3-T MRI safety assessments of magnetic dental attachments and castable magnetic alloys.

OBJECTIVES: To assess the safety of different magnetic dental attachments during 3-T MRI according to the American Society for Testing and Materials F2182-09 and F2052-06e1 standard testing methods and to develop a method to determine MRI compatibility by measuring magnetically induced torque. METHODS: The temperature elevations, magnetically induced forces and torques of a ferromagnetic stainless steel keeper, a coping comprising a keeper and a cast magnetic alloy coping were measured on MRI systems. RESULTS: The coping comprising a keeper demonstrated the maximum temperature increase (1.42 °C) for the whole-body-averaged specific absorption rate and was calculated as 2.1 W kg⁻¹ with the saline phantom. All deflection angles exceeded 45°. The cast magnetic alloy coping had the greatest deflection force (0.33 N) during 3-T MRI and torque (1.015 mN m) during 0.3-T MRI. CONCLUSIONS: The tested devices showed minimal radiofrequency (RF)-induced heating in a 3-T MR environment, but the cast magnetic alloy coping showed a magnetically induced deflection force and torque approximately eight times that of the keepers. For safety, magnetic dental attachments should be inspected before and after MRI and large prostheses containing cast magnetic alloy should be removed. Although magnetic dental attachments may pose no great risk of RF-induced heating or magnetically induced torque during 3-T MRI, their magnetically induced deflection forces tended to exceed acceptable limits. Therefore, the inspection of such devices before and after MRI is important for patient safety.

Numb chin syndrome secondary to Burkitt's cell acute leukemia.

We describe a case of Burkitt's cell acute lymphoblastic leukemia presenting with the bilateral numb chin syndrome as the initial symptom of the disease. Postmortem study of the trigeminal nerve showed heavy infiltrations of leukemic cells and destruction of axon and myelin by leukemic cells in the mandibular nerve.

ProNectin F-grafted-ethylene vinyl alcohol copolymer (EVAL) as a liquid type material for treating cerebral aneurysm--an in vivo and in vitro study.

The authors aimed to develop a liquid material for embolization of aneurysms. In vitro and in vivo performances of the new embolic material were examined by cell culture and using an aneurysm model made in common carotid arteries (CCAs) of adult rats. Engineered protein ProNectin F (PnF), which contains 13 sites of an arginine-glycine-aspartic acid (RGD), was grafted onto ethylene vinyl alcohol copolymer (EVAL-g-PnF). The liquid material, EVAL-g-PnF dissolved in DMSO, was infused into an aneurysm model. The blood segments were harvested 2, 5, and 14 days and examined histologically. A number of bovine coronary artery endothelial cells became able to attach to and form cobblestone-like islands on the EVAL by incorporating PnF. The aneurysm model infused with the EVAL-g-PnF solution revealed that the aneurysm lumen was filled with proliferated fibroblasts and macrophages. On the other hand, the aneurysm model treated with unmodified EVAL showed that the cavity was almost filled with EVAL mass and that fibroblasts and macrophages filled a narrow space between the EVAL mass and the cavity wall. The results indicate that EVAL-g-PnF could be more suitable for reorganizing the cavity of an aneurysm than native EVAL.

Defective neutrophil chemotaxis in Down's syndrome patients and its relationship to periodontal destruction.

The degree of defective neutrophil chemotaxis in patients with Down's syndrome (DS) and its relationship to the severity of periodontal disease were studied. Fourteen patients with DS and 14 healthy controls were examined. Oral hygiene, gingival inflammation, and pocket depths were measured in clinical surveys. Bone loss was evaluated on the oral radiographs. Neutrophil chemotaxis was measured by the agarose plate method and the Boyden chamber method. The chemotactic index of the agarose plate method and the mean numbers of migrated cells of the Boyden chamber method were correlated with statistical significance (rs = 0.066, P less than 0.01). DS patients showed significantly lower chemotaxis than healthy volunteers with both methods. No difference was shown between the two groups in the random migration of the neutrophils. From the oral radiographic analysis, the DS patients exhibited various prevalence of bone loss which was inversely proportional to the chemotactic index and a significant correlation between them was shown (rs = -0.612 P less than 0.05). A significant correlation was also found between the age of the patient and the prevalence of bone loss (rs = 0.591 P less than 0.05). These results indicate that defective neutrophil chemotaxis influences the progression of periodontal disease in DS patients.

