Eri Fujii

Role of Articular Disc in Condylar Regeneration of the Mandible

The articular disc in the temporomandibular joint plays an important role in mandibular growth. Functional appliances induce regeneration of the condyle even after condylectomy. The aim of this study was to examine the role of the articular disc in regeneration of the condyle after unilateral condylectomy with use of a functional appliance in growing rats. Fifty growing rats were subjected to unilateral condylectomy and then half of them underwent discectomy. The functional appliance was applied to half of the rats in each group to induce regeneration of the condyle. Four and eight weeks later, morphometric and histologic analyses of the mandible were performed. Regeneration of the condyle was demonstrated in the two condylectomy groups. In the condylectomy+appliance group, the shape and cartilage of the condyle were equivalent to a normal condyle. However, regeneration of the condyle was not observed in the two discectomy groups even with the use of the functional appliance. The articular disc appears to be crucial in the regeneration of a damaged condyle, suggesting that defects or damage to the articular disc may influence mandibular growth and regeneration or repair of the condyle.

Effects of Neodymium-Doped Yttrium Aluminium Garnet (Nd:YAG) Laser Irradiation on Bone Metabolism During Tooth Movement

INTRODUCTION The aim of this study is to evaluate the effects of low-level neodymium-doped yttrium aluminium garnet (Nd:YAG) laser irradiation on orthodontic tooth movement and histological examination. METHODS Eleven male Wistar rats (aged 10 weeks) were included. To produce experimental tooth movement in rats, 10 g force was applied to maxillary first molars with nickel titanium closed coil springs. Right molars were irradiated with Nd:YAG laser on days 0, 1, 2, 3, 7, 10, 14, 17, 21 and 24, while un-irradiated left molars were used as control. Distance between mesial side of second molar and distal side of first molar was measured on μCT image during tooth movement and the rats were sacrificed 4 weeks after the initiation of tooth movement. RESULTS The amount of tooth movement was significantly greater in the irradiation group (0.20 ± 0.06) than in the control group (0.14 ± 0.03) during the first week (P < 0.05). However, no statistically significant difference was found afterwards. There was a tendency of higher tartrate-resistant acid phosphatase (TRAP)-positive nuclei count in the pressure zones of the laser irradiation group, but it was not statistically significant. In immuno-histological examination, expressions of alkaline phosphatase (ALP) and receptor activator of nuclear factor kappa-B ligand (RANKL) were higher at the pressure site of the laser irradiation group than the control group, whereas there was no difference in osteoprotegerin (OPG) expression. CONCLUSION The results suggest that low-level Nd:YAG laser may stimulate osteoclast and osteoblast activation and accelerate bone metabolism during tooth movement.

Regeneration of condyle with a functional appliance.

Condylar regeneration with the use of functional appliances after condylectomy has been validated. However, the process during treatment remains unclear. In this study, we evaluated the condylar regeneration process and then examined mandibular growth and masticatory muscle activity after regeneration in growing rats. Seventy-five male Wistar rats aged 4 weeks were equally divided into 3 groups: unilateral condylectomy group, unilateral condylectomy + appliance group, or control group. The use of a functional appliance following condylectomy promoted mandibular growth and regeneration of the condyle 1 week after condylectomy. Condyle regeneration showing normal morphology was finally achieved 8 weeks after condylectomy. Asymmetrical masticatory muscle activity was observed after condylectomy. However, the use of a functional appliance produced symmetrical masticatory muscle activity. These results indicate a favorable regeneration process in the condylectomized area due to the use of a functional appliance. In addition, due to condylar regeneration, symmetrical masticatory muscle activity was achieved.

