Purpose: The purpose of this study was to apply in-vivo modal analysis to the maxillary dentition of the maxillectomy patient using obturator prostheses which were different in lateral wall height of the bulb: specifically a high type (H type), middle type (M type), and low type (L type). Methods: The left central incisor was struck with an impact hammer, and the response at each measurement point was detected using a Laser-Doppler vibrometer. The transfer function was then obtained from each measurement point using a fast Fourier transform analyzer. Finally, a computer analysis and simulation were performed based on the measured transfer functions to obtain the natural frequency, modal shape decay rate (DR), and maximum displacement (MDP). Results: The results showed that the natural frequency was different between with and without obturator prostheses, that the modal shapes with M and L type obturator prostheses are more suitable than that with H type. The DR of the maxillary dentition with the L type was significantly higher than that with the H or M types, and the MDP of the maxillary dentition with an obturator prosthesis was significantly lower than without an obturator prosthesis. Conclusion: From the standpoint of vibratory characteristics, the L type obturator prosthesis is the most suitable bulb design for the patient of the three types obturator prostheses. This is the first report to apply in-vivo modal analysis to the maxillary dentition of the maxillectomy patient using obturator prostheses and clarify the vibratory characteristics of the dentition.
Purpose: The purpose of this study was to investigate whether edentulous patients with a permanent acrylic resilient liner denture (RLD) in mandibles exhibit significant improvements in their satisfaction ratings at the first appointment following the delivery of RLD dentures when compared to those with conventional heat-activated acrylic resin dentures (ARD) in mandibles. Methods: Seventy-four subjects were randomly allocated into RLD and ARD groups by a random permuted block within the strata method after written informed consent. A parallel-randomized controlled clinical trial at two centers was conducted from April 2004 to July 2006. The outcomes were satisfaction ratings with a 100 mm visual analog scale (VAS) involving general satisfaction as well as satisfaction related to chewing, speaking, cleaning, stability, retention, comfort, and esthetics. The pain rating was also measured by the VAS. The outcomes were analyzed by Student t-test and Pearson's correlation coefficient. Results: A significant difference between the RLD and ARD group in the maxillary denture was only obtained in the satisfaction rating of speaking. A significant difference between the RLD and ARD groups for the mandibular dentures was obtained in every satisfaction rating. The pain rating of the RLD group was significantly lower than that of the ARD group. The satisfaction ratings of mandibular denture functions significantly correlated with ratings of comfort and pain. Conclusion: Despite the limitation of a short-term observation, the mandibular satisfaction ratings were dramatically higher in RLD wearers than in ARD wearers.
Purpose: The aim of this study was to evaluate the blood flow changes of a superficial temporal artery before and after low-level laser irradiation was applied to the TMJ area of healthy subjects. Methods: Right TMJ areas of six healthy subjects were irradiated with a CO2 laser. Variation of diameter, blood flow rate, and blood flow volume of the vessel, on both the irradiated side and opposite side, before and after irradiation on the TMJ were evaluated by using a Doppler flowmeter. Results: The diameter and blood flow volume of the vessel after irradiation increased significantly compared to that before irradiation. Conclusion: Low-level laser irradiation applied to the right TMJ area caused an expansion of blood vessels and an increase in blood flow volume. The same result on the contralateral side may be caused by the vasodilator reflex via the hypothalamic thermostat.
Purpose: For bone homeostasis, vitamin D plays an important role in the regulation of calcium. The enzyme CYP24 inactivates vitamin D and is involved in its regulation. However, the mechanism of expression of CYP24 in osteoblastic cells under mechanical stress is not clear. In this study we investigated CYP24 promoter activity in stretched osteoblastic cells and the participation of mitogen-activated protein kinase (MAPK) in expression of CYP24. Methods: MG63 osteoblastic cells were cultured on silicon-bottomed plates. Cells were transfected with a reporter gene that contained a CYP24 promoter. After activated vitamin D, 1,25(OH)2D3, was added or not added, cells were stretched. Stretched and non-stretched cells were investigated by luciferase dual assay. Cells were also investigated similarly using medium with an ERK1/2 inhibitor or p38 inhibitor. Results: The CYP24 promoter was activated by 1,25(OH)2D3 and the promoter activity decreased in stretched cells. Inhibitor of MAPK decreased CYP24 promoter activity. However, CYP24 promoter activity decreased with mechanical stress after addition of p38 inhibitor, while it did not decrease with mechanical stress after addition of ERK1/2 inhibitor. The CYP24 promoter was not activated without 1,25(OH)2D3 in any case. Conclusion: Mechanical stress and MAPK control CYP24 promoter activity in the presence of Vitamin D in MG63 osteoblast-like cells.
