Shuichiro Yamashita

A Newly Proposed Method to Predict Optimum Occlusal Vertical Dimension.

PURPOSE Establishing the optimum occlusal vertical dimension (OVD) in prosthetic treatment is an important clinical procedure. No methods are considered to be scientifically accurate in determining the reduced OVD in patients with missing posterior teeth. The purpose of this study was to derive a new formula to predict the lower facial height (LFH) using cephalometric analysis. MATERIALS AND METHODS Fifty-eight lateral cephalometric radiographs of Japanese clinical residents (mean age, 28.6 years) with complete natural dentition were used for this study. Conventional skeletal landmarks were traced. Not only the LFH, but six angular parameters and four linear parameters, which did not vary with reduced OVD, were selected. Multiple linear regression analysis with a stepwise forward approach was used to develop a prediction formula for the LFH using other measured parameters as independent variables. RESULTS The LFH was significantly correlated with Gonial angle, SNA, N-S, Go-Me, Nasal floor to FH, Nasal floor to SN, and FH to SN. By stepwise multiple linear regression analysis, the following formula was obtained: LFH (degree) = 65.38 + 0.30* (Gonial angle; degree) - 0.49* (SNA; degree) - 0.41* (N-S; mm) + 0.21* (Go-Me; mm) - 15.45* (Nasal floor to FH; degree) + 15.22* (Nasal floor to SN; degree) - 15.40* (FH to SN; degree). CONCLUSIONS Within the limitations of this study for one racial group, our prediction formula is valid in every LFH range (37 to 59°), and it may also be applicable to patients in whom the LFH deviated greatly from the average.

Relationship between stage II transport and number of chewing strokes as mastication progresses

As mastication progresses, little is known about the occurrence of the stage II transport (oro-pharyngeal bolus transport). This study aimed to investigate the relationship between stage II transport and bolus aggregation in the pharynx and the number of chewing strokes. Twenty-five clinical residents with natural dentitions were recruited. The subjects were asked to chew gummy jelly with their preferred rhythm and to swallow the bolus at their preferred timing. To investigate stage II transport and bolus aggregation in the pharynx, a transnasal endoscope was used. The number of chewing strokes was measured by electromyographic activity from the masseter muscle. The mean numbers of chewing strokes of pre-stage II transport and post-stage II transport were 29.8 and 8.1, respectively; the difference was significant (p<0.01). The ratio of the number of chewing strokes of pre-stage II transport to that of post-stage II transport was 4.0 to 1.0. This study showed that stage II transport started at four-fifths of the way along the progress of mastication, and that stage II transport and bolus aggregation in the pharynx are related to the number of chewing strokes.

Association between the variable number of tandem repeat polymorphism in the third exon of the dopamine D4 receptor gene and sensitivity to analgesics and pain in patients undergoing painful cosmetic surgery.

To elucidate the mechanisms of individual differences in pain and analgesic sensitivity, we analyzed the variable number of tandem repeat polymorphism in the third exon of the dopamine D4 receptor gene. Alleles that were less than four repeats long and four or more repeats long were considered Short and Long, respectively. We found that the Short/Short genotype group was significantly more sensitive to pain and less sensitive to analgesics than the Short/Long+Long/Long genotype group. Our data suggest that this polymorphism may predict individual differences in pain and analgesic sensitivity and help achieve adequate pain control in the future.

Location of main occluding areas and masticatory ability in patients with implant-supported prostheses.

BACKGROUND The purpose of this study was to locate the main occluding area when the reduced posterior occlusal support was treated with an implant-supported prosthesis and to evaluate the subsequent improvement in the masticatory ability as compared with removable partial dentures. METHODS Twenty-six patients with implant prostheses and 24 patients with removable partial dentures were recruited for this study. All patients had partially lost their posterior occlusal support. The first molar region in any quadrant was always included in the prosthetic region. Each subject was instructed to clench a piece of temporary stopping as a test food on the occluding area that was preferably used during mastication. The main occluding area was judged by locating the tooth on which the temporary stopping rested during clenching. Subjective masticatory ability was self-assessed by means of a questionnaire. RESULTS The main occluding area of the subjects in the implant group was located more posterior compared with the removable partial denture group. The level of masticatory ability in the implant group was the same as that in the control group. CONCLUSIONS The location of the main occluding area and the masticatory ability of the subjects with implants were equivalent to those with healthy natural dentition.

Newly designed gustatory test based on the number of chewing strokes required for recognition of the taste

PURPOSE The purpose of this study was to examine the usefulness of a new gustatory test based on the progress of mastication by counting the number of chewing strokes required for recognizing tastes. METHODS Thirty-nine subjects (20 males and 19 females, 25.3±6.4 years old) without missing teeth were selected. Four types of newly designed test materials made from 15% gelatine were prepared, containing sucrose, sodium chloride, tartaric acid, or quinine hydrochloride. Five or six concentrations, representing weak to strong tastes, were prepared for each tastant. Subjects were instructed to chew the food, and the number of chewing strokes necessary to recognize the taste was counted. RESULTS Female subjects recognized the sweet taste more accurately than male subjects (Friedman test: p<0.05). For each tastant of the test materials, the average number of chewing strokes (recognition threshold) was approximately 10. The frequency of correct responses and the average number of chewing strokes tended to be higher and lower, respectively, as the concentration of the taste in the test material increased (Kruskal-Wallis test: sweet p<0.01, salty p<0.01, sour p<0.01 and bitter p<0.01). CONCLUSIONS Using the newly designed test materials, counting the number of chewing strokes necessary for recognizing the taste would be a useful index of a new gustatory test to investigate taste sensation.

