Rapid canine retraction in a Class II bialveolar protrusion case using a lingually extended distraction screw / 대한치과교정학회지

Rapid canine retraction, first introduced by Liou, is a distraction osteogenesis applied to the periodontal ligament tissue. Rapid tooth movement was facilitated by establishing minimal bony resistance on the distal surface of the canine by socket preparation and by osteogenesis on the mesial side in response to the periodontal distraction. Since undesired buccal tipping or extrusion of the canine during retraction tends to occur, it is crucial to maintain the firm path of movement and the axis of the canine during retraction. In order to improve the predictability of the canine movement, lingually extended distraction screws with heavy labial guiding wires were designed. Prefabricated plastic canine models for the estimation of socket depth and miniscrew implants for anchorage reinforcement were also devised. Applying these devices to a female patient with Class II anterior protrusion, the whole treatment was effectively finished in 13 months. Loss of vitality or periodontal problems did not occur throughout treatment, and stable occlusion was maintained during 10 months of retention. This case report demonstrates that a predictable rapid canine retraction can be achieved through the use of this modified technique.

A study of the arch length discrepancy and the diagnostic analysis / 대한치과교정학회지

Predicting the arch length discrepancy by simply comparing the available arch perimeter with tooth materials is merely a 2-dimensional analysis of the teeth movement. However, the real teeth movement takes place 3-dimensionally and is affected by various factors such as, the arch form, the curve of Spee and the axis of the incisors. The purpose of this study is to clarify the relationship between the decrease in the arch perimeter and the horizontal positional change of the incisors after extraction of the 1st bicuspids, for more analytic evaluation of the arch length discrepancy at pre-treatment model analysis stage. In addition to that to evaluate the effect of the curve of Spee, teeth axis to the basal plane, and the incisional crowding to the treatment outcome. All patients were treated at the department of orthodontics, dental hospital, Yonsei university. Inclusion criteria for patients selection were as follows. -Angle classification I malocclusion with bialveolar protrusion -Extraction of 4 1st bicuspids -No tooth anomaly or prosthesis -No abnormal attrition -No ectopically erupted teeth -Angle classification I canine and molar relationship -Less than 3mm of crowding Model analysis of the above patients was performed and the following conclusions were obtained. 1. When the intercanine distance was maintained, the available space for the distal movement of the mandibular incisors after the extraction of the 4 1st bicuspids was larger than the space provided by the extraction of the 4 1st bicuspids. However the difference was less than 1mm. The more tapered the anterior arch form, the larger the difference. 2. Compared to the situation in which the intercanine distance was maintained, when the intercanine distance was expanded to meet the width of the posterior teeth, the incisors could move about 3mm more distally. 3. The positional difference of the incisal tip was insignificant whether the central incisors were moved by tipping or bodily movement. 4. When the anterior crowding was solved without changing the intercanine distance, the larger the anterior arch length was, the more the anterior movement of the incisors. 5. When the curve of Spee was levelled, the increase in the arch perimeter was less than half of the deepest curve of Spee.

The effects of maxillary protraction appliance (MPA) depending on vertical facial patterns / 대한치과교정학회지

Preadolescent children with deficient maxillae are suitable candidates for the maxillary protraction appliance(MPA). The theoretical effect of the MPA is protraction or anterior displacement of the maxilla. However, it is known that complex effects such as anterior displacement of the maxillary teeth, downward and backward rotation of the mandible, linguoversion of the mandibular anterior incisors, are known to play a role in improving the Cl III malocclusion. There have been much studies with regard to maxillary protraction, but the different effects of MPAs depending on the vertical facial pattern are not known precisely. This study was based on 67 patients (31 males, 36 females) aged from 6 years 6 months to 13 years 3months, who visited the Dept. of Orthodontics at Yonsei Univ., Dental Hospital and diagnosed as skeletal Class III with maxillary deficiency. They were divided into 3 groups (low, average, high angle groups) depending on gonial angle and the SNMP (Go-Gn) angle, respectively. Pretreatment and post-treatment lateral cephalograms were used to compare the effects of MPA and the following conclusions were obtained: 1) A significantly large amount of backward movement of the B point was observed in patients with a low SNMP angle. Those with a high SNMP angle had significant forward movement at A point. 2) The patients with low gonial angle had the least forward movement at the A point, and those with a high angle had more forward movement. 3) In comparing the arcTan of the A point, the high angle group showed more horizontal movement while the low angle group showed more vertical movement. 4) There was no significance between the treatment duration of the SNMP and the Gonial angle groups.

