Purpose: The purpose of this study was to develop an objective method of evaluating the swallowing function.
Materials and Methods: Ten healthy, fully dentate males (average age 28.6±3.5 years old) were selected as subjects. General-purpose ultra-sound diagnostic equipment was used with a 5 MHz electronic convex sector scanning probe to observe tongue movement while food was being swallowed. The sounds associated with swallowing were recorded using a heart sound microphone connected to ultra-sound diagnostic equipment. The tongue movements and swallowing sounds were simultaneously recorded on chart paper, and analyzed by plotting six inflection points (T₀, T₁, T₂, T₃, T₄ and T₅) of the movement curve, and two beginning points of the swallowing sounds (S₁ and S₂) using a digitizer. X-ray images using videofluorography were recorded simultaneously with ultrasound images in three of the ten subjects.
Results: It was confirmed that all the data from the ten subjects were reproducible. There were statistically significant correlations between T_t4 and S_t1, and T_t4 and S_t2, (p<0.001). S_t1 always preceded T_t4. The VF image S₁ indicated that the point in time when the epiglottis was about to shut and T₄ coincided with the time when the last of the test food reached the esophagus.
Conlusion: Our results suggested that this evaluation method could be useful for the diagnosis of swallowing.

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Purpose: To establish a simpler and more accurate method of measuring masticatory ability in routine dental practice compared to current methods.
Materials and Methods: To find the most suitable conditions for assessing masticatory performance using the test gummy jelly, variable factors were investigated, such as temperature and length of rinse time in water, temperature of distilled water, and dissolution time of glucose. The accuracy of this test was confirmed by correlating the surface area of the jelly and the glucose concentration. A student's t-test or ANOVA was used for statistical analysis at the 5% level of significance. The Bonferroni method was used for multiple comparisons.
Results: The glucose concentration decreased gradually (p<0.05) as the rinsing time increased but tended to remain unchanged at 30seconds or more. As the temperature of the distilled water for dissolving the glucose or the dissolution time increased, the glucose concentration constantly increased (p<0.05). A linear regression analysis showed that the concentration of glucose had a significantly high correlation to the surface area (mm²) of the comminuted jelly (r=0.993, p<0.01).
Conclusion: The concentration of glucose dissolved from the comminuted particles of the test gummy jelly indicated high reproducibility and accuracy when the rinsing time, temperature of the distilled water, and dissolution time of the glucose were strictly prescribed.

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Purpose: This study gathered basic information on the ability of healthy dentate individuals to discriminate interdental thicknesses in order to diagnose patients without evident occlusal abnormalities who complain about bite discomfort.
Materials and Methods: Twenty healthy dentate adults participated in the study. The interdental thickness discrimination test was performed at the maxillary and mandibular central incisors with 2-, 5-, and 10-mm thick standard blocks. A test block with a different thickness from that of the corresponding standard block was tested after the application of the standard block. The subjects were then asked to answer whether the test block felt thicker or thinner than the standard block. The number of wrong answers was statistically analyzed. The measurement was repeated three times on different days.
Results: There was no statistical difference in the number of wrong answers among the measurements on three different days. There were statistically significant differences in the number of wrong answers between the 2- and 10-mm, and 5- and 10-mm thicknesses (p<0.05, ANOVA). Significantly more wrong answers were observed for the test blocks that were thicker than the standard block compared to those that were thinner (p<0.05, ANOVA). There were significant differences between females and males in the distribution of wrong answers for the thinner test blocks (2- and 5-mm thicknesses) (p<0.01, ridit analysis).
Conclusion: There was reproducibility of the interdental thickness discrimination test and a gender difference in the thickness discrimination ability in the healthy dentate adults who participated in this study.

