S Minagi

Okayama University, Okayama, Okayama, Japan

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Publications (112)207.4 Total impact

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    ABSTRACT: Experimental loss of occlusal support caused by the extraction or grinding of molar teeth has been reported to foment the impairment of learning and memory in laboratory animals. The purpose of this study was to examine the effect of occlusal reconstruction after long-term loss of molars on spatial memory by using 8-arm radial maze and by assessing histopathological changes of neuron density in the hippocampus. Experimental dentures were inserted into the oral cavities of molarless rats to recover the occlusal support. Age-matched groups of control, molarless and denture-wearing rats were trained to perform the maze tasks. The difference of the error incidence in the maze task was evaluated between three groups. The difference of neuron density between three groups was also evaluated at the end of the maze task. Serum corticosterone levels were also measured to estimate the chronic stress, which could be caused by extraction, insertion of the experimental denture or any experimental procedure. The error incidence in the denture-wearing group was significantly higher than that of the control group, but significantly lower than that of the molarless group. Significant differences of neuron density were observed between three groups in each of the hippocampal CA1, CA3 and DG subfields. No significant difference of the serum corticosterone levels between three groups could be observed. From the results of this study, it was suggested that the recovery of occlusal support would bring amelioration of cognitive impairment concomitant with long period loss of molars in rats.
    Journal of Oral Rehabilitation 06/2014; · 2.34 Impact Factor
  • T. Sanagawa, T. Hara, S. Minagi
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    ABSTRACT: Aim of this study was to quantitatively evaluate the adaptation of the denture base to the mucosa using a non-setting pressure-indicating paste and to examine the relationship between quality of fit and the need for denture relining. A total of 123 dentures from 70 partially edentulous patients were studied. Examination paste extruded from the tip of the 18-G needle was applied to those denture surfaces contacting the alveolar crest. The denture was manually positioned with all clasps engaged on abutment teeth, and adaptation was assessed through paste distribution. Multiple logistic regression was used to analyse variables associated with diagnosing the need for a denture reline, producing odds ratios and 95% confidence intervals. The spread width was inversely proportional to the gap between the denture and mucosa. Regression analysis revealed statistically significant associations between the need for a denture reline and both the paste spread width and the duration of denture use. According to ROC curve analysis of the ‘reline’ and ‘non-reline’ groups, the need for a denture reline was indicated at a paste spread width of 2·0 mm or less. At this 2·0-mm threshold, the sensitivity was 85·1% and the specificity was 75·0%. The fit of removable denture bases was quantitatively evaluated by measuring the spread width of non-setting pressure-indicating paste extruded onto denture fit surfaces. The results suggest that the paste spread width is a useful parameter for discriminating the need for a denture reline.
    Journal of Oral Rehabilitation 06/2014; · 2.34 Impact Factor
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    ABSTRACT: Although body posture in relation to the dental condition has been of great interest in the dental profession, rumination bias has been a substantial obstacle to achieving a reliable objective evaluation of the intrinsic body posture. The aim of this study was to establish a posture control protocol that would minimize the effect of bias.
    Cranio: the journal of craniomandibular practice 04/2014; 32(2):98-103. · 1.11 Impact Factor
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    ABSTRACT: Previous work suggests a relationship between sustained low-level tooth clenching and the aetiology of myogenous temporomandibular disorder (TMD) pain. This study aimed to establish a reliable system with which to evaluate low-level electromyographic (EMG) activity related to low-level tooth clenching while discriminating speech activity, which is one of the most common facial muscle activities to be discriminated from low-level clenching. This device should facilitate the clinical evaluation of awake muscle activity in TMD patients. Eight female and eight male subjects (38·9 ± 11·3 years) participated in the study to evaluate the validity of estimation of speech duration. Actual speech duration was defined by one examiner by pointing out the timing of beginning and end point of each speech on wave-editing software. Speech duration, as detected by a voice sensor system, which was activated by a voice loudness of 54·71 ± 5·00 dB, was significantly correlated with the above actual speech duration (P < 0·01, R2 = 0·9935). An actual recording with the system was carried out in one TMD patient and one healthy volunteer and revealed that the duration of diurnal EMG activity higher than 5% MVC was 1649·16 s and 95·99 s, respectively. As the voice sensor system adopted in this study could define the exact onset and offset of each segment of speech, EMG activity during speech could be precisely discriminated. The results of this study demonstrate that the EMG system with voice sensor system would be an effective tool for the evaluation of low-level masticatory muscle activity.
