Shunsuke Minakuchi

Effect of mastication on regional cerebral blood flow in humans examined by positron-emission tomography with 15O-labelled water and magnetic resonance imaging

The interaction between mastication and cerebral blood flow was studied in 12 healthy volunteers (five males and seven females) aged 18-40 years. Positron-emission tomography (PET) autoradiography was carried out after bolus injection of 1.5 GBq H₂¹⁵O (¹⁵O-labelled water) with a half life of 2 min. The PET images were superimposed on magnetic resonance images of each participant. The regional cerebral blood flow images were normalized by the global cerebral blood flow value, and subtraction images (those during gum-chewing minus those during resting) were created and recut at the magnetic resonance image slice positions. Gum specially designed for chewing training was used. Mastication increased regional cerebral blood flow in the primary sensorimotor areas by 25-28%, in the supplementary motor areas and insulae by 9-17%, and in the cerebellum and striatum by 8-11%. These increases demonstrate that chewing activates widespread regions of the brain.

Meta-analysis of Bonding Effectiveness to Zirconia Ceramics

Dental zirconia can no longer be considered un-bondable to tooth tissue. In literature, an increasing number of papers indeed report on the bonding effectiveness of different luting techniques to zirconia. We aimed to disclose general trends in bonding to zirconia by systematically collecting zirconia bond-strength data. A search in PubMed and EMBASE revealed 1,371 bond-strength tests reported on in 144 papers. A macro-shear bond-strength protocol was most frequently used; it revealed significantly lower bond strengths and was less discriminative than the other test methods. Regarding luting technique, the combination of mechanical and chemical pre-treatment appeared particularly crucial to obtain durable bonding to zirconia ceramics. The cement choice was not revealed as a determining factor after aging conditions, as long as composite cement was used. Regarding test protocol, a tensile test appeared more discriminative, particularly when combined with ‘water storage’ aging.

Validity and reliability of a Self-Implementable method to evaluate masticatory performance: Use of color-changeable chewing gum and a color scale

PURPOSE The objective of this study was to confirm the validity of a Self-Implementable method to evaluate masticatory performance using a newly developed color scale and color-changeable chewing gum. METHODS We developed a dedicated color scale that enables anyone to easily check the color of the chewing gum instead of using specialist equipment. To examine the reliability of evaluating the masticatory performance by the subjects themselves, three groups of six subjects were recruited: a group of dentists, a group of adults and a group of elderly adults were asked to check the colors of the chewed samples using the color scale. The correlation between the use of the color scale and the use of a colorimeter to determine the color of the chewing gum was studied to confirm the validity of the color scale. To assess the reliability, intraclass correlation coefficients (ICCs) were determined. RESULTS A strong correlation was found between the a* value measured by the colorimeter and the mean scores from the color scale. The ICCs for intra-examiner and inter-examiner consistency were more than 0.88 for all three groups. CONCLUSIONS This research confirmed the validity and reliability of colorimetric analysis of color-changeable chewing gum using a color scale as a Self-Implementable method of evaluating masticatory performance.

Influence of sintering conditions on low-temperature degradation of dental zirconia

UNLABELLED The effect of sintering conditions and concomitant microstructure of dental zirconia (ZrO2) ceramics on their low-temperature degradation (LTD) behavior remains unclear. OBJECTIVES Therefore, their effect on LTD of dental ZrO2 ceramics was investigated. METHODS Three commercial pre-sintered yttria-stabilized dental zirconia materials were sintered at three temperatures (1450°C, 1550°C and 1650°C) applying three dwell times (1, 2 and 4h). Grain size measurements and LTD tests were performed on polished sample surfaces. LTD tests were performed at 134°C in an autoclave. The amount of monoclinic ZrO2 on the exposed surface was measured by X-ray diffraction (XRD). RESULTS Higher sintering temperatures and elongated dwell times increased the ZrO2 grain size. Simultaneously, a larger fraction of zirconia grains adopted a cubic crystal structure, resulting in a decreased yttria content in the remaining tetragonal grains. Both the larger grain sizes and the lower average stabilizer content made the tetragonal grains more susceptible to LTD. Overall, independent on the commercial dental zirconia grade tested, the specimens sintered at 1450°C for 1h combined good mechanical properties with the best resistance to LTD. SIGNIFICANCE In general, increased sintering temperatures and times result in a higher sensitivity to low-temperature degradation of Y-TZP ceramics.

