Keisuke Nishigawa

Assessment of allergic hypersensitivity to dental materials

Some metallic materials in dental prostheses may cause allergic hypersensitivity. Symptoms appear not only in the oral cavity, but also on hands, feet or the entire body. Release of metal ions is thought to cause the allergic reactions; micro-particles of the corrosion products of the metal and/or ionic metal hydroxides/oxides may be the allergens. The study purpose was to review clinical surveillance of dental allergic hypersensitivity in our dental hospital. From July 2000 to June 2005, 212 patients with suspected dental metal allergy were patch tested with 26 reagents, including 19 ready-made patch test reagents (Patch test reagents, Torii Pharmaceutical Corporation, Tokyo, Japan) and 9 custom-made reagents. One-hundred-and-sixty-seven patients were females (78.8%) and 45 patients were males (21.2%). A total of 148 patients (69.8%) had one or more positive patch test reactions. The most common allergens were nickel (25.0%), palladium (24.4%), chromium (16.7%), cobalt (15.9%) and stannum (12.5%). Typical allergic symptoms and diagnoses were Pustulosis palmaris et plantaris, lichen planus, stomatitis and contact dermatitis. This study indicates that dentists and dental researchers should be concerned about the allergenic potential of dental metal materials.

The relationship between lateral border movements of the mandible and the determinants of occlusion

Border movements of the mandible were measured with a jaw movement analyzer in nine subjects. This instrument records movement with 6 degrees of freedom and has the ability to accurately and linearly record the full range of jaw movement. The result of this study showed a relationship between the presence of balancing-side molar contacts and restricted contralateral jaw border movements. This restriction is probably due to aberrant external pterygoid muscle activity.

Allergic contact dermatitis caused by titanium screws and dental implants

PATIENTS Titanium has been considered to be a non-allergenic material. However, several studies have reported cases of metal allergy caused by titanium-containing materials. We describe a 69-year-old male for whom significant pathologic findings around dental implants had never been observed. He exhibited allergic symptoms (eczema) after orthopedic surgery. The titanium screws used in the orthopedic surgery that he underwent were removed 1 year later, but the eczema remained. After removal of dental implants, the eczema disappeared completely. DISCUSSION Titanium is used not only for medical applications such as plastic surgery and/or dental implants, but also for paints, white pigments, photocatalysts, and various types of everyday goods. Most of the usage of titanium is in the form of titanium dioxide. This rapid expansion of titanium-containing products has increased percutaneous and permucosal exposure of titanium to the population. CONCLUSIONS In general, allergic risk of titanium material is smaller than that of other metal materials. However, we suggest that pre-implant patients should be asked about a history of hypersensitivity reactions to metals, and patch testing should be recommended to patients who have experienced such reactions.

Effect of altered occlusal guidance on lateral border movement of the mandible

The purpose of this study was to evaluate the effects of a change in the lateral anterior guidance pathway on the lateral border movement pathway of mandible. The results showed that altered occlusal guidance reproducibly and reversibly changed (increased) the lateral border movement area in two subjects who had unilaterally restricted lateral border movements.

Effect of different head positions on the jaw closing point during tapping movements

This study aimed to investigate the effects of different head positions on jaw closing points during tapping movements. The jaw movements of 20 adult volunteers were assessed using a new jaw-tracking device. All subjects had stable maximal intercuspation with their natural dentitions. The subjects were asked to seat on a dental chair with their head upright, and tapping movements were recorded for 5 s without any further instructions. After the chair was reclined to the horizontal position, tapping movements were also recorded with the head in the supine position. The location of the tapping point was defined as the jaw position which was the most closed to the maximum intercuspal position during each tapping stroke. Fifteen tapping points were obtained from the upright and supine head positions of each subject. Six-hundred tapping points were compared to evaluate the effects of different head positions. With the head upright, tapping points were relatively stable and close to the jaw position at the maximum intercuspation. However, in the supine position, tapping points varied widely and shifted forward. The average distance between the positions of the incisal point at the maximum intercuspation and at the tapping points was 0.11 mm (SD, 0.10) in the upright position and 0.30 mm (SD, 0.08) in the supine position. A Wilcoxon signed rank test showed a significant difference (P < 0.01) between these distances. We conclude that tapping points shift anteriorly in the supine position.

