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Biomedical subjects

M Ai

Publications and source records attributed to M Ai.

At least 19 recordsLinked to original sources
PubMed2006

Relationship between tooth contacts in the retruded contact position and mandibular positioning during retrusion.

We conducted a series of studies with the purpose to investigate the locations of tooth contacts in the retruded contact position (RCP) and to discuss their significance in the stomatognathic system. In the present study, the relationship between the locations of RCP contacts and mandibular positioning during retrusion was examined. Thirty dentists and clinical residents were selected as subjects. One specialist in prosthetic dentistry examined each subject for the location of the RCP contacts. The mandibular positioning during retrusion was measured using a mandibular movement analysis system with six degrees of freedom. Originally programmed software was developed. Five reference points were selected: the central lower incisor (point I), the first molars on both sides (points RM and LM) and the condyles on both sides (points RC and LC). Tooth contact was observed most frequently at the second molar, followed by the first premolar. Points I, RM and LM all moved in an inferior-posterior direction, whereas points RC and LC moved in various directions ranging from superior-posterior to inferior-posterior. When the subjects were divided into two groups according to the most anterior tooth of occlusion in the RCP, the condylar positioning tended to be more superior in the group with molar contact than that with premolar contact. These results suggest that the locations of RCP contacts could be an important factor in jaw guidance during retrusion.

Adult↗
PubMed2003

Tooth contacts at the mandibular retruded position, influence of operator's skill on bite registration.

Occlusal conditions at the retruded contact position (RCP) have been thought to be among the aetiological factors for temporomandibular disorders. However, the role of these occlusal factors still remain unclear. The purpose of a series of studies was to investigate the locations of RCP contacts and to discuss their implication by the authors. In the study reported here, the influence of the operator's skill on bite registration was surveyed. Eighty-six dental students were selected as subjects. One specialist in prosthetic dentistry moved the subject's mandible up and down while guiding it gently backward until it rotated on its retruded axis. Once the initial tooth contacts were established, the operator checked them by using a thin articulating paper (direct method). On the other hand, six younger operators following precise instruction from the specialist about the technique of jaw guidance examined each of the subjects for location of RCP contacts using the indirect method. Silicone-based impression material was used for bite registration while the subject kept the jaw at this contact position (indirect method). Wilcoxon signed rank test was applied to evaluate differences between the expert operator and six younger operators regarding locations of RCP contacts. Results from the expert operator (direct method) showed that tooth contact at the first premolar was most frequently observed and the number of subjects who possessed unilateral tooth contacts was more than that with bilateral tooth contacts. On the other hand, in the case of the indirect method performed by younger operators, tooth contact patterns significantly differed from those of the direct method.

Adult↗
PubMed2002

Tooth contacts at the mandibular retruded position, comparison of two different methods for bite registration.

Occlusal conditions at the retruded contact position (RCP) have been thought to be among the aetiological factors for temporomandibular disorders. However, the role of these occlusal factors remains still unclear. The purpose of this series of studies was to investigate the locations of RCP contacts and to discuss their meaning. In this part of the study, two different methods for bite registration at the RCP have been compared. Twenty dentists were selected as subjects for this study. One expert operator moved the subject's mandible up and down while guiding it gently backward until rotating on its retruded axis. Once the initial tooth contacts were established, the operator checked them using a thin articulating paper (direct method). Silicone-based impression material was used for bite registration while the subject kept the jaw at this contact position (indirect method). Differences between the two registration methods regarding locations of tooth contacts were evaluated. Results from the direct method showed that tooth contact at the first premolar was most frequently observed. Statistical difference was not shown between the two registration methods regarding locations of RCP contacts.

Adult↗
PubMed2001

Relationship between plasma insulin concentration and plasma remnant lipoprotein response to an oral fat load in patients with type 2 diabetes.

