Head position affects the direction of occlusal force during tapping movement.

Despite numerous reports describing the relationship between head position and mandibular movement in human subjects, the direction and magnitude of force at the occlusal contacts have not been investigated in relation to head position. The objective was to investigate the effect of head position on the direction of occlusal force while subjects performed a tapping movement. Twenty-three healthy adult subjects were asked to sit on a chair with their back upright and to perform 15 tapping movements in five different head positions: natural head position (control); forward; backward; and right and left rolled. The direction and magnitude of force were measured using a small triaxial force sensor. The Wilcoxon signed-rank test and Bonferroni test were used to compare head positions in each angle of the anteroposterior axis direction and the lateral axis direction with respect to the superior axis. The force element in the anteroposterior axis shifted to the forward direction in the head position pitched backward, compared with control, pitched forward and rolled left positions (P = .02, <.01 and <.01, respectively). The force direction in the lateral axis with the head position rolled to the right or left shifted to the left and right directions, respectively, compared with those in the other positions (P < .05). Results of this study suggest that the head should be maintained in a position in which a stable tapping movement can be performed in a relaxed position without anteroposterior and lateral loading.

Short-term changes in chewing efficiency and subjective evaluation in normal dentate subjects after insertion of oral appliances with an occlusal flat table.

Oral appliances with an occlusal flat table are used as treatment dentures. However, the short-term effect of insertion of such oral appliances on chewing has not been reported. This study aimed to determine whether experimental and continuous insertion of oral appliances with an occlusal flat table has an effect on chewing efficiency and Oral Health Impact Profile (OHIP) in healthy participants. Ten participants each in the oral-appliance and control (no oral-appliance insertion) groups attended six data collection sessions for 5 consecutive days. Participants answered the OHIP questionnaire and underwent the chewing efficiency test. For each parameter, intergroup differences were investigated in terms of change from baseline to immediately after oral-appliance insertion (0 hour; P < .05) and from 0 hour to 24, 48, 72 and 96 hours after oral-appliance insertion (P < .05). There were significant differences between groups in the degree of change in chewing efficiency and OHIP scores for functional limitation, physical pain, physical disability and handicap from baseline to 0 hour (all, P < .001); among these, only OHIP scores for functional limitation and physical pain demonstrated significant differences in degree of change between the two groups at 96 hours after appliance insertion (P = .477 and .275, respectively). Differences between the two groups in the degree of change in other parameters were not significant. Insertion of oral appliances caused a decrease in chewing efficiency and an increase in OHIP scores. Continuous insertion improved functional limitation and physical pain within 96 hours.

Masseter motor unit recruitment is altered in experimental jaw muscle pain.

Some management strategies for chronic orofacial pain are influenced by models (e.g., Vicious Cycle Theory, Pain Adaptation Model) proposing either excitation or inhibition within a painful muscle. The aim of this study was to determine if experimental painful stimulation of the masseter muscle resulted in only increases or only decreases in masseter activity. Recordings of single-motor-unit (SMU, basic functional unit of muscle) activity were made from the right masseters of 10 asymptomatic participants during biting trials at the same force level and direction under infusion into the masseter of isotonic saline (no-pain condition), and in another block of biting trials on the same day, with 5% hypertonic saline (pain condition). Of the 36 SMUs studied, 2 SMUs exhibited a significant (p < 0.05) increase, 5 a significant decrease, and 14 no significant change in firing rate during pain. Five units were present only during the no-pain block and 10 units during the pain block only. The findings suggest that, rather than only excitation or only inhibition within a painful muscle, a re-organization of activity occurs, with increases and decreases occurring within the painful muscle. This suggests the need to re-assess management strategies based on models that propose uniform effects of pain on motor activity.

The effect of food bolus location on jaw movement smoothness and masticatory efficiency.

Masticatory efficiency in individuals with extensive tooth loss has been widely discussed. However, little is known about jaw movement smoothness during chewing and the effect of differences in food bolus location on movement smoothness and masticatory efficiency. The aim of this study was to determine whether experimental differences in food bolus location (anterior versus posterior) had an effect on masticatory efficiency and jaw movement smoothness. Jaw movement smoothness was evaluated by measuring jerk-cost (calculated from acceleration) with an accelerometer that was attached to the skin of the mentum of 10 asymptomatic subjects, and acceleration was recorded during chewing on two-colour chewing gum, which was used to assessed masticatory efficiency. Chewing was performed under two conditions: posterior chewing (chewing on molars and premolars only) and anterior chewing (chewing on canine and first premolar teeth only). Jerk-cost and masticatory efficiency (calculated as the ratio of unmixed azure colour to the total area of gum, the unmixed fraction) were compared between anterior and posterior chewing with the Wilcoxon signed rank test (two-tailed). Subjects chewed significantly less efficiently during anterior chewing than during posterior chewing (P = 0·0051). There was no significant difference in jerk-cost between anterior and posterior conditions in the opening phase (P = 0·25), or closing phase (P = 0·42). This is the first characterisation of the effect of food bolus location on jaw movement smoothness at the same time as recording masticatory efficiency. The data suggest that anterior chewing decreases masticatory efficiency, but does not influence jerk-cost.