    Journal of Oral Rehabilitation 04/2014; 41(4). · 2.34 Impact Factor
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    ABSTRACT: One obstacle to placing artificial posterior teeth in manufacturing complete dentures is a reduction of the space between the maxilla and the mandible. Occasionally, second molar placement is not performed, as it does not affect aesthetics, phonetics or comfort. The aim of this study was to compare the masticatory efficiency between patients wearing maxillary and mandibular complete dentures with reduced dental arches (without second molars) (WSM) and with full dental arches (FDA). Twenty subjects were divided into two groups and randomly received new complete dentures. Patients in Group 1 were given dentures WSM, and those in Group 2 were given dentures with FDA. After the post-placement visits, an initial masticatory efficiency test was performed with Optocal, an artificial test food. Fifteen days later, second molars were placed in Group 1 and removed from Group 2, and a new test was performed. Comminuted material was treated and sieved under vibration. The mean and standard deviation of masticatory efficiency with FDA were 10·4 and 8·1, respectively. In the tests WSM, the mean and standard deviation were 8·4 and 3·3, respectively. After removing the second molars in Group 2 and adding them in Group 1, the mean and standard deviation were 15·7 and 14·7 for Group 1 and 12·5 and 10·4 for Group 2, respectively. Within the limitations of this study, placing artificial teeth up to the first molars can be performed when needed without compromising masticatory efficiency.
    Journal of Oral Rehabilitation 04/2014; · 2.34 Impact Factor
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    ABSTRACT: The present study aimed to identify the effect of memory-related genes on male rats tested for spatial memory with either molar teeth extraction or its restoration by occlusal support using experimental dentures. Memory-related genes were detected from hippocampi of male Wistar rats (exposed to teeth extraction with or without dentures, or no extraction (control)) (7-week old) after behavioural testing (via the radial maze task) using a DNA microarray. The time course of the expression of these genes was evaluated by quantitative real-time polymerase chain reaction (PCR) (on 49-week-old rats). In preliminary experiments, to determine which memory genes are affected by spatial memory training, DNA microarray analysis revealed that thyrotropin-releasing hormone (Trh) and tenascin XA (Tnxa) were up-regulated and neuronatin (Nnat) and S100a9 were down-regulated after the maze training. The expression of Tnxa, Nnat and S100a9 of 49-week-old rats (during the time course) via quantitative real-time PCR was consistent with the results of microarrays of the preliminary experiment. Expression of Trh that was evaluated by quantitative real-time PCR did not agree with the results for this gene from the microarray for all groups. Therefore, expression of Trh may have increased in only young, trained rats. The expression of S100a9 prior to the maze task was down-regulated in only the extraction group. These results demonstrated that Trh, Tnxa and Nnat genes were affected according to the degree of memory in male rats. This study also indicated that S100a9 is a memory-related gene, which is affected by the presence of occlusal support.
    Archives of oral biology 02/2014; 59(2):133-41. · 1.65 Impact Factor
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    ABSTRACT: Because food texture is regarded as an important factor for smooth deglutition, identification of objective parameters that could provide a basis for food texture selection for elderly or dysphagic patients is of great importance. We aimed to develop an objective evaluation method of mastication using a mixed test food comprising foodstuffs, simulating daily dietary life. The particle size distribution (>2 mm in diameter) in a bolus was analysed using a digital image under dark-field illumination. Ten female participants (mean age ± s.d., 27·6 ± 2·6 years) masticated a mixed test food comprising prescribed amounts of rice, sausage, hard omelette, raw cabbage and raw cucumber with 100%, 75%, 50% and 25% of the number of their masticatory strokes. A single set of coefficient thresholds of 0·10 for the homogeneity index and 1·62 for the particle size index showed excellent discrimination of deficient masticatory conditions with high sensitivity (0·90) and specificity (0·77). Based on the results of this study, normal mastication was discriminated from deficient masticatory conditions using a large particle analysis of mixed foodstuffs, thus showing the possibility of future application of this method for objective decision-making regarding the properties of meals served to dysphagic patients.
