Comparative study of normal condyle and temporomandibular joint prosthesis movement during mouth opening by dynamic magnetic resonance imaging and computed tomography.

Background: To analyze and compare the trajectory of condylar motion during mouth opening in normal volunteers and patients after total joint replacement (TJR) of the temporomandibular joint (TMJ). Methods: Condylar movement during mouth opening was recorded by dynamic magnetic resonance imaging (MRI) for volunteers with normal TMJs and dynamic computed tomography (CT) for patients after TMJ TJR. Trajectories of the points selected every 5 mm from the superior point of the condyle (P0) along its axis to the mandibular angle (P-25) were recorded. The arc length and curvature radius of average trajectories for each point were calculated and compared between the normal joints and TJRs, especially P-10 which is the corresponding point of the prosthesis apex without lateral pterygoid muscle (LPM) attachment at the normal joint with LPM attachment. The location of the point with the most similar trajectory was identified in the normal joints and compared with the condylar prosthesis. Results: A total of 9 volunteers with 18 normal TMJs, and 5 patients with 6 prostheses were included in this study. For normal TMJs, the average condylar trajectories during mouth opening were a concave upward curve. Meanwhile, the trajectories of contralateral normal joints in patients with unilateral TJR and all condylar prostheses were significantly decreased. The arc length and curvature radius of average trajectories gradually decreased from P0. In the normal joints, P-20 had the most similar trajectories with the average arc lengths and a curvature radius of 13.0/4.2 mm. In P-10, the average arc lengths and curvature radius of the normal cases, natural TMJ of the unilateral replacement patients, prosthetic TMJ of the unilateral replacement patients, and prosthetic TMJ of the bilateral replacement patient, were 15.6/6.6 mm, 13.1/4.9 mm, 4.7/4.4 mm, and 6.4/5.8 mm, respectively. Conclusions: P-20 in the normal joint exhibited the most similar trajectory among individuals. The trajectory difference between the prosthesis apex without LPM attachment and the corresponding point at the normal joint with LPM attachment provides a reference for fossa prosthesis functional surface design.

Preliminary evaluation of Kovacs digital occlusal splint in the treatment of temporomandibular disorders: A single-centre, cross-sectional study.

BACKGROUND: Digital occlusal splint is a novel approach in the treatment of temporomandibular disorders (TMD) and there is a lack of evaluation. OBJECTIVE: To introduce Kovacs digital occlusal splint (KDOS) and evaluate its clinical and magnetic resonance imaging (MRI) outcomes and influencing factors in the treatment of TMD. PATIENTS AND METHODS: Patients diagnosed of TMD by MRI and treated with KDOS from June 2020 to December 2021 were retrospectively reviewed. They were divided into three groups: anterior disc displacement with reduction (ADDwR), anterior disc displacement without reduction (ADDwoR) and ADDwoR + osteoarthritis (ADDwoR + OA). Visual analogue scales (VAS) scores of pain, diet, mandibular function, quality of life (Qol) and maximum interincisal opening were compared before and at least 8 weeks after treatment. Binary logistic regression was used to analyse the influence of four factors including age, gender, Wilkes stage and the severity of symptoms on treatment. MRI was used to evaluate the condylar bone status and disc length after at least 3 months treatment. RESULTS: One hundred and eighty-four patients were included in the study. The average age was 30.9 ± 14.2 years and the average follow-up was 19.8 ± 10.0 weeks. Pain, diet, mandibular function and Qol were all significantly improved after KDOS treatment (p < .05), with the effective rates of 71.6%, 56.4%, 55.3% and 54.1%. Binary logistic regression showed that higher probabilities of improvement were related to the patients with older age, ADD without OA and higher VAS scores before treatment. MRI showed that 94.1% of the condylar bone status remained stable or improved and the disc length was unchanged after treatment. CONCLUSION: KDOS is effective for the treatment of TMD. Older age, ADD without OA and higher VAS scores before treatment had better results.

Biomechanical analysis of a temporomandibular joint prosthesis for lateral pterygoid muscle reattachment.

OBJECTIVE: To analyze the biomechanical properties of a novel temporomandibular joint (TMJ) prosthesis with an attachment area for the lateral pterygoid muscle (LPM). STUDY DESIGN: Three prosthesis models were created and compared using finite element analysis for the displacement, stress, and strain when simulating the maximum bite force loading. A verification experiment and a compression test were conducted. RESULTS: The displacement, stress, and strain of the novel TMJ prosthesis were larger than the solid condylar neck prosthesis and similar to the slotted condylar neck prosthesis, but the values were far less than the yield strength of titanium alloy. The maximum stress and strain in the novel TMJ prosthesis was concentrated in the inner and boundary areas of the LPM reattachment region beside the thinnest part of the prosthesis neck. The difference in the strain values measured using the verification test and those using finite element analysis was <20%. Compression testing of the novel TMJ prosthesis revealed that the mandible fractured when the force reached 588.97 N, whereas the prosthesis itself did not break or deform. CONCLUSIONS: The mechanical distribution of the novel prosthesis was feasible under maximum bite force for potential clinical application.

Disc repositioning by open suturing vs. mini-screw anchor: stability analysis when combined with orthognathic surgery for hypoplastic condyles.

BACKGROUND: Disc repositioning by Mitek anchors for anterior disc displacement (ADD) combined with orthognathic surgery gained more stable results than when disc repositioning was not performed. But for hypoplastic condyles, the implantation of Mitek anchors may cause condylar resorption. A new disc repositioning technique that sutures the disc to the posterior articular capsule through open incision avoids the implantation of the metal equipment, but the stability when combined with orthognathic surgery is unknown. The purpose of this study was to evaluate the stability of temporomandibular joint (TMJ) disc repositioning by open suturing in patients with hypoplastic condyles when combined with orthographic surgery. METHODS: Patients with ADD and jaw deformity from 2017 to 2021 were included. Disc repositioning by either open suturing or mini-screw anchor were performed simultaneously with orthognathic surgery. MRI and CT images before and after operation and at least 6 months follow-ups were taken to evaluate and compare the TMJ disc and jaw stability. ProPlan CMF 1.4 software was used to measure the position of the jaw, condyle and its surface bone changes. RESULTS: Seventeen patients with 20 hypoplastic condyles were included in the study. Among them, 12 joints had disc repositioning by open suturing and 8 by mini-screw anchor. After an average follow-up of 18.1 months, both the TMJ disc and jaw position were stable in the 2 groups except 2 discs moved anteriorly in each group. The overall condylar bone resorption was 8.3% in the open suturing group and 12.5% in the mini-screw anchor group. CONCLUSIONS: Disc repositioning by open suturing can achieve both TMJ and jaw stability for hypoplastic condyles when combined with orthognathic surgery.