口腔治疗中不同颌位与髁突位置

在口颌系统中,与颌位稳定相关的因素分别是、颞下颌关节和神经肌肉的稳定,其中髁突在关节窝中的位置与获得一个稳定的颌位密切相关。但口腔治疗中涉及到颌位的选择时,不同学者持不同的观点,对于髁突在关节窝中应处的位置也一直处于争议之中。本文对口腔修复和正畸治疗中颌位选择及“髁突前上位”、“髁突前下位”、“治疗性颌位”的适应证、理论基础及临床应用作一综述。文献复习结果提示,当关节无器质性改变或髁凹关系稳定时,髁突前上位即正中关系为传统建的理想颌位。当关节盘增生、变形、盘突关系紊乱无法寻找理想的髁突前上位时,可选择髁突前下位,缓解关节症状的同时促进骨质改建获得良好的稳定性;甚至对于部分安氏Ⅱ类高角或者轻度骨性错的病例,亦可以尝试利用髁突改建的潜力,前下定位髁突,通过掩饰性矫治简化正畸正颌手术方案;而“治疗性颌位”是针对颅下颌功能紊乱症导致的最大牙尖交错位异常或偏斜、肌肉症状和关节功能异常、颌位不稳定等,通过改变原有咬合或关节的异常引导,在有咬合支持和新的引导的基础上,建立并且稳定一个新的牙尖交错位。它摆脱了髁突定位的争论,但此颌位下髁突具体位置未见报道。不同颌位及髁突位置有不同的适用范围,临床选择时应根据患者关节是否有器质性改变及颌位的稳定性进行综合判断。但对于采用不同颌位和髁突位置进行口腔治疗的远期效果未来还需临床对照试验进一步验证。     

Electromyography of masticatory muscles in three jaw registration positions

The purpose of this study was to investigate whether anteroposterior changes in mandibular position affect masticatory muscle activity. The electromyographic (EMG) activity of masticatory muscles during full and partial (10%) clenching in three mandibular bite registration positions--retruded contact position (RCP), intercuspal position (IP), and muscular position (MP)--was studied. Three groups of subjects with different ranges of anteroposterior positioning of the condyles were evaluated (normal occlusion, Class II, Division 2 malocclusion, and dual bite malocclusion). A posterior stabilizing splint for each registration position was made. EMG data were obtained from three bilateral muscles (masseter, anterior temporal, and posterior temporal). Clenching in the RCP elicited the lowest masseter muscle activity during full clenching, and the highest anterior temporal and posterior temporal muscle activity during partial clenching. If the relationships of the masticatory muscles are analyzed through a ratio that represents the interaction between biting and positioning muscles (masseter/posterior temporal muscle ratio), the RCP as compared with other positions had the lowest ratio. The RCP required more positioning muscle activity and permitted less biting muscle activity. There was no significant difference in the muscle activity between the IP and MP registrations. Small changes in jaw position (anterior to RCP) are not critical for the masticatory apparatus provided there is good intercuspation. The results of this investigation suggest that intercuspation in RCP is not the optimal position.     

Microangiography of the rabbit temporomandibular joint in the open and closed jaw positions

The purpose of this investigation was to test the hypothesis that jaw position significantly affects the vascular morphology of the temporomandibular joint (TMJ). The study was performed using intravascular perfusion with 30% Micropaque and 40% gelatin. Six anesthetized New Zealand white rabbits were divided into 2 groups of three. Group 1 rabbits were perfused in the resting, closed-jaw position and group 2 rabbits were perfused while the jaw was held open. The animals were killed with an overdose of pentobarbital and frozen. The heads were hemisected, fixed, decalcified, and embedded in Cedukol. Sagittal sections were cut at the level of the meniscus and radiographed with a specimen x-ray unit on high-resolution film. The 6 rabbits (12 TMJs) demonstrated consistent microvascular differences. In 83% of the jaws in group 2 rabbits the anterior condylar vein was not seen or appeared patchy whereas the same vein was readily seen in all jaws of group 1 (P less than .01). The superior condylar vasculature was distended in 83.3% of group 2 jaws and in 16.7% of group 1 jaws (P less than .05). This study demonstrates significant changes in vascular morphology when the jaw is placed in the open position.     