    Journal of Oral Rehabilitation 01/2014; · 2.34 Impact Factor
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    ABSTRACT: The role of parafunctional masticatory muscle activity in tooth loss has not been fully clarified. This study aimed to reveal the characteristic activity of masseter muscles in bite collapse patients while awake and asleep.
    PLoS ONE 01/2014; 9(7):e101882. · 3.53 Impact Factor
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    ABSTRACT: To evaluate the role of the masticatory area in the cerebral cortex in the masticatory-salivary reflex, we investigated submandibular salivary secretion, jaw-movement trajectory and electromyographic activity of the jaw-opener (digastric) and jaw-closer (masseter) muscles evoked by repetitive electrical stimulation of the cortical masticatory area in anesthetized rats. Rats have two cortical masticatory areas: the anterior area (A-area) in the orofacial motor cortex, and the posterior area (P-area) in the insular cortex. Our defined P-area extended more caudally than the previous reported one. P-area stimulation induced vigorous salivary secretion (about 20µl/min) and rhythmical jaw movements (3-4Hz) resembling masticatory movements. Salivary flow persisted even after minimizing jaw movements by curarization. A-area stimulation induced small and fast rhythmical jaw movements (6-8Hz) resembling licking of solutions, but not salivary secretion. These findings suggest that P-area controls salivary secretion as well as mastication, and may be involved in the masticatory-salivary reflex.
    Brain research 12/2013; · 2.46 Impact Factor
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    ABSTRACT: OBJECTIVES: The functional monomer 10-methacryloxydecyl dihydrogen phosphate (10-MDP), recently used in more self-etch adhesives, chemically bonds to hydroxyapatite (HAp) and thus tooth tissue. Although the interfacial interaction of the phosphoric-acid functional group of 10-MDP with HAp-based substrates has well been documented, the effect of the long carbon-chain spacer of 10-MDP on the bonding effectiveness is far from understood. METHODS: We investigated three phosphoric-acid monomers, 2-methacryloyloxyethyl dihydrogen phosphate (2-MEP), 6-methacryloyloxyhexyl dihydrogen phosphate (6-MHP) and 10-MDP, that only differed for the length of the carbon chain, on their chemical interaction potential with HAp and dentin, this correlatively using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Commercial 6-MHP and 10-MDP containing adhesives were investigated as well. RESULTS: XRD revealed that on HAp only 10-MDP produced monomer-calcium salts in the form of 'nano-layering', while on dentin all monomers produced 'nano-layering', but with a varying intensity in the order of 10-MDP>6-MHP>2-MEP. TEM confirmed that 10-MDP formed the thickest hybrid and adhesive layer. XRD and TEM revealed 'nano-layering' for all commercial adhesives on dentin, though less intensively for the 6-MHP containing adhesive than for the 10-MDP ones. SIGNIFICANCE: It is concluded that not only the phosphoric-acid group but also the spacer group, and its length, affect the chemical interaction potential with HAp and dentin. In addition, the relatively strong 'etching' effect of 10-MDP forms more stable monomer-Ca salts, or 'nano-layering', than the two shorter carbon-chain monomers tested, thereby explaining, at least in part, the better bond durability documented with 10-MDP containing adhesives.
    Dental materials: official publication of the Academy of Dental Materials 06/2013; · 2.88 Impact Factor
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    ABSTRACT: OBJECTIVE: A theoretical model, based on fluid dynamics, was developed to measure impression pressure. The purpose of this study was to evaluate the validity of this theoretical model by comparing its theoretical analysis against actual pressure measurements conducted using an impression tray and edentulous oral mucosa analog embedded with pressure sensors. METHODS: In the theoretical model, a hollow tube was mounted onto an impression tray by penetrating through the tray. When force was applied to the tray, pressure was produced which then caused the impression material to flow into the hollow tube. Length of impression material which flowed into tube was denoted as l. In the calculation formula for theoretical model, pressure impulse I was expressed as a function of impression flow length l. For actual pressure measurements, four electric pressure sensors were embedded in an experimental edentulous arch. To visually observe and measure length of impression material flow, four transparent silicon tubes were mounted vertically at different positions on tray. During tray seating, impression material flowed into tubes and pressure which caused material flow movement was measured by the embedded sensor at each tube's position. RESULTS: Based on actual pressure measurements under one experimental condition, regression analysis of pressure data acquired from electric sensors yielded the formula, Y=0.056X2+0.124X. Based on theoretical analysis using a particular viscosity value, the numerical formula yielded was Y=0.057X2, which resembled that of the regression formula. SIGNIFICANCE: Theoretical model presented in this paper augured well for clinical application as an easy and economical means to examine magnitude and distribution of impression pressure by measuring lengths of impression material flow in tubes fixed to impression tray.
