Toshihiro Hirai

Osteoporosis and reduction of residual ridge in edentulous patients.

The relationship between the height of the mandibular residual ridge and the severity of osteoporosis in elderly edentulous patients was investigated. The height of the mandibular residual ridge was measured by use of the mental foramen on panoramic radiographs. The severity of osteoporosis was determined by examining frontal and lateral radiographs of the vertebrae. All of the patients received a blood analysis. The correlation coefficient between age and the height of residual ridge was -0.38, which was statistically significant (p < 0.01). The residual ridge in women was lower than that of men, showing a statistical significance (p < 0.01). The correlation coefficient was -0.42 between degree of severity of osteoporosis and the height of the residual ridge, which was significant (p < 0.01). The parathyroid hormone level was high in the patients with a low residual ridge, and the calcitonin (CT) level was low. This study indicates that osteoporosis strongly affects reduction of the residual ridge in edentulous patients.

Tongue motor skills and masticatory performance in adult dentates, elderly dentates, and complete denture wearers.

STATEMENT OF PROBLEM For complete denture wearers the tongue plays an important role in the retention and stability of dentures and has a great influence on masticatory function. PURPOSE OF STUDY The purpose of this study was to elucidate the relationship between tongue motor behavior and masticatory function. MATERIAL AND METHODS Thirty healthy, normal adult dentates, 10 normal elderly dentates, and 20 complete denture wearers whose dentures were constructed by the same methods and materials were selected. Tongue motor skills were examined by an ultrasound system and masticatory performance was evaluated by the sieving method. RESULTS The tongue motor skills of elderly dentates and complete denture wearers were statistically lower compared with those of adult dentates (p < 0.05, Duncan test). Tongue motor skills of complete denture wearers were statistically correlated with age (p < 0.01). Masticatory performance was statistically lower in relation to age in complete denture wearers (p < 0.01). The correlation coefficient was 0.74 between tongue motor skill and masticatory performance in complete denture wearers, which was statistically significant (p < 0.01). CONCLUSION Age-related decreases in tongue motor skills and masticatory performance were demonstrated by ultrasound observations and sieving methods.

Effect of Mastication on Functional Recoveries after Permanent Middle Cerebral Artery Occlusion in Rats

OBJECTIVES We evaluated whether solid feed is more effective for functional recoveries than liquid feed in rats with ischemic brain injury after permanent middle cerebral artery occlusion (MCAO). METHODS A total of 36 male Wistar/ST rats were subjected to MCAO or sham surgery. After MCAO or sham surgery, all rats were provided liquid feed for 14 days. Then, all rats were divided into 3 groups: the solid feeding group, the liquid feeding group, and the solid feeding group of sham. Effect of mastication on functional recoveries after permanent MCAO in rats was evaluated by the limb placement test and Morris water maze (MWM) task. RESULTS After surgery, limb placement test scores were equal in both MCAO groups. In the acquisition trials of MWM task, statistically significant differences in escape latency were observed between the liquid feeding group and sham groups at all days, and between the solid feeding group and sham groups at days 3 and 4 of the trials. In the probe trial, statistically significant differences in time spent were observed between the liquid feeding group and sham group. On day 5 of acquisition trials, the time spent in the periphery of the pool in MWM task was significantly different among the 3 groups. CONCLUSION This study suggested that solid diet mastication could be effective for the rehabilitation of sensorimotor and learning/memory dysfunction induced by cerebral infarction.

Ultrasound observations of tongue motor behavior

In this investigation of motor skills of the tongue and age-related changes in motor behavior, upward and downward tongue movements with the teeth in centric occlusion and regulated by a metronome were recorded. The recordings were made by use of ultrasound diagnostic equipment with a 5 MHz electronic convex section scanning probe and a physiologic signal unit connected to a heart sound microphone in a group of young subjects and a group of older subjects. The results were as follows. (1) The system provided a useful method to evaluate motor skills of the tongue with sound signals showing clear images of the tongue surface and its movements. (2) The rhythm of tongue movements in older persons varied more than in younger persons. (3) The velocity in the upward and downward movements decreased and were statistically significant (p less than 0.01) in the older group. (4) The time lag between the sound signal and the start of touching the palate and floor of the mouth was longer (p less than 0.01) and the variations were greater in the older group. (5) The study showed age-related changes in motor behavior of the tongue.

The expression of IGF‐I and myostatin mRNAs in skeletal muscle of hypophysectomized and underfed rats during postnatal growth

Aim:  To determine the roles of myostatin and insulin‐like growth factor‐I (IGF‐I) during postnatal growth, we examined IGF‐I and myostatin mRNA expression in the skeletal muscles of hypophysectomized and underfed rats during postnatal growth.

cGMP activates a pH-sensitive leak K+ current in the presumed cholinergic neuron of basal forebrain.

