Incisal Point Research Articles

A preliminary investigation into the effect of increased occlusal vertical dimension on mandibular movement during speech

Current methods of determining whether a patient will accommodate to an increased occlusal vertical dimension rely on a largely subjective assessment of the mandibular rest position and capacity to adapt whilst wearing a temporary appliance. The purpose of this preliminary study was to establish if mandibular movement during speech may provide an objective criterion in the assessment of adaptation to increases in occlusal vertical dimension. The closest speaking space, measured as the vertical distance between an incisor point and centric occlusion, as determined during pronunciation of sibilant speech sounds was chosen to depict mandibular movement. The closest speaking space was determined using a Sirognathograph for six young adult subjects and varied from a mean of 1.0 to 3.3 mm. An acrylic splint covering the entire occlusal surface of the lower arch, designed to increase the occlusal vertical dimension by 4 mm in the incisor region, was then cemented on each subject's mandibular arch. The closest speaking space was again determined after 5 days continuous wear of the splint and the mean values found to have decreased to a range of 0.0–1.0 mm. The differences between the mean values for the closest speaking space for each subject before and after splint wear were statistically significant. It was postulated that this method may lead towards an objective basis for deciding if patients will adapt to an increase in occlusal vertical dimension.

Relationship between tongue volume and lower dental arch sizes

The interrelation between the tongue volume and the lower dental arch sizes (arch width and area) was studied by the original methods that we developed. A plane perpendicular to the occlusal plane and 40 mm posterior to the lower incisal point was taken as the posterior border of the tongue and the arch. The tongue volume and the lower dental arch sizes were measured anterior to this border with plaster models. The correlations between the parameters obtained from 74 Japanese adults (37 men and 37 women) with normal occlusion were statistically analyzed. The results showed that (1) both the mean tongue volume and the mean lower dental arch sizes were significantly larger in men than in women; (2) the tongue volume and the lower dental arch sizes were significantly correlated; and (3) these correlations tended to be higher at the more posterior part of the dental arch.

An electrognathographic study of aspects of ‘deprogramming’ of human jaw muscles

Three-dimensional electrognathography of an incisor point was used to detect peripheral correlates of deprogramming of the jaw elevator muscles. Putative deprogramming was attempted through the clinically recommended use of a leaf gauge, placed for 10-15 min between the maxillary and mandibular anterior teeth and disoccluding the posterior teeth by about 2 mm. Studied mandibular displacements were those that occurred during voluntary elevation of the mandible from the postural to the intercuspal position. Use of the leaf gauge did not affect the displacement patterns. Within a freeway space of about 0.2 mm3, the incisor point moved about 2 mm vertically, about 1 mm sagittally, and about 0.2 mm laterally.

Comparison of 'normal' TMJ-function in Class I, II, and III individuals

Fifty-seven non-orthodontically treated young adults, judged as either clinically healthy or with only mild symptoms of TMJ-dysfunction, were divided into groups according to their sagittal molar relationship (Class I-, Class II-, and Class III-group). All underwent a standardized clinical and axiographic examination with an axiographic recording device (SAS-SYSTEM). The comparison of the lengths of the axiographical protrusive curves showed significantly higher values in the Class II group than in the Class I (P less than 0.01) and in the Class I group than in the Class III group (P less than 0.001). Analogous differences could be found in clinical protrusive measurements at the incisal point and in lateral excursions. It was concluded that the protrusive condylar movement capacity coincides with the dental sagittal relationship. In opening, significant differences were seen axiographically (Class I v. Class III: P less than 0.001; Class II v. Class III: P less than 0.01), but not clinically. Since axiographic measurements show only condyle translation, but not rotation in contrast to measurements at the incisal point, it can be concluded that the differences in opening are also translatory and not rotational. Measurements of the average change of curvature of axiographic tracings showed significantly less curved protrusive tracings in Class III than in Class I (P less than 0.001) and Class II individuals (P less than 0.01), supporting the concept that in the Class III group condyle movement is restricted to the straight posterior slope of the tubercle.(ABSTRACT TRUNCATED AT 250 WORDS)