Factors influencing jaw position sense in man

The relative contribution of muscle sensors, joint sensors and trigeminal exterosensors to the position sense of the mandible was investigated. Subjects compared the sizes of gauges placed between the teeth with the size of a previously explored standard gauge of 4.75 mm. The experimental conditions were either anaesthesia of both mandibular joints and the oral exterosensors, or load on the jaw-closing muscles, or adaptation to an extreme jaw position. The results were compared with control experiments under normal conditions. (1) All subjects marched to standard fairly well in control conditions, the imprecision of the match being ~ 0.5 mm. Under anaesthesia, the matches were 1–1.5 mm greater than the controls, the imprecision being almost unaffected. Anaesthetizing the joints and oral exterosensors before or after exploring the standard gauge did not affect the match. Imposing various loads ($\text{}\text{?}$ 3.4kg) did not change the match to the standard. Adaptation to a wide open position introduced a considerable mismatch of the standard, leaving the imprecision of the match unaffected. (2) The experiments provide evidence that muscle afferents are important sources in sensing jaw position and fulfil the criteria for an independent position servo in the trigeminal system. It is suggested that the engram of the standard is built up mainly from muscle sensor information.     

The regulation of the jaw bite force in man.

Experiments were carried out on 12 adult subjects to measure their ability to grade forces between their anterior teeth when using different conditions of perceptual reference. The subjects placed their anterior teeth across a force transducer to produce isometric forces corresponding to a series of integers called by the experimenter in random order every two seconds. The value zero was taken to be zero force and the largest integer as their maximum comfortable bite. The results, which were analyzed by a technique based upon information theory, demonstrated that the mean performance of the subjects as a group was 2.5 bits, S.D. ± 0.3 (approximately 5 discrete levels) when 10 levels were attempted. When reinforcing references were regularly interspersed between the test integers, the mean performance was raised to 2.8 bits, S.D. ± 0.2 (approximately 6 levels). The use of 20 input levels raised the performance of 4 selected subjects to 3 bits (approximately 8 levels). The results suggest that bite force discriminatory ability is much better when an immediately preceding reference is used, than when an overall conceptual reference is employed.     

Effects of positions of experimental premature contacts on jaw function

The effects of different positions of experimental premature contacts on the jaw function were investigated on 6 subjects. The metal castings of 100-microns thickness were fabricated to make experimental premature contacts on each of 4 mandibular posterior teeth (from the first premolar to the second molar on the preferable masticatory side). The EMG activity of the masseter, anterior and posterior temporal muscles during maximum clenching and gum chewing as well as the mandibular movement during gum chewing were evaluated. The experimental premature contacts reduced the muscle activity, especially on the contralateral side during maximum clenching. As the premature contact was moved more posteriorly, the following results were observed. 1. The activity of the posterior temporal muscle was decreased on the ipsilateral side while it increased on the contralateral side during maximum clenching in many subjects. 2. The duration of the occlusion phase during the ipsilateral chewing was shortened in many subjects. 3. During ipsilateral chewing, a larger muscle activity was produced during the closing phase and the muscle activity produced during the occlusion phase was the least on the first molar. 4. In any chewing side, the closing and opening paths tended to go toward the chewing side.     

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目的    探讨吞咽法所获得的全口义齿水平颌位关系的临床效果。方法    选择2008年5月至2009年9月在承德市口腔医院进行全口义齿修复的无牙颌患者80例,随机分为2组,每组40例。分别用吞咽法和卷舌法确定水平颌位关系,并完成全口义齿的制作。观察两组全口义齿在口内的咬合关系与模型的一致性。结果    用吞咽法所确定水平颌位关系的全口义齿在口内的咬合关系与模型一致性Ⅰ、Ⅱ、Ⅲ类者分别为39、1、0例,而对照组分别为29、7、4例,两组比较差异具有统计学意义（χ2 =7.382,P = 0.023 ）。结论    利用吞咽法所获得的全口义齿水平颌位关系准确性较高,可以做为确定全口义齿水平颌位关系的有效方法。     