In an earlier study, we demonstrated that nitric oxide (NO) causes the long-lasting membrane hyperpolarization in the presumed basal forebrain cholinergic (BFC) neurons by cGMP-PKG-dependent activation of leak K+ currents in slice preparations. In the present study, we investigated the ionic mechanisms underlying the long-lasting membrane hyperpolarization with special interest in the pH sensitivity because 8-Br-cGMP-induced K+ current displayed Goldman-Hodgkin-Katz rectification characteristic of TWIK-related acid-sensitive K+ (TASK) channels. When examined with the ramp command pulse depolarizing from -130 to -40 mV, the presumed BFC neurons displayed a pH-sensitive leak K+ current that was larger in response to pH decrease from 8.3 to 7.3 than in response to pH decrease from 7.3 to 6.3. This K+ current was similar to TASK1 current in its pH sensitivity, whereas it was highly sensitive to Ba(2+), unlike TASK1 current. The 8-Br-cGMP-induced K+ currents in the presumed BFC neurons were almost completely inhibited by lowering external pH to 6.3 as well as by bath application of 100 microM Ba(2+), consistent with the nature of the leak K+ current expressed in the presumed BFC neurons. After 8-Br-cGMP application, the K+ current obtained by pH decrease from 7.3 to 6.3 was larger than that obtained by pH decrease from pH 8.3 to 7.3, contrary to the case seen in the control condition. These observations strongly suggest that 8-Br-cGMP activates a pH- and Ba(2+)-sensitive leak K+ current expressed in the presumed BFC neurons by modulating its pH sensitivity.

Effect of wearing a palatal plate on swallowing function

PURPOSE The purpose of this study was to determine the effect of wearing a palatal plate on swallowing function. METHODS The subject group consisted of 10 healthy, fully dentate males. Two experimental palatal plates (EPP) were used in this study: one was 1.4mm thick (EPP1), and the other was 2.8mm thick (EPP2). Tongue movements and swallowing sounds were simultaneously recorded. The position of the surface of the tongue was recorded by using ultrasound diagnostic equipment in the sagittal plane. Swallowing tests were performed under three conditions: without EPP (WOE), with EPP1 (WP1), and with EPP2 (WP2). Swallowing index (SI) and tongue contact time (TCT) was calculated. RESULTS The value of SI was lowest under WOE, and highest under WP2, with a statistically significant difference. There was no statistical significance, however, between SI under WOE and that under WP1. The value of TCT was longest under WOE, and shortest under WP2, with a statistically significant difference. CONCLUSIONS This investigation suggests that the thickness of a palatal plate influences SI and TCT, which correlate with swallowing function.

Parasympathetic vasodilator fibers in rat digastric muscle

The present study examined whether parasympathetic vasodilator fibers exist in rat jaw-opening muscles such as the digastric muscle. The mental nerve was stimulated to activate the parasympathetic vasodilator nerve in the digastric muscle. Electrical stimulation of the mental nerve elicited intensity- and frequency-dependent increases of blood flow in this muscle. These increases were markedly reduced by hexamethonium in dose- and time-dependent manners, but pretreatment with phentolamine or propranolol had no effect. Pretreatment with atropine also attenuated the increase in blood flow in digastric muscle. When retrograde fluorogold was injected into the digastric muscle, labeled neurons were observed in the otic ganglion only on the ipsilateral side, but not in the pterygopalatine ganglion of either side. These results indicate that parasympathetic vasodilator fibers originate from cell bodies in the otic ganglion in rat digastric muscle.

Reinforcement of Adhesion between Precious Metal Alloys and Adhesive Heat-curing Type Resin Containing 4-META. Applying of Internal Oxidation Particles and SnO Electro-plating.

The purpose of the present study was to reinforce the strength of the bonding between dental precious metal alloys and adhesive heat-curing type resin.Three kinds of precious metal alloys were treated with three kinds of surface treatment methods, high temperature oxidation with pickling by acid solution and SnO electro-plating method, high temperature oxidation with pickling by acid solution, and only SnO electro-plating method. Adhesive heat-curing type resin containing 4-META was cured on the treated alloy surfaces. The adhesiveness was evaluated by a shear bonding strength test and a pigment percolation test after thermal cycling.The results were as follows:1. The porous structure on the alloy surface formed internal oxidation particles after pickling effectively reinforced the mechanical retention between alloys and resin.2. The SnO electro-plating effectively increased the chemical adhesion between alloys and resin.3. The method with internal oxidation and subsequent SnO electro-plating superiorly increased the durability and adhesiveness of alloys and resin.

1405 Effect of occlusal and masticatory function on acetylcholine and cholinergic neurons in aging rat brain

Masumi Endoh’, Akira Ueki3, Keikichi Takahashi2, Hideki Yamanaka2, Shinzo Izumi’, Takeshi Tabira2 In our previous study, elderly leprosy patients have a low prevalence of senile dementia of Alzheimer type (SDAT), but the frequency of apolipoprotein E (apo E) ~4 is elevated in non-demented elderly leprosy patients. Recent study has shown that Alzheimer’s disease (AD) risk associated with apo E ~4 is significantly increased by the al-antichymotrypsin (ACT)genotype AA. Therefore, we examined an association between ACT polymorphism and apo E ~4 allele in 350 leprosy patients. None of our data found the association of ACT genotype and apo E ~4 allele in leprosy patients. The allelic frequencies of the ACT gene did not differ even between demented patients with leprosy and age-matched controls. Our present data suggest that ACT polymorphism is not associated with the increased frequency of apo E4 in leprosy patients.