OBJECTIVES: The goal of this study was to evaluate the relative effects of hyperglycemia and hyperinsulinemia on postprandial remnant lipoprotein (RLP) concentrations in newly diagnosed type 2 diabetics. BACKGROUND: Increases in fasting RLP concentration have been described in type 2 diabetics, as well as in insulin-resistant nondiabetics. Given the atherogenicity of RLPs, we have extended these observations by assessing postprandial RLP concentrations and observing that hyperglycemia was necessary for the increase in RLP concentrations. METHODS: Patients with type 2 diabetes were subdivided on the basis of their plasma insulin response to oral glucose into hyperinsulinemic (H-DM) and normoinsulinemic (N-DM) groups of 15 patients each. Plasma triglyceride (TG), RLP-TG and RLP cholesterol (RLP-C) concentrations were determined before and 2 and 4 h after an oral fat load in these patients and 10 control (CTL) subjects. RESULTS: Plasma TG, RLP-TG and RLP-C concentrations peaked 2 h after the fat load in the CTL group, returning to baseline within 4 h. In contrast, concentrations of these variables increased throughout the 4-h study in both groups of patients with type 2 diabetes. Total integrated plasma RLP-TG and RLP-C responses above baseline after the oral fat load were significantly higher in the H-DM group compared with the CTL (p = 0.019 and 0.009, respectively) or N-DM (p = 0.026 and 0.029, respectively) groups. Post-heparin lipoprotein lipase activities and apo E phenotypes were similar in the H-DM and N-DM groups. CONCLUSIONS: Remnant lipoprotein response to an oral fat load is significantly increased in hyperinsulinemic patients with type 2 diabetes. These changes may increase the risk of coronary heart disease in these individuals.

Adult↗
PubMed2001

The relation of mandibular laterotrusion with ipsilateral TMJ clicking.

The purpose of this study was to investigate the association of temporomandibular joint (TMJ) clicking with the types of canine guidance, the tracing patterns of mandibular laterotrusion and, especially, with the movements of the working side condyle. In a young subject group, the movements of left and right mandibular laterotrusion were measured at the incisal and the lateral pole point of the working side condyle. All samples were divided into one of two groups according to the mesial (M) or distal (D) canine guidance. They were also divided into protrusive laterotrusion (PL) or retrusive laterotrusion (RL) groups according to the tracing patterns. The incidence of clicking was 23.8% in all 84 TMJs. There was no significant difference between the M and the D groups. However, clicking occurrence was significantly higher in the RL than in the PL group (P<0.05). The condyles in clicking joints moved more posterior in ipsilateral laterotrusion than the condyles in non-clicking joints. The condyles in RL also moved more posterior than those in PL. It is suggested that the posterior movement of the working side condyle in RL has a strong relationship with the internal derangement of the TMJ. However, it is not related to the type of canine guidance.

Adult↗
PubMed2001

Impact of balancing-side tooth contact on clenching induced mandibular displacements in humans.

This study investigated mandibular displacements during clenching in the lateral mandibular position in relation to lateral occlusal relationships. Twelve healthy human subjects (mean=26.7 years) volunteered for this study. Acrylic occlusal devices were fabricated for the lower working-side canine, working-side second molar and balancing-side second molar in order to simulate a dominant canine guidance, working-side interference (WI), balancing-side interference (BI) and bilateral balanced occlusion (BO). Vertical displacements of the mandible were recorded by linear variable differential transformers during submaximal clenching in the right lateral position. The four experimental occlusal conditions were revealed to have a significant effect on mandibular displacement patterns (ANOVA, P < 0.001). A dominant canine raiser caused a mandibular elevation with the smallest displacement at the working-side premolar and the largest displacement at the balancing-side second molar. Clenching on a WI or BI caused a mandibular elevation with the smallest displacement at the working- or balancing-side second molar, respectively. A BO resulted in the smallest upward displacement among the four experimental conditions. These results suggest that the nature of reaction forces at the temporomandibular (TM) joints caused by the elevation of the mandible varies in a predictable manner depending upon lateral occlusal relationships.

Acrylic Resins↗
PubMed2001

Influence of nocturnal bruxism on the stomatognathic system. Part I: a new device for measuring mandibular movements during sleep.