A study on the distributions and trends in malocclusion patients from department of orthodontics, college of dentistry, Yonsei university / 대한치과교정학회지

Distributions trends were examined in 9159 malocclusion patients had been examined and diagnosed at Department of Orthodontics, College of Dentistry, Yonsei University over a 6 year-period from 1992 to 1997. The results were as follows: 1. The total number of orthodontic patients in 1997 increased in comparing with that of 1992(86%)and after 1995, the number of annual patients showed an increase. 2. Age distribution had shown over-19 year-old group being the largest(39.9%) but percentages of pre-adolescent patients had been decreasing while that of adult patient had gradually increased. 3. Distributions in the types of malocclusion, the Angle's Classification had shown : 33. 3% for Class I, 28.6% for ClassII and the largest 38.1% for Class III. 4. Among Class I patients, crowding showed the largest(32.6%) and protrusion group had gradually increased to 33.9% in 1996. Otherwise openbite and groups tend to decrease, annually. 5. Geographic distribution showed a majority of patients from Seoul(above 70%). Among the patients from Seoul, group within the distance 3-6km from Yonsei dental hospital was the largest(32.3%) and group within 9km showed 69% of total patients.

A longitudinal study on the interrelationship between the growth change of the gonial angle and IMPA / 대한치과교정학회지

This study was undertaken to investigate the growth change of gonial angle and interrelationship between the growth change of gonial angle and IMPA in the longitudinal data from 7 years to 15 years. By analyzing the serial lateral cephalograms of 15 males and 18 females of 7 years old to 15 years old who had no abnomality in growth and development and no history of orthodontic treatment, the following conclusion were obtained. 1. Gonial angle gradually decreased with aging in 25 children and in 9 children increased or maintained. 2. There was a tendency that children who decreased gonial angle with aging showed gradual increase of IMPA and children who increased of maintained gonial angle with aging showed decrease of IMPA 3. There was a tendency that regardless of the change of gonial angle, interincisal angle decreased with aging.

Rationale and criteria for excellent finishing / 대한치과교정학회지

Finishing is usually accomplished about four to seven months before the removal of orthodontic appliance in order to achieve ideal occlusion and excellent aesthetics. This process, called finishing, is the key to obtain excellent final results. Some of orthodontists believe it can be accomplished at the final stage of orthodontic treatment, and they complete it without their special rationale and criteria for finishing. However, it should be considered as a part of the total treatment plan from the beginning to end, and a guideline for finishing, which is based on rationale and criteria for the removal of orthodontic appliance, is needed to obtain the desired results. The guideline should include a checklist for finishing. This checklist is divided into four categories: occlusal, aesthetic, periodontal, and habitual factors. Occlusal factors include alignment, marginal ridge discrepancy, interproximal contact, anterior inclination, posterior inclination, over-jet, over-bite, arch form, and functional occlusion. Aesthetic factors include gingival form, crown form, crown width, and crown length. Periodontal factors include root angulation, bone level, and black hole in periodontal factors. Habitual factors consist of mouth breathing, tongue position at rest, tongue thrust, lip biting, nail biting, and finger sucking.

A study on skeletal relapse patterns following orthognathic surgery of Class III patients : comparison between SSRO and IVRO / 대한치과교정학회지

To evaluate the relapse pattern and long-term stabilities depanding on surgical methods following orthognathic surgery of Cl III patients, the author selected 24 subjects(10 male, 14 female) operated by SSRO and 26 subjects(10 male, 16 female) operated by IVRO. Each subject took four lateral cephalograms: just before surgery(Tl), within 48hrs after surgery(T2), 4-8 wks after surgery(T3), 6 month or more after surgery(T4), and the landmarks were digitized. The differences of relapse patterns in each interval between two groups were compared and the significance of correlation among the variables of each group was tested The obtained results are as follows; 1. Horizontal early relapse was forward movement of mandible in SSRO group, as compared to the backward movement in IVRO group, and there was a statistical significance between the two groups. 2. Vertical early and late relapses were decreases in anterior facial height in both groups and there was no statistical significance between the two groups. 3. There was a statistical significance in negative correlation between mandibular hornontal late relapse and surgical change of articular angle in SSRO group. 4, There was a statistical significance in negative correlation between amount of mandibular set-back and mandibular horizontal early relapse in both groups.