Psychological stress-relieving effects of chewing — Relationship between masticatory function-related factors and stress-relieving effects —

PURPOSE The objective of the present study was to investigate the relationship between masticatory function-related factors (masticatory performance, occlusal contact area, maximum bite force, number of chewing strokes, and muscle activity) and the stress-relieving effects of chewing. METHODS A total of 28 healthy male subjects were instructed to rest or chew for 10min after 30min of stress loading with arithmetic calculations. Their stress state was assessed by measuring salivary cortisol levels. Saliva was collected at three time points: before stress loading, immediately after stress loading, and 10min after stress loading. Compared to resting, chewing produced a significantly greater reduction in the rate of change in salivary cortisol levels 10min after stress loading. RESULTS A negative correlation was observed between the rate of decrease in salivary cortisol levels and the number of chewing strokes. No significant correlation was observed between the rate of decrease in salivary cortisol levels and other measurement items. CONCLUSION In healthy dentulous people, the number of chewing strokes has been shown to be a masticatory function-related factor that affects stress relief from chewing, suggesting the possibility that more appropriate chewing would produce a greater effect psychological stress relief.

Transversal Width of Mandibular Bone and Neurosensory Disturbance after Bilateral Sagittal Splitting Ramus Osteotomy

Objective: This study evaluated the condition of mandibular cancellous and cortical bone on computed tomography (CT) images in order to investigate its relationship with the incidence of neurosensory disturbances (NSD) in the mental nerve region after bilateral sagittal splitting ramus osteotomy (BSSRO). Methods: BSSRO was performed on 58 lateral mandibles in 29 patients. From preoperative CT images, the width endpoints of the transversal bone were measured in region I immediately inferior to the mandibular foramen, region II in the mandibular angle region, and region III distal to the lower second molar. The incidence of NSD immediately after surgery and the residual NSD rate at 1, 3, and 6 months after surgery were investigated. The correlation between incidence of NSD in the mental nerve region and each transversal bone width endpoint immediately after and at 6 months after surgery was also comparatively evaluated. Results: The overall incidence of NSD immediately after surgery was 67.2% (39/58 sides) and the overall residual NSD rate at 1, 3, and 6 months after surgery was 53.4% (31/58 sides), 31.0% (18/58 sides), and 17.2% (10/58 sides), respectively. No significant differences were observed for any width endpoints of the transversal bone measured at regions I or III, but the transversal width of the entire mandible was significantly different in region II between patients with and without NSD at 6 months after surgery (p < 0.05). Conclusion: These findings demonstrate that the transversal width of the entire mandible may be an important factor in predicting NSD incidence.

Determinant Factors in Locating Main Occluding Area on Dental Arch

The purpose of this study was to investigate which were the most important factors in determining the location of the main occluding area by comparing its site on the dental arch between patients treated with implant-supported prostheses and those with a shortened dental arch (SDA). Twenty-five patients with Eichner B1 occlusion were enrolled in the study. The molar region in each quadrant was always edentulous. Fifteen patients were treated with implant prostheses, while the remaining 10 patients had SDA. Each patient was instructed to clench a piece of temporary stopping in the occluding area that was preferably used during mastication. The main occluding area was determined by locating the tooth on which the temporary stopping rested during clenching. The main occluding area was located ipsilaterally to the edentulous side in the molar region more often in the implant patients than in the SDA patients. The results of the present study suggest that the most important factor in determining the main occluding area is the presence of bilateral rigid molar occlusal support.

Treatment Capabilities of Postgraduate Dental Trainees at okyo Dental College Suidobashi Hospital Based on Dental Services Income

As of fiscal year 2006, it became compulsory for all newly licensed dentists in Japan to undergo a year of practical training at one of the designated training facilities found throughout the country as part of their postgraduate programs. The goal of this training is for the trainees to acquire diagnostic and therapeutic skills. While officially trainees, they are nonetheless regarded as members of staff. Clinical training emphasizes improving both technical skills and theoretical knowledge. However, taking on such trainees is sometimes considered unprofitable, as work productivity is claimed to be low. The purpose of this study was to compare work outcomes and income generated between trainees and part-time dentists working at the Tokyo Dental College Suidobashi Hospital. The part-time dentists comprised clinical instructors and dentists responsible for outpatients. Postgraduate dental trainees also generally conduct dental treatment for outpatients. Therefore, part-time dentists were considered the most suitable for a control group. No significant difference was observed in the total number of patients seen by either group by the final term of clinical training. Furthermore, no significant difference was observed in insurance-based dental treatment unit income (insured care unit income) per patient between the two groups from the mid-term period of training onwards. These results suggest that, although the trainees were less efficient in terms of time taken to provide a diagnosis and treatment, their performance was almost equal when viewed from the viewpoint of insured care provided. Taken together, this suggests that time-related care efficiency must be increased and specific training policies and strategies developed to improve the work productivity of dental trainees.