下顎運動における切歯点部のローテーションに関する臨床的研究

下顎運動における切歯点部のローテーションに関する臨床的研究

切歯路とか路の運動論的対応関係の研究 第１報 前後的運動距離の解析

Few studies have been reported on the kinematic correlation between incisal and condylar paths.We defined the parameters related to mandibular movement distance and analyzed the correlation between incisal point and condyles statistically in 20 normal subjects with Kyushu University 3-D movement analyzing system.The parameters are as follows: the incisal parameter “I” is 3-D linear distance of incisal point during mandibular movement. The condylar parameter “C” is the curve length of condylar path and “Cs” is the antero-posterior distance of condylar path projected on the Camper's plane.As a reault of this study, there were differences between the right and left condyle paths at the point of maximum opening and during protrusive and lateral excursive movements. In each of the above three movements, there was a high correlation between C and Cs. The Cs ratio of protrusion to maximum opening was about 50% and that of lateral excursion to maximum opening was the same. In protrusion we found a notable correlation between Cs and I. This has suggested we could estimate condylar movement from incisal movement stochastically.

A Cephalometric Study of Changes in Point A under the Influence of Upper Incisor Inclinations.

Today the ANB angle is commonly used for defining the anteroposterior apical base relationships of the jaws. The factors that influence the ANB angle have been studied by various investigators. The axial inclination of the maxillary central teeth is one of the factors influencing the location of point A. In this study the relationship between the axial inclination of the upper central incisor and the location of point A was studied. Four criteria that define the location of the maxillary central teeth were used: I (incisal point), Ap (apical point), R (rotation point), and I-SN (angle between I and SN plane). A significant positive correlation was found between the location of points A and R. We also calculated a regression equation for this relationship.

Predicting foodstuff from jaw dynamics during masticatory crushing in man

In previous in vitro experiments using an Instron instrument, each test food was found to have characteristic textural properties. In vivo experiments were now made (1) to determine the degree to which variations in the vertical jaw movements during the crushing phase of mastication can be explained by the inherent properties of the foodstuff being chewed, and (2) to establish the degree to which the foodstuff being chewed can be identified by certain features of the jaw dynamics. Five adults were used for chewing tasks with standardized pieces of beef, carrot or peanut. Each subject made two trials with each foodstuff. The movement of the lower incisal point was monitored; features of movement associated with jaw closing in the first chewing cycle were considered. Five of these features were not suitable to categorize the various test foods. Each of the remaining 4, however, was able to distinguish either one food from the 2 others (2 cases), or one from another (2 cases). Pattern recognition techniques based upon principal component analysis could differentiate jaw closing patterns associated with chewing beef from those involving peanut or carrot. The extent to which peanut could be distinguished from carrot was not as predictable as the categorization of peanut or carrot versus beef. Cross-correlation of in vitro force-time breakage characteristics and the jaw movement data showed that on average 52% of the variation in the vertical jaw movement during crushing of food could be explained by the inherent properties of the food. Because the masticatory apparatus acts as a low-pass filter, the high-frequency components of food breakage characteristics found in vitro were attenuated in vivo. It appears that the inherent filter properties of the masticatory apparatus limit the range of sensory and motor function of the jaw.

顎口腔機能異常者の下顎切歯点限界運動に関する研究 診断パラメーターの確立

In order to establish diagnostic and treatment system for temporomandibular (TM) disorder patients, data were collected on mandibular border and tapping movements at incisive point and compared with those from the subjects without any TM disorders. Significant differences on the ratio of left and right sides of maximum lateral deviation, maximum opening amount and length of pathway of lateral border movement were clearly obtained, the values of maximum speed and acceleration of closing phase in tapping movement obtained from TM disorder patients were also different significantly from those in the control subjects. These findings suggests that those measured indices in this study would be useful for diagnosis of TM disorders.