    Dental materials: official publication of the Academy of Dental Materials 03/2013; · 2.88 Impact Factor
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    ABSTRACT: OBJECTIVE: The study aims to investigate the dynamic perception of a force applied to the upper first molar for different rates of force increase. DESIGN: Six volunteers (four male and two female; mean age, 27.2±2.4 years) with full natural dentition (except for the third molars) participated in this study. The psychophysical threshold for a force applied to the right maxillary first molar and the reaction time corresponding to each threshold were measured for rate of force increase of 103.74, 236.23, 354.58, 478.22 and 584.63mNs(-1). The physical impulse, which is the integral of force over time, was calculated for each threshold. RESULTS: Psychophysical thresholds in the upper first molar increased with the rate of force increase. The reaction time corresponding to each threshold decreased with increasing force rate. Impulses corresponding to each threshold were independent of force rate. CONCLUSIONS: In the present study, the psychophysical threshold for a force applied to a molar tooth was shown to change depending on the rate of increase of the exerted force. From the viewpoint of the impulse, the dissipated energy necessary to reach the psychophysical sensation threshold was almost constant, regardless of the rate of force increase.
    Archives of oral biology 02/2013; · 1.65 Impact Factor
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    ABSTRACT: Previous research showed that the functional monomer 10-methacryloxydecyl dihydrogen phosphate (MDP) ionically bonds to hydroxyapatite (HAp) and forms a nano- layered structure at the interface with HAp-based substrates. Such hydrophobic nano-layering is considered to contribute to the long-term durability of the bond to tooth tissue. However, dental adhesives are complex mixtures usually containing different monomers. This study investigated the effect of the monomer 2-hydroxyethylmethacrylate (HEMA) on the chemical interaction of MDP with HAp by x-ray diffraction (XRD), nuclear magnetic resonance (NMR), and quartz crystal microbalance (QCM). We examined the chemical interaction of 5 experimental MDP solutions with increasing concentrations of HEMA. XRD revealed that addition of HEMA inhibits nano-layering at the interface, while NMR confirmed that MDP remained adsorbed onto the HAp surface. QCM confirmed this adsorption of MDP to HAp, as well as revealed that the demineralization rate of HAp by MDP was reduced by HEMA. It was concluded that even though the adsorption of MDP to HAp was not hindered, addition of HEMA inhibited interfacial nano-layering. Potential consequences with regard to bond durability necessitate further research.
    Journal of dental research 09/2012; 91(11):1060-5. · 3.46 Impact Factor
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    ABSTRACT: The objectives of this study were (1) to establish a reliable method for detecting the force threshold of the tooth tactile sensation while avoiding experimenter bias and (2) to examine the effect of occlusal force loading on the threshold for impulsive force stimulation in subjects with normal dentition. Twenty volunteers participated in this study (10 males and 10 females; mean age, 26.6 ± 2.9 years). To simulate the bite force during occlusal tapping, a force-loading device was designed to exert impulsive force to the occlusal surface in the direction parallel to the tooth axis. The impulsive force detection threshold of the periodontal sensation was measured before and after loading 98 N of occlusal force on the left upper first molar for 1 min. Transient mechanical loading of the upper first molar caused an increase in the absolute threshold for impulsive force. This increase did not vanish immediately, and the increment of the threshold was maintained during the remainder of the experiment. A computer-controlled method for the evaluation of tooth tactile sensation using impulsive stimulation was established. Transient occlusal force loading parallel to the tooth axis increases the threshold of periodontal sensation for mechanical impulsive stimulation.
