Katsuhiko Kimoto

Effect of implant-supported or retained dentures on masticatory performance: a systematic review.

STATEMENT OF PROBLEM While subjective patient-based measures have been increasingly recognized as critical outcomes for prosthodontic treatment, there continues to be a need to validate for patients what changes in masticatory function can be expected with the provision of new implant-supported or retained dentures. PURPOSE The purpose of this review was to evaluate the critical factors impacting change in masticatory performance following the provision of new implant-supported or retained dentures. MATERIAL AND METHODS Information retrieval followed a systematic approach using PubMed and the Cochrane Library. English articles published from 1966 to June 2007, in which the masticatory performance of subjects with implant-supported or retained dentures was assessed by objective methods and compared to performance with conventional dentures, were included. Ratings of the evidence provided in each article followed United States Agency for Healthcare Research and Quality recommendations. RESULTS From 281 articles identified, 18 peer-reviewed articles met prespecified criteria for inclusion. Specific outcomes of significance identified by these articles rated as level II are: (1) fixed implant-supported partial dentures do not provide significant improvement in masticatory performance compared to conventional removable partial dentures for Kennedy Class I and II partially edentulous mandibles; (2) the combination of a mandibular implant-supported or retained overdenture (IOD) and maxillary conventional complete denture (CD) provides significant improvement in masticatory performance compared to CDs in both the mandible and maxilla for a limited population having persistent functional problems with an existing mandibular CD due to severely resorbed mandible; and (3) the type of implant and attachment system for mandibular IODs has a limited impact. Specific outcomes of significance identified by articles rated as having a moderate level of evidence (level III) are: (1) mandibular fixed implant-supported complete dentures provide significant improvement in masticatory performance compared to mandibular CDs in subjects dissatisfied with their CDs; and (2) implant-supported mandibular resection dentures have an advantage over conventional dentures in masticatory performance on the defect side of the mouth. CONCLUSIONS Objective benefits in masticatory performance of implant-supported or retained dentures compared to conventional dentures are limited to a mandibular IOD in edentulous patients with a resorbed mandible and/or difficulty adapting to CDs.

N-acetyl cysteine (NAC)-mediated detoxification and functionalization of poly(methyl methacrylate) bone cement.

Currently used poly(methyl methacrylate) (PMMA)-based bone cement lacks osteoconductivity and induces osteolysis and implant loosening due to its cellular and tissue-toxicity. A high percentage of revision surgery following the use of bone cement has become a significant universal problem. This study determined whether incorporation of the amino acid derivative N-acetyl cysteine (NAC) in bone cement reduces its cytotoxicity and adds osteoconductivity to the material. Biocompatibility and bioactivity of PMMA-based bone cement with or without 25mm NAC incorporation was examined using rat bone marrow-derived osteoblastic cells. Osteoconductive potential of NAC-incorporated bone cement was determined by microCT bone morphometry and implant biomechanical test in the rat model. Generation of free radicals within the polymerizing bone cement was examined using electron spin resonance spectroscopy. Severely compromised viability and completely suppressed phenotypes of osteoblasts on untreated bone cement were restored to the normal level by NAC incorporation. Bone volume formed around 25mm NAC-incorporated bone cement was threefold greater than that around control bone cement. The strength of bone-bone cement integration was 2.2 times greater for NAC-incorporated bone cement. For NAC-incorporated bone cement, the spike of free radical generation ended within 12h, whereas for control bone cement, a peak level lasted for 6 days and a level greater than half the level of the peak was sustained for 20 days. NAC also increased the level of antioxidant glutathione in osteoblasts. These results suggest that incorporation of NAC in PMMA bone cement detoxifies the material by immediate and effective in situ scavenging of free radicals and increasing intracellular antioxidant reserves, and consequently adds osteoconductivity to the material.

Cell proliferation in the dentate gyrus of rat hippocampus is inhibited by soft diet feeding.