Reliability and validity of a Japanese version of the Oral Health Impact Profile for edentulous subjects

OBJECTIVE To evaluate the reliability and validity of the Japanese version of the Oral Health Impact Profile for edentulous (OHIP-EDENT-J) patients. BACKGROUND Oral Health Impact Profile for edentulous is an appropriate instrument for assessing the Quality of life (QOL) in edentulous patients. However, the reliability and validity of the Japanese version had not been evaluated. METHODS The study was conducted on 116 edentulous patients (Group A, requiring new dentures, n = 61; Group B, already having dentures, n = 55). Cronbachs alpha (α) was used to measure internal consistency of the summary scores for OHIP-EDENT-J and various subscales in Groups A and B. The interclass correlation coefficient (ICC) and 95% confidence interval of the summary scores for OHIP-EDENT-J and subscales were calculated. The summary scores for OHIP-EDENT-J in Groups A and B were compared with evaluate content validity. The Spearmans correlation coefficient between the summary scores for OHIP-EDENT-J and the satisfaction with dentures (100 mm VAS) was calculated for Groups A and B to evaluate concurrent validity. RESULTS The reliability of the summary scores for OHIP-EDENT-J was good (α = 0.93). The ICC of the summary scores for OHIP-EDENT-J was 0.85. Summary scores for OHIP-EDENT-J were significantly different (p = 0.027) between Group A and Group B, with Group A having the higher value. The Spearmans correlation coefficient for the degree of satisfaction with dentures and the summary scores for OHIP-EDENT-J, calculated for Groups A and B (n = 107), was -0.609. CONCLUSION The OHIP-EDENT-J, a questionnaire on oral health-related QOL comprising 19 items, showed good reliability and validity for edentulous patients.

Properties of a color-changeable chewing gum used to evaluate masticatory performance

PURPOSE To clarify the basic properties of a color-changeable chewing gum to determine its applicability to evaluations of masticatory performance under different types of dental status. METHODS Ten participants with natural dentition aged 26-30 years chewed gum that changes color during several chewing strokes over five repetitions. Changes in color were assessed using a colorimeter, and then L*, a*, and b* values in the CIELAB color system were quantified. Relationships between chewing progression and color changes were assessed using regression analysis and the reliability of color changes was assessed using intraclass correlation coefficients. We then measured 42 dentate participants (age, 22-31 years) and 47 complete denture wearers (age, 44-90 years) to determine the detectability of masticatory performance under two types of dental status. RESULTS Regression between the number of chewing strokes and the difference between two colors was non-linear. The intraclass correlation coefficients were highest between 60 and 160 chewing strokes. Dentate and edentulous groups significantly differed (Wilcoxon rank sum test) and values were widely distributed within each group. CONCLUSIONS The color of the chewing gum changed over a wide range, which was sufficient to evaluate the masticatory performance of individuals with natural dentition and those with complete dentures. Changes in the color values of the gum reliably reflected masticatory performance. These findings indicate that the color-changeable chewing gum will be useful for evaluating masticatory performance under any dental status.