A study on the mandibular growth prediction and size of the frontal sinus / 대한치과교정학회지

This author tried to find if the size of the frontal sinus can be used as a diagnostic aid to predict the mandibular growth pattern in growing patients-in lateral cephalogram utilizing the fact the the frontal sinus completes its growth in earlier stage but the mandible continues to grow until later. At this study, the 228 samples were divided into 3 groups as skeletal Class I , II, III malocclusions and three indicies(ANB, APDI, Wits) were measured which hidicate the mandibular body length and the antero-posterior relationship of maxilla and mandible to evaluate their relations with frontal sinus. And results were obtained as followings. 1. The size of frontal sinus is highly related to ANB, APDI, Wits and mandilar body length(p<0.001) 2. the size of the frontal sinus of the Cl III malocclusion group was on the lateral cephalogram larger than Cl I and C1 II group.

A study on the correlationship of submentovertex view and lateral cephalogram measurements / 대한치과교정학회지

Cephalometric measureements have disadvantage of representing cranio-facial structures in two dimension only and therefore they pose limitations in describing three-dimentional structures of cranio-facial region. More interests have been put on the correlation between the two planes. This study evaluated correlations between facial type score, which allows effects on malocclusion, growth change prediction and establishment of treatment method and prognosis, and measurements from submentovertex view. Cephalometric view and submentovertex view were taken of skeletal Class I adults with optimal profile and correlations between them have been observed. Following results were obtained: 1. To learn about factors that influence average condylar angulation, FACE, INT-CO-ANG, MN-CORPUS, CON-RATIO, GON-RATIO, MN-RATIO were used as variables and underwent multiple regression analysis. As a result, the following equation was obtained : CON-AVE=.l73(FACE)-.322(INT-CO-ANG)+36.34(GON-RATIO) +.420(MN-CORPUS) (R2=.85451) 2. The following equation was obtained concerning facial type score. FACE= .050(CON-ANG)+.023(INT-CO-ANG)-.075(MN-CORPUS)(R2=.31547) 3. Among the submentovertex measurements, MN-CORPUS, CON-RATIO, GON-RATIO, MN-RATIO showed close correlations. (P<0.05) 4. Average condylar angualtions were 23.37degrees on the right and 20.71degrees on left. There was a difference between the two. FACE: facial type soore. CON-ANG: mean value of condylar angulation. CON-AVE: mean value of Rt. Lt condylar angulation. INT-CO-ANG: angle between Rt. Lt condylar axis. MN-CORPUS : angle formed between RT. Lt gonion & pogonion. CON-RATIO: lntercondylar distance/mandibular body length. GON-RATIO: intergonion distanoe/mandibular body length. MN-RATIO: lntermylohyoid distance/mandibular body length. MX-RATIO: intermaxillary tuberosity distance/ANS-PNS distance.

Three dimentional force analysis of force system in continuous archwire by finite element method / 대한치과교정학회지

It is important to understand the operating mechanism and force system of fixed appliance that most effective for individual tooth movement in various orthodontic appliances. The arch wire system of fixed appliance is devided into 3 types, which is continuous arch, segmented arch and sectional arch. The last two types have longer interbracket distance and simple force operating points, so it is easy to control force system by operator. But the continuous arch has shorter interbracket distance and various bracket geometry, so it is hard to control and anaylze the force system. The purpose of this study was three dimentional force and moment analysis of continuous arch system by finite element method, which is similar situation to three dimentional elastic beam in structural engineering. Several sample form of various bracket geometry and artificial lower crowding typodont made by author were constructed, analyzed and compared each other. The results were as follows: 1. The force magnitude is linear proportional to the degree of displacement or tilting of the bracket. 2. The force magnitude is inversely non-linear proportional to the interbracket distance. 3. In three dimensional typodont model, while the force can be compared with that of the sample form in the area where adjacent bracket geometry is simple, the force is much more than the expected value in the area where adjacent bracket geometry is complex.

