Cyclic Fatigue Properties of Titanium Alloys for Application in Dental Implants.

The present study investigated the cyclic fatigue properties of titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb) as implant materials and compared their properties with those of commercially pure titanium. Ti-6Al-4V and Ti-6Al-7Nb cylinders with diameters of 3.0 mm were examined. The surfaces of the cylinders were roughened by sand blasting with alumina particles and acid etching. Static and cyclic tests were performed according to ISO 14801:2016. The yield force in the static test (YS) was measured in 5 specimens of each alloy using a universal testing machine. The yield force in a cyclic test (YC) was measured in 20 specimens of each alloy using the staircase method, which involved applying a cyclic load at a frequency of 10 Hz for 106 cycles. After the cyclic loading tests, cross-sections of the specimens were examined under an optical microscope. The YS values for Ti-6Al-4V and Ti-6Al-7Nb were 1463 N±93 N and 1405 N±79 N, respectively, and the YC values were 870 N±58 N and 853 N±202 N, respectively. Microscopic observation revealed cracks on the tensile side of some of the specimens, including run outs and failures. The results of this study suggest that the YC values for Ti-6Al-4V and Ti-6Al-7Nb were 40% less than those for YS. The yield force of Grade-4 Cp-Ti significantly decreased after cyclic loading. The YC values for Ti-6Al-4V and Ti-6Al-7Nb were approximately 900 N, which was markedly greater than that for commercially pure, Grade-4 titanium (700 N).

Oral function is associated with the body and muscle mass indices of middle-aged dental patients.

OBJECTIVES: Undernutrition is associated with frailty, one of the common reasons for seeking long-term care. In older adults, nutritional status is known to be associated with oral function; however, it is not yet known if there is a similar association in middle-aged adults. The present study determined the association between nutritional status and oral function in middle-aged adults. MATERIAL AND METHODS: This cross-sectional study was conducted in 117 outpatients aged 40-64 years who underwent dental check-up at a private dental clinic. Factors associated with oral function, including oral moisture, number of teeth present, oral diadochokinesis, tongue pressure, lip-seal strength, and masticatory performance, were evaluated. Body mass index (BMI), fat-free mass index (FFMI), and skeletal muscle mass index (SMI) were analyzed as nutritional statuses. Pearson's correlation analysis was conducted to determine the correlation between nutritional statuses and other variables. Multiple linear regression analysis was performed, with adjustment for age and sex, using BMI, FFMI, or SMI as response variables and oral moisture, maximum tongue pressure, lip-seal strength, oral diadochokinetic rate, and masticatory performance as explanatory variables. RESULTS: All nutritional statuses showed significant correlation with maximum tongue pressure and lip-seal strength. Multiple linear regression analysis revealed that BMI was associated with maximum tongue pressure and lip-seal strength, whereas FFMI and SMI showed significant association with sex, maximum tongue pressure, and lip-seal strength. CONCLUSIONS: In middle-aged outpatients at a regional dental clinic, lip-seal strength and tongue pressure were positively associated with BMI, FFMI, and SMI.

Effective training duration and frequency for lip-seal training in older people using a self-training instrument.

OBJECTIVE: To determine the effects of the training duration and frequency on lip-seal strength (LSS) in older people. BACKGROUND: Lip-seal is important for speaking, eating and swallowing. LSS decreases after training ends; therefore, continuous training is essential. MATERIALS AND METHODS: Participants underwent the resistance training of LSS. Regarding training duration, eight women aged ≥65 years participated in a crossover study with trainings A (direction: 1, duration: 50 seconds) and B (directions: 3, duration: 3 minutes), daily for 4 weeks. Regarding training frequency, 40 women aged ≥65 years were divided into four groups based on frequency (everyday, every-other-day, once-a-week and control groups), and all groups excluding the control group performed training B for 4 weeks. LSS was measured at weeks 0, 2 and 4 using a digital strain gauge. Friedman's test was used, followed by Steel-Dwass test (α = 0.05). RESULTS: Regarding the effects of the training duration, significant differences in LSS were noted between weeks 0 and 4 for training B, but no difference was noted for training A. Regarding training frequency, significant differences were observed between weeks 0 and 2 or 4 in the everyday and once-a-week groups. Significant differences were observed in the every-other-day group between weeks 0 and 4 and no difference in the control group. For all groups, median LSS was higher in week 2 or 4 than that in week 0. CONCLUSION: Lip-seal training for 3 minutes per session everyday, every-other-day or once-a-week for 4 weeks increased LSS of older people.

Rate of oral frailty and oral hypofunction in rural community-dwelling older Japanese individuals.

