S. Nakata

Relationship between the unilateral TMJ osteoarthritis/osteoarthrosis, mandibular asymmetry and the EMG activity of the masticatory muscles: a retrospective study

The purpose of this retrospective study was to investigate the relationship between the unilateral temporomandibular joint (TMJ) osteoarthritis/osteoarthrosis (OA), mandibular asymmetry and electromyographic (EMG) activity of the masticatory muscles. Twenty-two Japanese women (aged 23.2 +/- 5.4 years) and 10 Japanese men (aged 22.4 +/- 2.8 years) exhibiting unilateral TMJ OA were included in this study. Two angular and seven linear measurements were obtained for the analysis of the skeletal hard tissues. The cephalometric measurement values (CV) were normalized using the CV ratio for the evaluation of the degree of mandibular asymmetry. The EMG was recorded during maximal voluntary clenching efforts for 10 s in the intercuspal position. The average values of integral EMG (iEMG) of three trials were normalized using the iEMG ratio for the evaluation of the functional balance of the masticatory muscles. The mandibular midline was shifted to the TMJ OA side with a median value of 9.85 mm. The CV ratio of the ramus height of the TMJ OA side was significantly smaller than that of the non-OA side. For the masseter muscle, the iEMG ratio of the TMJ OA side was significantly larger than that of the non-OA side (P < 0.05). These results suggest that unilateral TMJ OA is related to the dentofacial morphology, thus resulting in a mandibular midline shift to the affected side and it is associated with a masticatory muscle imbalance.

Difference in tracks between habitual open and close mandibular movements at the condyle in children.

Although previous studies have paid much attention to the condylar movement in adults with permanent dentition, little attention has been paid to such movement in children. In this study, we therefore clarified the difference in habitual open and close movements at the condyle in children. Three groups of subjects were used; primary (10 children), early mixed (10 children), and permanent dentition (10 adults). The habitual open and close mandibular movement of each subject was measured using a TRIMET, which can three-dimensionally analyse the simultaneous movements of multiple points on the mandible of a subject. The measurements were then compared among the three groups. The three-dimensional analysis detected significant difference in all directions between children with primary dentition and adults with permanent dentition: primary dentition had the smallest anterior-posterior and superior-inferior directions, and the largest left-right direction. Coincidence of the open and close tracks occurred in the adults (adult group) but not in the children (primary and early-mixed dentition groups). The early-mixed dentition group showed tracks that were between those for the primary dentition group and the adult group. These results suggest that the regularity of the condylar track might be well established with dental development.

Condylar motion in children with primary dentition during lateral excursion.

ABSTRACT Normal development of primary and mixed dentition is indispensable for establishing a healthy mandibular function of the permanent dentition. Because condylar movements are crucial for mandibular function, extensive studies have been reported. However, most of these studies have dealt with mandibular functions in adults, and there is less known about children with primary dentition. The purpose of this study was to clarify the condylar movements during lateral excursions in children with primary dentition and compare these movements with those of adults from the viewpoint of functional development. With use of an optoelectronic recording system with six degrees of freedom, the lateral excursions of 24 children and 20 young women, with sound dentition, were recorded at 100 Hz. The results show that the balancing side condyle of the children had a significantly smaller vertical excursion and a significantly larger anteroposterior excursion than that of adults, indicating the shallower and more anteriorly directed movements of the entire mandible during lateral excursions in children with primary dentition.

Investigation of the relationship between the curved mesh diagram of mandibular excursion and the occlusal phase of mastication.

本研究の目的は, 下顎の重要な機能である咀嚼運動の終末路において, 上下の歯牙が接触しながら行われる滑走運動の範囲を計測する方法を開発することにある.25歳の個性正常咬合を有する男性を被験者として東京歯材社製TRIMETを用いて下顎運動を計測した.この装置は100Hzで下顎運動を計測することができる.被験者に30秒間の下顎の任意な滑走運動を4回計測した行わせた.これにより12000顎位を得た.これを使用して, 下顎切歯点の咬頭嵌合位を原点とした前方15mm, 後方13mm, 左右方向各々14mmの範囲における下顎滑走運動面を得た.また, その間隔は0.1mmとした.下顎滑走運動面上のメッシュの各点について, 水平面上で距離が最小距離となる顎位を12000顎位の中から探索し, その最小となった顎位のZ座標値をそのメッシュのZ値とした.この方法により, 下顎の任意の点で作成することが可能である.その結果, この下顎滑走運動面と咀嚼運動の終末路を比較することにより, 終末路での滑走運動範囲を計測することができ, この被験者のガム自由咀嚼運動の滑走範囲を計測したところ, 閉口時に, 約0.4mm, 開口時は約3.4mmであった.この下顎滑走運動面は, 下顎運動やその範囲を視覚化できることから下顎運動の理解や診査・診断に有用であると考えられた.