Growth change in the lips of the adolescence (from 8 to 16 years old) / 대한치과교정학회지

This study was undertaken to assess the effect of growth on the lips. Not only does lip growth influence the stability of such orthodontic treatment: it also directly influence facial profile, in which the lips have an important part. An understanding of the growth of lips is thus central to a consideration of profile change in orthodontics. By analyzing the serial lateral cephalograms of 15 male and 15 female of 8 years old to 16 years old who have normal occlusion. The result of this study were summerized as follows; 1. The largest growth increments in the length of the lips was occured age of 14 in both sexes. 2. The thickness of lips showed lager value for the male than that of the female in the most age group. The largest growth increments at A point was occured age of 14, while Ls, Li, B point decreased after the age of 10-11. 3. The largest increase in the interval between crest of lower lip and edge of upper incisors was occured between ages 9 and 11 in males. The interval decreased slightly from 8 to 16 years in females. 4. The nasolabial angle decreased slightly from 8 to 16 years in both sexes. 5. The mentolabial angle showed large variation.

A study on correlationship between craniofacial growth pattern and symphysis morphology / 대한치과교정학회지

Craniofacial growth pattern is an important diagnostic data in the course of orthodontic diagnosis and treatment planning ; it also has great influence in the establishment of occlusion as well as shaping and development of face. There have been many studies to classify different craniofacial growth patterns and attempts to predict growth patterns. This study aimed to correlate craniofacial growth pattern and symphysis morphology. 120 adult patients with age from 19 to 39 (mean age: 23.1) were chosen as subjects ; using lateral cephalometric films. their anterior to posterior facial height ratios were calculated. They were divided into 3 groupzs - clockwise growth pattern with 56%-62%(36subjects), counter-clockwise growth pattern group with 65%-80%(43subjects) and normal growth pattern group with 62%-65%(41subjects). Symphysis morphology and prominence evaluation in each subject were studied and the following conclusions were drawn: 1. In comparison of symphysis morphology between the sex groups, men showed large symphysis height and prominence. 2. Concerning the symphysis morphology, the clockwise growth pattern group showed larger height, H/D ratio and actual length but smaller depth, angle, effective length and E/A ratio compared to the counter-clockwise growth pattern group. 3. Those with smaller prominance of symphysis showed clockwise growth tendency and those with larger pro-minance showed counter-clockwise growth tendency.

A study on the orthodontic tooth movement under half sine-wave pulsed electromagnetic fields / 대한치과교정학회지

The biologic potential, which is different from the piezoelectric signals, relates tooth movement at least in part to changes in bone metaboliosm in bioelectric theory. The purpose of this experiment was to determine whether the application of half sine-wave pulsed electromagnetic fields (HSPEMF) could increase both the rate and amount of orthodontic tooth movement. Forty-three male Hartley guinea pigs, weighting approximately 255g, were utilized in this study. The animals were 35 days old at the start of the study. Laterally directed orthodontic force was applied to the maxillary central incisors of 40 Hartley guinea pigs (20 experimental, 20 control). According to the amount of orthodontic force (6g, 12g), they were divided into two sub-groups (10 experimental I, 10 experimental II, 10 control I, 10 control II). During the experimental period, experimental animals were placed in plastic animal holders with their heads positioned in an area of uniform electromagnetic field. Control animals were placed in similar plastic holders that did not carry the electric apparatus. The results were as follows: 1. The application of a HSPEMF to the experimental groups significantly increase the final amount of orthodontic tooth movement observed over a 10-day experimental period. 2. The application of a HSPEMF to the experimental groups significantly increase the velocity of orthodontic tooth movement observed over a 10-day experimental period. 3. There was no significant difference in the final amount of orthodontic tooth movement at the fourth day to the eighth day, but there was significant difference in the final amount of orthodontic tooth movement at the ninth, tenth day during a 10-day experimental period. 4. After 10 days of HSPEMF exposure & orthodontic force, the experimental groups demonstrated more osteoclasts in the pressure side than control groups.

Lip profile changes after orthodontic tooth movement in female adult with bimaxillary protrusion / 대한치과교정학회지

Facial esthetics is one of the most important goal of the orthodontic treatment and main concern of many patients. Facial esthetics should be considered in orthodontic diagnosis and treatment planning. Prediction of soft tissue profile changes after orthodontic tooth movement should be considered as well. The purpose of this study was to find out the effect of orthodontic treatment on lip profile in adult patient. The pre and post treatment cephalometric reontgenograms of 87 female adult with bimaxillary protrusion were used to analyze lip profile change. All subjects were treated with four bicuspids extraction. Obtained results were as follows: 1. Lip thickness changes after incisor retraction showed different patterns according to areas of the lip. The thickness of the red lip area showed 2.78 mm increase in average. In contrast the thickness of the cutaneous area showed 0.65 - 0.7 mm decrease according to the different cutaneous areas. 2. The length of the red lip area decreased(1.3mm) after incisor retraction. 3. The length of the cutaneous lip area increased(2.9mm) after incisor retraction.

