Tetsuro Konoo

Correlation between the Appearance of Neuropeptides in the Rat Trigeminal Ganglion and Reinnervation of the Healing Root Socket after Tooth Extraction

The neuropeptide substance P (SP) modulates bone metabolism. This study examined the temporal appearance of the neuropeptides SP and brain-derived nerve growth factor (BDNF) and their receptors (neurokinin-1 receptor (NK1-R) and Trk B, respectively) in the rat trigeminal ganglion to investigate the role of neuropeptides in healing after tooth extraction. Rats were anesthetized and their upper right first molars were extracted; the rats were sacrificed 3 hours and 1–21 days after extraction. Their trigeminal ganglion and maxilla were removed, and cryosections were prepared and immunostained using specific antibodies against SP, BDNF, NK1-R, and Trk B. In the tooth sockets after extraction, new bone and a few SP-immunoreactive nerve fibers were first seen at day 7, and bone completely filled the sockets at day 21. In the trigeminal ganglion, the proportions of NK1-R-, BDNF-, and Trk B-immunoreactive neurons changed similarly, i.e., they initially decreased, increased rapidly to maximum levels by day 3, and then decreased gradually to control levels until 21 days. These findings suggest that the appearance of neuropeptides in the trigeminal ganglion, the reinnervation of SP-immunoreactive nerve fibers, and bone repair in the tooth socket during healing after extraction were correlated.

Effect of 8-hour intermittent orthodontic force on osteoclasts and root resorption

INTRODUCTION The duration of force application is an important factor in optimizing orthodontic tooth movement with less root resorption. It has previously been shown that the amount of tooth movement achieved by 8-hour intermittent force application exceeds what would be the expected by the duration. The purpose of this study was to compare osteoclast recruitment and the extent of root resorption in response to an 8-hour intermittent force regimen with those from a continuous force. METHODS Rat molars (n = 110) were assigned to 3 groups: 8-hour intermittent force, continuous force, and control. A coil spring that exerted 40 cN of force was suspended between the maxillary first molars and the incisors. At 1, 3, 5, 7, and 14 days, osteoclast numbers, osteoclast surfaces, and root resorption were quantified histomorphometrically in the undecalcified sections and statistically analyzed. RESULTS At the mesial sites, osteoclast numbers in the intermittent force group were 100.5% of the continuous force group, and osteoclast surfaces in the intermittent force group were 68.2% of the continuous force group. At the mesial sites, root resorption of the intermittent group was approximately 30.0% of the continuous group (P <0.01). CONCLUSIONS Our results show that an 8-hour intermittent force efficiently recruits osteoclasts while causing minimal root resorption.

Neuropeptides modulate RANKL and OPG expression in human periodontal ligament cells

Abstract Neuropeptides, such as substance P (SP) and calcitonin gene-related peptide (CGRP), may be associated with bone remodeling in response to mechanical stress during orthodontic tooth movement. To investigate this hypothesis, we examined the effects of neuropeptides on the expression of receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) in human periodontal ligament (PDL) cells under compression in vitro. PDL cells were subjected to compressive force (2.0 g/cm2) continuously in the presence or absence of SP or CGRP for 2–4 days. The expression of the SP receptor, neurokinin 1-receptor (NK1-R), in PDL cells was confirmed by RT–PCR and immunofluorescent staining. The effects of neuropeptides (SP and CGRP) on the expression of RANKL and OPG mRNA were determined using RT–PCR. PDL cells constitutively expressed NK1-R on both the mRNA and protein levels. Compressive force decreased OPG mRNA expression and increased RANKL mRNA expression. In the presence of neuropeptides, the OPG level decreased synergistically with compression. Neuropeptides stimulated RANKL expression without compression, whereas they decreased RANKL mRNA expression with compression. These results indicate that PDL cell compression induces the up-regulation of RANKL and down-regulation of OPG, whereas neuropeptides suppress the RANKL expression induced by compression. Therefore, the neuropeptides SP and CGRP may modulate bone remodeling by PDL cells during orthodontic tooth movement.

Alterations of the Temporomandibular Joint on Magnetic Resonance Imaging according to Growth and Development in Schoolchildren

The paper explains the alterations of the temporomandibular joint (TMJ) visualized by magnetic resonance imaging (MRI) according to the growth and development of schoolchildren. Appearance and disappearance of a “double contour-like structure” (DCLS) of the mandibular condyle on MRI according to the growth and development of schoolchildren were demonstrated. In addition, possible constituents of DCLS and the significance of detection of DCLS on MRI were also speculated. The relationship between red marrow and yellow marrow in the articular eminence of temporal bone, the disappearance of DCLS, and alterations of the mandibular condyle have been elucidated.