Predominant role of local immunosuppressive effect in enhanced efficacy of liposomal FK506 in organ transplantation.

Liposomal FK506 is a new formulation of FK506 that increases FK506 levels in the liver and decreases them in the kidney in comparison to conventional IV formulation. In the present study, the efficacy of liposomal FK506 was evaluated in canine kidney and liver transplantation models. Liposomal FK506 increased the immunosuppressive efficacy of FK506 in the liver transplantation model, but decreased it in the kidney transplantation model. These results suggest that local immunosuppressive effects with increased intragraft FK506 level would play an important role in enhancing the immunosuppressive efficacy of liposomal FK506 in liver transplantation.

Different immunosuppressive effects of liposomal FK506 in liver and kidney transplantation.

The efficacy of liposomal FK506 was compared between a canine liver transplantation model and a canine kidney transplantation model. The present study revealed that liposomal FK506 increased immunosuppressive efficacy of FK506 in liver transplantation but decreased in kidney transplantation. Because liposomal FK506 increased FK506 levels in the liver and spleen, and decreased FK506 levels in the kidney, it was suggested that enhanced immunosuppressive efficacy in liver transplantation should be attributed to the local immunosuppressive effects in the hepatic allograft rather than effective suppression of splenocyte activity.

Finite element contact stress analysis of the RPD abutment tooth and periodontal ligament.

OBJECTIVES: The purpose of this study was to determine the influence of the occlusal rest position in removable partial dentures on the displacement of the abutment tooth and the stress distribution in the periodontal ligament (PL). METHODS: We constructed three-dimensional finite element models of the mandibular first and second premolars. A layer of the PL and a mesial or distal occlusal rest were produced on the second premolar as an abutment. A zero displacement was prescribed on the outer surface of the PL and the first premolar. In each simulation, the rest was moved 0.05 mm vertically to the apical direction, with or without restriction of horizontal movements. We simulated the contact phenomena on the abutment surfaces, and calculated the movements of the abutment and stress distributions in the PL. RESULTS: We observed a maximum distal displacement of 42 microm at the buccal cusp of the abutment and a principal compressive stress of 0.35 MPa in the PL when the abutment was vertically loaded by a distal rest that was allowed to move horizontally. However, the displacements and stresses were relatively small, and were all within the physiological limitations of the tissues. The restriction of the horizontal movement of the rests was effective in reducing the horizontal displacements of the abutment, regardless of the rest position. CONCLUSIONS: The single vertical load exerted from either the mesial or distal rest on the abutment was unlikely to cause any mechanical damage to its supporting tissues.

Foreign bodies of dental origin in the air and food passages.

6 cases in which a reamer or a cast object was swallowed into the stomach or into the bronchus during dental treatment are described, with a review of the Japanese literature. The foreign bodies were removed by duodenotomy in one case, by endoscopic or bronchoscopic procedure in three cases; spontaneous evacuation in the stool occurred in two cases. The management of patients who swallowed a foreign body into the airway or into the alimentary canal is discussed.

Prosthodontic considerations for patients with cleft lip and palate.

The prosthodontist provides the final active treatment for the patient with a cleft. He must anticipate and decide upon the prosthodontic procedures in collaboration with the plastic surgeon and/or the orthodontist during the period of their interventions. The purpose of prosthodontic treatment is to prevent the relapse of the maxillary segments and the teeth after surgical and/or orthodontic correction, as well as the rehabilitation of mastication, speech and aesthetics. The individual peculiarities of the cleft patient should be taken into consideration from the beginning. They are: discrepancy in the maxillo-mandibular relationship, malposition, malformation and tipping of teeth, caries, flat palate resulting from severe scarring, perforations. It is imperative to preserve the teeth in any condition with the exception of occlusal interference. Extraction of teeth adjacent to the cleft or in scar tissue leads to extensive bone resorption, enlargement of the cleft and gingival recession. Generally speaking, two teeth in each alveolar segment should be used as abutment teeth in bridge work. The teeth likely to relapse should be reconstructed in good intercuspal digitation and splinted primarily or secondarily. Bridge work is the first choice among the various prosthodontic procedures. If, however, a removable prosthesis is inevitable, rigid support should be obtained.