A comparative study on crowding according to the status of the third molars in mandibular arch / 대한치과교정학회지

It has been generally believed that the impaction or eruption of mandibular third molars has significant correlations with the growth of the mandible, size of mandibular arch and size of teeth. The purpose of this study was to examine if there is any correlation between the status of eruption of mandibular third molars and the amount of mandibular crowding. The effect of missing of third moalrs to mandibular crowding was studied as well. 140 adult students of Yonsei University were selected and divided into three groups according to the status of mandibular third molars, Group 1) congenital missing group, Group 2) eruption group, and Group 3) impaction group. The tooth size, dimensions of the mandibular dental arch, and the amount of crowding were measured and compared. Results were as follows; 1. There was no statistically significant difference in tooth size between the missing group and the eruption group(p<0.05). Impaction group showed larger total tooth material, incisal tooth material, and individual tooth size except central incisors compared to missing group (p<0.05). Impaction group showed larger total tooth material, incisal tooth material compared to eruption group as well(p<0.05). When individual tooth size was compared, impaction group had larger central incisors, canines, and second premolars than eruption group(p<0.05). 2. Missing group showed larger intermolar width than impaction group and it was statistically significant(p<0.05). 3. When compared the amount of total crowding, impaction group showed the largest amount of crowding, then eruption group, and missing group showed the least amount of crowding respectively(p<0.05). There was no statistically significant difference between missing group and eruption group in the amount of incisal crowding (p<0.05). Impaction group showed the largest amount of incisal crowding among all three groups(p<0.05).

The effects of horizontal orthodontic tooth movement on the periodontally diseased tissue in dogs / 대한치과교정학회지

Most adults, unlike growing children, have some periodontal problems which can influence the outcome of the orthodontic treatment. In cases where periodontal disease progression resulted in marked reduction of periodontium, orthodontic treatment could result in the worsening of the periodontal conditions, and therefore orthodontic treatment planning in such adult patients requires special considerations for the periodontal problems. This study investigates the effects of horizontal orthodontic tooth movement on the changes in the mesial, distal and furcation areas of the disease affected periodontium of adult dogs with advanced bone loss. Six adult dogs with healthy periodontium were selected, and mandibular 2nd premolars were extracted. In the mandibular 3rd premolars, angular bony defects in the mesial and distal sides, and horizontal bony defects in the furcation areas were created. Those that received the flap operation and plaque control were designated as the control, those that had horizontal tooth movement without plaque control after the flap operation as Experimental group I, those that had horizontal tooth movement under plaque control without the flap operation as Experimental group II, and those that had horizontal tooth movement under plaque control after the flap operation as Experimental group III. The control group was sacrificed 2 months postoperatively, and the experimental groups were sacrificed 5 months after the initiation of tooth movement. Specimens were histologically analyzed under light microscope. The results were as follows; 1. After the horizontal tooth movements, Experimental group I and II showed angular bony defects in the mesial sides of the roots and the distal side of the furcation areas, which correspond to the pressure sides. 2. After the horizontal tooth movements, Experimental group I and II showed decreased level of alveolar bone crest in the distal sides of the roots, which correspond to the tension sides. 3. Long junctional epithelium in the control group has not been replaced by periodontal connective tissue after the horizontal tooth movements. 4. Limited formation of new bone was observed in the angular bony defects in the mesial and distal aspects of the roots in the control group. 5. Inflammatory cell infiltration in the connective tissue was most severe in the Experimental group I, followed by Experimental group II, III, and the control group in that order. These results seem to indicate that plaque control was the most influencing factor in the alteration of the periodontal tissue after the horizontal tooth movements in the periodontal tissue with alveolar bone defects.

A study on the factors associated with compliances of orthdontic patient / 대한치과교정학회지

In orthodontic field, although lots of new materials have been developed and many mechanics intro duced, we can face the case patient cooperation still remain a problem to solve. So, factors related to the compliance of 254 adolescent orthodontic patients using intraoral elastic or extraoral orthopedic appliances were under investigation. The study subjects were 11 to 18 years old and from 5 exclusive orthodontic clinics in seoul. The subjects were asked to fill a questionnaire and compliances were evaluated by their assigned orthodontics. The questionnaire was consisted of 63 questions, and they represent 13 factors-7 psychological & 6 nonpsychological fators. The collected data were analyzed using ANOVA test between the compliance group and the factors. 1. The compliances were evenly distributed in both sex and age groups. 2. As a whole, it was found that the Attitude towards appliances factor affected the degree of compliance. 3. Besides that, in younger(11-12) age group, Pain and discomfort associated with treatment factor was also found to be related to the degree of compliance. 4. On the contrary, in older(16-18) age group, the degree of compliance was influenced by the factor of Achievement motivation, Role expectation, parental relationship.