A comparison between jerk-cost derived from a jaw-tracking system with that from an accelerometer.

Jerk-cost is an inverse measure of movement smoothness and can be calculated from the first-time derivative of acceleration obtained from a tri-axial piezoelectric accelerometer (TPA), or from the third-time derivative of position obtained from a jaw-tracking device. The aims of this study were to determine, in 10 asymptomatic subjects who are chewing gum, (i) jerk-cost measures derived from displacement/time data obtained from the JAWS3D jaw-tracking device and from acceleration data obtained from a TPA used in the same jaw movement recordings, (ii) whether there was a significant relationship between jerk-cost measures derived from both devices and (iii) the degree of agreement between the two measures. Jerk-cost data were calculated in the opening phase, the closing phase, and over the full chewing cycle as the first-time derivative from acceleration obtained from the TPA, and the third-time derivative from JAWS3D for each of the X-, Y- and Z-direction series. There was a significant correlation between both measures of jerk-cost over the full chewing cycle and during jaw-opening (r = 0·65, 0·75, respectively; P < 0·001). There was no significant correlation in the closing phase (r = -0·02, P = 0·99). The Bland-Altman test showed that jerk-cost derived from the JAWS3D can differ by up to 78% below and 21% above that derived from the TPA. These results suggest that jerk-cost measures derived from a jaw-tracking system cannot substitute for jerk-cost measures derived from an accelerometer.

Measurement of jerk-cost using a triaxial piezoelectric accelerometer for the evaluation of jaw movement smoothness.

Jerk-cost as a measure of jaw movement smoothness has been used to evaluate the masticatory function of patients with tooth loss and malocclusion. Jerk-cost measuring systems have thus far been unable to determine the jerk-cost of each chewing phase over time. The purposes of this study were (i) to develop a new method for measuring momentary jerk-cost of the jaw movement using a small triaxial piezoelectric accelerometer and (ii) to test the hypothesis that the lowest smoothness is seen during jaw-opening phase. The accelerometer was attached to the skin of the mentum of each subject. Vertical jaw displacement, acceleration, the jerk, and the time differential of jerk-cost during gum chewing were analysed as a function of time in five normal dentate subjects (n = 5). The system revealed intra-class correlation coefficients of intra-examiner, inter-examiner, and test-retest consistency of substantially high values (0.80-0.88). In all subjects, the highest jerk-cost was observed in the opening phase of each chewing cycle when the gum was parting from the teeth; the lowest jerk-cost was observed in the intercuspal phase throughout the chewing cycle, thus confirming the hypothesis. Significant differences were observed between the opening, closing, and intercuspal chewing phases (N = 5, P = 0.007). The smoothness measurement system used in this study evaluated the momentary smoothness of each chewing phase in the masticatory cycle. The system may serve as a diagnostic tool to evaluate the smoothness of the jaw movement in general dental practice.

Three-dimensional analysis of occlusal curvature in healthy Japanese young adults.

Knowledge of the standard value of the occlusal curvature would be helpful when providing oral rehabilitation for patients with or without occlusal derangement. Dentists often use a 4-inch radii arc as the standard based on Monson spherical theory. However, the validity of application of this theory in Japanese has not yet been verified. The objective of this study was to determine the typical shape of the occlusal curvature in Japanese adults and investigate the relative contribution of each factor to the depth of the curvature, as the initial phase, to prove the validity of determination of occlusal curvature. Seventy-nine Japanese adults (42 males and 37 females, aged 18 to 37 years) with intact dental arches were recruited, and the occlusal curvature was estimated by calculating the radius and center position of the approximate sphere. Besides, the relative contribution of gender, age, dental arch length and width, overjet, overbite for the radii was calculated. The median radius of the sphere was 110.6 mm, larger than the 4-inch value advocated by Monson. This indicates the necessity to reconsider the application of the method of occlusal plane analysis in Japanese individuals. Median position of the centre was 64.6 mm anterior to and 68.5 mm above the mid-point between condyles. Relative contribution of overbite for the radii was 10.9%, the highest amongst the factors. Therefore, a typical shape of the occlusal curvature was observed in Japanese subjects. Overbite is considered as one of the principal factors correlated to the depth of the occlusal curvature.

Diazepam potentiates the positive inotropic effects of histamine and forskolin in guinea-pig papillary muscles.