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Purpose: The aim of this study was to clarify the characteristics of masseter muscle fatigue induced by experimental sustained light clenching with rest intervals between clenching events.
Materials and Methods: The subjects consisted of 18 healthy young adults. For each recorded task, the subjects were asked to perform experimental tooth clenching 3 times, with a duration of 60s for each event and an interval (30s or 60s) between successive clenching events. The experimental clenching forces selected were 10% and 20% of maximum voluntary clenching (MVC). The electromyographic activity during the experimental procedure was measured. The mean power frequency (MPF) of muscle activity was used as an indicator of muscle fatigue. Changes to lower frequencies of the MPF were then analyzed.
Results: Despite the light clenching forces used (10% and 20% of MVC), masseter muscle fatigue occurred. When the subjects performed experimental clenching at 10% of MVC with intervals of 60s between clenching events, the MPF changes were gradually larger depending on the events. The regression line had the best fit to data when the subjects were asked to perform experimental clenching under the conditions mentioned above.
Conclusion: It was possible to obtain a regression line that represented the relationship between clenching events and masseter muscle fatigue.

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Purpose: Highly crystalline thin hydroxyapatite (HA) layers deposited on the surface of commercially pure titanium (cpTi) by discharge anodic oxidation and hydrothermal treatment (SA treatment) enhance the value of cpTi as endosseous implant material in clinical dentistry. The SA treatment in particular is important for the osteoconductive properties of cpTi. However, it is crucial to ascertain whether the HA layer retains its chemical stability during osseointegration. This study characterized the morphological, chemical and structural features of HA layers during in vitro bone matrix mineralization.
Materials and Methods: SA-treated cpTi disks were used in this study. Rat bone marrow stromal (RBM) cells were obtained from Wistar rats and cultured on SA-treated cpTi disks for 5, 7, 10, and 14 days. The thin HA layers of these samples were analyzed by electron probe microanalysis (EPMA), scanning electron microscopy (SEM), thin-film x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS).
Results: EPMA revealed an even distribution of P and Ca during all culturing periods. SEM and XRD analysis showed that the morphology or crystalline features of the thin HA layer were not altered during culturing. The XRD patterns showed a characteristic HA formation and peak that did not change with the length of time in the culture in comparison to the control samples. Finally, the XPS analysis indicated no change in the binding energy of P and Ca in the HA crystals among all the cultured samples and the control.
Conclusion: The thin HA layer formed on the SA-treated cpTi disks appeared to remain stable during the process of bone matrix mineralization.

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Purpose: Fe-Pt alloys have magnetic properties and can be cast using a dental casting machine. However, no studies have ever been conducted to examine the wear of Fe-Pt alloys. This study evaluated the in vitro wear resistance of magnetic Fe-Pt alloy teeth.
Materials and Methods: Maxillary and mandibular tooth patterns were duplicated from artificial first molars (Livdent FB30, GC, Japan) and cast from a custom-made Fe-Pt ingots (Fe-39.5 at % Pt-0.75 at % Nb) using a high-frequency centrifugal casting machine (Jelenko Eagle, Jelenko, NY, USA). The cast teeth were vacuum-enclosed in quartz-glass tubes, solution-treated at 1,325°C for 45 min., and then quenched in ice water. Subsequently, the teeth were aged at 600°C for 5 hours to acquire hard magnetic properties. As controls, Au-Ag-Pd alloy (Castwell MC, GC), Au-Pt alloy (PGA-3, Ishifuku, Japan) and Co-Cr alloy (Wisil, Austenal, Germany) were also prepared by conventional casting. The wear of the teeth (both maxillary and mandibular) was measured using an in vitro two-body wear testing apparatus that simulated chewing function (60 strokes/min., grinding distance: 2 mm under flowing water). Wear resistance was assessed as volume loss (mm³) at 49 N (grinding force) after 50,000 strokes. The results (n=5) were analyzed by ANOVA/Fisher's test (α=0.05).
Results: The wear resistance [Mean (SD)] of each alloy was: Au-Pt [0.55 (0.14)], Au-Ag-Pd [0.40 (0.05)], Fe-Pt [0.02 (0.03)], and Co-Cr [0.04 (0.01)]. Fe-Pt alloy had the least wear although there were no significant differences compared to Co-Cr alloy (p>0.05). The Au-Pt alloy had the worst wear resistance of all the metals tested (p<0.05).
Conclusion: Based on the results of this study, Fe-Pt alloy should wear very little when used for both maxillary and mandibular teeth.