The vibration analysis of obturator framework designs.

The purpose of this study was to analyze the vibration of obturator framework designs and investigate the vibration effects of connecting parts of the components. Four designs of maxillary obturator framework were used in this study: a partial palatal plate with continuous bar (A), with a part of continuous bar (B), without continuous bar (C) and without continuous bar and indirect retainer (D). In order to investigate the vibration of each framework (total) and some component parts, the measurement points of the retentive parts were divided into 3 groups; anterior, middle and posterior. The framework was activated by a vibration generator. The vibration of each measurement point was detected with a laser doppler vibrometer. The frequency response signals were conducted by an FFT Analyzer between 220-2000 Hz. The maximum displacement (MDP) and the decay rate (DR) of the vibration were analyzed statistically by ANOVA and Fisher's PLSD (p<0.05). The result showed that in the posterior group, MDP of D was higher than those of A, B and C. Regarding the anterior, middle and total group, the DR of D were lower than A, B and C. It was suggested that D might be clinically unfavorable.

Evaluation of obturator prostheses using vibration analysis.

Obturator prostheses have been extensively used in the functional rehabilitation of maxillectomy patients. The purpose of this study was to evaluate in vitro the vibration movements of three types of obturator prostheses. Three types of bulbs were used: the solid type, the buccal flange type, and the hollow type. Modal analysis was performed to identify the better form. The three types of obturator prostheses were excited by a shaker, and the frequency response functions were recorded on an FFT analyzer to identify their modal shapes. In addition, transient response simulations were carried out, and decay rates of the resultant transient response waves were compared to evaluate the energy absorption after the obturator prosthesis had experienced an impact. The results showed that the modal shapes were closely similar, while the amplitudes at the rests and clasps of the hollow type bulb were the smallest. In the transient response simulation, the decay rates of the hollow type were significantly the highest (p < 0.01). In this study, modal analysis demonstrated that the hollow type obturator prosthesis showed the steepest vibration decay slope, indicating that it might be the best among the three types of bulbs for use in clinical treatments.

Evaluation of athletic mouthguard through vibration test on maxillary teeth of human dry skull.

The athletic mouthguard has been used for the prevention of orofacial injuries in contact sports. In this research, the effectiveness of a mouthguard was evaluated for its protection of the maxillary teeth of a human dry skull through experimental modal analysis. The upper central incisor was excited by an electrodynamic shaker. The frequency response functions of the upper teeth were then recorded on an FFT analyzer in order to identify modal shapes of the maxillary arch with and without a mouthguard. In addition, transient response simulations were carried out and decay rates of transient response waves were compared. As a result, when the mouthguard was in place, the resonance peaks of the frequency response functions were dampened, and the nodes of the modal shapes for the anterior teeth were indefinite in the frequency domain over 1 kHz. In the transient response simulation, the decay rates of transient response waves when the mouthguard was used were significantly higher than those when the mouthguard was not used (p<0.01). The results suggest that the mouthguard relieves the stress concentrated on the anterior teeth in a frontal collision by absorbing and dispersing some of the shock energy, thus quickly stopping the vibration of the maxillary teeth. These findings support the clinical fact that mouthguards prevent orofacial injuries in sporting activities.

Effect of teeth clenching on isometric and isokinetic strength of ankle plantar flexion.

To investigate the effect of voluntary teeth clenching on the isometric and isokinetic exercises of the lower limbs, the association of muscle strength (peak torque, PT) and muscle activities (integrated electromyographic activity per unit of time, iEMG/s) of the three muscles of the triceps surae with teeth clenching during isometric and isokinetic plantar flexion were simultaneously measured for 12 healthy male volunteers using a Cybex 6000 Extremity Testing and Rehabilitation System and a surface EMG analyzing system. The statistical analysis demonstrated that for the isometric exercise, PT and each iEMG/s significantly increased in association with teeth clenching, and a positive correlation existed between the biting force and each variable. In contrast, no association was found with teeth clenching for the isokinetic exercise. In this study, therefore, it was found that the effect of teeth clenching differed between the isometric and isokinetic exercises.

