The influence of single molar crown placement on the smoothness of masticatory movement.

The jerk-cost is an index that can quantify the smoothness of various movements including human body movements. A previous study reported the usefulness of jerk-cost in the evaluation of masticatory movement, and proposed that the masticatory movement of subjects with good occlusion could be explained as a maximum smooth movement. The purpose of this study was to investigate the influence of a single prosthetic molar restoration on the smoothness of masticatory movement. Fourteen adults who visited this hospital seeking a single prosthetic restoration on a molar were selected. Each subject chewed a piece of chewing gum on the molars of the treated side before and after crown placement. Movement trajectory was recorded using the Sirognathograph Analyzing System. Normalized jerk-cost (NJC) was calculated on the closing phase of each chewing cycle and was compared before and after the crown placement. After the prosthetic restoration, NJC significantly decreased (P < 0.05) in seven subjects with a crown placed on a lower molar, whereas significant changes were not observed in seven subjects with a crown placed on an upper molar. These results suggest that restoring a crown on a lower molar could significantly improve the smoothness of masticatory movement on the same side.

Masticatory laterality--evaluation and influence of food texture.

The purpose of this study is the objective and quantitative evaluation of masticatory laterality and its daily variability. Various foods with different textures were used to investigate whether food texture influenced masticatory laterality. Ten healthy subjects and seven foods were used. Recordings of chewing movements were repeated three times at intervals of 1 week. Masticatory laterality was assessed with an Asymmetry Index [AI: (number of right side strokes - number of left side strokes)/number of total strokes]. Medians and ranges of the three recordings were calculated. The observed AI ranges in the three trials were limited with the exception of two subjects. Among the other subjects, averages of the absolute values of the medians were from 32.5 to 73.4%. Statistically significant differences between the hardest food and softer foods were observed in absolute value of AI medians. Masticatory laterality could be evaluated by an AI. Eight of 10 subjects showed limited ranges of AI in three recordings. It should be noted that a few people actually chew on either side but might chew on one side only on a particular day. Hard food evoked more masticatory laterality, and seemed more appropriate for laterality examinations.

A clinical study of the relationship between occlusal curvature and craniomandibular disorders.

The occlusal curvature should be harmonized with stomatognathic function, but excessive occlusal curvatures are found in some craniomandibular disorder patients. Forty healthy subjects and 95 patients with craniomandibular disorder (50 with clicking, 25 with locking, and 20 with myofascial pain dysfunction syndrome) were evaluated to investigate the functional significance of the occlusal curvature. Anteroposterior and lateral occlusal curvature were measured using the least-square approximation of the mandibular buccal cusps in a second-order quadratic and modification of Monson's 4-inch sphere. "Clicking" and "locking" groups had significantly greater occlusal curvatures than healthy subjects. There appeared to be a relationship between occlusal curvature and craniomandibular disorders.

[Clinical studies on the effect of contact at the non-working side on chewing movements].

In recent years, TMJ dysfunction is reported to be increasing, but at present its etiology is not clear now. We have been studying the chewing movements, which are the most important functional mandibular movements. The possibility is indicated that the interference at the non-working side of lateral movement have a harmful effect on the functional occlusion system. In this study, the effect of the interference at the non-working side on chewing movements was investigated. 30 people were selected as the interference group with the interference at the non-working side of lateral movement, and 10 people without that interference as the control group. the interference group was divided into two groups, interference normal group without TMJ dysfunction and interference abnormal group with TMJ dysfunction. Jaw movements were recorded and analysed by Sirognathograph Analysing System II. The results were as follows; Some characteristic patterns in the frontal plane were observed in the chewing movements of the interference group. 1. On interference side chewing, a concave opening pattern was significantly observed. Especially of the interference abnormal group, the working side deviate reverse crossover opening pattern was significantly observed. 2. On non-interference side chewing, a closing path with a step or a concave part was significantly observed.