Effect of occlusal contact stability on the jaw closing point during tapping movements

PURPOSE We studied the relationship between tapping point reproducibility and stability of occlusal contacts at maximum intercuspation. METHODS Tapping movements of 12 adult volunteers who had dentition with natural teeth were recorded, and distances between the tapping point (TP) and the intercuspal position (ICP) at the incisal point were calculated. Occlusal contacts at the ICP of individual subjects were also evaluated with black-colored silicone impression material. The correlation between TP-ICP distance and occlusal contact stability was studied. RESULTS TP-ICP distance exhibited negative correlations with the total number of teeth showing occlusal contact at the ICP. Standard deviations of TP-ICP distance also negatively correlated with the extension of occlusal contact area over dentition. CONCLUSIONS This finding indicates that occlusal contacts at the ICP affect the kinematic behavior of tapping movements. The results of this study also suggest that jaw movement data may provide useful clinical information for the evaluation of occlusal contact at ICP.

Comparison between flipped classroom and team-based learning in fixed prosthodontic education

PURPOSE We previously investigated the effects of team-based learning (TBL) on fixed prosthodontic education and reported that TBL could have higher efficiency with high student satisfaction than traditional lecture. In the current report, we introduced flipped classroom to the fixed prosthodontic education and compared their effectiveness based on the final examination score in addition to TBL. METHODS Participants were 41 students from Tokushima University School of Dentistry who attended a fixed prosthodontics course. The first six classes adopted the flipped classroom style while the latter eight classes adopted TBL. To evaluate the relationship between learning styles and their effectiveness, we compared results from the term-end examination between the curriculum covered by flipped classroom and TBL-style classes. To draw comparisons, a referential examination with the same questions was conducted to eight faculty members who had not attended any of these classes. RESULTS Term-end examination results showed that TBL classes had slightly higher scores than flipped classroom classes. Referential examination results also showed higher scores for the same curriculum and no significant interaction was found between class formats and the term-end and referential examination scores. Analysis revealed no noticeable difference in the effectiveness of the class formats. CONCLUSION Our previous study reported that TBL had higher efficiency than traditional style lecture. In the current study, there was no statistical difference in the examination score between flipped classroom and TBL. Therefore, we conclude that both styles are highly effective than traditional style lecture and constitute valid formats for clinical dental education.

Masticatory performance alters stress relief effect of gum chewing

PURPOSE We evaluated the effects of gum chewing on the response to psychological stress induced by a calculation task and investigated the relationship between this response and masticatory performance. METHODS Nineteen healthy adult volunteers without dental problems undertook the Uchida-Kraepelin (UK) test (30 min of reiterating additions of one-digit numbers). Before and immediately after the test, saliva samples were collected from the sublingual area of the participants. Three min after the UK test, the participants were made to chew flavorless gum for 3 min, and the final saliva samples were collected 10 min after the UK test. The experiment was performed without gum chewing on a different day. Masticatory performance was evaluated using color-changing chewing gum. RESULTS Salivary CgA levels at immediately and 10 min after the UK test were compared with and without gum chewing condition. Two-way repeated measures analysis of variance revealed significant interaction between gum chewing condition and changes in CgA levels during post 10 min UK test period. A significant correlation was found between changes in CgA levels and masticatory performance in all participants. CONCLUSION Our results indicate that gum chewing may relieve stress responses; however, high masticatory performance is required to achieve this effect.

Dental Metal Allergy

Dental metal allergy is the general term used to describe allergic diseases caused by reactions to dental metal materials. Recently, allergic symptoms involving other dental materials, such as organic compounds, have been reported, and these allergic diseases need to be referred to as either a dental allergy or dental material allergy. When safety evaluations involving biomaterials are performed, various kinds of risk factors, including the potential for cytotoxicity and/or allergization, need to be taken into consideration (Geurtsen, 2002, Wataha, 2000).

A preliminary investigation of reproducibility of EMG signals during daytime masticatory muscle activity using a portable EMG logging device

Continuous parafunctional masseter muscle activities (MMA) that are associated with daytime bruxism have been suspected to be one of the main pathoetiology for orofacial pain. The purpose of this study was to examine the long-term stability and reliability of daytime EMG measurement of MMA using a portable device (Actiwave; CamNtech Ltd). Daytime masseter muscle EMG of five subjects were recorded for four days in their normal living environment. There was no significant time dependent effect on EMG amplitude during recording period. A total of 4923 MMA events were detected in all analysis periods (129.4h) and classified into phasic type (1209 events, 24.6%), tonic type (1759 events, 37.0%), and mixed type (1377 events, 28.0%). There was no significant difference in the number of occurrence among three MMA types. With respect to the duration and peak MMA, there were significant differences among three MMA types. The result of this study indicated that Actiwave can be used to measure MMA events during daytime with high stability and reliability under the normal living environment and it was suspected that parafunctional habits may be associated with the occurrence patterns of MMA during daytime.