OBJECTIVE: To clarify the rate of oral frailty and oral hypofunction in rural community-dwelling older adults in Japan. BACKGROUND: Recently, the oral function of Japanese older adults has been evaluated multilaterally based on two concepts: oral frailty and oral hypofunction. Oral frailty is defined as a decrease in the oral function accompanied by a decrease in mental and physical functions. Oral hypofunction is a disease where the oral function is comprehensively decreased. However, their rates have not yet been elucidated. MATERIALS AND METHODS: Oral frailty and oral hypofunction were evaluated in 679 older adults from rural areas. To investigate the differences in occurrence rates due to the evaluation methods, one of the subordinate symptoms of oral hypofunction, the reduced occlusal force, was evaluated based on both the occlusal force (main method) and the number of teeth (alternative method). RESULTS: The rate of oral frailty was 22.3% in men and 22.7% in women. The rate of oral hypofunction was 39.0% in men and 46.9% in women. The overall rate of oral hypofunction was 43.6% when the reduced occlusal force of oral hypofunction was evaluated using the main method and 46.4% when evaluated using the alternative method. The proportion of participants with decreased occlusal force, the number of present teeth, oral diadochokinesis, tongue pressure and masticatory performance increased with age in both men and women. CONCLUSION: Among rural community-dwelling older adults, the rate of oral frailty was 22.5% and that of oral hypofunction was 43.6%.

Factors associated with masticatory performance in community-dwelling older adults: A cross-sectional study.

BACKGROUND: Decreased masticatory performance leads to deterioration of overall health among older adults. However, maintaining and improving masticatory performance in ways other than maintenance of natural teeth and appropriate prosthodontic treatment remains unclear. If the factors related to the mixing and shearing abilities for masticatory performance are clarified, it may be possible to maintain and improve the masticatory performance of older adults. We aimed to clarify the association among mixing ability, shearing ability, and masticatory performance-related factors. METHODS: Of the 707 community-dwelling older adults in Kusatsu Town, Japan, 344 who had been treated for any dental defects were enrolled in this study. Masticatory performance was evaluated on the basis of mixing ability and shearing ability. The number of natural teeth and artificial teeth, occlusal force, tongue pressure, and oral diadochokinesis /ta/ were measured as masticatory performance-related factors. Their relationship with mixing ability, shearing ability, and masticatory performance-related factors was examined by means of Spearman rank correlation coefficient and path analysis. RESULTS: Among masticatory performance-related factors, the number of natural teeth, occlusal force, and tongue pressure were directly associated with both mixing ability and shearing ability. Moreover, mixing ability was also directly associated with shearing ability. CONCLUSIONS: Tongue pressure, which can be improved by means of training, is a masticatory performance-related factor associated with both mixing and shearing abilities. PRACTICAL IMPLICATIONS: Training for tongue pressure after proper prosthetic treatment may provide an effective means of maintaining and improving masticatory performance in older adults.

Intra- and inter-investigator reliabilities of oral moisture measured using an oral moisture-checking device.

BACKGROUND: Oral mucosal moisture determined using oral moisture-checking devices is used as a mouth dryness evaluation method. Such devices are capable of evaluating the state of mouth dryness in a simple manner and have applicability in a wide range of subjects; however, their intra- and inter-investigator reliabilities have not yet been clarified. OBJECTIVE: This study aims to investigate the intra- and inter-investigator reliabilities of measuring oral moisture using an oral moisture-checking device for a wide range of age groups. METHODS: Intra- and inter-investigator reliabilities were investigated in 28 young subjects and 19 older subjects aged ≥65 years. Three trained investigators independently measured oral mucosal moisture values using an oral moisture-checking device. Intra-investigator reliability was assessed using the coefficient of variation (CV) and intraclass correlation coefficient (ICC) (1.1), and inter-investigator reliability was assessed using ICC (2.1). RESULTS: Mean CV was 0.015 and 0.016, mean ICC (1.1) was 0.806 and 0.877, and ICC (2.1) was 0.873 and 0.829 in the young and older subjects, respectively. CONCLUSION: In young subjects, the mean values of ICC (1.1) and ICC (2.1) of the oral moisture-checking device were 0.806 and 0.873, respectively, whereas in older subjects, these values were 0.877 and 0.829, respectively. Thus, this confirms that the examination of oral mucosal moisture using the oral moisture-checking device has sufficient intra- and inter-investigator reliabilities for a wide range of age groups.

Relationship between mild cognitive decline and oral motor functions in metropolitan community-dwelling older Japanese: The Takashimadaira study.