顎口腔機能異常診断への多変量解析の応用 下顎切歯点限界運動軌跡の解析

In order to establish a diagnostic system for temporomandibular (TM) disorder patients, data were collected on the mandibular border movement at incisal point from TM disorder patients and analized by multi valiable analysis comparing with data from the subjects with no TM disorder symptom.Seven parameters were identified as useful ones for the discrimination between TM disorder group and control group. With these parameters, 71% of TM disorder group and 91% of control group were correctly discriminated, respectively.These findings suggest that application of multi valiable analysis may be useful for a diagnosis of TM disorder patients.

開口運動における外側翼突筋下頭・顎二腹筋前腹の筋電図学的研究

This study investigated the functional roles of the inferior of the lateral pterygoid muscle (LPt) and the anterior belly of the digastric muscle (Da) during jaw-opening, in which EMG activity was simultaneously recorded at the condylar and incisor points. The LPt was found to slide the condyle along the articular tubercles and the Da was moved the incisor region downward-backward for condylar rotation. Therefore, rotation of the condyle and sliding of the mandible downward-forward apparently combined in a coordinated movement. Direct relationships were found between LPt activity and the distance of condylar movement, and between Da activity and the velocity of incisor movement during opening of the mandible. Therefore, the muscles primarily engaged in wide opening movement were mainly the LPt, and for rapid opening, mainly the Da.

骨格性下顎前突者のこう合に関する研究 第２報 側方滑走運動時の大臼歯部の対合関係とそしゃく運動パターンとの関係について

Patients having skeletal class III malocclusion are known to exhibit a wide variety of chewing patterns. This situation is believed to be caused by differences in occlusal conditions, the nature of which have not been clarified. I therefore investigated the relationship between their occlusal condition of the molars during lateral excursion and their chewing patterns.With regard to occlusion, I measured the distance between each occlusal surface of the lower molars and its opposing surface in a lateral occlusal position. Regarding masticatory patterns, I classified chewing strokes of the incisal point into 4 patterns, depending on whether or not the gliding phase was in evidence.The results were as follows: 1) In cases where gliding movements appeared during chewing strokes, the average of the measured distance on the working side was less than 0.7 mm; 2) even if this condition regarding distance was satisfied, gliding movement did not appear, if occlusal contact occurred on the non-working side.The results cited above show that disclusion of the working side molars and the tooth contact of the non-working side molars during lateral excursion directly affect the commencement of the gliding phase in chewing strokes.

MKG 記録時における頭部固定の必要性について

Mandibular Kinesiograph (MKG) enable us to observe three dimensional motion paths of the mandibular incisal point at function and is therefore used widely in clinical and research work. With improvements made on the apparatus, distortion is made less but abnormal images are sometimes produced. Various causes for this phenomenon are presumed and head displacement and inclination is cited as one cause. An experiment was undertaken, simulating patients' head inclination in the right, left, forward, and backward directions and rotation. First, the sensor alley and magnet were fixed on a platform in such a way that their relative positional relation would be the same. Then, the platform was inclined 10°and 30°left, right, forward, and backward, and was rotated, and positions of the null beam point were measured. Next, five patients as subjects were seated (1) in the dental chair, (2) on a stool without the back rest, and (3) on a stool with the back rest with the patients' head position fixed, and MKG recordings of masticatory motion under each condition were made. Results of the examination of recordings were as follows : 1. When the sensor was inclined or rotated and the positions of the null beam point was measured, inclination forward or backward had no effect but inclination left or right and rotation caused considerably great displacement in the null beam point. 2. The recordings of masticatory motion under each of the three conditions showed that the terminal masticatory points varied greatly in the case of dental chair. In the case of the stool with and/or without back rest, the head position was more easily stabilized than in the case of the dental chair and the terminal masticatory points were made to stabilize. Furthermore, fixing the head position made it possible to further less displacement of the terminal masticatory points. 3. In observation of the region of intercuspal position in enlargement and in prolonged recording with use of MKG, the head position must be fixed and left and right inclination and rotation of the head must be prevented.