Background: Recently it has become well accepted that neurogenesis occurs in the dentate gyrus of the hippocampus, a region important to memory and learning function in rodents and humans. Reports show that neurogenesis in the hippocampus is regulated by certain factors, such as exposure to an enriched environment, physical activity, aging and stress. The relationship between the change in the task of chewing as one oral environmental factor, and the mechanisms of hippocampal neuron generation are unclear. Objective: We examined whether cell proliferation varies by chewing tasks with different food textures in the dentate gyrus of the rat hippocampus. Methods: Wistar rats were divided into two groups, one was fed a solid diet, known as the hard-diet feeding group, and the soft-diet feeding group, which was fed a powder diet containing the same components as the solid one for 3, 7, 16 and 24 weeks. Thymidine analog 5-bromo-2′-deoxyuridine (BrdU) was used as a marker of cell proliferation within the dentate gyrus of the hippocampus and olfactory bulb. Results: The results of this study indicated that the total number of BrdU-positive cells in the hippocampal dentate gyrus significantly decreased with aging and were significantly fewer in the soft-diet feeding group than in hard-diet feeding group in 7-, 16- and 24-week-old rats after the BrdU injection. The change of BrdU-positive cell expression between soft and hard diets in 3- and 24-week-old rats was not observed in the olfactory bulb. Conclusion: It has been suggested that cell proliferation in the dentate gyrus of the rat hippocampus is characteristically suppressed by soft diet feeding.

Electrostatic control of protein adsorption on UV-photofunctionalized titanium.

Ultraviolet (UV)-photofunctionalization of titanium to enable the establishment of a nearly complete bone-implant contact was reported recently. However, the underlying mechanism for this is unknown. We hypothesized that UV-treated titanium surfaces acquire distinct electrostatic properties that may play important roles in determining the bioactivity of these surfaces. The objective of this study was to determine the protein adsorption capability of UV-treated titanium surfaces under various electrostatic environments. The amount of albumin adsorbed on UV-treated and untreated titanium disks was evaluated under different pH conditions above and below the isoelectric points of albumin and titanium. The effects of additional treatment with various ionic solutions were also examined. Albumin adsorption on UV-treated surfaces at pH 7.0 was considerably greater (6-fold after 3h of incubation and 2.5-fold after 24h) than that to UV-untreated surfaces. UV-enhanced albumin adsorption was abrogated at pH 3.0 or when these titanium surfaces were treated with anions, while maintaining UV-induced superhydrophilicity. Albumin adsorption on UV-untreated titanium surfaces increased after treating these surfaces with divalent cations but not after treating them with monovalent cations. These results indicated that UV-treated titanium surfaces are electropositively charged as opposed to electronegatively charged UV-untreated titanium surfaces. This distinct UV-induced electrostatic property predominantly regulates the protein adsorption capability of titanium, superseding the effect of hydrophilic status, and converts titanium surfaces from bioinert to bioactive. As a result, direct titanium-protein interactions take place exclusively on UV-treated titanium surfaces without the aid of bridging ions.

Suppression of Stress-induced nNOS Expression in the Rat Hypothalamus by Biting

Nitric oxide (•NO) modulates the activity of the endocrine system in the behavioral response to stress. The purpose of this study was to investigate the effect of restraining the body of an animal on expression of neuronal nitric oxide synthase (nNOS) in the paraventricular nucleus (PVN) of the hypothalamus, and the inhibitory effect of para-masticatory activity on restraint-induced nNOS expression. We observed an increase in nNOS mRNA expression and nNOS-positive neurons in the rat hypothalamus after 30 or 60 min of restraint. Biting on a wooden stick during bodily restraint decreased nNOS mRNA expression in the hypothalamus. In addition, the number of nNOS-positive neurons was significantly reduced in the PVN of the hypothalamus. These observations clearly suggest a possible anti-stress effect of the masticatory activity of biting, and this mechanism might be unconsciously in operation during exposure to psychological stressors.

Soft-diet feeding decreases dopamine release and impairs aversion learning in Alzheimer model rats

To examine the effects of soft-diet feeding on the dopaminergic system in a model rat for Alzheimers disease (AD), we measured dopamine release in the hippocampus using a microdialysis approach and assessed learning ability and memory using step-through passive avoidance tests. Furthermore, we immunohistochemically examined the ventral tegmental area (VTA), which is the origin of hippocampal dopaminergic fibers using tyrosine hydroxylase (TH), a marker enzyme for the dopaminergic nervous system. Feeding a soft diet decreased dopamine release in the hippocampus and impaired learning ability and memory in AD model rats in comparison with rats fed a hard diet; however, TH-immunopositive profiles in the VTA seemed not to be notably different between rats fed a soft diet and those fed a hard diet. These observations suggest that soft-diet feeding enhances the impairment of learning ability and memory through the decline of dopamine release in the hippocampus in AD rats.