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Purpose: A prospective cohort study was designed to determine the relationship between muscle pain and the parameters of masticatory muscle diagnostic tests. Masticatory muscle electromyograms (EMG) and pressure pain thresholds (PPT) were included as parameters to be analyzed.
Materials and Methods: One hundred ninety-six healthy volunteers (134 males, 62 females, mean age of 20.0±2.1 years old) were assessed by surface EMG and PPT on both sides of the masseter muscle. The EMGs were recorded during a maximum sustained contraction. All the subjects were asked to fill out a questionnaire in the initial year of the study regarding their general and oral health conditions. The second clinical examination took place 2.5 years later to determine the incidence of masticatory muscle pain. The PPT and EMG parameters were then evaluated to discover their relationship to the incidence of muscle pain by calculating the relative risk of pain.
Results: Out of 196 patients, seven subjects experienced masseter muscle pain 2.5 years later. Although the integrated EMG values did not show a significant change in the relative risk for pain, the PPT values and EMG power spectral changing patterns displayed a high risk for pain.
Conclusion: Since a low level of PPT and abnormalities in the EMG power spectral changing pattern indicated the possibility of future masseter muscle pain, pain sensitivity can be confirmed as one of the contributing factors to masseter muscle pain.

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Purpose: The purpose of the present research was to clarify the influence of load on the retention of the overdenture when placing a magnetic attachment.
Materials and Methods: A mandibular model with a root only in the left canine was fabricated. A root coping containing the keeper of a magnetic attachment was placed on the left canine. The thickness of the simulated mucosa in the residual ridge was 2mm. The mucosa was fabricated using a fitness test material. A magnet was placed on the keeper and then embedded in the denture base with quick self-curing acrylic resin. A load ranging from 4.9 to 29.4 N was applied to the occlusal surface of the denture.
Results: When loads of 26.4 or 29.4 N were applied, the attractive force of the overdenture was less than 10 N (p<0.01), which is significantly smaller than the attractive force obtained when a load of less than 23.5 N was used. These results are probably due to the rebound of the residual ridge membrane.
Conclusion: Although sufficient attractive force was obtained when a magnetic attachment was placed in the mouth and a small load was applied to the denture, the attractive force of the magnetic attachment may not be great enough under large loads, such as occlusal force. Care should be taken regarding the amount of load applied to the occlusal surface of the overdenture when placing magnetic attachments.

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Purpose: The purpose of the present study was to examine the relationship between the pH values of dental plaque adhering to well fitting and poorly fitting prostheses and to discuss the risk of caries for teeth in different locations in the mouth.
Materials and Methods: In experiment 1, the pH values of plaque on contralateral teeth in the same arch were measured among subjects having natural dentition with no restoration. A Cariostat^TM was used to measure the pH values of the dental plaque. Contralateral teeth in the same arch were compared using the Wilcoxon test at a significance level of 5%. In experiment 2, the pH values of dental plaque adhering to prostheses with good or poor marginal fit were compared. The teeth evaluated included contralateral molars with fixed prostheses in the same arch. They were divided into two groups, i.e., good and poor marginal fit. The pH values of the dental plaque were measured using the same method as in experiment 1.
Results: The results of experiment 1 indicated that there was no difference in the pH values of the dental plaque between the left and right teeth in subjects having natural teeth with no restoration. In contrast, the pH values of the dental plaque in experiment 2 from prostheses with poor marginal fit were significantly lower than those of the prostheses with good marginal fit.
Conclusion: In this study, the pH values of dental plaque were compared among prostheses with different marginal fit. The results showed that the pH of dental plaque adhering to prostheses with poor marginal fit was lower and suggested that prostheses with poor marginal fit presented a higher risk for caries.