Labial root torque: Effect on the maxilla and incisor root apex

This study was designed to determine the effectiveness of labial root torque on anterior nasomaxillary development. Quantification was made of the angular and linear changes in Down's point A (representing midsagittal basal bone) and incisor point A (representing the dentoalveolar bone) and any concomitant incisor root resorption. The study was divided into two parts: part 1 — to determine the anatomic configuration of the premaxillary region by use of laminagraphy on skulls, and part 2 — to use the morphologic landmarks found in part 1 to assess the development of the nasomaxillary complex in maxillary retrusive patients. The clinical study involved 17 maxillary retrusive patients, aged 8.0 to 15.7 years, who had been treated for a period between 0.31 and 3.70 years with edgewise advancing mechanics. Clinical results indicate that during the first phase of orthodontic treatment with labial root torque, encompassing a 0.63-year mean treatment period, a greater rate of advancement of Down's point A was produced when compared with normal growth. The skeletal convexity increased, whereas normal growth straightened the profile. Incisor point A advanced at a greater rate than Down's point A, suggesting that treatment caused a larger dentoalveolar effect than the effect on midsagittal basal bone. When treatment was extended to 1.57 years, similar changes were found but at a reduced rate. Overall apical root resorption was 12.7%/year. Sex and age were not found to have any correlation to the amount of apical root loss.

そしゃく時の歯牙滑走運動に関する研究 Ｉ そしゃく様空口運動時の歯牙滑走運動と側方滑走運動の比較

The purpose of this study is to clarify the relationship between grinding movements during chewing, and lateral excursions starting from the intercuspal position. For this purpose, I measured two different types of three-dimensional mandibular movement; lateral excursions and empty-jaw movement like chewing in 10 subjects, and compared these paths with each other in the lateral occlusal position, when the incisal point is 2.0 mm distant from the intercuspal position. The results can be summarized as follows: 1. The two positions of the incisal point were statistically coincident. 2. The position of both working and non-working side molars during chewing tended to be inferior to that during lateral excursion. 3. The moved distance of the working side condyle during chewing was significantly less than that during lateral excursion. 4. The position of the non-working side condyle during chewing tended to be medial to that during lateral excursion. 5. The difference in the condylar position was deeply related to that in the molar position. The differences mentioned above were considered to be originated from the difference in the masticatory muscle activity and the occlusal contact.

空えん下時における下顎の動態について Ｉ 歯牙接触および下顎安静位

We investigated the swallowing of saliva on 11 adults with a normal tooth alignment and a normal occlusion. The envelope of sagittal incisal point movements of the mandible was analyzed by means of the infrared sensor system. Frankfurt horizontal plane was used as a reference plane. The following conclusions were obtained based on the experimental results. 1. The mean linear distance between retruded tooth contact position (RCP) and intercuspal position (ICP) was 1.35 mm. 2. The mean linear distance between most retruded tooth contact position during swallowing saliva (SRCP) and ICP was 0.13 mm. The ratio of SRCP to RCP was about 10 percent. 3. The rest position of the mandible induced by swallowing saliva (RP) was 1.05 mm apart from ICP. 4. The maximum interocclusal distance during a cycle of swallowing saliva (MOP) was 1.70 mm in the average of 11 subjects. RP and MOP were significantly different from each other in the average of 11 subjects. However, individuals whose RP and MOP were significantly different were 6 subjects of 11.

Frontal chewing patterns of the incisor point and their dependence on resistance of food and type of occlusion

This study has shown that mastication in normal dentate subjects is associated with a great variety of movement modes. The dependence of chewing patterns on the resistance of food proves that the chewing system is capable of marked variations. A complete assessment of chewing behavior therefore demands the use of both tough and soft foods. Physiologic chewing of tough food is dominated by angulated grinding-type movements, whereas soft consistencies are chewed with drop-shaped or lenticular patterns. In a random sample of patients with good chewing function, approximately 95% of Angle class I and II occlusions were found, which statistically differed neither in chewing pattern distribution nor in movement parameters. As shown in this study, certain occlusal or functional properties cannot be characterized by a single type of chewing pattern but instead by a specific distribution of patterns. As a basis for the evaluation of such investigations, a method for the classification and ordered documentation of observed movement modes is necessary. The scheme used here includes all types of chewing movements that have been presently observed. It permits the recognition of patterns and the quantitative description of their frequencies and variations.

