二珪酸リチウム製テーブルトップの疲労破壊と成功率、セメント厚さの関数として

Fatigue failure and success rate of lithium disilicate table-tops as a function of cement thickness.

• Paolo Baldissara
• Brunilda Koci
• Carlo Monaco
• Nicola Scotti
• Lorenzo Breschi
• Leonardo Ciocca

抄録

目的:

薄くて部分的な被せ物の修復では，臨床的に適切なセメントの厚さを採用することが依然として問題となっている．本研究の目的は、セメントの厚さによる二珪酸リチウムの咬合面の失敗率と成功率を明らかにすることである。帰無仮説として，セメントの厚さは耐疲労性に影響しないとした．

PURPOSE: Under thin, partial coverage restoration the proper cement thickness to be clinically employed still remains an issue. The aim of this study was to determine the failure and success rates of simplified lithium disilicate occlusal veneers as a function of cement thickness. The null hypothesis was that cement thickness has no effect on the fatigue resistance.

方法:

ヒトの健全な大臼歯を咬合面に平行な面で切断し，エナメル質の縁に囲まれた平坦な象牙質面を作成した．厚さ1.0 mmのIPS e.max CAD LT製咬合つめ物45本をMultilink Automixレジンセメントで歯に接着し，セメント厚50，100，200 µmの3つの実験群（n=15）を作成した．この修復物は，ジルコニアとステンレススチールの球体を含むボールミルマシンを用いて疲労サイクルを行った。60分間のサイクルを12回行った。生存統計を "失敗 "と "成功 "に適用し，log-rank Mantel-Cox testとlog-rank test for trendsを用いて3群を比較した（α=0.05）．

METHODS: Sound human molars were severed in a plane parallel to the occlusal surface to create a flat dentin surface surrounded by enamel edges. Forty-five occlusal veneers 1.0 mm thick (IPS e.max CAD LT) were luted to the teeth with Multilink Automix resin cement, creating 3 experimental groups (n=15) with cement thicknesses of 50, 100, and 200 µm. The restorations were fatigue-cycled using a ball mill machine containing zirconia and stainless steel spheres. Twelve 60 min cycles were performed. Survival statistics were applied to "failure" and "success" events, comparing the three groups using a log-rank Mantel-Cox test and a log-rank test for trends (alpha = 0.05).

結果:

失敗率と成功率は、セメントの厚さによって有意な影響を受けなかった（それぞれP = 0.137とP = 0.872）ため、帰無仮説を受け入れた。しかし、失敗例に対してlog-rank検定を適用したところ、厚さが増すにつれて失敗が少なくなる傾向が統計的に有意に認められた（P = 0.047）。

RESULTS: The failure and success rates were not significantly influenced by cement thickness (P = 0.137 and P = 0.872, respectively); thus, the null hypothesis was accepted. However, when log-rank test for trends was applied to failure events, the tendency to have less failures with increasing thicknesses was found statistically significant (P = 0.047).

結論:

今回採用した範囲のセメント厚は，疲労現象を生じるランダムな衝撃応力にさらされた二ケイ酸リチウム咬合面板の破損率や成功率に有意な影響を及ぼさなかった。

CONCLUSIONS: The cement thickness within the range adopted here did not have a significant effect on the failure or success rate of lithium disilicate occlusal veneers when exposed to randomized impact stresses generating fatigue phenomena.