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Purpose: The purpose of this study was to evaluate the cleanability of a titanium dioxide (TiO₂)-coated acrylic resin denture base.
Materials and Methods: Two groups of acrylic resin denture base plate specimens were prepared: 1) the TiO₂-coated group, and 2) the Polished group made using a conventional polishing method. The surface roughness and contact angle of plate specimens from both groups were measured. Each plate was immersed in an experimental bolus. Subsequently, the amount of experimental bolus residue left on the surfaces of the plates after ultrasonic cleaning was compared between groups. The groups were further divided into two groups with and without ultraviolet-A ray irradiation during cleaning.
Results: The surface roughness of the TiO₂-coated group was greater than that of the Polished group. Inversely, the contact angle of the TiO₂-coated group was smaller than that of the Polished group (one-tenth that of the Polished group). There was a significant reduction in the experimental bolus residue ratio on the surfaces of the TiO₂-coated plates. The use of ultraviolet-A ray irradiation was not significantly different. The decrease in the experimental bolus residue ratio of the TiO₂-coated group was believed to be due to the considerable improvement in the wettability of the plates.
Conclusion: The TiO₂ coating on an acrylic resin denture base had a positive effect on its ease of cleaning by preventing the accumulation of experimental bolus residue.

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Purpose: The purpose of this study was to evaluate the relationship between either craniofacial or systemic symptoms and the gravity fluctuation area.
Materials and Methods: One hundred and five volunteers (72 males and 33 females; mean age 24.4±4.0) without symptoms of temporomandibular joint disorders (TMD) were examined for craniofacial and systemic symptoms (14 items); the subjects' gravity fluctuation areas were also measured. The volunteers were divided into six groups according to the range of their gravity fluctuation area. The relationship between the symptom score and gravity fluctuation area was thus evaluated.
Results: The mean craniofacial and systemic symptom score was 0.8±1.5. The mean symmetrical conditions score was 3.3±1.0, and the mean TMD symptoms score was 1.6±1.3.
Conclusion: No significant difference was observed between the craniofacial or systemic symptoms score and the gravity fluctuation area; however, the groups with a large gravity fluctuation area did tend to develop dizziness, headache, lumbago, masseter muscle pain, and malocclusion.

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Purpose: This study investigated the possibility of assessing the emotional state as it is influenced by changes in the oral environment through the use of the Emotion Spectrum Analysis Method (ESAM).
Materials and Methods: Comfortable experimental palatal plates (PP) and uncomfortable palatal plates (D−PP) were worn by 10 subjects with normal dentition. Electroencephalograms (EEG) of five subjects who sensed discomfort (D+) and of five subjects who did not sense discomfort (D−) while wearing PP were recorded before and while wearing both types of palatal plates with the subjects' eyes closed according to the International 10-20 Standard. The EEGs were analyzed chronologically using the emotional index based on ESAM, and the analyzed data were compared between the two groups. In addition, the subjects' sensations were evaluated by the Visual Analogue Scale (VAS) and compared between the two groups.
Results: The negative index (D−) significantly increased while the positive index (D+) significantly decreased while wearing the palatal plates. The tendency was clearer with D−PP, which had greater discomfort, and this result corresponded to the sensory evaluation reflected in the VAS score. The sensory evaluation seemed to correspond to the ESAM index that measured the influence of the changes in the oral environment caused by the palatal plates.
Conclusion: The results of this study suggest that it is possible to use ESAM to evaluate the psychological effects caused by changes in the oral environment.

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Purpose: This report describes a direct relining method using tissue conditioning material as the spacer.
Materials and Methods: Tissue conditioning material is applied to the denture base at the first visit, and the occlusion is adjusted. When the patient returns for the second visit, the denture base fit, function, and patient comfort are reexamined. The location of the tissue stoppers is determined to maintain the space for the relining material; possibilities for these tissue stoppers are the rests on the anterior abutments as well as the distal end area of the distal extension base. The tissue conditioning material is removed from the denture base except for the distal end stopper areas. The denture base surface is ground to expose the non-contaminated resin surface and the relining surface is treated with a primer for relining resin. The mixed new resin material is applied to the denture base, and then the denture is returned to the patient's mouth and pressed down with the operator's fingers at the most stable position until the initial curing stage. The remaining spacer area is removed and the above-mentioned procedure is repeated.
Discussion: Although the indirect method is predictable and precise, this approach requires a certain amount of lab procedure time and a relining device. Also there are some situations in which a direct relining method such as that described in this report is preferable, especially for removable partial dentures.
Conclusion: By utilizing tissue conditioner material as the stopper during the procedure, simple direct relining of removable partial dentures is possible.

