Junko Aoyama

Immunolocalization of vascular endothelial growth factor in rat condylar cartilage during postnatal development

It is well known that angiogenesis is essential for the replacement of cartilage by bone during skeletal growth and regeneration. To address angiogenesis of endochondral ossification in the condyle, we examined the appearance of vascular endothelial growth factor (VEGF) and its receptor Flt-1 in condylar cartilage of the growing rat. The early expression of VEGF at various sites during condylar cartilage development indicates that VEGF plays a role in the regulation of angiogenesis at each site of bone formation. From the findings of Flt-1 immunoreactivity, the VEGF produced by the chondrocytes of the hypertrophic zone should contribute to the promotion of endothelial cell proliferation and to stimulate migration and activation of osteoclasts in condylar cartilage, resulting in the invasion of these cells into the mineralized zone.

Shear Properties of the Temporomandibular Joint Disc in Relation to Compressive and Shear Strain

Shear stress can result in fatigue, damage, and irreversible deformation of the temporomandibular joint disc. Insight into the dynamic shear properties of the disc may give insight into the mechanism inducing tissue failure due to shear. We tested the hypothesis that the dynamic shear properties of the disc depend on the amount of shear and compressive strain. Twenty-four porcine discs were used for dynamic shear tests. The specimens were clamped between the plates of a loading apparatus under compressive strains of 5%, 10%, and 15%. Dynamic shear was applied to the specimen by a sinusoidal strain of, respectively, 0.5%, 1.0%, and 1.5%. Both the dynamic elasticity and viscosity were proportional to compressive strain and inversely proportional to shear strain. These shear characteristics suggest a significant role of compressive and shear strain on the internal friction of the disc.

Administration of MK-801 decreases c-Fos expression in the trigeminal sensory nuclear complex but increases it in the midbrain during experimental movement of rat molars.

Various studies reported c-Fos expression in the neurons in the trigeminal sensory nuclear complex (TSNC) following experimental tooth movement, which implies pain transmission to the central nervous system. Meanwhile, MK-801, a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors, was shown to markedly reduce the expression of c-Fos in the trigeminal subnucleus caudalis (Vc) following noxious stimulation but to enhance c-Fos expression markedly in other brain regions, i.e., the neocortex, dorsal raphe and thalamic nuclei. In the present study, we examined the nature of c-Fos expression in the brainstem including the TSNC and midbrain following administration of MK-801 and/or experimental movement of the rat molars. Twelve hours after the beginning of experimental tooth movement, c-Fos was expressed bilaterally in the superficial laminae of Vc (Vc I/II), dorsomedial areas of the trigeminal subnucleus oralis (Vodm) and rostro-dorsomedial areas of the trigeminal subnucleus oralis (Vor) with the ipsilaterally dominant distribution, but hardly in the periaqueductal gray (PAG), dorsal raphe nucleus (DR) and Edinger-Westphal nucleus (EW). Intraperitoneal administration of MK-801 (0.03, 0.3 and 3.0 mg/kg) prior to the onset of experimental tooth movement reduced c-Fos in the TSNC (Vc I/II, Vodm and Vor) but increased it in the nucleus raphe magnus (NRM), ventrolateral PAG (vl PAG), DR and EW. These results highly emphasize that during experimental tooth movement, a blockade of NMDA receptors induces neuronal suppression in the TSNC but increases neuronal activity in the descending antinociceptive system including the NRM, vl PAG, DR and EW.

Biomechanical behaviour of bovine temporomandibular articular discs with age

The purpose was to evaluate age-associated changes in the creep and restoration properties of bovine temporomandibular joint (TMJ) discs under and after sustained tensile stress. Forty discs were obtained from 7- and 10-year-old cattle, referred to as the adult and mature adult groups, respectively. Tension of 1.0 MPa was applied and sustained for 20 min to specimens from ten right discs and of 1.5 MPa to specimens from ten left discs. After the period of tension for the study of creep, the specimens were removed from the tension devices and their restoration observed for 20 min. For comparative purposes the relevant results for a young adult group were recruited from data on 3-year-old bovine TMJ discs reported in a previous study on viscoelastic properties. In all the specimens the time-dependent creep curves showed a marked change in strain during the initial 5 s, but the elastic moduli at the onset of stress were significantly larger in the mature adult group than in the other groups. After 20-min creep, the strains were decreased in relation to the age of the specimen and were significantly smaller in the mature adult than in the young adult. With regard to regional differences, the medial specimens exhibited significantly smaller strains than the central ones in all three age groups. Furthermore, the residual strains after 20-min restoration also decreased slightly with age. It is concluded that the bovine TMJ disc becomes stiff and acquires the capacity to recover from continuous deformation during growth and maturation. These findings suggest that the TMJ disc can modify its viscoelasticity in order to withstand extrinsic functional stresses.

Dynamic Properties of Bovine Temporomandibular Joint Disks Change with Age

The temporomandibular joint disk exhibits morphological and biochemical age-related changes. However, the possible age-related changes of the dynamic viscoelasticity in the disk are unclear. We tested the hypothesis that the dynamic viscoelastic properties of the disk change with age. Thirty-six disks from young-adult, adult, and mature-adult cattle were used for dynamic tensile tests. In all disks, the magnitudes of the complex modulus, the storage modulus, and the loss modulus increased as the frequency increased. The mature-adult disks had higher values of these moduli than did the younger disks. The loss tangent ranged from 0.1 to 0.3, which means that the disk has relatively large elasticity and relatively small viscosity. It was concluded that both the elasticity and viscosity of the disk increase with age. This may reflect age-related changes in biochemical composition.