    Odontology 07/2012; · 1.58 Impact Factor
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    ABSTRACT: Objective parameters that could provide a basis for food texture selection for elderly or dysphagic patients have not been established. We, therefore, aimed to develop a precise method of measuring large particles (>2 mm in diameter) in a bolus and an analytical method to provide a scientific rationale for food selection under masticatory dysfunction conditions. We developed a new illumination system to evaluate the ability of twenty female participants (mean age, 23·4 ± 4·3 years) to masticate carrots, peanuts and beef with full, half and one quarter of the number of masticatory strokes. We also evaluated mastication under suppressed force, regulated by 20% electromyographic of the masseter muscle. The intercept and inclination of the regression line for the distribution of large particles were adopted as coefficients for the discrimination of masticatory efficiency. Single set of coefficient thresholds of 0·10 for the intercept and 1·62 for the inclination showed excellent discrimination of masticatory conditions for all three test foods with high specificity and sensitivity. These results suggested that our method of analysing the distribution of particles >2 mm in diameter might provide the basis for the appropriate selection of food texture for masticatory dysfunction patients from the standpoint of comminution.
    Journal of Oral Rehabilitation 02/2012; 39(6):405-10. · 2.34 Impact Factor
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    ABSTRACT: The lifting-up movement of the posterior part of the tongue to touch the palate, which is a requirement for performing physiological functions such as deglutition and speech, is an important phenomenon that is difficult to objectively evaluate. The purpose of this study was to develop a new modality to evaluate the tongue-lifting function, especially in the posterior part of the tongue, and to elucidate the dynamic properties of the tongue in normal subjects. Twenty-three healthy volunteers (9 men and 14 women; mean age, 27·6years) participated in this study. A new device was developed that could evaluate the up-down movement of the posterior part of the tongue in a non-invasive manner. The experimental tasks were as follows: (i) /a/ pronunciation for 1s followed by /ka/ pronunciation (a-ka task), (ii) /a/ pronunciation for 1s followed by /ga/ pronunciation (a-ga task) and (iii) /a/ pronunciation for 1s followed by a voluntary push-up movement of the posterior part of the tongue (a-lift task). Maximum upward velocity in the a-ga task was larger than that in the a-ka task (P<0·05). The a-lift task showed the highest tongue lift range among the three tasks, and the a-ga task showed a higher range than that of the a-ka task (P<0·05). This study revealed that precise quantification of the motility of the posterior part of the tongue, which would be useful in rehabilitation of articulation and/or swallowing, could be achieved using this new device in a non-invasive manner.
    Journal of Oral Rehabilitation 01/2012; 39(5):370-6. · 2.34 Impact Factor
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    ABSTRACT: The activity of the lateral pterygoid muscle has been regarded to be related to the pathological condition of the temporomandibular joint (TMJ) in the craniomandibular disorders. Because the lateral pterygoid muscle is a deep muscle, a needle electrode is necessary for EMG recordings. The purpose of this study was to establish a non-invasive method for the evaluation of muscle activity of the lateral pterygoid muscle using mechanomyogram (MMG). In three male subjects, surface electromyogram (EMG) in the left masseter muscle, left anterior and posterior belly of the temporal muscle, left anterior belly of the digastric muscle and needle EMG of the inferior head of the lateral pterygoid were recorded during mandibular movement tasks simultaneously with the MMG derived from a condenser microphone in the external ear canal. There were significant positive correlations between the needle EMG signal of the lateral pterygoid muscle and the MMG signal for the tasks of static jaw opened position of 30 mm of interincisal distance (p=0.000, R(2)=0.725), static jaw opened position of 40 mm of interincisal distance (p=0.000, R(2)=0.753), 5mm protruded mandibular position (p=0.000, R(2)=0.653), the most protruded mandibular position (p=0.000, R(2)=0803). On the contrary, for the task of maximal clenching, there was no significant correlation between the EMG signal of the lateral pterygoid muscle and the MMG signal. These results suggest that the activity of the lateral pterygoid muscle could be evaluated by the MMG signals recorded in the external ear canal, unless jaw closing major muscles show active contraction.