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Purpose: Evaluation of tooth preparation during clinical training of students and residents is prone to subjective judgments by instructors. The purpose of this study was to develop an objective method of evaluation using numerical criteria.
Materials and Methods: As the first step, phantom epoxy resin teeth (PC-23, Nisshin Inc., Japan) from the same lot were subjected to three-dimensional morphometry using a high-speed laser scanner (Surfracer, Unisn, Osaka, Japan). A 3-D reconstruction was then made using the digitized data for each tooth. These data were superimposed with the reference axis at a right angle to the center of the base of the teeth. The taper angle of the preparation surface was evaluated every 45° around the axis, and the position of the margin was evaluated every 5° compared with data obtained from the instructor's standard preparation. Evaluations were made using numerical parameters.
Discussion: One tooth was prepared by an instructor (IN) and one by a resident at the beginning of the training (R0) and after three months of training (R3). The mean difference in the taper of the preparation between IN and R0 was +14.8°, while it was +2.7° between IN and R3. The difference in the margin location between IN and R0 at the 72 sites was 118.1mm, while it was 78.8mm between IN and R3. The value of the margin was determined by the differences between IN and R (R0, R3) preparations.
Conclusion: Using the difference in the numerical values between the abutment teeth, an objective and longitudinal evaluation is possible for technical assessment of tooth preparation during clinical training.

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Purpose: This article introduces a method of taking impressions accurately through the use of inner stoppers on a custom tray in order to fabricate precise prostheses.
Materials and Methods: The location of the stoppers is marked on the study cast with black or blue ink. Paraffin wax is placed on the study cast as spacers. The wax is perforated with a sharp hand instrument at the location of the stoppers in a cone shape at the posterior area and as four inclined planes at the anterior area. The custom tray material is mixed and placed on the study cast. The stability of the tray on the cast should then be checked.
Discussion: A cone-shaped stopper at the occlusal pit can guide the tray to the desired location. A stopper with an internal quadrangular pyramid can also guide the tray to its location.
Conclusion: The recommended shape and the location of stoppers stabilized the custom tray in the mouth, thus achieving an accurate impression.

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Purpose: This article describes a procedure to increase the visibility of a palatogram using gothic arch tracing ink.
Materials and Methods: The palatal surface of a denture is painted with gothic arch tracing ink. A thin layer of alginate impression powder is sprinkled on a layer of petroleum jelly. The patient is instructed to vocalize. The tongue contact area can then be evaluated.
Discussion: This technique is easy, fast, accurate, inexpensive and readily available to clinicians. If the palatal form must be modified, the modified area is easily discriminated. The technique can be used during the trial placement, insertion or post-insertion appointments.
Conclusion: This simple procedure is effective for the evaluation and correction of the palatal form of waxed or completed dentures.

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Purpose: This article introduces a facilitated method of mixing tissue conditioner to minimize the formation of air bubbles.
Materials and Methods: Tissue conditioner was mixed at the standard powder: liquid ratio for 5 seconds in a glass bottle. It was then poured on a mixing pad and spread with a spatula for 10 seconds to remove the bubbles. The formation of air bubbles in tissue conditioner spread for 10 seconds was compared with the formation of bubbles spread for 30 seconds using transmitted and reflected light.
Discussion: The results suggested that spreading tissue conditioner with a spatula for 10 seconds was better for removing air bubbles.
Conclusion: If the size and number of trapped air bubbles decrease, deterioration and contamination of the tissue conditioner can be prevented. This simple and quick technique minimizes the occurrence of trapped air bubbles.

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Purpose: This study developed a procedure to minimize the distortion of impressions.
Materials and Methods: The inner surface of the tray is abraded with powder or paper points, and vents are made at the top of the narrow space in the tray. The adhesive is applied and allowed to dry for 15 minutes. Any unnecessary undercuts are blocked out with soft wax, and impression material is injected into the narrow space in the tray.
Discussion: This recommended procedure maximizes the adhesive strength between the impression material and the tray, minimizes the amount of air trapped between the impression material and tray, and eliminates large undercuts.
Conclusion: This procedure was effective at minimizing the distortion of impressions.

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