Application of modal analysis to human subjects: comparison of healthy subjects and cleft lip and palate subjects.

To evaluate the vibrational characteristics of the maxillary arch, modal analysis was applied to human subjects. Twelve healthy human subjects and 2 cleft lip and palate (CLP) subjects with surgical failure in their cleft area were chosen for this study. The main measurement system was composed of an impact hammer, acceleration sensor, CF-6400 FFT Analyzer, PC-9821Xn personal computer, and Vibrant PC modal analysis software. The measurement points were established on 12 teeth between the upper first molars on both sides of the mouth in healthy subjects, and on 10 teeth in CLP subjects. In all subjects, one distinct resonance peak was observed in each transfer function at each measurement point. All of the transfer functions of a given subject strongly resembled each other in terms of shape. The amplitude and modal shapes of the maxillary arches of all the subjects were obtained by using a curve-fitting function in the software. In the healthy subjects, the maxillary arch expanded outward and shrank inward on vibration with no node after an impact. In the CLP subjects, the phase lag between the large and small segment was distinctly observed after an impact. In this study, the applicability of modal analysis for human subjects was demonstrated.

The vibratory properties of an obturator prosthesis with a soft lining material.

This study used modal analysis to evaluate the vibratory properties of cast obturator prostheses fitted with soft lining material. Three types of buccal flange bulbs were prepared: a resin (R) type; a 2 mm-thickness relined (RM) type; and a type fully relined with MOLTENO, (M) type. A vibration generator excited the obturator, while a Laser-Doppler Vibrometer detected the vibrations at specified measurement points. Both the excitation and response signals were sent to an FFT analyzer, which calculated the frequency response functions. Then, using DAMPCAL simulation software, the decay rates and the maximum amplitudes of rest and clasp parts were calculated. Statistical analysis was performed by means of one-way ANOVA with Fisher's PLSD test. The results indicated that for impacts simulated on both the defective and non-defective sides, the R type showed a significantly higher decay rate than did the other samples (p<0.0001). When impacts were directed at the non-defective side, the R and M types showed significantly smaller maximum amplitude values than did the RM type (p<0.0001). Only the M type, however, showed significantly smaller values when impacts were directed at the defective side (p<0.0001).

Study of mandibular movements in mandibulectomy patients--border movements and functional movements during mastication, deglutition and speech.

In mandibulectomy patients who have not undergone surgical reconstruction, the remaining mandibular segment is unstable and often deviated. Its movements have low reproducibility during mastication, deglutition and speech. The purpose of this study was to clarify three-dimensionally the differences in mandibular movements for each of these oral functions in mandibulectomy patients with and without mandibular continuity. Four mandibulectomy subjects (Group I) without mandibular continuity and three subjects (Group II) with mandibular continuity were selected. Their mandibular movements were recorded using a jaw movement tracking device with six degrees of freedom. Each movement was assessed graphically at the virtual incisor point and the rotational angles of the mandible in the frontal, sagittal and horizontal plane were analyzed. The findings were as follows; 1. In Group I, the border movements at the virtual incisor point exhibited an irregular and asymmetric envelope deviated to the resected side in the frontal plane, whereas Group II exhibited a smooth and symmetric envelope. 2. In Group I, the rotational angles in the frontal plane during border movements and mastication, in all planes during speech, and in the frontal and horizontal plane during deglutition were significantly larger than in Group II. A comparison among border and all functional movements in mandibulectomy patients revealed characteristic movements in the rotation of the mandible in the frontal plane. It is suggested that the rotational angle of the mandible is a useful parameter for assessment of mandibular movements in mandibulectomy patients.

Mobility of the obturator prosthesis in hemimaxillectomy edentulous patients.