Sensorimotor discrimination during free jaw movements in man

Subjects carried out voluntary, unrestrained movements of the jaw to estimate position in space, a task involving coordinated sensory and motor functions. Incisal separation was derived from three-dimensional coordinates of movement by a magnetometer-based transducer system. Two experimental paradigms were used. One, based upon information theory, was designed to measure discrimination in terms of the number of reliably attained levels when 10 were attempted over two different ranges in both the opening and closing directions. The other method measured the variation of mean step size when subjects moved their jaws in small, equally-spaced incremental steps, opening and closing at different speeds. Using perceptual references at the intercuspal and maximum jaw opening positions, 6.5 separate levels were distinguished with accuracy, irrespective of the direction of movement. The group performance was significantly less (4.5 levels) over the smaller range between intercuspal and half-open positions. Discrimination was always best near the intercuspal position and at maximum jaw opening. No significant differences were evident in mean step size for the group in either direction of movement or speed of performance but there were marked individual differences in performance. In some, variations in incremental step size were smaller in closing than in opening phases. The presence of a zone of heightened sensorimotor acuity near the intercuspal position during free jaw movement indicates a specific adaptation of the nervous system.     

Tooth pulpal reflexes in jaw musculature in man.

Electrical stimulation of the tooth pulp elicited a short-latency, transient bilateral suppression of the voluntary masseter electromyogram. The threshold of this pulp reflex was somewhat higher than the pulpal sensory threshold, which coincided with the occurrence of a slight but distinct painful pricking sensation. When tested following pulp stimulation, the myotatic masseter reflex exhibited a phase of depression that had a much longer duration in resting conditions than during voluntary jaw closure. It is concluded that nociceptive afferents in the oro-facial area, most probably belonging to the A-delta group, have oligosynaptic inhibitory reflex connections with jaw-closing motoneurons.     

Effect of different head positions on the jaw closing point during tapping movements

Summary  This study aimed to investigate the effects of different head positions on jaw closing points during tapping movements. The jaw movements of 20 adult volunteers were assessed using a new jaw-tracking device. All subjects had stable maximal intercuspation with their natural dentitions. The subjects were asked to seat on a dental chair with their head upright, and tapping movements were recorded for 5 s without any further instructions. After the chair was reclined to the horizontal position, tapping movements were also recorded with the head in the supine position. The location of the tapping point was defined as the jaw position which was the most closed to the maximum intercuspal position during each tapping stroke. Fifteen tapping points were obtained from the upright and supine head positions of each subject. Six-hundred tapping points were compared to evaluate the effects of different head positions. With the head upright, tapping points were relatively stable and close to the jaw position at the maximum intercuspation. However, in the supine position, tapping points varied widely and shifted forward. The average distance between the positions of the incisal point at the maximum intercuspation and at the tapping points was 0·11 mm (SD, 0·10) in the upright position and 0·30 mm (SD, 0·08) in the supine position. A Wilcoxon signed rank test showed a significant difference ( P  < 0·01) between these distances. We conclude that tapping points shift anteriorly in the supine position.     

Long latency components of the jaw jerk and blink reflex in man

In the present study, the electromyographic (EMG) activity in the masseter and temporal muscles during about 200 ms after chin taps (jaw jerk response) was compared with the EMG activity in the orbicularis oculi after glabella tap (blink reflex). In two of ten subjects components with long latency and duration, analogous to blink reflex components BR₂ and BR₃, were found in the masseter and temporal muscles. They may represent the mechanical contraction which results in jaw closure. In two of the subjects chin taps were found to elicit late responses in the orbicularis oculi with the same latencies (25–30 and 80–100 ms) as BR₂ and BR₃ associated with glabella tap.     

Progressive jaw muscle fatigue of experimental tooth clenching in man

To determine the onset of subjective fatigue and the subjective endurance of fatigue and pains in the masseter muscle, ten adult male subjects exercised maximal voluntary tooth clenching. Concomitantly, the electrical activity in the masseter muscle was recorded by bipolar surface electrodes and integrated. Onset of subjective fatigue occurred on average 21 s after onset of muscle hyperactivity and the isometric endurance time of the masseter muscle, during which period severe muscle pains were present, was on average 82 s. The electrical muscle activity of the threshold and endurance tests showed a curvilinear configuration (y = a+b logx), and it is suggested that progressive physiological, or peripheral, muscle fatigue accompanied the psychological, or central, endurance of tooth clenching.     

