Kazunori Yamaguchi

Electromyographic Activity of Lower Lip Muscles When Chewing with the Lips in Contact and Apart

Masticatory muscle activity is coordinated with perioral muscle during chewing. Subjects with competent lips usually chew with the lips in light contact, whereas subjects with incompetent lips possibly have dysfunctional chewing. In this study, the electromyographic (EMG) activities of the lower lip and masseter muscles were recorded when chewing with the lips in contact and apart. At first, 37 subjects were divided into an incompetent lip group and competent lip group on the basis of EMG activity of the lower lip muscle at rest. The durations of the masseter nonactive phase and total phase when chewing with lips in contact were shorter in the incompetent lip group than in the competent lip group. In the incompetent lip group, when chewing with the lips apart, the EMG activity of lower lip in the masseter nonactive phase was significantly (P < .05) higher than in the competent lip group, but there was no difference in the EMG activity in the masseter active phase between two groups. Our results suggest that subjects with incompetent lips have difficulty chewing while their lips are relaxed. We conclude that the inability of sealing the lips and lip dysfunction could possibly affect masticatory function.

Activation of satellite glial cells in rat trigeminal ganglion after upper molar extraction.

The neurons in the trigeminal ganglion (TG) are surrounded by satellite glial cells (SGCs), which passively support the function of the neurons, but little is known about the interactions between SGCs and TG neurons after peripheral nerve injury. To examine the effect of nerve injury on SGCs, we investigated the activation of SGCs after neuronal damage due to the extraction of the upper molars in rats. Three, 7, and 10 days after extraction, animals were fixed and the TG was removed. Cryosections of the ganglia were immunostained with antibodies against glial fibrillary acidic protein (GFAP), a marker of activated SGCs, and ATF3, a marker of damaged neurons. After tooth extraction, the number of ATF3-immunoreactive (IR) neurons enclosed by GFAP-IR SGCs had increased in a time-dependent manner in the maxillary nerve region of the TG. Although ATF3-IR neurons were not detected in the mandibular nerve region, the number of GFAP-IR SGCs increased in both the maxillary and mandibular nerve regions. Our results suggest that peripheral nerve injury affects the activation of TG neurons and the SGCs around the injured neurons. Moreover, our data suggest the existence of a neuronal interaction between maxillary and mandibular neurons via SGC activation.

Clinical estimation of mouth breathing

INTRODUCTION Breathing mode was objectively determined by monitoring airflow through the mouth, measuring nasal resistance and lip-seal function, and collecting information via questionnaire on the patients etiology and symptoms of mouth breathing. METHODS The expiratory airflow through the mouth was detected with a carbon dioxide sensor for 30 minutes at rest. Fifteen men and 19 women volunteers (mean age, 22.4 +/- 2.5 years) were classified as nasal breathers, complete mouth breathers, or partial mouth breathers based on the mean duration of mouth breathing. Nasal resistance, lip-sealing function, and the subjective symptoms of mouth breathing ascertained by questionnaire were statistically compared by using 1-way and 2-way analysis of variance (ANOVA) and the chi-square test in the breathing groups. RESULTS Nasal resistance was significantly (P <0.05) greater for the mouth breathers than for the nasal breathers, and significantly (P <0.05) greater for the partial mouth breathers than for the complete mouth breathers. There were no significant differences in the subjective responses to questions about mouth breathing among the 3 groups. CONCLUSIONS Detecting airflow by carbon dioxide sensor can discriminate breathing mode. Degree of nasal resistance and subjective symptoms of mouth breathing do not accurately predict breathing mode.

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.

Hemokinin-1 competitively inhibits substance P-induced stimulation of osteoclast formation and function

Hemokinin-1 (HK-1) is a novel member of the tachykinin family that is encoded by preprotachykinin 4 (TAC4) and shares the neurokinin-1 receptor (NK1-R) with substance P (SP). Although HK-1 is thought to be an endogenous peripheral SP-like endocrine or paracrine molecule in locations where SP is not expressed, neither the distribution of HK-1 in the maxillofacial area nor the role HK-1 in bone tissue have been examined. In this study, we investigated the distribution of HK-1 in trigeminal ganglion (TG) and maxillary bone, and assessed the expression of HK-1 during osteoclast differentiation. In vivo, rat molars were loaded for 5 days using the Waldo method. In vitro, rat osteoclast-like cells were induced from bone marrow cells. HK-1 distribution and expression were examined by immunofluorescence staining and reverse transcription polymerase chain reaction (RT-PCR). In vivo, HK-1 was localized in rat TG neurons; however, the number of HK-1-positive neurons was less than that of SP-positive neurons. In the maxillary bone, nerve fibers, blood vessels, and osteocytes were immunopositive for HK-1. Furthermore, HK-1-positive immunoreactivity was found in osteoclasts on the pressure side. In vitro, PCR showed that TAC4 and NK1-R mRNA was expressed in osteoclasts as well as in bone marrow cells. Although SP (10⁻⁷ M) treatment led to an increased number of osteoclasts, HK-1 (10⁻⁷ M) treatment did not. The numbers of biotin-labeled HK-1 peptides bound osteoclasts significantly decreased upon incubation with unlabeled SP and biotin-labeled HK-1 compared with biotin-labeled HK-1 alone. These results suggest that HK-1 may not stimulate the differentiation and function of osteoclasts. SP-stimulated osteoclast formation is competitively regulated by peripheral HK-1 through NK1-Rs.