In edentulous patients with maxillary defects, it is difficult to obtain sufficient retention, support, and stability of the obturator prosthesis, in addition, its mobility during various functions is considered to be large. A thorough understanding of the mobility of the obturator prosthesis is important to achieve successful results in the patient's oral rehabilitation. In this study, the ranges of movement of the obturator prostheses in three hemimaxillectomy edentulous patients were compared during tapping, chewing (biscuit), and opening and clenching jaw movements by simultaneously conducting three-dimensional measurements of three points that were established on the central incisor and the right and left first molars of the obturator prosthesis with a jaw movement tracking device having six degrees of freedom. This study indicates that the range of movement of the obturator prosthesis varied extensively from individual to individual. The ranges of movement were larger than those of normal complete dentures and differed considerably from each other when categorized according to the three functions and three measuring points in the patients.

Dynamic retentive force of a mandibular unilateral removable partial denture framework with a back-action clasp.

PURPOSE: The purpose of this study was to investigate the dynamic retentive force of a mandibular unilateral distal-extension partial denture framework with a back-action clasp that was designed in a buccally tilted cast on a dental surveyor. The retention mechanism of this framework was analyzed in comparison with other typical unilateral and bilateral frameworks for the mandibular Kennedy class II case. MATERIALS AND METHODS: Experimental gold alloy frameworks of three designs were repositioned to the master cast, and lifted upward to the vertical direction to the occlusal plane. The load required to dislodge each framework was recorded. The retentive force of each framework was determined by the maximum load in a dislodgment cycle. The bending strength of a plain clasp pattern of the same length as the clasp arm used in each framework was also measured by cantilever beam test. RESULTS: The mean retentive force of the unilateral framework with a back-action clasp of relatively low bending strength was significantly higher (P < 0.01) than that of the unilateral framework with two Akers clasps of relatively high bending strength, and 70 to 80% of the bilateral framework with two Akers clasps on the edentulous side and a double Akers clasp on the contralateral side. The unilateral framework with a back-action clasp showed the greatest early load resistance in the dislodgment cycle among the three designs. CONCLUSION: The reasonable retention mechanism was demonstrated by the unilateral framework with a back-action clasp.

Masticatory mandibular movements for different foods textures related to onomatopoetic words.

This study aimed to investigate the effects of different sensory-evaluated food textures on masticatory movements, and to identify meaningful factors that correspond to different food textures. Masticatory movements of three healthy subjects were evaluated with a jaw movement tracking device using five different test foods: almond, hard and light rice crackers, apple, and chewing gum. The movements of the incisor point, working and non-working condyle and the entire mandible at the occlusal phase in the horizontal plane were analyzed. For harder foods, the incisor entered the intercuspal position from a rear and lateral, the working condyle showed anterior and noticeable medial movements as the entire mandible translated posteriorly and medially. For soft foods, the incisor movements were nearly coincidental with the lateral border movements, and the mandible rotated towards the inner side near the working condyle. Although the overall paths of the mandibular movements are individually different, it appeared that jaw movement at the final closure is particular to the food texture. From the standpoint of mandibular movements, it is suggested that masticatory movements during the occlusal phase in the horizontal plane is useful for revealing the relationship between mandibular movements and food textures that were evaluated with onomatopoetic words.

Eight-year trend of new patients at Clinic for Disabled Patients, University Hospital, Faculty of Dentistry, Tokyo Medical and Dental University.

The trend of new patients was investigated at the Clinic for Disabled Patients, University Hospital, Faculty of Dentistry, Tokyo Medical and Dental University for eight years from 1989 to 1996. The purpose of this study was to explore the future role of this specialized clinic. The study revealed the following information: 1. A total of 1,388 new patients, corresponding to 173.5 new patients per year on average, visited the clinic. 2. The percentage of patients aged 30 or more increased. As a result, the mean patient age rose from 40.4 in 1989 to 47.6 in 1996. 3. Referrals accounted for more than 80% of new patients. Medical doctors referred more patients to our clinic than dentists did. 4. While the percentage of disabled patients tended to decrease, the percentage of medically compromised patients increased. 5. The predominant complaint was dental caries. Patients with cardiovascular diseases also complained of gingival bleeding and ill-fitting dentures. The growing percentage of medically compromised patients and the increasing mean age of patients over the eight-year period seems to reflect advances in medical science and the aging society. These tendencies could be more remarkable in the future. Therefore, much closer cooperation between dentists and medical doctors will be required.