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咀嚼時の総義歯下の痛覚に関連するバイオメカニクス的要因の評価における有限要素解析の使用
Use of finite element analysis for the assessment of biomechanical factors related to pain sensation beneath complete dentures during mastication.
PMID: 29961620
抄録
問題提起:
義歯装着者が咀嚼時に一般的に受ける痛みは、圧痛閾値の客観的な生体力学的基準には記載されていない。
STATEMENT OF PROBLEM: The pain commonly suffered by denture wearers during mastication is not documented in the objective biomechanical criteria for the pressure pain threshold.
目的:
この有限要素解析研究の目的は,咀嚼時に下顎総義歯の下に発生する圧力が,義歯床が許容できる耐荷重を有する患者において,平均圧力痛覚閾値を超えるかどうかを明らかにすることであった.
PURPOSE: The purpose of this finite element analysis study was to determine whether the pressures developed beneath a removable mandibular complete denture during mastication would exceed the average pressure pain threshold in patients for whom the denture foundation had an acceptable load-bearing capacity.
材料と方法:
義歯床が許容できる耐荷重を有する患者を有限要素解析でモデル化した.義歯と粘膜の界面は,滑走あるいは離開の界面としてモデル化した.凸状の下顎骨残稜,弾力性のある粘膜,および義歯を曲線と断面を用いてCADでモデル化した.片側垂直咬合荷重はモデル検証のためにのみ100Nとし,斜め咬合荷重は平衡咬合による咀嚼を模擬するために141Nとした.非作業側咬合接触は,義歯と非作業側上部の平坦な固体との間に0.1mmまたは1mmの初期距離を設定し,即時非作業側咬合接触と遅延非作業側咬合接触の2つの状況で模擬された.
MATERIAL AND METHODS: A patient with an acceptable load-bearing denture foundation was modeled with finite element analysis. The denture/mucosa interface was modeled as a sliding or detaching interface. A convex mandibular residual ridge, resilient mucosa, and denture were modeled in computer-aided design (CAD) software using curves and cross sections. A unilateral vertical occlusal load of 100 N was assumed only for model verification, and an oblique mastication load of 141 N was assumed for simulated mastication with balanced articulation. The nonworking-side occlusal contact was simulated in 2 situations: prompt nonworking-side occlusal contact and delayed nonworking-side occlusal contact by setting an initial distance of 0.1 mm or 1 mm between the denture and a flat solid above the nonworking side.
結果:
義歯は最大203kPaの垂直荷重で粘膜に固定された.義歯は斜め咀嚼荷重で傾斜し,非作業側咬合接触により安定を得た.つまり,義歯は義歯床だけでなく非作業側咬合接触によっても支持され,下向きの安定化反力を有していた.遅延型非作業側咬合接触では,速やかな非作業側咬合接触に比べ,義歯の支持力は弱く,義歯床への支持力も弱くなった.義歯下圧力は,遅延非作業側咬合接触では783kPa(圧力痛覚閾値以上)であったのに対し,即発非作業側咬合接触では484kPa(圧力痛覚閾値未満)であった.遅延非作用側咬合接触では,土台の反力が小さいにもかかわらず,義歯下の圧力が上昇し,義歯の傾斜位置による荷重伝達面積の減少が示唆された.また,粘膜面摩擦は遅延型非作業側咬合接触で14倍以上となった.
RESULTS: The denture was held to the mucosa under vertical force and a maximum pressure of 203 kPa. The denture was tilted under an oblique mastication load and achieved stability through nonworking-side occlusal contact. This means that the denture was supported not only by the denture foundation but also by the nonworking-side occlusal contact and had a downwardly directed stabilizing reaction force. The denture was weakly supported on the delayed nonworking-side occlusal contact compared with the prompt nonworking-side occlusal contact and weakly supported on the denture foundation. In delayed nonworking-side occlusal contact, the pressure beneath the denture was 783 kPa (>pressure pain threshold) compared with 484 kPa (<pressure pain threshold) in prompt nonworking-side occlusal contact. Despite the lower reaction force of the foundation in delayed nonworking-side occlusal contact, the pressure beneath the denture increased, indicating a reduction in the load transfer area due to the inclined position of the denture. Friction on the mucosal surface was over 14-fold higher for the delayed nonworking-side occlusal contact.
結論:
下顎総義歯の床圧は平均的な圧痛閾値を超え,大きなスライドで支持されているため,摩擦が生じた.咬合側荷重の値は変化しないが,義歯下の圧力は増加し,非加工側咬合接触までの距離が長くなるため,非加工側咬合接触の力は減少することが示された.
CONCLUSIONS: The pressure beneath a removable mandibular complete denture exceeded the average pressure pain threshold and was supported with a large slide, which produced friction. Although the value of the load on the occlusal side did not change, the pressure under the denture increased and the force of nonworking-side occlusal contact decreased because of increasing distance to nonworking-side occlusal contact.