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.

The effect of mouth breathing on chewing efficiency

OBJECTIVE To examine the effect of mouth breathing on chewing efficiency by evaluating masticatory variables. MATERIALS AND METHODS Ten adult nasal breathers with normal occlusion and no temporomandibular dysfunction were selected. Subjects were instructed to bite the chewing gum on the habitual side. While breathing through the mouth and nose, the glucide elution from the chewing gum, number of chewing strokes, duration of chewing, and electromyography (EMG) activity of the masseter muscle were evaluated as variables of masticatory efficiency. RESULTS The durations required for the chewing of 30, 60, 90, 120, 180, and 250 strokes were significantly (P < .05) longer while breathing through the mouth. There was no significant difference in the glucide elution rate (%) for each chewing stroke between nose and mouth breathings. The glucide elution rates for 1- and 3-minute chewing were significantly (P < .05) lower while breathing through the mouth. However, there was no significant difference in the glucide elution rate for 5-minute chewing between nose and mouth breathings. While chewing for 1, 3, and 5 minutes, the chewing stroke and EMG activity of the masseter muscle were significantly (P < .05) lower during mouth breathing. CONCLUSIONS It takes a longer amount of time to complete chewing to obtain higher masticatory efficiency when breathing through the mouth. Therefore, mouth breathing will decrease the masticatory efficiency if the duration of chewing is restricted in everyday life.

Nerve Growth Factor Involves Mutual Interaction between Neurons and Satellite Glial Cells in the Rat Trigeminal Ganglion

Nerve growth factor (NGF) plays a critical role in the trigeminal ganglion (TG) following peripheral nerve damage in the oral region. Although neurons in the TG are surrounded by satellite glial cells (SGCs) that passively support neural function, little is known regarding NGF expression and its interactions with TG neurons and SGCs. This study was performed to examine the expression of NGF in TG neurons and SGCs with nerve damage by experimental tooth movement. An elastic band was inserted between the first and second upper molars of rats. The TG was removed at 0–7 days after tooth movement. Using in situ hybridization, NGF mRNA was expressed in both neurons and SGCs. Immunostaining for NGF demonstrated that during tooth movement the number of NGF-immunoreactive SGCs increased significantly as compared with baseline and reached maximum levels at day 3. Furthermore, the administration of the gap junction inhibitor carbenoxolone at the TG during tooth movement significantly decreased the number of NGF-immunoreactive SGCs. These results suggested that peripheral nerve damage may induce signal transduction from neurons to SGCs via gap junctions, inducing NGF expression in SGCs around neurons, and released NGF may be involved in the restoration of damaged neurons.

Changes of Chewing Movement Before and After Orthognathic Surgical Treatment in Skeletal Class III Patients

Orthognathic surgical treatment has been provided for many patients with skeletal Class M malocclusion in order to correct deviated dentofacial morphology and to improve the impeded oro-facial function. In this study, we investigated the relationship between dentofacial morphology and mandibular movement in subjects with skeletal Class M malocclusion, while they were chewing gum. The subjects were 16 patients with skeletal Class M malocclusion scheduled to undergo orthognathic surgical treatment (jaw deformity group) and 21 with norrnal occlusion (normal group). In the jaw deformity group, records taken before treatment and at 1-6 months after completion of active treatment were used for this study. The dentofacial morphology was analyzed using lateral roentgen cephalograms. The rnandibuiar movement was recorded by tracing the incisal point (the midpoint between mandibular central incisors) while chewing gum using the integrated jaw function testing system (gnathohexagraph system, JM-1000, Ono Sokki Tokyo, Japan). The following results were obtained, 1. The mean duration of a chewing cycle was significantly longer in the jaw deformity group than in the normal group, 2. After treatment, the mean duration got shorter and approached that in the normal