Purpose: The purpose of this study was to evaluate the effect of a new gel-type denture adhesive on denture retention and ease of removal from the oral mucosa after use. Methods: Eleven complete denture wearing patients (3 males and 8 females; age range, 58-84 years; mean age, 73.7 years) with compromised maxillary denture-bearing tissues were included in the study. Denture retention and ease of removal were evaluated for a new gel-type denture adhesive. The results were compared with those obtained with and without a cream-type denture adhesive. Retention was evaluated by measuring unilateral bite force until these dentures were dislodged on the balancing side. Ease of removal was evaluated by scoring the remaining area of colored denture adhesives on the oral mucosa. Denture retention and ease of removal were also subjectively evaluated using questionnaires. Results: A significant improvement in objective denture retention was observed when either the cream-type or gel-type denture adhesive was used (p<0.05). A significant difference in objective ease of removal was observed between cream-type and gel-type denture adhesive when subjects had rinsed their mouth once (p<0.05). Subjective assessment showed no significant differences in either retention or ease of removal between gel-type and cream-type denture adhesives (p=0.26, 0.24). Conclusions: Objectively, denture retention was higher with the cream-type than with the gel-type denture adhesive. Removal of the gel-type denture adhesive from the oral mucosa was easier than that of the cream-type. Subjectively, there were no differences in either retention or ease of removal.
Purpose: To develop a new fluorine-containing soft denture lining material, the influences of fluorinated monomers on physical properties and contamination resistance were examined. Methods: Five experimental materials of different chemical compositions in fluorinated monomer and two plasticized acrylics (Supersoft, VertexSoft) were used to evaluate water sorption, solubility, staining resistance, Shore A hardness, and contact angle. Five specimens for each test were fabricated. The results were analyzed with one-way analysis of variance (ANOVA) and Tukey's HSD test using statistical software at p=0.05. Results: The amount of water sorption tended to decrease as the number of the fluorine atoms in fluorinated monomers increased. Similar solubility was shown regardless of the type of fluorinated monomer. The use of fluorinated monomers for immersion in coffee allowed suppression of discoloration. In β-carotene, there were no significant differences in color changes among four experimental materials with fluorinated monomer. Shore A hardness was decreased and the contact angles tended to increase as the number of fluorine atoms in fluorinated monomers increased. When comparing the experimental materials and commercially available materials, the experimental materials containing fluorinated monomers with large numbers of fluorine atoms showed adequate clinical properties except for staining test of β-carotene. Conclusion: Monomers with a large number of fluorine atoms can be used to develop applicable soft denture lining materials in clinical practice.
Purpose: The aim of this study was to assess the effect of acidic primers on adhesive bonding to prefabricated alumina material designed for fixed restorations. Methods: High-purity alumina disks (Procera AllCeram) were primed with one of the following materials: Acryl Bond, All Bond II Primer B, Alloy Primer, Estenia Opaque Primer, M.L. Primer, MR. Bond, and Super-Bond Liquid. The specimens were bonded with a dual-polymerizing luting composite (Variolink II). Unprimed specimen was prepared as the control. Bond strengths were determined both before and after thermocycling. Results: Average bond strength before thermocycling ranged from 12.0 to 39.1 MPa, whereas average bond strength after thermocycling varied from 0.0 to 26.9 MPa. The statistically highest post-thermocycling bond strength was obtained with the use of the Alloy Primer, Estenia Opaque Primer, and M.L. Primer agents. Conclusion: It can be concluded that the use of either the Estenia or Alloy Primer material, which contain 10-methacryloyloxydecyl dihydrogen phosphate (MDP), or the M.L. Primer, which contains 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA), is recommended for bonding the Procera alumina copings with the Variolink II composite.