Chewing-induced regional brain activity in edentulous patients who received mandibular implant-supported overdentures: A preliminary report

PURPOSE We used functional magnetic resonance imaging (fMRI) to investigate the change in brain regional activity during gum chewing when edentulous subjects switched from mandibular complete dentures to implant-supported removable overdentures. METHODS Four edentulous patients (3 males and 1 female, aged 64 to 79 years) participated in the study. All subjects received a set of new maxillary and mandibular complete dentures (CD), followed by a maxillary complete denture and a new mandibular implant-supported removable overdentures (IOD). A 3-T fMRI scanner produced images of the regional brain activity for each subject that showed changes in the blood-oxygenation-level-dependent (BOLD) contrast in the axial orientation during gum-chewing with CD and IOD. RESULTS Region-of-interest analysis showed that IOD treatment significantly suppressed chewing-induced brain activity in the prefrontal cortex. The chewing-induced brain activities in the primary sensorimotor cortex and cerebellum tended to decrease with IOD treatment, however they did not reach to significance level. There was no change in brain activity in the supplementary motor area, thalamus and insula between gum chewing with CD and IOD. Group comparison using statistical parametrical mapping further showed that, within the prefrontal cortex, the neural activity of the frontal pole significantly decreased during gum-chewing with IOD when compared to that with CD (P<0.05). CONCLUSION Despite the limitation of a small sample size, these results suggest that the gum-chewing task in elderly edentulous patients resulted in differential neural activity in the frontal pole within the prefrontal cortex between the 2 prosthodontic therapies-mandibular CD and IOD.

ESR Detection of ROS Generated by TiO2 Coated with Fluoridated Apatite

Specific materials used in the manufacture of dentures may enhance the removal of micro-organisms. The ultraviolet A (UVA) irradiation of acrylic resin containing titanium dioxide (TiO2) generates reactive oxygen species (ROS) by photocatalysis that shows antibacterial effects. In this study, we tested the hypothesis that TiO2 coated with fluoridated apatite (FAp-TiO2) can generate ROS via photo-catalysis by using electron spin resonance (ESR), and that acrylic resin containing FAp-TiO2 can show antifungal properties by measuring the viability of Candida albicans. We demonstrated that hydroxyl radicals (HO•) were generated through excitation of TiO2, TiO2 coated with apatite (HAp-TiO2), and FAp-TiO2. The HO• generation through excitation of FAp-TiO2 was higher than that of TiO2 and HAp-TiO2. Regarding antifungal activity, cell viability on acrylic resin containing FAp-TiO2 was lower than that of TiO2 and HAp-TiO2. FAp-TiO2 showed superior photocatalytic effects, and these characteristics may lead to novel methods for the clinical application of denture-cleaning treatments.

Effects of biting on elevation of blood pressure and other physiological responses to stress in rats: Biting may reduce allostatic load

We have investigated how biting modulates some of the physiological changes (blood pressure, core temperature, and chemical mediators in the serum) that are induced by restraint stress. We exposed rats to restraint stress for 60 min. Biting on a wooden stick during restraint significantly suppressed the increase of blood pressure at 30, 45, 60, and 75 min and significantly inhibited the rise in core temperature at 30, 60, 120, and 180 min compared with rats that were restrained but did not bite anything. These differences were visible in infrared thermal images of the restraint-only and restraint-with-biting rats after 60 min. Biochemical analysis revealed that biting significantly suppressed increases of plasma interleukin-1beta, interleukin-6, and leptin and that it significantly suppressed a decrease of thyroid-stimulating hormone. These observations suggest that biting produces an anti-stress effect and that para-functional masticatory activity plays an important role in coping with stressful events.

Management of oral candidiasis in denture wearers

In many cases, dentists try to manage denture pain by adjusting dentures. However, some patients complain of oral discomfort over a long period even after appropriate denture adjustments. In some of these situations, simple denture adjustment does not alleviate the discomfort of these patients. It is known that denture stomatitis may occur in response to plaque accumulation on dentures. One of the chief pathogenic microorganisms causing this type of inflammation is Candida albicans. A common symptom of oral candidiasis is pain in the oral mucosa complicated by angular stomatitis. In this paper, we report a case of oral candidiasis that was diagnosed and managed based on the patients complaints.