カスプ角が咀嚼機能の適応に及ぼす影響

[Effects of cusp angle on the adaptation of masticatory function].

抄録

本研究の目的は、メタルスプリントを用いて1人の天然歯列のカスプ角度を変化させ、咀嚼機能の適応を明らかにすることである。各実験において、数週間にわたって下顎運動と筋電図が記録された。試験食としてレーズンを咀嚼しながら、セルスポットシステムを用いて下顎切歯点変位で測定される下顎運動を3次元的に検出し、表面電極を用いて左右の前側頭筋と咬筋の咀嚼筋の電気的活動をピックアップした。タイムスケジュールは、(1)スプリント挿入前、(2)スプリント挿入後20日間、除去後30日間（実験-1）、(3)スプリント再挿入後14日間、除去後7日間（実験-2）の3期で構成された。測定は、(1)開口期、(2)閉口期、(3)サイクルタイム、(4)停止期(St)(咬合接触時に下顎が静止している期間)、(5)EMG活動持続時間、(6)EMG沈黙持続時間、(7)EMG沈黙期間(IA)(EMG活動終了から停止期終了までの期間)の7指標について行った。その結果、1）尖角を変化させると、サイクルタイム、閉鎖相、開放相、EMG活動持続時間、EMG沈黙持続時間が増加したが、停止相はスプリント挿入前より減少した。これら6つの指標は大きな変動を示し、最初は不規則になった。2) 咀嚼機能の不規則性は徐々に消失し、5日目、遅くとも20日目にはすべての指標がスプリント挿入前の値に近づいた。3)測定期間中、IAやサイクルタイムと開口相の比にはほとんど反応が認められなかった。4) 再挿入期間（実験2）の指標は、挿入期間（実験-1）よりも急速に挿入前の値に近づいた。また、抜去後の指数は挿入前の値に急速に近づいた。つまり、咀嚼機能の時間因子の指標は、カスプ角の変化の影響が外乱としてのみ扱われることを示していた。そして、最初の適応が完了すると、咀嚼機能は同じ刺激に対してより迅速に反応するようになった。

The purpose of this study was to elucidate the adaptation in masticatory function by changing the cusp angle of the natural dentition of one person using a metal splint. During each experiment mandibular movements and EMG were recorded during a period of weeks. While chewing raisins as test food, mandibular movements as measured by the lower incisal point displacement were detected three-dimensionally using the Selspot system, and electrical activity of the masticatory muscles was picked up for the anterior temporal and masseter muscles, at the right and left using surface electrodes. The time schedule was composed of three terms: (1) before insertion of the splint, (2) for 20 days after insertion of the splint and then for 30 days after removal (Experiment-1), (3) for 14 days after reinsertion of the splint and then for 7 day after removal (Experiment-2). The measurements were done for the following 7 indices: (1) opening phase, (2) closing phase, (3) cycle time, (4) stopping phase (St), which is the period when the mandible was stationary during occlusal contact, (5) duration of EMG activity, (6) duration of EMG silence, (7) the period of EMG silence (IA), which is the period from the end of EMG activity to the end of the stopping phase. The following results were obtained 1) On changing the cusp angle, there was an increase in cycle time, closing phase, opening phase, duration of EMG activity, and duration of EMG silence, but the stopping phase was less than before insertion of the splint. These 6 indices showed a great variation and became irregular at first. 2) The irregularity of the masticatory function disappeared gradually, and then all indices approached the value before insertion of the splint from day 5 or day 20 at the latest. 3) Scarcely any reaction was detected in IA or in the ratio of cycle time and opening phase throughout the measurement period. 4) The indices of the reinsertion period (Experiment 2) approached the value before insertion more rapidly than the period of the insertion (Experiment-1). And the indices after removal quickly approached pre-insertion values. In short, the indices of the time factor of the masticatory function showed that the effect of changing cusp angle was handled as only disturbances. And once the first adaptation was completed, masticatory function responded more quickly to the same stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)