The purpose of this study was to investigate the influence of bruxism on the stomatognathic system. A new device for measuring nocturnal mandibular movements was developed using a PIN photodiode sensor, integrated with polysomnography including electromyography (EMG), electroencephalography (EEG) and electro oculography (EOG). One bruxing event was defined depending upon EMG activities above 5% maximum voluntary contraction (MVC), and mandibular movement for each event was classified into three patterns (clenching, grinding and mix). Three subjects were selected for this study. Two of these reported a bruxing habit and one subject had some symptoms of temporomandibular dysfunction (TMD). Mandibular movement was analysed for these subjects. Frequency and duration of the bruxism events were 4.5-10.9 and 47.8-174.9 s h(-1) respectively. Clenching type bruxism was most frequently observed for all three subjects and EMG activities during clenching were stronger than grinding.

Adult↗
PubMed2001

Triglyceride-rich lipoprotein cholesterol exceeds low-density lipoprotein cholesterol in hypertriglyceridemia patients.

The atherogenicity of triglyceride-rich lipoprotein has been revealed. This study was performed to explore the clinical importance of triglyceride-rich lipoprotein by measuring its cholesterol content and comparing it with other lipoprotein fractions. Blood samples were obtained from 103 patients whose fasting plasma triglyceride concentration exceeded 300 mg/dl. The cholesterol monitor using the technique of high-performance liquid chromatography was used for the measurement of their plasma cholesterol concentrations and the determination of cholesterol distribution among lipoprotein fractions. This monitor showed 4 peaks: large-triglyceride-rich lipoprotein, small-triglyceride-rich lipoprotein, low-density lipoprotein, and high-density lipoprotein. Total cholesterol increased with increasing triglyceride. The increment of total cholesterol was nearly equal to that of small-triglyceride-rich lipoprotein cholesterol. Small-triglyceride-rich lipoprotein cholesterol exceeded low-density lipoprotein cholesterol where plasma triglyceride concentration was over 500 mg/dl. In conclusion, triglyceride-rich lipoprotein may be clinically important for hypertriglyceridemic patients as a source of cholesteryl ester in arteriosclerotic plaques, and increased triglyceride-rich lipoprotein cholesterol may be used as a basis for hypertriglyceridemia atherogenicity. Our study suggests that hypertriglyceridemia should be treated to prevent arteriosclerotic disease.

Apolipoproteins E↗
PubMed2001

Increased cholesteryl ester transfer protein and changes in lipid metabolism from initiating insulin therapy.

Insulin therapy is often necessary for glycemic control, and its effect on plasma lipids is an important issue with respect to arteriosclerosis. Previous reports suggested that increased cholesteryl ester transfer protein (CETP) appeared in diabetic patients with hyperinsulinemia or given a lot of insulin is atherogenic. We investigated whether insulin always increases CETP and whether increased CETP by insulin is always atherogenic. In 40 patients the amount and activity of CETP were assessed before and 2 weeks after initiation of insulin therapy. After starting insulin, plasma concentrations of total cholesterol, triglycerides, LDL-cholesterol, and remnant lipoprotein cholesterol decreased. No change occurred in HDL-cholesterol. Starting insulin therapy increased the amount and activity of CEIP. No significant correlation was observed between changes in CETP and in lipids including HDL-cholesterol or apolipoprotein concentrations. This is the first prospective study to show increased CETP activity after initiation of insulin therapy. After initiating insulin, CETP increases without accompanying atherogenic changes in lipid metabolism. Based on the changes observed, CETP in itself does not have atherogenicity and the increase, but no excess, of CETP by appropriate insulin therapy cannot be atherogenic.

Apolipoproteins↗
PubMed2000

Influence of clenching level on intercuspal contact area in various regions of the dental arch.