Purpose: To elucidate the influence of the improvement of denture function on brain activity in complete denture wearers. Methods: Eighteen complete denture wearers (5 males and 13 females, 63-87 years, mean: 75.2 years) participated in the study. To evaluate denture function, the occlusal contact area and occlusal force were measured for comparison before and after denture treatment using the Dental Prescale Occluzer (GC Co., Tokyo, Japan). To evaluate brain activity, electroencephalogram data obtained using an electroencephalographic measurement apparatus ESA-pro (Brain Functions Laboratory, Inc., Kanagawa, Japan) were analyzed using DIMENSION (Diagnosis Method of Neural Dysfunction). The duration of the measurement was 3 minutes before and after denture treatment. Results: The occlusal contact area significantly increased after denture treatment in all 18 subjects (p<0.05). The occlusal force significantly increased in 17 patients (p<0.05). Activation of brain activity was noted in 14 of the 18 patients (p<0.05). Measurement before denture treatment showed that 12 patients were in the sub-normal / impaired region and 6 were in the normal region. After denture treatment, brain activity was significantly activated in all 12 patients who were in the impaired/sub-normal region before treatment. Conclusion: An improvement in denture function was observed after denture treatment in complete denture wearers, and brain activity was enhanced by the functional improvement in the complete dentures. Not only denture function improvement but also brain functional activation was achieved by denture treatment in elderly complete denture wearers who were at risk of brain activity deterioration.
Purpose: To clarify the section showing minimal intra-individual variations in the movement of the mandibular incisal point during mastication of softened chewing gum. Methods: Twenty healthy subjects were asked to chew softened chewing gum on the habitual side for 20 seconds. The change in the spatial parameters (gape and masticatory width) and temporal parameter (cycle time) were investigated for 20 cycles from the first cycle. The coefficients of variation of these parameters were investigated for each of 10 consecutive cycles (first to eleventh series). Results: The spatial and temporal parameters were maximal at the first cycle, decreased progressively until the fourth or fifth cycle, and then remained almost unchanged thereafter. The coefficients of variation of the parameters were maximal during the first series, decreased progressively until the fourth to sixth series, and then tended to increase gradually thereafter. Minimal coefficients of variation were observed during the fifth and sixth series for the gape, during the fifth series for the width, and during the fourth series for the cycle time. Conclusion: These results suggest that the ten cycles after the fourth to the sixth cycle was the section showing minimal intra-individual variations in the masticatory movement during the chewing of softened chewing gum.
Purpose: To evaluate the artifacts generated by crownshaped dental alloys and a magnetic keeper quantitatively by analyzing digital MRI data. Methods: One pre-fabricated magnetic keeper and four clinical dental alloys (gold-silver-palladium, casting gold alloy Type 3, cobalt-chromium, gold porcelain alloy) were selected. Twenty metal crowns and 5 magnetic keepers were analyzed. The samples were placed in an acrylic phantom (150 mm × 150 mm × 150 mm) filled with agar, and then placed in the MRI apparatus. Various image slices were selected from the center (0 mm) to 70 mm at steps of 5 mm. The distribution of the signal intensity in the region of interest was calculated using ImageJ software and the mean coefficient of variation of each specimen was obtained. Statistical analysis was performed by Dunnett's test (p<0.05). Results: Compared to the resin control, cobalt-chromium showed significantly greater signal intensity up to 40 mm in coronal T2-WI images and up to 70 mm in axial T1-WI images for the magnetic keeper. The signal intensities of gold-silver-palladium and casting gold alloy Type 3 were not significantly different from that of the control. The signal intensity of gold porcelain alloy was significantly different from that of the control at 0 mm and 5 mm in coronal T1, T2-WI and in sagittal T1-WI at 0 mm. Conclusions: The artifacts generated by the magnetic keeper and the cobalt-chromium crown when they are used in a second molar can disturb the MR images of the temporomandibular joint.
Purpose: To date, the minimum thickness required for a mouthguard has been assumed to be around 2 mm to 4 mm. However, this figure is based mostly on experience and is yet to be standardized. The purpose of this study is to determine the minimum thickness required to obtain sufficient energy absorption. Methods: The thicknesses of the tested ethylene vinyl acetate) samples were 1, 2, 3, 4, 5, and 6 mm. The pendulum-type testing equipment used in the present study was also used in a series of earlier studies. Three types of sensors (strain gauge, accelerator, and load cell) and two different impact objects (a steel ball and baseball) were used. Results: The results showed that all the abovementioned mouthguard thicknesses reduced shocks for all the three types of sensors and both types of impact objects; little difference was observed between sensors and clear results were obtained for the steel ball. An improvement in the energy absorption was observed with an initial increase in the thickness. However, a further increase in the thickness from 4 mm to 5 mm and 6 mm tended to yield a smaller improvement in energy absorption. Conclusion: Within the limitations of this study, from the viewp int of energy absorption ability, the minimum thickness required for a mouthguard is 4 mm, which is generally too large from the viewpoint of player comfort. This finding indicates the necessity of improving the impact absorption ability of mouthguards by considering new designs and developing new materials.