後方咬合支持の喪失が三次元的顆頭変位に及ぼす影響

Influence of Simulated Loss of Posterior Occlusal Support on Three-dimensional Condylar Displacement.

抄録

本研究の目的は、後方咬合支持の喪失が下顎顆部の変位を引き起こすかどうかを生理学的観点から検証することである。12名の健常顎臼歯患者を対象に、スタビライゼーションタイプのスプリントを作製した。各スプリントは、両側の上顎歯を第二大臼歯まで覆うように設計した。後方咬合支持の喪失を再現するために、スプリントの範囲を両側から1歯ずつ縮小し、後方から順次前方に移動させた。各スプリントでタッピング運動と側方移動を行い、6自由度の顎運動追跡装置を用いて顆頭変位を観察した。実験的顎運動中の顆頭の運動軸の3次元（3-D）変位を、上顎第2大臼歯を含むすべての歯に咬合接触させた各咬合条件下で評価した。咬合位は習慣的閉鎖位を基準とした。咬合支持の喪失に伴い、タッピング運動の終点における運動軸の3次元変位が増大し、両顆頭で有意差が認められた。また、咬合支持の喪失に伴い、側方へのエキスカーション時の作業側の運動軸の3次元変位に増加が観察され、左顆で統計学的に有意な差が観察された。また、咬合支持の喪失に伴う側方加振時の非作業側の運動軸の3次元的変位にわずかな増加が観察された。本研究の結果から、後方咬合支持の喪失が下顎顆部の変位を誘発することが示唆され、臼歯部における咬合支持が顆頭位の安定化に重要な因子であることが示唆された。

The objective of this study was to verify whether loss of posterior occlusal support induced displacement of the mandibular condyles from a physiological point of view. Stabilization-type splints were fabricated for 12 healthy dentulous individuals. Each splint was designed to cover the bilateral maxillary teeth up to the second molars. To reproduce loss of posterior occlusal support, the extent of the splint was reduced one tooth at a time, bilaterally, starting from the back and moving forward sequentially. Tapping movement and lateral excursions were performed with each splint and a jaw movement tracking device with 6-degrees of freedom used to observe condylar displacement. Evaluation of 3-dimensional (3-D) displacement of the kinematic axis of the condyle during experimental jaw movement was performed under each occlusal condition with occlusal contact on all teeth, including the maxillary second molars. The habitual closing position was used as the reference. An increase was observed in 3-D displacement of the kinematic axis at the terminal point of the tapping movement with loss of occlusal support, and significant differences were observed in both condyles. An increase was also observed in 3-D displacement of the kinematic axis on the working side during lateral excursion with loss of occlusal support, and a statistically significant difference was observed in the left condyle. A small increase was observed in 3-D displacement of the kinematic axis on the non-working side during lateral excursion with loss of occlusal support. The results of this study suggest that loss of posterior occlusal support induces displacement of the mandibular condyles, suggesting that occlusal support in the molar region is an important factor in stabilization of the condylar position.