections within the same group or between groups, Spiral computed tomography data were obtained before (1 month) and after operation (10 to 12 months) to measure the total volume of airway (VT), the maximum sagittal area (MSA), the maximum cross-sectional area (MACA), the minimum cross-sectional area (MICA), the area of the most posterior plane(PPA), the area of soft-palate plane (SPA), the area of the most posterior point of tongue base plane (PTA), the area of the root of epiglottis plane (EA), the oropharyngeal airway volume (VO), the glossopharyngeal airway volume (VG) and the laryngeal airway volume (VL). Wilcoxon signed-rank test were used to complete statistical analyses for VO (T2),SPA (T2),ΔMSA,ΔMACA in group R as well as PTA (T1),EA (T2) in group O. Statistical analyses of other items were performed with student's t test. Results: VT, VO, VG, VL, MSA, MACA, MIC, PPA, PTA and EA of group R (T2) were significantly increased after TMJ prosthesis with Lefort I osteotomy (P<0.05). Meanwhile the VT, VO, VG, MSA, MACA, MICA, PPA and SPA of group O (T2) were significantly increased (P<0.05). There were significant difference in ΔVT and ΔVL between group R [(6 854.80±3 197.82) mm3, (2 252.85±1 527.96) mm3] and group O [(3 367.91±3 124.62) mm3, (413.21±1 244.44) mm3](t=2.27, P=0.038; t=2.74, P=0.015). Conclusions: Bilateral temporomandibular joint (TMJ) prostheses replacement and bimaxillary orthognathic surgery can both enlarge the areas and volumes of upper airway in patients who suffer from ICR and anterior open bite. Compared with bimaxillary orthognathic surgery, bilateral temporomandibular joint prostheses replacement plays a more pronounced role in enlargement and reconstruction of middle-inferior section of upper airway.

[Comprehensive measurement and quantification of bio-mechanical properties of the temporomandibular joint disc]

Objective: To comprehensively investigate the biomechanical properties of the temporomandibular joint (TMJ) disc and to perfect the mechanical testing system of the TMJ disc by conducting tests of compression, tension, cyclic compression, cyclic tension, creep and friction. Methods: Fifteen fresh goat heads (weighing 2.5-3.0 kg) were purchased from the market. They were all ordinary goats (9-12 months old, body weighing 18-21 kg) regardless of gender. Bilateral articular discs (a total of 30) were dissected within 30 minutes after execution. According to the national standard for mechanical testing of viscoelastic materials, fresh TMJ disc specimens of goat were prepared and tests were carried out in physiological conditions. The universal mechanical testing machine was utilized to test biomechanical properties of TMJ discs. Results: The compressive modulus of TMJ discs was (8.41±2.12) MPa and the tensile modulus was (9.54±3.26) MPa. The mechanical characteristics would be irreversibly altered once the load exceeded the physiological range. In addition, it underwent apparent creep relaxation under continuous strain (0.5 MPa or 3.0 MPa) and the surface friction coefficient of the TMJ discs (0.015+0.011) was much lower than that of general viscoelastic materials. Conclusions: The TMJ disc was a bio-viscoelastic structure with excellent tensile and compressive properties and its surface was extremely smooth in wet conditions.

Change in the posterior airway after mandibular distraction osteogenesis in patients with ankylosis of the temporomandibular joint: a retrospective study

Mandibular distraction osteogenesis (DO) has been shown to lead to considerable improvement in obstruction of the posterior airway space in patients with ankylosis of the temporomandibular joint (TMJ), and our objective was to find out if we could confirm these findings. Seventeen patients had spiral computed tomographic (CT) scans before and after DO. After treatment, the overall posterior airway space was enlarged in all three sections of the airway (oropharyngeal, glossopharyngeal, and laryngeal). We then compared rates of change in the airway among the sections using 2-dimensional and 3-dimensional assessments, and found that the rate of change in 3-dimensional assessment of volume was significantly higher than that in the 2-dimensional (62% compared with 34%). We also found that the higher 3-dimensional rate of change came from changes in the oropharyngeal and glossopharyngeal sections, while there was no significant difference between the 2- and 3-dimensional rates of change in the laryngeal section. Because the laryngeal section had the most robust enlargement after DO in both the overall area of the posterior airway space (increased by 54%) and volume (increased by 73%), we concluded that 3-dimensional assessments were more sensitive to smaller changes in the airway space during the operation. This suggests that 3-dimensional assessments are preferable in the prediction and evaluation of the effects of DO on the posterior airway space.

Estrogen aggravates iodoacetate-induced temporomandibular joint osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is clinically characterized by female preponderance, with a female-to-male ratio of more than 2:1; however, the underlying mechanism remains obscure. We examined the effects of estrogen on TMJOA induced by monosodium iodoacetate. Female rats were randomly and equally divided into 5 groups: control, sham-ovariectomized, and ovariectomized rats treated, respectively, with 17β-estradiol (E2) at doses of 0 µg, 20 µg, and 80 µg/day until the end of the experiment. After induction of TMJOA, TMJs were evaluated by histopathology and microCT, and the expression of Fas, FasL, caspase 3, and caspase 8 was evaluated by real-time polymerase chain-reaction or immunohistochemistry. Another 5 groups of female rats were used to evaluate the effect of estrogen receptor antagonist ICI 182780 on E2 effects on TMJOA, when injected intraperitoneally into the control, sham-ovariectomized, and 80-µg-E2-treated groups. We found that E2 potentiated cartilage degradation and subchondral bone erosion in iodoacetate-induced TMJOA. E2 also potentiated mRNA expression of Fas, FasL, caspase 3, and caspase 8 in the condylar cartilage. Moreover, the estrogen receptor antagonist partially blocked E2 effects on TMJOA. These findings suggest that E2 could aggravate TMJOA, which may be an important mechanism underlying the sexual dimorphism of TMJOA.