Effect of experimental pain on EMG-activity in human jaw-closing muscles in different jaw positions

We examined the effect of a standardized painful stimulus on the surface EMG-activity of the human jaw-closing muscles at rest and during two levels of jaw opening. Sixteen healthy women participated in two experimental sessions. In randomized order, hypertonic saline (HS: 5.8%) was infused into the left masseter muscle on one occasion, and isotonic saline (IS: 0.9%) on the other. The subjects scored the pain intensity continuously on a 0-10 visual analogue scale (VAS). The subjects were asked to hold the jaw in three different positions (rest, half-maximal, and maximal opening). Before, during, and after infusion, the EMG-activity was recorded from the masseter and temporalis muscles with the jaw in each of the three positions. HS induced significantly higher pain-levels than IS (mean VAS: HS: 5.2 ± 1.3, IS: 0.7 ± 0.2, P < 0.05). At rest, the EMG-activity in most of the jaw muscles increased significantly during both infusions (P < 0.05). At half-maximal opening, the EMG-activity in the infused muscle increased significantly with both HS and IS (P < 0.05). At maximal opening, the EMG-activity during infusion of HS decreased significantly in the right masseter and temporalis (P < 0.05). There was no significant difference in the position of the jaw at rest during infusions. However, the vertical opening distance was significantly decreased during infusion of HS at half-maximal and maximal opening (P < 0.05). Conclusions: It is concluded that experimental pain affects EMG-activity differentially in jaw-closing muscles in different opening positions of the jaw.     

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.(ABSTRACT TRUNCATED AT 250 WORDS)     

A tonic vibration reflex evoked in the jaw opening muscles in man.

Motor effects induced by vibration of the mouth opening muscles were studied in eight subjects. All exhibited a tonic motor response with many characteristics in common with the tonic vibration reflex (TVR) as previously studied in limb muscles and jaw elevators: an involuntary contraction appeared in the jaw openers with gradual onset and gradual decline. The contraction was accompanied by a reciprocal inhibition of the voluntarily activated jaw elevators; it was susceptible to voluntary control—when allowed visual feed-back from a torquemeter all subjects were able to suppress the TVR and keep contraction force in their jaw elevators constant. The results suggest that the jaw openers are supplied with proprioceptors functionally similar to spindle endings in that on sustained activation they can produce tonic autogenic excitation and reciprocal inhibition, i.e. the pattern of the classical tonic stretch reflex. However, the vibration-induced contraction in the jaw openers did not exhibit one of the features typical for the TVR in the jaw elevators. The marked grouping of discharges synchronous with each wave of vibration, seen in gross EMG recordings from jaw elevators, was not seen in any one of the three jaw opening muscles examined, the anterior belly of the digastric, the mylohyoid and one of the infrahyoid muscles. As the vibration-induced synchronization is considered to depend on monosynaptic projections, the results imply that the jaw openers are devoid of such projections and that the TVR is mediated through polysynaptic pathways.     

An electromyographic study of jaw opening and closing reflexes in man

The electromyographic activity of the right masseter and digastric muscles was recorded in 10 subjects. A jaw-opening reflex was observed shortly after a mechanical stimulation in subjects performing clenching and active jaw-opening exercises. The latency of this reflex activity was about 28 ms, coinciding with the termination of the silent period of the masseter muscle. The experiments show that this opening reflex can occur without masseter spindle-unloading and may respond to low-threshold afferents.     

Soluble proteins in fluid from non-keratinizing jaw cysts in man.

Fluids from non-keratinizing cysts of the jaws contain the main proteins found in plasma. The low relative concentration of macromolecular non-immunoglobulin proteins shows that there is no free passage of plasma proteins into the cyst fluid. Sufficient evidence was found to conclude that the immunoglobulins in cyst fluid are partly produced locally and partly derived from plasma. Cyst fluid immunoglobulins have antibody activity to rabbit erythrocytes. Accumulation of cyst fluid is primarily due to inadequate lymphatic drainage of the cyst cavity. Differential diagnosis between various types of non-keratinizing cysts cannot be based on the plasma protein patterns of their fluids.