Analysis of stress distribution of tooth restored with metal-ceramic crown covering abfraction lesion according to its finish line location under occlusal load

Abstract

[한글]치관의 굴곡으로 발생된 abfraction 병소에 집중된 응력은 병소의 진행과 치수 노출이 유발시키고 결과적으로 치관을 파절시킬 수 있다. 복합레진은 abfraction 병소의 치료 방법으로 가장 먼저 고려되지만 협설측 또는 치아 주위에 발생한 병소에서는 전장관이 추천되었다. 임상적으로 볼 때 근관치료를 받은 치아나 bridge의 지대치도 전장관의 적응증이 될 수 있다.수복물의 장기적 성공을 검증하기 위해서는 응력분포의 분석이 필요하다. 하지만 전장관이 abfraction 병소의 적응증인 경우 전장관이 응력 분포에 미치는 영향을 밝히는 연구는 아직 없다.본 연구의 목적은 abfraction 병소가 있는 치아를 수복하는 전장관이 바람직한 응력 분포를 나타낼 수 있는 조건을 알아 보고자 함이다. 치아, 주위조직과 금속도재관의 외형을 반영한 2차원 유한요소모델을 제작하고 교합력 하에서의 응력분포를 유한요소분석법으로 분석하였다. 전장관의 finish line 위치와 결손부의 수복 여부를 변수로 설정하였다. 금속도재관의 협측 finish line 위치를 쐐기모양의 결손부의 하연에(실험 0), 그리고 결손부의 하연보다 1㎜ 하방(실험 1)과 2㎜ 하방(실험 2)에 위치시켰다. 또한 결손부의 수복 여부에 따른 응력분포를 분석하였다.실험 0에서 von Mises stress는 금속도재관의 finish line과 결손부의 첨부에 집중되었고 응력띠는 치아 장축을 가로지르는 양상을 보였다. 이는 수평치관파절의 가능성을 시사한다. 실험 1과 실험 2에서의 응력분포양상은 비슷하게 나타났다. 응력은 결손부의 첨부에 집중되지만 협측과 설측의 응력띠는 서로 분리된 양상으로 나타났다. 이는 수평치관파절 가능성의 감소를 의미한다. 결손부를 복합레진으로 충전한 후 금속도재관으로 수복한 경우의 응력분포는 수평치관파절의 가능성이 감소하는 경향을 보였다.본 연구에서 치관 파절의 예방을 위해 전장관의 finish line은 abfraction 병소의 하연보다 하방에 설정하여야 하고 금속도재관으로 수복할 경우일지라도 결손부를 복합레진으로 충전하는 것이 추천된다.

[영문]Many studies have showed that occlusal force was concentrated at the apex of abfraction lesion and the lesion could cause enlargement of the lesion, pulp involvement and ultimately tooth fracture if not treated. The choice of treatment for the abfraction lesion was known as composite resin restoration. Full veneer crown was recommended when the abfraction lesion occurred both facial and lingual surfaces or circumferentially. Also, full veneer crown was clinically indicated in the case of endodontically-treated tooth and abutment for bridge.An analysis of stress distribution was needed to verify the future success of restoration. However, no study showed the effect of the full veneer crown on stress distribution when full veneer crown was the indication of restoration for abfraction lesion.The purpose of this study was to discover the condition that was absolute to favorable stress distribution at the indication of full veneer crown. The two-dimensional finite element model was developed to express tooth, surrounding tissue and full veneer crown. The stress distribution under occlusal force was analyzed using finite element analysis. The condition includes the buccal finish line of full veneer crown and restoration of wedge-shaped defect. The location of finish line was set just at the lower border of the lesion(experiment 0), 1㎜(experiment 1) and 2㎜(experiment 2) blow the lower border of the lesion. Additionally, the stress distribution was analyzed according to existence of restoration for the lesion.In the experiment 0, von Mises stress was concentrated at the finish line and the apex of the lesion. Also, the stress band crossed the long axis of the tooth. That meant high possibility of horizontal crown fracture. In the experiment 1 and the experiment 2, stress distribution was similar each other. Stress was concentrated at the apex of lesion, but the buccal stress band and the lingual stress band was separate. That implied decrease of the possibility of horizontal crown fracture. When the tooth with abfraction lesion was restored with full veneer crown after the defect was restored with composite resin, the stress distribution was favorable.In this study, the finish line of metal-ceramic crown should be set minimally below the lower border of abfraction lesion to prevent horizontal crown fracture. Also, It was recommendable that the wedge-shaped defect was restored with composite resin if though the tooth with the abfraction lesion was restored with full veneer crown.