CHARACTERISTICS OF ANKLE MUSCLE ACTIVITY DURING TILTING MOVEMENTS ON A WOBBLE BOARD

Background Balance training is a common component of rehabilitation after ankle sprains. A relatively high activity of the peroneus longus (PL) to the activity of the tibialis anterior (TA) (a low TA/PL ratio) is reported as an effective muscle activity pattern during balance training to prevent inversion ankle sprains. To date, no research has investigated ankle muscle activity during tilting movements on a wobble board. Objective To assess the magnitude of muscle activity of the ankle while inversion and eversion movements of the ankle joint are performed on a wobble board. Design Single-session randomized repeated-measures study design. Setting University laboratory. Participants Seventeen young adults (11 females and 6 males) with no history of ankle injury. Interventions Participants performed tilting movements on a wobble board in a medial and lateral direction while balancing on their non-dominant leg. The frequency of the movement was set at 40 bpm. Muscle activity of the TA and the PL during five cycles of inversion-eversion movements were collected and stored for analysis. Main Outcome Measurements Normalized RMS EMG values (percentage of each participants maximum voluntary isometric contraction; %MVIC) of the TA and PL, along with TA/PL ration in the inversion (wobble board tilted in the lateral direction) and eversion (wobble board tilted in the medial direction) phase. Results There was a significant difference in muscle activity of the PL (inversion phase; 41.6±15.3%MVIC, eversion phase; 59.2±21.5% MVIC, p<0.01) and TA/PL ratio (inversion phase; 52.6±22.3%, eversion phase; 34.1±16.3%, p<0.01). There was no significant difference in muscle activity of the TA (p>0.05). Conclusions The results of the present study indicate that tilting movements on a wobble board in the medial direction (eversion of the ankle joint) may be favorable as an exercise modality after inversion ankle sprains as a high PL activity and a low TA/PL ratio was acquired.

Role of articular disc in cartilaginous growth of the mandible in rats

Displacement of the temporomandibular joint (TMJ) disc causes a lateral shift of the mandible and less-developed and/or distally located mandible unilaterally and bilaterally, respectively, if occurred in growing individuals. The purpose of this study was to evaluate mandibular condylar growth in growing rats after TMJ discectomy and to explore a certain significant role of articular disc in the TMJ in mandibular or cartilaginous growth. Eighteen 4-week-old Wistar strain male rats were divided into two groups with nine in each group, i.e., rats with TMJ discectomy (discectomy group) and only sham operation (control group). Four weeks after initiating the experiment, morphometric analyses of the mandible were performed using a rat and mouse cephalometer and micro-computed tomography. Then, the mandibular condyles were subjected to histomorphometric analyses. Condylar and mandibular growth was reduced significantly in the discectomy group than in the control group. In the discectomy group, the condyle also became flatter and smaller. In addition, the 4-layer structure of condylar cartilage was unclear with thicker fibrous and thinner lower hypertrophic layers in the discectomy group when compared to the controls. It is shown that resection of the articular disc substantially affects condylar and mandibular growth in terms of the cartilaginous growth, suggesting that TMJ disc is indispensable for maintaining normal growth of the condyle and mandible, leading to optimal development of the TMJ and the entire mandible.

[The effect of different working postures while felling a tree with a chain-saw on trunk muscles' activity].

PURPOSE Many forestry workers who use chain-saws suffer from low back pain. Previous studies have reported that low back pain is related to the working postures while felling a tree with a using chain-saws. However, no previous study has investigated trunk muscle activities during work. The purpose of this study was to clarify the relationship between working postures while holding a chain-saw, and trunk muscles activities as measured by surface electromyography (EMG). METHOD Subjects were 10 males who were not forestry workers. Four task postures while holding a chain-saw were tested: standing, 30(o) trunk flexion, 90(o) trunk flexion and half-kneeling. EMG recordings were obtained bilaterally of the lumbar paraspinal (LP) muscles and rectus abdominis (RA) muscles. Raw EMG data were processed by integrating the EMG and normalizing them to %MVC. The paired t-test was used to detect statistical differences in the activities between the right and left LP muscles and RA muscles. One-factor repeated measures ANOVA was used to compare the bilateral LP and RA muscle activities among the 4 different postures. The significance level was set to less than 5%. RESULTS In the half-kneeling posture, the right LP muscle activity was 14.7% higher than the left LP muscle activity (p<0.05); however, there were no significant differences in muscle activities among the other postures. The right LP muscle activity of 30(o) trunk flexion posture was 25.6% higher than that of the standing posture, and 14.2% higher than that of half-kneeling posture (p<0.05). The bilateral LP muscle activities of the 90(o) trunk flexion posture were the highest of the 4 postures, 16.7% higher than the half-kneeling posture (p<0.05) right LP muscle activity. There was a tendency of increase in the left LP muscle activity when trunk flexion angle increased, but no significant differences among the 4 postures were found. The bilateral RA muscle activities were low and did not significantly differ among the 4 postures. CONCLUSIONS This study showed that when the trunk is flexed, the LP muscle activities change asymmetrically, with the right LP muscle activity increasing significantly compared to the standing posture and the half-kneeing posture, but there was no significant difference in the left LP muscle activity. These results suggest that working postures that involve trunk flexion while felling a tree with a holding chain-saw may lead to increased loading of the LP muscles.