BACKGROUND: Diminished oral motor function is considered to be a factor influencing cognitive decline, but this association has not been clarified. The aim of the present study was to clarify the association between cognitive and oral motor function in older people with either from normal cognitive function or mild cognitive decline. METHODS: A cross-sectional study was conducted across 1118 older people (445 men, 673 women) aged ≥70 years (mean age, 77.0 ± 4.7 years) who lived in a city of Tokyo Metropolis, Japan. Cognitive function was assessed using the Mini-Mental State Examination (MMSE). Older people who had an MMSE score of 23 points or lower were excluded. To investigate the relationship between cognitive and oral motor function, Pearson's correlation, multiple linear regression, and path analysis were performed. RESULTS: Pearson's correlation revealed that, among the oral motor functions assessed, masticatory performance, occlusal force, and tongue pressure were correlated with MMSE score. Multiple linear regression showed that tongue pressure and oral diadochokinesis (ODK) were significantly associated with MMSE score. Path analysis revealed that decreases in tongue pressure and in ODK were directly associated with decreases in MMSE score. Decreases in tongue pressure were also indirectly associated with decreases in MMSE score via decreases in ODK. CONCLUSIONS: Among the oral motor functions assessed, tongue pressure and ODK were associated with cognitive function in older people ranging from those with normal cognitive function to those with mild cognitive decline. Diminished tongue pressure and ODK might thus lead to cognitive decline.

Influence of grade and surface topography of commercially pure titanium on fatigue properties.

The objective was to investigate the influence of grade and surface topography of commercially pure titanium (Cp-Ti) on fatigue properties evaluated via staircase method. Cp-Ti grades 2 and 4 were roughened by shot blasting and acid etching, and compared with machined specimens. Yield force under static loading for Cp-Ti grades 2 and 4 were 672±51 and 1,088±93 N for machined and 724±99 and 1,118±96 N for roughened group. Yield force under cyclic loading for Cp-Ti grades 2 and 4 decreased 27 and 40% compared to static loading. Cp-Ti grade 4 demonstrated significantly greater decrease in yield force after cyclic loading; however surface topography had no effect.

Comparison of Adhesive Resistance to Chewing Gum among Denture Base Acrylic Resin, Cobalt-Chromium Alloy, and Zirconia.

The purpose of this study was to compare the adhesiveness of chewing gum to acrylic resin, cobalt-chromium alloy, and zirconia. Test specimens were fabricated using acrylic resin (resin), cobalt-chromium alloy (Co-Cr), and Ceria stabilized tetragonal zirconia polycrystal-based nanostructured zirconia/alumina composite (zirconia). Specimens of each material were attached to the upper and lower terminals of a digital force gauge. The operator masticated chewing gum, wiped off any saliva, and placed the gum on the lower specimen. The gum was compressed to a thickness of 1 mm between the upper and lower specimens. Thereafter, traction was applied to the upper specimen at a cross-head speed of 100 mm/min under 3 different conditions (dry, wet with distilled water, and wet with artificial saliva) to determine the maximum adhesive strength of the chewing gum. The statistical analysis was performed using the Bonferroni test after a one-way analysis of variance (α=0.05). Under dry conditions, adhesive force was 14.8±6.8 N for resin, 14.0±4.8 N for Co-Cr, and 4.3±2.3 N for zirconia. Significant differences were noted between resin and zirconia, and between Co-Cr and zirconia. When distilled water was applied to the specimen surface, the adhesive strength was 16.8±1.7 N for resin, 8.3±2.1 N for Co-Cr, and 2.7±0.8 N for zirconia. Significant differences were noted between resin and Co-Cr, resin and zirconia, and Co-Cr and zirconia. When artificial saliva was applied to the specimen surface, the adhesive force was 18.5±2.8 N for resin, 5.3±0.8 N for Co-Cr, and 3.0±1.7 N for zirconia. Significant differences were noted between resin and Co-Cr, and resin and zirconia. Chewing gum adhered less strongly to zirconia than to acrylic resin or cobalt-chromium alloy.

Evaluation of participants' perception and taste thresholds with a zirconia palatal plate.

PURPOSE: Zirconia and cobalt-chromium can withstand a similar degree of loading. Therefore, using a zirconia base for removable dentures could allow the thickness of the palatal area to be reduced similarly to metal base dentures. We hypothesized that zirconia palatal plate for removable dentures provides a high level of participants' perception without influencing taste thresholds. The purpose of this study was to evaluate the participants' perception and taste thresholds of zirconia palatal plate. METHODS: Palatal plates fabricated using acrylic resin, zirconia, and cobalt-chromium alloy were inserted into healthy individuals. Taste thresholds were investigated using the whole-mouth gustatory test, and participants' perception was evaluated using the 100-mm visual analog scale to assess the ease of pronunciation, ease of swallowing, sensation of temperature, metallic taste, sensation of foreign body, subjective sensory about weight, adhesiveness of chewing gum, and general satisfaction. RESULTS: For the taste thresholds, no significant differences were noted in sweet, salty, sour, bitter, or umami tastes among participants wearing no plate, or the resin, zirconia, and metal plates. Speech was easier and foreign body sensation was lower with the zirconia plate than with the resin plate. Evaluation of the adhesiveness of chewing gum showed that chewing gum does not readily adhere to the zirconia plate in comparison with the metal plate. The comprehensive participants' perception of the zirconia plate was evaluated as being superior to the resin plate. CONCLUSIONS: A zirconia palatal plate provides a high level of participants' perception without influencing taste thresholds.