Xerox copy of the dental cast for analysis of the stability of mandibular osteotomy

Stability of the mandible was analysed with a Xerox copy of the dental cast in 35 cases of mandibular prognathism corrected by ramus osteotomies. The occlusal relationship in the Xerox copy was illustrated by superimposing two contact points on the upper and lower dental arches and the change in the position of the lower dental arch in relation to the upper dental arch was obtained by superimposing the latter on preoperative, predicted postoperative, and six months postoperative occlusions. The stability of the mandible was analysed by measuring the movement of five landmarks (two posterior, two molar and one incisor points) set around the lower dental arch to represent the movement of the mandible. The relapse was estimated by the movements of the landmarks from the predicted postoperative occlusion to the six months postoperative occlusion. The mean estimated anterior relapses at the posterior and molar points with the larger predicted movement and the incisor point were between 0.9 mm. and 2.0 mm. at six months postoperatively, whereas on the side with the smaller predicted movement, the points moved posteriorly by 0.6 mm. and 0.5 mm. Despite the fact that the amount of the predicted lateral movement was much smaller than that of the predicted posterior movement at operation, the posterior points were estimated to relapse laterally by 2.0 mm. and 1.7 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

The acoustical characteristics of the normal temporomandibular joint.

Both clinical and empirical evidence suggests that the "normal" temporomandibular joint produces noise during function. The purpose of this study was to determine the conditions under which these noises might arise. Joint sounds and mandibular movements were recorded simultaneously from 200 adults who had no previous history or present symptoms of TMJ pain or dysfunction. The joint sounds were recorded bilaterally by means of two separate miniature vibration transducers mounted on a common headband, and incisal point mandibular movements were measured by a magnetometer tracking system. Recordings were made while each subject opened and closed the mouth, first in a natural and comfortable manner, and then to maximum displacement. Two types of measurements were made: the appearance, onset, and duration of joint-propagated sounds in relation to relative mandibular position; and the spectral properties of the detected sounds. The results of this study showed that for natural opening and closing movements of the mandible, the "normal" TMJ was silent for all age groups. However, for the maximum displacement condition, detectable sounds appeared at the points of maximum displacement in both the opening and closing phases of the cycle in over 80 percent of the subjects. However, these sounds were, as a class, substantially longer than, and spectrally distinct from, abnormal joint sounds, suggesting that they arise from a distinct physical substrate.

下顎前歯部正面形態の増齢的変化

With regard to the upper anterior teeth, many studies have been made on forms, sizes, standards for selecting colors, and state of dentition. However, little concern has been shown on the lower anterior teeth from the viewpoint of esthetics, although they are as clearly visible as the upper anterior teeth during speaking. Therefore, with 56 individually normal dentulous males, 20 to 40 years of ages, as subjects, incisal point, gingival point, and interdental papillary apex were measured and the horizontal and vertical relationships in position with aging among the measured items and changes in position of each measured item were examined. The prosthetic plane was used as the vertical base plane and the contact points of the lower left and right central incisors as the horizontal reference points. The results were as follows : 1. Incisal point, incisal embrasure apex, and gingival embrasure apex showed little changes horizontally and vertically with aging. 2. Gingival point showed a tendency to lower slightly with aging. For all ages, the gingival points of the central and lateral incisors were at about the same positions, and that of the canine was located at about 1.5mm below those points. 3. Interdental papillary apex lowered with a statistical significance with aging. The extent of lowering was about the same for all items. 4. Interdental papillary apex and gingival point both lowered vertically ; however, the former showed a greater tendency to lower with aging. 5. The coronal axis was positioned about vertically to the occlusal plane for the central and lateral incisors but inclined about 8°mesially for the canine. 6. The coronal twist angles of the central and lateral incisors and canine were 0°, 13-18°, and 31-35°, respectively. 7. Incisal embrasure area showed no changes with aging but gingival embrasure area tended to decrease with aging. 8. The clinical coronal lengths of the lateral incisor and canine were about the same for both the upper and lower jaws but that of the central incisors was greater for the upper jaw.