I investigated the relationship between mandibular closing velocity and masseter muscle (Mm) activity. Eight healthy subjects were instructed to perform two rhythmical opening and closing movements at normal opening and closing velocity (NOC) and maximum opening and closing velocity (MOC). Electromyograms were analyzed during three types of closing (ac-celerating, rapidly decelerating and slowly decelerating) and compared with mandibular kinesiograph vertical motion velocity curves (velocity curves). The distdnce the mandible was opened at maximum closing velocity was divided by the maximum opening distance. This ratio for NOC (58.6%) was similar to that for MOC (48.0%). The time of the decelerating phase at maximum closing velocity was divided by the total time of the closing phase. This ratio for NOC (52.0%) was similar to that for MOC (45.7%). The maximum velocity during the closing phase for MOC was significantly greater than that for NOC. Mm activity during the accelerating phase for MOC was significantly greater than that for NOC. However there was no significant difference between Mm activity during the slowly decelerating phase for NOC and that for MOC. During NOC, Mm activity increased significantly as the closing velocity increased. Paths of the smoothed raw Mm electromyograms were similar to those of the velocity curves, and there was a correlation between the smoothed raw electromyograms of Mm and the velocity curves. A comparatively large amplitude was found in the rectified electromyograms slighty ahead of the wave of velocity curves. These results clearly demonstrate that Mm activity regulates mandibular closing velocity.

View full abstract

I investigated the changes in condylar movements caused by intermaxillary elastics used in orthodontic treatment. The subjects included four adults (three males and one female) aged 23〜26 years (mean 24 years). All subjects had normal Class I occulusion with no signs or symptoms of temporomandibular disorder. Six degrees of jaw movement (three of translaton and three of rotation) were recorded and calculated using a Gnatho-Hexagraph at 20 mm jaw opening with and without Class II and Class III intermaxillary elastics. Class II elastics induced the condylar path to move forward. ClassIII elastics pushed it back and up, while increasing mandibular rotation. These results suggest that intermaxillary elastic force can affect condylar movements.

View full abstract

We examined the effect on cell viability of extracts obtained by metal couples of titanium, Ti6Al4V alloy, and 316L stainless steel. Extraction was carried out by freely moving cylindrical specimens of 6mm or 8mm diameter on disk-shaped specimens at 240rpm and 260rpm for 14days. L-929 cells were treated with extracts and filtrates, and cell viability was then evaluated by neutral red assay after 48 hours. The results of extraction at 240rpm were the same as those of the controls. Extraction at 260rpm, on the other hand, produced a marked difference in cell viability depending on the metal couples and diameter of cylindrical specimens. Low cell viability was found in metal couples of the disk-shaped Ti6Al4V alloy with cylindrical specimens. There was no difference in cell viability whether extracts or filtrates were used. These results indicate that dynamic extraction may be useful in evaluating the cytotoxicity of metal couples that mimic stress bearing restorations.

View full abstract

Some strains of Prevotella species isolated from the oral cavity show resistance to β-lactam antibiotics and produce β-lactamase. We examined the induction of β-lactamase by various β-lactam antibiotics in these β-lactamase producer Prevotella. We used seven species of Prevotella that originate from odontogenic infections, including P. intermedia TO126, P. nigrescens TO121 (Pn121), P. nigrescens TO167 (Pn167), P. melaninogenica TO130 (Pm130), P. buccae TO172, P. loescheii TO128 (Pl 128), P. corporis TO175 (Pc175) and P. oris TO177. With the exception of imipenem (IPM), the MICs of β-lactam antibiotics (ampicillin; ABPC, piperacillin, cephalexin; CEX, cefmetazole; CMZ, latamoxef; LMOX and aztreonam; AZT) against Prevotella species used were 32〜 > 1,024μg/ml. Although the MIC of IPM against Pn167 was > 32μg/ml, that of the remaining strains of Prevotella was 0.5〜2.0μg/ml. β-Lactamase activity of Prevotella species were 0.002〜0.046 and 0.010〜0.276 U/mg protein, respectively, after 15h incubation for substrates of cefazolin and ABPC measured by the spectrophotometer. β-Lactam antibiotics with high induction ratios (enzyme activity with β-lactam / enzyme activity without β-lactam) were observed in all Prevotella species used. The induction ability of β-lactam antibiotics was observed after exposure to CMZ, LMOX and CEX. The β-lactamase induction ratio of CMZ was very high in Pn121, Pl128, Pm130. The induction ratio of LMOX and CEX was also high in Pc175. These results suggest that β-lactam antibiotics induce β-lactamase in anaerobic gramnegative rod Prevotella species. Moreover, it seems that productivity and induction of β-lactamase in Prevotella species correlate with a high MIC of β-lactam antibiotics against these bacteria.

View full abstract

Guided tissue regeneration (GTR) attempts to promote new connective tissue fiber attachment and new cementum formation by excluding gingival epithelium and connective tissue proliferation into the wound adjacent to the root surface, which is done by creating space between the inner surface of the barrier membrane and the root surface. Using microvascular corrosion casts of the bone, we studied the sequential changes that occurred in the socket following tooth extraction and determined the correlation between new vascularization and bone formation during the healing process when various membranes were placed on the socket. Although the barrier membrane maintained space between the gingiva and bone for tissue regeneration and bone formation, it did not actively promote tissue growth. Therefore, although the membrane did not accelerate healing of the socket, it increased the amount of bone formed. We found that proper use of the membrane was necessary for GTR. Although the barrier membrane was useful for alveolar bone regeneration, its promotion of tissue regeneration was less than perfect from a microvasculatural point of view.

View full abstract

The first report on guided tissue regeneration (GTR) was published by Nyman et al. in 1982. They found that the ability of the periodontal ligament cells to form new attachment manifests itself only provided that epithelial cells, gingival connective tissue cells and bone cells are prevented from occupying the wound area adjacent to the root during the initial phase of healing. Since that time the GTR method has been used as a treatment for periodontal disease to create new attachment. In 1988 Dahlin et al. reported tissue regeneration in rats. They concluded that, "The results obtained demonstrate that a mechanical hindrance to connective tissue proliferation into a bone defect can be of profound importance for unimpeded bone healing. "Subsequently GTR was applied to implant therapy in humans. Originally implant therapy was restricted by anatomical considerations, such as the maxillary sinus and the mandibular canal. Recognition of the benefits of implant therapy has led to increased demand for this treatment. In the absence of GTR, treatments such as bone grafts were required. Although there have been continual improvements in the materials used, the surgical procedures are not easy. Future improvements will lead to increased application of GTR.

View full abstract

We examined speech intelligibility after glossectomy and analyzed electromyograms (EMG) of myoelectrical activity of the sternocleidomastoid and trapezius muscles at various head positions after radical neck dissection. Speech intelligibiljty after glossectomy became lower the larger the area of resection. Although articulation was very good in the case of partial glossectomy, it was markedly impaired with hemiglossectomy. However, patients who had reconstruction by a pectoralis major myocutaneous flap operation were able to recover an essentially normal social life.Analysis of electromyograms after radical neck dissection revealed compensatory activities in the middle part of the sternocleidomastoid muscle with ventral flexion, and in the trapezius muscle on the side of the operation with ipsilateral tilting.

View full abstract