    Journal of neuroscience methods 01/2012; 203(1):157-62. · 2.30 Impact Factor
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    ABSTRACT: For healthy chewing, well equilibrated occlusion is necessary to minimize unexpected overloading of the tooth. However, the current occlusal examination depends on techniques, skills and sense of doctors. In this research, we are focusing on that occlusal condition is related to sound from teeth, and have developed a novel occlusal checking system detecting the sound. The system is configured with multiple sound detecting devices. Each device consists of a soft suction cup and a miniature microphone. The suction cup can be adhered on a tooth by applying negative pressure through a tube, and the microphone is inserted into the tube. Therefore when a patient bites, generated sound from the target tooth can be detected by the microphone. First, we have found out the relationship between adhesion force and applied negative pressure to the suction cup, and decided optimum value of negative pressure. Then, by using two devices, we have conducted experiments of detecting occlusal sound using a jaw model for confirming the potential of this system. Furthermore, we carried out the experiments in the oral cavity, and we succeeded in detecting sounds from tooth by using fabricated devices.
    Mechatronics and Machine Vision in Practice (M2VIP), 2012 19th International Conference; 01/2012
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    ABSTRACT: To clarify the effects of the addition of silanized (S) and unsilanized (U) spherical silica filler to resin-modified glass-ionomer cement and of powder-liquid ratio on (1) the early marginal gap-width of restorations in both tooth cavities and Teflon molds, (2) the gap-formation of restorations in Class V cavities, and (3) the compressive strength of the cement. Resin-modified glass-ionomer powder (Fuji II LC EM, GC) was modified by adding 5 and 10 wt% of powder respectively, of S and U, and then the powder-liquid ratio was increased up to 4.8. Human premolars, extracted for orthodontic reasons, were used for this study. Cylindrical cavities (1.5 mm deep, 3.5 mm in diameter; one cavity was prepared in each tooth in the coronal region and medial surface) were prepared in extracted human premolar teeth and restored with resin-modified glass-ionomer cements. Each restoration margin was inspected immediately after curing and polishing (as the immediate condition was the most severe), the maximum gap-width and the opposing width (if any) were determined microscopically (n = 10). An additional test was conducted in model Class V cavities. After finishing of restorations in model Class V cavities, each tooth was sectioned in a bucco-lingual direction through the center of the restoration, and the presence or absence of gaps along the cavity interface was evaluated (n = 10). Additionally, the maximum marginal gap-width and the opposing-width along margins of restorations in cylindrical Teflon molds were measured (n= 10). The compressive strengths of the restorative materials were determined immediately after light-activation (n = 10). Marginal gap (tooth cavity: 0.32 to 0.25-0.20%, P < 0.05; Teflon cavity: 0.94 to 0.6-0.8%, P < 0.05) and cavity adaptation (no gap in the Class V: 22 to 40-50%, P < 0.05) of the restorations improved with increasing powder-liquid ratio (3.0 to 4.4-4.8) and compressive strength increased (111 to 150-170 MPa, P < 0.05). Highly significant correlation coefficients were found for the relationships between powder-liquid ratio and (1) percentage of marginal gap width in the tooth cavity (r = -0.96, P = 0.002, n = 6), (2) gap-free tooth/cement interfaces (r = 0.90, P = 0.015, n = 6), (3) percentage of marginal gap widths in the Teflon mold (r = 0.98, P = 0.0004, n = 6) and (4) compressive strengths of the cements (r = 0.95, P = 0.004, n = 6).
    American journal of dentistry 10/2011; 24(5):310-4. · 1.06 Impact Factor

Publication Stats

617 Citations
207.40 Total Impact Points


  • 1991–2014
    • Okayama University
      • • Department of Occlusal and Oral Functional Rehabilitation
      • • Department of Occlusion and Removable Prosthodontics
      Okayama, Okayama, Japan
  • 2013
    • Universitair Ziekenhuis Leuven
      Louvain, Flanders, Belgium
  • 2012
    • Osaka Dental University
      Ōsaka, Ōsaka, Japan
  • 2005
    • Universität Basel
      Bâle, Basel-City, Switzerland
  • 2001
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 1986–1990
    • Hiroshima University
      • School of Dentistry
      Hiroshima-shi, Hiroshima-ken, Japan