There have been diverse reports on the effects of diazepam on cardiac contractility. The purpose of this study was to examine whether diazepam modifies the inotropic response elicited by histamine on an isolated guinea-pig papillary muscle. The responses of electrically driven papillary muscle to histamine and cyclic AMP-related inotropic agents were recorded in the absence and in the presence of diazepam. Histamine and forskolin, which directly stimulate adenylate cyclase, significantly increased the contractile force in the papillary muscle in a concentration-dependent manner. A histaminergic H2-receptor antagonist, cimetidine, but not a H1-receptor antagonist, diphenhydramine, at 10 microM produced a rightward shift in the concentration-response curve for histamine. Diazepam (10 microM) shifted the concentration-response curve for histamine and forskolin to the left by 1.8 and 1.6 times, respectively. Neither a central type (fulmazenil) nor a peripheral type (PK11195) of benzodiazepine receptor antagonist modified the effect of diazepam on the histaminergic-evoked contraction. Phosphodiesterase blockade by 3-isobutyl-1-methylxanthine shifted the concentration-dependent curve for histamine to the left. A combination of 3-isobutyl-1-methylxanthine also produced a leftward shift of the curve. However, there was no significant difference between the 3-isobutyl-1-methylxanthine only group and the combination group. These results indicate that diazepam potentiates the positive inotropic effect produced by histamine, probably mediated via an increase in cyclic AMP levels induced by histamine.

Alveolar bone loss in rats infected with a strain of Prevotella intermedia and Fusobacterium nucleatum isolated from a child with prepubertal periodontitis.

Prevotella intermedia and fusobacterium nucleatum are associated with various forms of periodontal disease. The purpose of the present study was to infect the clinical isolates of these periodontopathic bacteria and to induce a significant loss of alveolar bone in specific pathogen-free (SPF) rats in the absence of ligatures. P. intermedia YKD8 and F. nucleatum YKZ5 were isolated from a prepubertal periodontitis patient, while P. gingivalis MWB13 was from a patient with juvenile periodontitis. At first, SPF Sprague-Dawley rats (70 days of age, male) were infected with A. viscosus Ny1R and subsequently superinfected with P. gingivalis MWB13, P. intermedia YKD8, or F. nucleatum YKZ5, respectively. The control group was infected with A. viscosus Ny1R alone. All rats were killed and periodontal bone levels were assessed morphometrically 135 days after the first infection with A. viscosus. P. intermedia YKD8 was recovered frequently from rats, with serum antibody levels remaining highly elevated throughout the experiment. Significant loss of alveolar bone was found in rats infected with P. intermedia YKD8, the virulence of which was equivalent to that of P. gingivalis MWB13. F. nucleatum YKZ5 also induced alveolar bone loss, but not significantly when compared with rats infected with A. viscosus Ny1R alone.

Clinical, microbiological and host defense parameters associated with a case of localized prepubertal periodontitis.

A 4-year-old Japanese boy was referred to Osaka University Dental Hospital because of severe mobility and pain of the right lower primary canine. The canine had severe bone loss and a pocket depth exceeding 5-6 mm. The left lower canine showed slight mobility and moderate alveolar bone loss. The other primary teeth showed no pathogenic findings. The subgingival microflora from the right lower canine was dominated by gram-negative rods, especially capnocytophaga and fusobacterium, while actinomyces sp. were the most common gram-positive bacteria. While neutrophil functions of the patient were within the normal ranges of healthy subjects, some lymphocyte functions such as IL-2 production and IgG and IgM syntheses were lower in the patient. 7 months after the extraction of the right lower primary canine, the patient complained of pain around the right lower primary lateral incisor. In 3-4 weeks, the alveolar bone was lost rapidly and mobility of the lower anterior teeth increased significantly. The primary lateral incisor was extracted and the other primary teeth were treated by sealing and systemic and local administration of antibiotics. After treatment, the lower anterior teeth became less mobile and the gram-positive cocci predominated.

Dental findings of the elderly with or without senile dementia at a special nursing home.

Survey of dental health condition was performed at a special nursing home for the elderly with senile dementia (28 subjects, 83.3 +/- 6.8 year-old; SD group) or without senile dementia (68 subjects, 84.6 +/- 7.2 year-old; NSD group). There was no difference in number of teeth survived between SD and NSD groups. However, the elderly in SD group had more unfunctionable and/or unrestorable teeth (C4) and less sound and filled teeth (SFT) than those in NSD group. Number of teeth of the elderly in 85- to 89-year-old group was smaller than those of not only younger but older age groups, irrespective of senile dementia. Lower canines showed the highest survival rate among all kinds of teeth in SD as well as in NSD group.

Semisynthetic beta-lactam antibiotics. 8 Structure-activity relationships of alpha-sulfocephalosporins.

Synthesis and in vitro activity of a number of cephalosporins having alpha-sulfoacyl- or other acyl groups, e.g., alpha-carboxyacyl- and alpha-sulfoaminoacyl- at the 7-position and bearing a variety of heterocyclic thioether or pyridinium moieties at the 3-position are described.