Reliability and validity of a quantitative color scale to evaluate masticatory performance using color-changeable chewing gum

In the present study, we developed a novel color scale for visual assessment, conforming to theoretical color changes of a gum, to evaluate masticatoryperformance; moreover, we investigated the reliability and validity of this evaluation method using the color scale. Ten participants (aged 26.30 years) with natural dentition chewed the gum at several chewing strokes. Changes in color were measured using a colorimeter, and then, linearregression expressions that represented changes in gum color were derived. The color scale was developed using these regression expressions. Thirty-two chewed gums were evaluated using colorimeter and were assessed three times using the color scale by six dentists aged 25.27 (mean, 25.8) years, six preclinical dental students aged 21.23 (mean, 22.2) years, and six elderly individuals aged 68.84 (mean, 74.0) years. The intrarater and interrater reliability of evaluations was assessed using intraclass correlation coefficients. Validity of the method compared with a colorimeter was assessed using Spearmans rank correlation coefficient. All intraclass correlation coefficients were > 0.90, and Spearmans rank-correlation coefficients were > 0.95 in all groups. These results indicated that the evaluation method of the color-changeable chewing gum using the newly developed color scale is reliable and valid.

Effects of aging and sarcopenia on tongue pressure and jaw-opening force

Aging and sarcopenia reduce not only body strength, but also the strength of swallowing muscles. We examined how aging and sarcopenia affect tongue pressure and jaw‐opening force.

Stress analysis of mandibular two-implant overdenture with different attachment systems

This study aimed to investigate the influence of different overdenture attachment systems on the stress generated in peri-implant bone during overdenture dislodgement and loading. Two implants were placed in the canine regions on an acrylic edentulous mandibular model. Four strain gauges were attached to the resin surface adjacent to the left implant. Bar, ball, and magnetic attachments were examined. Three experimental overdentures were fabricated, and the denture parts of the attachment systems were incorporated into the mucosal surface. Retentive forces and strains generated in peri-implant bone during three types of dislodgement (vertical, anterior and posterior) and loading (left first molar region, right first molar region and mid-anterior region) were measured. The bar attachment showed the highest retentive force and reduced strain on posterior dislodgement. The ball attachment demonstrated the largest strain on loading at molar regions. The magnetic attachment showed the smallest retentive force and little strain.

Fabrication of titanium alloy frameworks for complete dentures by selective laser melting.

STATEMENT OF PROBLEM Casting difficulties have led to the limited use of titanium in dental prostheses. The selective laser melting system was recently developed to fabricate biomedical components from titanium alloys. However, the fabrication of a titanium alloy framework for a maxillary complete denture by selective laser melting has not yet been investigated. PURPOSE The purpose of the study was to fabricate thin titanium alloy frameworks for a maxillary complete denture with a selective laser melting system and to evaluate their hardness and microstructure. MATERIAL AND METHODS A cast of an edentulous maxilla was scanned with a dental 3-dimensional cone-beam computed tomography system, and standard triangulation language data were produced with the DICOM Viewer (Digital Imaging and Communications in Medicine). Two types of metal frameworks for complete dentures were designed with 3-dimensional computer-aided design software. Two titanium alloy frameworks, SLM-1 and SLM-2, were fabricated from these designs with the selective laser melting system. Plate-shaped specimens were cut from the central flat region of SLM-1, SLM-2, and as-cast Ti-6Al-4V (As-cast). Vickers hardness testing, optical microscopy, and x-ray diffraction measurements were performed. RESULTS Thin titanium alloy frameworks for maxillary complete dentures could be fabricated by selective laser melting. The hardness values for SLM-1 and SLM-2 were higher than that for the as-cast specimen. Optical microscopy images of the SLM-1 and SLM-2 microstructure showed that the specimens did not exhibit pores, indicating that dense frameworks were successfully obtained with the selective laser melting process. In the x-ray diffraction patterns, only peaks associated with the α phase were observed for SLM-1 and SLM-2. In addition, the lattice parameters for SLM-1 and SLM-2 were slightly larger than those for the as-cast specimen. CONCLUSIONS The mechanical properties and microstructure of the denture frameworks prepared by selective laser melting indicate that these dentures are appropriate for clinical use.