Viscoelastic properties and residual strain in a tensile creep test on bovine temporomandibular articular discs

This study was designed to evaluate the creep characteristics and residual strain of bovine temporomandibular joint (TMJ) discs in tension. Twenty discs were divided into three specimens each: central, lateral and medial regions. Tension of 1.0 MPa was applied and sustained for 20 min to the specimens from 10 right-side discs, and tension of 1.5 MPa to specimens from 10 left-side discs. After the period of tension for creep, the specimens were removed from the tension devices and restoration observed for 20 min. Time-dependent creep curves showed a marked change in strain during the initial 5s. The essential time delay in strain ceased after 2 min, and strain reached an almost steady level after 3 min. At a tensile stress of 1.5 MPa, a strain of 14.5% on average was produced after 20 min creep in the central specimens; peripheral specimens showed strains of 12.4% on average. There were significant differences in strain between the central and peripheral specimens. The residual strain after 20 min restoration was 0.93% on average and there were no significant regional differences. This creep feature could be well represented by a generalized linear viscoelastic model. It was concluded that the regional differences in viscoelasticity might be caused by the complicated articulating functions of the TMJ, and that the residual strain caused by sustained stress could be an important factor in disc deformation.

Platelet-derived Growth Factor Enhances Proliferation and Matrix Synthesis of Temporomandibular Joint Disc–derived Cells

Platelet-derived growth factor (PDGF) is an essential signaling molecule for wound healing and tissue repair. This study was aimed at evaluating the effect of PDGF on the proliferation of temporomandibular joint (TMJ) disc-derived cells and extracellular matrix synthesis. The number of cultured cells were counted by COULTER Z1. The assay for collagen synthesis was performed using a sircol soluble collagen assay. Hyaluronic acid (HA) synthesis was analyzed by a high performance liquid chromatography. The expression of collagens, matrix metalloproteinases (MMPs), and the tissue inhibitors of metalloproteinases (TIMPs) were examined using SYBR Green in terms of the RNA levels. PDGF treatment significantly (P < .01) increased the proliferation rate of the disc-derived cells as compared with the controls when the dose was 5 ng/ mL or greater. Treatment with more than 5 ng/mL PDGF resulted in an amount of collagen synthesis significantly (P < .01) higher than the controls. HA synthesis was maximal with 5 ng/mL PDGF treatment. Quantitative real-time polymerase chain reaction analyses showed that treatment with 5 ng/mL of PDGF-BB upregulated the mitochondrial RNA levels of type I and II collagens, MMPs, and TIMPs within 6 hours. It is concluded that PDGF, if its concentration is optimal, enhanced proliferation and matrix synthesis of TMJ disc-derived cells, indicating that PDGF may be effective for use in tissue engineering of the TMJ disc.

An adult case of skeletal open bite with a severely narrowed maxillary dental arch.

Surgically assisted rapid maxillary expansion is proposed as an efficient approach for adult patients with transverse maxillary deficiency. This article reports the treatment of an 18-year, seven-month old male patient with an anterior open bite and a severely narrowed upper dental arch. A posterior crossbite was present on both sides. For the correction of the posterior crossbite, a lateral maxillary expansion of more than 8 mm was required. A surgically assisted rapid maxillary expansion with Le Fort I corticotomy and mandibular setback with a sagittal splitting ramus osteotomy were determined as the treatment plan. The total treatment time was 24 months including five months of post-surgical observation. After the treatment, an acceptable occlusion was achieved with a Class I molar relationship. The amount of actual maxillary expansion was 6.3 mm at the canines and 9.7 mm at the first molars. The relapse of the expansion was 0.9 mm and 0.1 mm at the corresponding regions two years after the surgically assisted maxillary expansion. It is emphasized that surgically assisted rapid maxillary expansion is a secure and efficient approach for achieving a desirable lateral maxillary expansion with stability in adult patients demonstrating transverse maxillary deficiency. Furthermore, it is suggested that longterm observation of the maxillary arch width after retention is of a great importance for the maintenance of the acceptable treatment outcome.

Biomechanical response of bovine temporomandibular joint disc to prolonged tensile stress

This study was designed to evaluate the influence of prolonged tensile stress on the viscoelasticity of the temporomandibular joint (TMJ) disc. Twenty discs from 10, 3-year-old cattle were used. Tensile stress of 1.5 MPa was applied to specimens from the discs for 10, 20, 40 and 60 min. Following the prescribed period of tension for creep, the specimens were removed from the tension device and any recovery observed for 20 min. In all specimens, strain increased at the onset of stress application and reached almost steady conditions after 5 min. Although, the strain became slightly larger when the creep time was longer, no significant differences were found in the strains between any two tests with different periods of creep. The residual strain increased significantly with creep duration, and similarly the degree of recovery decreased significantly. In 10- and 20-min creep tests, the residual strains were 0.1 and 1.0%, the specimens in 40- and 60-min tests revealed irreversible changes in length. It was concluded that continuous loading for >40 min causes creep damage in bovine TMJ disc, and that prolonged sustained tension affects the recovery of joint homeostasis.