A comparative study on reliability of the root parallelism of the posterior teeth projected on the orthopantomogram with the 45 degrees oblique cephalogram / 대한치과교정학회지

At present, many orthodontists regard the root parallelism of the posterior teeth important not only in diagnosis and treatment planning but also for predicting posttreatment stability. To evaluate it, they usually refer to the orthopantomogram. At this study, 97 samples were collected from students of Yonsei University, who have well-proportioned face, Angles's class I canine & molar relationships and no crown axis deviation of the posterior teeth including canines. Reliability of the root parallelism observed from orthopantomogram was evaluated by comparison with 45degrees oblique cephalogram. The results were as follows : 1. In comparing the differences between anglular measurements in 45degrees oblique cephalogram & orthopantomogram with 5degrees, those to mandibular plane were significantly less than to occlusal plane in number of items which showed less differences than 5degrees. 2. Compared the root parallelisms in the orthopantomogram with those in 45degrees oblique cephalogram with 1% significance level, parallelism between upper canine & 1st premolar, lower canine & Ist premolar, lower 1st premolar & 2nd premolar, and lower right 2nd molar & 3rd molar showed statistically significant differences. 3. When the significance between the differences of the root parallelism between above two kinds of film and 5degrees was verified by two sided paired t-test, more or less large difference was shown between lower right 2nd molar & 3rd molar, a little larger than 5degrees between lower canine & 1st premolar, smaller at the rest of them. 4. In 45degrees oblique cephalogram, lower canine & 1st premolar showed convergent root arrangements each other, while in orthopantomogram they were divergent each other. All the others except them showed convergency on the upper, divergency on the lower in both films.

A study of the shear bond strength of metal brackets and ceramic brackets and the condition after debonding / 대한치과교정학회지

Metal brackets and ceramic brackets were bonded to natural teeth, porcelain crowns and gold crowns. After stored in artificial saliva solution for 72 hours at 37degreesC, the shear bond strengths were measured by Instron and compared with them, the bonding sites and bracket bases were examined by scanning electron microscope and light optical stereomicroscope. The results were as follows: 1. The shear bond strengths of the group which metal brackets were bonded to natural teeth and the groups which ceramic brackets were bonded to natural teeth and porcelain crowns were comparable to each other, the shear bond strength of the group which metal brackets were bonded to gold crowns was significantly low. 2. The bond failed predominantly at the bracket base/adhesive interface with the bulk of adhesive remaining on enamel in the group which metal brackets were bonded to natural teeth. 3. The bond failed consistently at the crown/adhesive interface with all of adhesive remaining on the bracket bases in the group which metal brackets were bonded to gold crowns. 4. The bond failed at the enamel or crown/adhesive interface with the bulk of adhesive remaining on the bracket bases in the groups which cramic brackets were bonded to natural teeth and porcelain crowns. 5. The shear bond strengths of the groups which ceramic brackets were bonded to porcelain crowns were not affected by etching time.

A study of masseteric silent period on the normal subjects and temporomandibular disorder patients / 대한치과교정학회지

This study was conducted for the assessment of the usefulness of masseteric silent period on electromyogram as a diagnostic method for temporomandibular disorder. Of students and dentists in Dental College of Yonsei University and patients, 36 experimental subjects with symptoms such as clicking sound, pain in the temporomandibular joint area and limitation of jaw movement, and 33 control subjects without such symptoms were selected for this study. On each subject electromyographic masseter muscle silent period followed by mention tap was recorded with surface electrodes and analysed with computerized system. The following results were obtained: 1. The mean silent period was 36.97 +/- 9.23 msec in experimental group, and 25.62 +/- 5.24 msec in control group respectively. 2. There were no statistically significant differences in silent period between male and female in either experimental and control group. 3. Silent periods in experimental group were more prolonged than those of control group. (P<0.01) Taken all together, electromyographic masseter muscle silent period may be useful for diagnosis and evaluation of temporomandibular disorder.