The purpose of this study was to evaluate the relationship between the clenching level and the intercuspal contact area in different regions of the dental arch. Twenty-five healthy subjects with natural normal dentitions and good occlusal support performed clenching tasks in the intercuspal position at four different levels (10, 30, 70 and 100% levels of maximum voluntary contraction) through EMG visual feedback from bilateral masseter and anterior temporal muscles. Simultaneously, the occlusal contacts were recorded with a silicone occlusal contact checking material (Black Silicone, GC Dental Industrial Corp., Tokyo, Japan). The occlusal records were analysed by an image analyser. Every area of the thickness less than 50 microm was determined to be an occlusal contact area. The occlusal contact areas on the anterior teeth (incisors and canines), the premolars (first and second premolars) and the molars (first and second molars) were calculated separately. The posterior occlusal contact area increased with an increase in the clenching levels but that of the anterior did not. The results of this study indicate that the increase in clenching forces affects the anterior and posterior occlusal contact areas differently.

Adult↗
PubMed2000

Mandibular positions and jaw-closing muscle activity during sleep.

The aim of this study was to clarify the relationship between the mandibular position with tooth contacts and jaw-closing muscle activity during sleep using electromyography and newly devised equipment for detecting tooth contacts and also to confirm the validity of this system. Five males volunteered for this study and three of them reported their bruxing during sleep. Occurrences of tooth contacts at eccentric mandibular positions in addition to the intercuspal position during sleep were detected using micro photo sensors and sensor targets prepared for the individuals. Electromyographic activities (EMG) from right and left masseter and anterior temporal muscles were also recorded. Results of the polygraphic recordings demonstrated that the mandibular positions during bruxism could be distinguished clearly whether it's in the right or left position, or has no lateral deviation, and further, that bruxing events could be categorized based on mandibular position pattern. The relationship between the mandibular position and muscle activity could be evaluated using this system. The study suggested the validity of the system for measuring nocturnal bruxing events.

Adult↗
PubMed2000

The relation of canine guidance with laterotrusive movements at the incisal point and the working side condyle.

The effect of different types of canine guidance on the patterns of laterotrusive tracing at the incisal point and the relationship between the laterotrusive inclinations and the working side condylar movements were investigated in 42 young subjects. The subjects were divided into M and D groups according to their mesial and distal canine guidance, and were also divided into protrusive laterotrusion (PL) and retrusive laterotrusion (RL) groups according to their laterotrusive tracing patterns. No differences of laterotrusive inclinations and working side condylar movements were found between the M and D groups. The laterotrusive tracing pattern had no corresponding association with the type of canine guidance. In relation to the movements of the working side condyles, significant differences were found between the PL and RL groups. The condyles moved laterally and posteriorly in the RL group, but moved lateral and inferior in the PL one. The distance of condylar movement in the X direction was correlated with the horizontal and sagittal inclinations of laterotrusion. The results indicate that the movements of the working side condyle were affected functionally by the laterotrusion, but not by either the mesial or the distal type of canine guidance.

Adult↗
PubMed2000

Influence of alteration of occlusal relationship on activity of jaw closing muscles and mandibular movement during submaximal clenching.

The aim of this study was to investigate the relationships between occlusal contacts, responses of muscles, and jaw movements during simulated clenching. Seven healthy human males who possessed complete natural dental arches with normal occlusion, ranging from 24 to 29 years of age, volunteered for this study. Acrylic occlusal stops were fabricated for the lower jaw to simulate various occlusal conditions. Vertical movements of the lower jaw were measured by four sets of linear variable differential transformers. Simultaneously, electromyographic (EMG) activity from the bilateral masseter and anterior temporal muscles was measured. Under experimentally altered occlusal conditions, the subjects performed clenching tasks at 50% of their maximal voluntary contraction level. Analysis of EMG responses revealed clenching on the unilateral occlusal support tended to cause a unilateral activity of the ipsilateral anterior temporalis. Analysis of the movement amplitude revealed a significant difference between the experimental occlusal conditions (P < 0.05). Clenching on unilateral occlusal stops caused a larger upward movement on the contralateral side. Bilateral first premolar clenching without molar support caused a larger upward movement of the mandible in the posterior region, whereas bilateral second molar clenching did not cause a significant upward movement.

Adult↗